Abstract: The hydro-bending process of thin-walled tube provides several advantages：The section flattening is minimized by controlling the internal pressure, and the internal pressure delays the onset of wrinkling on the compression side and boosts the bending limit of the thin-walled tube. A new infinitesimal equilibrium equation for the hydro-bending process considering the effect of internal pressure is established. Then based on the plastic theory, the numerical solutions for the stress and strain components are obtained for a typical thin-walled tube. The finite element analysis is also conducted to verify the theoretical model. By comparing the theoretical result with the numerical results, it is found that the theoretical prediction and simulation results are in generally good agreement. The axial and circumferential stresses go up with the increasing of internal pressure. The circumferential strain increases linearly with pressure increasing, whereas the thickness strain decreases linearly as internal pressure increases.

Key words: Bending, Finite element analysis, Internal pressure, Plastic theory, Thin-walled tube