Benjamin Perlman

Impact tests of crash energy management passenger rail cars: analysis and structural measurements

Two full-scale impact tests were conducted to measure the crashworthiness performance of Crash Energy Management (CEM) passenger rail cars. On December 3, 2003 a single car impacted a fixed barrier at approximately 35 mph and on February 26, 2004, two-coupled passenger cars impacted a fixed barrier at approximately 29 mph. Coach cars retrofitted with CEM end structures, which are designed to crush in a controlled manner were used in the test. These test vehicles were instrumented with accelerometers, string potentiometers, and strain gages to measure the gross motions of each car body in three dimensions, the deformation of specific structural components, and the force-crush characteristic of the CEM end structure. Collision dynamics models were developed to predict the gross motions of the test vehicle. Crush estimates as a function of test speed were used to guide test conditions. This paper describes the results of the CEM single-car and two-car tests and provides results of the structural test. The single-car test demonstrated that the CEM design successfully prevented intrusion into the occupied volume, under similar conditions as the conventional test. During both CEM tests, the leading passenger car crushed approximately three feet, preserving the occupant compartment. In the two-car test, energy dissipation was transferred to the coupled interface, with crush totaling two feet between the two CEM end structures. The pushback of the couplers kept the cars in-line, limiting the vertical and lateral accelerations. In both the conventional tests there was intrusion into the occupant compartment. In the conventional two-car test sawtooth lateral buckling occurred at the coupled connection. Overall, the test results and model show close agreement of the gross motions. The measurements made from both tests demonstrate that the CEM design has improved crashworthiness performance over the conventional design.© 2004 ASME

Impact test of a crash-energy management passenger rail car

On December 3, 2003, a single-car impact test was conducted to assess the crashworthiness performance of a modified passenger rail car. A coach car retrofitted with a crash energy management (CEM) end structure impacted a fixed barrier at approximately 35 mph. This speed is just beyond the capabilities of current equipment to protect the occupants. The test vehicle was instrumented with accelerometers, string potentiometers, and strain gages to measure the gross motions of the car body in three dimensions, the deformation of specific structural components, and the force/crush characteristic of the impacted end of the vehicle. The CEM crush zone is characterized by three structural components: a pushback coupler, a sliding sill (triggering the primary energy absorbers), and roof absorbers. These structural mechanisms guide the impact load and consequent crush through the end structure in a prescribed sequence. Pre-test activities included quasi-static and dynamic component testing, development of finite element and collision dynamics models and quasi-static strength tests of the end frame. These tests helped verify the predicted structural deformation of each component, estimate a force-crush curve for the crush zone, predict the gross motions of the car body, and determine instrumentation and test conditions for the impact test. During the test, the passenger car sustained approximately three feet of crush. In contrast to the test of the conventional passenger equipment, the crush imparted on the CEM vehicle did not intrude into the passenger compartment. However, as anticipated the car experienced higher accelerations than the conventional passenger car. Overall, the test results for the gross motions of the car are in close agreement. The measurements made from both tests show that the CEM design has improved crashworthiness performance over the conventional design. A two-car test is performed to study the coupled interaction of CEM vehicles as well as the occupant environment. The train-to-train test results are expected to show that the crush is passed sequentially down the interfaces of the cars, consequently preserving occupant volume.

Development of Crash Energy Management Designs for Existing Passenger Rail Vehicles

As part of the passenger equipment crashworthiness research, sponsored by the Federal Railroad Administration and supported by the Volpe Center, passenger coach and cab cars have been tested in inline collision conditions. The purpose of these tests was to establish baseline levels of crashworthiness performance for the conventional equipment and demonstrate the minimum achievable levels of enhancement using performance based alternatives. The alternative strategy pursued is the application of the crash energy management design philosophy. The goal is to provide a survivable volume where no intrusion occurs so that passengers can safely ride out the collision or derailment. In addition, lateral buckling and override modes of deformation are prevented from occurring. This behavior is contrasted with that observed from both full scale tests recently conducted and historical accidents where both lateral buckling and/or override occurs for conventionally designed equipment. A prototype crash energy management coach car design has been developed and successfully tested in two full-scale tests. The design showed significant improvements over the conventional equipment similarly tested. The prototype design had to meet several key requirements including: it had to fit within the same operational volume of a conventional car, it had to be retrofitted onto a previously used car, and it had to be able to absorb a prescribed amount of energy within a maximum allowable crush distance. To achieve the last requirement, the shape of the force crush characteristic had to have tiered force plateaus over prescribed crush distances to allow for crush to be passed back from one crush zone to another. The distribution of crush along the consist length allows for significantly higher controlled energy absorption which results in higher safe closing speeds.Copyright

DESIGN OF A WORKSTATION TABLE WITH IMPROVED CRASHWORTHINESS PERFORMANCE

Work is currently underway to develop strategies to protect rail passengers seated at workstation tables during a collision or derailment. Investigations have shown that during a collision, these tables can present a hostile secondary impact environment to the occupants. This effort includes the design, fabrication, and testing of an improved workstation table. The key criteria for the design of this table are that it must compartmentalize the occupants and reduce the risk of injury relative to currently installed tables. Strengthening the attachments between the table and the passenger car body will ensure compartmentalization. Employing energy-absorbing mechanisms to limit and distribute the load imparted on the abdomen of the occupant will reduce injury risk. This paper details the design requirements for an improved workstation table, which include service, fabrication, and occupant protection requirements. Service requirements define the geometry of the table, the performance of the table under normal service loads, and the maintenance of the table over the period of installation. Fabrication requirements define the limitations on material usage and construction costs. Occupant protection requirements define the ability of the table to reduce injury risk to the occupants under collision loads. The table must also conform to federal regulations pertaining to interior structures on passenger rail equipment. Four design concepts are evaluated against these design requirements. These concepts present different modes of deformation or displacement that absorb energy during impact. These concepts have been evaluated, and the highest-ranking concept involves a crushable foam or honeycomb table edge attached to a rigid center frame. Preliminary results from a computer simulation demonstrate the effectiveness of this concept in reducing the injury risk to the occupants.Copyright

Rail car impact tests with steel coil: collision dynamics

Two full-scale oblique grade-crossing impact tests were conducted in June 2002 to compare the crashworthiness performance of alternative corner post designs on rail passenger cab cars. On June 4, 2002 a cab car fitted with an end structure built to pre-1999 requirements impacted a steel coil at approximately 14 mph. Following, on June 7, 2002 a cab car fitted with an end structure built to current requirements underwent the same test. Each car was equipped with strain gauges, string potentiometers and accelerometers to measure the deformation of specific structural elements, and the longitudinal, lateral and vertical displacements of the car body. The gross motions of the cars and steel coil, the force/crush behavior of the end structures, and the deformation of major elements in the end structures were measured during the tests. During the first test, the car fitted with the 1990s design end structure acquired more than 20 inches of longitudinal deformation causing failure at the corner post and resulting in the loss of operator survival space. During the second test, the corner post on the car fitted with the state-of-the-art design deformed longitudinally by about 8 inches, causing no failure and consequently preserving the survivable operator volume. In both cases, the steel coil was thrown to the side of the train after impacting the end structure. Prior to the tests, the crush behaviors of the cars and their dynamic responses were simulated with car crush and collision dynamics models. The car crush model was used to determine the force/crush characteristics of the corner posts, as well as their modes of deformation. The collision dynamics model was used to predict the extent of crush of the corner posts as functions of impact velocity, as well as the three-dimensional accelerations, velocities, and displacements of the cars and coil. Both models were used in determining the instrumentation and its locations. This paper describes the collision dynamics model and compares predictions for the gross motions of the cars and coils made with this model with measurements from the tests. A companion paper describes the car crush model and compares predictions made of car crush with measurements from the test. The collision dynamics was analyzed using a lumped-parameter model, with nonlinear stiffness characteristics. The suspension of the car is included in the model in sufficient detail to predict derailment. The model takes the force/crush characteristic developed in the car crush analysis as input, and includes the lateral force that develops as the corner post is loaded longitudinally. The results from the full-scale grade-crossing impact tests largely agree with and confirm the preliminary results of the three-dimensional lumped parameter computer model of the collision dynamics. The predictions of the model for the three-dimensional accelerations, velocities, and displacements of the car and the coil are in very close agreement with the measurements made in the tests of both cars, up to the time of failure of the corner post. The cars remained on the track in both tests, as predicted with the model.

A Collision Dynamics Model of a Multi-Level Train

In train collisions, multi-level rail passenger vehicles can deform in modes that are different from the behavior of single level cars. The deformation in single level cars usually occurs at the front end during a collision. In one particular incident, a cab car buckled laterally near the back end of the car. The buckling of the car caused both lateral and vertical accelerations, which led to unanticipated injuries to the occupants. A three-dimensional collision dynamics model of a multi-level passenger train has been developed to study the influence of multi-level design parameters and possible train configuration variations on the reactions of a multi-level car in a collision. This model can run multiple scenarios of a train collision. This paper investigates two hypotheses that could account for the unexpected mode of deformation. The first hypothesis emphasizes the non-symmetric resistance of a multi-level car to longitudinal loads. The structure is irregular since the stairwells, supports for tanks, and draglinks vary from side to side and end to end. Since one side is less strong, that side can crush more during a collision. The second hypothesis uses characteristics that are nearly symmetric on each side. Initial imperfections in train geometry induce eccentric loads on the vehicles. For both hypotheses, the deformation modes depend on the closing speed of the collision. When the characteristics are non-symmetric, and the load is applied in-line, two modes of deformation are seen. At low speeds, the couplers crush, and the cars saw-tooth buckle. At high speeds, the front end of the cab car crushes, and the cars remain in-line. If an offset load is applied, the back stairwell of the first coach car crushes unevenly, and the cars saw-tooth buckle. For the second hypothesis, the characteristics are symmetric. At low speeds, the couplers crush, and the cars remain in-line. At higher speeds, the front end crushes, and the cars remain in-line. If an offset load is applied to a car with symmetric characteristics, the cars will saw-tooth buckle.

Effectiveness of alternative rail passenger equipment crashworthiness strategies

Crashworthiness strategies, which include crash energy management (CEM), pushback couplers, and push/pull operation, are evaluated and compared under specific collision conditions. Comparisons of three strategies are evaluated in this paper: push versus pull operation (cab car led versus locomotive led consists); conventional versus CEM consists; and incremental CEM versus full-CEM. Rail cars that incorporate CEM are designed to absorb collision energy through crushing of unoccupied structures within the car. Pushback couplers are designed to recede into the draft sill under collision loads and enable the car ends to come into contact, minimizing the likelihood of lateral buckling. Push/pull operation refers to operating either a locomotive (pull mode) or a cab car (push mode) at the leading end of the train. Five cases using combinations of these three strategies are evaluated. The basic collision scenario for each case analyzed in this paper is a train-to-train collision between like trains. Each train has a locomotive, four coach cars, and a cab car. The impact velocity ranges from 10 to 40 mph. The following five cases are evaluated: (1) all conventional cars with a cab car leading (baseline case); (2) all conventional cars with a locomotive leading; (3) conventional coach cars with pushback couplers, with CEM cab car leading; (4) all CEM cars with a cab car leading: (5) all CEM cars with a locomotive leading. A one-dimensional lumped-mass collision dynamics model is used to evaluate the effectiveness of each strategy, or combination of strategies, in terms of preserving survivable space for occupants and minimizing secondary impact velocity (SIV). Test data is used to correlate SIV with head, chest, and neck injury. Probability of serious injuries and fatalities are calculated based on calculated car crush and injury values. The maximum crashworthy speed, or the maximum impact speed at which everyone is expected to survive, is calculated for each case. Of the five cases evaluated, the scenario of a cab car led conventional consist represents the baseline level of crashworthiness. The highest levels of crashworthiness are achieved by a consist of all CEM cars with a locomotive leading, followed by all CEM cars with a cab car leading. The results indicate that incremental improvements in collision safety can be made by judiciously applying different combinations of these crashworthiness strategies. A CEM cab car leading conventional cars that are modified with pushback couplers enhances the level of crashworthiness over a conventional cab car led consist and provides a level of crashworthiness equal to a locomotive leading conventional passenger cars

Development of a Standard for New Passenger Car Wheel Designs

The American Public Transportation Association (APTA) is seeking to develop specifications to ensure that wheels used in transit and commuter applications perform safely under the service conditions to which they are exposed. To this end, a design standard has been conceived to ensure that new wheel designs proposed for such applications are not susceptible to fatigue cracking in the wheel plate and hub. Historically, the Association of American Railroads (AAR) Standard S-660 has been applied in the industry for the purposes of qualifying wheel designs for use in passenger applications. The standard stipulates particular loads to apply in a simple finite element analysis of the new wheel design. The basis for approval is an empirical comparison (by an independent third party) of the results with those in a database of previous analysis results of other qualified wheels. The proposed “S-660 equivalent” design standard is envisioned to be self-qualifying, in that results of the analysis will directly determine whether the wheel design will perform safely in service; a review or approval body will not be required. The new standard is needed to overcome limitations embodied in the current wheel qualification process, namely, the assumption of purely elastic material behavior, the omission of residual stresses due to manufacturing, and the use of comparative approval criteria. The Union Internationale des Chemins de Fer (UIC) introduced a wheel design requirement based on finite element analysis, the results of which are subjected to a fatigue criterion in order to achieve acceptance of the wheel design. As in the current S-660 methodology, a set of thermal and mechanical loads are prescribed. This methodology is essentially self-qualifying as the results of the analysis (obtained following a prescribed procedure) determine whether the wheel design will perform safely in service. The proposed design standard is envisioned to be a combination of the current S-660 analysis requirements and the fatigue calculation-based approach of the UIC. The task force developing the standard is still resolving the specific details of the thermal and mechanical loading requirements. This paper explores the underlying methodology behind the developing standard. A finite element calculation forms the basis of the qualification procedure. Initial (asmanufactured) residual stresses present in a new wheel are determined. Mechanical and thermal loading representative of passenger operations are applied. The analysis yields three characteristic stress distributions: as-manufactured, mechanical, and thermal. The Sines criterion, with temperature-dependent material fatigue properties obtained from testing, is applied to infer whether the candidate wheel design is fatigue-prone. Results are presented for a wheel design currently in transit/commuter service. The APTA committee is currently investigating the thermal and mechanical load levels to be prescribed in the proposed standard.

Evaluating Abdominal Injury in Impacts with Workstation Tables

In rail passenger seating arrangements with workstation tables, there is a risk of serious thoracic and abdominal injury. Strategies to mitigate this injury risk are being developed through a cooperative agreement between the U.S. Federal Railroad Administration and the Rail Safety and Standards Board of the United Kingdom. The approach to developing the protection strategies involves collision investigations, computer simulations of the occupant response, and full-scale testing. During the train collision in Placentia, California, on April 23, 2002, many occupants hit workstation tables. The investigation indicated the likely modes of injury caused by the impact, the most traumatic being damage to the liver and spleen. A MADYMO computer simulation was created to estimate the loads and accelerations imparted on the occupants that brought about these injuries. Two experiments were designed and executed on a full-scale impact test with an occupant environment similar to the Placentia collision. These experiments incorporated advanced anthropomorphic test devices (ATDs) with increased abdominal instrumentation. The THOR (test device for human occupant restraint) ATD showed a more humanlike impact response than did the Hybrid III Railway Safety ATD. The full-scale test results are used to refine a MADYMO model of the THOR ATD to evaluate improved workstation tables. The occupant protection strategy that will be developed requires that the table remain rigidly attached to the car body and includes a frangible edge with a force-crush characteristic designed to minimize the abdominal load and compression. MADYMO simulations of this table design show a significantly reduced risk of severe abdominal injury.

Residual Stresses in Passenger Car Wheels

The purpose of this paper is to present the extension of previous studies aimed at understanding the residual stress distribution in as-manufactured railroad wheels. In order to address loading conditions which are not axially symmetric, a manufacturing simulation has been conducted with a 3-dimensional model. Results from the 2- and 3-dimensional models have been shown to be comparable. This agreement allows the manufacturing model to be integrated with other loading conditions such as contact. Manufacturing simulations using the 2D, axisymmetric model execute in about 50 minutes on a 2.8 GHz PC. Contact load simulations with the 3D model ran for about 60 hours on the same machine. An analysis methodology to estimate residual stresses in the wheel rim due to simulated wheel/rail contact was illustrated with a prototype calculation. A deformable representation of a portion of the rail was needed to capture the contact pressure distribution and patch size of the contact zone. The indenting rail was modeled with two regions. Load is applied to a rigid part. The second region is deformable. It acts to distribute the load as it forms a contact zone interacting with the surface of the wheel model. Initial manufacturing stresses were not considered in order to confirm the validity of the contact model. Previous work which attempted to develop residual stress estimates in wheels due to manufacturing and service conditions relied on a very simplified material model and crude means of accounting for contact pressure. An investigation of more realistic material models has also been conducted. While the as-manufactured residual stresses have not been included in the development work presented here, future efforts will concentrate on integrating the manufacturing, contact and thermal effects in a single model. Such a model is envisioned to form the basis for an analysis procedure for consideration as a replacement for the current AAR S-660 wheel design standard.