It seems that the B_bar method adopted in 'PlaneStrain.h' is not the common B_bar, but a specific Selective integration formulation , the B_bar is usually referred to as the mean-dilatation formulation.
*reference 'Generalization of selective integration procedures to anisotropic and nonlinear media' Hughes 1980
It seems that the B_bar method adopted in 'PlaneStrain.h' is not the common B_bar, but a specific Selective integration formulation , the B_bar is usually referred to as the mean-dilatation formulation. *reference 'Generalization of selective integration procedures to anisotropic and nonlinear media' Hughes 1980