Evaluation of Flow Stresses of Tubular Materials Considering Material’s Anisotropy

Abstract

The object of this paper is to evaluate the stress‐strain characteristics of tubular materials considering their anisotropic effects by hydraulic bulge tests and tensile tests. In this analytical model. Hill’s orthogonal anisotropic theory was adopted for deriving the effective stresses and effective strains under a bi‐axial stress state. Annealed C26800 copper tubes were used. The tube thickness at the pole, bulge height and the internal forming pressure were measured simultaneously during the bulge test. The effective stress — effective strain relations could be determined by those measured values and this analytical model. The flow stress curves of C26800 copper tubes obtained by this approach were compared with those obtained by the tensile test with consideration of material’s anisotropy. The finite element method was also adopted to conduct the simulations of hydraulic bulge forming with the flow stress curves obtained by the bulge tests and tensile tests. The analytical forming pressures versus bulge heights were compared with the experimental results to validate the approach proposed in this paper.