Performance Efficiency of a Crash Energy Management System

Previous work has led to the development of a crash energy management (CEM) system designed to distribute crush throughout unoccupied areas of a passenger train in a collision event. This CEM system is comprised of crush zones at the front and rear ends of passenger railcars. With a consist made up of CEM-equipped cars, the structural crush due to a collision can be distributed along the length of the train, crushing only unoccupied areas and improving the train’s crashworthy speed as compared with a conventional train in a similar collision. This paper examines the effectiveness of one particular CEM system design for passenger rail cars. The operating parameters of the individual components of the CEM system are varied, and this paper analyzes the effects of these variations on the behavior of the consist during a collision. The intention is to determine what modifications to the components, if any, could improve the crashworthiness of passenger railcars beyond the baseline CEM design without introducing new hazards to passengers. A one-dimensional, lumped-mass model of a passenger train impacting a heavy freight train was used in this investigation. Using this model of a collision, the force-crush behavior for each end of each car in the impacting consist was varied. The same force-crush characteristic was applied to each car end on the passenger train. The four components of the CEM system investigated were the draft gear, pushback coupler, primary energy absorbers, and occupied volume of the train car. The paper presents selected parameters of particular interest, such as the strength ratio of the primary energy absorber to the pushback coupler and the average strength of the occupied volume. The objective of this work was to ascertain the sensitivities of the various parameters on the crashworthy speed and to help optimize the force-crush characteristic. This investigation determined that modifications could be made to the baseline characteristic to improve the train’s crashworthy speed without creating new hazards to occupants. INTRODUCTION The Federal Railroad Administration (FRA) has been conducting research on passenger rail crashworthiness for a number of years. This research has included crash testing of conventional rail vehicles [1, 2, 3], as well as the design, construction, and crash testing of prototypical crash energy management (CEM) vehicles [4, 5, 6]. This testing program has been designed to understand the behavior of passenger rail equipment in collision events so that strategies can be proposed to increase the safety of passengers involved in a rail collision. Since full-scale testing of railroad vehicles is costly, accurate computer models of both vehicle and passenger behaviors are desirable to simulate how rail vehicles will respond in various collision scenarios. Accurate models are also necessary to design further full-scale tests. In a collision involving a conventionally constructed passenger train, the front end of the colliding car is generally subject to the largest amount of structural crush, with a resulting loss of passenger volume [1]. An alternative strategy for passenger railroad crashworthiness, known as CEM, has been developed to improve the safety of passenger railcars. The CEM system relies on strategically placed crush zones to absorb the collision energy. With a consist made up of CEM-equipped cars, the structural crush can be distributed along the length of the train, preferentially crushing unoccupied areas of the individual railcars. Background North American passenger cars are designed with a stiff, strong underframe to prevent the occupied volume from crushing. Figure 1 shows a schematic plan view of a typical underframe construction in a conventional car [7]. The draft sill