I want to change the friction angle with the plastic strain in Abaqus following mohr coulomb model.
Vermeer and de Borst (1984) proposed an equation for frictional hardening and I want to use that. In their equation, the shear hardening parameter obtains from below equation(first picture) and then the friction angle changes with the shear hardening parameter.
So I have to use the usdfld code in my model.
I code that to calculate the shear hardening parameter, and then I put it equal to FIELD1. I attached the usdfld code(second picture) to this post.
can anybody tell me what is wrong in my code?
Do everybody have Vermeer equation code in Fortran for using in Abaqus?