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Numerical simulations of forming limit diagrams (FLDs) are performed based on a rate-sensitive polycrystal plasticity model together with the Marciniak-Kuczynski (M-K) approach. Sheet necking is initiated from an initial imperfection in terms of a narrow band. The deformations inside and outside the band are assumed to be homogeneous, and conditions of compatibility and equilibrium are enforced across the band interfaces. Thus, the polycrystal model needs only to be applied to two polycrystalline aggregates, one inside and one outside the band. Each grain is modeled as an fcc crystal with 12 distinct slip systems. The response of an aggregate comprised of many grains is based on an elastic-viscoplastic Taylor-type polycrystal model. With this formulation, the effects of initial imperfection intensity and orientation, initial distribution of grain orientations, crystal elasticity, strain-rate sensitivity, single slip hardening, and latent hardening on the FLD can be assessed. The predicted FLDs are compared with experimental data for the following rolled aluminum alloy sheets: AA5754-

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Bendability is an important forming parameter in many applications, but particularly in automotive parts where the formed parts in structures can be quite complex, and where outer skins are joined to inner panels through the hemming process. In this paper the bend performance of two aluminium based automotive alloys, the heat treatable skin alloy, AA 6111 and the non-heat treatable structural alloy AA 5754, are assessed by the cantilever bend test. This test enables the load ± bend angle relationship to be monitored, and provides a bend surface that can be examined for different bend angles, since the bending pin does not contact the specimen surface in the local region of the bend. The results demonstrate that the cantilever bend test can differentiate between different bend performance, and the differences relate to the damage process involved in bending. In the heat treatable AA 6111 the bendability is dependent on the alloy temper, which controls the bend angle at which large surface cracks appear on the surface. This fracture process is a result of differences in the development of surface topography and surface damage with bending strain. The AA 5754 alloy has similar behaviour, but the performance is superior to the best of the AA 6111 tempers, and re¯ects a lower rate of surface topography development, and an absence of signi® cant surface cracking over the bend angle range investigated.MST/5130

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