Wheel/Rail Friction RCFS TestingWritten by Ananyo Banerjee, Ph.D., Principal Investigator; Yuqing Zeng, Principal Investigator; Daniel Thielemier, Senior Engineer; and Xinggao Shu, Principal Investigator, MxV Rail
MxV RAIL R&D, RAILWAY AGE MARCH 2022 ISSUE: MxV Rail (formerly TTCI) conducted a series of full-scale wheel/rail (W/R) rolling contact tests using its Rolling Contact Fatigue Simulator (RCFS) to investigate the effects of lubricating media (water and solid lubricant) on rolling contact fatigue (RCF) and wear with controlled traction ratios.
The RCFS has the unique ability to perform lubrication studies with full-scale W/R rolling contact that permits the observation of surface damage along the entire surface of the rail head and a portion of the wheel tread surface. The simulator also allows the study of the use of lubricants in controlled amounts during actual W/R interaction, which is usually difficult to control precisely on tracks in revenue service due to wayside lubricating systems.
In this study, the RCF tests were conducted using a wheelset with newly trued Class C wheels running on a 10-inch-long test zone on the top of the rails with a nominal 36,000 pounds-force (36 kips) vertical load and 15-mrad angle of attack (AOA), resulting in an approximate 18-kip lateral contact force under dry conditions. Two sets of intermediate strength rails were used: new rails and rails with pre-existing RCF from an earlier test.
The 10-inch test zone was conditioned into two different levels of friction: a dry surface condition with no lubricant in the first half of the rail and a wet surface condition with water applied between the center and the end of the rail (Figure 1, above). During testing with a commercial solid lubricant, the dry, unlubricated contact zone had a traction ratio of 0.40 to 0.50, and the lubricated zone had a controlled traction ratio of about 0.20 to 0.25. The same wheelset was used for all tests, but rotated to expose an unworn portion of the tread for each additional test condition.
For the used rail with pre-existing cracks, the typical mean crack depth observed on the gage side of the rail in the solid lubricant zone was approximately one-third less than the mean crack depth on the same side of the rail in the dry, unlubricated contact zone. This trend showed opposite results from the tests using water lubrication where the cracks tended to be deeper and two to three times longer than the cracks in the dry contact zone.
In the two series of tests performed with either water or solid lubricant, it appeared that the solid lubricant may have helped slow down the crack growth in the used rail, while water accelerated the crack growth in the used rail. There was a difference between the two application mechanisms. For the tests done with water, the water was applied directly on half of the rail as shown in Figure 1 (above). For the tests with solid lubricant, the lubricant was applied to the wheel tread above the dry section, as shown in Figure 2.
In both cases where lubricant was used, the lubrication slowed the wear rate leading to more time for the surface rail cracks to experience more wheel loads before wearing away. Due to the effect of water and solid lubricants, W/R wear decreased by 50% to 70% compared to dry contact conditions. Competing mechanisms of rail wear and fatigue crack growth, which are also influenced by a variety of factors including rail metallurgy and lubricant/crack interaction, can be observed from the wear analysis and estimation of crack lengths.
The underlying mechanisms of RCF initiation and propagation and the influence of lubricants on wear and crack growth need to be investigated further. This research was funded jointly by the Federal Railroad Administration (FRA) and the Association of American Railroads (AAR) Strategic Research Initiatives (SRI) program.
- Cakdi, S. and H. Tournay, June 2017, “Modeling of Low Rail & Wheel Rolling Contact Stresses,” Technology Digest TD17-014, AAR/TTCI, Pueblo, Colo.
- Banerjee A., Y. Zeng, D. Thielemier, U. Spangenburg, and X. Shu, April 2022, “Investigation of Wheel-Rail Rolling Contact Fatigue Using Lubricating Media,” Technology Digest TD22-001, AAR/TTCI, Pueblo, Colo.