We find solutions that describe the levelling of a thin fluid film, comprising a non-Newtonian power-law fluid, that coats a substrate and evolves under the influence of surface tension. We consider the evolution from periodic and localized initial conditions as separate cases. The particular (similarity) solutions in each of these two cases exhibit the generic property that the profiles are weakly singular (that is, higher-order derivatives do not exist) at points where the pressure gradient vanishes. Numerical simulations of the thin film equation, with either periodic or localized initial condition, are shown to approach the appropriate particular solution.

To understand the lubrication-dominated permeation through a membrane, numerical simulations of permeation through a moving corrugated permeable membrane is carried out with a fully validated numerical method. Through comparisons between the numerical results and the results of an asymptotic analysis of permeate flux (under an infinitesimal permeability condition) using Reynolds lubrication equation, the effect of permeation on lubrication and its inverse effect (i.e., the dependence of permeation on lubrication) are discussed. The linear and non-linear dependences of the relaxation of the lubrication pressure due to membrane permeation are identified. The effect of the tangential component of the permeate flux is evaluated by a linear analysis, and the limitation of Reynolds-type lubrication is discussed.

A better knowledge of synovial fluid (SF) ultrastructure is required to further understand normal joint lubrication and metabolism. The aim of the present study was to elucidate SF structural features in healthy joints from three mammalian species of different size compared with features in biomimetic SF. High-resolution structural analysis was performed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) and environmental SEM/wet scanning transmission electron microscopy mode complemented by TEM and SEM cryogenic methods. Laser-scanning confocal microscopy (LCM) was used to locate the main components of SF with respect to its ultrastructural organization. The present study showed that the ultrastructure of healthy SF is built from a network of vesicles with a size range from 100 to a few hundred nanometers. A multilayered organization of the vesicle membranes was observed with a thickness of about 5 nm. LCM study of biological SF compared with synthetic SF showed that the microvesicles consist of a lipid-based membrane enveloping a glycoprotein gel. Thus, healthy SF has a discontinuous ultrastructure based on a complex network of microvesicles. This finding offers novel perspectives for the diagnosis and treatment of synovial joint diseases.

We describe possible solutions for a stationary flow of two superposed fluids between two close surfaces in relative motion. Physically, this study is within the lubrication framework, in which it is of interest to predict the relative positions of the lubricant and the air in the device. Mathematically, we observe that this problem corresponds to finding the interface between the two fluids, and we prove that this interface can be viewed as a square root of a polynomial of degree at most 6. We solve this equation using an original method. First, we check that our results are consistent with previous work. Next, we use this solution to answer some physically relevant questions related to the lubrication setting. For instance, we obtain theoretical and numerical results, which can predict the occurrence of a full film with respect to physical parameters (fluxes, shear velocity, viscosities). In particular, we present a figure giving the number of stationary solutions depending on the physical parameters. Moreover, we give some indications for a better understanding of the multi-fluid case.

A new technology for lubricating the work rolls during hot rolling has been successfullytested in the finishing mill of ArcelorMittal Dunkirk. This new technology allows sprayingvery low quantities of pure oil on the work rolls to reduce the rolling forces by up to20% and with an increased efficiency of 50% compared with emulsions. The lubricant was apure natural oil without any additives.

Cet article présente un modèle de lubrification mixte en conjonction avec une analyse du mouvement secondaire du piston. Certains paramètres influent ce genre de mouvement tel que l'élasticité de la jupe et la forme de son profil (plat ou bombé). Les résultats montrent que ces paramètres ont une grande influence sur les forces de frottement, et par conséquent, ils ont le potentiel pour optimiser la perte de puissance par frottement du piston.

The present paper investigates the modeling of counterformal elastohydrodynamic lubricated (EHL) contacts in multi-body system (MBS) environments. The aim is to obtain a representation of the dynamic behaviour of machine elements and characteristic values as the lubrication film thickness for lifetime calculations. Two contact models are presented for the study of cam-roller tappet and raceway-roller systems. The first model is a one-dimensional representation of the EHL contact behaviour. It is based on the calculation of the central lubrication film thickness by means of dimensionless values (functions of the operating conditions) and provides a simplified model of the mixed lubrication. The second one, still under development, investigates the modeling of 3D dry and lubricated contacts. The fluid-structure interaction is here fully considered and a discretised form of the contact problem is solved using an iterative algorithm. This paper proposes, in the latter case, some perspectives and a discussion of its implementation.

Nous proposons dans notre article, la confrontation entre un modèle de lubrification mixte et une étude expérimentale sur le comportement au frottement lubrifié d'une denture d'engrenage droit, effectuée sur un tribomètre pion disque. La configuration de la machine ainsi que les éprouvettes ont été adaptées pour l'étude du contact linéaire hertzien cylindre sur plan. Les travaux ont été menés sur quatre lubrifiants de différentes viscosités avec trois niveaux de pression. Les résultats montrent la convergence partielle ou totale entre le modèle et l'étude expérimentale.

Many processes in nature and technology are based on the static and dynamic properties of solid–liquid interfaces. Prominent examples are crystal growth, melting, and recrystallization. These processes are strongly affected by the local structure at the solid–liquid interface. Therefore, it is mandatory to understand the change in the structure across the interface. The break of the translational symmetry at the interface induces ordering phenomena, and interactions between the liquid's molecules and the atomically corrugated solid surface may induce additional ordering effects. In the past decade, new techniques have been developed to investigate the structural properties of such (deeply) buried interfaces in their natural environment. These methods are based on deeply penetrating probes such as brilliant x-ray beams, providing full access to the structure parallel and perpendicular to the interface. Here, we review the results of a number of case studies including liquid metals in contact with Group IV elements (diamond and silicon), where charge transfer effects at the interface may come into play. Another particularly important liquid in our environment is water. The structural properties of water vary widely as it is brought in contact with other materials. We will then proceed from these seemingly simple cases to complex fluids such as colloids.

Une procédure numérique est développée pour étudier les effets de la forme du raccordement rainure/coussinet (carrée, et arrondie avec différents rayons de courbure) d'un palier hydrodynamique sur le développement de l'écoulement, le débit et la distribution de la pression. Les équations bidimensionnelles de Navier-Stokes, écrites pour un écoulement laminaire d'un lubrifiant incompressible, sont résolues numériquement par la méthode des éléments finis en utilisant la méthode de chargement par incrémentation. La simulation numérique utilise la vitesse de l'arbre et la pression d'alimentation comme paramètres dynamiques, alors que le rayon de courbure de raccordement rainure/coussinet est utilisé comme paramètre géométrique. Le travail présenté dans cet article souligne que la pression d'alimentation, l'interaction de la couche de cisaillement avec l'écoulement dans la cavité et l'interaction du coussinet avec le domaine de la rainure à travers un raccordement carré ou arrondi influencent l'écoulement, aussi bien que la magnitude et le profil des pressions et des vitesses dans la rainure. Il est en particulier montré qu'un choix judicieux de profil de raccordement – à pression d'alimentation égale – permet de doubler l'apport de fluide frais dans le film lubrifiant.

Hydrostatic bearings working at high rotational speeds are usually designed as hybrid bearings. They benefit of a load carrying capacity at low or zero speed and of a reduced torque at high working regimes. Therefore they are provided with pockets or recesses fed via hydraulic restrictors. Modeling the flow in these pockets and its coupling with thin film in the bearing is not a straightforward task. Comparisons with experimental data have shown that the capacity of correctly predicting the bearing characteristics (mainly the dynamic coefficients) is influenced by the accurate modeling of the pressure pattern in the pockets. The present work presents typical recess pressure patterns and shows the way they can influence on the bearing characteristics.

The uppermost superficial surface layer of articular cartilage, the ‘lamina splendens’ which provides a very low friction lubrication surface in articular joints, was investigated using atomic force microscopy (AFM). Complementary specimens were also observed under SEM at −10 °C without dehydration or sputter ion coating. Fresh adult pig osteochondral specimens were prepared from the patellas of pig knee joints and digested with the enzymes, hyaluronidase, chondroitinase ABC and alkaline protease. Friction coefficients between a pyrex glass plate and the osteochondral specimens digested by enzymes as well as natural (undigested) specimens were measured, using a thrust collar apparatus. Normal saline, hyaluronic acid (HA) and a mixture of albumin, globulin, HA (AGH) were used as lubrication media. The surface irregularities usually observed in SEM studies were not apparent under AFM. The articular cartilage surface was resistant to hyaluronidase and also to chondroitinase ABC, but a fibrous structure was exhibited in alkaline protease enzymes-digested specimens. AFM analysis revealed that the thickness of the uppermost superficial surface layer of articular cartilage was between 800 nm and 2 μm in adult pig articular cartilage. The coefficient of friction (c.f.) was significantly higher in chondroitinase ABC and alkaline protease enzymes digested specimens. Generally, in normal saline lubrication medium, c.f. was higher in comparison to HA and AGH lubrication media. The role of the uppermost, superficial surface layer of articular cartilage in the lubrication mechanism of joints is discussed.