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Fitting Data To Anisotropic Hyperelastic Models

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I am trying to fit my tensile test data in axial and circumferential direction to an anisotropic hyperelastic model (holzapfel 2006 energy function), I have taken derivatives of the energy function with respect to the stretch in each of the directions to derive the lagrangian stress (engineering stress) in each direction. but fitting the data of two tensile tests in two directions to one function is awkward in practice. Does anybody have any experience with this?

My other question is when giving the test data to abaqus we should give the nominal (Eng.) stress and strain, but with the new builtin holzapfel hyperelastic model im wondering how this works as the constants in papers by holzapfel are based on Cauchy stress.????!!

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I have calibrated anisotropic material models (both hyperelastic and non-linear viscoplastic) using experimental data in different directions. What I typically do is to solve the problem using a minimization approach. That is, use a minimization algorithm to find the set of material parameters that best fit all experimental data sets that I specify.

If you want to use Abaqus/CAE to find the material parameters then you need to use specific stress and strain types that they request. CAE will then internally convert the material parameters into the correct form.

- Jorgen

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