Aluminum alloy damage evolution for different strain paths – Application to hemming process

This work deals with ductile damage characterization of a 6000 series aluminum alloy. Tensile tests on both straight and notched samples at different orientations to the rolling direction, and equibiaxial expansion tests are performed up to fracture. The Gurson–Tvergaard–Needleman model, extended to the case of plastic anisotropy described by Hill’s 1948 yield criterion, is used to represent the material behavior. The parameters are identified by inverse analysis and by using finite element simulations for inhomogeneous tests. The coalescence criterion proposed by Tvergaard and Needleman is considered and a critical void volume fraction is then determined. The numerical simulation of a three-step hemming process of flat surface-straight edge sample is then performed, to investigate the influence of some process parameters on the damage development in the folded zone and thus to predict hemming limits.