Generalization of mixed mode crack behaviour by the plastic stress intensity factor

An elastic-plastic finite element analysis is performed for cruciform specimens of two configurations and a compact tension-shear specimen subjected to mixed Mode I/II loading. A Ramberg-Osgood stress-strain relation is used to characterise the properties of two types of steel and titanium and aluminium alloys. For the specified geometry of the specimen considered, the governing parameter of the elastic-plastic crack-tip stress field In factor, the stress triaxiality, and the plastic stress intensity factor are determined as a function of mode mixity and elastic-plastic material properties. Special emphasis is put on the analysis of the effect of specimen geometry. Analytical and numerical results are compared for the complete range of mixed-mode loading. A correlation between the plastic stress intensity factor and the constraint parameter based on the numerical analysis is found. Coupling between mode mixity and material nonlinearity is indicated. The applicability of the plastic stress intensity factor approach to large-scale yielding analysis is also discussed.