Research On Key Technology Of One Step Inverse Forming FEM And Fine Crash Simulation Of Vehicle

0. PrefaceThe auto panel is the main factor of the auto product, and the rapid development of the auto industry impels the development auto panel die. During the automotive design and manufacture period, it is the main factor of auto product development speed and quality that the design and manufacture level of the auto body die especially auto panel die. Now due to the rapid development of the auto industry of China, far more traffic accidents arising, a growing number of people in both the automotive manufacturers and consumers have come to the realization that automobile safety is a serious problem.The research works are supported by the key project of National Natural Science Funds"The basic theory, calculation method and key technique of stamping and die design"(19832020) and the cooperative project of Jilin University and CHANA Inc."study on the development and application of the key technology of automobile light weighting and light materials". A new algorithm for modifying the initial field is presented, and the question of unfolding the thick plate algorithm for the developable surface is researched also. At last, the fine crash and its effect on the occupant restraint system is studied in the paper.1. The key technology of the one step inverse forming FEMThe main assumption which is adopted by the one step inverse forming FEM is the proportional loading assumption. It only considers the initial and the final state without considering the medium state. The basic idea of this method is that we look for the nodal positions in the initial flat blank from the final part, and then the distribution of strain, stress and thickness in the final configuration can be calculated by comparing the nodal position in the initial flat sheet with the one of the final part.Based the one step inverse forming finite element method, a new algorithm, SIAMIB, for modifying the initial field is presented, which is applied to the parts of negative angles successfully. The method is a static implicit algorithm based on the theory of a minimal unfolded error optimization. Since the L-BFGS algorithm is used, the process not only occupies less resource, but also has relatively higher efficiency and precision.Research on the key technology of the thick plate unfolding algorithm for the developable surface is carried out, which is the algorithm of the allowance of bending process, the splitting surface in FE model and the radius fitting. Application to some industrial parts is presented to validate the algorithm. Then, the flow of the thick plate unfolding algorithm for the developable surface is summarized in the paper.2. The structure analysis of the auto fine crash simulationThe auto crash is an instantaneous complicated physical process, which contains the geometry nonlinear with large displacement, large rotation and large strain, the material nonlinear with elastic-plastic deformation and the boundary nonlinear with contact friction. The FEM is the main method for studying the auto crash simulation, which is based on the central difference method. But now the effect of the forming factor on the crash is ignored, that is to say, the existed distribution of the thickness, strain and stress in the part for the crash simulation is not considered.The paper expatiates on the explicit non-linear finite element method and builds the finite element crash model of an auto. Combined the one step inverse forming finite element method and the crash simulation, the fine crash process is simulated by analyzing the structure's energy absorbing of the vehicle through the software, LS-DYNA, which is compared with the normal crash simulation. Then, the flow of the vehicle fine crash is summarized in the paper.3. The effect of the fine crash simulation on the occupant restraint systemThe occupant restraint system affects the safety of human directly, which is the main domain of the study on the auto passive safety and studied by the finite element method and the kinematics of the multi-body method. Because the calculation speed of the kinematics of the multi-body method is faster than the finite element method, it is applied to study the occupant restraint system.In the aspect of the occupant restraint system, the Multi-body theory is introduced. In the paper the restraint system of a vehicle is built and validated by using the Multi-body software, MADYMO. The results are given by using two methods.