Repeatability of a dynamic rollover test system
ABSTRACT Objective: The goal of this study was to characterize the rollover crash and to evaluate the repeatability of the Dynamic Rollover Test System (DRoTS) in terms of initial roof-to-ground contact conditions, vehicle kinematics, road reaction forces, and vehicle deformation. Methods: Four rollover crash tests were performed on 2 pairs of replicate vehicles (2 sedan tests and 2 compact multipurpose van [MPV] tests), instrumented with a custom inertial measurement unit to measure vehicle and global kinematics and string potentiometers to measure pillar deformation time histories. The road was instrumented with load cells to measure reaction loads and an optical encoder to measure road velocity. Laser scans of pre- and posttest vehicles were taken to provide detailed deformation maps. Results: Initial conditions were found to be repeatable, with the largest difference seen in drop height of 20 mm; roll rate, roll angle, pitch angle, road velocity, drop velocity, mass, and moment of inertia were all 7% different or less. Vehicle kinematics (roll rate, road speed, roll and pitch angle, global Z′ acceleration, and global Z′ velocity) were similar throughout the impact; however, differences were seen in the sedan tests because of a vehicle fixation problem and differences were seen in the MPV tests due to an increase in reaction forces during leading side impact likely caused by disparities in roll angle (3° difference) and mass properties (2.2% in moment of inertia [MOI], 53.5 mm difference in center of gravity [CG] location). Conclusions: Despite those issues, kinetic and deformation measures showed a high degree of repeatability, which is necessary for assessing injury risk in rollover because roof strength positively correlates with injury risk (Brumbelow 2009). Improvements of the test equipment and matching mass properties will ensure highly repeatable initial conditions, vehicle kinematics, kinetics, and deformations.
Development of a higher-order model for a roll simulator
A four degree-of-freedom model of a roll simulator is developed. The roll simulator consists of a sled-platform assembly, where a recreational off-highway vehicle (ROV) is mounted to the platform which has the freedom to rotate up to 90 degrees. The purpose of the roll simulator is to re-create rollover manoeuvres ascertained from in-field vehicle dynamic experiments. Previous studies developed a two degree-of-freedom model; one for translational and one for rotational motion. This study expands on that model and increases the number of degrees-of-freedom to more closely emulate the roll simulator. The model incorporates non-linear stiffness models of the wire ropes and enables the model to have three translational degrees-of-freedom and one rotational degree- of-freedom. The equations of motion (EOM) are numerically simulated using Matlab’s Simulink. Comparisons are made with experimental data derived from the roll simulator to validate the model.
THE RELATIONSHIP BETWEEN VEHICLE ROOF STRENGTH AND OCCUPANT INJURY IN ROLLOVER CRASH DATA
This paper evaluates the effect of vehicle roof strength (as measured in FMVSS 216) on severe occupant injury using police-reported motor vehicle accident data from Florida, Texas, Michigan, and North Carolina. The paper also evaluates the effect of vehicle shape as measured by the overall height-to-track width ratio on severe occupant injury in rollovers. The validity of the state data was verified using NASS matched case data. The data was controlled for accident severity, restraint use, and driver demographics. Based on 60,758 single vehicle rollover accidents in the four states, conclusions were: There is no relationship between vehicle roof strength-to-weight ratio and the likelihood of severe injury for the vehicles studied. There is no relationship between the roof strength-to-vehicle-weight ratio and the likelihood of severe roof damage for vehicles involved in rollovers. There is a strong relationship between vehicle shape and severe roof damage for vehicles involved in rollovers. There is a weak relationship between vehicle shape and severe occupant injury.