Seventeen rear-end impacts with a nominal 8 km/hr change in velocity to five human subjects in four positions were conducted. The four seated positions consisted of the Normal position, with the torso against the seat back, looking straight ahead, hands on the steering wheel, and feet on the floor; the Torso Lean position, with the torso leaned forward approximately 10 degrees away from the seat back; the Head Flex position, with the head flexed forward approximately 20 degrees from normal; and the Head Flex / Torso Lean position, with the head flexed forward approximately 20 degrees from normal and the torso leaned forward approximately 10 degrees from normal position. Relative to the Normal position, it was found that in both positions involving the torso lean, the peak head acceleration for the subject's head was reduced during the head-restraint impact.Further, the inertial acceleration of the head due to the forces on the neck, prior to the head rest impact, was somewhat higher for the two positions involving torso lean. Minor, transient, whiplash associated disorder (WAD) symptoms were noted. The nominal change in velocity used in this study appears to be of a reasonable magnitude to continue human subject out of position (OOP) testing.
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.
The equations of rotational motion used to calculate preimpact vehicle speeds using the rotational displacement of the vehicles following a collision are well known. The technique uses the rotational momentum exchange during impact and the principle of conservation of rotational energy to calculate the post impact vehicle angular velocity from the energy dissipated during the vehicle's rotation to a stop (product of torque and rotational displacement). Integral to the calculation of the stopping torque on the vehicle is the determination of the effective rotational coefficient of friction (f r ) between the tires and the roadway. The interactions of the road with the tires to produce the rotational coefficient of friction (f r ) are more complex and less understood than those of linear coefficient of friction (deceleration factor). A derivation of the post impact equations of motion and the kinematics of vehicles in rotation are examined. The resultant parameters of motion that affect the rotational coefficient of friction (f r ) are presented. The effects of these various parameters on the rotational coefficient of friction (f r ) were studied using EDSMAC TM . Normalized coefficients, which can be multiplied by the roadway friction to obtain the rotational coefficient of friction (f r ) under common accident scenarios, are presented. Use of equations of rotational motion supplements linear momentum equations in a momentum analysis. They are not a substitute for other accident reconstruction techniques, such as computer crash simulations.
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