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Change in Elastic Modulus with Plastic Deformation

Amit Pandey's picture

Article on web

http://www.eng-tips.com/faqs.cfm?fid=1441

 

The physical basis of material
properties like Young's modulus can be understood by examining
materials on the atomic scale. There are two main things that influence
the value of the modulus:

1.)     The atomic microstructure
2.)     The interatomic bonds.

 So, what is the reason of change of elastic modulus with plastic deformation? Any References??

 

 

Comments

??? I don't understand your question. Who is changing the elastic modulus? you mean we during the simulation? or you mean elastic modulus actually cahnge during plastic deformation in the real scenario?

I recommend you to check a classic book written by Professor Ashby.

Within this book, there are several chapters talking about

atomic bond (equations shown in eng-tips)

elastic modulus (how to measure it?...) 

plastic deformation (in micro, meso and macro scale views to explain the plastic deformations)

 

Enjoy!

 

Ref: Engineering material 1

 By M. F. Ashby, David Rayner Hunkin Jones

 

Amit Pandey's picture

Ok my Q? was

the reason for the decrease of elastic modulus with plastic deformation (tension, compression ..etc..) as presented by various papers.

Hi ajay,

         Generally all physical materials contain voids at different scales, with plastic deformation void nucleation and growth occurs and finally their coalescence leads to ductile fracture. There are many ways to define it  one can say loss of ductility or loss of strength (elastic modulus)etc.

 

 

Amit Pandey's picture

@EnyangWANG 
thanks for the book escentially it takes about the physical basis of
Youngs modulus ie.d based on interatomic bonds. However, i was looking
for the explanation of << in E (stiffness) with plastic
deformation.
 @unsrohith the way i understand and i have read few references which talks about the change in modulus and reason due to the void or nucleation (which mainly comes in the picture close to failure or after softening for tension) but how about change in modulus at 2-5% strain (tension/compression) where essentially strain hardening is taking place with hardely any sign of void growth.  Also, based on  the theory of interatomic bonds and physical basis of E it should not change with deformation (could be due to temp.)

Ajay,

      void nucleation may start once after crossing the yield point. And all materials have some discontinuties by nature so once we observe the nonlinear behaviour in stress strain curve voids will grow. I myself observed the loss of youngs modulus after carrying cyclic loading and unloading tests in an uniaxial tension test and after certain amount of plastic deformation the modulus almost becomes constant according to the test data I observed but literature says it will decrease continuosly.I dont know anything abt theory of physical bonds etc I am not from material science. 

 Rohith

Amit Pandey's picture

@unsrohith Could you email me ur references. ya I can underdtand ur aurgument but as u said people who have material science background could not digest this experimental result and make point that the unloading data should be studied carefully.

 

Ajay,

     Yes I strongly feel that there is some amount of error invoved in measurement of youngs modulus, You can refer "Course on Dmage mechanics by Lemaitre". apart form the experimental observation it will not give any other details regarding to materials aspects.

Rohith

Amit Pandey's picture

I am wondering if anyone has done work on (or views on) about decrease in modulus due to the >> in anisotropy because of plastic deformation other than as we (@unsrohith ) have been discussing (growth of void etc )

http://www.springerlink.com/content/p6q5461225638r33/ 

Any comments

 It is well know fact of the  value of modulus is different in different crystallographic direction.

 

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