Finite element simulation of airbag deployment and optimization in crashworthiness design

Abstract: The passive safety of cars is of uttermost importance for the automotive industry. To improve the safety of cars, computer simulations of the vehicle and occupant system by the Finite Element Method (FEM), have become an industry standard tool. By using simulation techniques, the passive safety can be developed and assured already at early design stages.This dissertation addresses the problem of structural optimization in crashworthiness and the use of multi-physics simulations to understand the mechanics of airbag deployment.In the first part of the thesis, two types of optimization methods, based on local gradients and on global response surface approximations, respectively, are compared for a simplified side impact problem. The use of global approximations is shown to be more efficient and reliable than optimization based on local gradients. This response surface technique is then applied to a largo scale side impact problem. The second part of the thesis concerns the simulation of airbag inflation. A Multi Material Arbitrary Lagrangian Eulerian technique together with a fluid-structure coupling algorithm are utilized to accurately follow the fluid and the structure during the inflation process. A new fluid-structure coupling algorithm suited for permeable fabrics has boon developed. All simulation results are validated against experiments.The third part of the thesis uses the techniques from the previous parts to optimize the airbag inflator characteristics in a situation where an airbag is inflated against a head form at close range.