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

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

Observations of dry particles behaviour at the tyre/road interface

Previous studies highlighted that friction value measured on real road surface textures covered by particles depends on particle sizes. This paper focuses on identification of particles behaviours at the tyre/road interface in the presence of particles. Identification is made by visual observations through high-speed camera, focus-variation microscopy and Scanning Electron Microscopy on the contaminated surface as scratch analysis on the surface. Two particle types were collected into samples picked next to roads. They are composed of clay and quartz which have different behaviours at the interface and affect the friction. Clay has a lasting effect due to its adhesive behaviour. Quartz has a scratching and rolling behaviour and is quickly ejected to the contact area due to a pinching effect

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

Contribution to the Determination of In Vivo Mechanical Characteristics of Human Skin by Indentation Test

This paper proposes a triphasic model of intact skin in vivo based on a general phenomenological thermohydromechanical and physicochemical (THMPC) approach of heterogeneous media. The skin is seen here as a deforming stratified medium composed of four layers and made out of different fluid-saturated materials which contain also an ionic component. All the layers are treated as linear, isotropic materials described by their own behaviour law. The numerical simulations of in vivo indentation test performed on human skin are given. The numerical results correlate reasonably well with the typical observations of indented human skin. The discussion shows the versatility of this approach to obtain a better understanding on the mechanical behaviour of human skin layers separately

Modeling hydro-mechanical couplings between interstitial fluids and human skin soft tissues in vivo

La peau humaine est formée de cellules, de tissus et de systèmes circulatoires baignés par des fluides physiologiques interstitiels qui leurs apportent les nutriments et qui emportent les déchets. L'homéostasis est maintenue par les échanges continuels entre ces différentes entités. Ces échanges sont influencés par la réponse globale de la peau aux chargements extérieurs. La compréhension des mécanismes mis en ?uvre lors de ces échanges au niveau interstitiel est importante pour l'étude de l'évolution de la peau humaine in vivo. Ce papier propose une modélisation mathématique des flux de fluides interstitiels couplés à la réponse mécanique des tissus souples de la peau. Basé sur une approche phénoménologique thermo-hydro-mécanique et physico-chimique de milieu hétérogène (THMPC), le modèle tri-phasique de peau humaine in vivo considère la peau comme un milieu stratifié déformable comportant 4 couches, 4 solides dans la phase solide, 4 fluides interstitiels dans la phase fluide et un composé ionique. Dans chaque couche, le solide est décrit comme un solide linéaire élastique isotrope et le fluide interstitiel est supposé être un fluide visqueux newtonien. Une relation est élaborée pour estimer la pression du fluide interstitiel de chaque couche couplée au comportement mécanique dans la couche et entre les couches. Des simulations numériques d'essais d'indentation sur peau humaine in vivo sont présentées et comparées aux observations disponibles dans la littérature. L'étude conduit à l'estimation des paramètres mécaniques de chacune des couches de peau prenant en compte l'influence des flux des fluides interstitiels et du transport d'ions à travers ces couches

A comparative study of frictional response of shed snakeskin and human skin

Skin in biological systems, including humans, perform several synchronized tasks (mechanical, protec-tive, tactile, sensory, etc.). Tribological function is among skin tasks and may determine the survivabilityof many species. Cross comparison of tribological functional traits of skin of different species, albeit interesting, is rarely encountered, if at all exists, in tribology literature. One interesting example is that of snake and human skins. This skin pair was the subject of many studies for transdermal drug delivery. Results in that context concluded that snakeskin is highly compatible with human skin despite apparent differences in surface structure and topology. The reported compatibility raises curious question ofwhether there exists frictional or tribological compatibility between the two skins and if so, under what conditions, and which context. In this work, we report, for the first time in open literature, results of a comprehensive comparative investigation of shed snakeskin and human skin with respect to tribological behaviour. To this end, we compared the frictional response of shed skin obtained from P. regius and human skin from different anatomical sites, gender, and age. The results imply that, in essence, the mechanisms governing the friction response of human skin are common to snake skin despite difference in chemical composition and apparent surface structure. In particular, both skin types display sensitivity to hysteresis and adhesive dissipation. Human skin, however, being more sensitive to hysteresis than snakeskin. One interesting finding of the study is that the ratio of the coefficients of friction for snake and human skin, when sliding on the same interface, depends on the reciprocal of their respective moduli of elasticity