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Title: Understanding application and tribological mechanisms of lubricants and friction modifiers in the wheel-rail interface
Author: Harmon, M.
ISNI:       0000 0004 7655 2020
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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A literature review that focussed on friction management products identified a number of areas that were lacking in research. These were that research generally focussed on one scale of test without considering how the results may be affected by changing the scale of the test/experiment. The other main conclusion was that whilst there was a large body of research that focussed on friction management product performance, relatively little considered how the product was applied to the wheel-rail interface and what happened once it was in it. Additionally, there was a lack of small-scale laboratory methods that were validated against full-scale and field data. This led to the following aims of the thesis: • Assessment of fundamental product properties and how they relate to product performance • Bench mark tests to assess performance based on available test platforms across a range of scales • Develop new test methods to assess product properties and product application in the field • Understand the transferability of laboratory results to the actual, real world contact and between different laboratory test scales. After analysing field operations, tackiness was chosen to focus on as an indicator of grease pick-up performance. A new test method was developed based on an existing tribometer. The method was able to differentiate between different greases, as well as changes in amount of tackifier additive present in the grease. Friction Modifiers (FM's) were also tested using the same procedure and ranked according to how tacky they were. Pick-up tests using a Scaled-Wheel Rig (SWR) showed that the ranking for tackiness was the same as the ranking for pickup. The tackier the FM or grease the greater the pick-up. Additionally, the ranking was the same when the test was repeated using a Full-Scale Test Facility (FSTF). This means that the ranking of pick-up was independent of slip, load and lateral displacement of the wheel. Carrydown tests of grease using the SWR were performed and showed that an applicator bar that gave more pick-up did not necessarily result in more carry-down. This is because where on the wheel the grease gets picked-up is equally important. If the grease is collected by the wheel near to the flange tip, it does not enter the contact and is wasted. These types of tests have not been done before and the fact that the same results are seen across the test scales shows that the small-scale tests can be used to predict performance in the field. This can lead to these tests being incorporated into standards or used in quality assurance procedures. The other main outcome of this work is that longitudinal vibration has been shown to change depending on grease presence and top-of-rail contamination. Grease affected the vibration in the 700-1200 Hz range, whereas contamination (by leaves or water) on top of the rail affected the vibration across the frequency range. Additionally, it was shown that the vibration dramatically increased depending on the amount of wheel sliding due to leaf contamination. This could lead to longitudinal vibration being used as a condition monitoring device in known problem areas as an early warning system, or near lubrication sites to monitor lubrication effectiveness. Additionally, it could be used to indicate carry-down distance of friction management products.
Supervisor: Lewis, Roger Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available