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.
Repeatable Dynamic Rollover Roof Test Fixture
Experimental rollover tests have been criticized for their poor emulation of actual rollovers and for their lack of repeatability. We have designed and built a test fixture that overcomes both of these criticisms. The fixture holds a passenger compartment, weighted to match the inertia characteristics of a complete vehicle, or a complete vehicle at the appropriate pitch and yaw. The compartment is then rotated about its principal (longitudinal) axis through an arc that mimics the rolling motion of an entire vehicle. At the appropriate roll angle and falling velocity, the roof strikes a moving patch of concrete. The compartment is controlled throughout the sequence and is suspended after the impact, so that a sequence of impacts can be individually studied in separate tests. Initial tests have shown that we can achieve repeatable impacts. Test variables include pitch, yaw, roll rate and vehicle center of gravity motion (both lateral and vertical velocity). This test device addresses the various shortcomings of previous rollover tests, fixtures and the various static and drop tests of vehicles conducted to determine rollover performance.Copyright © 2003 by ASME
Biomechanical analysis of head-neck force in hybrid III dummy during inverted vertical drops.
The hybrid III dummy has been used extensively for crash testing. The comparison between the cadaver and dummy data provides the biofidelic nature of dummy head-neck system to predict cervical spine injury as a function of applied force. The existing dummy data are limited to a lower drop height up to 0.5 m. The present study quantified the head-neck biomechanical response of the dummy up to a drop height of 1.20 m. At 0.15 m, the head force was 5740 N and 5695 N at the upper neck and 4231 N at the lower neck. At 0.6 m, the head force was 13,000 N and 12,000 N at the upper neck and 8900 N at the lower neck. At 1.2 m, the calculated head force was 19,500 N and 18,600 N at the upper neck and 13,500 N at the lower neck. The present results closely match with data of previous studies. The data indicated that the hybrid III system transmits about 70 to 75% of the applied force from the head or upper neck to the lower neck area. In contrast, the cadaver studies showed for drops from 0.9 to 1.5 m, about 20 to 30% of the applied force was transmitted from the head to the lower neck. The comparison demonstrates the capability of the Hybrid III dummy head-neck force response to realistically predict injury and also the need for comparing the dummy's response to the human head neck force data for injury.