Im currently writing a lab report on combined bending and torsion and comparing yield points to theory. I'm not quite sure I know what is going on though. I understnad what Tresca and Von Mises is but I'm not sure how they apply. If I were to use the equations and obtain a value over 1 for each criteria, does this mean that the material has yielded and is now in plastic deformation? Has anyone got any simple explanations and applications of this theory, I'd really appreciate it.