Purpose: Wrought magnesium alloys have excellent strength to weight ratio and could therefore be used for lightweighting the auto body structure; however, they have poor formability at room temperature and are highly anisotropic. The feasibility of stamping these alloys in sheet form can be carried out by numerical simulation, but the inputs to the model are flow stress curves for different temperatures, strains, and strain rates, obtained by a long, expensive experimental campaign. Another approach to obtaining the needed input data is to model the behavior of the alloy as a function of texture and deformation mechanism for the range of strain rates, strain levels, and temperatures needed for the stamping simulation.
Research Methodology: The current work proposes to employ the well known viscoplastic self-consistent (VPSC) model for magnesium alloy AZ31B, where twinning and slip are active in different proportions, depending on the temperature and the strain rate. Flow stress curves for the rolling direction, 45°, and transverse directions were generated at several temperatures (50-, 75-, and 100-) and several strain rates (0.001, 0.01, 0.1 and 1) by the VPSC approach and then used as input to a finite element model of a punch stretching experiment, carried out at different temperatures. The surface strains on the sheet were measured by digital image correlation (DIC) and compared to the model results. The simulations are validated using the force vs displacement curves from the experiment, as well as using the strain patterns that were obtained by DIC.
Conclusions: The validation process will allow us to study the quality of the VPSC outputs indirectly, by comparing the finite element simulations to our stretch forming experiments. If successful, this approach provides a new low-cost approach for engineers to generate the data they need for modeling intricate forming operations in desirable, but complex alloys. Additional validation could be performed via tensile tests at different temperatures and strain rates.
