Hello dear connections, I'm developing a UMAT code for UY hardening constitutive model which describes accurately the hardening of sheet metals under cyclic loading-unloading. I did the main part of the subroutine and the code works without any syntax error. However, the Newton-Raphson algorithm does not work correctly and does not converge!! In this code, I'm trying to solve a system of 4 nonlinear constitutive equations via Newton-Raphson method. I thought this error may be due to the derived Jacobian matrix and checked the derivations several times, but couldn't find the error! Actually, the Jacobian matrix was correct. In the next step, I tried to derive variables analytically, however, for one scalar variable, the answer is not a scalar (it is a mix of vectors and matrixes)!! I'm totally confused because for my previous code when I checked the code, in the same way, it worked flawlessly and the answers were correct. Could anyone help me with this error and tell me how I can find the answers and how I can check my code, analytically or in any other ways?
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