Hi Robert,<br><br>Abaqus uses an updated Lagrange but this is not mandatory for me. I can use a total Lagrange of course, my material update routine updates the stress based on the increment in strains, we can have it in total Lagrange as well. Attached, you'll find an Abaqus UMAT I have written for J2 plasticity. This could give you an insight how an Abaqus UMAT works.<br><br>Thanks for looking into this.<br><br>Cheers,<br><br>Hadi<br>