Rollover Initiation Simulations for Designing Rollover Initiation Test System (RITS) 2014-01-0530
Some rollover test methods, which impose a touchdown condition on a test vehicle, have been developed to study vehicle crashworthiness and occupant protection in rollover crashes. In ground-tripped rollover crashes, speed, steering maneuver, braking, vehicle inertial and geometric properties, topographical and road design characteristics, and soil type can all affect vehicle touchdown conditions. It is presumed that while there may be numerous possible combinations of kinematic metrics (velocity components and orientation) at touchdown, there are also numerous combinations of metrics that are not likely to occur in rollover crashes. To determine a realistic set of touchdown conditions to be used in a vehicle rollover crash test, a lateral deceleration sled-based non-destructive rollover initiation test system (RITS) with a fully programmable deceleration pulse is in development.
A full-size SUV vehicle dynamics model was developed and validated with static test data and curb-trip rollover test data. Then, design constraints of the RITS were set considering available space and given range of vehicle mass and geometric properties. Since accelerating a test vehicle consumes the limited travel distance, the effect of the initial lateral speed of a test vehicle on the touchdown condition was evaluated to justify the use of minimum initial speed. Next, a functional form of a lateral deceleration pulse was defined based on a soil-trip rollover crash results from literature. Lastly, Monte Carlo simulations were performed by varying the deceleration pulse to examine the ranges of touchdown conditions that can be produced by RITS system.
Other than its touchdown translational speed, there was no effect of initial vehicle velocity on the touchdown conditions. This indicates that RITS tests can be performed at lower initial velocities while still predicting touchdown conditions relevant to higher velocity rollovers. This study suggest that the RITS can produce a wide range of touchdown conditions, which were comparable to the results from research. Vehicle energy at touchdown increased as the magnitude of the deceleration pulse increased. Also, the results of this study gave insights in determining the test input conditions of the RITS by suggesting quantitative values for the change of the sled speed, tripping time, and initial deceleration value of the sled speed. To use RITS to identify field-relevant touchdown conditions, further investigation on deceleration pulses that occur to vehicles in rollover crashes is required.