A B S T R A C T Flaking type failure in rolling-contact processes is usually attributed to fatigue-induced subsurface shearing stress caused by the contact loading. Assuming such crack growth is due to mode II loading and that mode I growth is suppressed due to the compressive stress field arising from the contact stress, we developed a new testing apparatus for mode II fatigue crack growth. Although the apparatus is, as a former apparatus was, based on the principle that the static K I mode and the compressive stress parallel to the precrack are superimposed on the mode II loading system, we employ direct loading in the new apparatus. Instead of the simple four-point-shear-loading system used in the former apparatus, a new device for the application of a compressive stress parallel to the pre-crack has been developed. Due to these alterations, mode II cyclic loading tests for hard steels have become possible for arbitrary stress ratios, including fully reversed loading (R = −1); which is the case of rolling-contact fatigue. The test results obtained using the newly developed apparatus on specimens made from bearing steel SUJ2 and also a 0.75% carbon steel, are shown.

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The influence of material factors, such as types of steels, steelmaking process, cleanliness, fiber orientation, forging ratio, subzero treatment upon rolling contact fatigue life, was investigated for rolling bearing steels produced recently. Rolling contact fatigue life of recent steels which have high cleanliness has increased remarkably, and the influence of fiber orientation or subzero treatment upon rolling contact fatigue life is negligible, contrary to previous steels. Rolling contact fatigue life levels of each type of steels tested under three different test conditions were described. Depending on test conditions, their rolling contact fatigue strengths relative to others differed significantly in some cases.

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