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Q: linear approximation of NL material (stress/strain)

Question asked by Tony Gatta on May 14, 2013
Latest reply on May 20, 2013 by Tony Gatta

Greets all.  Simple question here (I hope).. when running a linear analysis of a non linear material..

meaning I'm approximating a NL material with a straight line (single modulus), I've always taken that:


1. displacement based analysis will yield acceptable strain, but bogus stress

2. force based analysis will yield acceptable stress, but bogus strains.


this assumption from the fact that, by the book, displacement based strain formula are independent

of material properties.  strain is strain is strain.


so one could, for example, perform a linear analysis of what would be a NL material, compare the

resultant strain to the material's strain failure.. and have a reasonably accurate prediction without the

complications / time investment of a full blown NL analysis.


However, although this method has worked with some success, I'm not 100% certain this is true

in FEA.


Meaning that the numerical embodiement of the problem may not be as "clean" as the theoretical.


eg, fea is using material props in the stiffness matrix.


I don't know if those material props then become irrelevant in the strain results.. I'd assume they would.