brucedjones is correct. You should probably look up a good material model. However, you can also do a quick and dirty answer since you know the stresses.
If you know the material (steel, wood, etc.) why not just compare the stresses to the material's respective yield stress? This would allow you to see if it would fail under a elastic/perfectly plastic representation. You could then avoid brucedjones suggestion of using a plasticity model. BTW, yield strength in shear is usually around half of the materials yield strength.
Also, I'm assuming some when you say "withstand." If you want to go a little more advanced without more work, you can go with the fracture strength of the material. This will allow the material to stretch due to excessive forces before failure. The fracture strength in shear will be around 3/4th that of the materials fracture strength.
If you want to see the shape change, unfortunately you'd have to employ a good constitutive equation, which there are a lot of good ones. However, you'd have to go into some finite element modeling.