I am K.Bhanu Savarni. As for my project I need to write a subroutine for a damage model.Please help me by answering the questions .I am facing a problem in VUMAT subroutine and also I have some questions like when to use stress rate to update stress?
I have written UMAT subroutine for probabilistic damage model(A Probabilistic damage model of the dynamic fragmentation in brittle materials,2010).The model requires only the isotropic elastic and Weibull parameters. The compliance tensor is given in the paper(Multiscale model,Hild,2002).I attach the compliance tensor matrix with the email.D1,D2,D3,Alpha in the tensor are known..In the UMAT subroutine I inverse the compliance tensor to obtain the constitutive tensor matrix.I multiply the constitutive tensor matrix to the increment in strain and add it to the stress to obtain the new stress. Can I use the same procedure for VUMAT subroutine?. I have read that in VUMAT there is no need to update Jacobian then how to update stress?.
Note:I am dealing with impact problems.
To account for large deformations can I use Green-naghdi stress rate or just update the stress in VUMAT as specified in previous paragraph?.Using Green-Naghdi stress rate can I obtain cauchy stress rate and then use explicit integration to update stress rate?.stress new=stress old+stress rate*dt can I do this?.
Waiting for your reply.