Abstract
This paper presents a methodology to quickly design and economically validate the feasibility of thermoplastic energy absorbers (EA) for a given vehicle platform to meet pedestrian leg impact requirements and ECE-42 regulatory requirements for vehicle damageability. Xenoy, a thermoplastic (PC/PBT) material, is used to develop energy absorbing lobes to cater automobile applications, ranging from passenger vehicles to SUV’s with variable bumper beam curvatures and with a packaging space that varies from 45 mm to 75 mm.
The prototyped lobes of different sizes are arranged over the bumper beam to achieve the optimum stiffness profile for the EA throughout the vehicle span. The design procedure involves optimization of the geometry for the individual lobes and obtaining the required stiffness profiles for the vehicle front. Xenoy based EA designs achieve high initial stiffness to reach desired force and subsequently maintain the force value. Designs show high-energy absorption efficiencies with the benefit of tuning the stiffness to reach required force vs. deflection performance through controlled crushing of EA. Thus, EA’s designed and developed here, are able to absorb the required amount of impact energy incurred during impacts and are found to be helpful for the vehicles to meet the pedestrian safety requirements.
Finally, in order to validate the usefulness of this methodology, simulations are performed using Hypermesh and Ls-dyna to design EA’s for a commercial vehicle platform. Actual impact tests are carried out and correlations between test and simulation results are reported here. The obvious benefits of quick prototype energy absorbing lobes would lead for significant reduction in lead-time and testing costs.
Keywords: Thermoplastics, Xenoy prototype lobes, Energy absorption, lower-leg impact, pedestrian safety.