Constitutive Modelling of Rolled Aluminum Sheets

The development of constitutive laws for rolled products is of obvious practical importance for the analysis and design of forming operations. For typical applications large plastic strains are involved, which are generally accompanied by changes in microstructure. The evolution of texture and microstructural hardening during plastic deformation, for example, are important factors which can affect the formability characteristics of a rolled sheet during subsequent stamping or drawing processes. For the computer simulation of complex forming operations, phenomenological constitutive laws are usually employed because of their computational efficiency. Micromechanically based constitutive laws, however, have the distinct advantage of being capable of describing important microstructural effects such as texture evolution and the resulting induced anisotropy. In this paper we discuss our current work related to the development of appropriate constitutive models for rolled aluminum sheets. We consider both micromechanical models based on polycrystal plasticity theory, and simpler phenomenological models which attempt to capture the essential features of the behaviour of rolled sheets. The polycrystal plasticity formulation adopted in our work will first be presented, along with typical results of simulations based on this model. The important effects of microstructure (i.e., texture and slip system hardening) on formability will be illustrated. Our work on the experimental characterization of the stress-strain behaviour of aluminum sheets under biaxial deformation paths will then be discussed. Correlations of the model will be presented. Finally, an assessment of current phenomenological models of anisotropic plasticity will be made through comparisons with the experimental results.