Modified plasticity constitutive model for extruded aluminum alloys

Aluminum alloys have been increasingly used in a wide range of construction applications, especially in important public buildings. A plasticity constitutive model that can accurately describe the elastoplastic behavior of aluminum alloys under complicated stress states is of great importance in precisely simulating aluminum alloy structures under complicated working conditions. Also, a precise plasticity model serves as the foundation for studying the ductile fracture of metals, and is therefore crucial for structural analysis involving large deformation, such as progressive collapse analysis. The classic J2 plasticity model based on the von Mises yield criterion is the most commonly utilized model for ductile metal materials. However, it ignores the effect of stress state on metal plasticity behavior, making it inapplicable to aluminum alloy materials under various complicated stress states. This study experimentally demonstrated that stress triaxiality and Lode angle have a noticeable effect on the plasticity behavior of extruded aluminum alloys (6061-T6, 6082-T6, and 6063-T5). Accordingly, a plasticity constitutive model suitable for extruded aluminum alloys under complicated stress states was proposed and validated, including a full-range hardening law and a new yield criterion. In addition, the parameter calibration method for this new model was detailed. Finally, comparisons between the experimental and numerical results proved the high accuracy of the proposed model in predicting the actual response of a structural extruded aluminum alloy under complicated stress states. Compared with previous studies, the proposed model can not only consider the effects of stress triaxiality and Lode angle, but it can also provide a more reasonable description of yield surface under considerably high or low stress triaxiality.