Sliding-Induced Rehydration in Hydrogels for Restoring Lubrication and Anticreeping Capability.

Fluid exudation in cartilage under normal loading can be counteracted by a sliding-induced rehydration phenomenon, which has a hydrodynamic origin related to a wedge effect at the contact inlet. Similar to cartilage, hydrogels also exhibit tribological rehydration properties, and we mimic this phenomenon to restore hydration lubrication and overcome creeping. It occurs within a specific velocity range and is mainly dependent on the applied load and hydrogel network structures.

Tailoring the Coefficient of Friction by Direct Laser Writing Surface Texturing.

The modification of the surface topography at the micro- and nanoscale is a widely established as one of the best ways to engineering the surface of materials, to improve the tribological performances of materials in terms of load capacity and friction. The present paper reviews the state of the art on laser surface texturing by exploiting the technique of direct laser writing for tailoring the coefficient of friction, highlighting the effect of the textures' arrangement on the lubricated conformal and non-conformal contact behavior.

Cartilage rehydration: The sliding-induced hydrodynamic triggering mechanism.

Loading-induced cartilage exudation causes loss of fluid from the tissue, joint space thinning and, in a long term prospective, the insurgence of osteoarthritis. Fortunately, experiments show that joints recover interstitial fluid and thicken during articulation after static loading, thus reversing the exudation process. Here, we provide the first original theoretical explanation to this crucial phenomenon, by implementing a numerical model capable of accounting for the multiscale porous lubrication occurring in joints.

Laser Microtextured Surfaces for Friction Reduction: Does the Pattern Matter?

Frictional performances of different textures, including axisymmetric and directional patterns, have been tested in the mixed and the hydrodynamic lubrication regimes. Experimental results, corroborated by numerical simulations, show that the leading parameter is the geometrical pattern void ratio since a large number of dimples offers, at low speed, a trap for debris whereas, at high speed, due to the flow expansion in each micro-hole, fosters a fluid pressure drop, the consequent insurgence of micro-cavitation and, ultimately, the reductions of the shear stresses. Furthermore, in this paper, it is shown that, by means of directional textures, equivalent hydrodynamic wedges can be built up, thus establishing different friction performances depending on the flow direction.

Friction in rough contacts of linear viscoelastic surfaces with anisotropic statistical properties.

Viscoelastic rheology can have great effects on the contact mechanics of randomly rough surfaces with anisotropic statistical properties. In this paper, we investigate such effects in the framework of Persson's theory. We calculate the forces that arise in viscoelastic contacts because of the viscous dissipation occurring in the bulk material.

Soft Matter Lubrication: Does Solid Viscoelasticity Matter?

Classical lubrication theory is unable to explain a variety of phenomena and experimental observations involving soft viscoelastic materials, which are ubiquitous and increasingly used in e.g. engineering and biomedical applications.

Viscoelastic Damping in alternate reciprocating contacts.

Reciprocating motion between viscoelastic solids occurs in a number of systems and, in particular, in all the dampers which exploits, as a physical principle, the viscoelastic dissipation. So far, any attempt to predict the behavour of this field of dampers relies on approximate methodologies and, often, on a steady-state approach, with a consequent poor understanding of the phenomenon. Here, we develop a methodology capable of simulating the actual mechanics of the problem and, in particular, we shed light on how the presence of not fully relaxed viscoelastic regions, during the punch motion, determine the viscoelastic dissipation.

Theory of reciprocating contact for viscoelastic solids.

A theory of reciprocating contacts for linear viscoelastic materials is presented. Results are discussed for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. Depending on the size of the contact, the frequency and amplitude of the reciprocating motion, and on the relaxation time of the viscoelastic body, we establish that the contact behavior may range from the steady-state viscoelastic solution, in which traction forces always oppose the direction of the sliding rigid punch, to a more elaborate trend, which is due to the strong interaction between different regions of the path covered during the reciprocating motion.

Equilibrium states and stability of pre-tensioned adhesive tapes.

In the present paper we propose a generalization of the model developed in Afferrante, L.; Carbone, G.; Demelio, G.