In addition to the responses above, you may find the link in response #13 at this thread helpful: [url

I forgot to add the compressibility term which is required for VUMAT. The form is: W = K1(I1-3)^m + K2(I1-3)^p + K3(I1-3)^q + 1/D1(J-1)^2

Check out this other thread and see if it helps you get information for particular elements: [url