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Vehicle Linear and Rotational Acceleration, Velocity and Displacement during Staged Rollover Collisions

2007; Linguagem: Inglês

10.4271/2007-01-0732

2688-3627

Orion P. Keifer, Wesley C. Richardson, Peter D. Layson, Bradley C. Reckamp, Thomas C. Heilmann,

Agriculture and Farm Safety

Four full scale vehicle rollover tests, about the roll axis (X-axis), were staged using a sled attached to a large truck. Each vehicle was fitted with a nineaccelerometer array that approximated the center of gravity and two single axis accelerometers attached to the roof adjacent to the A-pillar/roof junction. The acceleration data was retrieved for three tests; however, the data recorder malfunctioned on the remaining test. Data was collected at 1000 hertz and processed to determine the linear and rotational acceleration with respect to each of the three vehicle coordinate axes. Rollover video and scene data were also collected to correlate vehicle rollover motion with the accelerometer data. INTRODUCTION Full scale rollover tests have been conducted over many years. Much of the work has been performed using various test sleds. One of the most common is the Federal Motor Vehicle Safety Standard (FMVSS) 208 sled test, which is conducted in accordance with SAE J2114, for example the Malibu tests (Orlowski, et al., 1985 and Bahling, et al., 1990). The FMVSS 208 test sled ramp angle is 23o and the test is conducted using an initial speed of 30 miles per hour. The sled is decelerated to a stop in less than 3 feet and a deceleration rate of at least 20 g’s for a minimum of 0.04 seconds. The test procedure used for this work has a sled angle of 34o and a deceleration rate of approximately 0.6 g’s; however, the tests required minimal apparatus that can be used for most vehicles and nearly any test surface. The test vehicles were instrumented to determine both the angular and linear acceleration, from which the angular and linear velocities and displacements could be determined. METHODOLOGY Vehicles The test vehicles for the testing included the following: Vehicle VIN Color 1989 Buick Park Avenue Ultra 1G4CU54C0K1668358 Gold 1994 Oldsmobile 88 Royale 1G3HN52L9R4818549 Blue 1997 Pontiac Grand Am 1G2NE52TXVC866133 White 1995 Mercury Tracer 3MASM10J9SR647656 Green Table 1. Vehicle data. Vehicle Mass kg Length m Width m SSF Buick 1462 5.00 1.83 1.44 Oldsmobile 1573 5.08 1.88 1.36 Pontiac 1307 4.75 1.73 1.34 Mercury 1095 4.34 1.70 1.37 Table 2. Vehicle data. * Static Stability Factor (half the track width divided by the center of gravity height). Sled The sled was manufactured using a utility trailer frame set side-ways. Two fixed axles were attached to the frame. Two ramps, one for the front and one for the rear axles, were welded in place at an angle of approximately 34o (Figure 1). The designed ramp angle was determined using a first order approximation, neglecting suspension compliance, such that all test vehicles would: first, be stable while the sled was stopped or accelerating and second, roll off the sled when the pusher truck was heavily braking. Rollover occurs when the line of action of the force through the center of gravity of the vehicle is forward of the front lip of the sled. That occurs when the sum of three angles exceed 90°. The three angles are the sled ramp angle, the angle formed by the ground and a line passing through the vehicle center of gravity, with the apex at the center of the outboard tire, which is calculated using the Static Stability Factor (SSF) and the friction angle due to braking, shown on Figure 2. In this first order approximation, the braking deceleration required to cause the vehicle to roll was calcuated between 0.35 and 0.4 g’s, depending on the test vehicle. The front bumper of the pusher truck was removed and brackets fabricated for this test were mounted on the frame members. The sled was then pinned to the frame brackets with two transverse pins, one for each side. Figure 1. Photograph of the sled arrangement. Instrumentation A computer system was assembled to collect data, the details of which are in Appendix A. All data was collected with 12 bit resolution. The monitored accelerometers included a nineaccelerometer array, as proposed by Padgaonkar, et al. (1975) and Mital and King (1979), including three mutually perpendicular channels on the center accelerometer and the two channels for each of the three legs. Figure 2. Diagram of the sled angles. Three channels of a 2g triaxial accelerometer, installed on the floor near the center of gravity, were monitored. Two single axial 50g accelerometers were placed near the right and left A-pillar roof intersection. The position and orientation, with respect to the vehicle coordinate axis varied from vehicle to vehicle, but in general were oriented mostly vertically with a forward and outboard component as dictated by the interior contour at the A-pillar to roof contour inside the vehicle. Additionally, one data collection channel monitored a microphone, used for video to data collection synchronization. Figure 3 shows a photograph of the test equipment installed in one of the test vehicles. Figure 3. Photograph of the nine-accelerometer array frame inside a test vehicle. Video Video cameras were used to capture the roll-over from the side and from the front. Cones were placed on the test surface and measured as reference points for photogrammetric processing. The positions of the cones and video cameras were surveyed. TEST PROCEDURE The truck and sled were lined up on the test track and the vehicle was placed on the test sled. A balloon was popped adjacent to the test vehicle to provide synchronization between the data collection system and the video cameras. The video cameras captured the frame during which the balloons popped and the data recorder captured the sound on the channel which monitored the microphone. The truck was accelerated and the speed of the truck was monitored with a Stalker radar gun. The truck steering was adequate to maintain a straight line of travel. As the truck crossed a predetermined line marked by cones, the driver locked up the brakes, causing the test vehicle to roll off the sled. When the vehicle came to final rest, a second balloon was popped adjacent to the final rest position of the vehicle, to synchronize the video with the data collection system. The data was downloaded from the data collection system via an Ethernet connection. The vehicle was photographed and marks on the pavement were documented. RESULTS The roll data and distance traveled is summarized in Table 3. Buick Oldsmobile Pontiac Mercury Lead direction Driver Passenger Driver Driver Initial Vel. (kph) 55.5 54.7 56.3 56.3 Rolls* 2 2 4 1/4 1 1/2 Yaw (final rest) 10oCW 70o CCW 35oCW 20oCW Distance to Rest (m) 26.1 23.5 39.6 28.1 Drag factor 0.50 0.54 0.34 0.48 Table 3. Roll and distance data for the tested vehicles. * Including the initial 34°. Figures 4 through 7 show the damage received by the four vehicles during the rollover. Figure 4. Buick Figure 5. Oldsmobile