Abstract
Research and/or Engineering Questions/Objective
This paper presents a research carried out to reduce the effects of a frontal crash in car occupants, in terms of peak forces/accelerations. The thickness of the car steel elements which contribute the most to the energy dissipation are selected as design variables. The objective function to minimize is variance of the force-time curve produced in a frontal impact test and an ideal, constant-force equivalent dissipator.
Methodology
A finite element model of a Dodge Neon car, model year 1996, which has been precisely correlated with experimental data, is chosen for the optimization. This model is subjected to a frontal impact test against a simplified rigid wall at the speed matching standard Euro NCAP protocols. Force-time curve is obtained from the analysis and suitably filtered. The objective function is calculated as the variance of the force-time curve produced in a frontal impact test. The objective is to obtain a force-time curve which is as close as possible to the ideal dissipator curve, with lower values of the peaks of acceleration experienced by the occupant. To that end, optimization strategies are planned carefully to deal with problems which are typical in crashworthiness optimization like expensive computation times and numerical noise. The thicknesses of the following parts have been selected as design variables: three thicknesses of the front rails, two thicknesses of the U-sections placed after them, the bumper and the hood and its reinforcement.
Results
The variance of the curve by 50-55%, producing a force-time curve which is clearly closer to the ideal one. The collapse modes of the involved parts are modified to achieve the best performance.
Limitations of this study
Besides a 50-55% of reduction of the objective function, depending on the selected surrogate model, the mass of the car is slightly increased for one of the models by almost 15 kg. As ongoing work, a multi-objective optimization to reduce the acceleration peaks while reducing or maintaining the total weight is being considered.
What does the paper offer that is new in the field including in comparison to other work by the authors
Usually, these optimization analyses are applied to individual car components. This paper optimizes the full frontal part of the car and its global response in a simplified standard test, with optimization methods specially tailored to deal with this problem.
Conclusions
An enhancement of the effects of a frontal crash in occupants has been achieved, improving the energy absorption capabilities of the car design. Optimization techniques have been successfully applied to a complex crashworthiness problem.
KEYWORDS – Euro NCAP test, frontal impact, injuries reduction, size optimization, surrogate models