Inverse method for flow stress parameters identification of tube bulge hydroforming considering anisotropy

Abstract

The objective of this paper is to determine the behaviour parameters of hydroformed tubular materials of annealed 25CrMo4 steel seamless tubes. An inverse identification procedure has been developed to determine the flow stress parameters from experimental free bulge and simple tensile tests. Two inverse identification strategies are proposed. In the first one, the tubular material behaviour is assumed isotropic, and then the parameters of the effective stress-strain relationship are derived from experimental bulge height versus the forming pressure. In the second one, the planar anisotropy of Hill'48 yield criterion is considered. Firstly, the simple tensile test is used to fit the isotropic strain hardening law. Secondly, the anisotropic parameter is identified by inverse technique from the experimental bulge test. The obtained results are compared with experimental measurements to validate the proposed strategies. It is proven that inverse identification methods could be a better alternative to analytical methods for flow stress parameters determination. Moreover, the anisotropy parameter has shown a large effect on the hydroformed tube responses, particularly on the wall thickness. Consequently, this material anisotropy should be considered within the flow stress identification of tube bulge tests.