Distortion of rectangular tubes in stretch bending

During stretch bending, considerable in-plane distortion occurs when a thin-walled rectangular tube is plastically bent. To minimize the distortion, fixed walls are used to limit the bulging of the side walls of the tube. Internal pressure can also be used to compensate for distortion. In this paper, analytical expressions for the amount of distortion and the needed internal pressure are derived based on energy minimization. The theory is in fairly good agreement with experiments.