Development of seat shock isolation systems

Abstract

A numerical model has been created to predict the behavior of seat shock isolation systems exposed to mine blast loaDing The model is a two dimensional, five degree-of-freedom, rigid body, mass-spring-damper approximation of the seat system and human occupant. The outputs of the model are the positions, velocities, and accelerations of the system masses, the forces of the connecting elements, such as the seat cushion force, the load limiter force, the spinal force, and the Dynamic Response Index (DRI) based on the pelvic z-axis acceleration. The model has been calibrated with drop tower test data collected by the Army Research Laboratory in Aberdeen, Maryland. The model and test results agree within 6% for z-axis acceleration, spine load, and DRI; Two conceptual seat shock isolation systems have been designed using the numerical model, and their components have been assembled and partially tested in the UNLV laboratory. Both designs use air-pneumatic seat cushion technology. For force limiting, one design uses coil rope spring isolators and the other uses an 8896-N (2000-lbf) honeycomb panel force limiter. Both designs are sized to fit in current U.S. military vehicle envelopes. The numerical model predicts the following performance indicators when the seat designs are exposed to a peak acceleration input of 395 g's with a duration of 5 ms, which is typical of mine blast exposure levels. The following results were obtained: (a) design with honeycomb force limiter - peak z-axis pelvic acceleration was 191 m/s2, spine load was 5344 N, and Dynamic Response Index was 13.1 and (b) design with cable rope spring - peak z-axis pelvic acceleration was 179.2 m/s2, spine load was 5368 N, and Dynamic Response Index was 13.1. These levels are acceptable according to Army and NATO recommendations for the survivability of seated crewmembers exposed to a mine blast.