Dear all,
I developed a constitutive mechanical model by using the external material model. I want to use the principle vectors corresponding to the principle stress in other physics. However, I found the principle vectors calculated from external material are not correct when they are presented in Surface plot, because the norm of the principle vectors is not equal to one. Some places are far more than one. Then I used a constant stress matrix to check the function used to calculate the principle direction, i.e. csext_eig(sTmatrix, vals, vecs). The result is correct. So I am very confused why it is not correct when calculated in the real simulation. Could you please give me some help about that?
Thanks a lot