Introduction to Aircraft Structural Analysis (Elsevier Aerospace Engineering)

366 CHAPTER 11 Structural Components of Aircraft

Atensilefailureintheplatewilloccuronthereducedplatecrosssectionalongtherivetlines.This
areaisgivenby

Ap=(b− 4 )×2.5mm^2

Thefailureload/unitwidthPfisthengivenby

Pfb=(b− 4 )×2.5× 125 (i)

Theareaofcrosssectionofeachrivetis

Ar=

π× 42

4

=12.6mm^2

Sinceeachrivetisindoubleshear(i.e.,twofailureshearplanes),theareaofcrosssectioninshearis

2 ×12.6=25.2mm^2

Then,thefailureload/unitwidthinshearisgivenby

Pfb=25.2× 120 (ii)

Forfailuretooccursimultaneouslyinshearandtension—thatis,equatingEqs.(i)and(ii)

25.2× 120 =(b− 4 )×2.5×12.5

fromwhich

b=13.7mm

Say,arivetspacingof13mm.

11.4.2 Joint Efficiency

Theefficiencyofajointorconnectionismeasuredbycomparingtheactualfailureloadwiththatwhich
wouldapplyiftherewerenorivetholesintheplate.Then,forthejointshowninFig.11.11,thejoint
efficiencyηisgivenby

η=

σultt(b−d)/b

σultt

=

b−d

b

(11.5)

11.4.3 Group-Riveted Joints

Rivetsmaybegroupedoneachsideofajointsuchthattheefficiencyofthejointisamaximum.Suppose
thattwoplatesareconnectedasshowninFig.11.13andthatsixrivetsarerequiredoneachside.Ifit
isassumedthateachrivetisequallyloaded,thenthesinglerivetonthelineaawilltakeone-sixthof
thetotalload.Thetworivetsonthelinebbwillthensharetwo-sixthsoftheload,whilethethreerivets
onthelineccwillsharethree-sixthsoftheload.Onthelinebb,theareaofcrosssectionoftheplate
isreducedbytworivetholesandthatonthelineccbythreerivetholessothat,relatively,thejointis
asstrongatthesesectionsasataa.Therefore,amoreefficientjointisobtainedthaniftherivetswere
arrangedin,say,twoparallelrowsofthree.