Hi,

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?

,

Use total plastic strain and Cauchy for 3D

strain=sqrt(0.5*(pe11-pem)^2+0.5*(pe22-pem)^2+0.5*(pe33-pem)^2+pe12^2+pe23^2+pe13^2)

pem=(pe11+pe22+pe33)/3

for explixit pe23=array(5) and pe13=array(6)

for implicit pe23=array(6!) and pe13=array(5!)*

for plainstrain: pe13 and pe23 do not exist

*

for explicit vgetvrm gives you e12,e23,e13

for implicit you maybe get y12,y13,y23: you have to check this