Plastic stress intensity factor in fracture mechanics

Application of fracture mechanics approaches and criterions for nonlinear deformation under complex stress state is concerned with special features. The influence of a complex stress state is realized through the plastic zone at the crack tip. In this case a nonlinear analysis of the stress-strain state in experimental specimens and elements of structures is needed. A generalization of the implemented approaches to solving problems of computational and experimental fracture mechanics on the base of a single parameter in the form of the plastic stress intensity factor (SIF) is presented. Plastic SIF takes into account the nonlinear behavior of the material, loading conditions, the stress state and the in-plane and out-of-plane constraint effects. The finite element analysis results presented in this paper show prospects for application of the plastic SIF as a nonlinear fracture resistance parameter that take into account loading conditions, stress state, influence of geometry of cracked bodies and the material mechanical properties in the temperature range. It is demonstrated that plastic SIF is a one-parameter approach that allows obtaining fracture resistance material properties under static loading. Efficiency of the plastic SIF implementation for interpretation of the fatigue crack growth data under complex stress state and mixed mode loading is shown. An application of plastic SIF for residual life prediction of the power steam turbine disk with a surface flaw is demonstrated.