Study On Key Techniques Of Vehicle Crash Simulation

In automotive design, Computer Aided Engineering (CAE) has become a key factor to reduce the development time and the cost of products, especially for the design of vehicle crash safety. In order to improve the performance of the simulation methods for impacting process, studies which focus on the inverse problem, the shell element method, hourglass control ideas, multiple time steps algorithm and crash safety improvement using CAE and optimization methods for a microbus are conducted in this paper.The main innovative points of this paper are given as follows:(1)The precise material parameters play an important role to an effective simulation. An identification scheme to couple the finite element method and IP -μGA(a modified micro genetic algorithm with the strategy of Intergeneration Projection)is developed and programmed. The idea is to match the calculated response with the measured one in least-squares sense. The optimization algorithm chooses the parameters which are putted into the finite element code to find the best coincidence between the observed response and the calculated one. This technique is an alternative approach to the conventional method. An identification scheme for the determination of plastic parameters of blank sheet material is presented. This identification scheme is based on the combination of the finite element method (FEM) and the response surface methodology (RSM). The FEM is employed to calculate the responses of a blank sheet and RSM adjusts the material parameters so that the calculated responses match the measured one in a least-square sense. An example shows that the accurate plastic parameters can be obtained from a sheet forming test by using the method. An identification scheme for characterizing the material plastic property directly by using the results of simulation is presented. A series of equations in which the material parameters become unknown are constructed based on results from the calculation of FEM. The macro genetic algorithm is used to solve these unknown parameters. It is found that the identification scheme presents with high computational efficiency and accuracy.(2)A general four-node shell element with a single point quadrature is developed in this paper. This formulation is based on a physical stabilization approach for the control of spurious zero-energy modes (the hourglass mode). In order to eliminate the over hardening response existing in the warped configurations produced by applying the assumed strain method and the physical stabilization approach, an hourglass stability factor is introduced. In this paper a concept of mini-warped domain is presented and the hourglass forces are calculated based on it. The numerical results show that the developed methods possess high stabilization, high convergence and high accuracy.(3)It can decrease significantly the computation time in transient structural analysis to use subcycling algorithms which permit multiple time steps in explicit integration. Several subcycling algorithms were tested and it was shown that constant velocity subcycling algorithm possesses the best accuracy and stability properties. A new subcycling algorithm based on special treatment of rigid joint and proper choice of damper is proposed. The numerical examples show that the algorithm presents with high computational efficiency.(4)Genetic Algorithm(GA) is employed to solve the problem of constrain system optimization. A Madymo frontal crash model is testified its validity and then is optimized to yield the lowest levels of the occupant injury value and at least satisfy the Chinese legal requirements for frontal crash. It wastes little time to run this problem by using GA, as each simulation time is very little. The accuracy of the method is verified by comparison with optimization results and the test results.