Small female and large male responses in rear impact

The objective of this study was to conduct rear impact sled tests using 5(th), 50(th), and 95(th) percentile Hybrid III dummies and evaluate proposed injury criteria. Head restraint positions of differing height (750, 800 mm) and backset (0, 50, 100 mm) were used to determine axial and shear forces, bending moments, and injury criteria (NIC, N(ij), and N(km)). The time sequence to attain each parameter was also determined. Three events were identified in the dummy rear impact response. Event I was coincident with the torso bottoming out the seat cushion, Event II occurred at the time of the peak neck flexion moment, and Event III occurred at the time of maximum head to head restraint involvement. Parameters such as backset, head restraint height, seat-head restraint interaction, and anthropometry affected impact responses. Head rotations increased with increasing backset and increasing head restraint height. However, the N(ij) and N(km) did not exhibit such clear trends. The 50(th) percentile dummy responded with consistent injury criteria values, e.g., the magnitude of the injury criteria increased with backset increase or head restraint height decrease. However, the 5(th) and 95(th) percentile dummies did not demonstrate such trends. These findings underscore the need to include subject anthropometry in addition to seat and head restraint characteristics for better assessment of rear impact responses.