A Tailor Welded Blanks Design of Automotive Front Rails by ESL Optimization for Crash Safety and Lightweighting 2018-01-0120

Utilizing the tailor welded blanks (TWBs) design along with the latest AHSS grades for the front rails on a sedan was studied to reduce the weight of the vehicle and improve the crash safety performance. To find the most efficient material usage, the front rail parts were tailored into multiple blanks with varying thickness. A structural thickness optimization study of the tailored front rails was conducted for IIHS moderate overlap frontal crash, and the tailored blank thickness was set as design variable. The equivalent static loads (ESL) method was adopted for the thickness optimization, which allows many design variables to be optimized simultaneously. The torsion and bending stiffness of the sedan body in prime were set as design constraints, and would not be compromised. The optimal thickness configurations of the TWB designs by ESL optimization suggest that the weight of the frontal rails can be reduced by more than 30% while still maintaining the crash safety performance. These TWB designs were validated by US-NCAP full frontal impact and show similar performance with baseline. A 3rd gen AHSS, NEXMET™1000, was selected on four parts of the front rails to replace the baseline HSLA350. The optimal tailored frontal rail design using NEXMET™1000 grade was obtained through ESL thickness optimization and validated by US-NCAP full frontal impact. Compared with HSLA350, the NEXMET™1000 grade offers better crash safety performance with more weight reduction potential.

An optimal thickness coefficient is proposed in this study to evaluate the material efficiency of the tailored blanks and the amount of thickness changes required for each blank to reach the most efficient material usage. The optimal TWB thickness configurations for HSLA350 and NEXMET™1000 grades through ESL were evaluated using this optimal thickness coefficient. The critical locations on front rails for crash safety were identified and the amount of thickness changes needed characterized. The tailor welded blanks technology can be implemented in the front rail design to reduce weight and improve crash safety. This optimal thickness coefficient can guide the automotive design for lightweighting.