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Coding Ogden hyperelastic model

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I am trying to implement Ogden hyperelastic model (N=1)(I want to modify it later) in Abaqus. The way in which I am coding is


[*]From degradNew and stretchNew get F and U. Hence get R = F * U^-1

[*]Compute b = J**(-2/3)*(F * F^T)

[*]Compute eigen values and eigen vector of b

[*]Compute lambda as sqrt of eigen values of b

[*]Compute principal Cauchy stress as s(k,k) = 2/J*mu/alpha*( lamda_k**alpha - 1/3(lamda_1**alpha + lamda_2**alpha + lamda_3**alpha) + 2/D(J-1)

[*]Rotate back the principal Cauchy stress, S = as eigenVec * S * eigenVec^T

[*]Get back to corotational frame as S = R^T * S * T


My results are not the same as what Abaqus gets. I am not sure what I am doing wrong. Any pointers


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Joined: 5 years ago

It is very important use return the stress in the right coordinate system.
For Abaqus/Explicit (which I assume you are targeting) you can simply use the stretchNew variable as the deformation gradient. That way you will automatically get the right frame of reference.


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