By incorporating the effects of interfacial adhesion in themechanics of rounded contact between two bodies, a new approach is proposedfor the quantitative analysis of a wide variety of contact fatigue situationsinvolving cyclic normal, tangential or torsional loading. In this method,conditions of "strong" and "weak" adhesion are identified by relating contactmechanics and fracture mechanics theories. Invoking the notion that for strongand weak adhesive contact, a square-root stress singularity exists at the roundedcontact edge or at the stick-slip boundary, respectively, mode I, II or III stressintensity factors are obtained for normal, sliding and torsional contact loading,accordingly. A comparison of the cyclic variations in local stress intensity factorswith the threshold stress intensity factor range for the onset of fatigue crackgrowth then provides critical conditions for crack initiation in contact fatigue. Itis shown that the location of crack initiation within the contact area and theinitial direction of crack growth from the contact surface into the substrate canbe quantitatively determined by this approach. This method obviates the need forthe assumption of an artifical length scale, i.e. the initial crack size, in the use ofknown fracture mechanics concepts for the analyses of complex contact fatiguesituations involving rounded contact edges. Predictions of the present approachare compared with a wide variety of experimental observations.
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