Theory of fatigue fracture under the complex stress state of metals with consideration of structural changes

A phenomenological model of metal fatigue failure at proportional loading is presented. The model is constructed within the framework of the physico-mechanical approach as a system of hypotheses about a probability of stage-by-stage grow of defects at different scale-structural levels (such as brittle micro- and macrocracks). The constitutive relations are formulated on the basis of this model. A number of fatigue curves are obtained for various failure states of metals.