Brake Shoe Coefficient of Friction Variation

2009 ◽  
Author(s):  
Scott Cummings ◽  
Tom McCabe ◽  
Glenn Guelde ◽  
Dan Gosselin
Keyword(s):  
Coefficient Of Friction ◽  
Prevention Research ◽  
Brake Shoe ◽  
Test Matrix ◽  
Potential Source ◽  
Defect Prevention ◽  
Research Consortium

A series of dynamometer tests were conducted by the Wheel Defect Prevention Research Consortium (WDPRC) to quantify the amount of expected variation in brake shoe coefficient of friction (COF) and resulting wheel temperature throughout the life of an individual brake shoe. Variations in brake shoe COF within an individual railcar are one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. High friction composition and tread conditioning brake shoes were installed in the “as manufactured” condition with no wear-in or machining at the beginning of the test matrix which consisted of seventeen stop tests and twelve grade tests. For each brake shoe tested, the average COF and maximum wheel temperature were recorded during eleven identical light grade tests interspersed throughout the test matrix.

Brake Shoe Force Variation

2009 ◽  
Author(s):  
Scott Cummings
Keyword(s):  
Elevated Temperatures ◽  
Prevention Research ◽  
Brake Shoe ◽  
Potential Source ◽  
Temperature Detector ◽  
Defect Prevention ◽  
Force Variation ◽  
Freight Car ◽  
Research Consortium ◽  
System Designs

The Wheel Defect Prevention Research Consortium (WDPRC) has conducted a review and analysis of existing literature and existing data related to brake shoe force (BSF) variation in freight car brake rigging. This work was conducted to explore the sources of BSF variation, define the expected amount of BSF variation, and describe some of the existing brake system designs that may help reduce the amount of BSF variation. Wheel temperature is related to BSF due to the use of the wheel tread as a brake drum. Variation in BSF within a given railcar is one potential source of elevated wheel temperatures and thermal mechanical shelling (TMS) damage to the wheels. At elevated temperatures, wheels become less resistant to fatigue damage due to changes in the material mechanical properties and relief of beneficial residual stresses. Data recorded by a wayside wheel temperature detector shows that eliminating wheel temperature differences within individual cars could reduce the number of wheels reaching temperatures of concern for TMS by a factor of eight.

Service Wheel Temperatures and Car Condition in Relation to Thermal Mechanical Shelling

2008 ◽  
Author(s):  
Scott M. Cummings
Keyword(s):  
Real Time ◽  
Large Temperature ◽  
Prevention Research ◽  
Replacement Rate ◽  
Temperature Detector ◽  
Defect Prevention ◽  
Research Consortium ◽  
Possible Cause

The Wheel Defect Prevention Research Consortium (WDPRC) examined data from a wayside wheel temperature detector (WTD) located near the bottom of a grade in order to explore the root causes of hot wheels and thermal mechanical shelling. Not surprisingly, the data showed that most hot wheels, defined in this paper as a wayside WTD reading of 260°C (500°F) or greater, are found in trains descending the grade (descending trains), although they can be found in trains ascending the grade (ascending trains) as well. The majority of cars with hot wheels in ascending trains have the brakes applied at all wheel locations in the car, with unreleased or partially released hand brakes as a possible cause. While relatively few descending trains (15 out of 393) had many cars with hot wheels, these trains accounted for more than 20 percent of the descending cars with hot wheels, indicating that operational improvements could substantially reduce the quantity of hot wheels. Seventy-six percent of the descending cars with hot wheels had only a single wheel at or above 260°C (500°F). While the wheels in these cars are generally at higher temperatures than the wheels of other cars in the train, there were large temperature differences between individual wheel locations. Evidence of repeated hot wheel behavior was found in about 37 percent of the group of descending cars with hot wheels and about 20 percent of individual hot wheel locations. Two different car inspections were conducted based on the WTD data. First, a “near-real-time” inspection was conducted in which cars were quickly checked for obvious problems without removing them from the train. Next, an intensive inspection/test/teardown was conducted on bad actor cars, which showed repeated hot wheel behavior. Good actor cars, which repeatedly did not show hot wheels, were also present at the inspection/test/teardown for comparison. The cause of the hot wheels was not evident for the majority of cars at both inspections, however, bad actor cars were found to have twice the historical wheelset replacement rate of good actor cars.

Brake Shoes and Thermal Mechanical Shelling

2008 ◽  
Author(s):  
Scott M. Cummings ◽  
Tom McCabe ◽  
Dan Gosselin
Keyword(s):  
Test Results ◽  
Brake Shoe ◽  
Test Parameters ◽  
Defect Prevention ◽  
Potential Benefits ◽  
C 50 ◽  
Force Time ◽  
Research Consortium ◽  
Test Individual ◽  
Dynamometer Test

The Wheel Defect Prevention Research Consortium (WDPRC) conducted a review of existing brake shoe tests to explore the combinations of brake shoe force, time, and wheel/brake shoe coefficient of friction (COF) needed to achieve the temperatures of concern for thermal mechanical shelling (TMS). Data was found involving normally expected brake shoe forces applied to a dynamometer wheel and a variety of test parameters and procedures. All temperatures were measured using a sliding thermocouple pressed lightly against the wheel tread. All testing reported involved new brake shoes that may have different COF properties from used brake shoes. Tests included brake shoe tests conducted in accordance with the Association of American Railroads (AAR) M-926 specification, constant horsepower tests, and simulated stuck brake tests. Tread conditioning brake shoes were investigated, as well as high friction composition brake shoes. Findings from these tests include the following: • Tread conditioning brake shoes produced lower wheel tread temperatures compared to high-friction composition brake shoes. The magnitude of this difference varied depending on the test conditions; • In the dynamometer test most closely simulating revenue service conditions, 37 kW (50 hp) was required to heat wheels above 316°C (600°F); • Different models of high-friction composition brake shoes produced similar wheel temperatures under the parameters of the AAR M-926 tests. The range of average wheel temperatures produced by different models of high-friction composition brake shoes was only about 28°C (50°F) at any point during the test; • Individual brake shoes of the same model usually produced consistent results with respect to wheel temperature. Two exceptions to this statement were observed in the AAR M-926 test results. In a laboratory dynamometer test involving service damaged wheels, the WDPRC was unable to produce any measurable reduction in wheel tread defect size through the application of tread conditioning brake shoes. However, four service trials of tread conditioning brake shoes showed potential benefits in using tread conditioning brake shoes to reduce the number of wheelsets removed for tread damage.

Wheel Spalling Literature Review

2008 ◽  
Author(s):  
Scott M. Cummings ◽  
Cameron P. Lonsdale
Keyword(s):  
Literature Review ◽  
Analytical Model ◽  
Analytical Models ◽  
Prevention Research ◽  
Multiple Sources ◽  
Slide Test ◽  
Defect Prevention ◽  
Train Speed ◽  
Adhesion Level ◽  
Research Consortium

As a means of determining the conditions under which a patch of martensite (and eventually a spall) is formed on a wheel tread, the Wheel Defect Prevention Research Consortium (WDPRC) has conducted a review of wheel slide test reports and analytical models for the prediction of contact patch temperature due to wheel slide. The relative merits of the analytical models are discussed and applied to the known/assumed conditions, i.e., speed, axle load, and wheel/rail coefficients of friction (COF) for each of the wheel slide tests. The accuracy of the analytical models is evaluated with respect to test data under a variety of conditions from multiple sources. After selecting the most appropriate analytical model, wheel slide temperature predictions are given for empty cars at a variety of speeds and wheel/rail COF levels. It is concluded that the potential exists to create martensite on sliding wheels with almost any realistic combination of axle load, wheel slide duration, train speed, and wheel/rail adhesion level. Additionally, sources of wheel spalling are discussed with a focus on misapplied hand brakes and malfunctioning air brake systems. Multiple authors noted the presence of tread damage on one wheel of a wheelset with no damage at the corresponding circumferential location of the mate wheel. The accompanying theories to explain this seemingly counterintuitive finding are restated in this literature review. At the end of the paper, the actions of the WDPRC to reduce wheel spalling are briefly outlined.

Inspections of Tread Damaged Wheelsets

2008 ◽  
Author(s):  
Scott M. Cummings ◽  
Don Lauro
Keyword(s):  
Impact Load ◽  
Damage Mechanism ◽  
Location Data ◽  
Root Cause ◽  
Frequent Use ◽  
Crack Band ◽  
Defect Prevention ◽  
Research Consortium ◽  
High Level ◽  
Contact Position

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.

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

2008 ◽  
Author(s):  
Daniel H. Stone ◽  
Scott M. Cummings
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Contact Stress ◽  
Fatigue Cracking ◽  
Fatigue Tests ◽  
Operating Conditions ◽  
Defect Prevention ◽  
Class C ◽  
Research Consortium

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.

Prediction of Rolling Contact Fatigue Using Instrumented Wheelsets

2008 ◽  
Author(s):  
Scott M. Cummings
Keyword(s):  
Urban Areas ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
Rolling Contact ◽  
Data Set ◽  
Track Geometry ◽  
Defect Prevention ◽  
Leading Position ◽  
Research Consortium ◽  
Research Initiatives

The measured wheel/rail forces from four wheels in the leading truck of a coal hopper car during one revenue service roundtrip were used to by the Wheel Defect Prevention Research Consortium (WDPRC) to predict rolling contact fatigue (RCF) damage. The data was recorded in March 2005 by TTCI for an unrelated Strategic Research Initiatives project funded by the Association of American Railroads (AAR). RCF damage was predicted in only a small portion of the approximately 4,000 km (2,500 miles) for which data was analyzed. The locations where RCF damage was predicted to occur were examined carefully by matching recorded GPS and train speed/distance data with track charts. RCF is one way in which wheels can develop tread 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 is concerning pure RCF, without regard to temperature effects or wheel slide events. It is important that the limitations of the analysis in this paper are recognized. The use of pre-existing data that was recorded two years prior to the analysis ruled out the possibility of determining the conditions of the track when the data was recorded (rail profile, friction, precise track geometry). Accordingly, the wheel/rail contact stress was calculated with an assumed rail crown profile radius of 356-mm (14 inches). RCF was predicted using shakedown theory, which does not account for wear and is the subject of some continuing debate regarding the exact conditions required for fatigue damage. The data set analyzed represents the wheel/rail forces from two wheelsets in a single, reasonably well maintained car. Wheelsets in other cars may produce different results. With this understanding, the following conclusions are made. - RCF damage is predicted to accumulate only at a small percentage of the total distance traveled. - RCF damage is predicted to accumulate on almost every curve 4 degrees or greater. - RCF damage is primarily predicted to accumulate while the car is loaded. - RCF damage is predicted to accumulate more heavily on the wheelset in the leading position of the truck than the trailing wheelset. - No RCF damage was predicted while the test car was on mine property. - Four unique curves (8 degrees, 7 degrees, 6 degrees, and 4 degrees) accounted for nearly half of the predicted RCF damage of the loaded trip. In each case, the RCF damage was predicted to accumulate on the low-rail wheel of the leading wheelset. - Wayside flange lubricators are located near many of the locations where RCF damage was predicted to accumulate, indicating that simply adding wayside lubricators will not solve the RCF problem. - The train was typically being operated below the balance speed of the curve when RCF damage was predicted to occur. - The worst track locations for wheel RCF tend to be on curves of 4 degrees or higher. For the route analyzed in this work, the worst locations for wheel RCF tended to be bunched in urban areas, where tight curvature generally prevails.

How SIMS microscopy can be used in medicine

1992 ◽  
Vol 50 (2) ◽  
pp. 1602-1603
Author(s):  
Philippe Fragu
Keyword(s):  
Mass Spectrometry ◽  
Biomedical Applications ◽  
Secondary Ion Mass Spectrometry ◽  
Chemical Elements ◽  
Biological Applications ◽  
The Past ◽  
Potential Source ◽  
Secondary Ion ◽  
Chemical Integrity ◽  
Scientific Endeavour

The identification, localization and quantification of intracellular chemical elements is an area of scientific endeavour which has not ceased to develop over the past 30 years. Secondary Ion Mass Spectrometry (SIMS) microscopy is widely used for elemental localization problems in geochemistry, metallurgy and electronics. Although the first commercial instruments were available in 1968, biological applications have been gradual as investigators have systematically examined the potential source of artefacts inherent in the method and sought to develop strategies for the analysis of soft biological material with a lateral resolution equivalent to that of the light microscope. In 1992, the prospects offered by this technique are even more encouraging as prototypes of new ion probes appear capable of achieving the ultimate goal, namely the quantitative analysis of micron and submicron regions. The purpose of this review is to underline the requirements for biomedical applications of SIMS microscopy.Sample preparation methodology should preserve both the structural and the chemical integrity of the tissue.

Academic centers for prevention research: Making prevention a practical reality.

1991 ◽  
Vol 46 (5) ◽  
pp. 525-527 ◽  
Author(s):  
S. Price Connor ◽  
John R. Livengood
Keyword(s):  
Prevention Research ◽  
Practical Reality
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