Study on Residual Stress Distributions in Press-Braked Stainless Steel Sections

The distribution of residual stresses is one of the substantial issues in determining mechanical behaviors of stainless steel structural members. Proper residual stress distribution models are necessary to include the residual stress influence in the analysis and design. Currently, the existing residual stress distribution model for press-braked stainless steel sections is either relatively complicated for the application, or only focuses on the longitudinal residual stress. In this study, a simplified residual stress distribution model was proposed based on the analysis of the key mechanisms in the press-braking process that was assumed as two-stage (bending and rebounding) plane strain pure bending process. The stress–strain relationship was represented as a simplified three–stage material model, and all the minor effects like the coiling and uncoiling, the material anisotropy, and the shift of neutral axis, etc. were neglected. Compared with test data, the predicted results by the proposed simplified model indicate good agreement for specimens within the commonly used ratio of internal corner radius over the thickness (r_i/t). Finite element models for the press-braking process were then developed in ABAQUS and validated using the available data from literature. A series of models with varied ratios of r_i/t were analyzed. Simulation results indicate that the center of the corner region in the press-braked sections has the largest equivalent plastic strain and residual stresses. From the center to the edge, the equivalent plastic strain and residual stresses declined significantly. As the ratios of r_i/t become smaller and smaller, the neutral axis moves towards to the compression side and the proposed simplified model gradually loses its prediction accuracy. Based on the theoretical and finite element analysis, the proposed simplified model is applicable for press-braked stainless steel sections with r_i/t ratios higher than 2.0.