Improving pedestrian safety of a vehicle CFRP engine hood via structural optimization 2020-01-0626
The rapidly developing automotive industry and stricter environmental protection laws and regulations drive lightweight materials, manufacturing methods and structural optimization methods used in automobile design. Therefore, in order to improve the performance of pedestrian protection during a collision, this paper presents a new structural optimization method for a sport utility vehicle (SUV) engine hood made of Carbon Fiber Reinforced Plastic (CFRP). Head injury criteria (HIC) is used to evaluate the performance of the hood in this regard. Also it defines the position of the 30 impact points on the hood. The inner panel and outer panel of CFRP hood are discretized by shell element in LS_DYNA. The Mat54-55 is used to model the CFRP. In order to reduce the computational costs, just the parts in contact with hoods are modelled. The simulation was done in the 30 impact points. According to these simulations, the HIC values in front of the hood are too high and the back of the hood fails to stop the head form. 3 impact tests results and the HIC values obtained from finite element analysis (FEA) with an unacceptable error between 54% to 86%. With the modifications of boundary conditions and adding friction between the head form and the hood in the simulation, the error is reduced to less than 10%. In order to keep the mechanical behaviors, both the stacking angle sequence and topometry of hood are constants. The solution is to stiffen the outer panel in poor area by adding some CFRP layers under the outer panel. The best optimization is done through Kriging model approximation and Hooke-Jeeves Algorithm. The optimized design is relatively light (added mass of 0.261 Kg) and reduces the HIC value of the critical point from 2397 to 876. This method can be a useful tool for pedestrian protection and related works.
Yunkai Gao, Chao Ma, Linli Tian
Tongji University, Wuhan University of Technology