Evaluation of the Benefit of Energy-Absorbing Material in Side Impact Protection: Part II

This paper refines the methodology presented in the companion paper linking reductions in biomechanical responses due to force-limiting material to projections of injury-mitigation in real-world side impact crashes. The revised approach was used to evaluate the potential injury reducing benefit for the chest and abdomen with either constant crush force or constant stiffness, crushable material in the side door and armrest. Using a simulation of the human impact response, a range in crush force or stiffness was determined which reduced the viscous response from that obtained with a rigid impact. NCSS field accident data for car-to-car side impacts provided information on the occupant exposure and injury as a function of the change in velocity (ΔV) of the struck vehicle. Since the velocity of the side door at contact with the occupant's chest is similar to the ΔV of the struck vehicle, the chest impact velocity in the simulation was assumed equal to the observed ΔV in the NCSS data. This related the simulation data to real-world injury data. Reductions in biomechanical response were related to lower injury risk using a sigmoidal injury probability function. This enabled a calculation of a reduction in injured occupants for the velocity range in which the EA material was effective. Reductions of up to 30% in seriously injured occupants may be possible with a low stiffness EA material that is effective in low-speed (ΔV = 4-8 m/s) crashes, whereas either type of padding was ineffective in high-speed crashes (ΔV > 10 m/s).