A new generalized philosophy and theory for rubber friction and wear

Abstract

The authors propose a new philosophy and theory for rubber friction and wear that are significantly different from the existing classical theories. Several distinctive features of rubber friction such as the exceedingly high friction coefficient and the intense stick-slip motion during frictional sliding all result from the sticky surface behavior exhibited by a cross-linked rubber, where there is a meniscus force brought about at the interface between the rubber and the rigid surface. The total friction coefficient μall incorporates three factors including an adhesion term μadh, a deformation term μdef and a crack formation term μcrac. This generates an equation μall =μadh +μdef +μcrac ≒ K1ηv[1+ K2 (tanδ2)+ 2Kεc) E-7/6 W1/6] where η is the viscosity of the uncross-linked phase, E the modulus of the cross-linked rubber, v sliding velocity, c crack length, W normal load, K1, K2, Kεare all coefficients whose characteristics also govern rubber wear. The adhesion term is the most dominant factor during rubber friction, which roughly contributes about 70–80% of the total friction coefficient according to a very rough estimation.The close relationships between the observed stick-slip motion, abrasion pattern formation and wear have been verified experimentally. The abrasion pattern is initiated by the high frequency vibration and the steady abrasion pattern together with steady wear is promoted by the stick-slip motion. Steady wear rate V˙ could be estimated theoretically as a function of the steady abrasion pattern distance Dab using an equation V˙ = k’Dab3, which indicates that many of the characteristics observed in rubber wear are also fundamentally governed by the intense stick-slip motion induced by the sticky rubber surface.