A. Benjamin Perlman

Train-to-Train Impact Test of Crash-Energy Management Passenger Rail Equipment: Structural Results

On March 23, 2006, a full-scale test was conducted on a passenger rail train retrofitted with newly developed cab and coach car crush zone designs. This test was conducted as part of a larger testing program to establish the degree of enhanced performance of alternative design strategies for passenger rail crashworthiness. The alternative design strategy is referred to as Crash Energy Management (CEM), where the collision energy is absorbed in defined unoccupied locations throughout the train in a controlled progressive manner. By controlling the deformations at critical locations, the CEM train is able to protect against two very dangerous modes of deformation: override and large scale lateral buckling. Frames from high-speed movies recorded at the train-to-train test of existing equipment and the train-to-train test of CEM equipment are included in this paper. In the train-to-train test of existing equipment at a closing speed of 30 mph, the colliding cab car crushed by approximately 22 feet. No crush was imparted to any of the trailing equipment. Due to the crippling of the cab car structure, the cab car overrode the conventional locomotive. The space for the operator’s seat and for approximately 47 passenger seats was lost. During the train-to-train test of CEM equipment, at a closing speed of 31 mph, the front of the cab car crushed by approximately 3 feet, and the crush propagated back to all of the unoccupied ends of the trailing passenger cars. The controlled deformation of the cab car prevented override. All of the crew and passenger space was preserved.

Evaluation of Rail Passenger Equipment Crashworthiness Strategies

Comparisons are made of the effectiveness of competing crashworthiness strategies—crash energy management (CEM) and conventional passenger train design. CEM is a strategy for providing rail equipment crashworthiness that uses crush zones at the ends of cars. These zones are designed to collapse in a controlled way during a collision, distributing the crush among the train cars. This technique preserves the occupied spaces in the train and limits the decelerations of the occupant volumes. Two scenarios are used to evaluate the effectiveness of the crashworthiness strategies—(a) a train-to-train collision of a cab-car–led passenger train with a standing locomotive–led passenger train and (b) a grade-crossing collision of a cab-car-led passenger train with a standing highway vehicle. The maximum speed for which all the occupants are expected to survive and the predicted increase in fatalities and injuries with increasing collision speed are determined for both train designs. Crash energy management is shown to significantly increase the maximum speed at which all the occupants could survive for both grade crossing and train-to-train collisions for cab-car–led trains, at the expense of modestly increasing the speeds at which occupants impact the interior in train-to-train collisions.

Train-to-Train Impact Test: Analysis of Structural Measurements

This paper describes the results of the train-to-train impact test conducted at the Transportation Technology Center in Pueblo, Colorado on January 31, 2002. In this test, a cab car-led train, initially moving at 30 mph, collided with a standing locomotive-led train. The initially moving train included a cab car, three coach cars, and a trailing locomotive, while the initially standing train included a locomotive and two open-top hopper cars. The hopper cars were ballasted with earth such that the two trains weighed the same, approximately 635 kips each. The cars were instrumented with strain gauges, accelerometers, and string potentiometers, to measure the deformation of critical structural elements, the longitudinal, vertical, and lateral car body accelerations, and the displacements of the truck suspensions. The test included test dummies in the operator’s seat of the impacted locomotive, in forward-facing conventional commuter passenger seats in the cab car and first coach car, and in intercity passenger seats modified with lap and shoulder belts in the first coach car. During the train-to-train test, the cab car overrode the locomotive; the underframe of the cab car sustained approximately 22 feet of crush and the first three coupled connections sawtooth buckled. The short hood of the locomotive remained essentially intact, while there was approximately 12 inches of crush of the windshield center post. There was nearly no damage to the other equipment used in the test. The measured response of the trains compare closely with predictions made with simulation models.Copyright

Analysis of Collision Safety Associated With Conventional and Crash Energy Management Cars Mixed Within a Consist

A collision dynamics model of a passenger train-to-passenger train collision has been developed to simulate the potential safety hazards and benefits associated with mixing conventional and crash energy management (CEM) cars within a consist. This paper presents a comparison of estimated injuries and fatalities for seven collision scenarios based upon the variable mix of conventional and CEM cars. Based on the analysis results, recommended car placement when mixing cars within a consist is identified. The model includes a 6 car cab car-led consist colliding with a 6 car locomotive-led stationary consist. The stationary consist is made up of all conventional cars. The moving consist has a variable mix of conventional and CEM cars. For comparison, the bounding scenarios are: - a moving consist with all conventional cars, and - a moving consist with all CEM cars. The collision speed ranges from 15 to 35 mph. Since the two car designs behave differently under impact conditions, there is a concern that there may be hazards associated with mixing the two designs in the same consist. In none of the cases evaluated is the mixed consist less crashworthy than the conventional consist. The modeling results indicate that the least crashworthy consists are ones in which a conventional cab car is leading any combination of vehicles. The conventional cab car incurs nearly all the damage and prevents trailing cars from participating in energy absorption, whether they are conventional or CEM. The most crashworthy consists are ones in which a CEM cab is leading. The CEM cab can absorb a significant amount of energy without intruding into the occupied volume. The CEM cab also allows trailing cars to participate in energy absorption, which provides further occupant protection. The recommended strategy for car placement is to put the CEM car(s) at the leading end(s) and the conventional car(s) at the trailing end or in the middle of the consist in push-pull operation. There is also significant benefit to placing the seats in the leading CEM car or two so they are rear-facing. Rear-facing seats can reduce the severity of secondary impact injuries because the occupant is already in contact with the seat in the direction of travel and does not develop a significant velocity relative to the seat.© 2003 ASME

Investigation of the Effects of Sliding on Wheel Tread Damage

Wheel tread spalling is the main source of damage to wheel treads and a primary cause for wheel removals from service. Severe frictional heating of the wheel-rail contact patch during sliding causes the formation of martensite, a hard, brittle microstructure. The martensite patches break away from the more resilient bulk of the wheel tread when subjected to contact loads, resulting in spall formation. Prolonged sliding allows a greater volume of wheel tread material to reach extremely high temperatures, which will lead to material ablation and the formation of a slid flat. Such flats are the cause of wheel impact loads, which are extremely damaging to truck components and rail. This paper outlines an approach developed to estimate the effects of sliding on wheel flat formation and the potential severity of spalling. The methodology is described and preliminary results are presented using an intentionally simplified idealization of the wheel-rail contact geometry. Material characterization (temperature-dependent properties and failure criteria) and management of model size are of equal importance to geometric fidelity and are the focus in the early stages of the development of the qualitative model present here.Copyright

Finite Element Estimation of the Residual Stresses in Roller-Straightened Rail

The purpose of this paper is to develop models to accurately predict the residual stresses due to the roller straightening of railroad rails. Several aspects of residual stress creation in rail due to roller straightening are addressed. The effect of the characteristics of the loads applied by the roller-straightener on the stress profile is examined. In addition, the analysis attempts to discern the relative influence of bending and contact on the residual stresses. The last goal is to determine how the heat treatment of rail alters the predicted roller-straightening residual stress field. The loads for the simulation are estimated from available data. To identify the most credible values, a baseline loading case is defined and modeled. These straightening loads are parameterized by considering alternative loading scenarios. Residual stresses and deformations are calculated using these loads. To separate the effects of bending and contact on the residual stress induced by the roller loads, each credible load case is analyzed with two models. One is a 2-dimensional generalized plane strain (GPS) model that accounts only for the flexural stresses. The other is a fully 3-dimensional analysis that includes roll-on-rail contact to make estimates of the true residual stress field. Comparison of the residual stress results from both models reveals the relative influence of local roll-rail contact and bending on the final profile. Comparison of the 2- and 3-dimensional residual stress results reveals that the magnitude of the contact loads is a decisive influence on the stress field, even in portions of the rail web located far from the contact interface. Therefore, it is critical to obtain accurate estimates of the straightening loads to make accurate roller straightening residual stress estimates. Heat treatment of the rail prior to roller straightening primarily affects the longitudinal residual stress in the web, causing a positive shift in the stress values.Copyright

Semi-Analytical Approach to Estimate Railroad Tank Car Shell Puncture

This paper describes the development of engineeringbased equations to estimate the puncture resistance of railroad tank cars under a generalized shell or side impact scenario. Resistance to puncture is considered in terms of puncture velocity, which is defined as the impact velocity at which puncture is expected to occur. In this context, puncture velocity represents a theoretical threshold limit. A given object striking the side of a tank car at an impact speed below the threshold velocity is not expected to penetrate the commodity-carrying tank. This definition for puncture velocity is similar to that for ballistic limit velocity, which is used to measure a target’s ability to withstand projectile impact in military applications [1]. The term “semi-analytical” is used to characterize the current approach in developing equations for shell puncture in order to distinguish the present work from the semi-empirical approach used previously to develop equations corresponding to head puncture. While several tests have been conducted to study tank car head puncture, only a limited number of tests have been performed to study tank car shell puncture. The semi-analytical approach employs a combination of three tactics to deal with the paucity of test data. The first tactic applies collision dynamics to derive an idealized relationship between impact speed and maximum force for a generalized tank car shell impact scenario. Specifically, the principle of conservation of energy is applied. The second tactic applies computational methods to simulate tank car shell impacts in greater detail. Specifically, finite element analysis is used to examine the force-deformation behavior of different tank car configurations under different loading conditions. Regression analyses are performed on the results of the detailed finite element results to develop best-fit curves to account for the effects of various factors such as shell thickness, tank diameter, internal pressure and indenter size. The third tactic is empirical, in which various factors are related to puncture force using empirical formulas that have been developed in research to examine impact resistance in pipeline applications. Results from applying the semi-analytical method to estimate shell puncture velocity are presented. Similarities and differences between the current method for shell puncture and the semi-empirical method for head puncture are discussed. In addition, results from sensitivity studies are presented to show the relative effect of different factors on estimated puncture velocity. These studies indicate that indenter size and internal pressure have the most significant effect on shell puncture velocity. Conversely, these studies indicate that tank diameter and ram car weight have a relatively weak effect on shell puncture velocity.

Deformation Behavior of Welded Steel Sandwich Panels under Quasi-Static Loading

For the past two decades, the Federal Railroad Administration (FRA) Office of Research and Development has sponsored research conducted by the Volpe National Transportation Systems Center (Volpe Center) in safety matters related to the transportation of hazardous materials by railroad tank cars. Recent research conducted by the Volpe Center has included the application of semi-empirical and computational (i.e., finite element analysis) methods to estimate the puncture resistance of conventional railroad tank cars under generalized head and shell impact scenarios. Subsequent work identified sandwich structures as a potential technology to improve the puncture resistance of the commodity-carrying tank under impact loading conditions. This paper summarizes basic research (i.e., testing and analysis) conducted to examine the deformation behavior of flat-welded steel sandwich panels under two types of quasi-static loading: (1) uniaxial compression; and (2) bending through an indenter. The objectives of these tests were to: (1) confirm the analytical and computational (i.e., finite element) modeling of sandwich structures, (2) examine the fabrication issues associated with such structures (e.g., material selection and welding processes), and (3) observe the deformation behavior and local collapse mechanisms under the two different types of loading. In addition, the uniaxial compression tests were performed to rank or screen different core geometries. Five core geometries were examined in the compression tests: pipe or tubular cores with outer diameters equal to 2, 3, and 5 inches; a 2-inch square diamond core; and a double-corrugated core called an X-core with a 5-inch core height. The compression tests showed excellent repeatability of structural (i.e., force-crush) response for panels with similar cores and welding. The 3-inch pipe core and the diamond core were selected as candidate cores for the next test series because they possess attributes of moderate strength and moderate relative density. In addition, force-crush curves calculated from finite element analysis were in reasonable agreement with the measured curves for all cores. Bend tests using a 12-inch by 12-inch indenter with 1-inch radius rounded edges were also conducted. The panels were simply-supported over 4-inch diameter rollers spanning 24 inches between the centers of the rollers. The bend tests included three variables: (1) core type (diamond core and 3-inch pipe core); (2) core orientation relative to the supports (cores running either parallel or perpendicular to the rollers used to support the panels); and (3) face sheet type (solid plates on both sides, strips used as face sheets on both sides, and a combination of solid plates and strips. Finite element analysis of the bend tests produced nearly identical shapes to the measured force-displacement curves.Copyright

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.