CRYSTAL PLASTICITY FORMING LIMIT DIAGRAM ANALYSIS OF ROLLED ALUMINUM SHEETS

Numerical simulations of forming limit diagrams (FLDs) are performed b ased on a rate-sensitive polycrystal plasticity model together with th e Marciniak-Kuczynski (M-K) approach. Sheet necking is initiated from an initial imperfection in terms of a narrow band. The deformations in side and outside the band are assumed to be homogeneous, and condition s of compatibility and equilibrium are enforced across the band interf aces. Thus, the polycrystal model needs only to be applied to two poly crystalline aggregates, one inside and one outside the band. Each grai n is modeled as an fee crystal with 12 distinct slip systems. The resp onse of an aggregate comprised of many grains is based on an elastic-v iscoplastic Taylor-type polycrystal model. With this formulation, the effects of initial imperfection intensity and orientation, initial dis tribution of grain orientations, crystal elasticity, strain-rate sensi tivity, single slip hardening, and latent hardening on the FLD can be assessed. The predicted FLDs are compared with experimental data for t he following rolled aluminum alloy sheets: AA5754-0-A, AA5754-0-B, AA6 111-T4-A, AA6111-T4-C, and AA6111-T4-D.