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How does ABAQUS calculate the hyperelastic material coefficients using the nominal stress and strain?. I mean how from the nominal stress and strain data, ABAQUS fits a hyperelastic model and then, true stresses and true strains are obtained in the simulation results following this hyperelastuc model?.
It is possible calculate the hyperelastic material parameters either using nominal stress & strain, or by using true stress & strain. What ABAQUS does is to simply use an appropriate form on the hyperelastic material model for the type of stress and strain that is used.
After the material coefficients have been found, ABAQUS internally uses true stress and strain for the calculations.
My doubt is to understand how internally ABAQUS calculates these true (Cauchy) stress and strain. For instance, I use a polynomial model, implemented with nominal stress/strain and ABAQUS plots in the simulation results true stress-strain. Which process is followed by the program to convert nominal test data to true test data?.
Thank you for your help.
I think that I now better understand what you are after. It is not trivial to convert from nominal stress and strain to true stress and strain - you need to know something about the volumetric response of the material.
I virtually never use the ABAQUS built-in method for finding the material parameters (I have written my own programs for doing that), so this is my guess more than anything: I suspect that ABAQUS is simply assuming that the material is incompressible when doing that conversion. Maybe someone knows else knows more about how the conversion is done, or you can read check out the ABAQUS manuals.
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