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The changes in wheel-rail traction coefficients under wet and oil-contaminated rail surfaces are evaluated using the state-of-the-art Virginia Tech-Federal Railroad Administration (VT-FRA) roller rig. This one-fourth scaled test rig provides a controlled environment to measure real-time contact forces under pre-defined conditions. In addition, the rig is equipped with a high-precision fluid dispenser to apply the exact amount of fluids onto the rolling surfaces. Two series of experiments are conducted with water and oil applied individually at the wheel-rail contact with 0.02cc, 0.10cc, and 0.50cc, using a precise dispensing system at a low flow rate of 0.3cc/min, a medium flow rate of 1.5cc/min, and a high flow rate of 7.5cc/min, respectively. The tests include three or fewer cycles of water or oil applications for 4.1s under stable traction conditions. All other test conditions, including creepage, duration, and wheel load, are maintained unchanged throughout the tests, to focus on the effect of water on traction values. The results indicate a high correlation between the amount of water or oil applied to the surface and reduction in traction, in some cases for a short duration and in some over a long period of time. For low and medium flow rates of water, traction reduces immediately upon the application of water but recovers quickly after a short duration to nearly the same level as the dry condition. The duration of reduced traction is directly proportional to the volume of water. A distinctly different result is observed for oil. Even a small amount of oil (0.3cc/min) causes a significant reduction in traction that prolongs over an extended period of time. For the medium application of oil (1.5cc/min), traction remains low for a long period of time and only recovers to approximately 1/2 of the dry condition. For high oil application (7.5cc/min), traction remains extremely low (approximately 1/5 of dry condition) for the duration of the test and does not show any indication of recovery. Oil residue can be felt at the running surface when rubbing a finger over the roller surface. The results indicate that both water and oil cause a significant reduction in traction, with traction recovering to its dry level shortly after the source of water (i.e., rain) stops. When oil is applied to the rail, even a small amount can significantly diminish traction for a prolonged period of time. This is attributed to the possible seasoning of the rail due to oil.

This study presents an experimental study of the effect of Top-of-Rail Friction Modifiers (TORFM) in quantities ranging from a small to a large amount on the progression of wheel-rail wear, using the Virginia Tech-FRA (VT-FRA) roller rig. TORFM behaves as a third body layer in between the wheel and rail and is applied to reduce wheel and rail wear while preserving a stable traction condition. An added benefit of TORFM is that it is estimated that it can reduce fuel consumption by controlling friction, although we are not aware of any proven data in support of this. Although widely used by the U.S. Class I railroads, there exists no proven method for determining, qualitatively or quantitatively, how the amount of TORFM and rail/wheel wear are related. Simply put, would increasing TORFM amount by a factor of two reduce wheel/rail wear and damage by one-half? How would such doubling effect traction or the longevity of TORFM on the wheel/rail surface? In this study, the VT-FRA roller rig is used to perform a series of tests under highly controlled conditions to shed more light on answering these questions. A series of controlled experiments are designed and performed in order to investigate the potential factors that may influence the traction performance. The wheel surface profile is measured by a high-precision, 3D, laser profiler to measure the progression of wheel wear for the duration of the experiments. The results indicate that it takes as much longer time for the traction force (traction coefficient) to reach a condition that is the same as the unlubricated rail, when compared between lightly-, moderately-, and heavily-lubricated conditions. The results further indicate that wear generation is delayed significantly among all lubrication conditions — even, the lightly-lubricated — when compared with the unlubricated conditions. A further evaluation of the results and additional tests are needed to provide further insight into some of the preliminary results that we have observed thus far.

This paper provides a statistical analysis of the effects of wheel load, angle of attack (AoA), and creepage on longitudinal traction force at the wheel-rail contact using experimental data collected on the Virginia Tech-Federal Railroad Administration (VT-FRA) Roller Rig. The VT-FRA Roller Rig is a unique piece of equipment designed and built with the specific goal of evaluating the wheel-rail contact mechanics and dynamics with a high degree of precision. Longitudinal traction forces are of great importance to the railroad industry since they provide the motive power needed to move a train. Various experiments are conducted in different settings to study the relationship between the aforementioned variables and the longitudinal traction force. The test data is split into “training” and “testing” sets, and the training sets (a total of four) are used to entertain statistical models in a standard parametric regression framework. The study carefully assesses whether the assumptions of the classical linear regression model hold by studying the empirical histogram and the normal Q-Q plot of the residuals. In the case of non-linearities, different transformations are applied to the explanatory variable to find the closest functional form that captures the relationship between the response and the explanatory variables. The developed models are then compared with their non-parametric counterparts such as natural cubic splines in terms of goodness of fit, and prediction error on the testing set. The study develops regression models that are able to accurately explain the relationship between longitudinal traction and creepage and AoA. The models are intended to be used for predicting traction under various operating conditions.

The study provides an accurate measurement of the longitudinal and lateral traction under precisely controlled angles of attack conditions, using the Virginia Tech-Federal Railroad Administration roller rig (“VT-FRA roller rig”). The tests are performed under field-simulated conditions that allow wheel wear and accumulation of worn material at the running surfaces, with angles of attack (AOA) that represent both left- and right-hand curves. Because the roller rig allows testing under extreme conditions, AOAs as large as two degrees (0.035 radian) are evaluated for a scaled wheel with a nominal AAR-1B profile. It is observed that the longitudinal and lateral traction coefficients increase with increasing time, for all AOAs, but far more significantly for large AOA. The effect is nonlinear, meaning that for shallower (lower-degree) curves the friction effect is far less than for steeper (higher-degree) curves. It is further observed that the influence is asymmetric for right- and left-hand curves. The wheel taper introduces a lateral force that adds or subtracts (depending on the orientation of the curve) from lateral curving forces. The curving forces resulting from a positive AOA (corresponding to a left-hand curve) are less than those for negative AOAs, mainly due to the force offset due to the wheel taper.

The surface profile wear and the resulting third-body layer accumulation are investigated on the Virginia Tech-Federal Railroad Administration Roller Rig (VT-FRA Roller Rig), using a high-precision 3D laser profiler by Keyence. It is observed that the wheel surface gradually wears and the fine worn material accumulates on the running surfaces. It is further observed that with the progression of the wear and accumulation of a powder-like material at running surface, a preocular change in wheel-rail traction occurs. The first step in exploring the physics of the changes in traction is quantifying, precisely, the micron-sized surface finish changes and wear material accumulation. This paper provides the process of choosing a suitable surface profiler for the VT-FRA roller rig adaptation, and the results of a series of tests under various wheel load and contact configurations. A baseline experiment is conducted to evaluate the wheel wear and the accumulation of the naturally-generated third body layer (the worn material) on the wheel’s running surface. Before each series of experiments, the wheel and roller running surfaces were polished and thoroughly cleaned to make sure that they are perfectly smooth (finished) and free of any debris or dust. The wheel surface profile is measured in the perfectly cleaned condition using the 3D laser scanner. Time controlled experiments are run with different wheel loads, % slippage, and angle of attack (AoA) for 500 seconds. For each run, the change with surface finish and accumulated third body layer build up is measured. It is consistently observed that the traction forces increase gradually with time until they reach a stable level, presented by a plateau in the traction-slippage curves. The time to reach the plateau is directly related to wheel’s dynamic conditions including load, %slippage, and AOA. For some of the conditions, such as wheel load, the relationship is linear and for others (such as AOA) it is nonlinear. Concentrating on the analysis of the baseline results, it is observed that the change in surface finish and the third body layer that naturally accumulates at the running surface — hence, referred to as “natural third body layer” or “NTBL” — is directly correlated and somewhat linearly with NTBL and change in the running surface from smooth to rough. The correlation is most noticeable for the NTBL. With increasing NTBL, traction increases rapidly until the running surface is saturated with the accumulated wear material, presumably a ferrous oxide. There is far weaker correlation between the change in surface finish and traction variations. It is noticed that the surface finish continues to change beyond the time that the traction forces reach their plateau, and its effect remains far more gradual than NTBL.

This study evaluates the wheel-rail contact patch geometry of the VT-FRA roller rig, designed and commissioned at the Virginia Tech’s Railway Technologies Laboratory (RTL). Contact patch measurements are crucial for better analyzing the underlying factors that affect the wheel-rail interface (WRI) contact mechanics and dynamics. One of the challenges is in determining the size and pressure distribution at the contact patch, under various conditions. Although past studies have attempted to reach a method that can be used to make such measurements, more research is needed in reaching a practical and consistent method. This is particularly true for making the measurements under dynamic conditions. The use of pressure sensitive films was considered as the means for contact patch measurements on the VT-FRA rig, however, the thickness of the film influences the contact patch area and shape. This paper provides the results of the measurements with films with different range of pressure sensitivities. Three types of pressure-sensitive films are used under static conditions. The films are placed in between the wheel and roller in exact positions to enable comparing the test results for various wheel loads. The contact patch measured by the most sensitive film, which reacts to pressures as low as 0.5 MPa, provides the most accurate outline for the contact patch, although it does not provide the highest resolution for the pressure distribution. The other pressure-sensitive films that are used have a higher pressure range, with minimums of 49.0 MPa and 127.6 MPa. The relationship between the size of the contact patch and average contact pressure is evaluated as a function of the wheel load. The results indicate that with increasing wheel load, the size of the contact patch changes minimally, with the average pressure increasing in a nearly linear relationship to the wheel load as expected.

The increase of tank car trains carrying oil in North America has increased safety concerns especially with regards to transit through populated areas in the aftermath of the 2013 Lac-Mégantic accident. Among other things, this has further led to the desire to have accurate models to predict the dynamic behavior of tank cars for assessing derailment safety. In pursuit of this, the FRA has funded research to develop a tank car model which includes the behavior of the fluid inside tank cars, so that the resulting forces can be accurately depicted in multi-body dynamic modeling codes without the use of computational fluid dynamics. Prior analytical research on linear fluid sloshing has been adapted to create a mechanical model (pendulum–mass system) that estimates the lateral fluid motion and resulting forces which can be added to a dynamic model of the tank car. The developed model parameters are compared to other works in which mass and frequency parameters are derived. The model derivation, equations, and comparison to test data are included in this paper. Parametric results are provided showing trends associated with different levels of fluid fill.

A detailed description of the Virginia Tech-Federal Railroad Administration (VT-FRA) Roller Rig measurement capabilities, along with the efforts in establishing the accuracy, repeatability, and integrity of the results are presented. The results of a series of baseline tests are also documented in an effort to provide an indication of the type of experiments that can be achieved on the rig. The one-fourth scaled rig is intended to be used for evaluating wheel-rail contact mechanics and dynamics with a high degree of precision. The rail is represented by a roller with a diameter that is five times larger than the wheel, in order to maintain the contact ellipse distortion to less than 10 percent. The primary point of differentiation between this rig and others that have been used in the past or are presently in use is that it is able to measure the wheel-rail contact forces with far greater precision than achieved in the past. The rig is also designed such that it provides a high degree of repeatability in testing, often needed for performing design of experiments accurately. The VT-FRA rig is capable of precisely controlling the lateral positioning of the wheel and rail, rail cant angle, the wheel-rail angle of attack, and the speed of the roller and wheel independently. The latter is intended to provide precise control of the relative speed of the wheel and roller, which amounts to precisely controlling creepage. Beyond presenting the rig’s capabilities, the paper provides a discussion of the initial results from the commissioning of the rig. It is concluded that the rig is ready to be commissioned for studies that are of interest to the practitioners in the rail industry and scientists in the research community.

This paper is the first of a two-part series describing a research project, sponsored by the Federal Railroad Administration (FRA), to study the structural integrity of joint bars. In Part I of this series, observations from field surveys conducted on revenue service track are presented. Automated and visual inspections of rail joints were conducted to identify defective joint bars. Detailed information and measurements were collected at various joint locations. The survey team consisted of personnel from ENSCO, Inc. and Transportation Technology Center, Inc. (TTCI), working in cooperation with staff from participating railroads. Part II of this series describes the development of finite element analyses of jointed rail, which is being carried out by the Volpe National Transportation Systems Center (Volpe Center).

Vehicle/Track Interaction (VTI) Safety Standards aim to reduce the risk of derailments and other accidents attributable to the dynamic interaction between moving vehicles and the track over which they operate. On March 13, 2013, the Federal Railroad Administration (FRA) published a final rule titled “Vehicle/Track Interaction Safety Standards; High-Speed and High Cant Deficiency Operations” which amended the Track Safety Standards (49 CFR Part213) and the Passenger Equipment Safety Standards (49 CFR Part 238) in order to promote VTI safety under a variety of conditions at speeds up to 220 mph. Among its main accomplishments, the final rule revises standards for track geometry and enhances qualification procedures for demonstrating vehicle trackworthiness to take advantage of computer modeling. The Track Safety Standards provide safety limits for maximum allowable track geometry variations for all nine FRA Track Classes — i.e., safety “minimums.” These limits serve to identify conditions that require immediate attention because they may pose or create a potential safety hazard. While these conditions are generally infrequent, they define the worst conditions that can exist before a vehicle is required to slow down. To promote the safe interaction of rail vehicles with the track over which they operate (i.e. wheels stay on track, and vehicle dynamics do not overload the track structure, vehicle itself, or cause injury to passengers), these conditions must be considered in the design of suspension systems. In particular, rail vehicle suspensions must be designed to control the dynamic response such that wheel/rail forces and vehicle accelerations remain within prescribed thresholds (VTI safety limits) when traversing these more demanding track geometry conditions at all allowable speeds associated with at particular track class. To help understand the differences in performance requirements (design constraints) being placed on the design of passenger equipment suspensions throughout the world, comparisons have been made between FRA safety standards and similar standards used internationally (Europe, Japan, and China) in terms of both allowable track geometry deviations and the criteria that define acceptable vehicle performance (VTI safety limits). While the various factors that have influenced the development of each of the standards are not readily available or fully understood at this time (e.g., economic considerations, provide safety for unique operating conditions, promote interoperability by providing a railway infrastructure that supports a wide variety of rail vehicle types, etc.), this comparative study helps to explain in part why, in certain circumstances, equipment that has been designed for operation in other parts of the world has performed poorly, and in some cases had derailment problems when imported to the U.S. Furthermore, for specific equipment that is not specifically designed for operation in the U.S., it helps to identify areas that may need to be addressed with other appropriate action(s) to mitigate potential safety concerns, such as by ensuring that the track over which the equipment is operating is maintained to standards appropriate for the specific equipment type, or by placing operational restrictions on the equipment, or both. In addition to these comparisons, an overview of the new FRA qualification procedures which are used for demonstrating vehicle trackworthiness is provided in this paper. These procedures, which include use of simulations to demonstrate dynamic performance, are intended to give guidance to vehicle designers and provide a more comprehensive tool for safety assessment and verification of the suitability of a particular equipment design for the track conditions found in the U.S.

This study derives explicit analytical expressions for comparing contact patch dimensions and Kalker’s coefficients for a wheel moving on a roller and compares the results with a tangent track arrangement. The expressions suggest that full size roller rig will underpredict Kalker’s traction coefficients (creepage forces per unit creepage) by a factor that depends on the roller radius. Studying rail-wheel contact mechanics and dynamics in the field conditions can prove to be challenging due to the difficulties in adequately controlling the test conditions that can significantly affect the results, such as track irregularities, rail surface condition, etc. Roller rigs can prove to be a useful tool for such studies. One, however, must be careful when interpreting roller rig test results because of the differences in wheel-rail contact mechanics and dynamics between the track and the roller. The findings of this study, which are consistent with other studies’ conclusions, will allow researchers to relate results with field testing.