Investigation of factors of breakage occurring on a hydroformed automotive part

Recently, tube hydroforming is getting increased attention, due to the increased requirements on the preservation of global environment and demand for impact-damage resistance for automobile bodystructures. Knowledge on the process is, however, still insufficient to produce high-quality products in an efficient way. In the research reported in this paper, an automotive part formed with multistage processes was analysed with an elastoplastic FE code which was developed with a static explicit method. The computed distributions of the thickness strain were compared with the experimental results. Good agreement was obtained, which confirmed the validity of the code. Further analysis revealed that the weld line of a tube is crucial for tube-hydroforming simulation, especially, for the thickness-strain distribution. Subsequently, factors to cause breakage at the inside of a bend of the product was investigated, which referred to both, deformation processes and strain paths. This investigation clarified factors which cause the breakage of the part.