Yield Point Final

8/13/2019 Yield Point Final

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YPES OF S RENG HIn engineering the term strength is always defined and is probably

one of the followingompressi!e strength

Tensile strength

Shear strengthdepending on the type of loading"

S RESSThis is a meas#re of the internal resistan$e in a material to an

e%ternally applied load" For dire$t $ompressi!e or tensile loadingthe stress is designated and is defined as&

stress s'load(area'w()

S R)IN*e m#st also define strain" In engineering this is not a meas#re of

for$e b#t is a meas#re of the deformation prod#$ed by the infl#en$eof stress" For tensile and $ompressi!e loads&

strain e'in$rease in length(original length'%(l

Strain is dimensionless"+O),-,EFOR.) ION /R0EThis graph is $alled a load-deformation $#r!e" It shows #s how themember deforms1and #ltimately how it fails1as the load is in$reased"

ENSI+E S RENG H)s we follow the $#r!e #p and to the right2 we noti$e that the $#r!e

is almost perfe$tly straight from 3ero all the way #p to abo#t 452666po#nds" The straight line means that the deformation in$reases in

dire$t proportion to the load" For e%ample2 the deformation at 762666po#nds is e%a$tly twi$e as large as the deformation at 862666 po#nds"

In this linear part of the load-deformation $#r!e2 the beha!ior ofthe steel bar is said to be elasti$" Elasti$ beha!ior means that2 if

the load is remo!ed2 the deformation will also ret#rn to 3ero"


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E+)S I 9EH)0IORElasti$ beha!ior means that2 if the load is remo!ed2 the deformationwill also ret#rn to 3ero"

P+)S I 9EH)0IORPlasti$ beha!ior means that2 if the load is remo!ed2 the deformationwill not ret#rn to 3ero i"e" the deformation will be permanent"

)s we follow the $#r!e #p and to the right2 we noti$e that the $#r!e

is almost perfe$tly straight from 3ero all the way #p to abo#t 452666

po#nds" The straight line means that the deformatio i $reases idire$t proportio to the load" For e%ample2 the deformation at762666 po#nds is e%a$tly twi$e as large as the deformation at 862666

po#nds" In this linear part of the load-deformation $#r!e2 thebeha!ior of the steel bar is said to be elasti$"Elasti$ beha!iormeans that2 if the load is remo!ed2 the deformation will also ret#rnto 3ero"


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)s the load is in$reased beyond 452666 po#nds2 the beha!ior of thebar $hanges rather abr#ptly" There is s#ddenly a h#ge in$rease in

deformation2 with !irt#ally no $hange in the load" The steel isbeginning to fail" *hen a material #ndergoes large deformations with

little $hange in load2 it is said to be yielding" The point on theload-deformation $#r!e where yielding begins is $alled the yieldpoint2 and the for$e at whi$h yielding o$$#rs is $alled the yield

strength"

YIE+,ING*hen a material #ndergoes large deformations with little $hange inapplied load2 it is $alled as start of yielding" The yield point2

$alled the yield strength :Y;2 signifies the start of the plasti$region"

)nd #nli


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R/P /RE*hen load after #ltimate strength point is in$reased then within$rease in load on member it a#tomati$ally start to loss applied

load and finally brea


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Tensile Strength depends on&$ross-se$tional area of a member

type of material the member is made of

Tensile Strength does not depends on&

length of the member

shape of the $ross se$tion

R/E S RESS )N, S R)INThe tr#e stress #ses the instantaneo#s or a$t#al area of the spe$imenat any gi!en point2 as opposed to the original area #sed in the

engineering !al#es"

The tr#e strain is defined as the instantaneo#s elongation per #nitlength of the spe$imen"

Note& For a gi!en !al#e of the load and elongation2 the tr#e stress

is higher than the Eng" Stress2 while the tr#e strain is smaller than

the Eng" Strain"


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.od#l#s of Elasti$ity

If the strain is ?elasti$?" Hoo


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It is !ery diffi$#lt to find the a$t#al yield strengthe%perimentally" Instead2 we #se a 6"7B offset yield strength"

6"7B offset yield strength is the point on the $#r!e whi$h is offset

by a strain of 6"7B :6"667; Cthe interse$tion of the $#r!e with aline parallel to the linear elasti$ line and is offset by a strain

of 6"667D

The stress at ma%im#m :Fma% ()o ; is referred to as the /ltimateTensile Strength :TS; and signifies&

the end of #niform elongation"

the start of lo$ali3ed ne$

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Yield Point Final