An experimental and numerical study of prestrained AA5754 sheet in bending

This study focuses on the effects of prestrain magnitude on 3 mm AA5754 sheet in bending at nominal applied strain rates of 0.001/s and 0.1/s. The necessity of incorporating prestrain and strain rate effects into numerical simulations of bending is also evaluated. A series of experimental bend tests using axial compression in the longitudinal material direction were performed following plane strain prestrain in the transverse material direction. An inelastic buckling mode of deformation was produced with the peak buckling load increasing and the minimum load decreasing with larger magnitudes of prestrain. A semi-empirical material model, referred to as the Voce-MA model, was developed which incorporates strain rate-sensitivity of the flow stress, the prestrain magnitude and their interaction. Simulations of the bend tests using this material model were then performed in LS-DYNA at nominal applied strain rates of 0.001/s and 0.1/s for samples with 0, 3, 6 and 12% plane strain prestrain. It was shown that for AA5754 sheet in bending, prestrain effects must be considered in terms of current sheet thickness and material hardening. While the peak and minimum loads are not strain rate sensitive at the low rates used in this study, a rate-dependant material model is still necessary in order to account for the deviations in local strain rate from the applied strain rate. The Voce-MA material model was capable of representing prestrain and strain rate effects for all cases of AA5754 sheet in bending considered in this study.