Particle extrusion in elastohydrodynamic line contacts: Dynamic forces and energy consumption

Abstract

The author’s model of particle entrapment and thermoviscoplastic indentation built and experimentally validated in recent publications is utilised to calculate the contact forces on ductile, isolated interference particles passing through elastohydrodynamic, rolling–sliding, line contacts. The model is detailed and enriched by supplementary equations. A parametric study deals with the effects of particle size and cold hardness, kinetic friction coefficient, rolling velocity and slide-to-roll ratio of the contact on the particle contact forces, mean friction coefficient, temperature, plastic work and power required to deform a particle, as well as on dent volume and plastic strain rates of the indented contact surfaces. A factual selection of optimal conditions and parameter values that minimise the disruption of a contaminated contact is thus greatly facilitated.

Particle Entrapment in Line Elastohydrodynamic Contacts and the Influence of Intermolecular (van der Waals) Forces

“…This is of great help in choosing a proper value for the "macroscopic" (Coulomb) coefficient of friction (µ 0 ) at points A and B in Figure 1. It is noted that past the pinch point, the dynamic coefficient of friction of a plastically deforming particle drops to very low values and bounces back near the entrance to the Hertzian zone [27]. However, what happens past the pinch point is obviously of no concern to this study.…”

“…Therefore, for most metals used in engineering applications, it is concluded that the magnitude of their elastic modulus per se is not influential in the process of particle entrapment. This conclusion exclusively concerns the momentary incident of particle pinching and not the subsequent deformation of the solids involved in the process [27] in the case the particle is indeed trapped. ) and the normalised fluid force (f-dashed lines with colours corresponding to those of g) (input data in Table 1).…”

“…According to the results of the experimentally verified, viscoplastic particle contact model of the author [27], the dynamic coefficient of friction at the instant of particle pinching is equal to the kinetic (lubricated) friction coefficient. By kinetic friction coefficient, we refer to that involving the lubricated contact of the particle with either surface 1 or 2.…”

“…Given that speed does not affect the net van der Waals force as already stated, the change of trend of the g-curve is solely attributable to the change in the reaction force N (Equation ( 30)) and, in particular, to the effect of the fluid force components F x and F z on N (Equation ( 27)). Recall that both fluid force components are strongly affected by speed; moreover, both tend to zero for small particles and their relative influence on N becomes critical, which can be realised by inspecting Equation (27).…”

Particle entrapment in elliptical, elastohydrodynamic, rough contacts and the influence of intermolecular (van der Waals) forces

“…Accordingly, μ (1) 0 = μ (2) 0 = μ 0 , where μ 0 is increased from 0.1 (boundary lubricated contact) to 0.4 (highly stressed, dry contact) as shown in Figure 6. In fact, through his analytical particle crashing model, 30 the author has shown that, at the critical moment of particle pinching, μ 0 is equal to the coefficient of kinetic friction for the greasy contact between the particle and a counter-surface (e.g. about 0.2 for steel counter-surfaces).…”