Composite Materials

• Two or more materials combined on a macroscopicscale to form a useful material

• Ideal for structural applications where high strength-to-weight and stiffness-to-weight ratios are required

• Conventional composites limited to in-plane distributed loads

Specific Strength & Specific Modulusm x 104

0 2.5 5.0 7.5Graphite/EpoxyBoron/EpoxyGlass/EpoxyTitaniumSteelAluminum

0 1.0 2.0 3.0Tensile Strength/Density (in x 106)

m x 106

0 5 10 15Graphite/EpoxyBoron/EpoxyGlass/EpoxyTitaniumSteelAluminum

0 1 2 3 4 5 6Elastic Modulus/Density (in x 108)

Specific Strength vs. Specific Modulus

Composite Product Forms

Tape - all fibers aligned in single direction

Cloth - fibers aligned in multiple (usually two) directionsPlain weave: over and under one fiber at a timeSatin weave: over several then under one fiberAS4/3501-6 6K5H

- 6000 filaments per yarn- 5 harness weave (over four under one)

• Composites referred to by type of fiber/type of matrix (AS4/3501-6)• Layers can be fiber only for later “wet” layup (adding resin), or can be “prepreg” (already containing the resin)

Representative Usage -- 1970’s

Boron/epoxy horizontal and vertical stabilizers (F-15)

Representative Usage/Research -- 1970’s

Boron/epoxy horizontal tail and fuselage sections (F-111)

Representative Research -- 1970’s

Carbon/epoxy fuselage component (F-5)

Representative Usage -- 1980’s

Carbon/epoxy wing, fuselage panels, control surfaces (AV-8B)

Representative Research -- 1980’s

Low cost composite fuselage concept (AV-8B)

Representative Usage -- 1980’s

Carbon/epoxy wingskins with integral titanium splice plates,carbon/epoxy control surfaces and stabilizers (horizontal and vertical)

Representative Research, 1980’s

Integrally stiffened C/E composite wing skin (large, cocured structure)

1980’s Research -- Composite Bulkhead

C/E wing carrythrough/landing gear support bulkhead (F-18)

1980’s Research -- Thermoplastic Tee

1980’s Research -- Composite Lugs

Representative Usage -- 1990’s

C/E wing skins, stabilizers, fuselage skins, control surfaces, internal structure (F-22)

Representative Usage -- 1990’s

JSF C/E wingskin layup and tool

Composite Tooling

Typical Fabrication Layup

Three-Dimensionally Reinforced Composites

Fiber Placement

C/E JSF inlet duct

Fiber Placed Inlet Duct

C/E JSF inlet duct

Joint Strike Fighter

C/E wing and fuselage skins, tails, control surfaces, inlet duct

X-36 Tailless Agility Research RPV

C/E aerodynamic surfaces28% Scale (18’ length, 3’ height, 10’ wingspan, 1250 lb.)Williams International F116 engine (700 lb. thrust)

Terminology• Fibrous Composites: Fibers in a matrix

» Fibers more “perfect” properties due to diameter on order of crystal size (no slip) & fewer internal defects» Whiskers low length to diameter ratio (<100)

­ More “perfect” than fibers­ Nearly perfect crystal alignment

» Lamina - arrangement of fibers in a matrix (single layer)

• Laminated Composites: Layers of at least two different materials bonded together

» Bimetals - significantly different CTE allows thermostat» Safety glass - glass transparent & hard but brittle; polyvinyl butryal tough but scratches» Laminate - stack of lamina with various orientations of materials

Terminology (continued)

• Laminated Fibrous Composites:» Hybrid of fibrous composites and laminated composites» Layers of different fibrous composites

• Particulate Composites: particles of one or more materials suspended in a matrix of another material

» Concrete (sand and gravel in cement matrix)» Flakes

Terminology -- Family

• Common industry practice to reduce allowed orientation angles to four: 0, 45, -45, 90

• Laminates with similar number of like orientations share similar properties (belong to same family)

• Family convention: %0/%+45/%90•50/40/10 (50 % 0 plies, 40% + 45 plies, 10% 90 plies)•25/50/25 (25 % 0 plies, 50% + 45 plies, 25% 90 plies)

Terminology -- SymmetrySymmetric laminate implies that the material and orientation of layers above the laminate midplane are identical to those below.

ABCCBA

Antisymmetric laminate implies that the material of layers above the laminate midplane are identical to those below, but the orientations are of opposite sign

ABC-C-B-A

Terminology -- Balance

Balanced laminate implies that for every +θ oriented layer there exists a -θ oriented layer of the same material

[45,0,90,-45,0,90] balanced, unsymmetric

[45,0,90,-45,90,0,45] unbalanced, symmetric

[10,0,45,-45,-10,38,-38] balanced, unsymmetric

[45,-45,0,90,0,-45,45] balanced, symmetric

Laminate Shorthand Convention

Disregarding material hybrids, the convention is to list the plies in stacking order, referencing the orientation

[45,-45,0,0,45,-45,90,-45,45,0,0,45,-45,90,-45,45,0,0,-45,45]

==> [±45,02,±45,90,+45,0]s (30/60/10)

Remove one of the centerline 0 plies:

[45,-45,0,0,45,-45,90,-45,45,0,0,45,-45,90,-45,45,0,-45,45]

==> [±45,02,±45,90,+45,0]os (26/63/11)

Lamina Coordinate System

Coordinates 1,2,3 are principal material directionsCoordinates X,Y,Z are transformed or laminate axes

Effect of Orientation on Mechanical Properties

AS4/3501-6: E1 = 20E6 psi, E2 = 1.0E6 psi, ?12 = 0.3, G12 = 1E6 psi? xy,x is a coefficient of mutual influence -- a measure of shear in xy-plane due

to normal stresses in x-direction

Lamina Design Allowables

AS4/3501-6 Unidirectional Tape

Effective Laminate Properties by Family

AS4/3501-6 Unidirectional Tape

Filled Hole Tension Properties by Family

Filled Hole Compression Properties by Family

Compression Strength After Impact (Damage Tolerance) by Family

Fiber, Matrix & Composite Properties

Comparison of Cross-Section Diameters for Various Fiber Reinforcements

Properties of Inorganic FibersFiber (Mfr.) ρ (g/cm3) σ Mpa (ksi) E Gpa (msi) Diameter (µm) Use temp. (C)AluminaFiber FP (duPont) 3.9 1.38 (200) 380 (55) 21 1316PRD166 (duPont) 4.2 2.07 (300) 380 (55) 21 1400Sumitomo 3.9 1.45 (210) 190 (28) 17 1249

MulliteNextel 440 (3M) 3.1 2.70 (250) 186 (30) 12 1426Nextel 312 (3M) 2.7 1.55 (225) 150 (22) 12 1204

b-SiCNicalon (Nippon Carbon) 2.55 2.62 (380) 193 (28) 10 1204SiC WhiskerVLS (Los Alamos) 3.2 8.3 (1200) 580 (84) 4-7 1400SiC MonofilamentSCS-6 (Textron) 3.05 3.45 (500) 410 (60) 140 1299Berghof 3.4 3.45 (500) 410 (60) 100 1259

Si3N4TNSN (Tonen) 2.5 3.3 (362) 296 (43) 10 1204

GraphiteT300 (Amoco) 1.8 2.76 (400) 276 (40) 10 >1648T40R (Amoco) 1.8 3.45 (500) 276 (40) 10 >1648

Elastic Constants of High Performance FibersFiber only in resin

Fiber E1 E2 ? t G12 ?? ν12 E1 E2 1 2 # Filaments Densitymsi msi ksi ksi ksi msi msi ksi g/cm3

Carbon/GraphiteAS4 34 1.2 520 13 260 0.3 34 1 520 3000 1.8T40 41 1 820 17 410 0.2 41 1 100 12 1.8Celion 6K-SKRSY 34 1.2 450 13 225 0.3 34 1.2 450 6000 1.8Celion 12K 30 1.2 245 12 122 0.3 34 1.2 200 12000 1.77ACP 31 .5 500 12 250 0.3 31 .5 1000 12000 1.8

Silicon CarbideSCS-6 60 30 500 26 250 0.17 50 25 400 1 3.1Nicalon 15 2 203 6.3 102 0.2 15 2 1000 500 2.6FP-5 23 23 84 9 42 0.3 55 55 1000 210 3.9FP-25 19 55 54 7 27 0.3 55 55 210 3.9

GlassE-glass 11 5 500 4 250 0.3 11 2 1000 12000 2.5S-glass 12.4 1 665 5 333 0.3 15 2 1000 1000 2.5

KevlarKevlar 49 17 1 250 6.5 125 0.28 17 1 250 1000 1.4

Properties of Metal and Ceramic Whiskers

Material Melting point Density Tensile Strength Young’s Modulus(F) (lb/in3) (ksi) (msi)

Iron 2768 0.284 1902 42Copper 1951 0.320 426 14Silver 1732 0.374 256 17Silicon 2538 0.084 554 23Al2O3 3700 0.143 4000 62BeO 4660 0.103 1900 50B4C 4400 0.091 2000 70SiC 4870 0.115 3000 70Si3N4 3450 0.115 2000 45Graphite 6600 0.060 2850 102

Glass Fiber Reinforcement

“E” lectrical “S” tructural QuartzCost/lb $1.00 $5.00 $100.00

TensileStrength, ksi 350 450 130Modulus, msi 10.6 12.6 10

Density, lb/in3 0.092 0.090 0.078

Dielectric Constant 6.33 5.34 3.70(conduct energy)

Loss Tangent 0.001 0.002 0.0002(absorb energy)

Graphite Fiber Reinforcement

Standard High Strain High Modulus Ultra High ECost/lb $18-35.00 $40.00 $65.00 >$275.00

TensileStrength, ksi 450 600 250-400 250-400Modulus, msi 34 35-45 50-55 75-120

Density, lb/in3 0.059 0.059 0.059 0.059

Advanced Composites Fiber Comparison

Fiber Fiber CompositeFiber Price ($/lb) Modulus (msi) Density (lb/in3)

E-glass 1 10.6 0.07S-glass 5 12.6 0.07Aramid 15-50 18.0 0.05Standard Graphite 17-35 34.0 0.06High Strain Graphite 40 42.0 0.06High Modulus Graphite 65 50.0 0.06Ultra-High E Graphite 275-650 75.0 0.06

Representative Properties of Unfilled Resins

* PC: polycarbonate, PS: polysulfone, PPO: polyphenylene oxide**Load specimen at room temp., heat until extensive creep

Thermoplastics* ThermosetsPC PS PP Polyester Epoxy-BPA Epoxy-CA Phenolic

Yield Strength, ksi 9 10 9 11 12 19 9

Tensile Modulus, msi 3.4 3.6 3.8 3.5 3.6 7.8 4.5

Elongation, % 80 50 30 4.5 4 3.5 2

Tg, C 150 190 210 155 170 190 -F 302 374 410 311 338 374 -

Heat Distortion**, C 132 174 130 140 155 175 170

Continuous Use, C 120 150 115 125 145 150 160Temp. F 248 302 239 257 293 302 320

Desired Characteristics of Matrix Resins

Mechanical & Thermal:High strengthHigh elastic elongationHigh shear strengthHigh modulusHigh heat distortion temp.Low creep at use temp.High toughness/impact strengthThermal expansion near fiberResistance to thermal degradationLow thermal conductivity

Chemical Properties:Good bond to fiber (directly or

with coupling agent)Resistance to solvents & chemicalsLow moisture absorption

Processing Characteristics:Low enough melt or solution viscosity

and surface tension to permit thorough fiber wet-out

Good flow characteristicsRapid cure or solidificationSuitable for precoated reinforcementCure temp. not greatly above use temp.Low shrinkage during and after noldingLong shelf life and pot life

Other Factors:Low costLow densityLow dielectric constant

Comparison of Thermoset and Thermoplastic Resins

Stepwise cure possible to permit Viscosity varied only by increase in control of viscosity & handling temperature and/or shear rate

Thermosets Thermoplastics

Most used Most suited to automated production

No flow under heat and pressure Softening and/or melting points so flowafter cure; scrap discarded readily under heat and pressure;

remolding of scrap usually possible

Amorphous May be crystalline

Applied to reinforcement as low High viscosity even in the melt;viscosity liquids or varnishes reinforcement by dry or melt compounding

Phenolics and most polyimides emit No volatiles emitted during moldingvolatiles on curing (not epoxies orpolyesters)

Comparison of Thermoset and Thermoplastic Resins

Thermosets Thermoplastics

Post curing often necessary for Post molding shrinkage may be severeoptimum properties due to slow crystallization

Higher strength, modulus and Tougher, less brittle and lower costaverage use temperature

Used with continuous fiber and Used mostly with discontinuous fiberdiscontinous fiber (usually >1/4”) (length usually <1/2”), though much

activity in last 10 years on TP prepregs

Low tensile elongations Relatively high tensile elongationspossible with some plastic yielding

Variability in mechanical properties High variability in mechanical properties

Maximum Useful Temperature of Representative Resin Based Composites

Density MaximumMaterial (lb/in3) Temp. (F)

E-glass/epoxy 0.072 350Boron/epoxy 0.075 350Graphite/epoxy 0.059 350

E-glass/polyimide 0.072 600Boron/polyimide 0.075 600Graphite/polyimide 0.059 600

Borsic/aluminum 0.100 600Borsic/titanium 0.130 1200

Effect of Reinforcement Shape on Mechanical Properties

Composite Materials Overview Homework Assignment (40 pts)

a) Type a 4 page essay/report (not including a title page) on the various types

of composite fibers, matrices, their relative properties, uses, characteristics.

Include both thermoset and thermoplastic matrices.

b) Include references to content, figures, tables, etc.

c) Use the lecture notes as one reference, other references could be your

textbook, other documents on the course web page, and so on.

d) For an extra 10 pts, discuss the difference between carbon and graphite

fibers.