Quantitative evaluation of the occupant kinematic response of the THUMS 50th-percentile male model relative to PMHS laboratory rollover tests

ABSTRACT

Objective: The objective of the current study was to evaluate the whole-body kinematic response of the Total Human Model for Safety (THUMS) occupant model in controlled laboratory rollover tests by comparing the model response to postmortem human surrogate (PMHS) kinematic response targets published in 2014.

Methods: A computational model of the parametric vehicle buck environment was developed and the AM50 THUMS occupant model (Ver 4.01) was subjected to a pure dynamic roll at 360°/s in trailing-side front-row seating position.

A baseline configuration was defined by a baseline posture representing the average of all PMHS postures, with a friction coefficient of 0.4 for the belt and 0.6 for the seat.

To encompass challenges in controlling boundary conditions from the PMHS tests and ensure the robustness of the model evaluation, a total of 12 simulations were performed to investigate the following:

1.	The effect of initial posture by adding 3 additional postures representing PMHS extremes.
2.	The effect of belt tension by varying tension from the nominal vehicle retractor belt tension of 5 N to the 35 N belt tension used in the PMHS tests.
3.	The effect of friction between the environment (belt, seat) and THUMS.

Trajectories (head, T1, T4, T10, L1, and sacrum), spinal segment rotations (head-to-T1, T1-to-T4, T4-to-T10, T10-to-L1, and L1-to-sacrum) relative to the rollover buck and spinal segment elongation/compression calculated from the simulations were compared to PMHS corridors using a correlation method (CORA).

Results: THUMS baseline response showed lower correlation (overall CORA score = 0.63) with the PMHS response in rollover compared to other crash modes. THUMS and PMHS demonstrated similar kinematic responses in the longitudinal axis and vertical axis but significantly different lateral excursion relative to the seat. In addition, no spinal elongation was observed for THUMS compared to the PMHS.

The posture, pretension, and belt frictions were found to alter model kinematics, especially on THUMS lateral axis motion. The posture was judged to be the most sensitive parameter evaluated because a change of 30 mm in the lateral axis results in up to an 80 mm of change in observed displacement.

Conclusions: Though the model response in the lateral axis is significantly different than that of the PMHS, it is unclear whether this difference is the result of extrinsic factors (posture, pretension, and friction), where exact values in experiment are unknown or by model intrinsic factors (e.g., spine stiffness). These differences in occupant kinematics could potentially subject the PMHS and THUMS to very different loading conditions under roof impact in rollover crashes: different occupant posture and different roof impact location. Therefore, different injury mechanisms and severity might be predicted by the current model relative to the PMHS. Consequently, though the information provided in the current study could be useful for improving model biofidelity for rollover crashes, additional studies are required to properly solve this issue.

KEYWORDS:

• Rollover
• human body model
• CORA
• biofidelity
• kinematics

Funding

This work was supported by funds from the Toyota Collaborative Safety Research Center (Toyota CSRC). The views expressed in this article are those of the authors and do not necessarily represent or reflect the views of the sponsors.