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Xiaogai Li's blog

How to develop a new constitutive model from scratch?

Dear all  iMechanica, I wonder if there is any good  material on constitutive modeling that explains how to develop a new constitutive model from scratch, e.g. from the experimental data say uniaxial tension and compression. Where should one start to develop a new constitutive model? What laws should the model obey?  These questions perhaps are addressed in many continuum mechanics text books. but I am looking for materials that explain in a concise (short) and easy to understand way.

Can microscopic coefficients always be derived from macroscopic coefficient (biot effective coefficient, skempton coefficient)?

Can microscopic coefficients always be derived from macroscopic coefficient?

To be more specific, 

alpha: Biot-Willis coefficient, Skempton coefficient 

These two parameters are derived from the macroscopic level which reflects the response of a porous material as a whole, without explicitly taking into account the individual contribution of its solid and fluid constituents.

From microscopic level, there are parameters (or bulk modulus) such as Ks (solid grain bulk modulus), Kf (fluid bulk modulus), and porosity. 

How to derive from poroelastic 3D equations to 1D Terzaghi equation?

In the terzaghi equation, there is a constant M (some books call is elastic oedemetric coefficient).
Since the terzaghi equation is a special case for the general 3D biot equations under oedemetric testboundary conditions, does any book or material explain the derivation?
If I want to mode the terzaghi problem using 3D model in FE program, the M is known, then how to get thecorresponding values of young's modulus and poisson's ratio in order to give the same response from the 3D model?
Thanks for your attention. Any suggestions would be appreciated.

A general question on dynamic structure problem: spatial resolution of high-frequency modes typically is poor by using the...

Hi Everyone,

I have a general question about dynamic strcture problem,

I read from some books that "spatial resolution of high-frequency modes typically is poor by using the conventional finite element spatial domain discretization"?

Could someone explain more on this? Does it because the element usually is not fine enough to capture the high frequency response or...?

Thanks a lot!



WhatDifference:same stress-strain curve for linear elastic material with nonlinear young's modulus and hyperelastic material

Hi everyone,

Now I am trying to implement Ogden model in Comsol Multiphysics, but I had some problem.

Then I realized that in Comsol, it's possible to implement a nonlinear young's modulus.

But I am a little confused.

If you have a nonlinear Young's modulus, in the stress-strain curve, E is the tangent of this curve.

For hyperelastic material, let's say Ogden material. It's usually a nonlinear stress-strain curve as well.

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