Shear stress evaluation 2D material

Hi all,

I am planning to simulate the shear test for 2D materials.The boundary condition that i am applying is fixing one edge and the apply lateral strain on the other edge. and the remaining edges are periodic boundary condition. However, how do I evaluate the shear stress? In tensile test I had used the pressure in x direction and evaluated the tensile strength. Any information would be helpful.

Thank you,
Deepak Behera