. ~ . 2 3 6L2 -~ ·, ·'" !~ it:CQ t tB 1 9 19lt

DARCOM PAMPHLET DARCOM-P 706-316

10~023

ENGINEERING DESIGN

HANDBOOK

JOINING OF ADVANCED COMPOSITES

US ARMY MATERIEL DEVELOPMENT AND READINESS COMMAND MARCH 1979

Documentlllo. Handbook !Used by DOC lllo. 70&· and IIITISl

201 AOA-022 007 202 AOA-033 216 203 AD901 657 204 AD-785 000 205 ADA-020 020 210 AD-889 245 211 AD-389 295 212 lSI AD-389 331 213 !Sl AD-389 330 214 lSI AD-389 333 215 AD·389 296 235 AD-894 910 238 ADA-023 513 240 !CI AD-386 896 242 AD-801 509 244 AD-830 290 245 AD·389 304 247 AD-830 296 248 A0-830 284 249 AD-830 266 250 AD-830 303 251 AD·838 748 252 AD-830 297 2531 255 AD-818 532 260 AD-868 578 270 ADA-016 716 280 AD-840 582 281 iSRDI AD-389 352 283 A0-830 377 284 AD-389 298 285 A0-861 082 286 AD-830 267 290 AD·501 329 300 AD·905 372 312 ADA-013 178 313 ADA-015 181 327 A0-830 809 329 A0-879 465 331 AD·830 275 340 A0-830 276 341 . A0-830 277 342 A0-830 281 343 A0-830 393 344 A0-830 396 345 ADA-003 347 346 A0-830 301 347 A0-830 291 350 AD·881 357 355 A0830 268 356 AD-817 023 357 AD-873 103 3591 ADA-035 445 360 A0-783 697 361 AOA-013 769 4101 AOA-038 803 411 lSI ADC-008 827

412 ICl AOC-008 828 4131SI ADC 008 829

4141Sl ADC·008 830 415/SI ADC·008 831 4161Sl ADC-008 832 417 IS/I 445 AD-903 789 4701 ADA-029 902

"UNDER PREPARATION-not ava1lable "REVISION UNDER PREPARATION

ENGINEERING DESIGN HANDBOOKS (cont'd)

Title IIIllS Price

Helicopter Engineering, Part One, Preliminary Oesign. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $17.50 Helicopter Engineering, Part Two, Detail Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $20.00

• • Helicopter Engineering, Part Three, Qua~fication Assurance . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $12.00 Helicopter Performance Testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $10.75 Timing Systems and Components.......... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $17.50 Fuzes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 9.25 Fuzes, Pro1imity. Electricel, Part One. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................ $ 4.75 Fuzes, Pro1imity, Electrical, Part Two lUI........... . ...................................... . Fuzes, Pro1imity, Electrical, Part Three lUI. . . . . . . . . . . . . . . . . ............................ . Fuzes. Pro•imity, Electrical. Part Four lUI. . . . . . . . . . . . . . . . . . . . . . . . . . . .............................. . Fuzes, Pro1imity, Electrical, Part Five. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................... $ 6.25 Hardening Weapon Systems Against RF ~nergy.................. .. .. . . . .. ............................ $10.75 Recoilless Rifle Weapon Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................... $20.00 Grenades lUI . . . . . ........................ · .... · . · · · · · · · · · · · · · · · · · · · · · · · · · · · · Design for Control of PrOJectile Flight Characteristics..... . . . . . . . . . . . . . . . . . . . . . . . . . .......................... $ 7.25 Ammunition, Section 1. Artillery Amftllnition-General, withTableof Contents, Glossary, and lndet for Series ................. $ 6.00 Ammunition, Section 2, Design for Terminal Effects. .. .. .. . . . .. .. . . . . . .. .. .. . . . . .. ...................... $12.50 Ammunition, Section 4, Design for Projection. . . . . . . . . . . . . . . . . . . ................... $ 9.00 Ammunition, Section 5,1nspection Aspects of Artillery Ammunition Design. . . . . . . . . . . . . . ........ $ 4.50 Ammunition, Section 6, Manufacture of Metallic Components ot Artillery Ammunition. . . . . . . . . . . . . . . . . . ......... $ 5.25 Guns-General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 6.00 Muule Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... $ 7.25

"'GunTubes.......... ........... ............................................... .. .... $6.50 ' Breech Mechanism Design .. . . .. .. . . . ............................................... .

Spectral Characteristics of Muzzle Flash. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................... . Automatic Weapons . . . . . . . . . . . . . . . . . . . . . . . . ............................................ . Propellant Actuated Devices. . . . . . . . . . . . . . . . . . . . . . ...................................... .

• • Design ot Aerodynamically Stabilized Free Rockets . . .......................................... .

. ... $ 6.50 $12:00

. $12.50 $ 9.25

Weapon System Effectiveness lUI. . . . . . . . . . . . . . . . . . . . . ......................................... . Aerodynamics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 6. 00 Trajectories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...................................... $ 6.50 Elements of Aircraft and Missile Propulsion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ $21.25

\Structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................. $ 6.00 Warheads-General.......................................... . .......................... $12.50

• • • Fabric Design !limited Document). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......................... . Rotational Molding of Plastic Powders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......................... $15.00 Short Fiber Plastic Base Composites................................. . ............................ $12.50 Fire Control Systems-General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......................... $15.25 Fire Control Computing Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................... $15.00 Compensating Elemants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... $ 6.50

•' Carriages and Mounts-General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................. $ 4.50 • • Cradles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $ 5.25 • ·Recoil Systems................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ $ 6.00 • • Top Carriages........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... $ 4.50 " Bottom Carriages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .......... $ 4.50 " Equilibrators. . . . . . . . . . . . .................. ·' . . . . . . . . . . . . . . . . . . . . . . . ....... $ 4.75 •' Elevating Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... $ 4.50 " Traversing Mechanisms.. .. . .. .. .. . .. .. .. .. .. .. . .. . .. . .. .. . $ 4.50

Wheeled Amphibians. . . . . . . . .. .. .. . . . .. .. .. . . . .. .. . . .. . . .. ................ $13.25 The Automotive Assembly. . . . . . . . . .. . . . . .. .. . . . . . . . .. . . .. . . . .. .. .. .. . .. .. .. .. . . . .. .. .. . . . .. $15.25 Automotive Suspensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $14.50 Automotive Bodies and Hulls. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... $13.25 Analysis-and Design of Automotive Brake Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $15.00 Military Vehicle Electrical Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $16.50 Military Vehicle Power Plant Cooling. . . . . . . . . .................................................. $20.00 Electromagnetic Compatibility IEMCI............... . .. .. .. . . . .. .. .. . . . .. . . .. .. . . . .. .. .. . . .. ... $22.50 Vulnerability of Communication-Electronic and Electro Optical Systems !Except Guided Missiles) to Electronic Warfare, Part One, Introduction and General Approach to Electronic Warfare Vulnerability lUI ... Part Two, Electronic Warfare Vulnerability of Tactical Communications lUI. ................ . Part Three, Electronic Warfare Vulnerability of Ground-Ba•ed and Airborne Surveillance and Target Acquisition Radars lUI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... . Part Four. Electronic Warfare Vulnerability of Avionics lUI. . . . . . . . . . . . . . . . . . . . . . . . . . ............... . Part Five. Optical/Electronic Warfare Vulnerability of Electro-Optic Systems lUI ....................................... . Part Si1. Electronic Warfare Vulnerability of Satellite Communications IU). . . . . ......................... . Vulnerability of Guided Mi•sile Sy•tems to Electronic Warfare lUI . . . . . . . . . . . . . . . . . ............... . Sabot T ethnology Engineering . . . . . .............. . $11.00 Metric Conversion Guide . . . . .............. . . ...................... $ 9.00

"'limitod Documents are not for sale by NTIS I DARCDM-P 706·

Document Ia. Handbook IUatHI by DDC lo. 706· and ITISJ

201 ADA 022 007 202 ADA·033 216 203 AD·901 657 204 AD-785 000 205 AOA-020 020 210 AD·889 245 211 A0·389 295 212 lSI AD-389 331 213 lSI AD·389 330 214 lSI AD·389 333 215 AD·389 296 235 AD·894 91D 238 ADA·D23 513 240 ICI A0·386 896 242 A0·801 509 244 AD·830 290 245 AD·389 304 247 AD·830 296 248 A0·830 284 249 A0·830 266 250 AD·830 303 251 A0·838 748 252 A0·830 297 2531 255 A0·818 532 260 A0·868 578 270 AOA·Ol6 716 280 A0·840 582 281 ISROI A0·389 352 283 A0·830 377 284 AD·389 298 285 A0·861 082 286 A0·830 267 290 AD·501 329 3DO A0·905 372 312 ADA·013 178 313 ADA·015 181 327 A0·830 809 329 AD879 465 331 AD·830 275 340 A0830 276 341 AD·830 277 342 A0·83D 281 343 AD·83D 393 344 A0·830 396 345 AOA·003 347 346 AD·830 301 347 A0·830 291 350 AD·881 357 355 A0830 268 356 A0·817 D23 357 A0·873 103 3581 ADA·035 445 360 AD·7B3 697 361 ADA·013 769 4101 AOA·038 803 411 lSI AOC·008 827

412 ICI ADC·OOB 828 413iS) ADC·OOB 829

414 lSI ADC·008 830 415 lSI AOC·008 831 416 lSI AOC·008 832 417 !Sit 445 AD·9D3 789 4701 AOA·029 902

"UNDER PREPARATION-not available ""REVISION UNDER PREPARATION

ENGINEERING DESIGN HANDBOOKS (cont'd)

Title

Helicopter Engineering, Part On a, Prelirrinary Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. .. t17. 50 Helicopter Engineering. Part Two, Detail Design ..................................................... , . . . . . . t20.00

• • Helicopter Engineering, Part Three, Qualificetion Assurance ........................................... , . . . . . . . . t 12.00 Helicopter Performance Testing ........................................................................ t1 0. 75 Timing Systems end Components ...................................................................... t1 7.50 Fuzes ......................................................................................... t 9.25 Fuzes, Proximity, Electrical. Part One .................................................................... t 4.75 Fuzes, Proximoty, Electricel, Part Two lUI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................ . Fuzes, Proxirrity, Electrical. Pert Three lUI ........................................................•........ Fuzas, Proxirrity. Electrical. Pert Four lUI. .............................................................•..• Fuzaa. Proxirrity, Electrical, Pert Fin .................................................................... t 8.25 Hardening Weapon Systems Against RF Energy ............................................................. t10. 75 Recoilless Rille Weapon Systams ....................................................................... t20.00 Grenades lUI ........................................ · ........................ · ...... · · · .. · ...... · Dosign for Control of Projectile Flight Characteristics ......................................................... t 7.25 Amrrunition, Section 1, Artillery Amrrunition-General, with Table of Contents, Glossary, and Index for Series .................. t 8.00 Amrrunition, Section 2, Design for Terrrinal Effects. . . . . . . . . . . .............................................. t12.50 Amrrunition, Section 4. Design for Projection .............................................................. t 9.00 Amrrunition, Section 5, Inspection Aspects of Artillery Amrrunition Design .......................... , ..........•.... t 4.50 Amrrunition, Section 6, Manufacture of Metallic Components of Artillery Amrrunition ............•..................... t 5.25 Guns-General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t 8.00 Muzzla Devices. . . . . . . . . . . . . . . . . . . . . . . . . . ...................................................... , t 7.25

• • Gun Tubes.. .. .. .. .. .. .. .. . . . . . . . ............................................................. t 8.50 • Breech Mechanism Design . . . . . . ..........................................................•......•.

Spectral Characteristics of Muzzle Flash .................................................................. t 8.50 Automatic Weapons ........................................................................•••.... t1 2.00 Propellant Actuated Devices ..............................................................•......•.... t12.50

• • Design of Aerodynarrically Stabilized Free Rockets . . . . . . . . .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .. . . . . .. .. .. .. . t 9.25 Weapon System Elf activeness lUI .................................•...................................•. Aerodynamics ...............................................................................•...• t 8.00 Traiot•ries ................. , . . . ...............................................•....•...... t 8.50 Elements of Aircraft and Missile Propulsion .................................................•....•........• *21.25 Structures .............................................................................•........ t B.OD Warheads-Ganeral. ............................................................................•.. t12.50

• • • Fabric Design llirritad Document) .......................................................... , ........... . Rotational Molding of Plastic Powders ............................................................•.•.... t15.00 Short Fiber Plastic Basa Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t1 2.50 Fire Control Systems-General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t15.25 fi11 Control Computing Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . t1 5.00 Compensating Elements ............................................................................. t 8.50

• • Carriages and Mounts-General ............................................................•........•.. t 4.50 • • Cradles. . . . . . . . . . . . .................................................................... t 5.25 • • Recoil Systems .............................................................................•..... t 6.00 • • Top Carriages............. . .........................................................•....... t 4.50 • • Bottom Carriages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...........•............................. t 4.50 • • Equilibrators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ................................................ t 4.75 • • Elevating Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . • . t 4.50 • • Travarsing Mechanisms .........................................................................•... t 4.50

Wlleeled Amphibians. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . ...............• t13.25 The Automotive Assenilly. . . . . . . ................................................................... t15.25 Automotive Suspensions .........................................................................•.. t14.50 Automotive Bodies and Hulls .....................................................................•.•.. t13.25 Analysis and Design of Automotiva Brake Systems . . . . . . .. .. .. . . . . . . . . . . . . . . . . . . . . . .. .. . . .. . . . . . . . . . . . . . . . .. t1 5.00 Military Vehicle Electrical Systarns . .. . . .. .. .. . . . . . . .. . . . . . . . . . . . . . . . . . .. . . . . . . .. .. . . . . . . . . . . . . . . . . • .. .. t1 8.50 Military Vehicle Power Plant Cooling ...............................................•.................... t20.00 Electromagnatic Compatibility IEMC) .................................................................... t22.50 Vulnerability of Conmmication·Eiectronic and Electro·Dptical Systems lhCIIIt Guided Millilal to Electronic Warfare, Part One.lntroduction and G-al ApproKh to Electronic War1ere Vulnerability IUJ ....................• Part Two, Electronic Warfare Vulnerability of Tactical Comrr~~nications lUI ..........•....... Part Three. Electronic Werf•e Vulnerability of Ground-Baled and Airborne Sllr<eiHIIIIU and Target Acquisition Radars lUI .............................................•......................... Part Four, Electronic Warfare Vulnerebility of Avionics lUI ...............................................••.•... Part Five, Opticai!Eiectronic Wer1are Vulnerability of Electro·Optic Systems lUI ...............•.............•.......... Part Six, Electronic Warfare Vulnerability of Satellite Comrrunications lUI ........................................... • Vulnerability of Guided Missile Systems to Electronic Warfare lUI ............................................... .. Sabot Technology Engineering..... . ............................................................... tll.OO Metric Conversion Guida . .. .. .. .. .. .. .. .. . .. . . . . .. .. .. .. .. .. .. .. .. .. .. .. . . . . .. . .. .. .. .. .. .. .. .. .. . t 9.00

• • "lirrited Documents are not for sale by NTIS t DARCOM·P 706·

•

DARCOM-P 706-316

DEPARTMENT OF THE ARMY HEADQUARTERS US ARMY MATERIEL DEVELOPMENT AND READINESS COMMAND

5001 Eisenhower Avenue, Alexandria VA 22333

DARCOM PAMPHLET No. 706-316

23 March 1979

Paragraph

ENGINEERING DESIGN HANDBOOK JOINING OF ADVANCED COMPOSITES

TABLE OF CONTENTS

LIST OF ILLUSTRATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1v Page

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vll

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vlll

CHAPTER l. INTRODUCTION 1-0 List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-1 Advanced Composites Defined . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-2 Preliminary Comments on Joint Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1-3 Mechanical vs Adhesive Bonded Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1-3.1 General ................................................................. 1-2 1-3.2 Mechanical]oints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 1-3.3 Adhesive Bondedjoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-4 Basic Joint Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-4.1 General ................................................................. 1-3 1-4.2 Important BondedJoint Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 1-4.3 Important Laminate and Adhesive Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 1-4.4 Advanced Component Joint Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 1-5 Surface Preparation of Advanced Composites Prior to Bonding . . . . . . . . . . . . . . . . 1-4

CHAPTER 2. COMPOSITE JOINT DESIGN 2-0 List of Sym bois . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2-1 Design Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2-2 Bonded joint Analysis and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 2-3 Bolted Joint Analysis and Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3 2-4 Fiber Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

References ................................................................ . 2-30

CHAPTER 3. DESIGN DATA REQUIREMENTS 3-0 List of Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 3-1 Baseline Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3-2 Laminate Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2 3-3 Mechanical Properties of Adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

DARCOM-P 706-316

Paragraph

3-4

3-4.1

3-4.1.1

3-4.1.2

3-4.1.3

3-4.1.4

3-4.1.5

3-4.1.6

3-4.1.7

3-4.2

4-0

4-1

4-2

4-2.1

4-2.2

4-2.3

4-2.4

4-2.5

4-2.6

4-3

4-3.1 4-3.1.1

4-3.1.2

4-3.1.3 4-4 4-5

4-5.1 4-5.2

4-5.3

4-5.4

4-5.5

4-6

4-7

4-8 4-9

4-10

4-11 4-11.1

i i

TABLE OF CONTENTS (cont'd)

Design Data Generation ................................................... . Composite Mechanical Property Tests ................................... .

Tension Properties ................................................... . Compression Properties ............................................... . Interlaminar Shear Properties (In-Plane Shear) ........................ . Interlaminar Shear Properties ......................................... . Flexural Properties of Laminates ...................................... . Bearing Stress of Laminates ................... : ....................... . Test Specimen Schematics and Data Reduction Equations .............. .

Summary .............................................................. . References ................................................................ .

CHAPTER 4. BASIC BONDED AND BOLTED LAP JOINT CONFIGURATIONS

AND DESIGN VARIATIONS List of Symbols ........................................................... . General .................................................................. . BondedJoints ............................................................ .

Bonded Single-Lap Joints ............................................... . Bonded Double-Lap Joints .............................................. . Bonded Scarf Joints ..................................................... . Stepped Lap Joints ..................................................... . Bonded Joint Performance Compared .................................... . Fiber Orientation vsJoint Strength-In-BondedJoints .................... .

Bolted Composite Joints ................................................... . Single- and Double-Lap Bolted Joints .................................... .

Plain Holes .......................................................... . Bushed Holes ................................................... ~ .... . BoltedJoints With Reinforced Edges ................................. .

Bolted and Bonded Joints .................................................. . Reducing Stress Concentrations in Joints ................................... .

Model ................................................................. . Strap Modifications ..................................................... . Increased Adhesive Thickness ........................................... . Influence of Strap and Adhesive Alterations on Joint Efficiency ............ . Variable Adhesive Stiffness .............................................. .

Typical Bolted Joint Configurations ........................................ . Bolted Failure Modes ..................................................... . Typical Bonded Joint Configurations ....................................... . Bonded Failure Modes .................................................... . Weight of Joints ........................................................ · · · · Fatigue ................................................................... .

Bonded Joints ......................................................... · ·

Page 3-20

3-23

3-23

3-32

3-32

3-32

3-32

3-33

3-33

3-33

3-34

4-1

4-1

4-1

4-2

4-2

4-5

4-23

4-23

4-23 4-23 4-28

4-28 4-28 4-28 4-28

4-34

4-34

4-34

4-36

4-36

4-36

4-36

4-36

4-36

4-36

4-38

4-41

4-41

•

Paragraph

4-11.2

OARC()M-P 706-316

TABLE OF CONTENTS (cont'd)

Pa.f!.e Bolted joints and Bolted-Bondedjoints 0. 0 0 0 0 0. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0. 0. 4-42

References 0 0 0 0 ••••• 0 ••• 0 0 0 0 • 0 0 0 0 0 •• 0 ••• 0 0 0 • 0 •• 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 • 0 ••• 0 0 •••• 0 0 0 4-63 Index .. 0 •• 0. 0 •• 0 0 0 0 0. 0 0 •• 0. 0 0 0 •••• 0 •• 0. 0 0 0 •••• 0 0 0 0 0 0. 0 0 •• 0 0 0. 0 0 •• 0 ••• 0 0 0.. 1-1

Ill

DARCOM-P 706-316

Figure No. 2-1

2-2

2-3 2-4

2-5 2-6

2-7 2-8 2-9 2-10 2-11 2-12

2-13 2-14 2-15 2-1"6

LIST OF ILLUSTRATIONS

Title Comparison of Photoelastic and Computer Calculated Normal Stress on

Centerline of Doubler ................................................... . Comparison of Photoelastic and Computer Calculated Stress at Edge

of Doubler .............................................................. . Actual and Idealized Joints ................................................ . Tensile Stress Along Inner Face of Sheet at Edge of Doubler

(Computer Calculated) ................................................. . Shear Stress Distribution in Adhesive (Computer Calculated) ................ . Shear Stress Distribution in Adhesive Using Layer Properties and

Gross Properties of Composite ........................................... . Tensile Stresses in Various Layers of Composite at Edge of Doubler .......... . Symmetrical Double-Lap Joint ............................................ . Comparative Discrete Element Analytic Analyses of a Bonded Joint .......... . Predicted Joint Strength as a Function of Joint Length (Analytic Solution) .... . Shear Stress Distribution in Adhesive for Various Adherends ................. . Comparison of Photoelastic and Computed Stress Distribution for

Pin-Loaded Tension Strip ............................................... . Local Stresses in Pin-Loaded Tension Strip ................................. . Stresses in Plain Laminate ................................................. . Tensile Strength of Boron Laminates ....................................... . Stresses in Bolted Laminates ............................................... .

2-17 Principal Tensile Stresses in Bolted and Pinned Composite Joints-±¢J Patterns ............................................................ .

2-18 Tensile Stress Limits for Bolted Joints ...................................... . 2-19 Shear-Out Stress Limits for Bolted Joints ................................... . 2-20 Machined Joints .......................................................... . 2-21 Single-Lap Joints ......................................................... . 2-22 Double-Strap Joints ....................................................... . 3-1 Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal Tension

and Transverse Compression-Strain Curves at -65°F ................... . 3-2 Unidirectional Graphite/Epoxy (Type ASJ3002-Batch) Longitudinal and

Transverse Tension and Compression Stress-Strain Curves at Room

Page

2-4

2-5 2-6

2-7 2-8

2-9 2-10 2-10 2-11 2-12 2-13

2-14 2-15 2-16 2-17 2-18

2-19 2-20 2-21 2-27 2-28 2-29

3-9

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10 3-3 Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal and

Transverse Tension and Compression Stress-Strain Curves at 350°F . . . . . . . 3-11 3-4 Graphite/Epoxy Typical Transverse Unidirectional Tension Stress-Strain

Properties (Type AS/3002 Continuous Treated Fiber) . . . . . . . . . . . . . . . . . . . . . 3-12 3-5 Graphite/Epoxy-In-Plain Stress-Strain Properties-Crossply

[Oj±4Sj90] 8 (Type AS/3002-Batch-Untreated Fiber) . . . . . . . . . . . . . . . . . . . . . 3-13

iv

•

Fi,~;ure No. 3-6

3-7

3-8

3-9 3-10 3-11

3-12 3-13

3-14 3-15 3-16 3-17 3-18 3-19 4-1

4-2 4-3

4-4

4-5

4-6

4-7 4-8

4-9 4-10 4-11 4-12 4-13 4-14

4-15 4-16 4-17 4-18 4-19 4-20

DARCOM-P 706-316

LIST OF ILLUSTRATIONS (cont'd)

Title Page

Interlaminar Shear Strength vs Temperature for Various Orientations-Type AS/3002 Batch, Graphite/Epoxy ................................... . 3-14

Tensile Tests, Epon 828/V 40, Stainless Steel Adherends as a Function of Temperature ......................................................... . 3-16

Tensile Tests, Epon 828/V40, Stainless Steel Adherends as a Function of Bond Thickness ...................................................... . 3-17

Fracture Stress Tests, Epon 828/V40, Stainless Steel Adherends ............. . 3-18 Shear Tests, Epon 828/V 40, Stainless Steel Adherends ...................... . 3-19 Tensile Tests, EC2214, Stainless Steel Adherends as a Function

of Temperature .......................................................... . 3-20 Tensile Tests, EC2214, Aluminum Adherends .............................. . 3-21 Tensile Tests, EC2214, Stainless Steel Adherends as a Function

of Bond Thickness ...................................................... . 3-22 Precision Elastic Limit Tests, EC2214, Stainless Steel Adherends ............ . 3-:23 Shear Tests, EC2214, Aluminum Adherends ................................ . 3-24 Tensile Tests, Metlbond 329, Aluminum Adherends ........................ . 3-25 Shear Tests, Epon 9601, Aluminum Adherends ............................. . 3-26 Precision Elastic Limit Tests, Metlbond 329, Aluminum Adherends .......... . 3-27 Reduction Equations for Different Types of Specimens Tested ............... . 3-28 Single-Lap Bonded Joint Streng\h .. , ....................................... . 4-3 Effect of Et Ratio on Single-Lap Adhesive Joint Strength ..................... . 4-4 Double-Lap BondedJoint Strength ........................................ . 4-7 Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Glass,

Boron/ Aluminum, Titanium Adherends ................................. . 4-9 Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Stainless Steel,

Titanium, Aluminum/Composite Adherends ............................. . 4-10 Predicted Joint Strength for Double-Lap BondedJoint Using

Shell 951 Adhesive ...................................................... . 4-13 Double-Lap Joint Showing Plastic Shear Distribution in Adhesive ............ . 4-14 Stress Distribution in Actual Test Joint Based on Computer Analysis ......... . 4-15 Idealized Scarf Joint ....................................................... . 4-16 Adherend Normalized Stress Distributions in a Scarf Joint ................... . 4-17 Shear Stress Distribution in the Adhesive of a Scarf Joint ..................... . 4-18 Tensile Stress Distribution in the Adhesive of a Scarf Joint ................... . 4-19 Stress Distribution in the Adhesive of an Aluminum/Boron Scarf Joint ....... . 4-20 Scarf AdhesiveJoint Strength-Composite-to-Aluminum .................... . 4-21 Scarf Adhesive Joint Strength-Composite-to-Composite .................... . 4-22 Idealized Two-Step Lap Joint .............................................. . 4-24 Stress Distribution in the Adhesive of a Two-Step Lap Joint .................. . 4-25 Stepped Lap Adhesive Joint Strength ....................................... . 4-26 Boron-to-Aluminum Joint Strength ........................................ . 4-27 Model of a Double-Strap Joint ............................................. . 4-34

v

DARCOM-P 706-316

Figure JVo.

4-21 4-22 4-23 4-24 4-25 4-26 4-27 4-28 4-29

LIST OF ILLUSTRATIONS (cont'd)

Tztle

Ways to Reduce Strap Thickness Locally ................................... . Methods of Reducing Stress Concentration at Strap Ends .................... . Idealized Shape for Variable Adhesive Thickness ............................ . Filled Step Strap Joint ..................................................... . Variable Stiffness Adhesive Joint ........................................... . Bolted Joint Designs ...................................................... . Bolted Failure Modes ..................................................... . Bonded Joint Designs ..................................................... . Bonded Failure Modes .................................................... .

4-30 Weight Increments vs Strength of Joints .................................... . 4-31 Strength-Weight Relationships for BoltedJoints ........................... . 4-32 Total Weight Comparisons for Panels and Joints ............................ . 4-33 Fatigue Data for Adhesive Scarf Joints ...................................... . 4-34 Fatigue Data for Adhesive Double-Lap Joints ............................... . 4-35 Fatigue Life of Boron Composite-to-Aluminum Alloy Bonded Joint ........... . 4-36 Single-Lap Bonded Joint Tension Fatigue S-N Curves-Type AS/3002-Batch,

Graphite/Epoxy, 350°F ................................................. . 4-37 Single-Lap Bonded Joint Tension Fatigue S-N Curves-Type AS/3002-Batch,

Graphite/Epoxy, Room Temperature .................................... . 4-38 Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves-

Type AS/3002 Batch, Graphite/Epoxy, Room Temperature and

Page

4-35 4-37 4-38 4-38 4-41 4-41 4-42 4-43 4-47 4-48 4-50 4-51 4-53 4-53 4-54

4-55

4-56

350°F, [0±45]28 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-57 4-39 Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves-

Type AS/3002-Batch, Graphite/Epoxy, Room Temperature and 350°F, [Oj±45j90] 2s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-58

4-40 Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves-Type AS/3002-Batch, Graphite/Epoxy, Room Temperature and 350°F, [02j±45] 2s ....................................................... · 4-59

4-41 Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy-to-Steel Single-Lap Flush Head Mechanical]oints-Type AS/3002-Batch, Graphite/Epoxy . . . . . . . . . . . .. . .. . . . . . .. . .. . . . . .. .. . 4-61

4-42 Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy-to-Steel Single-Lap Protuding Head Mechanical Joints-Type AS/3002-Batch, Graphite Epoxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-62

VI

..

Table No.

1-1 2-1 2-2 3-1 3-2 3-3 3-4

3-5 3-6

3-7 3-8

3-9 3-10

3-11 3-12 4-1

4-2

4-3 4-4

4-5

4-6

4-7 4-8

4-9 4-10 4-11 4-12

4-13

4-14

4-15

DARCOM-P 706-316

LIST OF TABLES

Title

Method for Preparing Surface .............................................. . Summary of Composite Joint Strength Tests-Mechanical Fasteners ......... . Predicted Strength Ranges for Bolted Joint Specimens ....................... . Unidirectional Laminate Properties ........................................ . Summary of Theoretical and Experimental Tension Properties ............... . Summary of Theoretical and Experimental Compression Properties .......... . Summary of Theoretical and Experimental In-Plane Shear Properties ........ . Interlaminar Shear Tests Results .......................................... . Pin-Bearing Test Results .................................................. . Summary of Mechanical Properties of Adhesive Films ....................... . Average Shear Microstrain Properties ...................................... . Average Tensile Microstrain Properties ..................................... . Elastic Properties of Adhesives ............................................. . Laminate Property Determination ......................................... . Adhesive Property Determination .......................................... . Summary of Single-Lap Bonded Joint Test Results Using Shell951 Adhesive .. Summary of Double-Lap BondedJoint Test Results (1-in. Specimen Width)

Using Shell 951 Adhesive ................................................ . Joint Specimen Laminate Patterns ......................................... . Summary of Double-Lap Bonded Joint Test Results for Various Et ratios

Using Shell 951 Adhesive ................................................ . Summary of Double-Lap Bonded Joint Test Results (1-in. Specimen Width) .. . Summary of Single-Lap Bolted Joint Test Results (1-in. Specimen Width) .... . Summary of Double-Lap Bolted Joint Test Results (1-in. Specimen Width) ... . Summary of Double-Lap Bolted Joint Test Results-Bushed Holes .......... . Summary of Composite-Reinforced BoltedJoint Test Results ................ . Summary of Shim-Reinforced Bolted Joint Test Results ..................... . Summary of Double-Lap Bolted and Bonded Joint Test Results .............. . Performance of Radiused Double-Strap Joint Employing

Carbon Fiber Reinforced Plastics ........................................ . Performance of Inversed Stepped Strap Joints Employing

Carbon Fiber Reinforced Plastics ........................................ . Summary of Bonded Joint Fatigue Test Results ............................. . Summary of Bolted Joint Fatigue Test Results .............................. .

Page

1-5 2-22 2-26 3-2 3-3 3-5 3-6

3-7 3-8 3-15 3-15 3-15 3-27 3-33 3-33 4-5

4-6

4-8

4-11 4-12 4-28

4-29 4-30 4-31

4-32 4-33

4-39

4-40

4-52

4-60

Vll

DARCOM-P 706-316

PREFACE This handbook should serve as a guide to designers concerned with the technology associated with

the joining of advanced composites. It deals with basic joint design practice as well as with those prac­tices specific to composite joining. Tabulated and graphical representations of joint property data ob­tained on both bonded and mechanically fastened composites are presented. These data can be used by designers to test the degree of conservatism in calculated joint properties for their composite joint designs and hopefully will impart the necessary degree of confidence or wariness in the early design stages where alterations can be made most economically.

It is hoped that the diversity of joint possibilities and the magnitude of the joint strength properties reported will prompt cautious designers of Army materiel to make use of the strength-to-weight advan­tages offered by advanced composites and also to recognize that the technology is available for prac­tical implementation of these valuable engineering materials.

The handbook was prepared by Mr. Andrew Devine, Plastics Technical Evaluation Center (PLASTEC), the Defense Department's specialized information center on plastics located at the US Army Armament Research and Development Command, Dover, NJ.

The US Army DARG_OM policy is to release these Engineering Design Handbooks in accordance with DOD Directive 7230.7, 18 September 1973. Procedures for acquiring Handbooks follow:

a. All Department of Army (DA) activities that have a need for Handbooks should submit their re-quest on an official requisition form (DA Form 17, 17 January 1970) directly to:

Commander Letterkenny Army Depot ATIN: SDSLE-AJD Chambersburg, P A 17201.

"Need to know" justification must accompany requests for classified Handbooks. DA activities will not requisition Handbooks for further free distribution.

b. DOD, Navy, Air Force, Marine Corps, nonmilitary Government agencies, contractors, private industry, individuals, and others-who are registered with the Defense Documentation Center (DDC) and have a National Technical Information Service (NTIS) deposit account-may obtain Handbooks from:

Defense Documentation Center Cameron Station Alexandria, VA 22314.

c. Requestors, not part of DA nor registered with the DDC, may purchase unclassified Handbooks from:

National Technical Information Center Department of Commerce Springfield, VA 22161.

Comments and suggestions on this Handbook are welcome and should be addressed to: Commander US Army Materiel Development and Readiness Command Alexandria, VA 22333.

(DA Form 2028, Recommended Changes to Publications, which is available through normal publica­tion channels, may be used for comments/suggestions.)

Vlll

DARCOM-P 706-316

CHAPTER 1 INTRODUCTION

Advanced composites are defined. A broad overview of joining advanced composites is presented - the efficiency of load bearing joints, advantages and disadvantages of mechanical versus adhesive bonded joints, factors affecting choice of joints, bonded joint properties, and surface preparation.

1-0 List of Symbols E = overall joint efficiency, dimensionless

EL = load bearing efficiency, dimensionless Ew = joint weight efficiency, dimensionless Lc = load continuous member can support, lb L1 load joint can support, lb

We = weight of continuous member, lb W1 weight of joined member, lb

1-1 ADVANCED COMPOSITES DEFINED

Advanced composites is a term that has come into use in recent years, suggesting composite materials which possess characteristics so superior to earlier composites as to warrant the term "advanced". It is a poor term from the standpoint of knowing what exactly is referred to when the term is used. The term "composite" taken by itself is a compound structure or mater­ial comprised of a number of parts. It must be prefixed by other terms to clarify its meaning. Terms such as glass-resin composites, graphite­resin composites, carbon-resin composites, and boron-resin composites comprise a class often referred to as "fiber reinforced composites". These fibers can be long and oriented, or short and random within the resin matrix. Composite materials can be made up of metal layers and ceramic layers, or as constructions of metal or fiber reinforced composite skins bonded to metal or paper honeycomb, or wood or foam cores. Thus the term "composite" is a loosely defined term taken by itself. When it is prefixed by "ad­vanced", it only becomes more nebulous.

For the purpose of this handbook, and in def­erence to its increased use in industry, the term

"advanced composite" is employed. The scope of this handbook is limited only to the class of com­posites known as fiber-reinforced resin compos­ites. These include glass, boron, and carbon or graphite reinforcing fibers. The term "advanced composite" refers to those composite materials employing high modulus reinforcing fibers in the resin matrix. In fact, the fibers serve less to rein­force the matrix than the resin serves to bind the fibers together. As a term, advanced composite is best understood when the composites described are compared with other composites employing lower modulus fibers. Advanced composites, by virtue of their high modulus fibers help make possible the strong, stiff, lightweight capability so vital to aircraft and munitions construction.

1-2 PRELIMINARY COMMENTS ON JOINT DESIGN

As a prelude to a discussion of joint design some comments should be made regarding the purpose of a joint. Very simply, the function of a joint is to unite two or more members together in order to transfer loads from one member or mem­bers to the other(s). How well a joint accom­plishes this task is judged best by its overall joint efficiency E which is the product of its load bear­ing efficiency EL and its weight efficiency Ew.

The load bearing efficiency EL of a joint is defined as

where:

--.!2._ , dimensionless

Lc

L1 load joint can support, lb

( 1-1)

Lc load continuous member can support, lb.

1-1

DARCOM-P 706-316

The weight efficiency Ew of a joint IS

We d. . I __ , 1mens10n ess (1-2) wj

where

We weight of continuous member, Ib wj weight ofjoined member, lb

therefore

E = r~·L X f.'w, dimensionless. ( 1-3)

The joint efficiency concept is easily un­derstood by considering the example that fol­

lows. If one takes a length of material, weighs it, tests it for strength in a particular mode, and then cuts the material in two, joins it in one man­ner or other, weighs the entire assembly, and tests the assembly for strength in the same mode, one can employ the given equations to measure

the success of the joint design chosen in matching the structural integrity and weight of the original unjoined material. The more closely EL, Ew, and

E approach unity, the better is the joint design from a performance standpoint.

Without belaboring the obvious, an EL as close to 1 as possible is the condition to strive for be­cause if EL exceeds 1 then it can be assumed that a weight penalty is being imposed and Ew will decrease - an undesirable trait in most designs. This situation implies that the entire structure is being reinforced, since loads cannot be trans­ferred between members which exceed the strength of the weakest member. Such a condi­tion would arise in the cocooning of a joint by fil­ament winding an entire area. However, this is essentially a rebuilding or remanufacturing pro­cess to correct a major design flaw and is not solely a joining process. Where joining two dis­similar members, the joint efficiencies must, of

course, be arrived at based on the weaker of the

two members being continuous. Another factor which should be taken into ac­

count is a processing factor or cost of the joint, but this is a more difficult contribution to quan­tify. This factor is best considered as a compari­son of the cost of making one joint design versus

1-2

another, rather than between the cost of making a joint or leaving the member continuous. The latter comparison is unrealistic since joints are

certainly not employed where it would be more feasible to omit them.

1-.3 MECHANICAL VS ADHESIVE BONDED JOINTS

1-3.1 GENERAL

The adversary tone of this paragraph is justi­fied because each joining technique produces a joint with significant differences in the manner in which they function. Mechanically fastened joints (bolts, rivets, screws, etc.) derive their strength from the strength of the fastener and the strength of members being joined such as in cases

where the members are threaded and screwed together. In mechanical joints, loads are trans­ferred by two locked surfaces bearing against each other. Bonded joints, on the other hand, derive their load bearing capabilities via a sur­

face attachment which is a function of the sur­face energies of the adhesive and substrate as well as the polymer chemistry of the adhesive. Loads are transferred from one member to another across a common interface or boundary created by interfacial molecular attractions. The para­graphs that follow comment on the merits and disadvantages of each type of joint.

1-3.2 MECHANICAL JOINTS

On the positive side, mechanical joints: 1. Require no surface preparation of the sub­

strate or white glove operations to assure cleanli­

ness. 2. Are not as adversely or irreversibly affected

by thermal cycling and high humidity as are

bonded joints. 3. Present no unusual inspection problems for

joint quality. 4. Permit disassembly without destruction of

the substrate. Mechanical joints are less favorable from the

following standpoints:

1. They require machining of holes in the members to accommodate the mechanical at­tachments and thereby weaken the members.

2. They concentrate stress at the bearing sur­faces, thereby creating stress risers which can in­duce failure in the joined member.

3. They are not generally as strong as are bonded joints unless they are heavy.

4. They add weight to the joint which reduces overall joint efficiency.

1-3.3 ADHESIVE BONDED JOINTS

Adhesive bonded joints have the following positive attributes:

1. They distribute load over a larger area than mechanical joints, thereby eliminating stress risers.

2. They can be designed so as not to weaken the joined members by machining operations in the joint area.

3. They are difficult to inspect for bond qual­ity and voids.

4. They adct a minimum of weight ·to the structure.

The drawbacks to bonded joints are: 1. They require adherend surface prepara­

tion and cleaning. 2. They are subject to degradation due to the

effects of temperature and humidity cycling. 3. They are difficult to inspect for bond qual­

ity and voids. 4. Disassembly cannot be effected in most

cases without destruction of the joined mem­bers.

1-4 BASIC JOINT DESIGN

1-4.1 GENERAL

Before a joint can be designed, the designer must possess some basic information. He must know the nature of the materials to be joined -physical yield strength, modulus of elasticity, thermal expansion and contraction behavior, and very often their chemistry. He must also know

DARCOM-P 706-316

the stresses which the joint is expected to with­stand in service, the environment in which the joint is to function, and its expected service time.

Knowing the nature of the materials to be joined and the service the joint is to provide, the designer can proceed to his next step -the selec­tion of the type of joint to be employed. This re­quires a consideration of the limitations imposed by the materials on the processing or manufac­ture of the joint as well as special requirements such as disassembly capability for maintenance and quality control requirements. For example, a structural joint requiring disassembly capability would probably exclude the selection of a struc­tural bonded joint. Similarly, if the joint is to be fabricated in a facility in which a manufacturer has no proper surface preparation facility, pro­cessing considerations would preclude use of a bonded joint. If on the other hand very thin members are to be joined which cannot be ma­chined or weakened with holes in the joint area, then a bonded joint would be in order or strength-to-weight requirements might mandate a bonded joint.

The decision whether to use a mechanical or bonded joint requires careful consideration of all variables which will effect the final outcome and requires a systems approach with the relation­ship between the joint and the entire structure kept in mind at all times. Once this decision has been made, then the process of configuring the joint and selecting or altering materials to meet the performance requirements of the end item can proceed. This last process is considered to be the actual design step but often it is embarked upon without proper preparation and guidance.

1-4.2 IMPORTANT BONDED JOINT PROPERTIES

Although specific test specimens have been devised to test specific end items, the basic prop­erties to test in an adhesive ioint remain the same - tensile strength, tensile and compres­sive shear strengths, and peel. Other forms of tests include bending which actually creates peel

1-3

DARCOM-P 706-316

and cleavage forces .• Few of the tests used ran isolate stress modes but merely attempt to do so as nearly as possible. Some tests accomplish this better than others but the basic reason for testing joint properties is to compare one adhesivejad­herend combination with another under similar loading modes and to extrapolate these data to specific configurations. No doubt a variety of tests could be devised to ascertain the behavior of a specific bonded joint under a specific test mode and this type of final design testing should in­deed be done. However, the basic design proper­ties must be determined by standard, widely accepted and used test methods so a wide range of data from many sources can be continually generated.

1-4.3 IMPORTANT LAMINATE AND ADHESIVE PROPERTIES

The strength properties of laminates and ad­hesives are very much time and temperature dependent so it is important to know the condi-

~

tions of service of bonded compcc.;ite joints. The environmental effects - temperature, humidity; and exposure to fuels, chemicals, and sunlight -on the properties of adhesives and composites are not fully known or quantified but can and do have detrimental effects in many instances. For these reasons data presented should be viewed as typical of the particular situation, and subject to verification and prototype testing under the ac­tual use conditions anticipated. In addition, fac­tors such as cure cycle, cure pressure, surface preparation, machining, and fabrication will further alter properties. It is therefore advisable to adequately characterize the specific' material design properties and their statistical accuracy before using them for design purposes. The tables and figures presented in this handbook are for guidance and comparison, and show trends. Absolute values given should be judged for their pertinence to a specific application and, if not en­tirely pertinent, then used with caution and with a sufficient safety factor for design purposes.

1-4

1-4.4 ADVANCED COMPOSITE JOINT CONSIDERATIONS

What has been said up to now has been gener­al in nature and applies to composite and non­composite alike. It should be remembered, how­ever, that unlike isotropic materials such as metals, orthotropic materials - like advanced composites - undergo severe damage and weakening when they are cut or machined and thus become more susceptible to interlaminar shear within the substrate. For this reason bond­ed rather than mechanically fastened joints are most frequently employed in advanced compos­ite joint design. More specifically, bonded joint configurations such as single and double laps or single and double strap type joints are preferred where feasible to avoid machining of the com~ posites even though a weight penalty may be im­posed. Exceptions to this practice would be beveling or tapering of the ends of a lap or strap to alleviate stress concentrations at the lap or strap ends. This practice does not damage any fibers in the bond area.

Along the same line, basic design practice for adhesive bonded composite joints should in­clude making certain the surface fibers in a joint are parallel to the direction of pull in order to minimize interlaminar shear or failure of the bonded substrate layer. On composites whose joint areas have been machined -to a step lap configuration, for example - it -is possible to have a joint interface comprised of fibers at other than the optimum 0-deg orientation to the load direction. This would tend to induce substrate failure easier than otherwise would be possible.

1-5 SURFACE PREPARATION OF ADVANCED COMPOSITES PRIOR TO BONDING

As with any bonding operation, the proper surface preparation is essential for obtaining quality bonds which fail cohesively rather than adhesively. Surface preparation for advanced composite substrates prior to bonding is accom­plished best by solvent wiping to remove loose

surface dirt and grime and, then abrading the surface by hand or machine. The first step re­moves loosely adhered weak boundary layers, and the second increases the surface energy of the faying surface as well as increasing the bond area by surface roughening. The abrading operation should be conducted with care, however, to avoid damaging surface fibers. The purpose is to roughen the resin matrix and expose, but not rupture, the reinforcing fibers. A surface roughening method having gained wide accep­tance is the use of peel ply. This technique sim­ply involves incorporating a nylon cloth in the outer layer of the composite during lay-up. The

DARCOM-P 706-316

peel ply is torn or peeled away prior to bonding, fracturing the resin matrix and exposing a clean roughened surface for bonding. Surface rough­ness can to some extent be determined by the weave of the peel ply. The peel-ply method is fast and eliminates the need for solvent cleaning and removal of abraded resin dust. All abrasion treat­ments should have the same principles in com­mon. These are (1) to thoroughly clean the sur­face prior to the abrasion step in order not to force dirt into the surface, (2) abrade, (3) remove abrasion dust, (4) clean again, and (5) Dry. One such met hod is outlined in Table 1-1.

TABLE 1-1. METHOD FOR PREPARING SURFACE

I. With a stiff brush and 2% aqueous solution of detergent at 104° to 122°F, scrub entire surface of panels.

2. Thoroughly rinse in tap water followed by immersion in distilled water. 3. Dry in forced air oven at 150°F for 30 min. 4. With 240 grit sandpaper, abrade bpnding area plus 0.5 in. margin. 5. Dust abraded area with vacuum. 6. Swab off abraded area with acetone wet clean gauze. 7. Rinse generously in distilled water (entire panel). 8. Dry in forced air oven at 212°F for 60 min, then bond parts immediately.

1-5

DARCOM-P 706-316

CHAPTER2

COMPOSITE JOINT DESIGN

The anisotropic nature of composites - a factor that must be reckoned with in joint design - is emphasized. The analysis of stress distributions of bonded joints, and pinned and bolted joints - as a function of distance along the joint - is presented in graphical form. Tables of tensile and shear strengths for mechanical and bolted joints are given for various composite fiber patterns and laminates.

2-0 LIST OF SYMBOLS

A = load area, in~ D = diameter of bolt, in. e = distance from edge of bolted joint

to center of bolt hole, in. E = elastic modulus, psi

E:r = elastic modulus of composite with fibers oriented parallel (longitudi­nally) to direction of applied stress, i.e.,¢ = 0 deg, psi

Ey = elastic modulus of composit~ with fibers oriented perpendicularly (transversely) to direction of applied stress, i.e.,¢= 90 deg, psi

G = shear modulus, psi Gxy = shear modulus in xy-plane, psi

K = principal stress factor, dimension-less

L = joint length, in. P = applied load, lb s = distance from side of bolted joint

to center of bolt hole, in. tl> t2 = thickness of adherends

t = thickness of adhesive layer, in. W = width of bolted joint, in.

x = longitudinal distance parallel to applied load, in.

y = transverse distance perpendicular to applied load, in.

/J.:ry Poisson's ratio of composite, relating contraction in y-direction to extension in x-direction,

dimensionless /J.yx = Poisson's ratio of composite,

relating contraction in x-direction to extension in y-direction, dimensionless

u laminate stress = Pj A, psi Uave average compressive stress based

on projected area of pin, psi uLr = tensile strength of composite with

fibers oriented parallel (longitu­dinally) to direction of applied load, i.e.,¢ = 0 deg, psi

ua = gross section stress level, psi urr tensile strength of composite with

fibers oriented perpendicularly (transversely) to direction of applied load, i.e., ¢ = 90 deg, psi

Uo:r applied longitudinal tensile stress, psi

u x = tensile stress at point x inches from doubler edge, psi

u :r/ U0 :r stress concentration factor at point x inches from doubler edge, dimensionless

(]1

T

Tmean

¢

tPc

=

=

=

principal stress on matrix, psi shear stress in adhesive, psi mean shear stress, psi angle between fiber laminate direction and direction of load, deg angle between longitudinal tangent to bolt hole and line drawn from corner of composite to bolt hole at tangent point of contact, deg

2-1

DARCOM-P 706-316

2-1 DESIGN PHILOSOPHY Most design techniques for joining com­

posites are extensions of techniques used for iso­tropic materials. This approach is acceptable provided the designer remains attuned to the anisotropic nature of composites and how this can alter bulk composite properties and failure modes, depending on the working direction of the composite. By combining joint stress anlayses with material properties and failure criteria, the strength and deflection charac­teristics of a joint are, to some extent, pre­dictable. For bonded joints, measurements of the strength and modulus of the composite mem­bers and cured films of the adhesive are re­quired.

The lack of composite and adhesive property data as well as inadequate stress analyses avail­able suggest that the best design procedure for bonded composite joints is to treat each joint as an individual structure, and test it and modify it as indicated. As more composite and adhesive data become available this process can be re­fined.

There are several stress analysis methods other than that discussed here. Each method, regard­les~ of simplifying assumptions made, requires knowledge of the shear and tensile properties of the adhesive and adherend. These properties should reflect the pertinent joint environments of temperature and humidity for the special cure and lay-up characteristics of the composite as well as adhesive cure conditions and bond line thickness. It is unlikely, in the near future, that these data will be readily available in handbook form for quick reference-the variable com­binations are too great. However, the data pre­sented in this handbook have been assembled from several sources and do show some of the im­portant work done as well as point out areas which require further study. Although the data available will grow with increased advanced composite and adhesive usage, it is unlikely to become available from a single source or data book.

2-2

A system needs to be established to deal with material property data generation. Ide4lly, all new data should be reported in a standardized format and placed in a centralized accessable data bank for computer-aided design and en­gineering purposes. The success of such a system requires the cooperation of all industry, uni­versity, and Government research and de~ign programs to insure that the design data gen­erated for specific purposes are reported in standard format for inclusion in the data bank and availability to all. The difficulty in com­piling a handbook such as this within fiscal and time constraints is that of searching for, finding, and screening data, and then putting the data on a uniform basis for comparison. It is a task re­quiring many man-years of effort, as a minimum, to assemble useful design data and continuous updating to keep the information complete and current.

The reliability of static test data for design purposes depends a great deal on the nature of the end product being designed. The re­quirements of the automotive, sporting, and air­craft industries for example, differ both for per­formance and safety, and therefore the con­sequence of a functional failure in a product will determine how tightly or reliably various com­ponents need be designed. Failure of a graphite composite tennis racket frame during com­petition in no way approaches a failure in a glass composite helicopter rotor blade during flight. It is with the consequences of component failure then that the designer concerns himself when he decides what design data will be required and what testing need be done to supplement that available from manufacturers and the literature.

2-2 BONDED JOINT ANALYSIS AND DESIGN

Discrete element idealizations can be es­tablished for bonded and bolted composite joints, using digital computer methods for stress

and deflection analysis. Photoelastic and com­puter calculated stress distributions can be com­pared for joints of given geometry. Once a satis­factory joint idealization is established, joint member materials and adhesives can be altered to evaluate how they effect stresses and de­flections under a given load. Figs. 2-1 and 2-2 compare photoelastic and computer calculated stresses for a single strap joint (Fig. 2-3) at the centerline and edge of the strap (doubler). Figs. 2-4 and 2-5 show the results of an analysis of S-994 glass/Narmco 5505 resin composite sheet bonded to an aluminum strap (doubler) using FM-47 adhesive in which tensile stresses (J"0 x in the main member and shear stresses T in the ad­hesive are depicted. The spike in tensile stress will have a marked influence on fatigue life. A similar analysis using the gross and layer proper­ties of S-994 glass/Narmco 5505 composite bonded with MB-408 adhesive is shown in Figs. 2-6 and 2-7.

Because discrete element analysis of joints consumes a good deal of time, even with the com­puter, a faster analytic solution using the com­puter was developed by McDonnell-Douglass Corp. based on an analytic solution for stresses in a symmetrical, double lap joint by Hahn.

Using this computer program to solve for stress in a symmetrical double-lap joint (Fig. 2-8), one obtained the stress distribution shown in Fig. 2-9. The assumptions made in generating this stess distribution were:

1. Only longitudin;J 1 stresses cause adherend deformation.

2. Shear stress is constant throughout the thickness of the glueline.

3. Adhesive tensile stress parallel to the glue­line is negligible.

4. The adhesive stress-strain curve is con­stant.

It can be seen that good agreement exists be­tween discrete element analyses and the ana­lytical method (Hahn) except at the strap ends. Fig. 2-10 is a plot of predicted failing load vs overlap for a boron/5505 composite bonded to

DARCOM-P 706-316

aluminum using MB-408. The curve obtained; typical of such plots. Fig. 2-11 indicates that varying the metal adherends from steel to ti­tanium to aluminum has little impact on ad­hesive shear stress distribution. Increased doubler modulus increases stress at one end of strap but decreases it at the other.

2-3 BOLTED JOINT ANALYSIS AND DESIGN

Computer analysis of bolted joints yields the stress distributions seen in Fig. 2-12 for pin­loaded holes along with photoelastic test results. Computer predicted stress distributions in an S-994 glassjNarmco 5505 resin pin-loaded ten­sion strip is shown in Fig. 2-13 where the elastic properties were calculated for a fiber volume con­tent of 65% with zero voids.

The strength of composite bolted joints is de­pendent on the geometrical parameters edge­distance bolt-diameter ratio ej D, side-distance bolt-diameter ratio s/ D, and laminate-thickness bolt-diameter ratio tjD; and orientation of rein­forcing fibers in the composite layup, and fabri­cation and processing methods. Even when fabri­cation processes are closely controlled, speci­mens can show large scatter.

Bearing failures account for very few bolted composite joint failing modes. Unless edge and side distance ratios are very large, full bearing stress limit is rarely achieved. Laminates com­prised primarily of ±rp layers generally fail along filament lines - indicating that the interfila­ment strength of the matrix is the limiting factor. Laminates with 50% of the fibers oriented at 0° and 50° at ±rp usually fail along 0-deg and 90-deg lines. When rp approaches 0, failure is usually by cleavage. This does not occur in a wide joint with side-by-side bolts. Generally, the tensile strengths of bolted specimens are some­what lower than the strength of laminates with­out holes, which is attributable to the effect of stress concentrations at the holes.

2-3

DARCOM-P 706-316

2-4

SHEET

0 ox

0.11

0.10

0.09

0.08

0.07

c 0.06

;:. 0.05

0.04

0.03

0.02

0.01

·2 ·1 0 2 3 4

A-.,

I y

I __ j_ I I

A_J

+ COMPUTER CALCULATED (REF. 4)

0 PHOTOELASTIC

5 6 7 8 9

Stress on Section A·A

10

Figure 2-1. Comparison of Photoelastic and Computer Calculated Normal Stress on Centerline of Doubler3

DARCOM-P 706-316

" 0 t:>

~ .... 0 ti <U .... c: .g <U !: c: .., u c: 0 u "' "' .., ....

cri

0

1.6

1.4

a or

1.2

1.0

0.8

0.6

0.4

0

0 PHOTOELASTIC (REF. 4)

0 COMPUTED

DOUBLER

~ +X

0 0 0

0

0.2~--~--~----._ __ _. ____ ~--~--~~------~----------------0.040 -0.020 0 0.020 0.040 0.060 0.080

Distance from Doubler Edge x, in.

Figure 2-2. Comparison of Photoelastic and Computer Calculated Stresses at Edge of Doubler

2-5

DARCOM-P 706-316

SINGLE STRAP JOINT

0.005 ADHESIVE LAYER

L ~1-3/8 2-3/4-----+-1

0.072

(A) Actual Joint

DOUBLER _\ I I

ADHESIVE

\SHEET

~~ ~ ........................................ ~ ~ .......... ""-.~ ':Y I

I

(B) Idealized Joint

Figure 2-3. Actual and Idealized Joints3

Failure in a bolted joint depends on the inter­filament strength of the matrix. In the plain lami­nate illustrated in Fig. 2-14, the interfilament line AB intersects the edges of the specimen. The load components of Sand T introduce shear and tensile stresses on AB. Combined, these stresses produce a principal tensile stress on the matrix

(2-1)

where (J' == laminate stress == Pj A, psi

2-6

K == principal stress factor, dimensionless

(1/2)sin2¢(1 + y' 1 + 4 cot2 ¢).

When ¢ == 90 deg, K = 1 and the strength of the laminate becomes the ultimate tensile strength of the resin matrix. Test results indicate that lami­nate transverse tensile strength exhibits large scatter due most likely to varying void content and cure cycles. When ¢ approaches 0 deg, the laminate strength is limited by the combined fila­ment strength. Fig. 2-15 shows this effect clearly

0~

'"t;" ... .9 '-' as

'"" c 0

'.::I as b c "' ~ 0 u ~

"' b [f)

DARCOM-P 706-316

1.8

' ~ SHEET (S994 GLASS/5505 RESIN)

1.6

1.

l. 4 J

I -~' DOUBLER I l

CALUMINUN) l .....__l ao%- -t- .. •1

2

L0.071 \_I

/' ~ '-0.102

FM-47 ADHESIV ., (Forest Product Lab.)

E

1. 0

0. B •\

\ 6

1\. ~

" "" r---4

0.

o.

0. 2 , -0.040 -0.020 0 0.020 0.040 0.060 0.080

Distance from Doubler Edge x, in.

Figure 2-4. Tensile Stress Along Inner Face of Sheet at Edge of Doubler (Computer Calculated)3

2-7

N I

00 l~•t--------1 •375-----------:0:o:O:':"U~B~L'='E=R----------_,.,~,

(ALUMINUM)

.g "'

I 0.4

1 ,, I \

0.005 ADHESIVE (FM·47)

SHEET ~ 0

(S994 GLASS/5505 RESIN ~e)

0.102 0. 144 (2 PLCS)

a ~~-f~~2===0~-r;i:~~

0.31 \ I ~,SYMMETRICAL I JOINT

I

0ar~~t: ~: 5~

\ \ UNSYMMETRICAL ar t if

JOINT

/~ !l::: 0.1 /

0.1 0.2. 0.6 0.5

0.3 0.4 Distance from Doubler Edge x, in.

/ /

0.4 0.3 0.2 Distance from Edge of Sheet, in.

0.1

I I

0 I

I 0

I

Figure 2-5. Shear Stress Distribution Adhesive (Computer Calculated)3

0.1

0 -0.02

0 > :a n 0 3:

I ., """ 0 0)

w .... 0)

DARCOM-P 706-316

0.6.---------------------------------,

~ " 0.4

SHEET (S 994 GLASS/6606 RESIN =X= 46°) 0.160 (ALUMINUM)

" ~ 0 3

" ~ '<i) .., ..c "0 -< c:: ·-<h <h .., !::

rJ)

.... "' OJ

..c rJ)

'-0

.2

"' 0::::

c c h .... " ..0

E " :::; c::

"' :::; c:: ·-<h

"' \l)

!:: rJ)

~

"' c:: "' E-

0.3

0.2

0.1

0 0 0.05 0.1 0.15

0 LAYER PROPERTIES

0 GROSS PROPERTIES

0.2 0.25 0.3 0.35

I Distance from Edge of Doubler, in.

I I I I I I I 0.35 0.3 0.25 0,2 0.15 0.1 0.05 0

Distan!'e from Edge of Sheet, in.

Figure 2-6. Shear Stress Distribution in Adhesive Using Layer Properties and Gross Properties of Composite3

as well as tests for ±¢-fiber orientations. Al­though both ¢- and ±¢-patterns should yield identical monolayer matrix stresses, the ± ¢­pattern cannot fail along a ¢-interfilament line in one direction without shearing filaments in another. This is a synergistic advantage of cross­ing filaments.

Fig. 2-16 illustrates the case of the bolted laminate. The filament line AB running from the side of the hole to the edge of the speci­men is a maximum when B coincides with C, the corner of the laminate; and ¢ = tPc· Test results show peak strengths at this condition~ Fig. 2-17 plots the principal tensile stresses in bolted and pinned composite joints against

±¢ from a number of referenced sources. The envelope of test results shows a fall off as ¢ ap­proaches 0 deg or 90 deg. This is thought to result from the bolt applying load locally as filaments become unidirectional, causing shear or tension failures originating adjacent to the bolt. When 0-deg layers are used in conjunc­tion with ±¢-layers, failures will usually be along 0-deg or 90-deg lines-the 90-deg failures thought to be secondary failure.

Tensile and shear-out stress limits for boron laminates using 0-deg and ±¢-layers are shown in Figs. 2-18 and 2-19. Table 2-1 summarizes some bolted boron composite joint strengths from referenced data sources. Table 2-2 shows

2-9

DARCOM-P 706-316

2-10

2.0

o.s

-0.04 0

DOUBLER (BORON/5606 RESINI

0.040TVP

0.005 ADHESIVE (MB-4081

SHEET (BORON! 5605 RESIN!

2,6

~ 1,5

45~ 4.8 3,7

(LAVER NO.)

Ex • 30.38 x 106 FOR LAVERS 1, 4, 5 Ia 8

Ex • 1.344x106 FORLAVERS2,3,61a7

(LAVERS 6 Ia 7 ARE ALMOST THE

SAME AS LAVER 31

0.04 0.08 0.12 0.16

Distance from Edge of Doubler, in.

Figure 2-7. Tensile Stresses in Various Layers of Composite at Edge of Doublers

Material l

Figure 2-8. Symmetrical Double-Lap Joints

....

r 0.080 0.0060

DARCOM-P 706-316

DOUBLER IBORON/6606 RESIN ~ ) ~50

1-~,---r=============~=======r==*=~

"' .., .... < ~

1:::: ·c; ....., ..,

·= .:: w .... .., >

0 "' "' .., ....

ci) .... "' ..,

..c: CFl

1::::

"' .., ::; B .., .::: "' ..,

..c: -c < .::

"' "' .., ....

ci) ....

"' .., ..c: CFl ....... 0

.g "' c:::;

ADHESIVE MB - 408 ~60 SHEET IBORON/6606 RESIN! ~

6

6

4 "' "' .., ~ .S "' 1:::: ..,

.§ -c J

.., > ·;;; .., c

..c: "' -c ..,

"' E .... .... 2

0 O.t 0.2 0.3 0.4

0 DISCRETE ELEMENT

A HAHN ICASE E)

0.6 0.6 0.7 0.8 0.9

Distance from Edge of Strap, in.

i,SYM

1.0

Figure 2-9. Comparative Discrete Element and Analytic Analyses of a Bonded Joine

2-11

DARCOM-P 706-316

0.006 ADHESIVE (MB-408}

DOUBLER (ALUMINUM}

~-=:!::::=ۤ~~- p r -P

~L 0.160 12 PLCS}

SHEET (BORON/5505 RESIN)

~oor---------------------------------------------~

500

0~----------~--------.. ----------~--------~ 0 0.6 1.0 1.6 2.0

Lt•nAth of Joint L, in.

Figure 2-10. Predicted Joint Strength as a Function of Joint Length (Analytic Solution)3

2-12

-~

DARCOM-P 706-316

0,12080/EPOXY E; 16.12 X 106 .----...L--._ p

2?----~----~---L~~ 1---:----- p

"' 0 600

X MB 408 ADHESIVE "(jj E = 139,000 0 ALUMINUM ALLOY 0.. G = 49,000 E •10.3 X 1o6 ~ 400 t- I = 0.006 -o l:l. TITANIUM "' E • 16 X 106 a ~

300 ~ .s 0 STEEL il.)

~ E • 29 X 106 :l

Q § il.)

( .:: ~

"' 200 e -v t) <l.l AVERAGE SHEAR I g ..c:

0 -o 0 0 < 1:

.... 100 "' <f)

<l.l .... en .... "' 00 0.20 0.25 0.30 0.35 0.40 0.45 0.50 "' 0.06 0.10 0.15 ..c:

ifJ Distance from Edge of Doubler, in.

Figure 2-11. Shear Stress Distribution in Adhesive for Various Adherends3

predicted strengths for vanous bolted speci- quired to produce this configuration. Figs. 2-20

mens. through 2-22 show some acceptable and unac-

2-4 FIBER ORIENTATION

As stated in par. 1-4.4, composites must not be stressed in a manner likely to induce de­lamination. This is why it is desirable in bonded joints to have surface fibers oriented parallel to the load direction, and to employ lap and strap joints when this is the case. The use of lap and

strap joints precludes machining the bond area.

When this is not the case, i.e., when surface fibers

are oriented at other than 0 deg to the load di­rection, then joints such as scarf and landed scarf

joints are useful even though machining is re-

ceptable bonded composite joints as related to fiber orientation. As can be seen, machining of bond-line areas can result in disadvantageous load to fiber orientation which ultimately would result in failure by delamination of the com­posite. The proper orientation of the surface fibers in a bonded composite joint should not be an accident but should be included in the de­

sign. Even if a stepped lap joint is contemplated, very often it may be easier and less costly to lay

up the step configuration prior to cure. This

would eliminate the machining process and pre­vent damage to composite fibers.

2-13

DARCOM-P 706-316

.500

r1.21 aav•

111.13 am

-----l~----PIN LOAD

COMPUTED RADIAL STRESS DISTRIBUTION

COMPUTED NORMAL STRESS DISTRIBUTION ON TRANSVERSE SECTION

PHOTOE l.ASTIC-NORMAL STRESS DISTRIBUTION ON TRANSVERSE SECTION (REF. 8)

I

I It

a...---4-----4~---.625-------------~

aav• : AVERAGE COMPRESSIVE STRESS BASED ON PROJECTED AREA OF PIN

ac : GROSS SECTION STRESS LEVEL

0.39 ac ~:I 0.53ac

Figure 2-12. Comparison of Photoelastic and Computed Stress Distributions for Pin-Loaded Tension Strip3

2-14

COMPUTED RADIAL STRESS DISTRIBUTION

DARCOM-P 706-318

---~T"'" LOAD

~------~~---------------------1.000~----------------------~

.750

S·994 GLASS NARMCO 5505 RESIN

Ex = Er = 0.381 X .. 107 psi 1'-xy = 1'-yx = 0.352

Gxy = 0.141 X 107 psi

t :: 0.120

COMPUTED NORMAL STRESS DISTRIBUTION ON TRANSVERSE SECTION

0.24ac--J

Figure 2-13. Local Stresses in Pin-Loaded Tension Strip3

2-15

DARCOM-P 706-316

p

A

B

p

Figure 2-14. Stresses on Plain Laminate

2-16

DARCOM-P 706-316

200~~~----------------~~~~----------------~ ..,. _;r- FILAMENT STRENGTH

150

J. "' ~

(f) 100 ..:: ·;n

:::: "' E-

50

MATRIX STRENGTH

'(., FILAMENT DIRECTION

MONOLAYER: aLT = 200,000 psi

aTT = 10,000 psi

INCREASE IN STRENGTH DUE TO CROSSING OF FILAMENTS

Angle Between Laminate Fiber Direction and Load Direction t/l, deg

Figure 2-15. Tensile Strength of Boron Laminates3

2-17

DARCOM-P 706-316

Figure 2-16. Stresses in Bolted Laminates8

2-18

DARCOM-P 706-316

II ' D

SYMBOL AEF TEST D D t REMARKS

X 2 1ST SEAlES 2.67 3.33 1.88 PINNED

+ 2 2ND SEAlES 3.00 2.67 2.24 PINNED

0 2 2ND SEAlES 3.00 2.67 2.24 BOLTED

[!] 3 3AD SERIES 3.00 2.67 1.12 PINS AND BOLTS

* 3 4TH SERIES 3.00 2.67 1.12 CSK BOLTS

4 TABLES 4.80 3.00 2.60 PINNED • XLIX AND L

w 4 TABLE L 2,00 3.00 2.60 PINNED

A 5 2.00 2.38 4.80 PINNEO

18r---------------------------------------------------------------..,

0 14

X )C

12 t: i + + ~ t + ....

·u; • .><:

"' "' " ... cii ..!::! ·u; = 8 ..,

E-<

6 CSK BOLTS

4 PLAIN BOLTS AND PINS

Angle Between Laminate Fiber Direction and Load Direction <b, deg

Figure 2-17. Principal Tensile Stresses in Bolted and Pinned Composite Joints -±t/1-Patterns3

2-19

DARCOM-P 706-316

~r-----------------------------------------------------------~

TENSILE STRESS LIMITS 0° ANO ±~PATTERNS

40

30

·:;; ...:.:

TENSILE STRESS = P![t(W - D)]

;i <I> !:: r.n

-= ·;;; c "' ......

20

10

Angle Between Laminate Fiber Direction and Load Direction <b, deg

Figure 2-18. Tensile Stress Limits for Bolted Joints3

2-20

"<ii -"' <£ "' l1l !:: (fJ .. "' l1l ...c:

(fJ

SHEAR-OUT STRESS LIMITS

o0 AND :te/)PATTERNS

DARCOM-P 706-316

20r-----------------------------------------------------------------------~

18

' '100'lHC/)

PREDICTION RANGE

12

8

6 - SHEAR-OUT STRESS • P/(2et)

4 ~- t I I e

2 _j

! p

10 20 60 70 80 90

Angle Between Laminate Fiber Direction and Load Direction rb, deg

Figure 2-19. Shear-Out Stress Limits for Bolted Joints3

2-21

DARCOM-P 706-316

TABLE 2-1 SUMMARY OF COMPOSITE JOINT STRENGTH TESTS-MECHANICAL FASTENERS2

CALCULATED STRENGTH LIMITS, tb

TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD, tb FAILURE MODE

REF. 2 0 704 s 1056 s 1040 SHEAR FIRST SERIES 697 s 1045 s 1045 (CLEAV ACE) (PINNED)

±IS 1000 s 1480 .s 1410 ALONG 1010 s 1493 s 1420 FILAMENT ....

LINES

±30 1260 s 1831 s 1730 1283 s !870 s 17.10 1213 s 1762 s 1660

±45 950 s 1694 s 1565 960 s 1712 s 1545 970 s 1730 s 1730

±60 878 T 1240 T 1130 878 T 1240 T 1150 878 T 1240 T 1165

±75 494 T 815 T 815 4gs T 799 T 780 474 T 783 T 750

±90 2171 T 542 T 300 TENSIO!'i 291 T 586 T 317 284 T 568 T 284

REF. 2 0 712 s 1070 s 715 CLEAVAGE SECOND SERIES (PINNED) ±10 910 s 1.170 s 1025 ALONG

920 s 1380 s 1110 FILAMENT LINES

±15 1010 s 1498 s 1120 1010 s 1498 s 1140

±20 1040 s 1643 s 1140 1027 s 1626 s 1170

±25 1107 s 1583 s 1130 1120 s 1600 s 1140

±30 1227 s 1780 s 1255 1240 s 1800 s 1240

±.15 1226 s 1903 s 1320 1226 s !903 s 1290

±40 1083 s 1614 T 1180 1096 s 1611 T 1200

±45 988 T 1.191 T 990 999 T 1407 T 1060

±50 835 T 1198 T 1040 (cont'd) 844 T 1210 T 1102

.. S Ar\D T INDICA' IE WHETHER SHEAR (S) OR TENSION (T) LIMITS ARE CRITICAL.

(cont'd un next page)

2-22

DARCOM-P 706-316

TABLE 2-1 (cont'd)

CALCULATED STRENGTH LIMITS, I b

TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD, lb FAILURE MODE

REF. 2 ±60 577 T !!20 T 5KO SEC:< )NJ) SERIES 570 T lll2 T 74!! (PINNED) (!'Ont'd)

±75 .~14 T 51!! .,. 315 317 T 524 T 424

±90 201 T 401 T 217 TE:\'SION

REF. 2 ±10 9111 s I 3()() s 1300 ALONG SlCOND SERIES ± 15 990 s 1463 s 1390 FILA:v!ENT (BOLTED) ± 20 1 120 s 1620 s 1520 LINES

±35 1227 s 1902 s 1655 ±411 1 JHO T 161:1 T 1555 ±45 9HO T 1190 T 1:155 ±60 SiD T H30 T H20 ±75 31H T 524 T c., I 0

REF. 2 () 1:164 s 2024 s 1620 SHI':AR THIRD SERIES 13.D s 20011 s 2000 (CLEA V/\GE) (PINNED & 1341 s 21110 s 2010 NOTED)

Oj15/-15JO J9BO s 2930 s 2410 ALONG (BOLTED) 1923 s 2845 s 2270 0° AND 90°

1979 s 2910 s 2530 LINES

OJ30J-30JO 24!!0 s 3600 s 2960 2425 s 3520 s 3190

Oj45j-45JO J9BO s 3882 s 3310 1926 s 3775 s 3715 1938 s 3796 s 3550

OJ60j-60JO 1756 s 3660 T 3615 (BOLTED) 1710 s 3560 T 3560

1727 s 3600 T 3400

0/90 2046 T 2480 T 2050 2036 T 2470 T 2050

REF. 4 ±45 1748 T 2456 T 2453 ALO:-\G (PINNED) 1763 T 2480 T 2456 FILA:v!E:-IT

1715 T 2412 T 2346 LI:-\ES

OJ60j-60 2855 s 4290 T 4250 BEARI:-\G 2630 s 3950 T 393) 2815 s 4225 T 3HSO

0/90 2520 T 3060 T 2915 TEI\'SIOI\ 1960 T 2380 T 2352 2030 T 2460 T 2347

OJ60J-60JO 2550 s 3825 T 3685 TENSI0:-1 3640 s 5470 T 5170 TENSION 2280 s 4890 s 4550 SHEAR 1520 s 3260 s 3255 TENS lOr\

0/90 1990 T 2416 T 2334 TENSIO:\ (coni 'd) 1363 s 2416 T 1450 TENSION

S AND T INDICA IE WHETHER SHEAR (S) OR TENSION (T) Ll~IITS ARE CRITICAL

(coni 'don next page)

2-23

DARCOM-P 706-316

TABLE 2-1 (cont'd)

CALCULATED STRENGTH LIMITS, lb

TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD,lb FAILURE MODE

REF. 4 0/45j-45 3640 s 7125 s 5190 TENSION (PINNED) 2273 s 4450 s 4370 SHEAR (cont'd) 151) s 2970 s 2970 SHEAR

±45 1760 T 2474 T 2445 TENSION 1053 s 1882 s 1277 SHEAR

0/15/-l:i 5700 s 8460 s 5700 BEARING 3910 s 5800 s 4000 SHEAR 2443 s 3624 s 2540 SHEAR 1630 s 2416 s 1960 SHEAR

REF. 5 e = 2

s =1 303 s 367 T - - 310

(PI;\INED) D IJ 2 303 s 593 s 303 0/45/-45 3 303 s 593 s 383 PATTERN 4 303 s 593 s 445

e I 356 T 367 T 360 - = 1 D 2 394 s 772 s '\56

3 394 s 772 s 489 4 394 s 772 s 535

f ~ 4 I 356 T 367 T 367 - 606 s 1148 T 712 D 2

3 606 s 1187 s 820 4 606 s 1187 s 711

e 2 757 s 1148 T 820 - = 5 D 3 757 s 1484 s 835

4 757 s 1484 s 871

REF. 5 0/% 672 s 857 s 702/813 (PINNED)

0/90 504 s 643 s 5os;sso

±45 504 s 887 T 600/644

Z3824815 ( -1) 2620 s 5130 s 4440 SHEAR (1/4 in. DIA PIN) 0/45/-45/0 2620 s 5130 s 3620

2615 s 5120 s 4230

( -503) 3590 HEARING 0/45/-45/90 3640

3800

(-507) 0/45/-45/0 2650 s 5190 s 2960 SHEAR

2%SiC/ A 1,0, 2646 s 5180 s 4500 NOT FAILED WHISKERS 2646 s 5180 s 3620 SHEAR/TENSION

(-509) 0/45/-45/0 2585 s 5060 s 3710 HEARING

1 %SiC/ A 1202 2594 s 5080 s 3910 SHEAR WHISKERS 25HO s 5050 s 3670 SHEAR

(-511) 0/45/-45/0 2620 s 5130 s 4200 BEARING A 1203/ AI N 2620 s 5130 s 4050 BEARING

WHISKERS 2620 s 5130 s 3660 l\OT FA! LED . ' SANDT INDICATE WHE1 HER SHEAR (S) OR TEl\iSION (I) LIMITS ARE CRITICAL.

(cont 'd on next pa~e)

2-24

DARCOM-P 706-316

TABLE 2-1 (cont'd)

CALCULATED STRENGTH LL\1ITS, lb

TEST DATA SOURCE PATTERN MINIMUM MAXIMUM LOAD, lb FAILURE MODE

OTHEK E!'JD (1/2 in. HOLE)

Z3H24815 (-I) 2910 s 'i700 s H40 ;\;UT F:\1 LED (In in. DL\ PIN) Oj4Sj-45jtl 2910 s ')700 s 3620

2900 s 5700 s 4230

(-50:1) 3590 Oj4Sj-45j90 3640

3HOO

(-SO?) 2944 s 5780 s 2960 l'iOT FAILED 2%SiC/ 1\ 1,0, 2940 s 5760 s 4.500 BL\KI!\:G WHISKEKS 2940 s 5760 s 3620 !\lOT F.\! LEU

(-509) Oj45j-4Sj0 2873 s 5630 s 3710

I %SiC/:\ 1,0, 2880 s 5650 s 3lJIO WHISKEKS 2865 s 'i620 s \670

(.;I I) 0/45/-45/0 2910 s 5700 s 4200

2%;\ 1,0,/ AIN 2910 .s ')7()() s -+050 NOT F.\ILED WHISKERS 2910 s 5700 s 3660 SHf.\K

SANDT INDICATE WIIETHE.K SHEAR (S) OR TENSION (T) LI:-Ill·s :\KE CRITIC.\L.

2-25

DARCOM-P 706-316

TABLE 2-2 PREDICTED STRENGTH RANGES FOR BOLTED JOINT SPECIMENS8

PREDICTED LOAD, lb

DRAWING NO. PATTERN A* r, in. I, in. MINIMUM

z 3824831 50 0.75 012 1745 s 33 1/3

z 3824832 50 0.50 0.12 1163 s 50 0.16 1552 s 33 1/3 0.12 1163 s 25 0.16 15.'i2 s

z 38248.'\1 so 0.75 0.12 1745 s 50 0.16 2328 s 33 1/3 012 !745 s 25 0.16 2328 s

z 3824834 so 1.25 0.12 2910 s 51l 0.16 3880 s DljJ 0.12 2910 s 25 () 16 3880 s

WITH 5/16 IN BUSHINGS

50 0.50 0.12 1163 s 50 0.16 1552 s 3.1 1/3 () 12 1163 s 25 016 1552 s

50 0.75 0.12 1745 s 50 0.16 2328 s 33 l/3 0.12 1745 s 25 0.1& 2128 s

50 125 0.12 2910 s so 0.16 3880 s 33 1/3 0.12 2910 s 25 0.16 3880 s

•A INDICATES% FIBERS AT ±45°. BALANCE OF FIBERS AT oo •• ASSLMED BEARING STRESSES: 150,000 PSI FUR 50% AT ±45°

200,000 PSI FOR 33 1/3% AT ±45° 225,000 PSI FOR 25% AT ±4.'i 0

.

MAXIMUM

3420 s

2280 s 3040 s 2280 s 1040 s

3420 s 4560 s 3420 s 4560 s

4580 T 6110 T 45RO T 6110 T

22RO s 3040 s 22KO s 3040 s

3420 s 4560 s 4320 s 4560 s

3880 T s 170 T 3880 T 5170 T

S AND T INDICATE WHETHER SHEAR (S) OR TE!'<SION (T) LL'viiTS ARE CRITICAL.

2-26

BEARING LIMIT, lb**

1375 4500

337.i 4500 4500 6750

.D75 4500 4500 6750

3375 4500 4500 6750

5625 7500 7500

11250

5625 7500 7500

11250

562S 7500 7500

11250

•

DARCOM-P 706-316

-~ -~ -~ -® -® -

h~>ud lirw

~ () ' ) ') I) () ( )

0 0 0 0 c 1)

u 0 0 0 0 0

() 0 0 0 () ()

I) ') 1 ) I) () ') :) () () I) () 0 ()

(II) Sl':trl

/bond line· / rc·srn

0 0 0 J r) r J U 0 r J 'J CJ 0 0"' J iJ r,..

i~~ig&~ijtiE~~~6~6 000000000 000000

, .... •., ,·. ·,·.•,•.•.•, -,· •,· .. ,, .•. ·.· ·.•.w .• ,-.-.·,.·.--:-·- -~-.-··--, ...

0000000000000 bOOUO

() () 0 0 (J 0 0 0 () 0 0 0 1! p () 0 0 0

.·ltTt'jJ!uiJh· !liJ.('hirlt'd ,ioint nniliguralion:-. with nunprDmi .... ing load dirc·l'lion !IJ fit1er ori~·nla!ion.

fiLns

r b l I Olll ine

11 ·•'· ''•'•' · .. -;:•:.: .. -.---··- • •,-,r

0000 )00 0 ooooooooovoooo 0 0 0 c 00 00 0.00 0 0000(!)000 0

0 0

00 0 0

v-W·'-""··• ,, . .., .. .,. ..• ,.,, .•.·

oo 0000000 0 u pooooooo 0 0 0 0 00 0 00 0 0 )0000000

0 0 0000 0 00 0 0 booooooo ·-·-·-·-.. ·-··.·'"·,··-· ·.-.-·-·-··· ·····.·.·· ..... -.·.·-··-·-·--:--.··-:-

(C) Steppt'(l Lap

Unac!'eptab/e bt•cause of possibility of having load bearing surfaet• fjl.J,·rs perpendi<·ular to load.

® - fiber ori('nlation normal to page

4-+- fiber orientation para I I~ I to page

Figure 2-20. Machined Joints

fihe rs

- resrrr

2-27

N ' N 00

bonrl lirw () u u u 0 ~) 0 0 0 0 0 :) 0 0 0 0

o_o n n :) o o o o o t) o r:) o o o

res;~~~~_;,....;;;.....;;1~0c(,:., ~(=_;:Q:\c,_:, =Ot:C":;:c_,:,:C~J~C=J~o~:~' ~:,~'dO~;O~. ~o~· •0~0;it~J fibers .... . , .... ·.·.-§··· . . ..... {··· ... +---~: ''"•··{

(A) Poor--ourlare fibers normal to load

fibers

(B) Good--surface fibers paral!t:-1 to load

Figure 2-21. Single-Lap Joints (no machining)

•

•

0 )> :XI (') 0 3: ' '"0

"'-1 0 0)

w ... 0)

N I

N '0

.. !4---- composite or other material

U J C_J_ J 0 0 0 () IJ () _(_) ........................... fibers

(jr ',_)()_(!

c J J 0 u () ()..._() 0 u

l

(A) Poor--surface fibers normal to load

(B) Good--surface fibers parallel to load

Figure 2-22. Double-Strap Joints (no machining)

0 )> ::a 0 0 ~ ' "g

""" 0 Ol

I w ... Ol

DARCOM-P 706-316

REFERENCES

1. K. F. Hahn and D. F. Fauser "Methods for Determining Stress Distribution in Ad­herends and Adhesives", Symposium of Ad­hesives for Structural Applicahon, M. J. Bodnar ed., Picatinny Arsenal, Dover, NJ, 1961.

2. Structural Airframe Application of Advanced Com­posite Materials General Dynamics Fourth Quarterly Progress Report for Contract AF33 (615-5257, Wright-Patterson Air Force Base, OH, June 1967.

3. G. M. Lehman and A. V. Hawley Investigation of Joints in Advanced Fibrous Composites for Air­craft Structures, AFFDL-69-43, Air Force Flight

2-30

Dynamics Laboratory, Wright-Patterson Air Force Base, OH, June 1969.

4. F. Wilson, Research on Resin-Impregnated, Collimated Boron Filaments and Improved High­Modulus, High-Strength Filaments and Com­positions, Whittaker Corp., AFML-TR-6 7-20, Wright-Patterson Air Force Base, OH, January 1967.

5. V. H. S~.ffire, Applications of Advanced Fibrous Reinforced Composite .Mate rials, General Electric Co., AFML-TR-66-272, Wright-Patterson Air Force Base, OH, September 1966.

DARCOM-P 706-316

CHAPTER 3

DESIGN DATA REQUIREMENTS Graphs and tables of values of the ultimate strength and stress/ strain behamor of composite joints in tension, compres­

sion, shear, and bearing are presented as a function of various fiber orientations and fibers. Graphs of bond strength as a functirm of temperature are presented. Properties of various adhesives also are presented.

3-0 LIST OF SYMBOLS

A = area of joint, in~ E = elastic modulus, psi

EL = elastic modulus of composite with fi­bers parallel (longitudinal) to direc­tion of applied stress, i.e., ¢ = 0 deg, psi

E1,,. = compressive elastic modulus of com­posite with fibers parallel (longitudi­nal) to direction of applied stress, i.e., ¢ = 0 deg, psi

EL, tensile elastic modulus of coihposite with fibers parallel (longitudinal) to direction of applied stress, i.e., ¢ = 0 deg, psi

Er elastic modulus of composite with fi­bers perpendicular (transverse) to di­rection of applied stress, i.e., ¢ = 90 deg, psi

ETc compressive elastic modulus of com­posite with fibers perpendicular (transverse) to direction of applied stress, i.e., ¢ = 90 deg, psi

ET, tensile elastic modulus of composite with fibers perpendicular (transverse) to direction of applied stress, i.e., ¢ = 90 deg, psi

Ex elastic modulus in direction of applied load, psi

FLc compressive strength of composite with fibers parallel (longitudinal) to direction of applied load, i.e., ¢ == 0 deg, psi

FL, tensile strength of composite with fi­bers parallel (longitudinal) to direc­tion of applied load, i.e.,¢= 0 deg, psi

F. = in-plane shear strength, psi Fr,. = compressive strength of composite

with fibers perpendicular (transverse) to direction of applied load, i.e.,¢ = 90 deg, psi

Fr, = tensile strength of composite with fi­bers perpendicular (transverse) to di­rection of applied load, i.e., ¢ = 90 deg, psi

fbru ultimate bearing strength, psi f'u ultimate compressive strength, psi pt" interlaminar shear strength, psi PSI" ultimate interlaminar shear strength,

psi

r shear stress, psi ru ultimate shear strength, psi f~" = ultimate shear strength of adhesive

joint, psi f 1

" ultimate tensile strength, psi G = modulus of rigidity (shear) of adhe­

sive, psi

La P= S= t=

W=

/'xy

l

shear modulus with fibers parallel (longitudinal) to direction of applied shear, psi shear modulus in xy-plane, psi length of specimen, in. distance between fulcrum and load, in. length of adhesive joint, in. loads (as indicated in text), lb distance, in. thicknesses-i.e., of ply, adherend, specimen as indicated in text-in. width, in. shear strain, in./in. shear strain in xy plane, in.jin. strain, in.jin.

3-1

DARCOM-P 706-316

JJLT Poisson's ratio with stress applied par­allel (longitudinally) to fiber orienta­tion of composite, dimensionless

JJ.rL Poisson's ratio with stress applied per­pendicularly (transversely) to fiber ori­entation of composite, dimensionless

(J pure tensile strength of adhesive, psi T pure shear strength of adhesive, psi ¢ angle between fiber laminate direction

and direction of load, deg

3-1 BASELINE DATA

An essential part of joint design is to charac­terize the properties of the members to be joined. This means that the ultimate strength and stress­strain behavior should be ascertained in tension, compression, shear, and bearing. Similarly, when a bonded joint is contemplated, the impor­tant adhesive properties to characterize are those in shear and tension. This information will characterize adherend stiffness and adhesive strength adequately.

3-2 LAMINATE MECHANICAL PROPERTIES

The laminate properties of interest can be ob­tained from the results of tension tests, compres­sion tests, in-plane (edgewise) shear tests, inter­laminar shear tests, and pin bearing tests.

For a specific glass and boron composite, the elastic moduli in tension and compression are given in Tables 3-1 through 3-3. Table 3-4 re­ports the shear moduli for the same glass and boron composite obtained from in-plane shear tests. Some interlaminar shear test data can be found in Table 3-5 and pin bearing strengths in Table 3-6. The pin bearing results are for both boron and glass composites with a nominal pin diameter of 0.25 in., an edge-distance bolt­diameter ratio ej D = 4.5, and a side-distance bolt-diameter ratio sj D = 3.

For Type AS/3002 graphite composite the ten­sile and compressive strengths and moduli are presented in Figs. 3-1 through 3-4. In-plane shear stress strain data are given in Fig. 3-5 and interlaminar shear strengths are given in Fig. 3-6.

TABLE 3-1. UNIDIRECTIONAL LAMINATE PROPERTIES 1

S-994 FIBERGLASS BORO"l'

82H-1 031 N!\RMCO SSO'i BIJ:v!A-MI\A

RESIN RESIN Ni\RMCO 5505 RESIN

EXPERI:VIENT LITERATURE* EXPERIMENT LITERATURE*

ELASTIC PROPERTIES Ec, I 06 psi S.HS-'J .. 10 7.65 (I) Er, 106 psi 1.59-2.25 2.24 (1) GLT• 1 o• psi 0.84-1.4.1 0.78 (I) /hr 11248-0.308 0.270 (I) !lrL 0.027-0.075 0.079 (I)

STRENGTH PROPERTIES FL, 1 C!' psi 17 5.3-242.0 2M 0 (I) FL" I 03 psi -- 1730{1) Fr,. 103 psi 7. 96-9.61) 7.5 (.1) Fr,.IO'psi -- 29.0 (I) F., I 0' psi 9.62- n.s8 8.5 (I)

(1) Data from Ref. 4, page 2:W. Ftberglass/828-1031 BDMA-:VfN,\ Lammate. (2) Data from Ref. 5. (3) Data estimated from Rei. 6.

24.8-29.6 30.00 (2) 1.90-2.21 3.00 (2) 0. 73-0.88 1.10(2)

0.163-0.266 0.380 (2) 0.018-0Jl29 0.038 (2)

152-1'!0.7 200.0 (2) 0 - 2'10.0 (2)

(>.80-8 . .1 7 7.0 (3) --- 20.0 (3)

11.04-15.00 12.0 (3)

*Data from literature were used in analysis. These gave better correlation of predicted properties with test results for multidirectional laminates used in specimens.

3-2

LA~II!';.\ Tt: PATTER,'\

ALL0°

ALL 90°

0°(45°(-45°(0°

u-.

~ oo /45°/-45°/0° "' 0 ;.,

§ "' z 0°/45°(-45°/00 2 2 0 45° ;oo ;oo /-45° :Q

oo(45o /-45o ;oo

0°/45°/-45°/0°

0°/45°/-45°/90°

0°/45°/-45°/90°

TABLE 3-2 SUMMARY OF THEORETICAL AND EXPERIMENTAL TENSION PROPERTIES1

ELASTIC COJ'\STA!'\TS STRE~GTH PROPERTIES VOLUl\!E FRACTIO:'IlS

PREDICTED ACTUAL PREDICTED ACTUAL

FIRST LA~!l!';ATE FAILURE ULTIMATE ULTIMATE

THICK!':ESS E" E,, STRESS, STRESS, STRESS, 10. 1 o• psi Jll'"y 108 psi 1-l:cy ksi ksi ksi FILAME~T RESJ:--1 VOIDS

0.030 h50 0.250 158.5 24.80 0.241 158.5 27.20 0266 171.0 25.80 0.164 190.7 27 60 0.167 180.0 29.60 0.163 152.0 0.595 0.381 0.024

AVG26.75 AVG 0.209 AVG 168.5

0.050 2.21 0018 7.15 2.03 0.029 6.80 1.90 0.021 8.37 0.621 0.324 0 055

AVG201 AVG 0.023 AVG 7.44

0.040 16.80 0.722 95.0 16.10 0.714 99.5 17.40 0.745 88.0 0.636 0.332 0.032

17.13 0.688 AVG16.90 AVG0.727 94.0 J()J. 5 AVG 94.2

0.040 14.8 0.704 1000 15.7 0.706 95.0 0.545 0.412 0.043

17.13 0.688 AVG15.3 AVG0.705 94.0 101.5 AVG'17.5

0.080 15.1 0.710 98.2 14.7 0.616 102.5 0.5~7 0.436 0.027

17.13 0.688 AVG14.9 AVG 0.663 94.0 1015 AVG100.4

0.120 17.0 0.687 102.0 16.7 0.720 104.3 0.612 0.342 0.046

17.13 0.688 AVG 16.9 .\VG 0.704 94.0 101.5 AVG 103.2

0 160 17.2 0.777 93.3 17.0 0.700 98.5 0.597 0 .'\30 0.073

17.11 0.688 AVG 17.1 AVG 0.738 94.0 101.5 AVG 95.9

0.040 11.5 0.331 60.0 11.5 0.312 43.8 112 0.329 53.8 0 602 0.342 0.056

11.87 0.336 AVG11.4 AVG0.324 31.1 66.4 .'\VG 52.5

0.120 10.8 0.394 66.0 l) 7 0.200 57.4 0.609 0.346 0.045

11.87 0.336 AVG 10.3 .'\ VG 0.298 31.1 66.4 AVG 61.7

(cont'd on next page)

0 l:o :c (")

0 ~

LAMINATE LA~-.1!NATE THICKNESS PATTERN in

ALL0° 0.060

0.030

"' 0 ALL90° 0.060 "' "' c u § 0.050

"' z ~ "' (3

.... "' oo /45o /-45o ;oo 0.080 "' r),

0°/45°/-45°/90° 0.080

TABLE 3-2 (cont'd)

ELASTIC CO!\STANTS STRENGTH PROPERTIES

PREDICTED ACTUAL PREDICTED ACTUAL

FIRST FAILURE ULTIMATE ULTIMATE

E,, E,, STRESS, STRESS, STRESS, 10' psi !lry 10' psi jlxy ksi ksi ksi

7.70 0.308 7.80 0.248 9.30 0.26J'"

5.85 0.266 175.3 6.56 0.288. 203.3 6.40 0.260 242.0

AVG 7.27 AVG 0.272 AVG 206.8

2.20 0.075 7.48 2.19 0.068 8.00

2.25 0.063 8.17 1.84 0.027 7.96 1.59 0.071 9.60

AVG2.01 AVG0.061 AVG 8.24

4.55 0.591 120.0 4.06 0.575 143.4 5.77 0.577 137.0

5.10 0.453 AVG4.79 AVG0.581 19.6 115.3 AVG 133.4

3.66 62.6 3.80 55.4 3.75 57 3

3.92 0.308 AVG3.74 6.6 65.3 AVG 58 4

VOLUME FRACTIONS

FILAMENT RESIN VOIDS

0.548 0.411 0.005

0.548 0.411 0 005

0.594 0.401 0.005

0 ,. ::IJ n 0 s: . "D ..... 0 m w ... m

TABLE 3-:3. SUMMARY OF THEORETICAL AND EXPERIMENTAL COMPRESSION PROPERTIES1

ELASTIC CONSTANTS STRE~GTH PROPERTIES

ELASTIC MODULUS POISSON"S RATIO E JJ.:rl· PREDICTED .\CTL\L

CONFIGURATION SPECIMEN PREDICTED ACTUAL FIRST F.\ILCRE l"L Tl~l.\TE CLTI:'-1.\TE Z38248l8 NUMBER 10' psi to• psi PREDICTED ACTC.\L STRESS. ksi STRESS. ksi STRESS. ksi Rnl.\RKS

-1 1 17.1 17.0 0.688 0.638 <J3.2 I.HS 9~ ~

0°/41°/-45'/0' 2 17.1 16.1 0.688 09'i0 9~.2 13U -1=0120in 2 16.4 13.3 0.688 O.i3S " lJ:'.2 lHS 105.6 SECO~D LO.\Dl~G

BORONjNARMCO SS05 3 I~ J 17.4 0.688 0.169 9=i 2 13~.8 !00.9

-501 I 5.1 5.0 0.453 0.130 .17 ~ 80 .. i 86 0 0°/45' /-45'/0' 2 5.1 5.0 0.453 0.095 .F~ 86.5 89.3 I= O.J21lin S-994/NARMCO 5505 3 5.1 4.12 0.453 0.119 3-.~ 80s H9.)

-503 I 19 7 14.3 0.439 0.063 l'iO.O 1-6.0 100 H P.\ TTER~ CO~SISTED OF PATTERN NOTED ~ll'o CIRCl"L.\R. 20"", .\T I= O.IODin 2 19.7 18.8 0.439 0.09J iStl.O 1-6.0 105.0 ±~5' .. \~D Oll""o BORONjNARMCO 5505 LO:\C!Tl 01~.\L-CIRCl·-AND NOTED 3 J 9.7 24.7 0.4J9 0.0)5 l:iO.ll 1-6.0 1-u L.\R \\"R.\PS \\"ERE S-99~

-505 J 5.65 6.5 0.247 0.06o ~6.:::. II 0.- 990 P.\ TTER:\ CO:\SISTED OF PATTERN NOTED 2 s 61 5.0 0.247 0 06) -l6.:) 110.- 99.5 2tl"", CIRCTL.\R. 2ll""o .\ T I= 0.100 ±~o' .. \.\;D 60", S-994/1\ARMCO 5505 3 5.65 4.76 0.247 ll.ll:il ..f6 .. 1 Jill.~ T3 LO.';GITl"Dl~.\L

-507 I 17.1 20.0 0.688 (I 173 96.2 13~.8 l :i~ H 0'/45'/-45'/00 SiC-.\ I.\; WHISKERS 1 = 0.120in. 2 17 I l 5.14 0.6HH 0 tOO 9<>.:: l.q H t.1.i - .\ODED TO L.\:1.11:\.\ TE .\T BORON/NARMCO 550.1 ~,.,OF RES!:\ \\"EIGHT +NOTED WHISKERS .3 17.1 17.24 ll.68H ll.l6ll 96.2 1.>~. H tr-

-S09 I' J7.1 11.10 0.688 0.111 9:).2 (qH tr .. >• 0'/4S 0 /-4S'/0' SiC-.\1:-.: WHISKERS 1 = 0 120in. 2 17 l 14.10 0.6HH 0.13H 9-) 2 l.1~.H 161.(> .\DOEll TO L.\~11:\.-\TE .\ T IIORON/NARMCO S.\0.1 l'"o OF RESIN WEICHT +NOTED WHISKERS .1 17.1 12.20 0 llHH 0.171 9:,.2 ~-~.8 (.=)9_9

-511 I 17.1 16.2 0.088 o. !_;~ 9_=i_2 U~.S nu O' /45' j-4S' jO' .-\1,0,--.-\1:\ WHISKER~ 1 ~ 0.120 in 2 17.1 IM.H li.6HS 0 IHH l):'.2 1.1~.H l ~-l.2 .-\DIJE!l TO L\:\II.';.YrF. AT BORON/l':ARMCO SSOS 2'';, OF RESI:\ \\"EIGHT + NOTED WHISK 1-:RS .1 17.1 13.2 0.6HH 0.1.39 l)_~.2 lq H l(l).J

•N,etammg: rmg fatlrd

0 J> ::D 0 0 :!:: . , ..... i . w ... CD

TABLE 3-4 SUMMARY OF THEORETICAL AND EXPERIMENTAL IN-PLANE SHEAR PROPERTIES 1

ELASTIC CONSTANTS STRENGTH PROPERTIES

SHEAR :V!ODULUS, G PREDtCTED ACTUAL VOLUME FRACTIONS

THICKNESS, PREDtCTED, ACTUAL, FIRST FAILURE liLTI\>lATE FIRST FAILURE ULTIMATE :>,IATERIALS PATTERN in. 10' psi 10' psi STRESS, ksi STRESS, ksi STRESS, ksi STRESS, ksi FILAMENTS RES!!'\ voms

S-994/N.\R~!CO 5505 .\LL oo 0.100 1.43 8.3 13.58 - 0.91 - - 7.1 11.0

0.84 6.0 9.62 0.627 0.365 0.008

AVE 1.06 AVE 7.1 AVE1140

0°/±45°/0° !.52 2.03 10.7 46.6 34 . .'i 1.79 - 42.1 !.50 34.9

AVE 1.77 AVE 372

oo; ±41° /90° 1.52 2.08 10.7 46.6 )4 8 2.24 - 34.2 1.93 33.7

AVE 2.08 AVE 34.2

BORO:'I.'/N.\R~!CO 5505 .\LL 0° 0.100 0.88 NONE 15.00 0.77 6.9 12.50

- 0.73 - - 7.3 11.04 0.589 0.367 0.044

AVE0.79 AVE i I AVE 12.84

0°/ ±45°/0° 4.45 6.22 20.4 52.0 46.0 6.17 41.} 6.05 41.0

AVE6.15 AVE 42.7

0°j±45°j90° 4.45 5 48 20.4 52.0 31.7 6.23 33.8 5 80 33.7

:\ VE 5.84 AVE331

0 l> :2:1 n 0 3:

CO:\FIGCRA-TIO~

-1

-501

-503

-505

-507

- 'i09

-511

TABLE 3-5. INTERLAMINAR SHEAR TEST RESULTS1

SPECIY!EN Y!ATERIALS GAGE, WIDTH, AREA, FAILURE LOAD, 1!\TERLAMINAR SHEAR

A~D FIBER PATTERN m. in. A, in~ P,lb STRENGTH= 3Pj(4A), psi

BOROr-:/NARMCO SS05 0.1203 0.4248 0.0511 715 10,480 0°/45°/-45°/0° 0.1194 0.4156 0.0496 657 9,940

0.1158 0.4323 0.0501 683 10,200

S-994 GLASS/NARMCO 5505 01364 0 3625 0.0494 790 12,000 0° /4S 0 /-45°/0° 0.1283 03720 0.0477 795 12,500

' 0.1384 0.3690 0.0511 845 12,400

BOROr-:jr-:ARMCO 5505 0.1179 0.3988 0.0470 488 7,780 0°/45°/-45°/90° 0.1280 0.3950 0.0477 518 8, ISO

0.1217 0.3906 0.0475 570 9,000

S-994 GLASS/NARY!CO 5505 0.1370 0.4007 0.0549 501 6,850 0°/45°/-45°/90° 0.1373 0.3648 0.0501 526 7,875

0.1278 0.3900 0.0498 519 7,805

BORON/NAR~1CO 5SOS 0.1152 0.3422 0.0394 705 13,425 SiC-AI20 3 WHISKERS AT 2o/o 0.1201 0.3620 0.0435 712 12,250 OF RESIN WEIGHT 0.1189 0.3651 0.0434 721 12,450 0°/45°/-45°/0°

BORON/NARY! CO SSOS 0.1181 0.3509 0.0414 680 12,300 SiC-AI 20, WHISKERS AT 1 o/o 0.1173 0.3548 0,0416 669 12,040 OF RESIN WEIGHT 0.1162 0.3532 0.0410 671 12.250 0°j4S 0 /-4S 0 /0°

BORON/NARMCO 5505 0.1190 0.3689 0.0439 629 10,720 AlN-AI.O, WHISKERS AT 2% 0.1242 0.3681 0.0457 661 10,830 OF RESIN WEIGHT 0.1233 0.3678 0.0453 640 10,600 00/45°/-45°/0°

0 )> :D 0 0 s:: , ..... 0 m w .... m

TABLE 3-6. PIN-BEARING TEST RESULTS 1

AVERAGE STRESS AT FAILURE

BEARING HOLE PIN BEARING ULTIMATE STRESS AT

SPECIMEN MATERIALS GAGE, DIA, DIA, AREA, LOAD, BEAR I!\/ G. SHEAR-OUT, 4%0FFSET, AND FIBER PATTERNS in. in. in. in~ lb psi ·psi psi

BORON/NARMCO 5505 0.1200 0.258 0.257 O.Q308 4,440 144,000 14.800 121,000 0°/45°/-45°/0°

0.1200 0.260 0 257 O.Q308 3,620 117,500 12,100 72,700 0.1198 0.2569 0.257 O.Q308 4,230 137,500 14,100 136,500

0.1295 0.255 7 0.255 0.0330 3,562 108,000 11,000 98,000 0.1286 0.2554 0.255 0.0328 3,723 113,500 11,500 82,400 0.1286 0.2565 0.256 0.0329 3,590 109,000 11,100 97,200

0.1260 0.2552 0.2540 0.0320 3.585 112,000 11,400 ~

0.1293 0.2565 0.2560 0.0331 3,665 110,800 11,300 ~

0.1254 0.2563 0.2550 0.0320 3,570 111,500 11,300 ~

S-994 GLASS/NARMCO 5505 0.1368 0.255 0.2550 0.0349 I ,800 53,100 5,300 48,000 0°/45°/-45°/0° 0.1260 0.255 0.2550 0.0321 1,950 60.700 6,200 29000

0.1320 0.254 0 2530 0.0334 I ,990 59,600 6,040 41,400

BORON/N ARMCO 5505 0.1200 0.260 0.25 70 O.Q308 3,590 116,500 12,000 95,500 00/45°/-45°(90° 0.1200 0.260 0.25 70 0.0308 3,640 118,100 12,100 76,000

0.1200 0.264 0.2630 0.0316 3,800 120,000 12,700 49,500

0.1150 0.2555 0.2550 0.0293 4,145 141,300 14,400 119,400 0 1150 0 2546 0.2540 0.0292 4,255 145,700 14,800 113,000 0.1190 0.2550 0.2540 0.0302 4,055 .134,300 13,600 ~

0.1182 0.2552 0.2540 0.0300 3,718 123,900 12,600 ~

0.1171 0.2550 0.2540 0.0298 4,115 138,000 14,000 --0.1192 0.2551 0.2540 0.0302 3,780 125,000 12,700 -

S-994 GLASS/NARMCO 5505 0 1250 0.255 0.2550 0.0319 1,965 61,600 6.300 25,200 0°/45°/-45°/90° 0.1390 0.255 0.2550 0.0354 2,210 62,500 6,350 46,200

0.1360 0.256 0.2550 0.0347 2,185 63,000 6,430 57,000

RORON/NARMCO 5505 0.1215 0.2569 0.2570 0.0313 2,960 96,600 9,770 56,600 SiC-AI,O, WHISKERS AT 2% OF RESIN WEIGHT 0.1212 0.2569 0.2570 0.0312 4,500 144,200 14,800 135,800 oo /45°/-45° ;oo

0.1212 0.2580 0.2580 0.0313 3,620 115,900 11,900 81,000

BORON(NARMCO 5505 0.1185 0.2569 0.25 70 O.G305 3,710 121,800 12,500 90,600 SiC-AI,O, WHISKERS AT 0.1189 0.2559 0.2560 0.0304 3,910 128,600 13,200 39,700 1% OF RESIN WEIGHT 0°(45°/-45°/0° 0 1182 0.2559 0.2560 0.0302 3,670 121,300 12,400 118,600

RORON/NARMCO 5505 0.1200 0.2610 0.2610 0.0313 4,200 134,100 14,000 79,500 AIN-AI,O, WHISKERS AT 0.1200 0.2610 0.2570 O.Q308 4,050 131,500 13,500 98,800 2% OF RESIN WEIGHT 0.1200 0.2630 0.2630 0.0315 3,660 - ~ 85,000 0°/45°/-45°/0°

0.1163 0.2570 0.2560 0.0298 3,860 129,500 13,300

l. 124,000

0.1163 0.2564 0.2560 0.0298 3,775 126,600 13,000 117,200 0.1170 0.2560 0.2550 0.0298 4,040 135,500 13,800 115,400

FAILURE MODE

COMBINED SHEAR AND BEARING SHEAR-OUT COMBINED SHEAR AND TENSION

SHEAR-OUT

SHEAR-OUT

BEARING

BEARING

REARING

BEARING

BEARIJ>;G

COMB!:\ ED SHEAR AND BEARING BEARIKG (AT y, DIAMETER LOADIKG PIN) CO:\·!BINED SHEAR AND TENSION

BEARING COMBIK ED SHEAR AND BEARING COMBINED SHEAR A;-.;D BEARING

REARING BEARING SHEAR (AT v, DIAMETER LOADI;-.;G PI:-o:)

SHEAR-OUT

TEST DATE

7j67

12/68

12j68

10/67

7 j67

12/68

12/68

10j67

12/67

12j67

'!6'

12/68

. ., ..... i

I

w -A

en

120

100

80

40

J I I

20

~//~ 0

0

1

I v I I I v

,, /~

,, /

4,000

DARCOM-P 708-318

-65°F I

l (O) 6T

SPECIMEN T-UL-7 IITR I COUPON LONGITUDINAL TENSION

i I

EL = 18.6 Msi I t i

I .. Er = 4.17 Msi _j c I I

I J i I

i ,.. .. ..... I ,.. SPECIMEN EC-UT-7 ..,P'

SANDWICH PANEL ,-"' ~.,. TRANSVERSE COMPRESSION

~,

!-''

8,000 12,000 16,000 20,000 Strain f, JLin./in.

Figure 3-1. Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal Tension and Transverse Compression Stress-Strain Curves at -65°F (Ref. 2)

3-9

DARCOM-P 706-316

200 .------r------r--- SPEC I MEN TLBB-UL I

LONGITUDINAL TENSION~ (BEAM) ~

180~----~~------~-------+'-------+----~~J' __ • ____ ~------

/

,7, ROOM TEMPERATURE

;' ;"

, .. , .. [O] 6T ,,""

160~----~---+- -+-----+~----4--~~~-4-----~

/( ,,,,.-"

,' ,1 /~SPECIMEN CLBB-ULI

,, I ----t---1----+--7 LONGITUDINAL -----1

/~ /1 COMPRESSION (BEAM)

/ I , ;' ~·

---+r---1[ l

1401---

Er = 3.1 Msi c

EL = 19.6 Msi l

EL = 16.0 Msi c

Er = 3.7 Msi l

120 ~----

/

t •' T-UL- 10

] I ~LONGITUDINAL TENSION .n / (COUPON) ~ lQQ~----~----+--~--~L__ I

ifJ I l/l,,l p I / .'/////// ~/lli/J/1:

ao~------~----~--~- -

/,// 1111111 ~ Ill ~ 1111111 I. 6 l' N .

60 1-------l~f----/;_...,.l~/-/l~-rr +:~I::: t j I I I I

40 .. • t--- SPEC I MEN CLBB-UT I ___ _

/;

" / TRANSVERSE COMPRESS ION :r~ v SPEC I MEN TLBB-UT 1 (BEAM) . -···" 1

' ~RANSVERSE TENS I ON li ............ --·····r· (BEAM) ...... .............. T-UT-10

20 ~-~--1----- 1 -- ~........ TRANSVERSE TENSION

' J? ~~-- (COrN) I I 0 ~~--~ ~ - -l- - -- - - l- -1 -

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Strain ~. 1-1in./in.

Figure 3-2. Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal and Transverse Tension and Compression Stress-Strain Curves at Room Temperature2

3-10

"' ~

DARCOM-P 706-316

140 t-----+---+-------;---1 SPEC I.Jl-13 I I COUPON l LONGITUDINAL TENSION

~8 -+--l--l-+----+--+----t--t-----1f------t---J

(0]6T 120~--~ ~--+,~--+--~---~--~-----r---r--~-~

EL :::: 18.8 Msi

I OO t----lr----+-~-.......,/r----t----t---T EL~ :::: 14.8 Msi Er = 0.44 Msi

t

Er = 1.18 Msi

80

I c

~ J

l I !

I I I

"' I SPECIMEN CCLB-UL-10

~ SANDWICH BENDING BEAM "' 11) .... ci)

60 1---+--+------ LONGITUDINAL COMPRESS I ON -+--~----~-~-------1

ll I

Ill . 40~--~,~.--+--4------+---4--~----4----~--4---r-~,

j/ SPEC I MEN EC-UT-11 I r----!J.-1:··'~: ---t---t------t---t---r---+-- SANDWICH PANEL

• TRANSVERSE EDGEWISE COMPRESSION

20 J' .. -1 --

I __.......--......-spECIMEN T-UT-13 O ~~ •••••••••"I TRANSVERSE TENS I ON

0 4,000 8,000 12,000 Strain E, J.Lin.lin.

COUPON

16,000 20,000

Figure 3-3. Unidirectional Graphite/Epoxy (Type AS/3002-Batch) Longitudinal and Transverse Tension and Compression Stress-Strain Curves at 350°F (Ref. 2)

3-11

DARCOM-P 706-316

8 I I I I I IITRI COUPON FIBERITE PREPREG

7 TRANSVERSE TENSION [90]6T

6

5

l (ACTUAL) = 0.00767 IN/PLY (RT) /

350oF t (ACTUAL) = 0,00817 IN/PLY (3soo F) ·'

.. ' . . '

~/ • . . ;->

·;;; ..:.:

<Ji "' ., .!:::

4 IJl Ill

"' c Ill

,' ' . .. . I . .

RT . . • j . . ,.

r7 . . .. . . . ~

3 I • . , . . . . .

I~

4 ) I IIIII

I I

.... -

I • I . . . -·· I I I I I

•• -

/ . . ,~··

TEMP RT 350° F .,. .. - -

2.

I ,. .. FT, ksi 4.51 5.56 •• [ .• • -v.· ET, Msi 1.35 0.964 .• [

~ ••• 0.0266 0.0300 -

~· li-TL

I I I I I I 0 0 I ,000 2,000 3,000 4,000 5,000 6,000

Strain t, ~-tin./in.

Figure 3-4. Graphite/Epoxy Typical Transverse Unidirectional Tension Stress-Strain Properties (Type AS/3002 Continuous-Treated Fiber)2

3-12

DARCOM-P 706-318

40 -~

ll' RT

v /

'f'

/350° F t (ACTUAL) = 0.00588/PLY /i.,

~ ·~ p

35

30

25

·:;; ...><: ,.; <rJ Q.) 20 !:

CFl .... "' Q.)

...c: CFl

15

~r;'

_J~/ RT 350°F

Gxy = 2. 43 2.29 Msi

g~

I ~~

\

I/! \

'--" /: v W'

p~ '' ~\

I' RAIL \

7 SHEAR \

10

5

0 rt 0 0.004 0.008 0.012 0.016 0.020 0.024

Shear Strain -y xy• in.lin.

Figure 3-5. Graphite/Epoxy-In-Plane Shear Stress-Strain Properties-Crossply I 0/±45/90is (Type A/3002 Batch-Untreated Fiber) 2

3-13

DARCOM-P 706-316

.3-3 MECHANICAL PROPERTIES OF ADHESIVES

ture stress in a JOlnt. With regard to Young's modulus for an adhesive there needs to be re­

solved the difference between the tensile modu­

lus of an adhesive in free bulk, free film, and con­strained film Uoint) form. Kutsha and Hofer3

assumed that the tensile modulus obtained from

The important mechanical properties to iden­tify for an adhesive are Young's tensile modulus, shear modulus, precision elastic limit. and frac-

'<;) .... _r;

~ c:: ::: iii .... "" v

...::: (/)

.... "" c:: .E ~ 2: c:: -

32 I I I

30 - - O [O] 13T

28 r---· 0 [0/!45J ZS

0 [0/±45] 25

26 ·-r--r -¢' [0/'!'45/90] 25

24 . • [90/±45] 25

22 •[90/+45]

- 25

~ [±45] 35

20

18

16

14

12

10

--._, ~ ~ ....

~

~ I

~

v "-... .~g: Lo -+,-:-"' ~ - ":._· . ...,. ~o,, / ... i.4' ' ~ "·:· ~ ' j ! _,., """'-......,

8 ~/ -<)- ...... ~. ~L

~t-.. 1"---. ~~4. . -~-- -·

1-'& i I • ~ . - . :: .. :1::. 6

4

2

0 -100

_.,.. .. -.-r .... -J::J"'"

0

~·-+·- ~ ... '!lb. - • - • ~ I ._ .. -. ... ..., ·--4~- I I

~-.,..~~~~ .. r I --...... J ... I

100 200 300

Tl'mpl'ralure, °F

-

l

I I

I I

Figure .3-6. lnterlaminar Shear Strength vs Temperature for Various Orientations­Type AS/3002, Batch, Graphite/Epoxy2

3-14

the behavior of adhesives in free film form could be used to characterize their general behavior. Table 3-7 summarizes the mechanical proper­ties of several adhesives determined from tensile tests performed on adhesive films. Rutherford and Hughes4 maintain that the important ten­sile modulus to determine is the effective tensile modulus £*-the modulus of the adhesive in thin

DARCOM-P 706-316

film form constrained between two adherends. In such a constrained state the adhesive cannot de­form according to its own Poisson's ratio but conforms to that of the adherend which is gener­ally lower. Such restriction effectively increases the tensile modulus. Tables 3-8 and 3-9, and Figs. 3-7 through 3-18 show the results of their work on several adhesives. In the case of Epon

TABLE .3-7 SUMMARY OF MECHANICAL PROPERTIES OF ADHESIVE FILMS3

Tensile Maximum Deflection Chemical Type Strength, Strain, Modulus, Rate,

Adhesive Manufacturer psi % I 0' psi in.jmin

FM 1000 Polyamide Epoxy 3400 >300 1.60 0.05 American Cyanamid, Bloomingdale Division

Metlbond 400 Nylon Epoxy 7310 200 2.92 2.0* Whittaker Corp. Narmco Materials Div.

AF 131 Modified Epoxy 5300 1.15 4.82 0.05 3 .M Co.

FM47 Vinyl Phenolic 8300 1.50 6.21 0.5* American Cyanamid, Bloomingdale Division

*No strain rate efTect on modulus.

TABLE 3-8. AVERAGE SHEAR MICROSTRAIN PROPERTIES 4

,---EC-2214 ADX-41.2

-65°F 74°F 200°F -6]Cf 74°F

Virgin Moclulus, psi 301,300 2HO,fl00 L\7,900 26 7,000 lll9,000 Modulus After Stress, psi 296,300 216,300 12'i,OOO 201,(,00 140,SOO Prercision Elastic Limit, psi 134 II S <51 433 II 0 Microyield Stress, psi 1250 390 <57 17:\4 290 Fracture Stress, psi 12,904 7600 3996 41.'i0 7400 Fracture Strain 221.8 X 10 _, 206.5 x to-• 344.79 X 10 _, 2H.64 X 10 3 '!441lX I0- 3

--

TABLE .3-9. AVERAGE TENSILE MICROSTRAIN PROPERTIES'

Virgin Modulus, psi

Modulus After Stress, psi Precision Elastic Limit, psi Microyield Stress, psi Fracture Stress, psi Fracture Strain

•0.003 in. bond line .. 0.012 in. bond line

EC-2214

-670f 14° F

I ,621,300 I, 120,000

I ,402,200 1.11:1.000 - \7 50 - )360

12,.'i.'i0 11,140 1263 X JO-> 22.HO X 10 '

.----ADX-41 2

200°F -07°F 74°F

410,900 963,3(Xl HOO,HOO* 707,800••

39H,Il00 95),7()() 707,H00**

102 j l.'i3 4060 90.5X I0- 3

J210 2790 .121 () 'iHIO 15. H26 9260 20.4X 10' 17.~4 x to-•

·-

:\)()Of

29,500 2\700 <3H <38 .'\ 1.\0 S2S.O X to-•

.100°F

3.'12,400•

261,400• 7H llH 6300 82.11 X 10 _,

3-15

y> ........ o-

"' ::;

"' ::l ;:; -o

0 ::; ~ ·;;; c: ..,

E-..,

·= '-' '-'

'"'"' '"'"' ~

1.0

.8

lo ()

.6

.4

.2

0 -100 0 100 200

Temperature, °F

Figure 3-7. Tensile Tests, Epon 828/V40, Stainless Steel Adherends as a Function of Temperature4

c )> :II n 0 3: . ., ..... 0 CJ) . w ... CJ)

"' "' c "' b

"' .. u ~

700~--------~----------~----------~----------~----------~--------~

~ 500

425L---------~~--------~--------~L----------J----------~--------~ 10 20 30 40 50

Bond Thickness, mils

Figure .3-8. Tensile Tests, Epon 828/V40, Stainless Steel Adherends as a Function of Bond Thickness~

60

c J:lo ::u (') 0 3:

~ 0 ' - )> 00 :;g

(")

12 0 ~ ' "tJ

-..1 0 ~

c:., ... 10 ~

on .....:

ii 0) ...

8 tfl .., ... 3 '-'

"' ~ ~

6

4 0 5 10 15 20 25 30 35 40

Bond Thickness, mils

Figure 3-9. Tensile Tests, Epon 828/V40, Stainless Steel Adherends4

DARCOM-P 706-316

192 ............... 0

~ 160

oo~B 128

·;;; ..:.: .n

..2 ;:::

"tl 0 96 :e ... "' <l)

...<: rJJ

64

32

0 -SO

0 0

0 50 100

0

ISO 200

0 \

Temperature, °F

Figure 3-10. Shear Tests, Epon 828/V40, Stainless Steel Adherends4

828/V 40 epoxy adhesive the effective tensile modulus in a stainless steel joint is nearly twice the bulk tensile modulus. Generation of this type of effective mechanical data is essential to reli­able joint design data input. Table 3-10 presents data on some additional adhesives.

The tensile property data are obtained by the tensile testing of films or cast coupons of adhe­sive. The effective tensile property data are yield­ed by circular butt tensile bonded joint speci­mens. The shear modulus G is obtained from napkin or torsion ring tests which provide the stress-strain behavior of the adhesive in pure shear. The shear properties of several adhesives

are presented in Tables 3-8 and 3-10 and Figs. 3-10, 3-15, and 3-17. Hughes concludes the follow­ing regarding the tensile modulus of the adhe­sives tested:

1. E* increases as bond line thickness de­creases.

2. E* generally decreases with rising temper­ature.

3. Permanent adhesive strain lowers E*. 4. Increasing the strain rate for viscoelastic

adhesives raises £*. 5. Tensile and compressive moduli are the

same.

3-19

DARCOM-P 706-316

2.0

co ·;;; ~ ,; ::J 1.5 ::J co........._

-o 0 OS ~

..9: ·;;; I::

"' E-< 1.0 oo ..,

" . .;: u ~ oo .....

\ '"" 0.5 0

\

0 -100 0 100 200

Temperature, °F

Figure 3-11. Tensile Tests, EC2214, Stainless Steel Adherends as a Function of Temperature•

Hughes concludes the following regarding the shear modulus G of the adhesive tested:

1. G decreases with rising temperature. 2. Permanent adhesive strain lowers G. 3. Increasing the strain rate increases G. 4. G is independent of adhesive thickness be­

tween 4 and 40 mils. It is clear therefore that the conditions under

which shear and tensile modulus are obtained for a given adhesive adherend system can alter their values and must be taken into consideration.

.3-4 DESIGN DATA GENERATION

Although there are much published data on the mechanical properties of composites and

3-20

adhesives, it will always be necessary to conduct tests on specific composite fiber orientations and on adhesives under the special environmental conditions in which a design is to provide service. Published graphical or tabulated data represen­tations are useful primarily as a starting point for the designer but the data represented and the manner of generation may not be directly ap­plicable to a given design. Testing for materials acceptance is also a requirement. The data ob­tained for a given property are a function of the test specimen configuration and the test method employed. The paragraphs that follow discuss some test methods and the type of data they yield.

2.0

·;:;; :::;: 1.5

"' -= ;;:s -c 0

:::;:

0.5

0 -100 0 100 200

Temprraturr, °F

Figure 3-12. Tensile Tests, EC2214, Aluminum Adherends4

(.).> I

N N

1.6

--. ·~ 1. 2 ::g 00 E ::s

-o 0

::g ~ .·;;; o.a c

Q.J

E-< Q.J

>

'-' Q.J

::::: ~

0.4

0 5 10 15 20 25 30 35

Bond Thickness, in. X I03

Figure 3-13. Tensile Tests, EC2214, Stainless Steel Adherends as a Function of Bond Thickness4

0 > :a n 0 s: ' "tt

.,.j 0 0)

w .... 0)

40

DARCOM-P 706-316

0

5000.

4000

<FJ c.. ...: 3000 E

...J

.=: ;;; ~ w c 2000 0

.1£:. u ..,

0::

1000

0

-100 0 100 200 Tt•mperaturt', °F

Figure 3-14. Tensile Tests, EC2214, Stainless Steel Adherends4

3-4.1 COMPOSITE MECHANICAL PROPERTY TESTS

3-4.1.1 Tension Properties

The properties of laminates m tension are usually determined either from tension coupons or sandwich bending beams. The tension coupons are either the dog bone type used in ASTM D638 Type 1, or a tab-ended, straight­sided specimen or a modified bow tie (long­necked) specimen. For military applications a modified ASTM D638 Tensile Properties of Plastics is to be employed (Ref. 5) for woven fabric (bi­directional) laminates. For nonwoven (direc­tional) laminates ASTM D-3039 Tensile Properties of Oriented Fiber Composites is the method called for

with modifications (Ref. 5). The specimen em­ployed is commonly referred to as the IITRI (Illinois Institute of Technology Research In­stitute) coupon.

Another means of obtaining tension property data employs the sandwich bending beam (Fig. 3-19). The sandwich bending beam method is a more expensive method because of the nature of the specimen but the higher strengths obtained with the sandwich beam indicate that the localized stress concentrations inherent in the IITRI coupon serve to yield lower strength data. Figs. 3-1 through 3-3 present tension stress­strain data for Type AS/3002 from both IITRI coupon and sandwich bending beam tests.

3-23

-100 0 100 .2()()

Temperature, °F

Figure .3-15. Shear Tests, EC2214, Aluminum Adherends4

2.0~--------------~------~~------,-------~--------r-------,-----,

1.5

~ 1.0 ·;;;

c::: 111

E-< 111 ... c::; ~ ~ 0.5

-100

-co----o ----0 ~

0

o __ o ____ _

-o-

0 100 200

TPmpcrature, °F

Figure 3-16. Tensile Tests, Metlbond 329, Aluminum Adherends4

0 > ::a n 0 !: ' "11

..... i w .... G)

120,000

·:;; .....

"' 80,000 ::I -a

-o 0

::s .... <U

"' -= r.n

40,000

0

0 0

--- 0 ~0 ---..::0~---i

-100 0 100 Temperature, °F

Figure 3-17. Shear Tests, Epon 9601, Aluminum Adherends'

200

0 l> ;, 0 0 ~

CJ)

0..

E ;.3

·= "' __<.g .... c .s "' ·;:::: OJ ...

0...

DARCOM-P 706-316

4000

3000

2000

1000

0 0

-100 0 100

Temperature, °F

200

Figure 3-18. Tensile Tests, Metlbond 329, Aluminum Adherends~

TABLE 3-10. ELASTIC PROPERTIES OF ADHESIVES 1

MATERIAL F, psi

t\F-110 (MOD-EP) 123,<PH REI>UX K-6 (MOD-PH) .100,00() FM-47 (VINYL-PH) 125,000 MB-40!1 (NY-EP) 1.'\'). 000 FM-1000 (NY-EP) 1!10,000 EPON 422.) (EP-PH) 395,000 EP0:'\1 VIII (EP-P.-\) S0!\,000

MOD-EP = 1\.IOIJIFIED EPOXY MOD-PH = MODIFIED PHENOLIC

PH = Pll ENOLIC NY= NYLON EP = EPOXY Pi\ = PASTE

G, psi J1. T, psi u, psi SOURCE

- - -- 'J2'>H 3~1 CO~IP.\NY

1!14,000 0 . .160 !1200 !1300 FPL-011 117,000 0 .. "\!\~ .1720 4350 FPL-011 49,100 0.410 5550 !1000 FPL-011 64.100 0.40!1 7910 69'>0 FPL-011

I (J(), 000 0.294 5'\20 2560 FPL-011 I HO,OOO 0.412 6050 - FPL-011

FPL = FOREST PRODUCTS LAB 1·: = :-..tOIJULUS OF ELASTICITY G = l\.lODULUS OF RI(;IDITY JJ. = POISS()I\'S RATIO T = PURE SHEAR STRENCTH cr = PLIRETENSILESTRE;\/(;TH

3-27

DARCOM-P 706-316

E = tensile stress/tensile strain = J/ E, psi

p .. t:f'==/?=;E=w==;:!.~P'&=A~.. p

t~

pu P/ ( Wt), psi where

pu ultimate tensile strength, psi

P = failure load, lb

(1) Tension Test:

COR E

I "' (2) Compression Test:

tz

~

t P/2

J=:j_ P/2 ~·

p

J. t I

W = coupon width, in. E = elastic modulus, psi f = tensile stress, psi f = tensile strain, in./in.

(A) Tension Coupons

Jtu = Pl. ----:(;;--------..)~ , ps1

2!1 w (; + i + i

ru PJ.

J~ ( ) , psi

1 lt !2 2!2~ C+T+T

where pu ultimate tensile strength, psi ru ultimate compressive strength, psi

tb !2 laminate thickness, in.

C= core thickness, m. W= width, in.

P= failure load, lb J. = length between fulcrum and load, in.

(B) Sandwich Bending Beams

(cont 'don next page)

Figure 3-19. Reduction of Equations for Different Types of Specimens Tested

3-28

p

p

p

r I

(!) (!) I I e G)

I C!) (!)

L I I

L (!) (i)

I I (!) (!)

I I

p

CORE

DARCOM-P 706-316

G = shear stress/shear strain = .f"/ "Y = psi .f"u = Pj(Wt), psi

where G = shear modulus, psi

feu = ultimate shear strength, psi P = failure load, lb

W = width, in. t laminate, thickness

j" shear stress, psi "Y shear strain, in./in.

(C) Edgewise Compression Specimens

G = shear stress/shear strain = ri"Y j•u = Pj(Lt), psi

where G= shear modulus, psi

.f•u = ultimate shear strength, psi f"= shear stress, psi "Y = shear strain, in.jin. I' = failure load, lb L = length, in. t = laminate thickness, in.

(D) Rail Shear Specimens

p•u = 3P/ ( 4 Wt), psi where

ps1

p•u = interlaminar shear strength, psi P = failure load, lb

W = width, in. l = laminate thickness, in.

(E) Interlaminar Shear Specimens

(com'd on next page)

Figure 3-19. (cont'd)

3-29

DARCOM-P 706-316

(1) Single-Lap Joints:

j {lex: ult

where !'lex ult ultimate flexural strength, psi

P = failure load, lb S = distance between fulcrums, in.

W = width, in. t = laminate thickness, in.

(F) Flexure Specimens

ADHESIVE

NOTE: For compression sandwich specimens, there were two face sheets (one per face joint) and, hence, the equation must be divided by 2, i.e.,

jgu Pj(2WLa),psi

(2) Symmetric Double Scarf joint:

Pj (2 W La), psi

NOTE: For compression sandwich specimens, there were two face sheets (one joint per face sheet) and, hence, the equation must be divided by 2, i.e.,

j!,u P/(4 WLa), psi

(cont 'd on next page)

Figure 3-19. (cont'd)

3-30

DARCOM-P 706-316

where j;_u ultimate shear strength of adhesive joint, psi

P = failure load, lb W = width, in. La == length of adhesive joint, in.

(G) Bonded joints (Adhesive Shear Strength)

FASTENER

(1) Bearing Strength:

jbru == Pj(Dt), psi

(2) Net Tension Strength:

p

2Dt ( ~ -0.5) , ps1

(3) Shear-Out Strength:

p j•u == ---r---~-

2Dt ( ;) -0.5) , psi

NOTE: Compression mechanical joints all failed in bearing; hence, bearing strength is defined as

rru PI ( DtN), psi

(cont'd on next page)

Figure .3-19. (cont'd)

3-31

DARCOM-P 706-316

where f/Jru flu =::

j'u P== I

D e ==

s =

ultimate bearing strength, psi ultimate tensile strength, psi shear-out strength, psi load for appropriate failure mode, lb laminate thickness, in. bolt hole diameter, in. distance from edge of bolted joint to center of bolt hole, in. distance fron: side of bolted joint to center of bolt hole, in .

. N == number of fasteners, dimensionless

(H) MechanicalJoint

Figure .3-19. (cont'd)

.3-4.1.2 Compression Properties

Compression data should be obtained b~ the sandwich bending beam method (Ref. 5J for nonwoven laminates tested in tht> direction of the fibers (0-deg orientation). Woven fabric lami­nates tested in the 0-deg or 90-deg direction, and nonwoven laminates tested in the 90-deg direc­tion should be tested in accordance with ASTM 0695 Compressive Propertie5 of Rigid Plastics with modifications as outlined in Ref. 5.

Another method uses a tubular specimen, as described in Ref. 1, to generate the compression data on glass and boron composites presented in Table 3-3.

3-4.1..3 Intralaminar Shear Properties (In-Plane Shear)

These properties are obtained by the use of the "rail shear test" (Ref. 5) for any angle for which shear characteristics are desired. Ultimate shear stress f'u is determined as follows:

(3-1)

where P == load on the rails, lb

3-32

t = length of specimen, in. t = thickness of specimen, in.

The shear modulus is obtained as follows:

shear stress p . G = = - ps1 (3 2)

shear strain 'Y ' -

.3-4.1.4 Interlaminar Shear Properties

These properties have been determined ac­cording to the method prescribed in ASTM 02733 lnterlamlnar Shear Strength of Structural Rein­forced Plastics at Elevated Temperatures, Method A. However, for other reinforcements such as boron, graphite, and Kevlar, ASTM 02344 Apparent Hrm:;,ontal Shear Strength of Remforced Plastic by the Short Beam .i!ethod is recommended. It is sug­gested that the fiberglass reinforced composites be tested this way as well.

3-4.1.5 Flexural Properties of Laminates

These properties should be determined ac­cording to ASTM 0790 flexural Properties of Plastics. Like interlaminar shear, a simple beam specimen is used but the calculations differ as shown in Fig. 3-19.

DARCOM-P 706-316

3-4.2 SUMMARY 3-4.1.6 Bearing Strength of Laminates

Bearing strength determinations should be conducted according to ASTM 0953 Bearing Strength of Plastics.

3-4.1.7 Test Specimen Schematics and Data Reduction Equations

Fig. 3-19 depicts the specimens and equations to be used to obtain the materials property data needed for design.

Variations on some of the tests discussed here have been used and the data they yield may be more representative of the material than the tests recommended. What is important is that the test method used be known and that the limitations and inherent imperfections in the test and resul­tant data be recognized. No single data source should be regarded as infallible or absolute. Tables 3-11 and 3-12 summarize the tests used and data yielded for both laminates and adhesives.

TABLE 3-11 LAMINATE PROPERTY DETERMINATION

Test Method

Sandwich Beam

ASTM 03039 (IITRI Coupon)

ASTM 0638 (Long Bow Tie Coupon)

Tubular Compression

Rail Shear

ASTM 02733

ASTM 02344 (Short Beam)

ASTM 0953 (Pin Bearing)

Data Yielded

Tensile and Compressive Properties f'",Jc", EL, Er

Tensile Properties (nonwoven) F'", EL, Er

Tensile Properties (woven) /'", EL, Er Compression Properties j"",E

Intralaminar (in-plane) Shear JIJUt (;

lnterlaminar Shear (fiberglass only) f'lJJ

Interlaminar Shear (fiberglass, boron, graphite, Kevlar)

l'" Bearing Strength j•'

TABLE3-12 ADHESIVE PROPERTY DETERMINATION

Test Method

Napkin Torsion Ring Test

Thick Adherend Lap Shear

Circular Butt Joint

Data Yielded

Shear Properties !'", G Shear Properties !'", G Tensile Properties /'", E

3-33

DARCOM-P 706-316

REFERENCES

1. G. M. Lehman and A. V. Hawley, Investigation of Joints In Advanced Fibrous Com­posites for Aircraft Structures Vol 7, Technical Dis­cusrion and Summary, Technical Report AFFDL-TR-69-43, Vol. 1, Wright-Patterson Air Force Base, OH, June 1969.

2. L. M. Lackman, et al., Advanced Composites Data for Aircraft Structural Design, Vol. IV, ~[aterial and Basic Allowable Development Graphite/Epoxy, Tech Report AFML-TR-70-58, Vol. IV, Wright-Patterson Air Force Base, OH, September 1972.

3. D. Kutscha and K. E. Hafer, Feasibility of Joining Advance Composite Flight Vehzcle Structures, Tech Report AFML-TR-68-391, USAF Contract No. AF33 (615)-3962, Wright-Patterson Air Force Base, OH, January 1969.

3-34

4. E. J. Hughes and J. L. Rutherford, Study of Micromechamcal Properties of Adhesive Bonded Joints, Pica tinny Arsenal Tech Report 3 7 44, Performed under contract DAAA 21-6 7 -C-0500 by Aerospace Research Center, General Precision Systems, Inc., Little Falls, NJ, August 1968.

5. Guidelines for the Generation and Use of Data In Mihtary Handbook 77A Part 7, PLASTEC Report R47, Picatinny Arsenal, Dover, NJ, January 1977.

6. Advanced Composite Wing Structures, Boron/ Epoxy Design Data, Vol. II, Analytical Data, Tech Report AC-SM-ST -8085, F33615-68-C-1301, Grumman Aerospace Corporation, Wright-Patterson Air Force Base, OH, November 1969.

DARCOM-P 706-316

CHAPTER4 BASIC BONDED AND BOLTED LAP JOINT CONFIGURATIONS

AND DESIGN VARIATIONS The design and strength of basic type joints -singLe Lap, double lap, scarf, stepped, boLted, and combinations- are

presented as functions of adhesives, .fiber onenlation, andjibers. Comparisons of Joint strengths and u•ei.ehts are made. Methods of reducing stress concentration in joints are presented. The response of various bonds to fatigue are presented.

4-0 List of Symbols

D = bolt hole diameter, in. e = distance from edge of bolted joint

to center of bolt hole, in. E = joint efficiency, dimensionless

elastic modulus of adhesive, psi EL = elastic modulus of composite with

fibers parallel (longitudinal) to direction of applied stress, psi

Er elastic modulus of composite with fibers perpendicular (transverse) to direction of applied stress, psi

£ 1 elastic modulus of composite, psi £ 2 elastic modulus of joined material,

ps1 fnr bearing strength, psi

pu·u ultimate bearing strength, psi n shear strength of joint, psi

f:na:r maximum shear strength of adhesive, assuming plastic shear stress distribution, psi

]"" ultimate shear strength, psi f'" ultimate tensile strength, psi

Fs average stress, psi G shear modulus, psi

La length of adhesive joint, in. N = cycles to failure P = applied load, lb R = radius, in.

.r - distance from side of bolted joint to center of bolt hole, in.

ti thickness of materials, i = I, 2, ... , in. We maximum width of plastic zone of

joint, in. a ... = tensile stress in region A, psi

a 8 tensile stress in region B, psi r shear stress in adhesive, psi

shear stress at bond line, psi

4-1 GENERAL

Designing composite JOints generally can follow the same priorities established for mechanical and bonded joints using isotropic materials. The relatively low shear strength of epoxy resin composites, however, make this property limiting in many composite joint designs - mechanical and bonded.

4-2 BONDED JOINTS

When designing a bonded joint, composite or otherwise, the bonded area should be as large as possible and as much of the bond area as possible should be working, i.e., transferring loads. This implies good strain compatibility between joint members and good stress distribution in the adhesive. The joint design should be stressed in the maximum strength mode which, for adhe­sives, is shear or tensile. Peel and cleavage stress­es should be minimized. Good bonded joint design requires that the adherend materials, joint configuration, and load directions work toward the aforementioned aims. This serves to distribute stress and avoid stress concentrations, particularly at edges, which create peel and cleavage forces .

In selecting adhesives it is important to con­sider the rate at which the load is to be applied to the joint. When loads are applied suddenly, as impulse or impact loads are, the adhesive must be elastic enough to take shock loading without

4-1

DARCOM-P 706-316

failing. Often there can be conflict in this area. Thermosetting adhesives, usually rigid and of high tensile and shear strength under static and dynamic loads, are often impact sensitive and ex­hibit poor impact strength. Elastomeric adhesives generally possess poor shear and ten­sile strength but have good peel and cleavage strength and can withstand shock loads. Sustained dead loading of bonded joints can cause creep of some adhesives, and this behavior must be ascertained to avoid creep weakening of and dimensional changes in the structure.

Bonded joint strength depends greatly on the properties of the adhesive but maximum strength is achieved when the relative stiffness of the adherends is the same. This situation provides a symmetric stress distribution and the best joint efficiency. For highly loaded joints, however, the ultimate shear strength of the adhesive alone (determined from torsional ring tests) is not a good criterion for adhesive selection. Where strain incompatibility exists in the adherends, a more ductile adhesive can improve joint strength:

To achieve strain compatibility in a joint com­prised of two adherends of the same material, the thicknesses of both adherends must be equaL When bonding different adherend materials it is important to match adherend stiffness by matching the products of the elastic modulus E and thickness t, i.e., Et*, of the joined materials.

When large loads are required and length L to thickness t (L/t) ratios approach 25, the inter­laminar shear strength of the laminate is limiting. For improved bonded joint capability, interlaminar shear strength improvements in the laminate must go hand in hand with improved adhesive shear strength.

4-2.1 BONDED SINGLE-LAP JOINTS

This type joint is the simplest of bonded joint configurations. In joints of this type the offset loading characteristics produce the highest stress

*In subsequent discussions we will refer to "Et ratio" for convenience. The correct interpretation is "a ratio of Et's ", i.e., E,t,j(E2t2 ).

4-2

concentration factor (SCF) and carry the least load at the center of the joint. Stiffness mismatch in the adherends will serve to further aggravate an already poor stress distribution situation in the joint. Fig. 4-1 shows this effect for several combinations of boron, glass, and aluminum joints using Shell 951 adhesive (shear stress in adhesive T = 6000 psi). When the results fall along the T = 6000-psi line, the adhesive is equalizing the shear stress over the entire area. As lap length increases, stress concentrations are set up at the lap ends causing failure at lower loads. Fig. 4-2 illustrates how increased Et ratio improves the average adhesive stress in the joint. (Pattern configurations are shown in Table 4-1.) The improvement is even more pronounced for larger L/ t ratios. In addition, as lap length in­creases, peel stresses are introduced due to bending. The ability of the adhesive to equalize stresses over the joint area also becomes less as adherend materials are mixed (E1t1 ,.,e. E2t2 ).

When adherends are not of the same material, unfavorable thermal stresses can also be set up between adherends during adhesive cure which adversely affect joint strength. Table 4-2 sum­marizes some single-lap test results, using Shell 951 adhesive on boron/aluminum and fiber­glass/ aluminum joints.

4-2.2 BONDED DOUBLE-LAP JOINTS The double-lap joint configuration eliminates

much of the bending and peel stresses present in the single-lap joint. Fig. 4-3 and Table 4-3 show the results of boronjaluminum and glass/ aluminum joints. It can be seen that for the boron/aluminum joints a higher average bond stress was realized probably due to the lower bending and peel forces. The same was not true for the glass/aluminum double-lap specimens.

The effect of stiffness matching in double-lap joints is clearly illustrated in Figs. 4-4 and 4-5. It is easily observed that as the Et ratio (smaller Et divided by larger Et) approaches unity, there was a general increase in joint strength. Table 4-4 summarizes test results for some composite/ metal double-lap joints of varying Et ratios.

4

3

·;;; ...:.: ~ be 0::

b lfJ 2

= 0 -.

0 0

4

3 . iii ...:.:

.rJ ~ 0:: ., ...

cil 2

0::

0

0

0

I

tl T I I I

T

PATTERN B

':'/;~: / ,_ I

5!1 I - I f:J I

PATTERN A

.r ' 0 ..

BORON/BORON

BORON I a 0.04 IN.

SHELL 951 ADHESIVE

0.5 1.0 2.0

Lap Length, in. ..

-·

~ T

g ! PATTERN A

~ ... ... I -I

"" ...

f:J· " ~ .r ""~~~ 0 ... ~ .. T .,."" !>-~ / '?

... ~ ; I I I " I I

I ; ;

J. 1 ,,

FIBER GLASS I FIBER GLASS

GLASS t 2 0.04 IN, SHELL 951 ADHESIVE

0.5 1.0 2.0

Lap Length, in.

4

3

'iii ...:.:

.rJ ~ 0:: ., !:: lfJ 2 c 0

0 0

4

3

"' ...:.:

~ 1:11)

0::

b lfJ

2 0:: '5 -.

0 0

DARCOM·P 706-316

:1 &I T' I I I I ,

•' PATTERN B . :

if 0 "(I

I

0.5

4 8 IDt II I

~ iJi

J T "( I

I I

I I

0.5

' I

BORON I ALUMINUM

BORON t ~ 0.04 IN.

ALUMINUM L = 0.063 IN.

SHELL 951 ADHESIVE

1.0 2.0

Lap Length, in .

T I

~~~~ ...... ~ '?"'~ ......... : ...... -PATTERN A

FIBER GLASS I ALUMINUM

GLASS = 0.04 IN.

ALUMINUM t = 0.0631N.

SHELL 951 ADHESIVE

1,0 2.0

Lap Length, in.

Figure 4-1. Single-Lap Bonded Joint Strength2

4-3

DARCOM-P 706-316

6 r-----------------------------------------------------------,

5

LAP LENGTH

L----------~~------------;O~.S~I:N~.----------4

·u; ..:.<

<ti if>

"' .... cFl "' > ·u;

1: 3 "C

""' "' !:>()

"' .... "' >

""' 2

2.0 IN.

0 ~----------~----------._----------~----------~--------~ 0 0.2 0.4 0.6 0.8 1.0

Ratio Et, dimensionk,;s

Figure 4-2. Effect of 1~·1 Ratio on Single-Lap Adhesive Joint Strength1

Comparing the test data of Table 4-5 with the predicted adhesive stress at failures for corres­ponding l.jt in Fig. 4-6 indicates that the test results generally fall below the predicted failing stress for an Et ratio of 1.00 for boron/aluminum and 0.31 for glass/aluminum. Theoreticaly, for joint lengths of less than 2/3 in. (Lj I ;:::; 8 ), the ul­timate average adhesive shear stress of 6650 psi

4-4

(Shell 951) should be achieved with either glass or boron composite. The double-lap test results do not achieve the maximum design ultimate of 6650 psi but are within the range of experimen­tally determined results obtained on the torsion ring shear tests for Shell 951 (4640- 7220 psi). Several variables can account for this including bond line thicknesses which were only about 1/3

DARCOM-P 706-316

TABLE 4-1 JOINT SPECIMEN LAMINATE PATTERNS

LAMiNATE PATTERN

0°;±45°/0°

+45o ;oo /0°/-45°

±JSo

±45o /±45° ;oo (16 LA YERS)/±45° ji45o

±45o /±45° ;oo (24 LAYERS)j14.'i 0 /±45°

±45°/0°(8 LAYERS)/±45°

±45°/0°(12 LAYERS)j±45°

those for which the torsion ring data were ob­tained as well as differences in curing rates and pressures, surface condition, voids in bond line, etc. This necessitates the inclusion of a safety fac­tor in the design to allow for such variables.

The curves developed in Fig. 4-7 are based on the assumption that the adhesive is an elastic/ perfectly plastic material that becomes plastic at the joint extremities under high load. In this plastic zone the stress reaches the ultimate shear strength of the adhesive. The Width We of this zone is assumed constant for a given joint type and adhesive, and for any one-lap distance. Fig. 4-8 depicts the elastic and assumed stress dis­tributions in the adhesive. The ultimate shear stress is determinable either from very short lap joints or, as in this case, by torsion shear tests. We is determined by testing a joint of long Lj t ratio and determining the elastic stress distribution in the adhesive. Fig. 4-8 shows the elastic stress dis­tribution which gives the same average stress F8

as in the test joint. ru was determined to be 6650 psi. Since the stress cannot exceed j'u, the elastic stress distribution is truncated at this value and the area of the elastic distribution above ru, areas A and C, are added below as areas B and D. We then is the maximum width of the plastic zone. For identical adherends, the plastic zone

PERCENT OF PATTERN PLIES AT

DESIGNATION ±45°

A 50

B 50

c 0

D 33-1/3

£ 25

F 33-1/3

G 25

would be the same at both extremities. For dif­ferent adherends andjor thicknesses, only one end achieves maximum. Other joints can then be analysed to determine the shape of the elastic distribution and, with ru and we known, the average stress F. can be determined. This is the manner in which Fig. 4-8 was prepared.

For boron and glass composites whose outer layers are oriented at 0 deg, adhesive failure is anticipated and the curves should be valid. At a 45-deg outer layer fiber orientation, there are some data to indicate failure in the laminate resin at lower stress levels.

4-2.3 BONDED SCARF JOINTS

In theory, a bonded scarf joint approaches the ideals of strain compatibility in the adherends and uniform stress distribution in the adhesive. In practice, however, one may find it difficult to realize the full potential of a scarf joint due to the peculiar processing and fabrication problems en­countered in machining steep scarf angles, hand­ling the frangible scarf ends, and applying uni­form pressure to the angled bond line to control bond line thickness.

Fig 4-9 shows a finite element stress analysis for an idealized scarf joint, and Fig. 4-10 shows the adherend normalized stress distributions in a

4-5

p A T

TABLE 4-2 SUMMARY OF SINGLE-LAP BONDED JOINT TEST RESULTS

USING SHELL 951 ADHESIVE2

AVERAGE AVERAGE ADHEREND JOINT DESCRIPTION, T AVERAGE ADHESIVE TENSILE STRESS AT FAILURE

MATERIALS, AND E NOMINAL GAGES R LAP LENGTH,

in. N@ in.

SINGLE LAP A 0.50 BORON (0.040)/ A 1.00t

BORON (0 040) A l.OOtt A 2.00 B 0.50 B 100 B 2.00

SINGLE LAP A 0.50 FIBERGLASS (0.040)/ A 1.00

FIBERGLASS (0.040) A 2.00 B 0.50 B 1.00 B 2.00

SINGLE LAP A 0.50 BORON (0.040)/ A 1.00t

7075-T6 (0.063) A 100ft A 2.00 B 0.50 B 1.00 B 2.00

SINGLE LAP A 0.50 FIBERGLASS (0 040)/ A 1.00

707 5-T6 (0 063) A 2.00 B 0.50 B 1.00 B 2.00

SINGLE LAP A 1.00 BORON (0.040)/

7075-T6 (0 063) EXTERNAL SCARF

SINGLE LAP A 1.00 FIBERGLASS (0.040)/

7075-T6 (0.063) EXTERNAL SCARF

•AVERAGE OF FIVE TESTS •• (1) ADHESIVE

(2) IJI\TERLAMINAR SHEAR

ADHESIVE THICKNESS,

in.

0.0029 0.0010 0.0034 0.0024 0.0019 0.0020 0.0019

0.0017 0.0014 0.0020 0.0010 0.0010 0.0021

0.0019 0.0019 0.0030 0.0020 0.0013 0.0022 0.0019

0.0016 0.0030 0.0026 0.0034 0.0030 0.0022

0.0054

0.0035

(3) TENSION IN BASIC LAMINATE SECTION

ULTIMATE SHEAR STRESS STATIC LOAD, AT FAILURE•,

lb psi

2905 5722 3908 3875 3385 3336 3959 1957 2362 4678 3898 3868 4209 2155

2648 5087 3538 3424 3650 1794 2496 5056 2719 2665 3708 1839

2416 4738 2514 2480 3040 3016 3670 1832 2009 3570 3645 3630 3780 1928

2006 3958 2318 2229 2463 1226 2121 4100 2553 2589 3094 1560

2781 2677

2383 2306

tTESTED IN jAJI\UARY 1968 t+TESTED IN DECEMBER 1968 ®SEE TABLE 4-1

COMPOSITE, ALUMINUM, FAILURE psi poi MODEs••

72,500 NOT (1) 97,700 APPLICABLE (2) 84,000 (2) 99,000 (2) 59,000 (2) 97,500 (2)

105,000 (3)

66,300 NOT (I) 88,500 APPLICABLE (I) 91,300 (1) 62,400 (I), (2) 68,000 (1), (2) 92,700 (1), (2)

60,400 39,300 (1 ), (2) 62,700 39,900 (I), (2) 75,800 48,300 (1), (2) 91,600 58,300 (1), (2) 50,200 31,900 (2) 91,200 58,000 (2) 94,500 60,000 (2), (3)

50,100 31,800 (I) 58,000 36,800 (I) 61,500 39,100 (I) 53,000 33,700 (I) 64,800 41,000 (I) 77,300 49,000 (1)

69,500 44,200

59,500 37,900

c l> ::D (') 0 3:

10

9

8

7

·;;; .... 6 ..c

bo c: ~ 5

cii c: 4 ·o ......

3

2

0 0

o AOHEREND FAILURE ~ --·-·f !I PATTERN A

7 • - .... .l'..q

' ... ::&ty T ... ,1\16' I

.... I 6 ... I .... ... I ... ~ 5 1 0.0631N.~ I T PATTERN B

I "(ii - - -y- -- - - - - - - - -? I ...:.::

_1~1 ..l.

-5 ~ J.

4 ~ ! 0.0631N.l c:

O.OBIN. "' .... BORON COMPOSITE rfJ 3

OOOIN _};TIT ALUMINUM c: 0 ......

2 GLASS COMPOSITE

SHELL 951 ADHESIVE ALUMINUM

SHELL 951 ADHESIVE

0 0.5 1.0 2.0 0 0.5 1.0 2.0

Lap Lo·n~th, in. Lap L•·ngth, in.

(A) Boron (B) Fillt'r~lass

Figure 4-3. Double-Lap Bonded Joint Strength2

0 > :a n 0 ~

-+>-' 00

TABLE 4-3 SUMMARY OF DOUBLE-LAP BONDED JOINT TEST RESULTS

(1-IN. SPECIMEN WIDTH) USING SHELL 951 ADHESIVE2

p A T

JOINT DESCRIPTION, T AVERAGE MATERIALS, AND E NOMINAL ADHESIVE

GAGES R LAP LENGTH, THICKNESS, in. N@ in. tn.

DOUBLE LAP A 0 so 0.0011 BORON (0.080)/ A I.OOt 0.0012

7075-T6 (0.126) A I.OOtt 0.0020 A 2.00 0.0010 B 0.50 0.0015 B 1.00t 0.0012 B l.OOtt 0.0026 B 2.00 00014

DOUBLE LAP A 0.50 0.0023 FIBERGLASS (0.080)/ A 1.00 0.0033

7075-T6 (0.126) A 2.00 0.0034 B 0.50

l 0.0019

:I 1.00 0.0023 2.00 0.0025

• AVERAGE OF FIVE TESTS • • (I) ADHESIVE

(2) INTERLAMINAR SHEAR (3) TENSION IN BASIC LAMINATE SECTION (4) TENSION IN BASIC ALUMINUM SECTION

AVERAGE ADHESIVE

ULTIMATE SHEAR STRESS STATIC LOAD, AT FAILURE,•

lb psi

5769 5625 9104 4406 9746 4482 9378 2)40 5982 5793 8327 4160 9502 4751 6180 1540

5038 4986 5713 2743 5297 1347 4059 4008 4530 2257 4561 1110

tTESTED IN FEBRUARY 1968 tt TESTED IN DECEMBER 1968 @SEE TABLE 4-1

AVERAGEADHEREND TENSILE STRESSES

AT FAILURE

COMPOSITE, ALUMINUM, psi psi

72,000 45,700 113,600 72,200 122,000 77,300 117,000 74,500 74,700 47,500

104,000 66,000 118,700 75,400

77,200 49,000

63,000 40,000 71,500 45,400 66,200 42,000 50,900 32,200 56,600 36,000 57,100 36,200

FAILURE MODES""

(I), (2) (2), (3)

(3) ( 1 ), (4) (1 ), (2)

(3) (3)

(2), (3)

( 1) (I), (2) (1 ), (2)

(2) (2) (2) I

0 l> ::D () 0 ~

0

-g ...... 0 0)

w -' 0)

·:;; ..><:

"' "' ;: ci)

"' ;... ·;;;

"' .r:: -o < "' t:>O o'd .... "' ;>

<

DARCOM-P 706-316

LAYER 2 1 4 3 LENGTHWISE 1 2 3 4

PATTERN A PATTERN B

sr-------------------------------------------------------------,

4

3

2

0

X GLASS- PATTERN A +BORON- PATTERN A 0 GLASS-PATTERN B 6, BORON- PATTERN B

JOINED TO ALUMINUM AND TITANIUM ADHERENDS

0~--------~----------~----------~----------~--------~ 0 0.2 0.4 0.6 0.8

Ratio Et, dimensionless

Figure 4-4. Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Glass, Boron/ Aluminum, Titanium Adherends 1

1.0

4-9

OARCOM-P 706-316

4-10

5 r-------------------------------------------------------------~

"' "' "' ;:; ci)

Q.)

;. ·;;; "-'

4

;:5 3 ...-:

2

'V 17·7 PH STAINLESS STEEL/COMPOSITE

0 TITANIUM 6 Al4V/COMPOSITE

0 ALUMINUM 7075·T6/COMPOSITE

ONE INCH OVERLAP

PATTERN A

/ /

FIBER GLASS

/ /

/ /

/

/

BORON

0~----------~----------_.------------~----------~------------J 0 0.2 0,4 0.6 0.8

Ratio Et, dimensionless

Figure 4-5. Effect of Et Ratio on Double-Lap Adhesive Joint Strength for Stainless Steel, Titanium, Aluminum/Composite Adherends2

l.O

~ I

TABLE 4-4 SUMMARY OF DOUBLE-LAP BONDED JOINT TEST RESULTS FOR

VARIOUS Et RATIOS USING SHELL 9.51 ADHESIVE2

p

A T AVERAGE T AVERAGE ADHESIVE

JOINT MATERIALS, E NOMINAL ADHESIVE ULTIMATE SHEAR STRESS AND GAGES, R LAP LENGTH, THICKNESS, STATIC LOAD, AT FAILURE,'

psi in. N@ in.

BORO:'\ (0.080)/ A 1.00 S STI.Ll (0.040)

BORON (0.080)/ A 1.00 S STL (0.050)

BORON (0.080)/ :\ 1.00 S STL (0.064)

BORON (0.080)/ A 1.00 Ti (0.064)

BORON (0.080)( ,\ 1.00 Ti (0 090) I

BOROI\i (0.080)/ i\ 1.00 Ti (0.!26)

FIBERGLASS (0.080)( A 1.00 S STL (0 040)

FIBERGLASS (0.080)( :\ 1.00 S STL (0 010)

FIBERGLASS (11.080)/ A 1.00 S STL (0.064 J

FIBEIU;t.ASS (0.080)/ ,\ 1.00 Ti (ll064)

FlllERC:t.ASS (llll80)/ A 1.00 Ti (0.090)

FIBERLCASS (0.080)/ A I 00 Ti (0126)

'AVER.'\C;E OF FIVE TESTS "(I) AllHESIVt:

(2) 11\:TERI.AI\.IINAR SHE.'\R (>) TENSION IN IHSIC L:\1\.!IN:\Tt: SECTION (4) TENSION I~ BASIC METAL SECTIO~ LIS STI. ~ STAINLESS STEEL

lR.

0.0016

0.0020

0.0045

0.0042 00036

0.0032 0.0030

0.0040

0.0012

0.0016

0 0010

0.0042

0.0027

0.0045

lb

8065 4040

8650 412)

7290 364)

6600+ 31-18 9S30tt .j746

8760+t n~o

8812t .j)7S

8100 4088

657' J21F

6460 .1230

621'> 3 I I :i

)9)7 29:i2

o8t'> 28.18

SuO~ 2691

tTESTED 1:'\ !\1.\Y 19M ttTESTEil IN J.\Nl'.·\RY 1%9 (!!SEE TABLE ~-I

(;.'\(;ES NOTED FOR l\lt:TALS INCLUDE THOSE FOR BOTH !\1£T.\L .\DHERESDS.

AVERAGE ADHEREND TENSILE STRESSES

AT FAILURE

COMPOSITE, METAL, psi psi

101.000 202.000

108.000 !73.000

91.200 114.000

B2.S0ll !03.0Ull 119.000 149.000

110.000 98.000 1\\9.'>00 9~.300

lOUllO (>4.300

B2.JOO I 1>4.)00

BO.~SO 129.\10(1

-~.Otlll q-_:lllO

-4.500 9.1.00\)

- 2.<.00 o4.:il1ll

~0.200 H.:iOl\

FAILURE MODES"

( 1 ). ,21. ( 1)

\I). \2). (31

( 1). (3 I

( l l. \:'l. 1JI

i:'l r11

,JI

(ll. (21

(I\. \2\

(I\ \~ \

(II

\I I. (2\

\I\. (2\

0 J> :a n 0 3: . ., ..... 0 ~

w .... ~

~ I ......

N

TABLE 4-5 SUMMARY OF DOUBLE-LAP BONDED JOINT TEST RESULTS

(1-IN. SPECIMEN WIDTH) 2

p A T

JOINT DESCRIPTION, T AVERAGE MATERIALS, AND E NOMINAL ADHESIVE

GAGES, R LAP LENGTH, THICKNESS, In. N@ 1n. I fl.

DOL'BLE LAP A 0.50 0.0011 BORON (0.080)/ A LOOt 0.0012

7075-T6 (0.126) A l.OO+t 0.0020 A 2.00 0.0010 B 0.50 0.0015 B lOOt 0.0012 B I OOtt 0.0026 B 2.00 0.0014

DOuBLE LAP A 0.50 00023 FIBERGLASS (0.080)/ A 100 0.0033

7075-T6 (0.!26) A 2.00 0.0034 B 0.50 0.00!9 B 1.00 0.0023 B 2.00 0.0025

• AVERAGE OF FIVE TESTS **(!) ADHESIVE

(2) ll\:TERLAMINAR SHEAR (3) TENSIO!\ IN BASIC LA:-.1!:-.iAT£ SECTION (4) TENSION IN BASIC ALUMINUM SECTION

AVERAGE ADHESIVE

ULTIMATE SHEAR STRESS STATIC LOAD, AT FAILURE.,

lb psi

5769 5625 9104 4406 9746 4482 9378 2340 5982 5793 8327 4160 9502 47 51 6180 1540

5038 4986 5713 2743 5297 1347 4059 4008 4530 2257 456! 1110

+TESTED IN FEBRUARY 1968 tt TESTED IN DECEMBER 1968 @SEE TABLE 4-1

AVERAGE ADHEREND TENSILE STRESSES

AT FAILURE

COMPOSITE, ALUMINUM, psi psi

72,000 45,700 113,600 72,200 122,000 77,300 117,000 74,500 7 4, 700 47,500

104,000 66,000 JI8,700 75,400 77,200 49,000

63,000 40,000 71.500 45,400 66,200 42,000 50,900 32,200 56,600 36,000 57,100 36,200

FAILURE MODES ..

(1), (2) (2), (3)

(3) ( 1 ), ( 4) (l ), (2)

(3) (3)

(2), (3)

(l) (I), (2) ( 1 ), (2)

(2) (2) (2)

0 Jlo :ll 0 0 s: ' '1l

..... 0 01 w ... 01

DARCOM-P 706-316

ADHESIVE SHELL 961

E = 99,500 G = 35,500

;< . k."

"' "' "' !::: lfl

Q,)

> ·v; "' ..c:

-o ...: "' lOll

~ Q,)

> ...:

7,000

6,000

5,000

4,000

3,000

2,000

1,000

~J{_j = 0.31 (S-994 GLASS/ALUMINUM) Eztz

1.00 (BORON/ALUMINUM)

SHEET FAILURE

100 KSI

0~--~----~--~--~~--~----~--~----~--~~--~ 0 6 10 15 20 25 30 35 40 45 50

Lit!

Figure 4-6. Predicted Joint Strength for Double-Lap BondedJoints Using Shell95l Adhesive8

4-13

DARCOM-P 706-316

ADHESIVE

2P

l

I

\ \

'

I I

,

"-

p

, p

L4/,2- w

L/2 ---.+-+-- L/2

Figure 4-7. Double-Lap Joint Showing Plastic Shear Distribution in Adhesive1

boron/boron composite scarf joint. Figs. 4-11 and 4-12, respectively, show shear and tensile stress distributions in the adhesive of a scarf joint. For the variable Et ratios of a boron com­posite/aluminum scarfjoint due to different fiber orientations present in the bond line, the adhesive stress distribution would look like that shown in Fig. 4-13.

Actual test results on boron/boron and boron/aluminum scarf joints using Shell 951 adhesive were found not to be as strong as expected and achieved just over 75% of the adhesive shear stress design value. As stated earlier it is suspected (1) that, because of the nonflat configuration, it is difficult to maintain bond line pressure during cure; and (2) that

4-14

bond quality, especially on. small overlaps with steep scarf angles, is not optimum. In addition, bond line thicknesses ( ,0.014 in.) tended to be larger by several-fold over flat lap type joints. This is probably due to the inability to control bond line pressure. Figs. 4-14 and 4-15, respec­tively, plot the joint strength of com­posite/ aluminum and composite/ composite joints versus overlap length and scarf angle.

An alternative to the scarf joint, which avoids some of the processing difficulties of scarf joint manufacture, is the external scarf or beveled single-lap joint. This joint retains the strain com­patibility of the adherends but introduces the offset loading characteristics of the single-lap joint. However, improved processing ease and

DARCOM-P 708-318

4176 ~,---_.c:=:=::::;:::=:~:=:J= .060 BORON .J I I

}+-.470~ .063 AL

TEST JOINT

WIDTH • .769

F, • 5,775 PSI

1~~~----------------------------------------------------~

I I I I I I I

,....... __ We ...J

I

Figure 4-8. Stress Distribution in Actual Test Joint Based on Computer Analysis1

4-15

t I 0.00525 0.15~-0.250--..1

1-'-t-----------0.5516----------l~l

APPLIED LOADS r IDEALIZEO - STRIP

-~ -- ~ --- --- .£:" -----~ADHESIVE

Figure 4-9. Idealized Scarf Joint3

-~-, -REACTIONS\

0 l> :a n 0 3:

I 0

PROPERTIES USED

LAMINATE EL • 16.12X106

ET • 300,000

G • 109,000

ADHESIVE

oa

E .. 139,000 G • 49,000

1.0

LOAD----I

BORON/EPOXY

0.90

1.00

~ORON/EPOXY

1.15

1.10

1.00

0.90

0.80

Figure 4-10. Adherend Normalized Stress Distributions m a Scarf Joint3

REACTIONS

I 0.5516

c l> :::D n 0 3: ' .,

..... 0 ~ w .... ~

~ I ...... 00

~r-----------------------------------------~.-----------------------------------------~

7000 AVE STRESS (ENTIRE JOINT)

AVE STRESS (LOWER HALF) CALCULATED AVE STRESS

AVE STRESS (UPPER HALF)

0~--------~--------~~--------~~------~~--------~----------~--------~--------~ ·1.0 ·0.75 -0.50 ·0.25 ft. 0.25 0.50 0.75 1.0

Fraction of Distance from Center to End Joints

Figure 4-11. Shear Stress Distribution in the Adhesive of a Scarf Joint3

0 ~ :xr n 0 s:: . ., .... 0 g)

w .. g)

~.---------------------------------------~~~-----------------------------------------,

AVE STRESS

oL---------~----------~----------~--------~L---------~----------~----------~--------~ -1.0 -0.75 -0.50 -0.25 0.25 0.50 0.75 1.0

Fraction of Distance from Center to End Joints

Figure 4-12. Tensile Stress Distribution in the Adhesive of a Scarf Joint3

~ I

_.,.. I

N 0

8000 t

7000

1000

7075-TSAL

E • 10.3 X 106

G • 3.9 X 106

/'\. t t t t /

AVE SHEAR STRESS

AVE TENSILE STRESS

BORON

E o• • 30.38 X 106

E 45

• • 1.344 X 106

E t • 300,000

G • 109,000

oL-----------------------------------------------------------------------------------~ Distance Along Adhesive

Figure 4-13. Stress Distribution m the Adhesive of an Aluminum/Boron Scarf Joint3

0 J> :lJ (')

0 s: . ., ~

0 0)

w ... 0)

DARCOM-P 706-316

9 .------------------------------------r------------------------.

"' .... ..;£ bo

8

7

6

~ 5 rJ)

c ·c; -. "' ;;.

·;;; "' ;:§ 4

-..:: ..... .... .. "' rJ)

3

2

0

I

0.5 1.0

I

A

BORON/ALUMINUM PATTERN A

BORON/ALUMINUM PATTERN 8

GLASS/ALUMINUM PATTERN A

LENGTHWISE

B

FIBER PATTERNS

GLASS/ALUMINUM PATTERN B

GLASS/ALUMINUM PATTERN A

BORON/ALUMINUM PATTERN A

BORON/ALUMINUM PATTERN B

1.5 2.0 Lap Length, in.

9°05'

Scarf Angle

Figure 4-14. Scarf Adhesive Joint Strength - Composite-to-Aluminum 1

4-21

DARCOM-P 706-316

4-22

9r-------------------------------------~r-----------~

·;;; .... ..::: be s:::

8

7

6

b 5 <Fl

= 0 ,_, ., -~ "' .,

::; 4 <:

3

2

0.5 1.0

I

LENGTHWISE

A 8

FIBER PATTERN

GLASS/GLASS PATTERN B

GLASS/GLASS PATTERN A

BORON/BOFION PATTE FIN B

BORON/BORON PATTERN A

1.5

Lap Length, in.

9°os·

Scarf Angle

2.0

Figure 4-15. Scarf Adhesive Joint Strength - Composite-to-Composite1

resultant bond quality improvements can result due to the flat nonmachined bonding surfaces whose fibers can be oriented parallel to load direction.

4-2.4 STEPPED LAP JOINTS

Fig. 4-16 depicts an idealized two-step lap joint whose adhesive stress distribution is presented in Fig. 4-17. The results of tests on boron and glass composites bonded to aluminum using Shell 951 adhesive reveal, rather sur­prisingly, that joint strength was independent of the number of steps employed in Fig. 4-18. These results were for a joint overlap of 2 in. Joint ef­ficiency of a two-step lap joint is improved over the single-lap joint. The center of the two-step lap is seen to carry some stress but stresses at the end seem to spike higher. The percentage of adhesive working is about the same for a two­step lap as for a single lap. If more steps and shorter Lj t ratios are employed, this configura-

• tion should prove very worthwhile. Since a scarf joint can be considered to be a multistepped lap joint in which the number of steps approach in­finity, a scarf joint is considered the limiting case for a multistepped lap joint. However, due to the processing difficulties discussed for a scarf joint, it achieved only 75% of the design limit com­pared with about 95% for boron/aluminum step­ped lap joints. For glass/aluminum stepped lap joints, only about 65% of the design limit was achieved.

4-2.5 BONDED JOINT PERFORMANCE COMPARED.

Fig. 4-19 compares the test results of single, double, and stepped lap joints with a scarf joint on boron/aluminum bonded with Shell 951. It can be seen that the single lap joint is quite ef­ficient for low Ljt ratios but rapidly yields diminishing returns on increased lap length. In contrast, the double-lap joint is more than twice as strong as the single lap which has the highest stress concentration at lap ends and carries the least load at the center of the joint. Stepped lap

DARCOM-P 706-316

and scarf joints can potentially achieve the highest average adhesive shear strength.

4-2.6 FIBER ORIENTATION VSJOINT STRENGTH- IN-BONDED JOINTS

The fiber orientation patterns used in bonded joints are extremely important since the layers adjacent to the bond carry an increasing share of the stress as shown in Fig. 2-7. It is known that laminate modulus is a significant factor, so the nature of the substrate member is important. However, since the gross modulus is the same for a given laminate-regardless of fiber orientation- and the modulus ratio of 0-deg to 45-deg layers is approximately 10 to 1, then bond strength differences can be expected depending on outer layer fiber orientation. Since surface fiber orientation has no effect on gross laminate strength or stiffness, it is a variable which effects bond strength only. Bonded composite joint ddta must always present composite lay up patterns where possible since fiber orientation, par­ticularly in the surface layers, has a profound ef­fect on bonded composite joint strengths.

4-3 BOLTED COMPOSITEJOINTS

Generally only 25-50% of the basic laminate strength is achieved with mechanical fasteners. The use of metal interlayers (shims) are sometimes employed to bring joint efficiency over 50% but this results in reduced weight efficiency. Mechanical joints usually are designed to fail in bearing rather than shear-out or tension. This re­quires that edge-distance bolt-diameter ej D and side-distance bolt-diameter s/ D ratios higher than for metals are required to avoid shear-out or tension failures in composites. In unsymmetrical joints, such as single laps, multiple rows of fasteners are suggested to minimize bending. Generally, in order to achieve full bearing strength, Dj t ratios < 2 are recommended.

Design variations for bolted composite joint specimens can include different edge distance e,

side distance s, fastener diameter D, laminate

4-23

0 l> ::D 0 0 ~

SHELL 951 ADHESIVE

' ., 0.020 ~

0

I 7075-T6 ALUMINUM

t CJ)

w 0.040 _.

_j_ CJ) T 0.040

BORONfNARMCO 5505

1 I 0.005

REACTIONS

APPLIED LOADS

Figure 4-16. Idealized Two-Step Lap Joint2

DARCOM-P 706-316

1319w---------------------------------------------------------,

Ul 0..

oS ,.. ·:;;

"' ...<:: -o <: .5 J::

.g ::l

..0

"5 "' Ci Ul

"' "' !:: rJl .... "' "' ...<::

rJl

200

0 0

\ . \ .

' \ . \ \

~\ \ \ \ . \ \ \ . \ \ \ . \\ \ . ,, ,.

0.2

--- MOMENT ON RIGHT END - •- MOMENT ON LEFT END - - - EQUAL MOMENTS ON

BOTH ENDS

0.4 1.0 1.4

I I

2.0

Distance Along Joint, in.

Figure 4-17. Stress Distribution in the Adhesive of a Two-Step Lap Jointl

thickness t, laminate lay-up patterns, and bolt arrangements. Bolt strength should be cho~en to preclude bolt failure. When properly chosen, these parameters provide a balanced joint design in shear, tension, and bearing strengths, respec­tively. Because lay-up patterns can alter the

shear, tension, and bearing properties of the laminate, the optimization of joint proportions must be geared to these laminate patterns. A bolted joint differs from a pinned joint in that clamping friction is an added factor in con­tributing to joint strength. With friction a factor

4-25

DARCOM-P 706-316

~

..z bD ::::

"' = tl)

:::: ·c; -. "' ...

'iii .., ..<: "'0 <

4-26

12

10

8

6

4

2

COMPOSITE/ALUMINUM SHELL 951 AOHESI VE

I • 0.16

I I I I I I

I I I I I I I ,, ,,

t LENGTHWISE

A 6

COMPOSITE PATTERNS

PATTERN 8

SCARF

SINGLE LAP I I • 0.04)

oL---------~----------~--------~----------~------------------~ 0 2 4 6

Number of Steps

8

Figure 4-18. Stepped Lap Adhesive Joint Strength4

10 12

14

12

10

4

2

BORON PATTERN: 0/45/-45/0 SHELL 951 AOHESIVE

DARCOM-P 708-318

0.5 1.0 1.5

Length of Joint L, in.

2.0 2.5

Figure 4-19. Boron-to-Aluminum Joint Strength4

in bolted joint strength, the surface condition and roughness as well as bolt torques must be specified in a bolted joint.

Specimen width should be chosen to allow suf­ficient side-distance bolt-diameter ratios s/ D to preclude failure in tension through the bolt holes. Test results indicate that to achieve full bearing

stress, tj D ratios should not be less than about 0.5. Similarly published test results suggest that the edge distance be great enough to yield an ej D ratio ~ 5. Beyond this, bearing stress did not in­crease. Thus, to achieve full bearing stress, an ej D > 5 and tj D > 0.5 are suggested.

4-27

DARCOM-P 706-316

4-3.1 SINGLE- AND DOUBLE-LAP

BOLTED JOINTS

4-3.1.1 Plain lioles

Tables 4-6 and 4-7, respectively, show the strengths of single- and double-lap joints of

boron and glass composites bonded to themselves and to aluminum. These results indicate only

slight improvement in strength for the double-lap

composite/aluminum joints over the single lap. Failing modes in both cases were predominatly

shear-out of the composite with some in­terlaminar shear and tension failures in the com­

posite for the double-lap joints. The added weight considerations may not justify the small gain in strengths obtained.

4-3.1.2 Bushed lioles

Table 4-8 summarizes the test results obtained

on double-lap joints with bushed holes. Since joint dimensions differ from the plain hole joint

results in Tables 4-6 and 4-7, direct comparison

cannot be made. However, from examining the

average laminate stresses at failure, the bushed hole joints exhibit significantly lower laminate stress bearing capability for all their excess weight; for this reason they are not efficient joints.

4-3.1.3 Bolted Joints With Reinforced Edges

Reinforcing the edges of bolted joints can be employed to reduce the edge distances needed to

develop full bolt strength and reduce shear-out failures. The reinforcement can be in the form of laminate buildup at the edge, or the inclusion of

a shim of metal or other reinforcement. Tables

4-9 and 4-10 show the results of tests on com­posite and steel shim-reinforced laminates,

respectively. It can be seen that the steel shim­reinforced joints failed primarily by tension in

the laminate at the base of the shim and by shim deJa ruination and laminate shear-out, but oc­casional bolt shear did occur - indicating that reinforcement can help the joint approach full bolt strength.

4-4 BOLTED AND BONDED JOINTS

Bolted and bonded joints yield strengths which are superior to either bolted or bonded joints of

similar configuration when used alone. Table 4-11 shows that the bolted and bonded

glass/aluminum joints were three times as strong as their bolted-only counterparts, and bolted and

bonded boron/aluminum joints were five times

TABLE 4-6 SUMMARY OF SINGLE-LAP BOLTED JOINT TEST RESULTS

' (1-IN. SPECIMEN WIDTII)*•

AVERAGE LAMINATE STRESSES AT FAILURE

LAMINATE ULTIMATE -JOINT DESCRIPTION THICKNESS, STATIC LOAD••, SHEAR-OUT TENSION,

AND MATERIALS in. lb psi psi

SI~GLE LAP FIBERG LASS/7075-T6 0.112 2523 15,200 28.030

SINGLE LAP BOR0Nj7075-T6 0.116 2823 16,160 29,640

SINGLE LAP FIBERGLASS/ FIBERGLASS 0.114 2087 12,430 23,SAO

SINGLE LAP BORON/BORON 0.116 2560 14,720 27,210

'-----

•0.190-IN. BOLT DIA:\1ETER, 0. 750-1~. EDGE DISTAI\CE, Pi\ TTERN A. TABLE 4-1. ••AVERAC;E OF FIVE TESTS

4-28

BEARING, psi

119,920

127,740

98,120

115,240

FAILURE MODE

SHEAR-OUT

SHEAR-OUT

SHEAR-OUT

SHEAR-OUT

TABLE 4-7 SUMMARY OF DOUBLE-LAP BOLTED JOINT TEST RESULTS

(1-IN. SPECIMEN WIDTH) 2

I ULTIMATE AVERAGE LAMINATE STRESSES STATIC LOAD, AT FAILURE

LAMINATE EDGE AVERAGE JOINT AND THICKNESS, DISTANCE, OF 5TESTS, SHEAR-OUT, TENSION, BEARING MATERIALS in. tn. PATTERNt lb psi psi pst

DOUBLE-LAP 0.100 0.50 A 1862 18,600 23,000 98,000 FIB ERG LASS/707 5-T6 0.102 0.75 A 2359 15,400 28,600 122,000

0.104 1.25 A 2583 9,900 30,700 131,000 0.110 0.50 F 1133 10,300 12,800 54,200 0.102 0.75 F 1630 10,600 19,700 84,000 0.108 1.25 F 2226 8,200 25,400 108,500

0.148 0.50 A 2559 17,300 21,300 91,000 0.138 0.75 A 3244 15,700 29,000 123,000 0.146 1.25 A 3782 10,400 32,000 136,500 0.13R 0.50 G 1340 9,700 12,000 51,100 0.151 0.7) G 2302 10,200 18,900 80,000 0.143 1.25 G 2600 7,300 22,400 95,500

DOUBLE-LAP 0.128 0.50 A 2189 17,100 21,200 90,000 BOROI'\/7075-T6 0.117 0.75 A 3028 17,200 32,000 136,000

0.120 1.25 A 3420 11,400 35,200 150,000 0.133 0.50 D 1524 11,500 14,200 60,600 0.115 0.75 D 2059 11,900 22,100 94,500 0.116 1.25 D 3107 10,700 33,000 141,000

0.168 0.50 A 2621 15,600 19,200 82,000 0.160 0.75 A 4214 17,500 32,500 138,700 0.163 1.25 A 4756 11,700 36,000 154,000 0.166 0.50 E 1648 9.900 12,300 52,100 0.157 0.75 E 2604 11,000 20.500 87,500 0 165 1.25 I E 4317 10,500 32,300 138,000

* (1) SHEAR-OUT r SEE TABLE 4-1 (2) TENSIO;-.; AT SECTION THROUGH BOLT HOLE (3) BEARING (4) INTERLAMINAR SHEAR

**THESE STRESSES COMPUTED AS THOUGH ADHESIVE WAS 1'\0T INCLUDED.

FAILURE MODE•

( 1 ), ( 4) (1), (4) (3),(4) (1), (4) (1), (4) (1), (4)

(1),(4) (1), (4) (3), (4) (1), (4) (1 ), (4) (1),(4)

( 1) (1)

(1), (2), (4) (1) (1) (1)

( 1) (1),(2)

(1),(2),(4) (1) (1) ( 1)

c )> ::n (") 0 s: ' "'0 ....,

0 en w ..... en

TABLE 4-8 SUMMARY OF DOUBLE-LAP BOLTED JOINT TEST RESULTS- BUSHED HOLES2

ULTIMATE AVERAGE LAMINATE STATIC LOAD STRESSES AT FAILURE

JOINT DESCRIPTION, LAMINATE BOLT EDGE FIBER AVERAGE OF MATERIALS, AND THICKNESS, DIAMETER, DISTANCE, ,. AT '45°, 5 TESTS, SHEAR-OUT, TENSION, BEARING, SPECIMEN WIDTH in. m. in. PATTERN* o/o lb psi psi psi

DOUBLE LAP 0.171 0.3125 1.0 A 50 4773 11,690 24,670 74,800 BOR0:-.1-ALUMINUM 0.171 0.3125 1.5 A 50 4524 8,820 27,930 84,640

0.176 0.3125 2.0 A 50 4565 6,480 27,360 83,020 I .250-IN. 0.127 0 3125 1.0 A 50 3595 13,460 28,820 86,100

SPECIMEN 0 126 0.3125 1.5 A 50 3865 10,220 32,340 9fl,OOO WIDTH 0.127 0.3125 2.0 A so 4683 9,230 39,240 118,240

DOUBLE LAP 0.167 0.3125 1.0 A so 4253 12,710 26,860 81,380 FIBER- 0.166 0.3125 1.5 A 50 4889 9,820 31,490 94,260 CLASS/ALU~1INUM 0.146 0.3125 2.0 A 50 5001 8,590 37,210 110,000 1.250-IN. 0.128 0.3125 1.0 A 50 3487 13,660 29, !90 87,480

SPECIMEN 0.122 0.3125 1.5 A 50 3825 10,480 33,740 100,540 WIDTH 0.121 0.3125 2.0 A 50 4174 8,810 37,120 110,200

t (I) SHEAR-OUT (2) TENSION AT SECTION THROUGH BOLT HOLE (3) BEARING FAILURE •

*SEE TABLE 4-1

FAILURE MODESt

(I) (2)

(I), (2) (I), (2) (1 ), (2) (I), (2)

(I) (3) (3) ( 1) (3) (3)

c J> ::D (") 0 ~ ' "V ....,

0 01 ' w ....

01

TABLE 4-9 SUMMARY OF COMPOSITE-REINFORCED BOLTED JOINT TEST RESULTS2

JOINT DESCRIPTION, LAMINATE BOLT EDGE MATERIALS, AND THICKNESS, DIAMETER, DISTANCE,

SPECIMEN WIDTH •n. m. in. PATTERNt

DOUBLE-LAP 0.278 0.190 0.50 A BORON/STEEL•• 0.279 0190 0. 75 A 0.750-IN. 0.279 0.190 125 A

SPECIMEN WIDTH 0.292 0.190 0.50 D 0.301 0.190 0. 75 D 0.289 0.190 1.25 D

DOUBLE-LAP 0.283 0.190 0.50 A FIBERGLASS/ 0.268 0.190 0.75 A

STEEL"" 0.275 0.190 1.25 I A 0.750-IN. 0.257 0.190 0.50 F

SPECIME]'; WIDTH 0.274 0.190 0.75 F 0.257 0.190 1.25 F

DOUBLE-LAP 0.366 0.250 0.75 A BOROJ';jSTEEL•• 0.373 0.250 1.00 A l-IN. 0.361 0.250 1.50 A

SPECIMEN WIDTH 0.346 0.250 0. 75 E 0.373 0.250 1.00 E 0.343 0.250 1.50 E

DOUBLE-LAP 0.381 0.250 0. 75 !\ FIBERGLASS/ 0.151 0.250 1.00 A

STEEL•• 0.324 0.250 0.75

I G

l-IN. 0.342 0.250 1.00 G SPECIME]'; WIDTH 0.353 0.250 1.50 G

"(1) SHEAR-OCT tSEE TABLE 4-1 (2) INTERLAMINAR SHEAR (3) TENSION AT SECTION THROUGH BOLT HOLE

""RIGID TEST FIXTURE

ULTIMATE AVERAGE LAMINATE STRESSES STATIC LOAD AT FAILt:RE

FIBER AVERAGE OF AT'45°, 5 TESTS, SHEAR-OUT, TENSION, BEARING,

% lb psi psi psi

50 4,602 16,500 28.600 87,300 50 6,910 16,600 44,300 130,000 50 7,215 10.400 45,900 137,000 43 3,885 13.300 23.500 70,000 43 6,785 15.000 39,700 118,500

" 43 7,140 9,900 43,600 130.000

50 5,975 21,100 37,500 111,000 50 6,390 15.800 42,400 125.500 50 6.725 9,800 42.900 129,000 43 4,763 18.500 33,100 97,500 43 6.470 15,700 41,800 124,000 43 6.420 10.000 44,500 131,000

so 9,179 16,700 33,500 100,000 50 11.914 15.800 42.000 126,000 50 12,021 1!, 100 44,400 133,000 39 6.284 12,100 24.200 72,500 39 10,715 14,400 38,300 115.000 39 10,300 10,000 40,000 120,000

50 10,796 18,900 37,700 113.000 50 11.200 15.900 42,500 127,700 39 7,463 15.300 30.700 92,000 39 8,742 12,800 34,100 102.000 39 10,430 9,800 39,500 118,000

FAILURE MODES"

(I)

I ( 1 ), (3)

I (1),(3)

(1) ( 1) ( 1 )

( 1 ), (2) (I). (2) (I). (2) (I). (2) ( 1 ), (2) (1 ), (2)

(I) ( 1 ), (3) ( 1 ), (3)

( 1) ( 1) (I)

( 1 ). (2) ( 1 ), (2) ( 1 ), (2) ( 1 ), (2) ( 1 ), (2)

0 )> :a n 0 ~ . "V .... 0 G)

w ... G)

TABLE 4-10 SUMMARY OF SHIM-REINFORCED BOLTED JOINT TEST RESULTS2

ULTIMATE AVERAGE LAMINATE STRESSES STATIC LOAD

]01:'\T DESCRIPTION, LAMINATE BOLT EDGE AND MATERIALS, AND THICK!'iESS, DIAMETER, DISTANCE, NO. TESTS, SHEAR-OUT,

SPECI:\1EN WIDTH m. Ill. in. PATTERN+ lb psi

DOLHLE-L\P 0.192 0.100 0.37) A 6.'J38 (5) 4'J,100 BORO:'\jSTEEL .. 0.192 0.1'JO 0.500 ,\ 6,670 (4) 34,700 (!750-I:'\. (J.192 0.100 1.000 A 7,H!3 (5) 20,400 SPECI\IE:'\ \\lOTH I) 192 0.190 0.375 D 6,8'J3 (5) 4 7, HOO

0.192 0. 190 0 500 D 7,600 (5) 40.000 0.192 0.190 1.000 D 8,360 (4) 21,800

DOLBLE-L\P 0.192 0.100 0.375 A 4,550 (4) 31,60(1

FIBERGLASS/ 0. JCJ2 0.190 0 500 t\ 5,300 (5)

I 27,600

STEEL* (I 192 0 190 1. 000 A 5,006 (5) 13,000 0.750-l:'\. (). 1 CJ2 0.190 0 )7) F 4,070 (5) 2H,200 .SPECI\IE:'\ WIDTH run 0 100 0.500 F 5,354 (5) 27,900

0 192 (J190 !.000 F 5,316 (5) 13,800

DOLBLE-LAP 0 260 () 250 0.43 7 5 A 11,905 (5) 52,500 BORO:'\/STEEL ** 0.260 0. 250 0 500 A 12,H20 (5) 49,400 1-1:'\. 0.2i>fJ 0.250 (J750 A 12,800 ( 4) .'l2,KOO SPECI\11:::'\ \VIDTH 0.260 0 250 (J437S E 10,800 (3) 47,500

0.260 0.250 () 500 E 11 ,HI 'i (5) 4'i ')()()

0.260 0.250 0.750 E 14,\100 (5) 38,200 0.260 0.2SO 1.250 E 14,HSO (2) 22,KOO

DOLBI.E-LAP (J 260 () 250 0.500 A 7,172 (5) 27,600 FIBERGLASS/ (L260 0.250 0.750 A H,HHH (5! 22,800 STEEL** 0.260 0.2'i0 0.500 G 7,1 ()() (5) 27.400 1-I:'\ (J 260 0.250 0.750 G 7,3\12 ('i) 1H,90() SPECI\IE:'\ WIDTH 0 260 0.260 1.250 G K, 142 ('i) 12,500

* 1. BOLT SHEAR t SEE TABLE 4-1 2. TE:'\SIO:'\ 1:'\ LA\-11:'\ATE /\T HASE OF SHI~S 3. SHI\1 DELA\1I:'\ATIO:'\ A:'\IJ LA:V11NATE SHEAR-OUT 4. TJ::i'\SIO:\ I:\ LA\11:'\ATE A:--.:D SHI\-1 OF SECTION THROUGH FASTENER HOLE ). TE:\SIO:\' I:\ LA.\11:'\/\TE A:'\D O:'>.'E SHI\-1. TENSION AND SHEAR-OCT IN SECOND SHIM 6. SHEAR-OUT OF LA.\11NATE AND ONE SHI\1, TE.\JSION IN SECOND SHIM 7. TENSIO;-.; 1;--.; OLTER PLIES OF LA\-1INATE AT BASE OF SHIMS AND AT SECTION

THROUGH FASTESER HOLE IN PLIES BETWEEN SHIMS; PARTIAL DELAMINATION OF SIIIMS. •• RIGID TEST FIXTURE

AT FAILLRE

TENSION, BEARING, pst pst

64,)00 191,000 62,000 184.000 72,600 215,000 64,000 1H'),500

71 '50() 212,000 77,800 130.000

42,400 125,000 49.400 146,000 46,500 137,500 37,')0() 112,000 49,800 147,400 49,400 146,000

61,300 1K4,000 6),800 107,000 65,700 197,100 :; 'i' )()() 166,000 6(),(,()0 184,000 7(J,500 229,000 76,200 228,000

36,800 110,000 45,500 137,000 36,500 109,400 37,900 113,700

41 '700 12.'i,OOO

FAILURE MODES*

I (2), (3), (4) (2), (3), ( 4)

(2), (7) I (2), (3) I

(2). (1) ( 1), (3)

(2), (3) (2), (.\) (2), (3)

(2), (3), (4) (2)

(2), (3)

(4) ( 4 ), (5)

(4) (6)

(3 ). (4) (2), (3), (4)

(I )

(3 ), ( 4) (3) (3) (3)

0!. (4)

c )> ::JJ C')

0 3: I -g .... 0 en c., ... en

TABLE 4-11 SUMMARY OF DOUBLE-LAP BOLTED AND BONDED JOINT TEST RESULTS2

LAMINATE EDGE JOINT AND THICKNESS, DISTANCE, MATERIALS lfi. in.

DOUBLE-LAP FIBERGLASS/7075-T6 0.!20 0.75 BOLTED AND BONDED

DOUBLE-LAP BORON/7075-T6 0.120 0.75 BOLTED AND BO:-.IDED I

• (I) TENSION AT SECTION THROUGH BOLT HOLE (2) INTERLAMINAR SHEAR

ULTIMATE STATIC LOAD, AVERAGE OF

5TESTS, PATIERNt lb

A 7470

A 12,875

l

••THESE STRESSES COMPLTED AS THOUGH ADHESIVE WAS NOT INCLUDED.

tSEE TABLE 4-1

AVERAGE LAMINATE STRESSES AT FAILURE

SHEAR-OUT, TENSION, BEARING, psi psi psi

41,500 .. 77,000 .. 328,000 ..

71,500** 132,000** 564,000**

FAILURE MODE•

(1), (2)

(I), (2)

c J> ::D 0 0 s: ' "'0

...... 0 G)

w ..A

G)

OARCOM-P 706-316

as strong as bolted only. The presence of a bolt in a bonded double-lap joint of 3-in~ area is seen to increase average bond shear stress in glass from 1800 psi to 2717 psi, and in boron from 3300 psi to 4300 psi. There is, therefore, a synergistic ef­fect of the bolt and adhesive on one another.

4-5 REDUCING STRESS CONCENTRATIONS IN JOINTS

4-5.1 Model

The double-strap joint pictured in Fig. 4-20 will be used to illustrate some of the things which can be done to reduce stress concentrations due to stress risers resulting from abrupt con­figurational changes in bonded joints.

Assume undirectional composites with fibers parallel to load direction, then three types of failure are likely:

1. Tensile failure of main member of region A 2. Tensile failure of strap through region B. 3. Bond failure and shear-out originating at

points C. The stress diagrams in Fig. 4-20 show the

stress concentrations in the main members, straps, and bond line as cr A, CTs, and r, respec­tively.

4-5.2 STRAP MODIFICATIONS

Strap and main member failures can be minimized by proper sizing of members -e.g.,

:>I-

t T

making straps the same thickness as the main member (if the strap and main member are the same materials) to reduce strap failures, and in­creasing strap length to eliminate bond failure and shear-out. Main member failures at region B can be alleviated by reducing the stress concen­trations in this area due to the abrupt load transfer between strap and main member. This can be done in several ways -by reducing strap thickness at the strap ends or by increasing adhesive thickness at the strap ends. Fig. 4-21 shows a number of ways to reduce strap thickness locally.

The stepped strap configuration (Fig. 4-21 (A)) affords greater n~xibility and reduced stress concentration at the strap/main member bound­ary. While this reduces the probability of ~a in member failure in the aforementioned location, the steps create stress risers in the strap thus in­troducing a new possible mode of failure- strap delamination originating at the step corners. Fig. 4-21 (B) shows a tapered strap which accom­plishes the same stress concentration reduction as the stepped strap but in a continuous fashion. Finite element analysis by Sage5 showed that stress concentration factors as low as about 1.1 were possible for a taper angle of under 5 deg with no step at the strap end. However, the end produced by machining to this angle is so frangi­ble as to cause problems in machining, handling, and bonding. This led Sage to a radiused strap

r = shear si:Tess at bond line a A = tensile si:Tess in region A a8 = tensile si:Tess in region B

aa--+

Figure 4-20. Model of a Double-Strap Joint

4-34

DARCOM-P 708-318

(A) Sl!~pp!'d Strap--Good

(8) Tapned Strap--Better

•

(C) Radiu~ed Strap--Best

Figure 4-21. Ways to Reduce Strap Thickness Locally

configuration (Fig. 4-21 (C)) which solved anum­

ber of problems. First, the tangent to a large enough radius can easily approximate the 5-deg taper at the strap end and thereby meet the reduced stress concentration requirement. Second, a straight taper of this angle would re­quire the removal of a large mass of strap and is not necessary after a modest distance from the strap end. Third, a flat strap can be bonded on and the radius machined afterward, allowing for uniform pressure application during cure and

eliminating the handling problems. Small radii were found to cause interlaminar shear failure in the strap skin similar to that cautioned against in

the stepped strap configuration. Larger radii cir­cumvented this failure mode. The following equation suggests the minimum radius R to avoid this failure mode:

( pu ) t .

R = fsu X 2, m. (4-1)

pu = ultimate tensile strength of the composite, psi

ru = ultimate shear strength of the

composite, psi t = thickness of the joined composite

members, in.

4-35

DARCOM-P 706-316

A factor of 2 was built into this equation in an effort to make R large enough to eliminate tensile failure as well. Fig. 4-22 shows us that a key ad­vantage of the radiused strap is that, even for a short strap length, the favorable 5 deg angle at the strap end can be achieved for lowered stress. A modified straight taper is also shown which might offer a further advantage over the radiused strap yet avoid the difficulties of a straight taper.

4-5.3 INCREASED ADHESIVE THICKNESS

Another way to overcome the stress concentra­tion at the ends of a strap is to increase the adhesive thickness at the main member I strap end interface. This avoids the abrupt load transfer in a manner much the same as reducing strap thickness or reducing stiffness in the region, thereby relieving rather than restraining stresses and distributing them more efficiently over the whole joint area. Fig. 4-23 is the configuration suggested by Sage to accomplish this in a double­strap joint.

Machining of the straps depicted in Fig. 4-23 would be rather tedious so a stepped strap con­figuration (Fig. 4-24) is suggested.

By forming the steps in the strap using prepreg, the machining of steps can be elimi­nated; however, filling the steps with adhesive is required. The performance of these joints is il­lustrated in Table 4-12. Load bearing efficiencies of greater than 100% have been achieved. This means that failure occurred outside the joint area in the main member. Thus, the joint could be considered too efficient from ·a load bearing standpoint and perhaps weight could be saved by design refinements.

4-5.4 INFLUENCE OF STRAP AND ADHESIVE THICKNESS ALTERATIONS ON JOINT EFFICIENCY

Tables 4-12 and 4-13 summarize the results of tests on type I and II carbon fiber reinforced plastic double-strap joints conducted by Sage.

. The load bearing efficiencies can be observed to

4-36

respond to strap length, strap composition, strap radius, or step filler; and failure modes reflect the stress concentrations which result from the dif­ferent configurations.

4-5.5 VARIABLE ADHESIVE STIFFNESS

Another means of reducing stress concentra­tion at joint extremities is by the use of two ad­hesives of varying stiffness (Fig. 4-25) in the bond line. A lower stiffness adhesive at the joint ends will provide better stress distribution by relieving itself of the higher stresses at the joint ends and transferring the load into the center of the joint where a higher stiffness adhesive can carry a larger share of the load.

4-6 TYPICAL BOLTED JOINT CONFIGURATIONS

Several examples of bolted joint configura­tions are presented in Fig. 4-26. Variations on these basic joints can involve varying bolt place­ment on large joints but little else.

4-7 BOLTED FAILURE MODES

The types of failures which can occur in bolted joints are shown in Fig. 4-27. Bolted joints usually are designed to fail in bearing rather than tension or shear-out but all types of failure are encountered - usually a mixture of several modes. Another possibility, though rarely en­countered, is bolt failure. Bolt strength should always be chosen to preclude this type of failure.

4-8 TYPICAL BONDED JOINT CONFIGURATIONS

Bonded joint design alternatives are more numerous than for bolted joints and are depicted in Fig. 4-28. Included are single and double laps; single and double straps; scarfs; and pinned, keyed, and variable stiffness and thickness adhesive types.

4-9 BONDED FAILURE MODES

Bonded joints should ideally fail cohesively since that indicates the adhesive has been stressed to its ultimate in load transfer

All can provide for an ex = 5 deg at strap end but a radiused or modified straight taper permits a shorter more practical strap length.

Figure 4-22. Methods of Reducing Stress Concentration at Strap Ends

0 l> :a () 0 !:

DARCOM-P 706-316

Figure 4-2.3. Idealized Shape for Variable Adhesive Thickness

Figure 4-24. Filled Step Strap Joint

capability. Adhesive failure indicates that,poor adhesion is present due usually to poor process­ing or to adverse environmental effects such as moisture displacing the adhesive at the adhe­sive/ adherend interface. Interlaminar shear failure in the composite is encountered frequent­ly due to the anisotropic nature of laminates and the many processing parameters which can in­duce flaws in the composite. Fig. 4-29 depicts possible failure modes.

4-10 WEIGHT OF JOINTS

As discussed in Chapter 1 the weight of the joint is critical to its overall efficiency and ul­timate usefulness. Load carrying efficiencies of 100% or more are possible but excessive weight is the price paid. A load carrying efficiency of 100% accompanied by a weight efficiency of 50% yields an overall joint efficiency E of just 50% as de­fined by Eq. 1-3. High joint efficiencies are achieved by keeping the load carrying capability of the joint design as close to that of the continu­ous unjoined member while keeping the weight increment added as small as one can.

4-38

A weight study conducted on different boron composite and aluminum joints (bonded and bolted) 1 yielded data on weight added to achieve different joint strengths. The results (Fig. 4-30) show that a weight increment of about 0.04 lb/in. of bonded joint width was required to ob­tain a single-lap joint strength of about 3500 lb/in.; double-lap joint strength, of about 5500 lb/in.; and a scarf joint strength, of about 20,000 lbjin. Just 0.01 lbjin. of joint width yields a strength of 20,000 lb/in. for a four-step lap joint. Thus a stepped lap or scarf joint is seen to be much more efficient than a double- or single-lap joint. Data from the bolted joint study (Fig. 4-31) show an almost linear relationship between strength, and weight, i.e., those bolted configur­ations which were the strongest were also the heaviest. It is significant to note that the incor­poration of adhesive into a bolted lap joint raised joint strength approximately threefold with no weight penalty as shown in Fig. 4-31. Fig. 4-32 compares the weight added by different joint de­signs to achieve the same load. The bonded scarf and stepped lap joint are shown to add little or

TABLE 4-12 PERFORMANCE OF RADIUSED DOUBLE-STRAP JOINTS EMPLOYING CARBON FIBER REINFORCED PLASTICS5

STRAP DIMENSIONS, mm RADIUS R, FIBER TYPE MAIN MEMBER STRAP LENGTH WIDTH THICKNESS mm

FAILURE MODE UNDER STATIC AXIAL TENSION

JOINT EFFICIENCY

76 24

76 24

grp• 76 24

grp 76 24

50 24

II II 76 24

II II 76 24

II II 76 24

• grp- glass reinforced plastic

t crfp - carbon reinforced plastic

1.27 200

1.27 76

1.27 76

1.27 200

1.27 76

1.27 76

1.27 200

1.27 200

Tension in main member away from joint area

Tension in main member away from joint area

lnterlaminar shear in grp strap close to bond

lnterlaminar shear in grp strap close to bond

Tension in strap at center

Shear in strap

Tension in main member a\·•ay from joint area

Tension in main member and strap at strap end

0.7

0.7

0.7

COMMENT

Failure outside joint indicates o1·er design and excess weight. Shorter strap length is possible.

Same as abO\·e.

Strap strength is too low. Lower stiffness grp chases stress to joint center.

Same as abo\"e.

Increased stress concentrations due to shorter strap length

Radius is insufficient to alle1·iate stress concentration in the stiffer Type II crfp. t

Shorter strap length is possible. Larger radius chased failure back to main member outside of joint.

.\F-130 adhesi\"e used. ~lore brittle than BSL 312/3 used on others

FIBER TYPE MAIN MEMBER STRAP

II II

II II

•carbon reinforced plastic

TABLE 4-13 PERFORMANCE OF INVERSED STEPPED STRAP JOINTS EMPLOYING CARBON FIBER REINFORCED PLASTICS~

FAILURE MODE LOAD BEARING STRAP DIMENSIONS, mm FILLING UNDER STATIC EFFICIENCY

LENGTH WIDTH THICKNESS IN STEPS AXIAL TENSION E COMMENT

127 24 1.00 crfp• Tension in main member Joint overdesigned. Shorter strap could cut weight.

90 24 1.00 crfp Tension and shear at 0.7 crfp fibers transverse to load unable to with-strap end stand increased stress at this strap length.

127 24 1.00 Adhesive Tension in main member Larger strap length with adhesive step filler BSL 312/3 outside joint area yields same result as with crfp filler.

Some strap length between 127 mm and 90 mm seems optimum.

90 24 1.00 Adhesive Tension and shear at 0.9 Failure mode similar to crfp filler at this BSL 312/3 strap end strap length but higher failing load and

shear location indicate isotrophic adhesive filler cohesively stronger than transverse crfp.

90 24 1.00 crfp Tension and shear at 0.7 Same as configuration 2. strap end

90 24 1.00 Adhesive Same as configuration 4 but higher strength BSL 312/3 main member fails at higher load.

0 )> ::0 0 0 3: ' .,

...., 0 en c:., ... en

DARCOM-P 706-316

higher stiffness adhesive

Figure 4-25. Variable Stiffness Adhesive Joint

/ I

(A) Single Lap (B) Double Lap (including bushings)

(C) Reinforced Edge

(D) Shim Joint (E) Bolted-Bonded

Figure 4-26. Bolted Joint Designs2

no weight whereas the bonded double-lap and bolted double-lap joints added in excess of 30% to the basic panel weight.

4-11 FATIGUE

4-11.1 BONDED JOINTS

The fatigue behavior of several types of glass/aluminum and boron/aluminum bonded joints is shown in Table 4-14. Clearly, although the scarf joints had among the highest average adhesive shear stress by comparison with the

other joint types, the low stress concentration factor (SCF) in the scarfed configuration resulted in less severe stressing of the joint. This is graphically depicted in Fig. 4-33. S-N (Stress­Number of Cycles to Failure) curves for boron/aluminum bonded scarf and double-lap joints are shown in Figs. 4-34 and 4-35. Similar curves for a graphite/graphite single-lap and graphite/titanium scarf joints are shown in Figs. 4-36 through 4-40 for both room tempera­ture and 350°F. Elevated temperature is seen to reduce fatigue endurance substantially.

4-41

DARCOM-P 706-316

(A) Shear Out (B) Tension

(C) Bearing (D) Tension/Shear Out

(E) Bearing/Shear Out (F) Bearing/Tension/Shear Out

Figure 4-27. Bolted Failure Modes

4-11.2 BOLTED JOINTS AND BOLTED-BONDED JOINTS

A tabulation of single- and double-lap boron and glass bolted joint fatigue results is presented in Table 4-15 as well as data on bolted and bond­ed glass/aluminum and boronjaluminumjoints. Double-lap bolted joint fatigue endurance was greater than for the single lap. Failure was through the aluminum bolt hole not the boron bolt hole. Direct comparisons between the bolted

4-42

and the bonded joints are not possible because of the different configurations but, generally, the maximum loads on the bolted joints were less than those on the bonded joints.

Adding adhesive to the bolted joint permitted the maximum and minimum load on the joint to be increased 250% with good results. Failures in the configuration were a mixture of laminate and aluminum through the bolt hole, and aluminum through the basic section.

...

DARCOM-P 708-318

L ~ 7 simple

/ I [;?'

beveled (external scarf)

22 ~ 7 < radiused

(A) Single-Lap Joints

simple

beveled

radiused

(B) Double-Lap Designs

(cont'd on next page)

Figure 4-28. Bonded Joint Designs

4-43

DARCOM-P 706-316

--------~~ ~ ce;r tc----.----rtr ___ f?? single strap

double strap

beveled straps

radiused straps

I recessed double strap

(C) Strapped Joints

(cont'd on next page)

Figure 4-28. (cont'd)

4-44

DARCOM-P 706-316

r/ z ,: CJ I

simple stepped lap

z c ~ () ..-.. recessed stepped lap

c/ : ~ v scarf (single taper)

/ I z (?)

scarf (double taper)

increased thickness scarf joint

landed scarf

(D) Stepped Lap and Scarf Joints

(cant 'd on next page)

Figure 4-28. (cont'd)

4-45

DARCOM-P 706-316

variable adhesive thickness

variable stiffness adhesive

pin

key

(E) Adhesives

Figure 4-28. (cont'd)

4-46

DARCOM-P 706-316

5 T~ I

l_

(A) Cohesive

-

I (B) Adhesive

(C) I nterlaminar Shear

Figure 4-29. Bonded Failure Modes

4-47

DARCOM-P 706-316

0.18 r-----r---------,.-----------~....,

SHELL 951 ADHESIVE

0.16

Q. 0,14 a.. j c(

_I w w ...J _I en (.!) :::l 2 0 Ui Q

0.12

<:::

.:0

e; 0.10 <1

= ., E ~ u

= ..r: 0.08 bC

"' ~

0.06

Joint Strength, (lb/in. of bonded joint width) X w- 3

(A) Weight Increments for Bonded Joints in Boron Panels

Figure 4-30. Weight Increments vs Strength of Joints2

4-48

c::

:?i

~ <l

c (l.J

E "' ... (.)

..:; -C

tl.O (l.J

ss

0.03 .---~-

0.02

O.D1

SHELL 951 ADHESIVE

NO. OF STEPS = 4

5 10

DARCOM-P 706-316

15 20

Joint Strength, (lb/in. of bonded joint width) X 10 ~ 3

(B) Comparison of Weight Increments for Stepped Lap Joints

Figure 4-.'30. (cont'd)

S-N curves for f1ush head and protruding head bolted graphite joint configurations are shown in Figs. 4-41 and 4-42, respectively. Fatigue behavior is not predictable at present based on mechanical property data. Factors which affect fatigue life are numerous. They include joint type and configuration, fiber orientation, adhesive type, processing variables for laminate manufac-

ture, surface preparation of laminate if it is to be bonded, adhesive cure schedule, and environ­mental effects of temperature and humidity. These factors make prediction of static strength of joints difficult and the introduction of dynam­ic cyclic loads compounds the difficulty. For this reason S-N curves must be developed for a joint design representative of the end item.

4-49

DARCOM-P 706-316

16.----------------------------------------------------------------------

"' I 0

X

...... 0

.5 g

14

12

..c 6 bo c: 01)

t: en

2

UNREINFORCED D • 0.190 l =0.120

BOLTED +BONDED

D = 0.190 I = 0.120

SHIMMED D = 0.250 I = 0.160

\_ REINFORCED- D = 0.250

·, = 0.160

D = 0.190 t = 0.120

0=0.190 I = 0.120

0~--------~--------~--------~--------~--------~--------~--------~--------~

0 O.Q1 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Weight Increment AW, lb/in.

Figure 4-31. Strength - Weight Relationships for Bolted Joints2

4-50

...

::9

..c:: 1:lD Q)

~

~ 0 .....

DARCOM-P 706-316

ALUMINUM AND BORON PANELS 24r-----------------------------LOAD = 10,000 LB/IN.

B

4

DOUBLE LAP BONDED

> X 0 Q,

u; z 0 a: 0 Ill

DOUBLE LAP BOLTED

> X 0 Q, w :Z 0 a: 0 Ill

PANEL WIDTH = 20 IN.

PANEL LENGTH = 60 IN.

SCARF STEPPED LAP BONDED BONDED (N = 4)

> > X X 0

~ Q, w tJ,l :Z z 0 0 a: a: 0 0 Ill Ill

Figure 4-32. Total W,tight Comparisons for Panels and Joints2

4-S 1

.... I U1 N

TABLE 4-14 SUMMARY OF BONDED JOINT FATIGUE TEST RESULTS•2

MAX!Ml!M ~1ATERIALS OVERLAP "'AX!:I.H;.\1 LO.•D LOAD% ot-· A:-;D GAGES, LEXGTH, "1!~!.\ft:M LOAD STATIC

JOI:\TTYPE in. in. lb/lb l:LTIMATE

BORO:-..-f_\L L'~II:\LC.I I I~IJ0j90 72

(() 040)/10063) SI:\C, LE L\P

FIBERCL\SSj_\LV,IL'\L\1 I 1600/RO 69

((1_040)/10.063)

BUR( l:\/ ALL\11.'\L:...I I 6•HJOj260 70

(0081J;ji1J 126)

I 4200/ZIJO 73

FIBERC;L\'iSf-\LL:-..11:'\L'\1 DOLBLE L\P

IIJ OHIJ J/ 10.121J!

I 341JOj171) 60

BORO:\f_\ L L .\II:\ L :...1 2 6600j331J 56

11!.160;/ 10.16111

2 8200/410 7()

llORO:\/ ,\ LL:-..11:\L\1 II!. 161! )/ (() 160;

Ff JL'R-STEP PATJ'ER:\ C L\P 2 6(,()()(_)\0 .J/

Fl BERC ;L\SSj,\LL\11:'\L\1 2 IJ61JO/-).l1J 75

IIJ JI,IJJ/111.160)

llO RO:\j ;\ l.l':'-.11 :\L :'.I I 3300/ 16.) 7()

(fJ.I{J()Jj((J liJIJ) -:,\RF

II BERC; LAS.'i/ ALL\11:\L'\1 I .1HorJjiWJ 7[)

(fJ.IIJIJJ/(0.160)

1-1:\ SPECI~1E:\ WIDTH -, R = ,0.05

VE LA.\11:\ATE PATTERN A, SEE T'\BLE 4-1

(SCF) X ADHESI\'l AVERAGE STRESS AT STRESS AT "'AXl:l.lt::\.1 APPROXI\IATE .\!AXI.\Il!\1

LOAD, SCFI:\ LOAD, TESTS p!oi ADHESIVE P"

5 1.800 4.H H,600

5 - - --

5 .UOIJ .14 10900

2 - - -

3 - - -

3 .1.11!0 3.1J 11,9()1)

2 4, IIJ() 1 () 14,7011

2 .1. )iii! l.iJ 11, 111!1)

j - - --

s _),}()() 14 4,(,(1(1

s - - ~

R.,:-;GE OF CYCLES TO FA!Lt:RE

FAILCRE \lODE

8,000 l() ADHESIVE

35,000

I 10,700 f'() ADHESIVE

19 400

480 Til r\llHESI\'E

I ,K60

I, /01! j'() :\llHESI\T

2_:llliJ

1,600 j'() ADHESIVE

H,SOIJ

1,1!00 '10 .\llHES!\'1::

.o,ooo

7:)0

'" ,\lli!ES!VE 2,1JIJ()

7,)1!1! ")41 1\ll!IESI\'E

12,721!

201!

'" 1\lliiESIVE 100

1\000 J() AllllESIVE

ll'J,()()()

I ,400 jl) A Ill! E~ IV 1·.

20,000

.... tO .,

..<::: ifJ

3.5

3.0

DARCOM-P 706-316

.-------~---- -------------- --- ------

SPECIMEN

Z3824858-501 I11NCHI

'o ' b.

SPECIMEN

Z3824858-1 {1-1/2 INCH)

0 .0

0 0

b.

BORON/NARMCO 5505 LAMINATE TO 7075 T6 AL. STRESS RATIO. R - •005 SHELL 951 ADHl.SIVE

~-------6----.~ 2.5 "' .,

..<::: -o < ., ~

"' .... ., ;>

<

·;;.; ..><:

-o

"' 0 ...... E ::l E

•;< "' ::E '.;

"' "' ., !:::

ifJ .... 01 .,

..<::: ifJ .,

;> ·:n ., ..<::: -o < ., ~ tO .... ., ;>

<

0 DENOTES 1-IN. SCARF

b. DENOTES 1-1/2-IN. SCARF

CLOSED SYMBOL DENOTES RUNOUT

2.0 ~-----------L----------------~------------------L---------------~

1.5

1.0

0.5

104

Cycles to Failure N Figure 4-33. Fatigue Data for Adhesive Scarf Joints1

SPECIMEN

Z382486Q--503 (1 INCH} 0/45/-45/0

SPECIMEN Z382486Q--1 (2 INCH} 0/45/-45/0

'b. b. SPECIMEN -..... 6 6

0

BORON/NAAMCO 5505 LAMINATE TO 7075 T6 AL STRESS RATIO. R = +0.05 SHELL 951 ADHESIVE

•

. .. 0 ••

Z3824860-501 (2 INCH} -..._b. b. 6

------

0~

0 DENOTES 1-IN. LAP. 0/45/-45/0 PATTERN

0 DENOTES 2-IN. LAP, 0/45/-45/0 PATTERN

b. DENOTES 2-IN. LAP, 45/0/0/-45 PATTERN

CLOSED SYMBOL DENOTES RUNOUT

b.----•:. •

0 ~----------~------------~--~----------------L---------------~ 10

4 105 106

Cycles to Failure N

Figure 4-34. Fatigue Data for Adhesive Double-Lap Joints 1

4-53

DARCOM-P 706-316

CONSTANT AMPLITUDE R • +0.05

SCARF JOINTS

105

SINGLE LAP ~ JOINTS ., ... ..2 ·o;; ~

104

.8

FOUR STEP LAP JOINTS

1 I

<ll .., u >.

u DOUBLE FOUR STEP LAP JOINTS LAP JOINTS

103 I 1

4 4 6 8 10 12 14 16

Average Maximum Cyclic Stress X (SCF), ksi

Figure 4-35. Fatigue Life of Boron Composite-to-Aluminum Alloy Bonded Joints6

4-54

~

' U• \.JI

·u; ....:

~ :2 ::: ;)

.... "' 01

-"' rJ)

""0 c: 0

IXl

E "' E ,., "' ~

2.0

' ' 1.8

1.6 '~"-· .......

1 • 4

1.2 ). -1.0

0.8

0.6

0.4

0.2

' -....~

~

"' Ill.. '

GRAPHITE/EPOXY TO GRAPHITE/EPOXY

350°F

IlL I R = 0.05 /AOH~SIV~ I II I " Nx _, ~ METLBOND 329-7

I ~ ,_ La --+j 0, 5 \+-- N

X

- -..... """~'... l J l .. ... 411_ ..........

~ --

1 10

I

-~

- -

!

i

.._, -~~ ... .....

.... ·-. .... ~ - - -

I

I I I

~ ~l fa'== N) La u [0/:!:45) s

"""""' ' o- - [0/:!:45/90)5 ··~oo. r ···;

"""""' ~ .. ..... :... ~~~~... 0······-- [0 /:!:45]

r-.. jt • .......,. 2 s - ~ - .. ~-.. ' • k .... ... :--~ ......... I '· n

"•r-, .. ~ f::_ .. .. .. I

~~ ~ r--~

Itt~

I

Cvcle~ to Failurt• N

Figure 4-36. Single-Lap Bonded Joint Tension Fatigue S-N Curve -Type AS/3002-Batch, Graphite/Epoxy, 350°F (Ref. 7)

0 l> ::a C') 0 3: ' "Q .... 0 Gl w ... Gl

2. 3

2.0

"' ..>(

~ "' 1 • "' "'

5 !::: rJl ... "' <l)

.;::: rJl ""0

= 0 ~

E :l E

"' 1. 0 "' ~

I

1---·

I

0. 5 -->

I

N. -I

I I

f.' == N.f La - - -- --

I

I I

I

I I I

GRAPHITE/EPOXY TO GRAPHITE/EPOXY ROOM TEMPERATURE

R 0 05 "" I -,· f

ADHESIVE

L 1..----METLBOND 329-7 , ___

L" -+I 0.51+-- N,

I s:s

,-w- 0- -

' 0 •••••••

('\

" \.

' "\

~' '~ " r ~,.,. ' """--..., ...._

'· ..... ~ ~

-~ -~ .... "-' ""' .... "'-~ .....

'· -.. ~ .. " .0

.......... r---.. .. -w J-r--.... .... .... -....

,...., ...... --~ .r "-' ~. --...

.. r----. ...,' --I I

i

I I

Cycle,; to FailurP N

Figure 4-37. Single-Lap Bonded Joint Tension Fatigue S-N Curve­Type AS/3002-Batch, Graphite/Epoxy, Room Temperature7

(0/±45) 5 (0/±45/90)5

(02/±45)5

............. ...... r--.; ... ~~ ~ ...... ..

... ~ ~

0 l> ::1:1 (') 0 s:

'

GRAPHITE/EPOXY TO TITANIUM

5.0 R = 0.05

J .I I I I I I . .1 I I I

I I I I I j_ -Ti"l r-- [0

' = l\','(2L0

) Nx _. II ~ ... _

4.5

Nx 4.0 .=------:-r---1-ffr \ l -

.. "' OJ

3.5

(J5 2.5 "'0 t: 0

a:!

~ 2.0 § .. "' ;:g

1.5

1.0

0.5

METLBOND 329-7 1

() iolo...

ADHESIVE GRAPHITE/EPOXY

-- ...... ~ ~~ ARROWS INDICATE NO FAILURE OCCURRED ['"'. ~ 1-oo 0 ROOM TEMP ---r--. ~ ... tl 350°F ..............

-...., ........ ~ll> I .......... ~ ~

I ¢ l~ I

""" ....... u-~ ... ~- ~- ..... ..... ·--· .. ..... ~ --~ --. .. '

"·~- .... :s ....... ~- - I ........... .. , ..

I"• ·-- ..... .. . ... --·

Cycles to Failure N

Figure 4-38. Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves - Type AS/3002-Batch, Graphite/Epoxy- Room Temperature and .350°F, [0/±45hs (Ref. 7)

-

-

-

--

0 )> :a 0 0 ~ ' "0

..... 0 Gl w ... Gl

~ I

U"l 00

5.0

4.5

4.0

·;;; 3.5 ..... ~

<I> <I>

3.0 ., !::

tJl .... <"<I

"' ..r:: tJl

-c 2.5 " 0

IXl

E 2.0 "' E ... <"<I

:::; 1.5

1.0

0.5

GRAPHITE/EPOXY TO TITANIUM

R 005 = I I

I I I Ti j_ fa'= Nx/(2La) L

~ ....._ - .;:>.1 -~

Nx ......... -- ----- r- La .,_. ti .......

""" ................

............. ....... METLBOND 329-7

...... P- ADHESIVE ............... GRAPHITE/EPOXY ~

"' -... ... """' ' I

~ ~ ...

' '----- ~ ~~ ~- -· ~-- ...... .... .. ..

~· .... ['-.. ... . .. ··~· ....... .. tl .. _ .. .. r-...

L .. - -r---. .... . -·· •. It! ..... .. .J.. - INDICATE NO ~ ARROWS FAILURE OCCURRED

·- 0 ROOM TEMP.-

r-- tl 350°F ····-----·

Cycles to Failure N

Figure 4-39. Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves- Type AS/3002-Batch, Graphite/Epoxy- Room Temperature and 350°F, [0/±45/90hs (Ref. 7)

I

Nx

-~ -

0 l> :a n 0 ~ . ., .... 0 0)

(., ... 0)

·;;; -"'

~ <Jl

"' "' .... ci'i

.... "' "' ..c

Cf)

-o c: 0

lXI

E ::> E

"' "' ::E

GRAPHITE/EPOXY TO TITANIUM 5.0

4.5

4.0

3.5

) IR 0.05

I I I I I I I I T. T TT T I Ill .... = ........... ~

I I I Ti' ... fa'= N,J(2La) ~

~·-"' .. . ..

~ ~ ~-........ Nx Nx

__.-A"' f+- L -+ "f ""--~ ~ METLBOND 329-7 a t

~ ~ ADHESIVE ~

GRAPHITE/EPOXY ~~1!11..

3.0 1--' ......

~ '"' !Ill. ')

I ,.... ~,

' 2.5 ;L. •• ~ ~ ~ .... I"

1.5

2.0

~

1.0 1-

1-

0.5

0.0 0

10

"'·· '"· ~-····· I,....,__., ... __ , .•. ··:-. r--.. - r- r-. t-• ......... ..•. •.. . ,,

I "1"-.... .... . ARROWS INDICATE NO FAILURE OCCURRED -u ........

0 ROOM TEMP ss Sl 350° F ••••••••••••

Cycles to Failure N

Figure 4-40. Bonded Symmetrical Scarf Joint Tension Fatigue S-N Curves- Type AS/3002-Batch, Graphite/Epoxy - Room Temperature and 350°F, [02/±45]a:,; (Ref. 7)

....

107

0 )II ::D (') 0 ~ I

-a .... c G)

w ... G)

TABLE 4-15 SUMMARY OF BOLTED JOINT FATIGUE TEST RESULTS•2

MATERIALS AND GAGES,

JOINT TYPE in.

BORO)';jBORON

(0.120)/(0.120)

BORONj7075-T6

(0.120)/(0.160)

SINGLE L\P FIBERGLASS/ FIBERGLASS (0. 120)/ (0. 120)

FIBERGLASS/7075-T6

(0.120)/(0.160)

BORO)';j7075-T6

(0. 120)/(0.200)

DOCBLE LAP FIBERGLASS/7075-T6

(0.120)/(0.200)

BORON/7075-T6

DOL:BLE LAP (0.120)/ (0.200) BOLTED :\:'\D BO:'\DED

FIBERGLASS/7075-T6

(0.120)/(0.200)

*STRESS RATIO. R = .0.05 BOLT DIA:-.lETER. D = 0.19011\

EDGE MAXIMUM LOAD DISTANCE, MINIMUM LOAD

in. lbjlb

0. 750 1800/90

1960/98

1460/73

1765/88

2100/105

1650/83

1890/95

4950/248

0.750

4950/248

l-IN. SPECIMEN WIDTH LAMINATE PATTERN A, SEETABLE4-I.

MAXIMUM LOAD%0F RANGES OF

STATIC CYCLES TO

UlTIMATE TESTS FAILURE FAILURE MODES

4,000 70 5 TO BEARING AND SHEAR-OUT

13,000

1.000 BORON-BEARING 70 5 TO

24,000 ALL:MINUM THROUGH FASTENER HOLE

1,700 70 5 TO DELAMINATION AND

7,000 SHEAR-OUT

1,100 70 5 TO DELAMINATION AND

62,700 SHEAR-OUT

130,000 ALUMINL:l\1 THROUGH 70 5 TO FASTENER HOLE

2,677,000 NONE (RUNOL'TS)

1,000,000 70 3 TU NONE (RU:-.IOUTS)

7,591,000

I ,247,000 NONE (RUNOUTS) 80 2 TO

1,731,000 ALUMI)';L'M THROUGH FASTENER HOLE

101,000 LAM IN ATE AND ALUMINUM TO THROUGH HOLE

38 5 176,000 ALUMINUM THROUGH BASIC SECTION

11,400 66 5 TO DELAMINATION AND ADHESIVE I

49,200

c )> :J:I n 0 3: ' .,

..... 0 a» w ... 01

200

180

160

·;;; 140 ... <II "' "' ...

rfi 120 """ c

·;: .. "' lXI 100 .::: " »

u E 80 "' E

"' .. ~

60

40

20

r--

FLUSH HEAD FASTENER D = 0.19 in.

l l

-o [0/±45]45

e!D = s/D == 2.63 NOMINAL

R = 0.05

---···0 [0/!45/90]25

- --o- [02/±45]25

~ .. .. I ....... ---....a--T .. : .... --- --- -- - -·--t---~-- 1'-'

~-~

Cycles to Failure N

CYCLING RATE: 95 TO 100 Hz

1 I l l I ARROWS INDICATE NO FA I LURE

I I I I

l' = PI(Dt)

- -~ IS" •j ~---..:··· --~- ··-........ ~

, ... -( ,.... ... <0- r--or-

~

--

Figure 4-41. Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy to Steel Single-Lap Flush Head Mechanical Joints - Type AS/3002-Batch, Graphite/Epoxy'

I

0 )> :a 0 0 3:

.j>.. I

0'-N

200

180

160

·;;:; 140 .Jo<

,£

"' ., .. ~ 120 c: .. .. .,

a:l )

.::! 100 u >-u E ;;l 80 E ·;:; ..

::;:

60

40

20

PROTRUDING HEAD FASTENER D = 0.19 in. e!D == s!D = 2.63 NOMINAL

R • 0. OS

CYCLING RATE: 95 TO 1 00 Hz

I I I I l ARROWS INDICATE NO FAILURE

/' = PI(Dt)

~-- • l""l ~--· ,., .... ~ ..... ~"···- ....... - - - .......

~ :-~ - - - ·~ . . .;; ~ ----~--~ --- -~- ~-

9 .- -- ···- -···· ~ .. ~d .--~-~ --....

,...

n.

-o [D/!45Js

·-··-· 0 [0/:!:45/9Dls

- --o- [olt4S]s

J I

Cycles to Failure N

Figure 4-42. Room Temperature Fatigue S-N Curves for Various Crossplied Graphite/Epoxy to Steel Single-Lap Protruding Head Mechanical Joints -

Type AS/3002-Batch, Graphite/Epoxy7

'

I

!

_, I I

0 )> :::D C')

0 s::

I ., .... 0 m w .... m

DARCOM-P 708-318

REFERENCES 1. A. V. Hawley, et al., Investigations of]oints and

Cutouts in Advanced Fibrous Composites for Air­craft Structures, Fifth Quarterly Progress Report, Contract No. F 33615-67-C-1582, Wright-Patterson Air Force Base, OH, July 1968.

2. G. M. Lehman and A. V. Hawley, Investiga­tions of ]oints in Advanced Fibrous Composites for Aircraft Structures, Vol. 7, Technical Discussion and Summary, Technical Report AFFD L-TR-69-43, Vol. 1, Wright-Patterson Air Force Base, OH, June 1969.

3. A. V. Hawley, et al., lnvest(r,ations of}oints and Cutouts in Advanced Fibrous Composites for Air-

craft Structures, Third Quarterly Progress Re­port, Contract No. F33615-67-C-1582, Wright-Patterson Air Force Base, OH, January 1968.

4. A. V. Hawley, et al., lnvestzgations of}oints and Cutouts in Advanced Fibrous Composites for Air­craft Structures, Fourth Quarterly Progress Re­port, Contract No. F33615-67-C-1582, Wright-Patterson Air Force Base, OH, April 1968.

5. G. N. Sage, "Some Aspects of Bonded Joint Design in CPFP", Composites 7, No. 4, IPC Science and Technology Press Ltd., Guild­ford, Surry, England (October 1976 ).

4-63

DARCOM-P 706-316

INDEX

A Adhesives

bonded joints, advantages/disadvantages of, 1-3 environmental effects on, 1-4 failure, 4-1, 4-2, 4-36, 4-38 important properties of, 1-4, 3-14,3-15,3-19,

3-27, 3-33 Advanced composites, definition of, 1-1

B Bolted composite joints

bushed holes, 4-28, 4-30, 4-31, 4-32 compared to bonded joints, 4-52

fatigue, 4-42 strength, 4-33 weight, 4-38

design considerations, 2-3 double lap, 4-28, 4-29 failure, 4-36 plain holes, 4-28 reinforced edges, 4-28, 4-33, 4-34 single lap, 4-28 strength, 2-22

. Bolted joints, strengths of, 2-26, 4-60 Bonded joints

compared to bolted joints, 4-28, 4-33, 4-34 fatigue, 4-41, 4-52

design considerations, 2-2, 2-3, 4-1, 4-2 discrete element analysis, 2-3 double lap, 4-2, 4-8, 4-11, 4-12, 4-23 failure, 4-36 length/thickness ratio, 4-2, 4-4, 4-5 properties, 1-3, 1-4 scarf, 4-5, 4-15 single lap, 4-2 stepped lap, 4-23 strap, 4-34, 4-35, 4-36 weight increment to achieve strength, 4-38

c Composite

advanced, 1-1 defined, 1-1 failure, 1-4, 4-36 fiber reinforced, 1-4 machining, effect of, 1-4, 2-13

properties of general, 1-4 mechanical, 3-23, 3-32 (see also: Mechanical

properties of composites) surface preparation prior to bonding, 1-4 thickness/bolt diameter ratio, 2-3, 4-23, 4-27

D Data

baseline design, 3-2 mechanical properties of

adhesives, 3-14, 3-15 (see at.ro: Adhesives) laminates, 3-2, 3-3, 3-5, 3-6 (1el! also:

Laminates) Design

bolted joints, 2-3, 2-6 bonded joints, 2-2, 2-3 data generation, 3-20 philosophy, 2-2 techniques, 2-2

Discrete element analysis of bonded joints (.rei': Bonded joints)

Double-lap joints, 4-2, 4-4, 4-5 test results, 4-8, 4-11, 4-12, 4-29 weight increment to achieve strength, 4-38

E Edge distance/bolt diameter ratio, 2-3, 3-2, 4-23,

4-27 Efficiency of joints, 1-1, 4-23, 4-36, 4-39, 4-40 F:t (product of elastic modulus E and thickness I)

ratio bonded composite/aluminum scarf joints, 4-14 bonded double-lap joints, 4-2, 4-4, 4-11 bonded single-lap joints, 4-2 comparison of bonded joint performance, 4-23 effect on joint strength, 4-2 importance of matching to equalize stress, 4-2 significance of, 4-2

F Failure

adhesives, 4-1, 4-2, 4-36, 4-38 bolted joints, 2-3, 4-36 bonded joints, 4-36, 4-38 composites, 1-4, 4-36

I-1

DARCOM-P 706-316

INDEX (cont'd)

Fatigue bolted-bonded joints, 4-42, 4-49, 4-60 bolted joints, 4-42, 4-49, 4-60 bonded joints, 4-41, 4-52

Fiber orientation, 2-13, 4-2, 4-5, 4-23 (ser aho: Laminate patterns)

J Joints

adhesive bonded, 1-2, 1-3 bolted composite (see: Bolted composite joints) bonded (.ree: Bonded joints) configurations, 4-1, 4-36 definition of, 1-1 design of, 1-3, 2-2, 2-3, 2-6, 3-2, 3-28 double lap, 4-2, 4-4, 4-5 efficiency, 1-1, 4-23, 4-36, 4-39, 4-40 mechanical (.ree: Mechanical joints) performance comparisons of different types,

4-23 scarf (see: Scarf joints) single lap, 4-2, 4-6 stepped lap, 4-23 weight

comparisons, 4-51 increments to achieve strength, 4-38

L Laminates

mechanical properties, 3-2, 3-3, 3-5, 3-6, 3-33 patterns, 4-2, 4-5, 4-25

M Machining of composites, 1-4 Mechanical joints

advantages/ disadvantages, 1-2 definition, 1-2

Moduli effective tensile, 3-14, 3-15 elastic

compression, 3-14, 3-15 tensile, 3-14, 3-15

shear adhesive, 3-14, 3-19, 3-20 laminate, 3-2, 3-6

Young's, 3-14

p Patterns, laminate, 4-2, 4-5, 4-25 Properties, mechanical, of composites, 3-23, 3-32

test methods, 3-33

1-2

tests for bearing, 3-33 compression, 3-32 flexure, 3-32 tension, 3-23

R Ratios

composite thickness/bolt diameter, 2-3, 4-23, 4-27

edge distance/bolt diameter, 2-3, 3-2, 4-23, 4-27 length/thickness, 4-2, 4-4, 4-5 side distance/bolt diameter, 2-3, 3-2, 4-23, 4-27

s Scarf joints, 4-5, 4-14

stress distribution, 4-5, 4-14 weight increment to achieve strength, 4-38

Side distance/bolt diameter, 2-3, 4-23, 4-27 Single-lap joints, 4-2

test results, 4-6, 4-28 weight increment to achieve strength, 4-38

Stepped-lap joints, 4-23 Stiffness, 4-2 Strain capability, 4-1 Strap joints, 4-34

radiused, 4-34 stepped, 4-34 straight taper, 4-35

Stress analysis, 2-2, 2-3

bolted joints, 2-3, 2-6 bonded joints, 2-2, 2-3 discrete element, 2-3 photoelastic, 2-3

concentration, 4-1 distribution of, 4-2 factor, 4-2 reduction in strap joint by, 4-34

increased adhesive thickness, 4-36 strap modification, 4-34 variable adhesive stiffness, 4-36

Surface preparation, 1-4 composite prior to bonding, 1-4 peel-ply, 1-5 purpose of, 1-5

T Testing, 3-20 (ue a/.w: Properties, mechanical, of

composite: Tests for) equations, 3-23, 3-32

methods, 3-23 specimens, 3-33

w Weight efficiency, 4-23

INDEX (cont'd)

y Young's modulus, 3-14

DARCOM-P 706-316

1-3

(DRCDE-L)

FOR THE COMMANDER:

OFFICIAL:

LTC, Adjutant General

DISTRIBUTION: Special

DARCOM-P 706-316

ROBERT L. MOORE Major General, USA Chief of Staff

<r U.S. ~Iff I'I!AITIIIG OFFICE, 19/'l-280-964/5968