転がり疲労における表面起点型き裂の進展

抄録

This paper describes a mechanism of surface initiated crack growth in rolling contact fatigue. Experiments with epoxy resin disk specimens were carried out using a newly developed test rig for rolling contact fatigue. Rolling contact occurred between an epoxy resin disk of 100 mm dia. and steel disk of 290 mm dia. under normal force of 400 N/mm and tangential force of 40 N/mm. After rolling cycles of 2.4×10⁴, surface-initiated cracks were observed. The cracks initially grew along the radial direction up to depth of 2.8 mm, and propagated to the circumferential direction, which coincides with the direction of tangential force. By optical microscopic examinations, striation-like marks were observed on the radial crack surfaces and the striation spacing decreased with increasing crack length. Stress intensity factors K_I and K_II of a crack under rolling contact fatigue were analyzed by finite element method. When the crack length is short, the calculated value of stress intensity factor range ΔK₁ is larger than that of threshold stress intensity factor range ΔK_th for epoxy resin. It is shown that the cracks can propagate under mode-I mechanism. The crack growth transited from radial to circumferential direction was predicted by maximum circumferential stress around the crack tip.