A question about Umat for beam element

[Joe Chu]

Dear all,

I am conducting to write a umat for simulating 2D or 3D beam. I am confused with DDSDDE of Umat.

Actually, as we know, we must define a 6*6 matrix for 3D Solid element.

I was wondering which kind of matrix should we define for beam element. 2*2 or 3*3?

I have define a 3*3 ddsdde and found there is a warning that Zero pivot when processing D.O.F. 6 of 1 nodes. I guess it is caused by incomplete DDSDDE matrix.

Could anyone kindly help me ?

Thanks in advance

Joe