WEAR THROUGH THE PLASTIC INTERACTION OF CYLINDRICAL ASPERITIES IN SLIDING

Wear under mild conditions is known to occur by the progressive extrus ion of thin silvers and their subsequent break-off. In an experiment o n a large scale model asperity, Kapoor and Johnson [Proc. R. Soc. Lond . 445, 367 (1994)] have found that the process of progressive extrusio n is driven by pummelling of the soft surface by the roughness of the harder surface. The case of pummelling by a hard surface with isotropi c roughness, i.e. in which the asperity crests may be considered hemis pherical, was analysed using the classical kinematical shakedown theor em and the ratchetting thresholds, i.e. the asperity contact pressure above which progressive extrusion of silvers takes place, were obtaine d. However, most bearing surfaces are machined by using turning and gr inding, which produces asperities which are elongated in the direction of machining rather than hemispherical as assumed by Kapoor and Johns on. In the present paper, we assume the hard surface to have such long asperities and analyse the process of pummelling. A striking feature of the results is that the shakedown limit and its dependence on the c oefficient of friction is not very sensitive to the detailed morpholog y of the contacting surfaces.