An investigation into the contact between soft elastic and poroelastic bodies rotating under load

Abstract

This paper explores the contact of soft elastic and poroelastic bodies rotating under load and inspects the differences in load carrying capacity between the two types of material. Both materials have been widely used to describe the behaviour of biological systems such as articular cartilage in mammalian joints, however we demonstrate here that there are fundamental differences between the responses generated in which the poroelastic response has an additional fluid contribution to the solid structural response. In order to produce the same load carrying capacity it is shown that the poroelastic material must deform more than an incompressible soft elastic material with the same stiffness and that the solid load generated by a poroelastic material is the same as a soft elastic material with a zero Poisson's ratio.

A porohyperelastic lubrication model for articular cartilage in the natural synovial joint

“…Previous studies have explored this case by neglecting the volumetric contribution to strain energy in Eq. (2) and only considering deformation as a process which occurs under isochoric conditions [36]. Here the strain energy density is not limited in this way and α can take any value between 0 and 1, implying that any change in volume leads to both changes in the fluid phase and volumetric compression/expansion of the solid material itself.…”

“…It is of note from Table 3 that the geometry defined considers a 1 mm thick layer of articular cartilage rotating against a rigid impermeable surface under load. These values were chosen to best represent the material properties of articular cartilage and its operation in the natural synovial joint based on similar studies and experiments described in the literature [26,36]. The value chosen for the solid-on-rigid coefficient of friction is μ was selected based on experiments conducted considering dry cartilage against a hard metal surface under sliding conditions [2,46].…”

“…There have also been developments in creating finite element codes specifically built for biomechanics simulations and material characterisation [34]. There has been less attention focused on incorporating lubrication phenomena into these simulation [35,36]. These phenomena are necessary to determine the operating friction and the fluxes across the porous boundary.…”

Tribology and Dowson

“…In many cases, these stresses depend on surface coatings that are often used for a multitude of reasons such as wear-resistance, reduced friction, etc. Dowson was an early contributor to this area of research [10,48], advancing predictive methods for soft overlays in hip and knee joint prostheses [49,50] and for coatings in bearings and gears [51].…”

Compliant-poroelastic lubrication in cartilage-on-cartilage line contacts

“…While it is clear that the lubrication processes at the boundary is complex, it has been shown that the resulting friction coefficients from a cartilage-on-glass case form a Stribeck curve similar to those in non-porous materials [28]. Soft fluid-filled porous materials of this nature have been modelled by coupling the continuum mechanics that describe a compliant-poroelastic material with thin film theory to describe the lubricating boundary [29], [30]. Recently, this was expanded to include a Stribeck type analysis of a compliant-poroelastic (or porohyperelastic) material rotating against an impermeable surface to show that the lubrication modes (boundary, mixed and hydrodynamic) can be predicted at given operating conditions [31].…”