Mechanical Models’ Adaptability Analysis And Software Development In Hydroforming Numerical Simulation

As one of the most important ways in automotive light weighting industry,hydroforming technology has been received rapid development in recent decades.Compared with conventional manufacturing technique, hydroforming will offerseveral advantages, such as improved structural strength and stiffness, lower toolingcost, fewer secondary operations. The hydroforming technology has now been used inmany areas, such as aviation, aerospace and ship with the development of thecomputer and the super-high hydraulic pressure controlling technology. Meanwhile,many factors can influence the accuracy of the numerical simulation of hydroformingprocess, such as material’s mechanical model, hydraulic loading mode and othertechnological parameters. This study is funded by GF973Program. The main contentof this study can be divided into two parts:1. Developed a constitutive model based on LS-DynaThis study firstly discussed the three different kinds of constitutive numericalintegral algorithms. Then the semi-implicit backward Euler stress integration methodwas applied to deduce the algorithm equation based on the three-dimensional Hill’48anisotropic yield criterion. Finally, the three-dimensional Hill’48yield criterion wasimplemented in the commercial finite element software LS-Dyna by using userdefined material models UMAT. This algorithm was validated by the tensile test ofsingle element and complicated hydroforming process. What’s more, the adaptabilityanalysis was made in T-shaped tube hydroforming with carbon steel material. The numerical simulation results achieved by two-dimensional Hill’48yield criterion andthree-dimensional Hill’48yield criterion respectively were compared with physicaltest results. It was found that the developed constitutive model in this paper candescribe the hydroforming process much more reasonably.2. Developed a rapid modeling simulation tool in hydroformingThis paper made a comprehensive comparison between LS-Dyna’s ownpreprocessor LS-PrePost and hydroforming module in Dynaform. Then the C++language was used to develop a rapid modeling simulation tool in hydroforming basedon the LS-Dyna Solver. This tool has greatly simplified the operation of hydroformingprocess. Besides, this tool includes three kinds of element model (conventional shellelement, shell element considering normal stress and solid element), two kinds ofhydraulic loading mode (pressure loading and volume loading) and new constitutivemodels, including three-dimensional Hill’48, two-dimensional Barlat’91andthree-dimensional Barlat’91considering normal stress. Compared with conventionalsoftware, this tool provides mechanical models with higher accuracy and thereforecan describe the hydroforming process more accurate.