//

ARR No. 5H28

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

Ir/IRTIMI RI P()RT' _Y ISSAJED

December 1945 as

Advance Restricted Report 5H28

FAT_.GUE STRENGTH OF FLUSH-RIVETED JOINTS FOR

AIRCRAFT MANUFACTURED BY VAR/OU8 RIVETING METHODS

ByG. A. Maney and L. T. Wyly

Northwestern University

NACA

WASHINGTON

NACA WARTT.ME REPORTS are reprints of papers oriKinallyissued to pro_de rapid distributionadvance resear:h resets to an authorizedgroup requiringthem for the war effort. They were pre-

vlou.Styheld '_der a security statusbut axe now unciRsstfled. Scme of these reports were not tech-

nlc_ty edited. All l-._vebeen reproduced '#ithoutchange in order to expedite general dlstributi_=.

_up D.ATA 19"75

W-82

NACA A_R No. 5H28

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

ADVA_CE RESTRICTED REPORT

F_TIGUZ STRENGTH OF FLUSH--kITETED JOINTS FOR

AIRCRAFT MANUYACT_ED BY VARIOUS RIVETING METHODS

By G. A. Maney and L. T. Wyly

SUMMA_RY

The results of au investigation to determln_ the fati,_e

strength of flush-rlvetcd Joimts manufactured by different

rlvctin_ methods are presented. T_sts were made on a direct

stress fatigue machine at room t_mperatures. The rivet_ were

made of aluminum alloy A17_-T and the u!_te_ of aluminum

alloy 24S_T. Prellmin_r_ tests at 70 ° Y on speci_cns h_vin_

varyin_ ratlo_ of rivet dinmoter to plate thickncs_ w_r_ zud_

under both z_ntic and dynamic loads to check the efficiency

of the _pecimen grips.

Tn_' results of the tests shov_d theft the fntiyun

strength of the Joints was directly affected by the method

of riveting used The endurance llzit of the rLvcts in com-

pletely reversed .hear was greatest for coza_roin! cou::ter-

sunk rivets wlth the head O. CIO inch _bove the plate surface

before driving, while the endurance limit was low_zt for _=_--nercial countersunk rivets with the hond 0.003 inch below

the surface before driving. The endurnzce ii_It fcr rev_r_e-

driva:_ rivets (Method E) was intermediate between the

extremes. In severnl cas:_ considerable v_rlation in be-

havior under th_ sa_e fatigue lo_ds was found in specimens

of the sa_e series. The lowest _ndur_nce li_it fcun_ in

this investigation was about 9_00 psl whilc the z xi_u-

found was _bout 15,000 psi. Static tests on th_ r_vorze

driven rivets _hcwed nn ultimate strength of r_bout SS,CIO

psi, this bein_ the highest strength d_velop_i by any c f

the joists.

DE? INi- ICUS

The Joint_ were tested in ten_ion, thus putti_ tLerivets i_ _hear. The term 'ultl_te tensile strength _ as

1976

NACA _R No. 5H28

used in this report refers to the ultimate strength of the

Joints a_ a unit. The term "static ulttzate strength _ cf

the rivets refers to the ul_.imate shearing unit stress de--

veloped by the rivets at rupture. The term "unit stress"

in this report refers to the shearing u_it stress in therivets.

I NTR 0DUCT I 0N

Tests by Hartn_nn, Lyst, _nd Andrews (reference 1) and

by Andrews and Holt (reference 2) on aluminum alloy riveted

connecti_n_ h_ve r_centl7 been published. The literature

on fatigue tests of riveted Joints is still meager, however,

and so far as the author_ know e_ investigation of the size

and the type of aluminum alloy rivets here studied has not

previously bc_n z_deo After soze prell_in_ry study, it was

decided t¢ limit the scape of the investlgatlon to one size

cf rivet, one thlckness of plate, one type of specizen, and

four z_thcds af riveting. (See fi_. i,)

T_Is investigation , conducted at the Northwestern

Un_verslty, was sponsore_ by and conducted with the financi_lassistance of the National _dvieory Committee for Aeron_utic_o

The _ethod_ of riveting inve_ti_at_d are th_se for which

static strca_th has been invamtig_t_d by the Langley Ma-

norial Aercnautlcal L_boratory of the Natlon_l Advisory

Cc_;_ittee for Aeronr_atics. (See reference _.) The work

wa_ conducted under the directlca of th:, _uthorso

Crodlt for performing a_st of the actu_l testing should

be glvcn to the follcwln_ students: H_l_ut Abt, Victor Archer,

Gorvas_ Gauer, Paul Gouwens, Eenneth Lenzen, Frank Phalcn,

Willie. _ss, _n! Mlle_ ?_urtellctte. The w^rk oe re=odcl--

in, _ _nd c_librnti_g the testing machine was done by L. T.

Wyly.

AFPAPoATUS A_TD ,_.ETHCDS

_!yati___eth_ds.-- The hotbeds of riveting used are

those d_veloped by the Lan_l_y structures research l_bora--

tory of the NACA and described In reference 3. The types

of rivets u_ed and their dimensions, th_ _n_Ics of the

countersunk hole_, end t_e tide from which the ri-._ts _re

insert_,I are shown in figures 2 _o 5. The dlstinguishin_

fer.tures of the riveting aethcd_ used in this In_esti_tion

NACAARRNo_ 5H28

Method C. The manufactured head of the countersunk

rivet t_ driven with a vibrating gun while the shank end is

bucked _ith a b_r. The driven rivet he_d is flat. All speci-

mens riveted by this mothod _re given the prefix C in the

designation.

Method E. The _anufactured round head of the rivet is

driven wlth a vlbratlag gun while the shank end is bucked

with a bar. After the rivet is driven, the portion of the

formed head that protrudes above the skin surface is milled

off and finished smooth wlth the sheet. All specimens riveted

by this method have the prefix N.

_mm___mnm.- Details of the speciaens for the

tPrelim]nary Tests" are sho_n in figure 6. Details of the

specimens for the "_aln Tests _ are shown in figure i. The

prell_Inary speclJ;ens were detailed by the Northwestern

University. The Langley labcratory made the final details

of the main test specl_ens and furnished all specimens for

beth preliminary and r_gular tests.

M_tex_lal_.-- The plates were made fro:- sheets _f 24S-T

alumlnu_ alley. The rivets were made from A175-T alu_,Inu_

alloy.

SReci_eB_gX_s.- The gri_s used to mount the specizon_

in the testin_ machines are split screw fittiug_ which were

secured to the ends of th_ speclz:ens by drlv_ flt 4owels,

by frlction, and by split tapered dowuls. Deta1!s at, shcwn

in figure 7.

_InE__nch_m.-- The preliminary stP tic t_sts were

run on a Southwark-E_ry univers_l hy_reulic te_ting machine.

The preliminary dynazlc tests were run on _ Rlehle p_ndulum

impact machine which i_ equipoed for tension impact testing.

Both of these machines have been described in a report of

previous study (referenc9 4).

The fatigue tests were run on an H. Y. Mo_re type

repeated direct stress machine (fig. _ :,cdffled asnecessary for this s_rles. This machine h_s been d_scribel

in reference 5. Several _diflcations w_re mad_ in _he

Northwestern mod61 beth to handle the specimens use_ _nd

also to insure the d._sired a_cur_cy in de_lln_ with th_

s_all loads desired. This m,:ch_ne is of the cc_st_n_-str_z

type. Wlth the eccentric set at zero, inlti_l co_pr_s_on

is applied to the specimen by tlghtenin_ the calitra_,.d

helical spring. Tension tc th_ d£slred amount th_n is

NACA JLRR No. 5H28

applied through the proving ring. The eccentric then isset to give the proper amount of throw to the actuatin_

l_ver bar which causes the load on the specimen to vary"between the desired values of maximum tension and z_xinun

compression. The calibration curve for the helical spring

is shown in figure 9. A cpeclal dlal gage was used to

me_sure the spring extension, readings on two sides beingaveraged. The calibration curve for the proving rin_ is

shown in figure I0, and in figure Ii is shown a calibration

of the spring working against the ring and _iving actual

lord delivered to the specimen. In determining the last

two curves, two electric resistance wire strain g_es mounted

on opposite sides of a steel specimen placed in the tgsttngmachine, were used.

It was necessary to take a number of precautions to

secure and hold the lends to the desired accuracy, some ofwhich were as follows:

!. A specially selected and hardened tool steel eccen-

tric was made, to avoid error from wear,

2. A buzzer was used to br_k up the friction in the

proving ring _tal indicator. The mounting _nd

setting of this dial was never disturbed through-

out the investigation.

3. The O. O07-tnch shim steel diaphragms wore slotted

to avoid any dishing. The proper position of

the rin_ _haft (lower end of specimen mount)

to eliminate any vertical force in the diaphragms

w8s determined by test and this position was

marked by _ special gage.

a. Care was used to avoi_ stresses due to change inroom temperature.

5. Frequent checks of load on each specimen were made

during a test and adjustments made when necessary.

6. Check of spring calibration at interveis showed no

change.

The speed cf the t_stin_ zachine gives about 1_50

reversals per _Inute. An investigation was m_de t_ deter-

mine whether vibration of the actuating lever might produce

loads on the specimens differing appreciably from st_tlc

loads, i dlal indicator _cuated on a micrometer screw

NACAARRNo. 5H28

and set in a frame rigidly bolted to the cast iron base of

the testing machine at various stations along the lever was

used. It was found possible to establish the fact that therewas no deflection of the lever which would appreciably change

the lead on the specimen.

PRELIMINART TESTS

The preliminary tests were made to investigate:

1. The strength of the shank for the purpose required

2. The possibility of a slip between the specimens

and the grips

3. The static strength of the _olnts

The investigation of these questions was carried out in

connection with an impact study recently made on the same

series of Joints, and the description of the preliminarytests is covered in detail in the report on that study.

(See reference 4 .)

The first two of the abGve questions were investi-

gated thrcugh specimens of the preliminary tests. (See

fig . 6.) The specimens were tested under both very slowstatic leads and impact loads. The specimen grips used were

stullar to the gripe used in the _ain tests fatigue series(see fig. 12) except that the latter are ioa_er t:nd con-

tain two dowel pins instead of one. Stntic strength testswere made on speclmens of the main series. (See fi_. i_.)

Preliminary Test Results

Strength of shank.-- No weakness in the shanks of the

specimens was discovered in any of the tests.

_liu in the _ri_.-- The preliminary tests establishedthe fact that no measurable slip of the speciLe_ occurred

either under static or impact loads. The evidence cn this

point was quite conclusive. The energy required to rupture

the specizens varied fro_ 0.4 foot--pcund to 4 foot--pounds,

due to the varylr_ ratios of rivet diazeter to plate thick-

ness used, but th_ a_reement between the energy required to

rupture a _iv_n specimen type under static ard under /ynamic

loads was remarkably g_od.

6 _ACA _R No. 5E28

j_L_ strf_.- The static strength of the Joints is

recorded in table 1. The countersunk rivets for Method C

with hb = -0.003 showed the least strength, and the rivetsfor Method E showed the greatest strength; _nd there was a

unifor_ variation of the strength from one type of rivet to

another. The maximum difference in static strength was not

l_rge.

MAIN TESTS

It is generally agreed that the endurance licit for

co=pletely reversed s_ress and the static ultimate strength

_re the _ost significant properties since, fro_ this in-

for_ation, the variation in fatigue strength with range ofstress _cy be approximated by either a Goodman-Johnson

(reference 6) or a Haig--Soderberg (reference ?) type of

diagram.

The Lain purpose of the investigation was to establish

by means of S-N diagrams the endurance liuit at room tempera-ture of e_ch of the four types of specimen of the _ain test

serieso

Main Test Procedure

All _ain tests were run at room temperature. All

specimens were subjected _o completely reversed loading.The cycles at the endurance limit were carried to ten

_illion or over for each type.

_he procedure was to start a series with fairly high

stresses, testing each specimen to rupture, an_ gradually

reduce th_ stress on succeedin_ specimens until a point was

re_ched where failure did not occur after ten million

reversals.

Constant care at all stages was used. End connections

were placed on a line scribed through the rivet center end

all holes were drilled while the specicen was _ounted in

Ji_. Careful watch was kept of the rco_ _o=perature sincethe spect=en would respond much z_re quickly than the machine

to _ir temperature changes. As it was d_ired to h_ld theload constant on a given specimen throughout the test, fre--

quent checking of the load was necessary with so=e _li_ht

adjustments at ti_es.

NACAARR No. 5H29

A few Joints were found with obviously defective rivets.

These specimens held the static load during adJu_t=:ent of

the machine but failed after a few cycl_s of stress. In the

CB series an vnusuelly wide spread of results occurre_ Just

above the endurance limit, necessitatln_ a large number of

tests. In one or two cases the specimen failed not in the

rivets but by fal_Igue fracture in the shank where the corner

ha_ been cut without a p_opor fillet.

Main Test R_sults

The results of the mai_ tests are shown in table i and

in figures 14 to 17. They arc su_,_arized in table 2 and

figur_ 18. Enlarged phcto_raphs of typical rivet fracturesare shown in figure I_.

Discu_lon of Main Te3t Results

The principal results of the main tests are as follows:

i. The 3tatic strength of the joints varied unlforzly

fro_ 31,500 psi for type C_ wltL h b = --0.0C3 to $5,5C0 for

type CC with h b = 0.010 and 38, I00 for type ._A, reverseLethod.

_-. The e_durance linit (fatigue strength) varied

unlfornly from about 9,300 psi for type CA to 15,000 psi

for type OC with type NA Rhowing an inter:..edlato str_n_th

of about ll,000 pci. Thi_ is a very sub_tnntlal vuriation

in strength.

3. In general, the S-N curves show the usual sharp

break in _he neighborhood cf a million cycles of str_s :_nd

a very gentle slope between oae and t_n :_illlcn cycles.

4. The individual ,.ariation or spread in resultz in

cert,.in cases was quite bread, es is frequentl:: the c_sein fatigue tests.

The zest outstandinr, result of the tests is the eff,_ct

of the _ethod of riveting upon fatigue strength and, in

_articul_r, the low fatigue stren_,th developed by the _;A

specimens, that is, reverse m_thod. Equally inter_stlng is

the zark_d Increase in fatigue strength as the v_luo cf

h b is l_cre_.s0;d.

_orthwest ern _rniver s ity,

Evanston, Ill., June 7, 194 5.

NACA ,IL.R.R No. 5E28

REFERENCES

1. Hartmann, E. C., Lyst, J. 0., and Andrews H. J.: FatigueTests of Riveted Joints. Progress Report of Tests of

I?S--T and 53S--T Joints. NACA ARR No. 4115.

2. Andrews, H. J., snd Holt, M.: Fatigue Tests on 1/8-Inch

Aluminum Alloy Rivets. NASA TN No. 971, 1945.

S. Lundquist, Eugene E., and Gottlleb, Robert: A Study of

the Tightness and Flushness of Machine-Countersunk

Rivets for Aircraft. NACA RB, June 1942.

4. Mauey, G. A., and Wyly, L. T.: Impact Properties at

Different Temperatures cf Flush--Riveted Joints forAircraft Manufactured by Various Riveting Methods.

NACA ARR No. 5F07, 1945.

5. Moore, H. Y., and Krouse, Glen N.: Repeated-Stress

(Fatigue) Testing Machines Used in the Materials

Testing LaboratorF of the University of Illinois.

Circular No. 23, Eng. Exp. Sta.,Univ. of Illinois,

1934, pp. 27-32.

6. Moore, H. F., and Kommer_, J. B.: The Fatigue of Metals.

}_icGr:_w-Hill Book Co., Inc., 1927, pp. 173--186.

7. Soderberg, C. R.,: Working Stresses. Trans. A.S.M.E.,

vol. 55, 1933, APM-55-16, pp. 131--144.

c_

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26

TABLE1

FATI_E TEST

load perz_lm

lb

2__3_3

_3.5

85.5

75.5

217

6e.5

63.5686_6_6665._

9_._

93.59O96.5

210

ua_t

p_

36_00_00

38 OOO

381O016100I_9_013 3_012koo11)oo11koo11'+001150011OOO1150O1_ 15o109o0

33. _0_O'JO

99"J08].1.0

11 7_0

9 8_0

93OO

23_C)

o_03_000_5 950

to& 19 100_00._ _L _09e ik2oo

_SOLTS

60000

2OO0O03OOOOOO

6OOOOO/,m ooo

201.40001OOOOO0OZo _o ooo

2 kTO 0_01o _76 ooo

55 000k00 000

7520000235 000

6 01_ 000_75 000

i? _01 0001110O000

?00 0002O0OOO0

lk ;51 000k ooo ooo11 g6_ 000I 3k7 0ooi 13_ 000

_0ook2ooo

10e 000

st_Ao t4_tII II

II •

II n

ii •

• ii

N _

• I

m I

m •

I #

/.

10 |ACA ARR Eo 5_

m

load pez'z_wlt

lb

32 9;..533 9/_53k 9635 9_.536 90.53"Ii _.539 9J_5_t 92.5

93°5_3 95J_ 98.5

37 Z_596

13 105.519 109

25 9726 1312728 3_.529 110.530 123.531 _7.532 117.533 138.53435 ).1.0.5_6

m_tb

pet

1_Co137oo139OO137oo131o0 1113 550].37oo13_0013 550 113 76O ]-3_0

35 50O13 92O 63.5 1_0 1215 3OO 215 8OO132OO 10136OO 5_06o 919oo01796O 115 COO 91602O 917 930 617 05017 050_OO_O2O0OO16O0O_8980

of

227005_335371190300

27O800

OOO_003D14.1.

425792175759652

9OO

l&5

5OO4OO000000000COO000COO000000000

0000000000000000000008OOOOO000000000CO0000COOCO0CO0000

IIot_8

me n

II I

U II

I_.w_t, not mptm__wt_ mptm_

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II •

_wt_ net mptm_

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TAN..E 2.- _ OF MAIN TEST RESULTS.

$tat_ t4nLS.te strength po£

Endnasnce ].t_tt at 1(37 cycles pei

5

Series CA

3O

Series C9

32 5oo

1290o

40

$_z_Les_ SmrJ_sn

29

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N._A IRR Iio. Figs. I,_,3

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Specl-aeD

CAItO

0A24

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C¢1to 3132

CC24

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Rivet IbeaddlsmeTer I _le

78

?8

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bb

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._ C

.010 C

-- Reverse

Method De_h ofof counter- Numb er

drlvlng ,,ink req'd.

0.050 24

.047 ?4

•037 24

._30 24

Figure I.- Details of soeclsens for main _estm.

(All d%sensJ.one in inches)

?8°_

L/4

__i

_ 8zo

._":.-|o. 30 drill

F18ure 2.- Dimensions oC =acaine-countersunkrivet _nd an_le of countersink

used in r_veting aethod C for l/8-in. _,vet.

_ 60°_/

k

Ii

5116

I

rli;ure 3.- Dimensions o.S roundhead rivetan_le of countersink used In

riveting setbod r for 1/B-in. rivet.

..___

Llr2brat In4gun

Metno_ _"

Ling1"

Method C

Ft_ure 4.- _et_ods of rivet-_r_g use_ tn this

t_ves_lgatlon.

Cb

Focltlve h b

FLgs. 4,5,6

ab

Negative h b

Before _riving

ha _&

Positive _a Ne_,atlve h a

After driving

FISure 5.- !lluP_ratlons oF h b and na for m,chlne-Countersunk rivets.

_/

[

!

i

!

D

_t l8

(XZl dimenslon_ in inches)

J Rivet

Specl- diameter

Me_hod _;

C1A _/32

C2A S/_.2C2_

03A 1/_0_

_4_ 1/8

_IA 3/32

_3A _18

W_A I _/eI

_hee_

t_lcknees $ D A

t in.) (_n.) (in.)(!_.)

h b = 0; rlve_-_ead angle, ?8 °

0.040 3/4

.064 3/4

.o4o 7/8

.o64 ?Is

getbod l; flyer-head

0.040 314

o_4 _/4

.040 ?/8

.064 ?/_

_/zs _-_/s

7/16 1-1/4

_IS _-zls

_/e _-z/4

angle, 60°

7/16 1-1/8

_/_s _-_14

_/_ _-_/_

_/_ _-_/4

Depth o[COUnt ._r-

O.Ot7

.047

.060

.(_0

0. 030

• 030

.050

• 050

Figure 6.- Detal_s of s_eel_en_ for

_reltminary tests.

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CO

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J/

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-_._rden_ steel _rlpe, faces qalnst

speclsen grooved to de_th of

._S s, t_re_ 1 _ dt_eter by 8

L/4* dl_eter douel _la,

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J---T_ "-lz.

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F_gu_e ?.- Details o_ grips used _o .-',ount specimens In tes_ln_ _acr.lnee.

1975

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40

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Static ultimatestre_th ", /_""_

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