Failure Prediction in Hydroforming of Pre-Bent HSLA Tube Using an Extended Stress-Based Forming Limit Curve

This paper examines the prediction of failure during the hydroforming of pre-bent HSLA350 tubes using the Extended Stress-Based Forming Limit Curve (XSFLC) [1]. The process of obtaining a strain-based forming limit curve (ε-FLC) for the tube and its application to the prediction of failure in tube hydroforming, utilizing the XSFLC, is presented in detail. The XSFLC was obtained from ε-FLC that was calibrated using the results of free expansion tube burst tests. Tube bending and hydroforming experiments were carried out and modeled using the dynamic explicit finite element code, LS-DYNA. An LS-DYNA user subroutine that utilizes the XSFLC to predict the onset of necking was used to model the tube material. The predicted failure location and pressure at the onset of necking were found to be in a good agreement with the experimental results.