The Effects of Wheelset Position and Operating Environment on Rolling Contact Fatigue

The Wheel Defect Prevention Research Consortium (WDPRC) conducted analyses of wheel impact load detector (WILD) data to explore how wheelset position and operating environment affect rolling contact fatigue (RCF). The typical three-piece freight car truck used in North America produces higher tangential wheel/rail contact forces on the wheelset in the lead position than on the wheelset in the trail position of a truck as a car negotiates a curve. An analysis of WILD data shows that these higher forces are contributing to more shelling damage on wheelsets that are consistently in the lead position of a truck. Datasets in which the cars are frequently oriented with the A-end leading show the largest percentage of elevated WILD readings in the lead position of the lead truck (axle 4) followed by the lead position of the trail truck (axle 2). Likewise, datasets in which the cars are frequently oriented with the B-end leading show the largest percentage of elevated WILD readings in the lead position of the lead truck (axle 1) followed by the lead position of the trail truck (axle 3). Additionally, datasets in which there is an equal mix of car orientations show a much more evenly distributed location of elevated WILD readings. Another analysis of WILD data from five trainsets of nearly identical cars shows that any differences in wheel tread damage due to component differences are insignificant in comparison to the differences in wheel tread damage associated with environmental factors. While this analysis does not address component specification differences that could potentially have a large influence on shelling (such as M-976 trucks in comparison to standard trucks), it does show that environmental factors can play a large role in wheel tread damage. Car routing and loading characteristics were investigated as possible wheel damage factors. It appears that cars running on routes through terrain with longer, steeper grades may be prone to increased wheel shelling, probably due to thermal mechanical shelling (TMS). Side-to-side imbalanced loading appears to play a minor role in wheel shelling for two of the five trainsets.

Parametric Simulation of Rolling Contact Fatigue

Simulations of dynamic vehicle performance were used by the Wheel Defect Prevention Research Consortium (WDPRC) to explore which track and vehicle variables affect wheel fatigue life. A NUCARS® model was used to efficiently examine the effects of a multitude of parameters including wheel/rail profiles, wheel/rail lubrication, truck type, curvature, speed, and track geometry. Results from over 1,000 simulations of a loaded 1,272 kN (286,000-pound) hopper car are summarized. Rolling contact fatigue (RCF) is one way that wheels can develop treads defects. Thermal mechanical shelling (TMS) is a subset of wheel shelling in which the heat from tread braking reduces a wheel’s fatigue resistance. RCF and TMS together are estimated to account for approximately half of the total wheel tread damage problem [1]. Other types of tread damage can result from wheel slides. The work described in this paper concerns pure RCF, without regard to temperature effects or wheel slide events. Much work has been conducted in the past decade in an attempt to model the occurrence of RCF on wheels and rails. The two primary methods that have gained popularity are shakedown theory and wear model. The choice of which model to use is somewhat dependent on the type of data available, as each model has advantages and disadvantages. The wear model was selected for use in this analysis because it can account for the effect of wear on the contacting surfaces and is easily applied to simulation data in which the creep and creep force are available. The findings of the NUCARS simulations in relation to the wear model include the following: • Degree of curvature is the single most important factor in determining the amount of RCF damage to wheels; • The use of trucks (hereafter referred to as M-976) that have met the Association of American Railroads’ (AAR) M-976 Specification with properly maintained wheel and rail profiles should produce better wheel RCF life on typical routes than standard trucks; • In most curves, the low-rail wheel of the leading wheelset in each truck is most prone to RCF damage; • While the use of flange lubricators (with or without top of rail (TOR) friction control applied equally to both rails) can be beneficial in some scenarios, it should not be considered a cure-all for wheel RCF problems, and may in fact exacerbate RCF problems for AAR M-976 trucks in some instances; • Avoiding superelevation excess (operating slower than curve design speed) provides RCF benefits for wheels in cars with standard three-piece trucks; • Small track perturbations reduce the overall RCF damage to a wheel negotiating a curve.

Inspections of Tread Damaged Wheelsets

Inspections of 163 wheelsets conducted by the Wheel Defect Prevention Research Consortium (WDPRC) have produced critical information in identifying the high-level root causes of tread damage. While the overall wheel tread damage problem appears to be split fairly evenly between shelling and spalling, the type of tread damage on a wheelset is strongly linked to the type of car from which it was removed. Coal car wheels, which generally run in heavy axle load, high-mileage service with minimal yard handling, are almost exclusively subject to shelling damage with little spalling damage. On the other hand, mixed freight cars, such as tank cars and covered hopper cars, tend to run in lower mileage service with more yard handling, resulting in fewer loading cycles under lighter stress and more frequent use of hand brakes. Not surprisingly then, wheels from these types of cars were observed to have a mix of spalling and shelling damage, with spalling being the predominant damage mechanism. Nearly every high impact wheel (HIW) inspected showed either spalling, shelling, or some combination of the two. As expected, wheel impact load detector (WILD) readings and radial tread run out data were found to be related. Rim thickness deviations and rim lateral face deviations were not found to be important contributors to shelling. The lateral tread location of radial run-out deviations and crack bands could be an important clue in discovering the root cause of shelling. Radial run-out data and crack band location data shows that shelling damage is most prevalent outboard of the tapeline. This is the expected wheel/rail contact position of a wheel in the lead wheelset position of a truck, while riding on the low (inside) rail of a curve. Many of the wheels that were removed for wear causes were found to have noncondemnable shelling and spalling, indicating that tread damage is more prevalent than repair records would indicate.

Development and Fabrication of State-of-the-Art End Structures for Budd M1 Cars

The Volpe Center and the Federal Railroad Administration are engaged in active research aimed at improving rail vehicle crashworthiness. One component of this research is focused on improving the performance of passenger train cab cars during collisions with heavy objects at grade crossings. New standards have been approved by the American Public Transportation Association that increase the strength requirements for cab car end structures and impose further requirements on their ability to absorb energy during a collision. The FRA has issued a notice of proposed rulemaking (NPRM) to include these new standards in 49CFR238.211. These standards include requirements for demonstration of energy absorption through either quasi-static or dynamic tests. The intent of each test method is to demonstrate a minimum level of energy absorption—120,000 ft-lbs for a corner post load and 135,000 ft-lbs for a collision post load—while limiting occupied volume intrusion to less than 10 inches. To aid in the development of these new standards, the FRA and Volpe Center are conducting a set of three tests: quasi-static loading of both the collision and corner posts, and dynamic loading of the collision post only. (A dynamic test of the corner post was conducted as part of an earlier program). These tests were developed to illustrate testing methodologies and to demonstrate the feasibility of the new energy absorption and large deformation requirements. In+ each test, the post is loaded 30 inches above the underframe by a proxy object that is 36-inches wide, with a 48-inch diameter cylindrical face. In support of this testing program, the research reported here focused on the design and fabrication of end frames suitable for retrofitting onto the cab end of a Budd M1 cab car. The design of an end frame for retrofit onto the cab end of a Budd Pioneer cab car was modified to account for differences between the two car designs. In addition, reinforcements to the M1 car body and connections from the end frame to the car body were designed and fabricated. An FEA model of the end frame retrofit onto the M1 cab car was developed based upon the detailed design. A series of linear and nonlinear static, quasi-static, and dynamic FEAs were performed to evaluate the performance of the design. Preliminary analyses revealed the need for a few minor modifications to the connections in order to meet design requirements; these were incorporated into the final design for manufacture. Components for the end frame, connections between the end frame and the car body, and reinforcements to the car body were fabricated based on detailed design drawings and then assembled and connected to the reinforced M1 Car, from which the original end frame had been cut off. A successful dynamic test was completed in April, 2008; quasi-static tests are scheduled for summer 2008. The results of FEA model predictions are compared with the results of the dynamic test.

Improved System of a Braking Lever Transmission for Rail-Cars

Operating lifetime of rail-cars greatly depends on fitness of braking systems and on effectiveness of their constructions. Various braking systems are being elaborated in this trend where lever transmissions are used. Designing of a braking lever transmission for rolling stocks is a very urgent problem. A transmission should be simple and should contain minimum number of levers and hinges. Increased reliability and operating lifetime of braking lever transmissions for rail-cars are achieved in the work. A new construction of rail-car braking lever transmission is elaborated where number of levers and braking joints are decreased significantly and it ensures increase of traffic safety and economic efficiency. A calculating dynamic model of a new construction is elaborated in the work, which obey the basic provisions of mathematical analysis. Dynamical loads in joints of the construction are calculated taking into account increased wear and stresses. Accomplished work provides with possibility for solution of urgent problems. Introduction of the mentioned construction will significantly increase reliability and operating indices of modern rail-cars.

Effect of Residual Stress, Temperature and Adhesion on Wheel Surface Fatigue Cracking

The Wheel Defect Prevention Research Consortium (WDPRC) conducted an analysis pertaining to the fatigue cracking of wheel treads by incorporating the effects of residual stresses, temperature, and wheel/rail contact stress. Laboratory fatigue tests were conducted on specimens of wheel tread material under a variety of conditions allowing the analysis to properly account for the residual stresses accumulated in normal operating conditions. Existing literature was used in the analysis in consideration of the effects of contact stress and residual stress relief. This project was performed to define a temperature range in which the life of an AAR Class C wheel is not shortened by premature fatigue and shelling. Wayside wheel thermal detectors are becoming more prevalent on North American railroads as a means of identifying trains, cars, and wheels with braking issues. Yet, from a wheel fatigue perspective, the acceptable maximum operating temperature remains loosely defined for AAR Class C wheels. It was found that residual compressive circumferential stresses play a key role in protecting a wheel tread from fatigue damage. Therefore, temperatures sufficient to relieve residual stresses are a potential problem from a wheel fatigue standpoint. Only the most rigorous braking scenarios can produce expected train average wheel temperatures approaching the level of concern for reduced fatigue life. However, the variation in wheel temperatures within individual cars and between cars can result in temperatures high enough to cause a reduction in wheel fatigue life.

Wheel Spalling: Simulation of High Speed Wheel Slip

The Wheel Defect Prevention Research Consortium (WDPRC) conducted an analysis of the possibility of wheel spall creation under revenue service conditions when a car traverses perturbed and/or lubricated track with the brakes applied. When the brake retarding force acting on a wheelset is greater than the wheelset vertical load multiplied by the wheel/rail coefficient of friction (COF), the wheelset rotational speed will begin to decrease, because the braking force has exceeded the available wheel/rail traction. Due to its large rotational inertia, the wheelset will not immediately stop rotating. As the wheelset slows rotationally, a relative motion (slip) between the contact patch of the wheel and the rail will be introduced due to the continued forward motion of the vehicle. Any sliding action generates heat in the contact patch. If sufficient heat is generated, martensite can form and spalling problems can be initiated. However, as long as the wheelset is rotating, the contact patch is cooled by continually moving circumferentially around the wheel and the tread surface temperature is limited. A NUCARS® multi-body computer simulation model was used to determine wheel normal forces at a variety of speeds across perturbed track. The wheel slip rate was then calculated for each discreet output time step of the NUCARS model. The resulting wheel tread temperature due to the wheel slip was calculated. The predicted contact patch temperature was compared to the austenitic transformation temperature to form a prediction about whether or not martensite would be created. Based on the results of this analysis, it does appear to be possible to create martensite on the wheels of loaded cars under heavy braking while traversing track surface irregularities. However, most operating conditions would not provide the required conditions and this is probably not a major source of spalling.

Rail RCF and the Effects of Different Wheel Profiles

Wheel lateral profile has considerable effects on the wheel/rail dynamic interactions such as the shape and size of the contact area, instantaneous rolling radius and contact forces. Theses themselves have indirectly important roles on the rolling contact fatigue (RCF) which is known to be the main reason for large portion of rail maintenance costs. In this study the wheel/rail dynamic interaction of an Iranian railway passenger wagon under three different wheel profiles are investigated using ADAMS\Rail commercial simulation software. The dynamic simulation results regarding contact load and contact features of the wheel and rail are used for fatigue analysis to calculate RCF damage to the rail using reliable damage criteria reported in the literature. The two major parameters having serious roles on the RCF are believed to be the contact stress and the tangential force at the contact patch. These parameters are obtained from vehicle dynamic simulation studies. This paper describes and compares the effects of three different wheel profiles known as S1002, P8 and IR1002 on the rail RCF in both the curved and tangent sections of a track. The primary results clearly identify the effects of wheel profile on the RCF.

Finite Element Analyses of Railroad Tank Car Head Impacts

This paper describes engineering analyses of a railroad tank car impacted at its head by a rigid punch. This type of collision, referred to as a head impact, is examined using dynamic, nonlinear finite element analysis (FEA). Commercial software packages ABAQUS and LS-DYNA are used to carry out the nonlinear FEA. The sloshing response of fluid and coupled dynamic behavior between the fluid inside the tank car and the tank structure are characterized in the model using both Lagrangian and Eulerian mesh formulations. The analyses are applied to examine the structural behavior of railroad tank cars under a generalized head impact scenario. Structural behavior is calculated in terms of forces, deformations, and puncture resistance. Results from the two finite element codes are compared to verify this methodology for head impacts. In addition, FEA results are compared to those from a semi-empirical method.

Development of Residual Stresses in a Railroad Wheel Through Rim Spray Heat Treatment

Understanding how residual stresses develop during a typical rim spray quench and subsequent tempering operation is a fundamental objective necessary to gain knowledge of how wheels behave when under service loads. In this study, we have used specially modified and validated ANSYS software to calculate plastic deformations as they develop during the heat treatment process. Plastic deformations, including creep, were determined to follow stages which were both dependent on time of quench and depth from the taping line. Residual stresses developed from these deformations are also discussed.