Investigation of the forming limit strains at fracture of AA5086 sheets using an in-plane biaxial tensile test

An in-plane biaxial tensile test with a dedicated cruciform specimen is performed to determine the forming limit strains at fracture for aluminium alloy 5086. A method based on the evolution of strain in the central area of the specimen and the observation of the macroscopic image of specimen surface is proposed to identify the onset of fracture and the forming limit strains at this moment. The forming limit strains at fracture are determined under different strain paths provided by the two independent axes of the experimental device. Finite element simulations are performed to determine and compare numerical forming limit strains with three ductile fracture criteria (Cockroft and Latham, Brozzo and Ayada). The critical damage values of the criteria are determined by the experimental results under different strain paths.