Effect of the uncertainty of multi-cut contour method and friction coefficient on residual stresses of constrained groove pressing process

Constrained groove pressing (CGP) process is a severe plastic deformation (SPD) method that can create ultrafine-grained microstructure in the sheet metals. In this study, residual stresses of the CGP process and the effect of the friction coefficient on the residual stresses were investigated. The residual stresses were measured in two directions using a multi-cut contour method and a mathematical-finite element model was developed to estimate the uncertainty of results of the multi-cut contour method. In order to study the effect of the friction coefficient on the residual stresses, a 3D finite element model was employed and the results of it were validated with the experimental results of the CGP process. According to the results, residual stresses in the first pass of CGP are compressive on the surface and gradually change to tension at the center of the thickness. Investigation of the effect of the first cut on the residual stresses and uncertainty of the second cutting plane showed that the effect of the first cut is only confined to regions near the intersection of the two cuts. Distancing from the intersection of two cuts causes the effect of the first cut to be ineffective on the second cut. Also, evaluation of the effect of friction coefficient on the residual stress illustrated that friction has a direct relationship with the residual stresses.