Metamodel based design optimization for vehicle crashworthiness

In automotive industry, all companies have struggled to have better crash behaviour in vehicles. For achieving that target, a vehicle has to be designed in an optimum way considering crashworthiness. Better crash performance of the bumper beam and rails helps reduce the effect of crash load transmitted to the other vehicle components, and thereby reduces the crash related damage on them and reduces the risk of injury of occupants in a crash. The nonlineer of crash process in vehicle structures make the design optimization for crashworthiness a very challenging task. Furthermore, large scale and highly nonlinear nature of crashworthiness simulations of vehicle structures make it impractical to conduct direct optimization on the full nonlinear model of the structure. The main purpose of this thesis is to find a practical methodology to conduct vehicle crashworthiness design optimization efficiently at early stages of vehicle design. The proposed methodology is based on identifying the main vehicle structural components absorbing the impact energy during a crash and then optimization of these components using metamodels. The objective of this thesis is to investigate the crash energy absorbtion of crashbox and vehicle's rails subjected to 40% offset ECER94 impact loading. Nonlinear finite element models are created by using the software ANSA and then the impact analysis is completed by using the software Ls-Dyna. Metamodelling technique is used to predict large number of design parameters and the Genetic algorithm in Ls-Opt software is employed to solve the associated multiobjective optimization problem . Computationally efficient surrogate models for expensive nonlinear finite element simulations are developed and then employed with the genetic algorithm in optimization tasks to maximize the strain energy while minimizing the force rate and for a priori pedal displacement. In the optimization chapter of the thesis, there are two optimization examples. The first example has two objective functions which are the maximization of strain energy and minimization of force rate. The results of the optimization task are employed to understand a relation between the minimum force rate and maximum strain energy. The proposed methodology is based on the principle of Pareto front and multiobjective optimization. The methodology enables the designer to evaluate the crashworthiness performance of any suggested design easily and effectively. The second example has three objective functions which are the maximization of strain energy, minimization of force rate and minimization of a priori fix pedal displacement. Numerical results imply that the obsorbed energy during crash can be increased using optimization methods.