Experimental and Fracture Mechanics Study of the Pit Formation Mechanism Under Repeated Lubricated Rolling-Sliding Contact: Effects of Reversal of Rotation and Change of the Driving Roller

Abstract

Five rolling contact fatigue tests, Tests {1}–{5} have been conducted. In Tests {1}–{3}, when a fatigue crack was initiated on the surface of a follower, the test was halted. Then, in Test {1} the rotating direction was reversed. In Test {2} the follower and driver were interchanged, and in Test {3} the test was continued unchanged. In Test {3} the original crack grew to a pit. In Tests {1} and {2} the original crack immediately stopped 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 pit occurred in Test {4}. In Test {5}, surface damage substantially different from a typical pit was generated. Based on these experimental results, a 3-D crack analysis including the effect of frictional force on the contact surface and oil hydraulic pressure on crack surfaces, was conducted to elucidate the mechanisms of pit formation and surface damage in contact fatigue.

Modelling of Surface Crack Growth under Lubricated Rolling–Sliding Contact Loading

“…Kaneta and Murakami (1987) showed that cracks formed on the negative sliding surface grow faster than the cracks on the positive sliding surface. Murakami et al (1997) experimentally observed that cracks, whose length is longer than half Hertzian contact width, grow only on follower surface when crack is inclined at a small angle to the surface in direction of load movement and frictional forces are opposite to this direction (region of negative sliding). Negative sliding (regions a in Figure 4 for given rotation) is characteristic for rolling-sliding contact conditions in the tooth root contact area of a gear tooth.…”

“…Kaneta and Murakami (1987) experimentally showed that the lubricant hydraulic pressure on crack surfaces in rolling-sliding contact can cause steep crack propagation to the free surface, as it is shown in Figure 1. When the oil pressure action is absent, the crack stops growing (Murakami et al, 1997).…”

Surface and subsurface rolling contact fatigue characteristic depths and proposal of stress indexes

“…Murakami et al [47] investigated the S/R effect with a discs testing equipment. They confirmed that the microcracks initiate because of the shear stress, indeed the crack orientation was related to the sliding speed.…”

“…Way [43] was the first who obtained an experimental evidence of fluid pressurization enhanced pitting. After this initial experimental work, the pressurization mechanism was investigated (both experimentally and numerically) in many other papers [34,37,42,[44][45][46][47].…”

A coupled approach for rolling contact fatigue cracks in the hydrodynamic lubrication regime: The importance of fluid/solid interactions

“…Experimental and theoretical work carried out in the past three decades [2,[10][11][12][13][14][15] has led to the following theories on the role that the fluid may play in fatigue crack growth by: (i) reducing the friction between the crack faces [11] ("friction reduction" shear mechanism); (ii) applying direct pressure on the crack faces as fluid flows into the crack and becomes pressurized under the contact loading [3] ("hydraulic pressure" tensile mechanism); (iii) "fluid entrapment effect" [8] which causes a hydrostatic pressure build up at the crack tip (combined shear and tensile mechanism). Together with these three quasi-static mechanisms, a fourth mechanism has also been proposed, which is based on "the squeeze fluid layer" and therefore considers some of the transient effects which take place inside the cracks [1].…”