Strain hardening effect on TES collapse moment of different angled pipe bends subjected to bending moments

Piping systems carry fluid from one location to another and pipe bends are one of the most critical component due to its large deformation and high stress bearing nature. Collapse moment is one the criteria that helps to determine the strength of the pipe bend. The present study carries extensive three dimensional analyses to calculate the collapse moment of pipe bends (30° to 180° with interval of 30°) using twice-elastic-slope (TES) method. This paper focuses on the strain hardening (SH) effect on TES collapse moment based on elastic perfectly-plastic (EPP) material model for different bend angle and piping thickness under in-plane (closing (IPC) and opening (IPO)) and out-of-plane (OP) bending modes. From the results, it is clear that pipe thickness has significant role on hardening effect. Under IPC and OP bending modes, thicker pipe bend shows maximum hardening effect whereas under IPO mode least pipe thickness shows maximum hardening behavior due to its deformation pattern. Strain hardening effect changes maximum when bend angle changes from 30° to 60° for all bending modes. The hardening effect does not changes much for bend angle 60° to 180° under IPC and OP bending modes. Under IPO bending, hardening effect depends on bend angle for thinner pipe bends and for thicker pipe bends, it is independent of bend angle. This study helps to evaluate the bend angle hardening behavior influence on TES collapse moment which ultimately help determine the SH material model TES collapse moment based on the EPP material model.