Overview No. 129 - Aspects of equivalence between contact mechanics and fracture mechanics: Theoretical connections and a life-prediction methodology for fretting-fatigue

We identify aspects of quantitative equivalence between contact mechanics and fracture mechanics via asymptotic matching. An analogy is invoked between the geometry of the near-tip regions of cracked specimens and that of the sharp-edged contact region between two contacting surfaces. We then demonstrate that the asymptotic elastic stress and strain fields around the rim of the contact region, as derived from classical contact mechanics analyses, are identical to those extracted from linear-elastic Fracture mechanics solutions for analogous geometries. Conditions of validity of this model for contact mechanics are established by recourse to the singular fields and small-scale-yielding concepts of Fracture mechanics. With this method. the geometry of the contact-pad/substrate system naturally introduces a fictitious crack length, thereby providing a physical basis to analyze contact-fatigue fracture initiation and growth. Possible extensions of this crack analogue model are then suggested, for situations where static or cyclic mechanical loads are superimposed parallel to the direction of interfacial friction, using the two-parameter fracture characterization that involves the stress intensity factor K and the non-singular T-stress, or alternatively, the J integral and the triaxiality parameter, Q. The predictions of the crack analogue model are then compared with fretting-fatigue experiments and are shown to be in agreement with a variety of independent experimental observations. A new life-prediction methodology for fretting Fatigue is also proposed on the basis of the present approach. (C) 1998 Acta Metallurgica Inc.