Mike Rife
Ansys Employee

Hi cheng089413 

Please see section 4.4.2.1.2 here:  https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/ans_mat/amp8sq21dldm.html%23matRIPtheory

Using the Hill's criteria is a isotropic elastic, anisotropic plastic strain model.  You can add it to the BKIN model as you have shown; then the Hill's material model inputs are scale factors that define the yield strength in the differing directions.

Mike