Michael Carolan

Evaluation of occupant volume strength in conventional passenger railroad equipment

To ensure a level of occupant volume protection, passenger railway equipment operating on mainline railroads in the United States must be designed to resist an 800,000-lb compressive load applied statically along the line of draft. An alternative manner of evaluating the strength of the occupied volume is sought, which will ensure the same level of protection for occupants of the equipment as the current test, but will allow for a greater variety of equipment to be evaluated. A finite element (FE) model of the structural components of a railcar has been applied to examine the existing compressive strength test and evaluate selected alternate testing scenarios. Using simplified geometric and material properties, a generic single-level railcar model was constructed that captured the gross behaviors of the railcar without excessive processing time. When loaded, the carbody structure exhibits some single beam-like behaviors. Application of the existing 800 kip compressive load results in a significant bending moment as well as significant compressive forces. The alternative load cases examined show that a larger total compressive force may be distributed across the end structure of the railcar and result in similar stress levels throughout the structural frame as observed from application of the conventional proof load.

STRATEGY FOR ALTERNATIVE OCCUPANT VOLUME TESTING

This paper describes plans for a series of quasi-static compression tests of rail passenger equipment. These tests are designed to evaluate the strength of the occupant volume under static loading conditions. The research plan includes a detailed examination of the behavior of conventional equipment during the 800,000-pound buff strength test. The research will also include a demonstration of an alternative static test that is designed to load and test the occupant volume at a location other than the buff lugs. The alternative test will demonstrate a testing and evaluation method for the occupant volume strength of passenger rail cars that accounts for the collision load path through the occupant volume. Per current Federal Railroad Administration (FRA) regulations, all passenger cars must support an 800,000-pound static load applied to the car’s line of draft without undergoing permanent deformation. However, more operators are looking to introduce equipment built to foreign standards. Many international manufacturers are implementing alternative designs that make use of crash energy management design features, articulated truck designs that span two cars, and low floor designs. These changes in the form and function of the designs require alternative means of applying a compressive load to assess occupant volume strength. FRA has reviewed several proposed alternatively designed equipment under requests for waivers for specific corridors of operation. Because the number of requests has increased significantly, FRA is trying to establish reasonable alternative means for assessing adequate and equivalent occupant volume strength to conventional equipment. This paper proposes an alternative static test procedure that will provide a means of evaluating a similar level of occupant volume integrity and passenger protection during a collision. The test will allow for greater design variation for newer rail cars and cars built to foreign standards. For the alternative test, the load may be introduced through the available structure at the floor level and at the roof level. These loading locations will enable the load to be applied directly into key longitudinal members in the load path of collision loads through the occupant volume. Finite element models are used before testing to determine appropriate alternative load levels and locations. The test article is a modified Budd Pioneer car. No significant modifications are planned for the longitudinal members of the car, or for the occupant volume.

FUEL TANK INTEGRITY RESEARCH: FUEL TANK ANALYSES AND TEST PLANS

The Federal Railroad Administration’s Office of Research and Development is conducting research into fuel tank crashworthiness. Fuel tank research is being performed to determine strategies for increasing the fuel tank impact resistance to mitigate the threat of a post-collision or postderailment fire. In accidents, fuel tanks are subjected to dynamic loading, often including a blunt or raking impact from various components of the rolling stock or trackbed. Current design practice requires that fuel tanks have minimum properties adequate to sustain a prescribed set of static load conditions. Current research is intended to increase understanding of the impact response of fuel tanks under dynamic loading. Utilizing an approach that has been effective in increasing the structural crashworthiness of railcars, improved strategies can be developed that will address the types of loading conditions which have been observed to occur in a collision or derailment event. U.S. rail accident surveys reveal the types of threats fuel tanks are exposed to during collisions, derailments and other events. These include blunt impacts and raking impacts to any exposed side of the tank. This research focuses on evaluating dynamic impact conditions for fuel tanks and investigating how fuel tank design features affect the collision performance of the tank. Research activities will include analytical modeling of fuel tanks under dynamic loading conditions, dynamic impact testing of fuel tank articles, and recommendations for improved fuel tank protection strategies. This paper describes detailed finite element analyses that have been developed to estimate the behavior of three different fuel tanks under a blunt impact. These analyses are being used to understand the deformation behavior of different tanks and prepare for planned testing of two of these tanks. Observations are made on the influence of stiffeners, baffles, and other design details relative to the distance from impact. This paper subsequently describes the preliminary test plans for the first set of tests on conventional passenger locomotive fuel tanks. The first set of tests is designed to measure the deformation behavior of the fuel tanks with a blunt impact of the bottom face of the tanks. The test articles are fuel tanks from two retired EMD F-40 locomotives. A blunt impact will be conducted by securing the test articles to a crash wall and impacting them with an indenter extending from a test cart. This set of tests is targeted for late summer 2013 at the Transportation Technology Center (TTC) in Pueblo, Colorado. Both blunt and raking impact conditions will be evaluated in future research. Tests are also being planned for DMU fuel tanks under dynamic loads.

Occupied Volume Integrity Testing: Elastic Test Results and Analyses

The Office of Research and Development of the Federal Railroad Administration (FRA) and the Volpe Center have been conducting research into developing an alternative method of demonstrating the occupied volume integrity (OVI) of passenger rail equipment through a combination of testing and analysis. This research has been performed as a part of FRA Office of Research and Development’s Railroad Safety Research and Development program, which provides technical data to support safety rulemaking and enforcement programs of the FRA Office of Railroad Safety. Previous works have been published on a series of full-scale, quasi-static tests intended to examine the load path through the occupant volume of conventional passenger cars retrofitted with crash energy management (CEM) systems. This paper reports on the most recent testing and analysis results. Before performing any tests of proposed alternative loading techniques, an elastic test of the passenger car under study was conducted. The elastic test served both to aid in validating the finite element (FE) model and to verify the suitability of the test car to further loading. In January, 2011, an 800,000 pound conventional buff strength test was performed on Budd Pioneer 244. This test featured arrays of vertical, lateral, and longitudinal displacement transducers to better distinguish between the deformation modes and rigid body motions of the passenger car. Pre-test car repairs included straightening a dent in one side sill and installing patches over cracks found in the side sills. Additionally, lateral restraints were added to the test frame due to concerns in previous tests associated with lateral shift in the frame. As a part of this testing program, a future test of a passenger car is planned to examine an alternative load path through the occupied volume. In the case of Pioneer 244, this load path places load on the floor and roof energy absorber support structures. Loading the occupant volume in this manner more closely simulates the loading the car would experience during a collision. FE analysis was used in conjunction with full-scale testing in this research effort. An FE model of the Pioneer car was constructed and the 800-kip test was analyzed. The 800-kip test results were then compared to the analysis results and the model was adjusted post-test so that satisfactory agreement was reached between the test and the model. In particular, the boundary conditions at the loading and reaction locations required careful attention to appropriately simulate the support conditions in the test. Because the 800-kip load was applied at the line of draft, this test results in significant bending as well as axial load on the car. To ensure that both the axial and bending behaviors are captured in the model, the key results that were compared between test and model are the longitudinal force-displacement behavior and the vertical deflections at various points along the car. The post-test model exhibited good agreement with the compared test results. The validated model will be used to examine the behavior of the occupant volume when loaded along the alternative load path.

Improved tank car design development : ongoing studies on sandwich structures

The Government and industry have a common interest in improving the safety performance of railroad tank cars carrying hazardous materials. Research is ongoing to develop strategies to maintain the structural integrity of railroad tank cars carrying hazardous materials (hazmat) during collisions. This paper describes engineering studies on improved tank car concepts. The process used to formulate these concepts is based on a traditional mechanical engineering design approach. This approach includes initially defining the desired performance, developing strategies that are effective in meeting this performance, and developing the tactics for implementing the strategies. The tactics are embodied in the concept. The tactics and concept evolve through engineering design studies, until a design satisfying all of the design requirements is developed. Design requirements include service, manufacturing, maintenance, repair, and inspection requirements, as well as crashworthiness performance requirements. One of the concepts under development encases the pressurized commodity-carrying tank in a separate carbody. Moreover, this improved tank car concept treats the pressurized commodity-carrying tank as a protected entity. Welded steel sandwich structures are examined as a means to offer protection of the commodity tank against penetrations from impacting objects in the event of a collision. Sandwich structures can provide greater strength than solid plates of equal weight. Protection of the tank is realized through blunting of the impacting object and absorption of the collision energy. Blunting distributes impact loads over a larger area of the tank. Energy absorption reduces the demands on the commodity tank in the event of an impact. In addition, the exterior carbody structure made from sandwich panels is designed to take all of the in-service loads, removing the commodity tank from the load path during normal operations. Design studies described in this paper focus on the protection aspect of using sandwich structures. Studies are conducted to investigate the influence of different parameters, such as sandwich height and core geometry, on the forcedeformation behavior of sandwich structures. Calculations are carried out numerically using nonlinear finite element analysis. These analyses are used to examine the crashworthiness performance of the conceptual design under generalized impact scenarios.

CRITERIA AND PROCEDURES FOR ASSESSING OCCUPIED VOLUME INTEGRITY

With the potential for tremendous growth in the passenger rail industry, providing for the safety of the train-riding public and the crews who transport them becomes an ever-greater priority. To provide for safety while making best use of its resources and to facilitate passenger rail industry growth, the Federal Railroad Administration (FRA), in consultation with the rail industry, has developed alternative Criteria and Procedures for assessing the crashworthiness and occupant protection measures of rail passenger equipment. These Criteria and Procedures are intended to be applicable to a wide range of equipment designs, particularly equipment designs not complying with current U.S. standards and regulations. Because the latest technology in rail equipment crashworthiness has been used to develop the Criteria and Procedures, aspects of the resulting Criteria and Procedures are fundamentally different from their corresponding regulations. While technical results from sophisticated analyses and tests have been necessary, judgment was also needed to develop the Criteria and Procedures. This judgment was provided by the Engineering Task Force (ETF), and ultimately accepted by FRA. The ETF is a government/industry working group, organized under the auspices of the Railroad Safety Advisory Committee (RSAC). The Criteria and Procedures are intended to provide an engineering-based methodology for comparing the crashworthiness of alternatively-designed equipment with that of compliant designs. One particularly important aspect of passenger car crashworthiness is occupied volume integrity (OVI). It is essential that all passenger vehicles meet some base minimum level of OVI. A primary goal of crashworthiness is to maintain a volume for occupants to ride out a collision. In the U.S., this base level has been demonstrated through a vehicle’s ability to react a quasi-static load of 800,000 pounds along its line of draft without experiencing permanent deformation. This car-level requirement has existed, in some form, since the early 20th century. However, alternatively-designed vehicles may not be able to demonstrate the ability to support this load, but may still prove to be equivalently crashworthy. Based on analyses performed on conventional and alternatively-designed passenger equipment, three options have been developed to demonstrate the OVI of alternatively-designed equipment. These options consist of three load magnitudes placed along the collision load path with a corresponding pass/fail criterion for each load. OVI may be demonstrated by sustaining an 800,000 pound load with no permanent deformation, a 1,000,000 pound load with limited permanent deformation, or a 1,200,000 pound load without exceeding the crippling load of the occupied volume. This paper discusses the pass/fail criteria associated with each option, the analysis and test procedures used in applying each option, and the technical basis used in developing the Criteria and Procedures for OVI evaluation. By applying such techniques, the results of evaluations of alternatively-designed equipment can be compared with the Criteria values for compliant designs. In this manner, the crashworthiness performance of alternatively-designed equipment can be assessed relative to the performance of compliant designs. A companion paper to this one discusses the development of the train-level Criteria and Procedures.© 2010 ASME

On Railroad Tank Car Puncture Performance: Part II - Estimating Metrics

This paper is the second in a two-part series on the puncture performance of railroad tank cars carrying hazardous materials in the event of an accident. Various metrics are often mentioned in the open literature to characterize the structural performance of tank cars under accident loading conditions. One of the consequences in terms of structural damage to the tank during accidents is puncture. This two-part series of papers focuses on four metrics to quantify the performance of tank cars against the threat of puncture: (1) speed, (2) force, (3) energy, and (4) conditional probability of release.In Part I, generalized tank car impact scenarios were illustrated. Particular focus is given to the generalized shell impact scenario because performance-based requirements for shell puncture resistance are being considered by the regulatory agencies in United States and Canada. Definitions for the four performance metrics were given. Physical and mathematical relationships among these metrics were outlined. Strengths and limitations of these performance metrics were discussed.In this paper (Part II), the multi-disciplinary approach to develop engineering tools to estimate the performance metrics is described. The complementary connection between testing and modeling is emphasized. Puncture performance metrics, which were estimated from other sources, are compared for different tank car designs. These comparisons are presented to interpret the metrics from a probabilistic point of view. In addition, sensitivity of the metrics to the operational and design factors is examined qualitatively.

Results of a Conventional Fuel Tank Blunt Impact Test

The Federal Railroad Administration’s Office of Research and Development is conducting research into passenger locomotive fuel tank crashworthiness. A series of impact tests is being conducted to measure fuel tank deformation under two types of dynamic loading conditions – blunt and raking impacts. This program is intended to result in a better understanding of design features that improve the puncture resistance of passenger locomotive fuel tanks. One reason for performing this program is to aid in development of appropriate standards for puncture resistance to be applied to alternativelydesigned fuel tanks, such as on diesel multiple unit (DMU) passenger rail equipment. This paper describes the results of the third blunt impact test of retired F-40 locomotive fuel tanks. The test setup was designed for the Transportation Technology Center (TTC) in Pueblo, Colorado, to impart blunt impacts to the bottom of each fuel tank specimen. The specimens tested to date are from FRA-owned retired F-40 passenger locomotives. To conduct the test, each tank was emptied of fluid and mounted on a crash wall with the bottom surface exposed. A rail cart modified with a “rigid” indenter measuring 12 inches by 12 inches, was released to impact the bottom of fuel tank at a target impact speed. The first two tests, conducted on October 8 and 9, 2013, were designed to impact the center of two different tank designs. Tests were conducted at impact speeds of 4.5 and 6.2 mph and caused maximum residual dents of 5 inches and 1.5 inches, respectively. On August 20, 2014 the test of fuel tank 234 was conducted to impact the tank off-center between two baffles. Forcedeformation measurements were collected for each tank during the three tests. The series of tests provide information regarding the influence of tank design on puncture resistance. In the test of tank 234, the target impact speed was 12.5 mph, and the actual impact occurred at 11.2 mph. The test resulted in a residual dent depth of approximately 9 inches, and buckling of several internal baffles. The impact did not result in puncture of the tank. Following the test, the tank was cut open to permit examination of the baffles. This examination revealed a different baffle geometry than was modeled based on pre-test measurements. Finite element analysis (FEA) was used to predict the behavior of the tank during the test. The FE model of the tank required several material properties to be defined in order to capture puncture behavior. The combination of metal plasticity, ductile failure, and element removal would permit the model to simulate puncture for this tank. Following the test, the tank was cut open, revealing a different baffle arrangement than had been initially thought. The post-test FE model was then updated to include the actual baffle arrangement of tank 234. With the actual baffle arrangement included in the model, the FE results are in fairly good agreement with the test. Additional changes to the ductile failure criterion were also made in the post-test model. The objective of this research program is to establish the baseline puncture resistance of current passenger locomotive fuel tanks under dynamic impact conditions and to develop performance requirements to ensure an appropriate level of puncture resistance in alternative fuel tank designs, such as DMU fuel tanks.

Fracture Mechanics and Beam Theory Analyses of Semi-Elliptical Cracks Originating in the Base of Rail

In May 2011, a derailment of a passenger train occurred in a tunnel in the northeast region of the United States. Fortunately, no serious injuries or fatalities resulted from this derailment. The probable cause of the derailment was determined to be a broken rail from a defect originating in the base of the rail. This internal rail base defect is characterized as having a crescent, thumbnail, or semi-elliptical shape. In addition, the formation and growth of this defect may have been exacerbated by corrosion.This paper describes engineering calculations to estimate the growth rate of this type of rail base defect. These engineering calculations are based on applying the principles of fracture mechanics and beam theory. Fracture mechanics principles are applied to determine stress intensity factors for the semi-elliptical shaped defect with different aspect ratios. Stress intensity factors are then used to estimate the growth of the defect under the accumulation of tonnage from repeated wheel passages. For this purpose, the rail is assumed to behave as a beam in bending.