Evaluating a proper profile in free hydraulic bulging test on stainless steel type 316 for determination the tubular material properties

This paper aims to evaluate the properties of tubular materials by hydraulic bulge tests combined with an analytical model. A setup is built for these tests and stainless steel type 316 tubes are used as specimens. Five specimens are tested in five different internal pressures and the tube thickness and bulge height are measured at the pole for each tube. A digitizer is used to measure the profile of the free bulge region and the result profiles are estimated by using Spline for each specimen. Using this profile and calculating its radius of curvature, and from above experimental data, one effective stress and effective strain can be derived for each specimen by the analytical method. Using these data points and the least square method, the constants of the effective stress-effective strain relation based on Ludwik equation for stainless steel type 316 tubular materials can be achieved. The flow stresses of the tubular materials by this approach are compared with those obtained by the tensile test. The samples are cut from the same tube used in bulge test. The finite element simulation of hydraulic bulge forming is carried out, using mechanical behavior of tubular materials and flow stresses obtained by the above-mentioned approach. The simulation results of forming pressures versus bulge heights and pole thicknesses are compared with the experimental results to validate the approach proposed in this paper.