Analysis of ridging in aluminum auto body sheet metal

A finite-element model is presented for the analysis of surface roughening of aluminum sheet metal. A hybrid finite-element model is developed which accounts for the elasto-viscoplastic constitutive response of a single crystallographic orientation. Initialization of a finite-element mesh representing several grains is performed using data gathered through automated collection of backscattered Kikuchi diffraction data. To handle a region that contains sufficient variation (contains numerous distinct grains), the implementation is carried out using distributed computation strategies. Application is made to 6111-T4 sheet metal intended for auto body applications. The numerical simulations are complemented with mechanical testing in plane strain and biaxial stretch. Based on the simulation results, there are two conclusions that can be drawn concerning the action of surface grains deforming through crystallographic slip. One is that grains can act collectively to form localized regions of thinning. The other is that grain interactions can lead to behavior which is different from that expected if grains deform with the average (macroscale) strain. Neighbor interactions can alter the deformation from that computed using the macroscale deformation rate.