Hello, veryone. I am usint the VUMAT to define a new material behavior. There are questions about the calculation of shear stress.

The sheet metal forming was took as a plane stress problem in many relevant articles. So only three stress components:sigma_{11},sigma_{22},sigma_{12}

(sigma_{33}=0)are included in stress apdate algorithm such as the return mapping algorithm(J.C SIMO, R.L. Taylor. A return mapping algorithm for plane stress

elastoplasticity. International journal for numerical methods in engineering.Vol 22,649-670(1986)). However, regarding the sheet metal forming, the shear

stress sigma_{23}and sigma_{31} should be included, for example,in LS-DYNA THEORETICAL MANUAL, the stress sigma_{23}and sigma_{31} were included indeed. How

to update the shear stress:

sigma_{23} and sigma_{31}? In User Subroutine Manual, for the shell elements, reader was recommended to use the the transverse shear stiffness to calculate

the shear stress, but how to calculate it in detail?

Thank you.