Shear Stress Help

[yaston4]

Hi all,

I know if I have a simple 2D model a model a square along x-y, then I could simply look at S12 to determine the shear stress, but what about the shear stresses of a complex 3D model? I know there is also S13 and S23, but need some advice on this. I am particularly interested in the shear stresses between two contact surfaces of complex shapes.

Also, I havent seen any form of scalar measure of shear stress i.e. von Mises type criterions for contact shear stresses, but maybe other have heard of something like this?

Thanks