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

Railway flange lubrication can be unreliable, resulting in intermittent rat her than continuous lubrication. Twin-disc contact simulation tests were ca rried out to investigate the influence of intermittent lubrication on rail steel fatigue life, using both a colloidal suspension of molybdenum disulph ide in an oil carrier fluid (similar to a commercial flange lubrication pro duct) and water. A brief interruption of the lubricant supply during molybd enum disulphide lubrication produced rapid surface failure of the rail stee l, which was followed by rapid contact fatigue crack growth upon reapplicat ion of the lubricant. During water lubrication the interruption of the lubr icant (water) supply did not produce such rapid crack growth. The results w ere found to be in qualitative agreement with the predictions of the three- mechanism model of rolling contact fatigue, which combines the mechanisms o f ratchetting (accumulation of unidirectional plastic strain until the crit ical failure strain of the material is reached) and the fracture mechanics- based mechanisms of shear stress driven and tensile fluid assisted crack gr owth. Analysis of the test results using this model revealed crack face fri ction to be an important factor controlling crack growth, which may be resp onsible for the difference in behaviour between contacts lubricated with th e molybdenum disulphide-based lubricant and those lubricated by water.