Investigation for small shear-mode fatigue cracks in bearing steels

Since flaking and spalling caused by rolling contact fatigue associate with a small crack,a special testing method and machine are required to study the small fatigue crack behavior undershear mode loading. It was found by authors that the behaviors of small shear-mode fatigue cracksfrom the inclusions and from the artificial defects could be successfully observed by applying thefully-reversed torsion coupled with static axial compressive stress. However, the servo-hydraulicfatigue testing machine is quite expensive for purchase and maintenance, and large installationspace is necessary for the hydraulic and cooling systems. Moreover, the presence of axialcompression significantly lowers the frequency of torsional loading, which consequently results inlow testing speed. In this study, a cost-effective, space-saving and high-speed fatigue testingmethod was newly proposed, and the shear-mode fatigue crack growth tests were carried out byusing the developed machine. Based on the obtained experimental data, the potential of the newtesting machine is discussed.