CoA Note No. 50
rtCHNISCHE HOGESCHOOL
VLIEGTUIGBOUWKUKDE Kanaalstraat 10 - DELFT
1 h AUG. 1956
THE COLLEGE OF AERONAUTICS
CRANFIELD
DOUBLE SHEAR STRENGTH OF B.S. L.69
SNAP HEAD RIVETS IN L.72 AND L.73
ALUMINIUM ALLOY SHEET
by
TECHNISCHE HOGESCHOOL VUEGTUIGLOUWKUNDE Kanaalstraat 10 - DELFT NOTE NO. 50 JULT. 1956. T H E C O L L E G E O F A E R O N A U . T I C S C R A N F I E L D
The double shear s t r e n g t h of B.S, L«69 snap head r i v e t s i n L.72 and L.73 aluminium a l l o y s h e e t
b y
-D, Howe, D.C.Ae,, A,M,I,l.Iech.E,, A.F.R.Ae.S.
Sm^IARY
A limited series of tests has been carried out en single and double shear riveted joints using L.69 (D.T.D.327) snap head rivets and L.72 (D.T.D,610) and L,73 (D.T.D. 546) sheets. The specimens were similar to those used by the RoycJ. Aeronautical Establishment (ref,l), the double shear
specimens being essentially two single sihear specimens placed back to back,
In each case the 1 per cent, 2 per cent and ultimate strengths were found, the single shear values being in agree-ment with the equivalent R.A.E, tests (ref, 2 ) ,
It was found that at high bearing stresses the permissible shear stress in the double shear joint falls below that of the single shear joint having the same noninal beai'ing stress. This reduction of permissible shear stress was found to increase with joint extension and to be
independent of the sheet materials tested. Design curves cro given,
-2-saiBoia
A area of one rivet d diaznster of rivet
K.Q ratio of the permissible shear stress of the double shear joint compared with that of the
equivalent single she£a: joint, corresponding
*°^10
K2Q ratio of the permissible shear stress of the double shear joint cccipared with that of the
equivalent single shear joint, corresponding
torgo
Kjj ratio of the permissible shear stress of the double shear joint compared with that of the
equivalent single shear joint, con^sponding to R
r^Q 1 per cent proof strength of joint, defined as that corresponding to a joint extension of 2 per cent of one rivet diameter
rgQ 2 per cent proof strength of joint, defined as that correspci.'Ijjig to a joint extension of 4 per cent of one rivet diameter
R ultimate strength of joint
t sheet thickness of one plate of single shear joint, and one outer plate or half the centre plate of the double shear joint (see Figure 1;, The 'equivalent' single shear joint is that having the same value of A/dt or t/d as the double shear joint,
The development'' by the Royal Aircraft Establishment of an improved method of testing the strength of riveted joints, has led to a systematic investigation of the subject. The joints considered include a vd.de variety of rivet and sheet materials and types of rivet. In all cases the 1 per cent,
2 per cent and ultimate strengths of the joint have been
estimated, but the work has been lijiiited to the case of rxvets in single shear,
It has long been known that the permissible shear stress of a joint in double shear tends to fall below that of the equivalent single shear joint, especially as the bearing stress becomes large. The extent of this loss in strength, especially in the proof cases, is not immediately apparent, and accordingly it vms decided to initiate a series of tests on double shear riveted joints,
Tests
Pull details of the specimens tested appear in Figure 1, In all cases both the single and double shear joints vrere tested. The single shear specimen is identical to that used by the R.A.E."" The double shear joint is essentially two single shear specimens placed back to back, it being assumed that a joint having equal total thicknesses of sheet is the worst case.
The specimens were loaded in tension, the extension over the rivets being measured. The 1 per cent proof load is defined as that corresponding to a joint extension of 2 per cent of one rivet diameter, v/hilst the 2 per cent proof load is defined as that corresponding to a joint extension of h- per cent of one rivet diameter. These proof loads v/ere obtained by using the 'permanent set' technique.
For all the specimens the nominal shear and bearing stresses corresponding to the 1 per cent, 2 per cent and ultimate loads were calculated. The nominal rivet diameter
and actual sheet thickness were used for this purpose, Results
The results are presented in Figures 2 to 7 as the variation of shear stress with bearing stress for each load case. In all cases a mean line has been drawn through the experimental values. Comparison of the single shear results
for the L,73 ( D , T , D , 546) material with those obtained by the
TECHNISCHE HOGESCHOOL
VLItGTUIGBOUWKUNDE Kanaalstraat 10 - DELFT
•V-a slightly lower 1 per cent proof v•V-alue in the present tests, It is of interest to note the way in which the mean line turns back on itself for high values of A/dt in the ultimate case, Figure 4.
The double shear results are similar ±n form to the sin.gle shear c-vcvos except that in the ultimate case there is no do-ablijr^-g bjick of the mean line. This difference is explaired by consideration of the nature of the failure of the joints. The straight initial portion of the single shear curve represents a shear failure of the rivets. The cux^.'-ed port-ion corresponds to the onset of rivet and sheet bearing failure. The final straight portion is failure by
the tearing of the sheet over the rivet heads due to the offset of the applied load. For the double shear specimens the type of failure is similar except for the last stage, Since tiie load is not offset there is a less tendency for the sheet to tear over the rivet heads, and hence bearing of the rivets and sheet is the main cause of failure,
As thi-s difference between single and double shear joints will not necessarily occur in actual structures a
'design' curve has been estimated to bring the double shear results in line with the single shear values,
The ratios of the permissible shear stress sustained by the double compared with the single shear joints, as a
function of the parameter t/d are given in Figure 8, These ciu-'ves indicate that, I'/ith the exception of the ultimate case, the ratio is independent of the sheet materials tested. Use of the 'design' curve overcomes this exception and final
curves appear in Figure 9,
It will be seen that the loss in shear stress of the double shear- joint, whilst present for values of t/d less thojcï 0,4, is not very great. This loss increases vd-th increase of joint extension,
Conclusions
The peiroissible shear stress of a double shear joint is less than that of the equivalent single shear joint for values of t/d less than 0,4.
The ratio of loss in shear stress is independent of the materials tested, and increases with increase of joint extension. For values of t/d less than 0,4 the design curves. Figure 9» should be used,
-5-References
1, Ripley, E,L,
2, Henwood,ïi,J,, Ripley, E.L.
Strength of B,S,L,37 Snaphead Rivets in D,T,D,546 Aluminium Alloy Sheet, R,A,E. Tech. Note Structures 104, July, 1952.
Strength of B,S,L,57 Snaphead Rivets in D.T,D,546 Aluminium Alloy Sheet, R,A,E, Tech, Note Structures 141, January, 1955»
TABLE I
Experimental Results for L.72 Aliminiim Alloy Sheet
R i v e t D i a . i n s , - d 1/8 5/32 3/16 Norn, T h i c k -n e s s 10 G 12 G 14 G 16 G 18 G ' 20 G 22 G 24 G 24 G 16 G 18 G 20 G 22 G A c t u a l T h i c k -n e s s i n s , - t 0 . 1 3 0 0 . 1 0 4 0,085 0,063 0 . 0 4 8 0,036 0 , 0 2 8 0 , 0 2 3 0 , 0 2 3 0 . 0 6 3 0,01S 0.036 0,029 S i n g l e I ^10 l b s 700 670 670 730 704 665 520 465 628 1320 1190 1130 800 ^20 l b s 780 720 780 800 764 715 584 520 682 1420 1330 1230 860 Shear R l b s 834 820 807 896 834 817 766 650 736 1720 1642 1430 892 Double ^10 l b s 1150 1470 1360 1530 1400 1360 1150 1000 1252 2820 2480 2050 1670 ^20 l b s 1350 1580 1510 1650 1486 1430 1225 1030 1336 3010 2650 2170 1790 Shear
1 ^
l b s 1564 1728 1660 1725 1622 1622 I 4 I 6 1360 1383 3390 3050 2570 2164TABLE II
Experimental Results for L.73 Aluminiim Alloy Sheet
Rivet
Dia.
i n s , - d
1/8
3/32
3/16
Nom,
Thick-ness
10 G
12 G
14 G
16 G
16 G
20 G
22 G
24 G
24 G
26 G
16 G
18 G
20 G
22 G
24 G
Actual
Thick-ness
i n s , - t
0,125
0,104
0,082
0,064
0,051
0,037
0,029
0,023
0.022
0,019
0,065
0.051
0,036
0,029
0,023
Single Shear
^10
lbs
650
670
680
800
670
600
570
490
656
619
1340
1360
1170
960
843
r !
^20
l b s
708
727
730
838
720
630
600
550
732
648
1450
1460
1260
1050
898
R
lbs
812
818
804
892
770
766
743
644
867
653
1644
1684
1456
1108
930
Double Shear
^10
l b s
1270
1388
1350
1420
1330
I38O
1250
1060
1340
1088
2800
2540
2290
1860
1544
'. _. . —^20
l b s
1400
1470
1450
1500
1400
1410
1320
1100
1380
1190
298O
2720
2390
1980
1684
1R
l b s
1634
1640
1618
1674
1620
1652
1360
1130
1524
1282
3290
3180
2540
2178
1906
.- ..
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DOUBLE SHEAft M A T t f t l A L - 1 ( 0 - J R I V E T CHAMCTER^4l
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l-S SHEAR f Stress / //
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r y //
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$15 lO 2 0 DOUBLE SHEAR R - U l t i m a t e Stress • L 72 SHEET L 73 SHEET ' D E S I G K T C U R V E S,r
'IS
r
" i o io5^ "8o~SEARING STRESS > lO P.S.I.
K) C ^ • *.
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V4 ^^ 3 "^ K K 10 2 0 1% •9 '<20 -8 C PROOF RA PROOF RA ) • TIO TIO y^ •2 -.^ % > •' 1 • 5 • 1 0 KR 5 <i^^T"
/ / o '1 -2 . -3 -4 -5 -6 Vd L 7 2 SHEET L 73 SHEE T ' D E S I G K T CURVE RATIO OF DOUBLE TO SINGLE SHEAR STRESS1-0 0*9 K20 KR 0.7 0* t 0 ' y •j-'^ ^ ^ i ' ''
