Prediction and analysis of wrinkling in tube hydroforming process

Critical stress for the onset of axisymmetric wrinkling in tube hydroforming was derived by separating the wrinkling into the elastic phase and wrinkling phase. The theoretical solution was then validated by the experiment. Moreover, the effects of mechanical properties, stress ratio and geometry on the critical wrinkling stress were analysed and discussed by using this model. It is shown that the theoretical solution is in good agreement with the experiments. Critical wrinkling stress is greater for the tube with higher reduced modulus or higher yielding strength. However, the critical wrinkling stress magnitude of the tube with higher reduced modulus but lower yielding strength should be determined by the relative value between the reduced modulus and yielding strength. If the relative value is greater than zero, the critical wrinkling stress will increase. Besides, critical wrinkling stress will decrease first and then increase as stress ratio increases for longer tubes, but it will increase all along for shorter tubes. Higher ratio of wall thickness to tube diameter will make wrinkles more difficult to produce.