The effect of chin-to-chest contact on upper neck axial force in UN Regulation No. 129 frontal impact tests of child restraint systems

Abstract

Objective The objective of this study was to investigate the effect of chin-to-chest contact on upper neck axial force in United Nations (UN) Regulation No. 129 frontal impact tests of child restraint systems. Methods Frontal impact pilot experiments were carried out according to the test procedure in UN Regulation No. 129. Q-Series child dummies were seated in a small convenience sample of forward-facing child restraint systems. The timing and duration of chin-to-chest contact were determined using the procedure for calculating external head impact force in SAE J2052. Results Chin-to-chest contact was observed in all of our experiments and generated a tensile peak in the upper neck axial force of the Q-Series dummies. Prior to chin-to-chest contact, a purely inertial, noncontact peak was observed in the axial tension force. The tensile peak due to chin-to-chest contact was often greater than the inertial, noncontact peak force. Conclusions Chin-to-chest contact can increase axial neck tension force beyond the level it would reach under purely inertial loading. Adopting upper neck axial force in regulation, without considering how the force is generated, might encourage child restraint designs that mitigate only chin-to-chest contact, rather than the true inertial neck loading.