Experimental and numerical investigations into the ductile fracture during the forming of flat-rolled 5083-O aluminum alloy sheet

The present research aimed to investigate the ductile fracture during the forming of 5083-O aluminum alloy sheet and establish a rational criterion to predict it. Seven specimens with different shapes were tension-tested, and the main deformation areas of the specimens were subjected to various stress states ranging from shear to plane strain. Fracture strains, representing the forming limits, were determined by applying a combined experimental–numerical approach. Surface strain fields were measured by using the two-dimensional digital image correlation (DIC) method, while the local stress and strain histories were predicted by finite element (FE) simulations. The stress triaxiality and Lode parameter (characterizing the stress state) of fracture onset were calculated for each specimen. The analysis indicated that the fracture strain was insensitive to the Lode parameter but strongly dependent on the stress triaxiality. The fracture locus in the space of the fracture strain and stress triaxiality fitted in with the Johnson–Cook fracture criterion. The Johnson–Cook fracture criterion was then implemented into the ABAQUS/Explicit code to predict the fracture onsets of three specimens subjected to ball punch deformation. The strain fields of these specimens measured by DIC-3D were in agreement with the numerical results. Their fracture locations and strokes were accurately predicted by using the Johnson–Cook fracture criterion.