On the Determination of Stress Triaxiality in a Cast Aluminum Alloy

Abstract

This study presents a prediction of fracture behavior in the cast material AlSi10MnMg-T7 under multiaxial loading conditions. The main goal is to establish a triaxiality locus, which is a diagram illustrating the relationship between the equivalent plastic strain to fracture and the stress triaxiality factor. This factor is primarily defined as the ratio of the hydrostatic stress to the equivalent stress. The triaxiality locus provides in-depth insights into how the material's fracture behavior varies under different stress states. Experimental tests involving different specimen geometries are conducted to obtain essential data for the analysis and to facilitate the development of a Finite Element (FE) model. Quasi-static uniaxial tensile tests are performed on four specimen types, each featuring different forms of notches to induce different stress states in the specimens. The deformation up to fracture is captured using two high-speed digital cameras, and the displacement and strain data are calculated using a digital image correlation (DIC) system. Subsequently, the simulation results from the FE models are compared with the experimental measurements to validate the accuracy of the models. These FE models are then used to calculate the equivalent fracture strain and stress triaxiality factor with the help of collected test data. The calculations facilitate the generation of a stress triaxiality locus via a curve-fitting process. An exponential curve-fitting function is selected to appropriately relate the equivalent plastic strain to the fracture and stress state for the material. The results are also compared with those outlined in the FKM-Guideline, which is employed for the analytical calculation of mechanical component strength across different materials, and excellent agreement is obtained. By establishing the triaxiality locus and using experimental and numerical techniques, this study provides valuable data and insights for accurately predicting fracture strain and evaluating the stress state of structures made from the cast aluminum AlSi10MnMg-T7.