Analysis of springback for multiple bending considering nonlinear unloading-reloading behavior, stress inheritance and Bauschinger effect

Abstract

Multiple bending faces more challenges in accurate springback prediction for difficult-to-form metals such as aluminum alloys and high-strength steels. This is attributed to stress inheritance (the effect of residual stress on subsequent bending), the Bauschinger effect and nonlinear unloading-reloading behavior, which have a more significant effect on the springback of difficult-to-form metals. A new analytical model considering these key factors was established, and the solution method of a series of key equations were given. The Chaboche hardening model and two elastic models (chord modulus and nonlinear elastic model) were used to characterize the constitutive properties. Experiments were performed to verify the analytical model, and the effects of the above three factors on springback were investigated. The results show that the analytical results are in good agreement with the experimental results, and the average relative error of the 6061 aluminum alloy rectangular section beam under two cycles of positive and reverse pure bending is within 3 %. Compared with the existing models, the analytical model established in this study has higher prediction accuracy and faster solution speed. • A new analytical model of springback for multiple bending was established. • Yoshida and Amaishi nonlinear elastic model was introduced in the analytical model. • Nonlinear unloading-reloading behavior, stress inheritance and the Bauschinger effect are comprehensively considered. • Accurate prediction of springback for multiple bending was achieved, and the effect of the three factors on springback was investigated.