The effect of intermittent lubrication on the fatigue life of pearlitic rail steel in rolling-sliding contact

Abstract

Railway¯ange lubrication can be unreliable, resulting in intermittent rather than continuous lubrication. Twin-disc contact simulation tests were carried out to investigate the in¯uence of intermittent lubrication on rail steel fatigue life, using both a colloidal suspension of molybdenum disulphide in an oil carrier¯uid (similar to a commercial¯ange lubrication product) and water. A brief interruption of the lubricant supply during molybdenum disulphide lubrication produced rapid surface failure of the rail steel, which was followed by rapid contact fatigue crack growth upon reapplication of the lubricant. During water lubrication the interruption of the lubricant (water) supply did not produce such rapid crack growth. The results were found to be in qualitative agreement with the predictions of the three-mechanism model of rolling contact fatigue, which combines the mechanisms of ratchetting (accumulation of unidirectional plastic strain until the critical failure strain of the material is reached) and the fracture mechanics-based mechanisms of shear stress driven and tensile¯uid assisted crack growth. Analysis of the test results using this model revealed crack face friction to be an important factor controlling crack growth, which may be responsible for the difference in behaviour between contacts lubricated with the molybdenum disulphide-based lubricant and those lubricated by water.

The potential for suppressing rail defect growth through tailoring rail thermo-mechanical properties

“…For the left crack tip (Figure 4a), K I shows a rise with increasing crack size, but is small even for a 15mm crack. For comparison a threshold stress intensity factor of 6 MPa.m 1/2 for tensile growth of cracks in carbon steel is available from Otsuka et al [15] and has been applied in previous work on crack growth in rail steel [16,17]. The mode II data for the left crack tip (Figure 4b) shows much larger stress intensity factor values, but a low sensitivity to crack size of the total range during passage of the contact.…”

Rail surface fatigue and wear

“…This was not conducted for a railway application, but it did reveal the crucial involvement of fluids in the generation of cracks for this contact configuration. The effects of changes between lubricated and unlubricated contact were also investigated, and this has continued to receive attention since it is an inevitable aspect of rail operation (Tyfour et al, 1996;Fletcher and Beynon, 2000a). Way suggested that the lubricant acted as a hydraulic pressure transmitter in the manner of mechanism 2 in Fig.…”

Field and laboratory assessments of the friction coefficient at a railhead

“…The latter can occur due to leaking trains or lubricant deliberately applied at the wheel flange/rail gauge contact in sharp curves to prevent excessive wear, noise and rail corrugation. [1][2][3] The oil lubricant is supplied between the wheel and rail generally using mobile lubricators, wayside lubricators or on-board lubricators. High-viscosity liquids can form a film between the wheel and rail and this can reduce the levels of traction.…”

“…6 Additionally, contamination by oil can affect crack growth due to rolling contact fatigue in a similar manner as to water; if the lubricant is left on the rail then there may be sufficient time for the oil to seep into a crack before it is rolled over by the wheel. 2 The metro in Mexico City is extensively used: last year more than 1,600,000,000 journeys were made on this system. It has 226.48 km of track spread over 12 lines.…”