Abstract
The combination of severity and frequency of injuries sustained in vehicle rollover is a major public health concern. The National Highway Traffic Safety Administration (NHTSA) addressed these concerns by enacting a federal standard to evaluate rollover crashworthiness using a quasi-static roof crush test (Federal Motor Vehicle Safety Standard 216) despite the fact that rollover is a dynamic event. Public comments to the NHTSA’s proposal to upgrade FMVSS 216 criticize the NHTSA’s lack of a dynamic test requirement. However, the NHTSA discussed concerns with current dynamic rollover tests stating that they lacked demonstrated repeatability, they did not produce real-world rollovers, and they are not as repeatable as the current quasi-static test in place (NHTSA, 2009). The NHTSA wanted to perform research to address the concerns posted by the public and one of the results was the Dynamic Rollover Test System (DRoTS). Since repeatability was a concern of the NHTSA the goal of this thesis is to evaluate repeatability of the DRoTS relative to standardized crash tests using an objective rating method by presenting two studies followed by a discussion of the limitations of the method and final conclusions.
The first study presents four rollover tests, one pair of late model subcompact sedans and one pair of late model compact multi-purpose vans (MPV), conducted on the DRoTS fixture to evaluate repeatability in terms of initial roof-to-ground contact conditions, vehicle kinematics, road reaction forces, and vehicle deformation. Initial conditions (roll and pitch angle, roll rate, road speed, vertical velocity, mass, and moment of inertia) were found to be 7% different or less while drop height was at most 20mm different in both repeated tests. Plotted data signals of the vehicle response suggest repeatability of the DRoTS fixture however, the measures of repeatability described were subjective and involved qualitative assessments of plotted signals.
The second study used a quantitative approach to assess repeatability of the DRoTS fixture relative to other crash modes. The objective rating method published by the ISO (2014) was used to compare vehicle accelerations, forces, and deformations of frontal, frontal offset, small overlap, small overlap impact (SOI), oblique, deceleration rollover sled (DRS), and DRoTS tests against one another. Based on the average overall rating of the dominant acceleration in each crash mode the crash tests ranked as: 1) Frontal Offset, 2) Frontal, 3) Oblique, 4) SOI, 5)DRoTS, 6) Small Overlap, 7) DRS. As expected frontal crash tests ranked highly when comparing acceleration data and received good repeatability ratings (R>0.8) when comparing reaction force data. DRoTS showed good to excellent (R>0.94) ratings when comparing deformation measures and ranked well above the deformation ratings in SOI tests which all received poor grades. The objective rating method found that the DRoTS tests were as repeatable as other crash modes when comparing the dominant accelerations and showed greater repeatability than the DRS in nearly every other kinematic metric, suggesting that the DRoTS fixture is a highly repeatable dynamic rollover testing device.
