CHAP-5 Strain-Hardening of Metals

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Introduction

• With elastic deformation, the strains areproportional to the stress

• After plastic deformation starts, the

total strain is the sum of the elasticstrain (which still obeys Hooke’s lawand the plastic strain

• !he term strain-hardening is used todescribe

the increase of the stress le"el necessary

to continue plastic deformation


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Strain Hardening


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Strain Hardening


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Mobility of #islocations


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Strain Hardening


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$

Strain Hardening

New yield strength σyi higher than initial

yield strength, σ y0. Reason strain

hardenin .


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%

Strain Hardening

Yield strength + hardness increased due to

strain hardening, but ductility decreased

(material becomes more brittle).


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Strain Hardening


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T R

&

&


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athematicala!!ro"imations


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'roblem

• !wo points on a true stressstraincur"e are

) *+++ M'a at * ./ and

) * 00M'a at * .1/.

• 2ind the "alues of 3 and n in45uation (c that best 6t the data.

• !hen using these "alues of 3 and n,predict the true stress at a strain of *.0.


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'roblem

• !wo points on a stressstrain cur"efor a material are 7 ) * +$%M'a at * .% and

• ) * 0++M'a at *.18.

A. 2ind 3 and n in the power-law

appro9imation and predict ) at *.+.

:. 2or the appro9imation ) * 3( o ; n

with o * .1, 6nd 3 and n and


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problem

• !he following true stresstrue straindata were obtained from a tensiontest

2ind K and n in the power-lawapproximation

CHAP-5 Strain-Hardening of Metals

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