Wear by plastic ratchetting

Abstract

Wear debris in the form of thin platelets is observed in wear of sliding, rolling and eroding components. The paper discusses two mechanisms in which such platelets can be generated: (i) extrusion of material from below the contact into thin slivers which subsequently break off to provide lamellar wear debris, and (ii) fracture of a thin layer leading to delamination wear debris. Both these mechanisms are manifestations of plastic ratchetting of material in a thin sub-surface layer. The plastic deformation in one cycle can be small but over many cycles it accumulates to large values. It is driven by (i) stress concentration at the edges of the hard slider, (ii) roughness on the hard slider, which causes the high contact pressure at the taller asperities to transverse all over the surface, and (iii) erosion where instead of sliding contacts, impacting erodent subjects the sub-surface layer to high contact stresses. The paper describes these mechanisms and discusses the associated uncertainties in predicting accurately the wear rate.