The role of adhesion in contact fatigue

Abstract

AbstractÐBy incorporating the eects 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. #

Ion implantation of titanium based biomaterials

“…In fretting fatigue there is contact between two surfaces, where small, oscillatory sliding displacements occur between the surfaces while one or both of the contacting surfaces could be subjected to fluctuating stresses. Considerable oxidation can occur in the presence of aggressive environments to cause wear and material removal at the fretted surface [125,126]. The problem of fretting is it increases tensile and shear stresses at the contact surface and generates flaws, which lead to premature crack nucleation [127].…”

Fatigue of Restorative Materials

“…Contact fatigue, such as that induced by cyclic loading of an indenter into the surface of a material, has also been used because of its perceived relevance for the study of wear processes. The indentation causes tensile stresses at the contact edges, which can lead to crack formation (Gioannakopoulos et al, 1999). This technique has been used with ceramic materials, where it is found that the damage mode depends on material microstructure; in homogeneous ceramics, a cone-shaped crack (Hertz crack) emanating from the circle of contact can ensue, while in heterogeneous ceramics, a diffuse damage zone driven by shear stresses forms underneath the indenter (Kim et al, 1999).…”

Life prediction of titanium and aluminum alloys under fretting fatigue conditions using various crack propagation criteria. Part 1. Experimental and calculation techniques

“…As an alternative to the above-described techniques based on the Rooke-Jones formula, the approach [36,37] based on analogy between the stress field in a half-plane close to the edge of flat rigid punch (Fig. 5a) and that at the tip of a crack growing from a V-notch ( Fig.…”

“…For comparative analysis of the Otsuka and Richard criteria applicability to the materials under study, we'll use one coordination system for assessment the crack deviation angle and therefore transform the respective criterial dependences (14)-(17) from the coordinate system (13) to system (4). This allows one to use the advantages of the approach [36,37] and to apply formulas (2) for unambiguous calculation of the global parameters K I and K II in a fictitious crack at the contact boundary, whereas the ratio K K II I is equal to the friction coefficient m. Thus, the initial crack direction will coincide with the contact surface, i.e., q j = . Then formulas (16) and (17) will be re-arranged in the coordinate system (4) in the following way:…”