Analysis of Biomechanical Neck-Loading Metrics as a Function of Impact Severity in Low-to-Moderate Speed Rear Impacts: Results from Hybrid III 50th Percentile Anthropomorphic Test Devices

We model neck loading as a function of impact severity in aligned rear impacts. Neck loading is understood and expected to vary as a function of factors including crash severity, occupant compartment design, and occupant metrics. Within occupant compartment design, seat and restraint characteristics are expected to influence the biomechanical response and occupant kinematics. We investigated the relationship between biomechanical neck-loading metrics and impact severity expressed as speed change (delta-V) by examining 47 low to moderate speed rear-impact crash and sled tests utilizing the Hybrid III (HIII) 50th male Anthropomorphic Test Device (ATD). Our hypothesis was that the relationship between severity expressed as delta-V and the neck metrics examined could be modeled as linear consistent with an understanding that neck loading in a rear impact results from the acceleration of the vehicle. As such, linear regressions were used to fit the dataset and examine the relationship between each metric and delta-V. The results of the analysis demonstrated that neck flexion/extension moment, as well as neck tension, individually exhibited a correlation with severity that was significant at the F-value < 0.05 level. No significant relationship with severity was observed for neck compression or shear forces, which was consistent with expectation. Neck injury criteria (N_ij) were calculated from the neck-loading metrics from each test. Results indicated that N_ij loading combinations of tension-flexion, tension-extension, and compression-extension were significantly correlated with severity. Our results are summarized in numerical models that are applicable for the determination of median and upper/lower bounds of biomechanical neck metrics associated with rear impacts in the low-moderate speed range, specifically within 5.6 km/hr to 30 km/hr of delta-V.