Effects of grain size and heterogeneity on the mechanical behavior of foil rolling

When the part size is scaled down to micro-scale, the material consists of only a few grains and the material properties and deformation behaviors are quite different from the conventional ones in macroscale. This paper focuses on the effect of grain size and heterogeneity on the mechanical behavior of foil rolling using a grain level finite element analysis in combination with a rate dependent crystal plasticity constitutive model. Voronoi tessellation has been applied to describe the polycrystalline aggregate. Based on a heterogeneity crystalline plasticity model identified for metal foil, simulations of rolling tests were performed for samples with different grain orientations and sizes. The simulation results have been validated by comparing with the experimental observations. It is predicted that detrimental effects on the mechanical performance will generate by reducing the number of grains through the foil thickness and changing the grain orientation sets. The simulations correctly reproduce the softening effect which has been experimentally characterized linked to decreases in the number of grains through the thickness. The analysis of the plasticity deformation mechanisms shows that the softening is due to surface grain effect which is discussed in terms of grain orientations, activity of slip systems and strengthening of interior grains versus weakening of surface grains. (C) 2015 Elsevier Ltd. All rights reserved.