Crystal plasticity finite-element analysis of surface roughening behaviour in biaxial stretching of steel sheets

Abstract

Because of the increasing demand for automobile outer panels with sharper streamlines, prevention of surface roughening during press forming is important to obtain outer panels with better surfaces. It is crucial to examine the effects of deformation-mode on surface roughening, because steel sheets are subjected to various deformation modes during press forming. Moreover, surface roughening behaviour of interstitial free (IF) steels, which are now commonly utilized for fabricating outer panels, has not been studied enough. In this study, surface roughening behaviours of IF steel under various deformation modes were simulated by crystal plasticity finite-element analysis (CPFEA). First, the validation of a CPFEA model was carried out for investigating the stress-strain relationships in simple shear deformation and for studying changes in crystal orientations during biaxial tension. Then, the influence of microstructures on surface roughening was investigated. The results showed that surface roughening was larger for plane-strain tension than for equi-biaxial tension in IF steels. To predict surface roughening, it is essential to consider the difference of deformation resistance between crystals and the distribution of crystal orientations in the thickness direction.