Modeling ductile fracture in third stress invariant sensitive materials: Application to Al 2024-T351

Abstract

Triaxiality alone is not sufficient to account for the role of stress state on ductility in materials that exhibit shear effects on fracture strain. For these materials, it has been proposed that ductility also depends on the third invariant of the stress deviator. Recently, Bonora and Testa [N. Bonora, G. Testa, Plasticity damage self-consistent model incorporating stress triaxiality and shear-controlled fracture mechanisms – model formulation, Eng. Frac. Mech. 271, 108634 (2022).] derived a plasticity damage self-consistent (PDSC) model considering damage contributions due to intervoid necking, shearing, and sheeting for an arbitrary stress state. In this work, the PDSC model has been applied to Al 2024-T351 considering the experimental results reported in the literature obtained on several different sample geometries and material batches. Specifically, the model was verified by predicting the load-displacement conditions for which fracture occurs in 9 specimen geometries loaded in tension, compression, and torsion over a wide range of triaxiality, from positive to negative, and of the third stress invariant related parameter. The ability of the model to predict the transition from cup-cone to slant fracture for different stress states is shown. Finally, the simulation of non-proportional bi-axial compression test confirmed the possibility for ductile fracture to occur at negative stress triaxiality lower than −0.5 as long as the deformation state is shear dominated.