An Investigation into the Effects of Body-borne Equipment on Occupant Injury Under Simulated Vertical Impact with Seat 'Bottom-out'

Over recent years, military personnel have been required to carry increasing amounts of equipment, raising the overall mass of the occupant. A crashworthy seat is designed to a specified mass range, including equipment; and only provides energy absorption protection to the occupant within its designed mass and velocity range. If the increased mass causes the impact energy to be excessive, a phenomenon called bottoming out will occur when the seat stroking mechansim is exhausted and the occupant is exposed to excessive and likely injurous loads. In this study, an 8-degree-of-freedom mass-spring-damper system was modelled to represent an occupant with body-borne equipment and simulated under a crash test. Equations to represent a fixed load energy absorption device on a seat and a spring stiffness to characterize bottoming out were developed. The model was solved using the fourth-order-Runge-Kutta method in Matlab and the results indicate that with increased equipment mass, bottoming out will occur and the accelerations experienced by the occupant will increase significantly. This model can be used to analyse the loading affects at a number of locations on the occupant when experiencing bottoming out.