Interface roughness effect on friction map under fretting contact conditions

In many industrial applications where fretting damage is observed in the contact (e.g. rotor/blade, electrical contacts, assembly joint, axe/wheel, clutch) the external loadings or geometry design cannot be changed. Therefore, the surface preparation and finishing process become essential to control and reduce the damage caused by fretting. In this paper, the authors present the experimental study of the initial surface roughness and machining process influence on fretting conditions in both partial and full sliding regimes. Surfaces prepared by milling and smooth abrasive polishing processes have been analysed. The influence of roughness on sliding behaviour and analysis of friction have been reported. Also, the contact pressure influence and qualitative analysis of fretting wear scar have been presented

Frequency-based image analysis of random patterns: an alternative way to classical stereocorrelation

The paper presents an alternative way to classical stereocorrelation. First, 2D image processing of random patterns is described. Sub-pixel displacements are determined using phase analysis. Then distortion evaluation is presented. The distortion is identified without any assumption on the lens model because of the use of a grid technique approach. Last, shape measurement and shape variation is caught by fringe projection. Analysis is based on two pin-hole assumptions for the video-projector and the camera. Then, fringe projection is coupled to in-plane displacement to give rise to 3D measurement set-up. Metrological characterization shows a resolution comparable to classical (stereo) correlation technique (1/100th pixel). Spatial resolution seems to be an advantage of the method, because of the use of temporal phase stepping (shape measurement, 1 pixel) and windowed Fourier transform (in plane displacements measurement, 9 pixels). Two examples are given. First one is the study of skin properties; second one is a study on leather fabric. In both cases, results are convincing, and have been exploited to give mechanical interpretation

Preliminary Investigation of the Frictional Response of Reptilian Shed Skin

Developing deterministic surfaces relies on controlling the structure of the rubbing interface so that not only the surface is of optimized topography, but also is able to self-adjust its tribological behaviour according to the evolution of sliding conditions. In seeking inspirations for such designs, many engineers are turning toward the biological world to correlate surface structure to functional behavior of bio-analogues. From a tribological point of view, squamate reptiles offer diverse examples where surface texturing, submicron and nano-scale features, achieve frictional regulation. In this paper, we study the frictional response of shed skin obtained from a snake (Python regius). The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional response of snakes. The coefficient of friction depends on the direction of sliding: the value in forward motion is lower than that in the backward direction. In addition it is shown that the anisotropy of the frictional response may stem from profile asymmetry of the individual fibril structures present within the ventral scales of the reptil

Démystifier les douleurs ulnaires au poignet

Travail d’intégrationIntroduction : Les douleurs ulnaires au poignet ne sont pas rares et affectent une large gamme de la population allant des jeunes athlètes aux personnes âgées. Leurs physiopathologie, évaluation physiothérapique et traitement conservateur demeurent toutefois peu connus des cliniciens. Objectifs : L’objectif de ce travail consiste à préciser les structures et pathologies pouvant être responsables des douleurs ulnaires au poignet, répertorier les évaluations en physiothérapie et leurs qualités pour poser un diagnostic physiothérapique et recenser les traitements possibles ainsi que les données probantes disponibles en lien avec les diverses pathologies causant des douleurs ulnaires au poignet. Stratégie méthodologique : Recension des écrits dans les bases de données reconnues, les livres de référence et autres ressources électroniques. Résultats : Les douleurs ulnaires au poignet sont principalement causées par les lésions du complexe triangulaire fibrocartilagineux, les fractures, les instabilités, les atteintes arthritiques, les lésions tendineuses et les atteintes nerveuses. Le diagnostic est basé sur l’anamnèse, le subjectif et l’objectif, les imageries et les examens médicaux. Dans l’évaluation physiothérapique, l’anamnèse et les tests spécifiques représentent actuellement la meilleure façon de différencier les différentes pathologies. La prise en charge des douleurs ulnaires au poignet en physiothérapie, quant à elle, varie selon la pathologie en cause. L’éducation, les conseils et la modification des activités constituent les approches conservatrices les plus souvent préconisées. Conclusion : À ce jour, l’évaluation physiothérapique et les traitements conservateurs des douleurs ulnaires au poignet ont peu été explorés dans les écrits scientifiques. Il en résulte un manque de données probantes pour guider les cliniciens dans leur pratique

Energy efficiency optimization of engine by frictional reduction of functional surfaces of cylinder ring-pack system

International audienceFriction reduction, lower oil consumption, and limitation of greenhouse gases emissions are the chief objectives of the automotive industry in order to improve the environmental efficiency of vehicle engines.In this paper, a strategy for ring-pack friction reduction through cylinder liner finish optimization based on coupling instrumented honing experiments and numerical prediction of elastohydrodynamic friction is proposed.The results show that honed surfaces produced by fine abrasion by honing stones yield the optimal elastohydrodynamic friction. They also demonstrate the limitations of ISO 13565 standard roughness parameters in giving a complete description of the functional performances of cylinder surface finishes

Effect of particles' characteristics and road surface's texture on the tire/road friction

This paper presents a laboratory study to investigate the lubrication induced by particles deposited on road surfaces which is responsible for the increase of accidents at the first rain after a long dry period. Particles are extracted from sediments collected at a catchment area and characterized by their chemical composition and size distribution. Protocol to simulate the particle deposit on the road surface and their compaction by the traffic is described. The test program includes variables such as particle concentrations, particles' size fractions and surface textures. Dry friction tests are conducted using the Skid Resistance Tester which simulates the sliding friction between a rubber slider and the test surface. Friction is lowered when the surface is covered by particles, compared with a clean surface. Repeated passages of the slider induce an increase of friction coefficient until reaching a stable value. Particles' flows during a friction run are separated into those ejected from the sample, those stored by the surface macrotexture and those that stay on the test surface; this study demonstrated that the friction coefficient is closely related to the quantity of particles available on the test surface. SEM analysis shows on the other hand that these particles are mainly trapped by the surface microtexture. Similar behavior between fine particles and powder in terms of lubrication mechanisms is observed

Assessment of the in-plane biomechanical properties of human skin using a finite element model updating approach combined with an optical full-field measurement on a new tensile device

International audienceHuman skin is one of the most important organ of the body. The assessment and knowledge of its properties are very useful for clinical or cosmetic research. Many techniques are used to measure the mechanical properties of this organ, like suction, indentation, torsion or tension tests. The aim of this paper is to present a new device based on tension technique and combining mechanical and optical measurements. The whole procedure used to assess the displacement field as described, and first results of tests performed in vivo are shown