Strengths of avdel light alloy blind rivets in DTD 546 b sheet

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TECHNISCHE HOGESCHOOL

VLI£GTUIGBOUWKüNDE

Kcmaalstraat 10 - DELFT Q^^ ^^^.g ^ ^ ^3

1 6 JULI 1957

THE COLLEGE OF AERONAUTICS

CRANFIELD

STRENGTHS OF AVDEL LIGHT ALLOY

BLIND RIVETS IN DTD 546 B SHEET

by

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TECHNISCHE HOGESCHOOI VLIEGTUIGBüUVvKUNDt Kanaalstraat 10 - DELFT NOTE NO. 63 A p r i l , , 1957. 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

Th.G Double and S i n g l e Shear S t r e n g t h s of Avdel L i g h t i'illoy B l i n d R i v e t s i n DTD 546 b M u n i n i u n A l l o y S h e e t ,

b y

-B»M, L e m p r i e r e , B . S c ( E n g , ) , M»Ae,E,

Tests have been perforiaed to corapare the double- and single-shear sti-cngtlis of joints in DTD 546 b light alloy sheets using Avdel blind rivets, Tl'je tests were an extension of v/ork done on solid rivets, and follov/cd conventional procedures,

The double-shear proof and ultimate strengths \vere fovtnd to be a.ppreciably better t haxi the single-shear strengths over a useful

range of shoot thickness/rivet dianeter ratio,

The effect of manufacturing tolerajace was examined ajid found to be important, though adherence to the rivet nuuiufacturer' s recaxiondod procedures ensures good strength,

The above conclusions lead to a consideration of the physicrJL bcha.viour cf the joints whj.cli is seen to differ in three rajages of tliickness/dicjiieter ratio,

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-2-A cross-sectional area of a rivet d dianeter of rivet

k,-. ratio of double-shear to equivalent single-shear strength for 1 /o loroof case

kp ratio of double-shear to equivalent single-shear strength for 2 /o proof case

K ratio of double-shear to equivalent single-shear strength for ultimate case

r.,^ 1 /o proof strength of joint (defined as that load

TJTO-ducing a permanent extension of 2 /o of one rivet diameter)

TpQ 2 /o proof strength of joint (defined as that load pro-ducing a permajient extension of 4 /o of one rivet diameter)

R xiltimate strength of joint

t sheet thickness of plate of single-shear joint, or half the centre plate of the double-shear joint

Equiva-lent single- and double-shear joints have the sarae vaJ.ue of ^-/dt or d/t,

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-3-Introdtiction

2

A series of tests were recently performed by HoT/e to in-vestigate the double-shear strength of conxion snap-head rivet joints, and it was felt to be of interest to extend the work to a majidrel type rivet. Accordingly, a limited series of tests ha.ve been made, follov/-ing the R.A.E, method-^, on the Avdel blind rivet,

Description of Tests

A range of single- and double-shear lap)-joints of DTD 346 b sheet were tested with 1/8" and 5/32" dianeter rivets, i?nd sheet thicknesses frar.-i 10 to 26 sv/g. The sx^ecimens (Fig, l) were identical to those used previously, having tvro rivets in line, raid equal thick-ness of sheet, (the double-shear ones hearing t\,TO strips on each side of the joint), Tlie rivets v/ere used in accordance v/ith the manu-facturer ' s directions,

It v/as found to bo of interest to check the effect of fit (of the rivet holes) on strength, so three tests vrore made on single-shear joints v/hich vrore nominally identical, though in manufacture had been finished with different drill sizes,

Follov/ing these tests, a second series of tests v/ere performed to check and augment the first set,

The tests v/cre made in a Denison Testing Machine, using a dial-gauge typo extensometer to measure the extension over the joint, The permanent set method was used to determine the 1 /o and 2 /o proof loads, and the ultimate loads were also fotind,

Results

Tte 1°/o and 2°/o proof loads and u l t i n a t e loads are

t a b u l a t e d f o r l / 8 " d i a , r i v e t s i n t a b l e 1, and for 5 / 3 2 " d l a , r i v e t s

i n t a b l e 2, These are p l o t t e d i n f i g . 3 but I'-evoal considerable

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-4-scatter. The curves on this fig, are obtained HB mentioned belov/. The manufacturer's figures are a.lso reproduced, shovdng favourable

com-parison, The nominal shear and bearing stresses (based on measured thickness of sheet) and the ratio of shear area to bearing area, 7i/dt, have been calculated. The sherjr stress is then plotted against the area ra.tio (fig, 4) for each case (1 /o and 2 /o proof and ultimate loads for single- and double-shear) , This representation is found to give least scatter, while ostensibly representing the measured

quantities, so that meaji curves can best be dra.vm. Little weight has been pla.ced on the early results for l/8"dia, rivets as they appear

to have wide and irregular» scatter, with IOVT strengths. Investigation has shovm this to be due to incorrect hole size,

The plots of fig, 4 are essentially a representation of the strength of the joint (compensaLted for rivet size) o.gainst diameter/ single sheet thidaiess ratio,

The results are plotted in fig, 5 as nominal shear- to bearing-stress. This representation permits en understanding of the differences between single- and double-shear to be seen more clearly,

Finally, the ratio of double-shear to single-shear strength is plotted in fig, 6 as a function of the thiclcnes^diameter ra.tio, These curves have been obtained from the mean curves of fig, 4,

For an understcnding of these curves, the joints must be divided into three classes as in fig, 2: those v/hich fail primarily in shear, in bearing, ruid by tearing. The first class obtains for values of A/dt less than 1,5 and i/as characterised by double-shear strength deteriorating vriLth increasing thickness, \Jhilu the proof stresses for both types reach a similar maxixium sheer stress (the proof for the rivet or sheet material), the double-shear joint shows

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_5-a loss of strength beloTir this for incre_5-ased thickness, Tliis is not apparent in the ultimate strength. The cause of this would appear to be bending of the rivets within the inner sheet causing increased extensions, though not affecting the ultimate loa,ds. This v/ould be aggravated as rivet length increases, due to decreasing " tie-rod" effect (the restraint due to tensile load). The divided inner sheet used in these tests in the double-shear joints would falsely weaken the restraint en rivet bending, so that it is doubtful vdiether this effect woiild be as narked in practice. It is significant to note that this behaviovir can be detected in the i-esults for the solid rivets, though the bending strength of a mandrel rivet would be less than that of a solid one,

In the second class of joints (for A/dt betvroen 1,5 and 5 ) , virhere failure is primarily due to bearing, the strength in double-shear is considerably greater than in single-double-shear. The elongation of hole and crushing of rivet due to high bearing stresses would res\ilt in an ill fit which vrould have a more severe effect in single-shear than in double-shear. The stability of the rivets in the latter, vrauld restrain deformation by tilting of rivet and ultimate failure by pull-ing througli of the rivet head or tensile failtire of the rivet, A crushing of the rivet would be more serious in mandrel rivets (where the sheath is more ductile than the mandrel), than in solid rivets,

The third class, of tearing failure (for ii/dt greater than 5 ) , is again characterised by a deterioration of double-shear strength, In a single-shear joint, tilting of the rivet would cause slight

stress concentrations at the inner bearing edges of the holes, but some of the load would be taicen as a tensile load in the rivet and reacted over the area under the heads, thereby alleviating the bear-ing stresses and so the onset of tearbear-ing. The fact that the bearbear-ing stresses in singpLe-shear are lower than those in double-shear is

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obvious in fig, 5« The ultimate strength would be similarly affected as the proof strengths, since for thin sheet the te&ring strength vrould be less than the " pull-through" strength. This effect woxild occur with any type of rivet, to a greater or lesser extent, as found vidth

solid rivets,

Finally, the results of the tests on effect of fit are presented diagramatically in fig, 7j where an appraisal of the manu-facturer's recommendations may be made. It is obvious that it is important to take heed of these. The reason for a great variation of strength vd.th fit is that the mandrel rivet is self eiq^anding to fill the hole, and this can only be useful vn.thin a reasonable limit. Over-size holes would not be filled, and imderOver-size holes would result in a broaching of the rivet, separation of sheets or poor gripping by the rivet,

Conclusions

Over a usefvil range of thickness/diameter ratios, the double-shear strength of Avdel riveted joints is better than the single-double-shear,

It is extremely important with a self-fitting rivet to follow correct manufacturing procedure.

The strengths of the joints compare favourably with quoted figures,

References 1,

2 , Ifowe, D,

Handbook, ' Avdel Self Sealing Blind Riveting

System" , Aviation Developments, Ltd, High Holbom,

London,

Double shear s t r e n g t h of BS Lé9 Snap Head Rivets

i n L72 and L73 /auminiura Alloy Sheet - Co A Note 5 0 ,

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-7-References (oontd,)

3, Ripley, E,L, Strength of BS L 37 Snaphead Rivets in DTD 546 Aluminium Alloy Sheet - R.A.S. Tech Note,,

Struct, 104. TABLE I

Eirperimental Results; l/8" Dia, Rivets,

Thickness Single Shear Double Shear

26 G 26 G 24 G 24 G 22 G 20 G 18 G 18 G 16 G 14 G 14 G 14 G 14 G 14 G .019 .019 ,022 ,022 ,028 .037 .052 .048 ,063 ,082 ,082 .082 ,082 ,082

Mo

298 575 330 460 346 390 510 714 508 540 812 625 820 330 " 2 0 335 407 378 495 420 532 682 783 732 700 887 715 885 620 R 454 457 450 510 553 730 906 857 1002 1030 996 925 984 1018 _^ "10 745 837 507 970 975 1230 1060 1640 1270 807 1370 -"2Q 815 385 790 1030 l l Z f O 1480 1485 1750 1675 1210 1590 -R 998 1004 1062 1126 1648 1841 2100 2020 2200 2178 2093 -Notes: Recent results,

Different fits - drill sizes: I/8" (.I250); N0.3O (.1285); No.29 (,1360),

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TECHNISCHE HOGESCHOOT VUEGTUIGBOUWKUNL . Kanaalstraat 10 - DEi^l 8 -Thickness Ncan, 26 G 24 G 24 G 20 G 20 G 18 G 14 G 12 G 12 G 10 G 10 G A c t u a l .020 ,022 .022 .037 .038 .052 ,082 .105 .105 .125 .127 T.,V3LË JI E x p e r i m e n t a l R e s u l t s : S i n g l e Sliear ^10 415 543 ,— 741 770 1000 1150 1290 1085 1200 1400 ^20 478 605 -781 830 1093 1325 1435 1310 1415 1510 R 557 668 -982 940 1200 1648 1723 1720 1773 1780 5/32 " Dia . R i v e t s • Double Sliear ^10 1010 917 1215 -1850 2480 2700 2460 -1780 2000 ^20 1090 1017 1275 -2040 2685 2970 2840 -2460 2560 R 1153 1/H40 1413 -2400 3140 3282 3590 -3410 3500 Notes: Recent r e s u l t s .

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DIA.

• f

-(H

= K . > ° 2 l O '

O

AVDEL SNAPHEAD RIVETS

FIG. I DETAILS OF S P E C I M E N S

1 . 5 - 5 < s

( ï ï )

C

)

LONG RIVET IN DOUBLE SHEAR IS SUBJECT TO BENDING.

HIGH BEARING STRESS PRODUCES TILT IN SINGLE SHEAR RIVET

TEARING STRESS IN DOUBLE SHEAR IS CRITICAL.SINGLE SHEAR

LOAD ALLEVIATED BY TENSILE LOAD IN RIVET.

FIG. 2 C L A S S E S OF JOINTS SHOWING DIFFERENCES IN BEHAVIOUR FOR RANGE OF A / d t VALUES.

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0 2

SINGLE SHEET THICKNESS ( I N S ) — K

- ^ -06 OS lO 12 r " o 2 0 4 O 6 OS lO 12 1 0 2 ^ 4 0 6 0 8 lO 12

FIG. 3 STRENGTH OF AVDEL RIVET JOINTS (2 RIVETS)

( C U R V E S DERIVED FROM FIG. 4 )

KEY o EARLY RESULTS ) I t n i A A RECENT RESULTS) + EARLY RESULTS \ 5 / ' 0 RECENT RESULTS ] '32 DIA.

SO I % PROOF STRESS SINGLE SHEAR 2 % PROOF SINGLE - 6 — « - 0 i STRESS SHEAR

N

V

X

₅₅

K

ULTIMATE STRESS SINGLE SHEAR

^H"

3 4 5 6 7 8 I I 4 S 6 7 8 | I 4 5 6 7 8

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I % PROOF STRESS SINGLE SHEAR A_ 4t 2% PROOF STRESS SINGLE SHEAR

KEY: O EARLY RESULTS A RECENT RESULTS + EARLY RESULTS • RECENT RESULTS DOUBLE SHEAR jIbDI/ CM A . d f A-dt • ULTIMATE STRESSES SINGLE SHEAR / / ^ ^

^9

y

3 4 5 /

A

\ /

V

B /' / / / DOUBLE SHEAR 6 0 SO K ) 0 2 0 4 0 6 0 8 0 ICO N O M L . BEARING STRESS C l O ^ p , , ) 2 0 4 0 6 0 e o no

FIG. 5 NOMINAL SHEAR AND BEARING STRESSES

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FIG.6 1-4 1-2 l O O 8 0 6

i

'

r

^ ^ ^-, — ^ - I«20 "^"lO k | Q = l % P R O O F RATIO k 2 o = 2 % PROOF RATIO K = ULTIMATE RATIO t / d l O • i 1 1 -6 4 3 1 I 2 1-5 A / d t —

RATIOS OF DOUBLE TO SINGLE SHEAR STRENGTHS FOR 1 % AND 2 % PROOF AND ULTIMATE CASES.

l O O O U) ^ 5 0 0 z lU a: A ULTIMATE STRENGTH. 0 2 % PROOF STRENGTH 0 1 % P R O O F STRENGTH MANUFACTURER'S RECOMENDED SIZE •125 • I 3 0

FINAL DRILL DIA. (IMS')

•135

FIG.7 EFFECT OF FIT ON STRENGTH OF AVDEL RIVET LAP