Impact of strain rate sensitivity on the identification of the material parameters scattering and on the formability of zinc sheet

The mechanical behavior of zinc alloys drastically depends on strain rate and temperature, which are not constant during forming processes. During the production of zinc sheets, the slight variations of the industrial equipment parameters induce different local thermomechanical conditions. These variations could be stemming from a non-homogeneous cooling during rolling process, or local segregation of alloys and so on horizontal ellipsis . The result of these differences entails a significant scattering of material parameters as shown in (Milesi et al. J Mat Process Tech 245:134-148, 2017). This paper tackles the scattering of material parameters through an adapted Norton-Hoff behavior law. Then, four parameters have been identified with a standard Generalized Reduced Gradient method (GRG). Moreover, an exhaustive analysis of the entire rolled coil has been carried out to differentiate the variation coming from the material from the one due to the process. This study also encompasses the influence of strain rate on the forming limit diagram and therefore on the calculation of the forming limit stress diagram.