Parameter Identification of Sled Test Method to Simulate Vehicle Soil Trip Rollover Dynamic Accurately by Numerical Simulation Considering Soil-Vehicle Interaction

摘要

FMVSS 226 will become effective on September 1, 2013 with the purpose of mitigating occupant ejections through the vehicle side windows. In order to use deployable counter measures to mitigate ejection, vehicle rollover tests are needed to design deployment algorithms for rollover conditions. Vehicle manufacturers have to define their own test procedures, because FMVSS 226 does not define any rollover test methods. The soil trip rollover test is a vehicle rollover test method in which a vehicle is propelled into a soil pool to measure its rollover characteristics. Some of difficulties in soil trip rollover tests include proper maintenance of soil, for example, under fluctuating humidity and homogeneity of soil in the pool, so as to ensure stable repeatability of test results. Protection of onboard measurement equipment in a test vehicle from soil incursion when the vehicle rolls over can also be a challenge. Therefore, sled test methods without a soil pool that can simulate a soil trip rollover test with a soil pool are helpful in ensuring repeatability of results and maintenance of onboard equipment. Sled test methods that do not use a soil pool are needed to simulate the interaction between a vehicle and the soil that is greatly deformed by the vehicle. Sled test methods should simulate the interaction force and the loading position from the onset to the completion of vehicle rollover, This is important because dynamic rollover tests are necessary for deployable device to determine the firing time of deployment. However, it is generally not easy to measure soil deformation behavior and interaction force with the vehicle at every instant. In contrast, numerical simulation can be an effective way to obtain time history data of soil deformation behavior and interaction force. Eulerian description was used in this study for modeling a soil pool with extremely large deformation in order to secure computational stability and accuracy. A vehicle for this simulation was modeled by Finite Element Analysis(FEA) to simulate tire deformation so as to obtain a highly accurate solution for the interaction between the tires and soil. The simulated vehicle-soil trip rollover dynamics agreed well with test results. This model can simulate soil deformation behavior and the contact pressure distribution between the tires and soil at each moment of the soil trip rollover event. Various sled test methods based on a curb trip rollover test procedure to simulate a soil trip rollover test using a soil pool were also simulated by numerical simulation and evaluated in comparison with the simulation results for soil trip rollover using a soil pool. Sled lateral deceleration, curb movement for depth and tilting, and curb material used in the sled test methods were evaluated using time histories of the vehicle roll angle and roll rate and pressure distribution on the tires. Time histories of the roll angle and roll rate are used to design deployment algorithms. The pressure distribution on the tires indicates the tripping force and its loading position.