Analysis of bending behavior of ultra-thin austenitic stainless steel sheets considering surface effect

In this study, the influence of the surface effect on the bending behavior of ultra-thin austenitic stainless steel sheets was investigated. The presence of grains on the surface, which induces softening due to the absence of grain boundaries, can significantly impact the bending behavior. This phenomenon introduces errors in predicting bending behavior solely based on the tensile properties. To evaluate the strain-path dependent behaviors in bending, three-point bending experiments were performed on both unstretched and stretched austenitic stainless steel specimens with a thickness of 0.2 mm. To account for the distinct behavior of surface and inner grains, a surface layer model was developed, dividing the sheet thickness into surface and inner layers. Machine learning-based multi-objective optimization was used to calibrate the material parameters for each layer. The study examined the influence of the surface effect, thickness of the surface layer, and the choice of hardening model on the material behaviors. The findings revealed the important role played by the surface layer and highlighted the differences between the surface and inner layers. These results contribute to a better understanding of the bending behavior of ultra-thin austenitic stainless steel sheets, ultimately improving the accuracy of bending force predictions in engineering simulations.