Paper 45: Tribological Implications of Surfaces

Abstract

A major part of an engineer's concern with surfaces relates to their interaction within machine elements and to their degradation as a consequence of wear. Relevant work in this field is reviewed with particular reference to the Conference on Lubrication and Wear held at the Institution in September 1967.

Two important quantitative measures which relate surface finish with functional factors have been described. One, the Plasticity Index, relates the topographic with the material characteristics of a surface and is defined as follows:

where H = hardness, σ = standard deviation of asperity height distribution and β = asperity radius. γ₁ and γ₂ and E ₁ and E ₂ are the Poisson's ratios and moduli of elasticity of the materials of the two surfaces respectively. The other relates particularly to conditions of elastohydrodynamic lubrication and takes the form

where h = uniform macroscopic lubricant film thickness and σ₁ and σ₂ are the r.m.s. surface roughnesses of the two surfaces in contact respectively.