Hi George,
For abaqus there is a very good explanation (including an example) on how to create a user defined material card (http://studylib.net/doc/13771040/lecture-6-writing-a-umat-or-vumat-overview). Is there something like this for Radioss? I try to convert a user-material card from abaqus to radioss that was developed by another research group.
Best, J