Fracture of an anisotropic rare-earth-containing magnesium alloy (ZEK100) at different stress states and strain rates: Experiments and modeling

Fracture of an anisotropic rare-earth-containing magnesium alloy (ZEK100) sheet is investigated at different stress states and strain rates. A variety of sample geometries, loading conditions, and loading orientations are used to achieve different stress triaxiality and deformation mechanisms. Digital image correlation (DIC) technique is used to measure the surface strains up to fracture for all the specimens. We show that ZEK100 exhibits larger strain at fracture across the gage section of the test specimens aligned with the transverse direction (TD) than specimens aligned with the rolling direction (RD); however, the opposite is shown for the local strain measurements at fracture. With an increase in the strain rate, the strains at fracture decrease for all loading paths. A crystal plasticity finite element model is used to simulate the local stress state and deformation mechanisms for each loading condition. ZEK100 exhibits an anisotropic fracture behavior that is a function of the stress triaxiality and Lode parameter. We show that extension twinning also plays an important role in the fracture response of ZEK100. Overall, the local effective strain at fracture is lower for the specimens that exhibit the largest volume fraction of extension twinning. A novel anisotropic extension to the Hosford-Coulomb (HC) fracture model is then developed to account for the effect of extension twinning on the anisotropic fracture response of ZEK100.