Lightweighting of an Automotive Front End Structure Considering Frontal NCAP and Pedestrian Lower Leg Impact Safety Requirements

The present work is concerned with the objective of design optimization of an automotive front end structure meeting both occupant and pedestrian safety requirements. The main goal adopted here is minimizing the mass of the front end structure meeting the safety requirements without sacrificing the performance targets. The front end structure should be sufficiently stiff to protect the occupant by absorbing the impact energy generated during a high speed frontal collision and at the same time it should not induce unduly high impact loads during a low speed pedestrian collision. These two requirements are potentially in conflict with each other; however, there may exist an optimum design solution, in terms of mass of front end structure, that meets both the requirements. In the current optimization problem definition, the peak deceleration extracted from the NCAP (New Car Assessment Program) crash pulse and the deceleration generated on a pedestrian legform are considered as constraint parameters. Assuming the gages of bumper beam, front rails, and bumper fascia as well as foam strength as design variables, the mass of the front end structure (i.e. effectively the total mass of the parts mentioned) of a previously validated Dodge Neon finite element model is optimized. Using the response surface method (RSM) and the design of experiment (DOE) technique, second order polynomial response surfaces are generated for the constraint parameters. Using the response surface equations and the design constraints, an optimum solution is then obtained by using a sequential quadratic programming (SQP) algorithm in MATLAB. It is noted the optimal solution gave a 9 kg reduction in the mass of the front end structure along with meeting the constraints imposed by crashworthiness performance in full frontal impact against a rigid barrier as in a US-NCAP test and pedestrian impact safety requirement according to EEVC/WG17 standard.