A Study On Crashworthiness Simulation Of The Frontal Longitudinal Beam Of A Passenger Car And Optimization Of The Beam Structure

The frontal longitudinal beam is a primary part for energy absorbtiion in the frontal crash of passenger car. The energy absorption ability and deformation mode of the frontal longitudinal beam can affect the vehicle acceleration response and the force transfer route in frontal impact. The vehicle crashworthiness is obviously affected by design of the frontal longitudinal beam. The computer simulation analysis is an important means to investigate the structure crashworthiness. In order to increase the accuracy and efficiency of analysis and optimization of the structure crashworthiness, it is greatly significant to improve the simulation technique.The aim of present study is to investigate the key factors which influence the crashworthiness of frontal longitudinal beam in the crash simulations. Furthermore, this study is to explore the robust optimization method and its application in the crashworthiness analysis of the frontal longitudinal beam based on the product quality engineering.Firstly, a spot weld model was developed and implemented by using one single solid element in the LS-DYNA software. The base metal of the spot weld model was represented by using shell elements. The region of weld nugget and heat affected zone was represented by one single solid element. The two types of spot weld models using solid element and beam element were applied in the FE modeling of a frontal longitudinal beam in sled crash test. The corresponding sled test with the frontal longitudinal beam was carried out to validate these models. Secondly, the strain rate response of metal sheets was studied based on the finite element model of the frontal longitudinal beam. Besides, influences of other important factors to the beam impact responses were analyzed in terms of the mesh size, spot weld size, stamp forming of metal sheet and friction in contact in the simulations of the frontal longitudinal beam in frontal crash. Finally, the six sigma robust optimization design method based on the product quality engineering was used to analyze and optimize the crashworthiness of the frontal longitudinal beam, in combination with experiment design, response surface method and Monte Carlo simulation technique.The results of the study indicated that the spot weld model without considering more detailed mesh size of the sheet metal is more efficient with reliability. It has better accuracy than the exsiting spot weld model using beam element. The crash simulation of the fontal longitudinal beam was obviously affected by the strain rate response of metal sheets. The static and dynamic tensile tests of metal sheets show that different metal sheets have different strain rate responses. The effect on the strain rate response of the metal sheet with low stiffness is larger than that with the high stiffness. The simulation was also affected by the mesh size, spot weld size, stamp forming of the sheet metal and friction in contact. The smallest mesh size of the sheet metal was not the best, and the best mesh size should be defined by the geometry of section and the thickness of the metal sheets. The frontal longitudinal beam had the best simulation result with the mesh size of sheet metals of 5 X 5 mm. The metal sheets with different property or thickness should choose different value of spot weld size in crash simulation. The stamp forming response of the metal sheet should be considered in the crash simulation. The right friction coefficient should be defined in the crash simulation in order to reflect the effect of the friction in contact. The robust optimization based on the product quality engineering can improve the reliability and robustness of the optimization result for the crashworthiness of the frontal longitudinal beam.The results from this study are useful to improve the quality of analysis of the finite element simulation, which provide a good engineering method for the structure optimization.