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

WTC2005-64215 MULTI SCALE STUDY OF ABRASION SIGNATURE BY 2D WAVELET DECOMPOSITION

Abstract The high performance of industrial applications, requires increasingly technical functional surfaces, particulary from the point of view of topography and microtexture. To study the effect of abrasive finishing in a wide range of wavelengths of surface topography, we developed a multi-scale approach, based on the decomposition of surface topography by 2D continuous wavelet transform. This new approach made it possible to determine the multi-scale transfer function of machining by abrasion for each stage of finishing. The methodology can be extended to characterize abrasive wear in a wide range of scales. Introduction The use of hard turning as a finishing process is often limited by surface quality requirements in the case of component surfaces designed to support high stress. Low roughness can be achieved only at low feed rates. Moreover, tool wear leads to a deterioration in the surface after the tool has been in use for some time. A subsequent finishing operation can both increase the range of permissible feed rates towards higher values and prolong the life of the tool's cutting edge. One finishing operation whose working principle suits especially well for combination with hard turning is the belt grinding. This abrasive operation makes it possible to create surfaces of high quality, with specific functions like mechanical bearing pressure, sealing of metal joints, friction and noise of friction. Abrasive finishing modifies the surface topography in a wide range of scales of roughness and waviness, and consequently modifies the functionality of the surface in terms of bearing area, local plasticity and durability. This paper introduces a new approach based on a multi-scale decomposition of the surface topography before and after finishing by using a 2D continuous wavelet decomposition. This approach makes it possible to follow the effect of the various stages of finishing on a wide range of wavelengths, and makes it possible to determine th

Dissipation of vibration in rough contact

The relationship which links the normal vibration occurring during the sliding of rough surfaces and the nominal contact area is investigated. Two regimes are found. In the first one, the vibrational level does not depend on the contact area, while in the second one, it is propor- tional to the contact area. A theoretical model is proposed. It is based on the assumption that the vibrational level results from a competition between two processes of vibration damping, the internal damping of the material and the contact damping occurring at the interface

On Material Removal Regimes for the Shaping of Glass Edges: Force Analysis, Surface Topography and Damage Mechanisms

Glass shaping, which corresponds to the removal of the edges of a specimen, is the last finishing operation in glass manufacturing. This process has several functions on the final shaped glass including removing sharp edges, improving mechanical resistance, decreasing surface damage and giving it an aesthetical aspect. This article addresses the effects of working parameters, including grinding forces and consumed power, on surface edge finishing and damage mechanism induced during glass grinding. Microscopic observations and multi-scale analysis have also been conducted to investigate the surface edge characteristics. Experimental results show three damage regimes. The first (regime I) is a partial ductile regime with cutting action accompanied by chip formation. The second (regime II) is a crushing (or fragmentation) regime. The last (regime III) is also a partial ductile regime but by ploughing action with displaced material. The shaped surface obtained in the regime II has a better roughness than that obtained in regime I and III. However, regimes I and III include streaks and form defects which are not present in regime II. Similar to metallic materials, the evolution of force components show a linear relationship between normal and tangential forces. This implicates a constant average contact pressure and friction coefficient (l) between the flat grains and the workpiece

The role of tactile perception during stone-polishing in Aegean prehistory (5th–4th millennium B.C.)

International audienc

Analyse de la topographie des pièces de monnaie du San Pedro de Alcantara

La caractérisation des micro-reliefs de pièces de monnaie trouvées sur le site du naufrage du vaisseau de guerre espagnol San Pedro de Alcantara (1786) à son arrivée du Pérou hispanocolonial est placée dans le contexte méthodologique de l'analyse spatiale d'un site sousmarin de grande dispersion. L'analyse tribologique (étude quantitative du micro-relief) d'un lot de dix pièces d'argent a dégagé une grille classificatoire (corrosion piquage/corrosion érosion/stries d'abrasion, surface en plateaux). Inspirée des travaux de I. MacLeod sur des sites sous-marins côtiers, une relation entre la profondeur d'eau et deux paramètres de rugosité (SPvm - profondeur de la vallée moyenne de la rugosité - et SPtm (altitude moyenne pics vallées) a été observée sur deux lots, respectivement de trois et quatre pièces, classés selon le type de micro-relief. L'analyse tribologique d'une pièce d'or trouvée sur le site du naufrage à proximité de la zone dite "d'impact" a porté sur les zones d'actions mécaniques observables sur le micro-relief de la pièce. Les propriétés multi-échelles de l'analyse tribologique conduisent à souligner le potentiel de l'étude quantitative de la rugosité appliquée à la topographie du site sous-marin lui-même et à son croisement avec l'analyse de dispersion des artefacts.A caracterização dos microrrelevos das moedas encontradas no sítio do naufrágio do navio de guerra espanhol San Pedro de Alcantara (1786) à sua chegada do Peru hispano-colonial é colocada no contexto metodológico da análise espacial de um sítio submarino de grande dispersão. A análise tribológica (estudo quantitativo do microrrelevo) de um lote de dez moedas de prata permitiu elaborar uma grelha de classificação (corrosão por picotado (piquage)/corrosão erosão/estrias de abrasão/superfície em planaltos). Inspirada nos trabalhos de I. McLeod em sítios submarinos costeiros, uma relação entre a profundidade da água e dois parâmetros de rugosidade (SPvm - profundidade do vale médio da rugosidade - e SPtm - altitude média dos picos e vales) foi observada em dois lotes, respectivamente com três e quatro moedas, classificados a partir do tipo de microrrelevo. A análise tribológica de uma moeda de ouro encontrada no sítio do naufrágio na vizinhança da zona dita "de impacto" incidiu nas zonas de acções mecânicas observáveis no microrrelevo da peça. As propriedades multi-escalas da análise tribológica levam a sublinhar o potencial do estudo quantitativo da rugosidade aplicado à topografia do próprio sítio submarino e ao seu cruzamento com a análise de dispersão dos artefactos

Analyse de la topographie des pièces de monnaie du San Pedro de Alcantara

La caractérisation des micro-reliefs de pièces de monnaie trouvées sur le site du naufrage du vaisseau de guerre espagnol San Pedro de Alcantara (1786) à son arrivée du Pérou hispanocolonial est placée dans le contexte méthodologique de l'analyse spatiale d'un site sousmarin de grande dispersion. L'analyse tribologique (étude quantitative du micro-relief) d'un lot de dix pièces d'argent a dégagé une grille classificatoire (corrosion piquage/corrosion érosion/stries d'abrasion, surface en plateaux). Inspirée des travaux de I. MacLeod sur des sites sous-marins côtiers, une relation entre la profondeur d'eau et deux paramètres de rugosité (SPvm - profondeur de la vallée moyenne de la rugosité - et SPtm (altitude moyenne pics vallées) a été observée sur deux lots, respectivement de trois et quatre pièces, classés selon le type de micro-relief. L'analyse tribologique d'une pièce d'or trouvée sur le site du naufrage à proximité de la zone dite "d'impact" a porté sur les zones d'actions mécaniques observables sur le micro-relief de la pièce. Les propriétés multi-échelles de l'analyse tribologique conduisent à souligner le potentiel de l'étude quantitative de la rugosité appliquée à la topographie du site sous-marin lui-même et à son croisement avec l'analyse de dispersion des artefacts.A caracterização dos microrrelevos das moedas encontradas no sítio do naufrágio do navio de guerra espanhol San Pedro de Alcantara (1786) à sua chegada do Peru hispano-colonial é colocada no contexto metodológico da análise espacial de um sítio submarino de grande dispersão. A análise tribológica (estudo quantitativo do microrrelevo) de um lote de dez moedas de prata permitiu elaborar uma grelha de classificação (corrosão por picotado (piquage)/corrosão erosão/estrias de abrasão/superfície em planaltos). Inspirada nos trabalhos de I. McLeod em sítios submarinos costeiros, uma relação entre a profundidade da água e dois parâmetros de rugosidade (SPvm - profundidade do vale médio da rugosidade - e SPtm - altitude média dos picos e vales) foi observada em dois lotes, respectivamente com três e quatro moedas, classificados a partir do tipo de microrrelevo. A análise tribológica de uma moeda de ouro encontrada no sítio do naufrágio na vizinhança da zona dita "de impacto" incidiu nas zonas de acções mecânicas observáveis no microrrelevo da peça. As propriedades multi-escalas da análise tribológica levam a sublinhar o potencial do estudo quantitativo da rugosidade aplicado à topografia do próprio sítio submarino e ao seu cruzamento com a análise de dispersão dos artefactos

Static and active tactile perception and touch anisotropy: aging and gender effect

Abstract Although the human finger is the interface used for the touch process, very few studies have used its properties to provide a description of tactile perception regarding age and gender effects. Age and gender effects on the biophysical properties of the human finger were the main topics of our previous study. Correlating tactile perception with each parameter proved very complex. We expand on that work to assess the static and dynamic touch in addition to the touch gestures. We also investigate the age and gender effects on tactile perception by studying the finger size and the real contact area (static and dynamic) of forty human fingers of different ages and gender. The size of the finger and the real contact area (static and dynamic) define the density of the mechanoreceptors. This density is an image of the number of mechanoreceptors solicited and therefore of tactile perception (static and dynamic). In addition, the touch gestures used to perceive an object’s properties differ among people. Therefore, we seek to comprehend the tactile perception of different touch gestures due to the anisotropy of mechanical properties, and we study two different directions (top to bottom and left to right)