Head injury metric response in finite element ATDs and a human body model in multidirectional loading regimes

Abstract

Objective: The objective was to quantify head injury metric sensitivity of the 50th percentile male Hybrid III, THOR, and Global Human Body Models Consortium simplified occupant (GHBMC M50-OS) to changes in loading conditions in loading regimes that may be experienced by occupants of spaceflight vehicles or highly autonomous vehicles (HAVs) with nontraditional seating configurations.

Methods: A Latin hypercube (LHD) design of experiments (DOE) was employed to develop boundary conditions for 455 unique acceleration profiles. Three previously validated finite element (FE) models of the Hybrid III anthropomorphic test device (ATD), THOR ATD, and GHBMC M50-OS were positioned in an upright 90°-90°-90° seat and with a 5-point belt. Acceleration pulses were applied to each of the three occupants in the ± X, +Y, and ± Z directions, with peak resultant acceleration magnitudes ranging from 5 to 20 G and times to peak ranging from 32.5 to 120.8 ms with duration 250 ms, resulting in 1,248 simulations. Head injury metrics included peak linear head acceleration, peak rotational head acceleration, head injury criteria (HIC15), and brain injury criteria (BrIC). Injury metrics were regressed against boundary condition parameters using 2nd order multiple polynomial regression, and compared between occupants using matched pairs Wilcoxon signed rank analysis.

Results: Across the 416 matched-simulations that reached normal termination with all three models, HIC15 values ranged from 1.0–396.5 (Hybrid III), 1.2–327.9 (THOR), and 0.6–585.6 (GHBMC). BrIC ranged from 0.03–0.95 (Hybrid III), 0.03–1.21 (THOR), and 0.04–0.84 (GHBMC). Wilcoxon signed rank analysis demonstrated significant pairwise differences between each of the three occupant models for head injury metrics. For HIC15, the largest divergence between GHBMC and the ATDs was observed in simulations with components of combined underbody and rear impact loading. The three models performed most similarly with respect to BrIC output when loaded in a frontal direction. Both the GHBMC and the Hybrid III produced lower values of BrIC than the THOR on average, with the differences most pronounced in rear impact loading.

Conclusion: In conclusion, observed differences between the occupant models’ head injury metric output were quantified. Loading direction had a large effect on metric outcome and metric comparability across models, with frontal and rear impacts with low vertical acceleration tending to be the most similar. One explanation for these differences could be the differences in neck stiffness between the models that allowed more rotation in the GHBMC and THOR. Care should be taken when using ATDs as human volunteer surrogates in these low energy events.

Keywords:

• TBI
• head injury
• HIC
• BrIC
• spaceflight

Acknowledgments

Views expressed are those of the authors and do not represent the views of NASA or KBRwyle. Joel Stitzel and Scott Gayzik are members of Elemance, LLC, which provides academic and commercial licenses of GHBMC-owned models. The authors would like to thank Bharath Koya, Xin Ye, and Kyle McNamara for simulation support. Simulations were performed on the Wake Forest DEAC Cluster, a centrally managed resource with support provided in part by the university.

Additional information

Funding

This study was supported by NASA Human Health and Performance Contract (HHPC) through KBRwyle (NNJ15HK11B). This study also used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF grant OCI-1053575. Specifically, it used the Bridges system, which is supported by the NSF award ACI-1445606, at the Pittsburgh Supercomputing Center (PSC).