Evolution of subsequent yield surfaces with plastic deformation along proportional and non-proportional loading paths on annealed AA6061 alloy: Experiments and crystal plasticity finite element modeling

Abstract

This work presents an experimental and numerical investigation of annealed aluminum alloy AA6061 subjected to proportional and non-proportional loading paths at various finite levels of pre-strain. A careful mechanical characterization program is conducted for subsequent yield surfaces in the σ11−3σ12 stress space using an equivalent 10με offset linearity definition of yield. Electron backscatter diffraction (EBSD) is also used to characterize the microstructure of the material in the annealed condition. Each subsequent surface shows a very well-known shape of being nearly flat in unloading and having a prominent “nose” in the loading direction that deviates substantially from a generalized isotropic behavior. All proportional loading conditions show a rapid evolution of the mixed hardening effect that was characterized by the first load reversal in the first yield surface probe. Differences associated with the path-dependent effect in shifting the non-proportional yield surfaces are also observed in experiments. The experimental program is followed by Taylor-type crystal plasticity finite element (CPFE) simulations of the observed mechanical phenomenon. The Taylor-type CPFE model is calibrated using only the proportional uniaxial tension response and the EBSD imaging to predict all subsequent proportional and non-proportional loading paths. All CPFE show good predictive capabilities in capturing the experimental yield surface measurements for both proportional and non-proportional loading conditions. The CPFE simulations predict both the resulting shape and magnitude of the “nose” in the yield surfaces, as well as the mixed hardening, distortion, and yield surface translations. A systematic study is presented to investigate the effects of latent hardening on the yield surface predictions. This work highlights the promising results of advanced material model developments for larger-scale component simulations of lightweight aluminum alloys.