A practical expression for evaluating the small shear-mode fatigue crack threshold in bearing steel

The ranges of the threshold stress intensity factor (SIF), ΔKIIth and ΔKIIIth, for small shear-mode cracks in bearing steel are measured using torsional fatigue testing under static compression. The threshold values are described as a function of the crack size and the crack-face interference. In addition, to simplify the evaluation of the shear-mode threshold, a single parameter, Kτ, is introduced to represent the SIF of shear-mode cracks. Moreover, a practical expression for approximating Kτ is proposed on the basis of the area parameter model. Finally, the threshold SIF range ΔKτth is found to exhibit a dependence on the crack size similar to that of small mode I cracks, i.e., ΔKτth ∝ (area)1/3, for the regime of small shear-mode cracks with area values ranging from 0.01 to 1 mm.