Improvement of Response Surface Quality for Full Car Frontal Crash Simulations by suppressing Bifurcation using Statistical Approach

In recent years, importance of optimization is rising in automotive industry, since needs in fulfilling conflicting requirement such as light weight, rigidity, and safety in high level are continuously increasing, while car structure becomes complex due to new material and new connection techniques. RSM (Response Surface Method) is one of key technology for the purpose, and various approaches have been made. However, quality of response surfaces tend to be poor when it comes to frontal or rear crash where contact and buckling is dominant, since bifurcations in behavior bring high non-linearity to response surfaces. One measure is to increase the number of simulation runs in order to improve the accuracy of response surface, but as the size of full car simulation models becomes bigger, it is not realistic to run over 100 times. The fundamental problem is that the response surface is with high complexity due to bifurcations such as buckling and contact so that trying to fit highly non-linear response surface by adding points is not the absolute solution, but to reduce non-linearity of the surface in order to make it easy to fit. In this study, scatter propagation mechanism is visualized based on statistical calculations, and structural design of front structure of an automobile is enhanced in order to suppress bifurcations with help from a statistical analysis software DIFFCRASH. Triggers of bifurcation are located and mechanisms of the bifurcations are studied, and design modifications are made to stabilize the deformation modes. As a result, the complexity of response surface has been reduced, and accuracy of the response surface has been improved.