338 CHAPTER 10 Materials
Otherbendingtestsaredesignedtomeasuretheductilityofamaterialandinvolvethebendingofabar
aroundapin.Theangleofbendingatwhichthebarstartstocrackisthentakenasanindicationofits
ductility.
Shear Tests
Twomaintypesofsheartestareusedtodeterminetheshearpropertiesofmaterials.Onetypeinvestigates
thedirectortransverseshearstrengthofamaterialandisusedinconnectionwiththeshearstrengthof
bolts,rivets,andbeams.AtypicalarrangementisshowndiagrammaticallyinFig.10.5,wherethetest
pieceisclampedtoablockandtheloadisappliedthroughthesheartooluntilfailureoccurs.Inthe
arrangementshown,thetestpieceissubjectedtodoubleshear,whereasifitisextendedonlypartially
across the gap in the block, it would be subjected to single shear. In either case, the average shear
strengthistakenasthemaximumloaddividedbytheshearresistingarea.
The other type of shear test is used to evaluate the basic shear properties of a material, such as
the shear modulus,G, the shear stress at yield, and the ultimate shear stress. In the usual form of
test,asolidcircular-sectiontestpieceisplacedinatorsionmachineandtwistedbycontrolledincre-
mentsoftorque.Thecorrespondinganglesoftwistarerecordedandtorque–twistdiagramsareplotted,
from which the shear properties of the material are obtained. The method is similar to that used to
determine the tensile properties of a material from a tensile test and uses relationships derived in
Chapter3.
Hardness Tests
The machinability of a material and its resistance to scratching or penetration are determined by its
“hardness.” There also appears to be a connection between the hardness of some materials and their
tensilestrengthsothathardnesstestsmaybeusedtodeterminethepropertiesofafinishedstructural
memberwheretensileandothertestswouldbeimpracticable.Hardnesstestsarealsousedtoinvestigate
theeffectsofheattreatment,hardeningandtempering,andcoldforming.Twotypesofhardnesstests
areincommonuse:indentationtestsandscratchandabrasiontests.
Indentation tests may be subdivided into two classes: static and dynamic. Of the static tests, the
Brinellisthemostcommon.Inthis,ahardenedsteelballispressedintothematerialundertestbya
staticloadactingforafixedperiodoftime.Theloadinkgdividedbythesphericalareaoftheindentation
Fig.10.5
Shear test.