Thanks for hypoplasticity sand UMAT provided by Prof. Masin.
During studying hypo sand UMAT, I am encountered with a question about consistent tangent stiffness calculation.
subroutine ”perturbate_h“ seems to be used for computing ddsdde. In subroutine ”perturbate_h“ , another subroutine “get_tan_h” is called for computing LL, NN and MM. Here, LL and NN denote the forth order tensor and the second order tensor respectively, without considering intergranular strain. MM denotes the forth order tensor considering intergranular strain. About tensors are demonstrated in Voigt notation in the hypo sand UMAT. The detailed code is shown as following: