ABAQUS DDSDDE numerical Evaluation

Hello Dr.Jorgen

I am trying to numerically evaluate the consistent tangent moduli in ABAQUS for my UMAT (Finite strain plasticity).

I am following Wei Sun (2008)([url] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2724673/ [/url]).

I got perfect predictions with my UMAt for single cube element but have convergence problems when I use multiple elements.

The consistent tangent mod I used is as follows

C_IJKL=(1/(J*e))*(T(F_delta)-T(F))

J=det(F)

e=10^-8

F_delta=F+delta

delta=(e/2)*(e_i(ten.prod)e_j(dot)F+e_j(ten.prod)e_i(dot)F)

Am I using the correct expression for C_ijkl. Do I need to change something in .inp for multiple elements?

Thanks

-Ravi