Download - 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