Pii: S1359-6454(99)00312-2

ÐBy incorporating the e€ects of interfacial adhesion in the mechanics of rounded contact between two bodies, a new approach is proposed for the quantitative analysis of a wide variety of contact fatigue situations involving cyclic normal, tangential or torsional loading. In this method, conditions of ``strong'' and ``weak'' adhesion are identi®ed by relating contact mechanics and fracture mechanics theories. Invoking the notion that for strong and weak adhesive contact, a square-root stress singularity exists at the rounded contact edge or at the stick±slip boundary, respectively, mode I, II or III stress intensity factors are obtained for normal, sliding and torsional contact loading, accordingly. A comparison of the cyclic variations in local stress intensity factors with the threshold stress intensity factor range for the onset of fatigue crack growth then provides critical conditions for crack initiation in contact fatigue. It is shown that the location of crack initiation within the contact area and the initial direction of crack growth from the contact surface into the substrate can be quantitatively determined by this approach. This method obviates the need for the assumption of an arti®cal length scale, i.e. the initial crack size, in the use of known fracture mechanics concepts for the analyses of complex contact fatigue situations involving rounded contact edges. Predictions of the present approach are compared with a wide variety of experimental observations. # 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.