Experimental and fracture mechanics study of pit formation mechanism under rolling-sliding contact (Contact fatigue: Effects of reversal of rotation and exchange of driving and driven rollers)

Five rolling contact fatigue tests, Tests (1) to approximately (5) were conducted. In Tests (1) to approximately (3), in the first step, when a fatigue crack was initiated on the surface of a follower, the test was stopped. In the second step, the rotating direction was reversed in Test (1), the roles of follower and driver were exchanged in Test (2), and the same test as the first step was continued in Test (3). In Test (3) the original crack grew to a pit. On the other hand, in Tests (1) and (2) the original crack immediately ceased propagating. In Tests (4) and (5), mating with a harder roller, a softer roller was used as the follower in Test (4) and as the driver in Test (5). A typical arrowhead pit appeared in Test (4). In Test (5), however, surface damage substantially different from a typical pit was generated. Based on the experimental results, the mechanism of pit formation was analyzed by 3-D crack analysis, in which the effects of frictional force on contact surface and oil hydraulic pressure on crack surfaces were considered in particular.