Hi all,
I am implementing the constitutive behaviour of two-crystal CuAlNi shape memory alloy during uniaxial loading using UMAT. My aim is to pass single crystal to polycrystal model. So, I am trying two-crystal problem firstly. I have no trouble with implementing single crystal and I get results of volume fraction and stress. However, in two-crystal problem, the solution doesn't converge. I use only elastic region and there is no plastic region in my problem. I transform only elastic matrices and transformation strains local to global in two-crystal program. (I calculate the consistent Jacobian by using the finite difference method.)
Thank you.
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cont.
I try to mention my problem more detailed. Our model is 3-D. We use two-crystal. One crystal's local coordinate is same with the global coordinate. And the other crystal is rotated 10 degree around z axis. I implement transformation only in my fortran code (umat subroutine). Actually, I don't know the usage of *orinetation card in the input file exactly. I think it is not essential. In my subroutine, I use rotation tensor and I rotate our elastic stifness tensors and transformation strain tensor but I don't get results. After phase transformation starts, the solution does not converge. I tried single crystal which is 10 degree rotated crystal and I got results.
In addition, I use C3D8 element in Abaqus with 8 integration points and I seperate elements with such as "if (noel.eq.1) ; rotation tensor= [1 0 0 ; 0 1 0 ; 0 0 1 ] for untransformed crystal. "
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