Numerical validation of crack closure concept using non-linear crack tip parameters

Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, some authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Numerical models with and without contact of crack flanks were built for a wide range of loading parameters. The non-linear crack tip parameters studied were the range of cyclic plastic strain, the crack tip opening displacement (CTOD) and the size of reversed plastic zone. Well defined relations between non linear parameters and K were obtained without contact of crack flanks which reinforces the validity of linear elastic fracture mechanics. When the CTOD with contact is plotted versus ΔKeff the values are coincident with those obtained without contact, which shows that the crack closure concept is valid and able to explain the influence of mean stress. The analysis of overloads and high-low load blocks demonstrated the validity of crack closure concept for variable amplitude loading.