A Study on Lightweight Design of Automotive Front Rails Using Tailored Blanks by Nonlinear Structural Optimization

Tailored blanks offer great lightweighting opportunities for automotive industry and were applied on the front rails of a sedan in this research. To achieve the most efficient material usage, all the front rail parts were tailored into multiple sheets with the gauge of each sheet defined as a design variable for optimization. The equivalent static loads (ESL) method was adopted for structural optimization and the Insurance Institute for Highway Safety (IIHS) moderate overlap frontal crash as the nonlinear analysis load case. The torsion and bending stiffness of the sedan body in white (BIW) were set as design constraints. The occupant compartment intrusion in IIHS moderate overlap front crash was set as design objective to be minimized. The optimal thickness configuration for the tailored front rail designs was obtained through ESL optimization for multiple mass saving targets.

The optimal thickness configuration for tailored front rails was updated in full vehicle crash model, and IIHS moderate overlap frontal crash analysis was conducted again to validate the results from ESL optimization. The section force and crash energy absorption of the tailored front rails were obtained. It is found that the section force on front rails is reduced for tailored blank design. Yet the crash energy absorbed by tailored front rails is very close to the baseline (over 95%) with lightweighting achieved. What is more, the energy absorbed by the whole system is the same or even higher than baseline, attributed to the tailored front rails leveraging the energy absorption of the full vehicle and deformable barrier. A 23.59% mass saving on front rails can be achieved using tailored design with improved crash safety rating for IIHS moderate overlap frontal crash. Without compromising the crash safety performance, a 34.43% mass saving can be achieved using tailored front rails. The tailored front rail designs of the sedan were validated by the United States New Car Assessment Program (US-NCAP) full frontal impact, and the vehicle acceleration curves using tailored designs show similar or lower peak value than the baseline. The tailored blanks can be implemented in front rails of the sedan to reduce mass and improve the crashworthiness.