Experimental and analytical evaluation on flow stress of tubular material for tube hydroforming simulation

For the finite element simulation in tube hydroforming process, the flow stress must express the bi-axial state of stresses similar to that of the actual hydroforming operation. In this work, experimental and analytical methods to acquire the flow stress of tubular materials for hydroforming application were performed. Conventional tensile tests on specimens extracted from both a flat sheet and a roll-formed tubular material were conducted. And then, in order to consider the bi-axial state of stress, free bulge test of a simple tubular material was carried out and analysis results using flow stresses obtained from both test methods were compared and evaluated with the free bulge test. Therefore, it is concluded that the flow stress obtained from the free bulge test should be used for input material property for the numerical analysis of the tube hydroforming process to enhance the accuracy of those.