Comprehensive Computational Rollover Sensitivity Study Part 2: Influence of Vehicle, Crash, and Occupant Parameters on Head, Neck, and Thorax Response 2011-01-1115

Fatalities resulting from vehicle rollover events account for over one-third of all U.S. motor vehicle occupant fatalities. While a great deal of research has been directed towards the rollover problem, few studies have attempted to determine the sensitivity of occupant injury risk to variations in the vehicle (roof strength), crash (kinematic conditions at roof-to-ground contact), and occupant (anthropometry, position and posture) parameters that define the conditions of the crash. A two-part computational study was developed to examine the sensitivity of injury risk to changes in these parameters. The first part of this study, the Crash Parameter Sensitivity Study (CPSS), demonstrated the influence of parameters describing the vehicle and the crash on vehicle response using LS-DYNA finite element (FE) simulations. This paper presents Part 2 of the study, the Occupant Parameter Sensitivity Study (OPSS), which extends the CPSS to quantify the influence of vehicle and crash parameters, as well as intermediate vehicle response metrics such as roof crush magnitude and vertical acceleration, on occupant response and injury risk. Computationally, this study uses the output from the FE simulations to prescribe input conditions to MADYMO multi-body simulations of belted occupants. Injury risk was quantified using injury risk functions, which assessed the risk of head, spine, and thoracic injuries. Parameters describing the occupant anthropometry (5th female, 50th male, and 95th male), seating position (leading/trailing side), and initial posture (baseline, forward-leaning, inboard-leaning, and outboard-leaning) were varied to evaluate their influence on injury risk. For each set of variations in the seven vehicle and crash parameters used to drive FE simulations for the CPSS (N=129), MADYMO simulations representing the 12 possible combinations of anthropometry and stature were conducted. Each MADYMO simulation utilized facet surface human models seated in both the leading and trailing sides of the vehicle to generate a total of 2,532 usable conditions. Statistical analyses of the OPSS results demonstrated that drop height of the vehicle was significant (p≺0.05) to the prediction of both vehicle response and occupant injury risk. For the near-side occupant, the roll angle at which the vehicle first impacts the ground was the most significant predictor of injury risk across all anthropometries and postures. For the far-side occupant, roll angle, pitch angle, and strength scale showed a significant influence on head and neck injury risk, while trip velocity showed the most significant influence on chest injury risk due to lateral deflection. Overall, the far-side occupant showed a greater risk of injury than the near-side occupant, while the 95th percentile anthropometry showed a lower head injury risk than the 5th and 50th percentile anthropometries. A statistically significant positive relationship was demonstrated to relate maximum roof crush to head and neck injury risk for the far-side occupant. However, these relationships did not demonstrate a strong capacity for the overall prediction of head, neck, and chest injury risk, nor did they demonstrate causal relationships.