Learning Forum

[mwhitte6]

I am working on implementing a user defined hyperelastic material which needs a push forward operation. I saw the push_forward_2s(), I'm using the scalar version for now, in Manual 1 Appendix A. However, it does not describe in sufficient detail for me to understand what this function does. 

Detailed questions:

1. What stress is this function expecting as input? First Piola-Kirchhoff? Second Piola-Kirchoff? Something else? 
2. Does it account for the change in volume from the reference to the current configuration with 1/detF or do I need to handle that outside of this subroutine? 
3. What stress is the ouptut from this function? I am assuming Cauchy but I would like confirmation.

I have implemented my own push forward code in the user-defined material to go from the second PK stress to Cauchy stress using the well known equation sig = 1/detF * F * 2PK * F^T. However, the results do not match. It is also possible I have made a mistake in my code but the push forward is relatively straight-forward. 

Thanks in advance.