Failure theories are used to predict when a material will fail due to static loading. They do this by comparing the stress state at a point with material properties that can be easily determined from testing, like the yield or ultimate strengths of the material determined from a uniaxial test. In this video I cover some of the main theories for ductile and for brittle materials - Rankine (maximum principal stress theory), Tresca (maximum shear stress theory), von Mises (maximum distortion energy theory) as well as the Coulomb-Mohr and Modified Mohr theories.