Fracture in the Viscoplastic Range.

A mechanical theory of fracture is developed which is based on the concept of effective stresses. Using the thermodynamics of irreversible processes, a continuous variable of fracture-deformation coupling is introduced which makes it possible to carry out indirect measurements of creep and fatigue fracture and then identify the evolution model. A generalization of the concept of the rate of energy release, which is well-known in linear fracture mechanics, is extended to problems of nonlinear viscoplasticity. In this case, too, thermodynamic considerations lead to a model of crack growth due to fatigue and fracture which takes into account their interaction.