New void growth-based ductile fracture models incorporating interaction effects of stress triaxiality and Lode angle parameter

The void growth rate in ductile fracture is influenced by both the stress triaxiality and Lode angle parameter. Traditional ductile fracture models often treat these effects independently, combining them as the product of two isolated terms. However, since both stress states affect void geometry, either through volume expansion or shape distortion, the geometry change induced by one may influence that caused by the other, indicating an interaction between the two stress states. This study investigates this interaction through numerical simulations using three-dimensional micromechanical finite element models with a single spherical void. A wide range of stress states are analysed, with both stress triaxiality and Lode angle parameter varying from −1 to 1. Based on the observed interaction effects of the two stress states on void growth, two new ductile fracture models are proposed: the Positive Stress Triaxiality-Lode Angle Parameter Interaction Model (PTLIM), proposed for specimens under monotonic tensile loading, and the Full-range Stress Triaxiality-Lode Angle Parameter Interaction Model (FTLIM), applicable to tension, compression and tension–compression cyclic loading. Both models are validated against 198 fracture coupons, and shown to offer significantly improved accuracy in the prediction of fracture strains over other published models that treat the effects of stress triaxiality and Lode angle parameter as independent terms. This highlights the advantage of accounting for the interaction between these two stress state parameters in fracture strain prediction.