Deformation behavior of tubes with thickness deviation in circumferential direction during hydraulic free bulging

The influence of the initial thickness deviation of the tube wall on the deformation behavior during free hydraulic bulging was studied. The experimental study was performed with tubes that had an initial thickness deviation of approximately 1–4%. FEM simulation and theoretical speculation were also carried out in order to examine the experimental results. It was clarified that the cross sectional shape of the bulged tube maintained its circular shape until just before tube bursting. This tendency appeared independently of the amount of the initial thickness deviation. On the other hand, increase in thickness deviation during tube bulging depended on the degree of the initial thickness deviation, n-value and r-value. When the initial thickness deviation was large and n-value and r-value were small, the increase in thickness deviation was large.