3-DIMENSIONAL FRACTURE-MECHANICS ANALYSIS OF PIT FORMATION MECHANISM UNDER LUBRICATED ROLLING-SLIDING CONTACT LOADING

The mechanism of so-called arrow headed pit formation on contact surfa ces under lubricated rolling-sliding cyclic contact loading was analyz ed by fracture mechanics. The stress intensity factors of Modes I, II and III for an arrow-headed crack were calculated by three-dimensional numerical analysis. The analytical results support the hypothesis tha t an arrow headed crack in pitting phenomenon first propagates in shea r mode, and that crack growth by tensile made follows due to a hydraul ic effect on crack faces by the oil that has penetrated into the crack . The analysis predicts that the values of contact pressure and fricti onal force dominantly determine the final surface apex angle of an arr ow headed crack. The shape of an arrow headed crack observed under ser vice loading is considered to be useful to estimate the operating cond itions in the service loading.