74 research outputs found

    Wetting of anisotropic sinusoidal surfaces - experimental and numerical study of directional spreading

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    Directional wettability, i.e. variation of wetting properties depending on the surface orientation, can be achieved by anisotropic surface texturing. A new high precision process can produce homogeneous sinusoidal surfaces (in particular parallel grooves) at the micro-scale, with a nano-scale residual roughness five orders of magnitude smaller than the texture features. Static wetting experiments have shown that this pattern, even with a very small aspect ratio, can induce a strong variation of contact angle depending on the direction of observation. A comparison with numerical simulations (using Surface Evolver software) shows good agreement and could be used to predict the fluid-solid interaction and droplet behaviour on textured surfaces. Two primary mechanisms of directional spreading of water droplets on textured stainless steel surface have been identified. The first one is the mechanical barrier created by the textured surface peaks, this limits spreading in perpendicular direction to the surface anisotropy. The second one is the capillary action inside the sinusoidal grooves accelerating spreading along the grooves. Spreading has been shown to depend strongly on the history of wetting and internal drop dynamics

    Roughness Signature of Tribological Contact Calculated by a New Method of Peaks Curvature Radius Estimation on Fractal Surfaces

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    This paper proposes a new method of roughness peaks curvature radii calculation and its application to tribological contact analysis as characteristic signature of tribological contact. This method is introduced via the classical approach of the calculation of radius of asperity. In fact, the proposed approach provides a generalization to fractal profiles of the Nowicki's method [Nowicki B. Wear Vol.102, p.161-176, 1985] by introducing a fractal concept of curvature radii of surfaces, depending on the observation scale and also numerically depending on horizontal lines intercepted by the studied profile. It is then established the increasing of the dispersion of the measures of that lines with that of the corresponding radii and the dependence of calculated radii on the fractal dimension of the studied curve. Consequently, the notion of peak is mathematically reformulated. The efficiency of the proposed method was tested via simulations of fractal curves such as those described by Brownian motions. A new fractal function allowing the modelling of a large number of physical phenomena was also introduced, and one of the great applications developed in this paper consists in detecting the scale on which the measurement system introduces a smoothing artifact on the data measurement. New methodology is applied to analysis of tribological contact in metal forming process

    Influence of roughness on ZDDP tribofilm formation in boundary lubricated fretting

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    Influence of initial surface topography on tribofilm formation in ZDDP lubricated contact was analysed. A small displacement fretting tests with sinusoidal motion were carried out in classical sphere/plane configuration. A range of surfaces with different initial roughness were prepared by milling and grinding processes. Tests were carried out using variable displacement method where amplitude of imposed displacement was gradually increased after every 1000 cycles from 2 to 30 ”m. The surfaces after tribological tests were measured by interferometric profiler. Main findings confirm that initial roughness has a significant influence on antiwear tribofilm formation in boundary lubricated contact. Tribofilm form faster and require less energy to activate in case of rough surface obtained by milling process than in case of smooth grinded surface. However, in contact lubricated by ZDDP additive a significant transfer of material occurred from plane to sphere specimen

    Surface Texturization of Breast Implants Impacts Extracellular Matrix and Inflammatory Gene Expression in Asymptomatic Capsules:

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    Background: Texturing processes have been designed to improve biocompatibility and mechanical anchoring of breast implants. However, a high degree of texturing has been associated with severe abnormalities. In this study, the authors aimed to determine whether implant surface topography could also affect physiology of asymptomatic capsules. Methods: The authors collected topographic measurements from 17 different breast implant devices by interferometry and radiographic microtomography. Morphologic structures were analyzed statistically to obtain a robust breast implant surface classification. The authors obtained three topographic categories of textured implants (i.e., “peak and valleys,” “open cavities,” and “semiopened cavities”) based on the cross-sectional aspects. The authors simultaneously collected 31 Baker grade I capsules, sorted them according to the new classification, established their molecular profile, and examined the tissue organization. Results: Each of the categories showed distinct expression patterns of genes associated with the extracellular matrix (Timp and Mmp members) and inflammatory response (Saa1, Tnsf11, and Il8), despite originating from healthy capsules. In addition, slight variations were observed in the organization of capsular tissues at the histologic level. Conclusions: The authors combined a novel surface implant classification system and gene profiling analysis to show that implant surface topography is a bioactive cue that can trigger gene expression changes in surrounding tissue, even in Baker grade I capsules. The authors’ new classification system avoids confusion regarding the word “texture,” and could be transposed to implant ranges of every manufacturer. This new classification could prove useful in studies on potential links between specific texturizations and the incidence of certain breast-implant associated complications

    The Relative Importance of Topography and RGD Ligand Density for Endothelial Cell Adhesion

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    The morphology and function of endothelial cells depends on the physical and chemical characteristics of the extracellular environment. Here, we designed silicon surfaces on which topographical features and surface densities of the integrin binding peptide arginine-glycine-aspartic acid (RGD) could be independently controlled. We used these surfaces to investigate the relative importance of the surface chemistry of ligand presentation versus surface topography in endothelial cell adhesion. We compared cell adhesion, spreading and migration on surfaces with nano- to micro-scaled pyramids and average densities of 6×102–6×1011 RGD/mm2. We found that fewer cells adhered onto rough than flat surfaces and that the optimal average RGD density for cell adhesion was 6×105 RGD/mm2 on flat surfaces and substrata with nano-scaled roughness. Only on surfaces with micro-scaled pyramids did the topography hinder cell migration and a lower average RGD density was optimal for adhesion. In contrast, cell spreading was greatest on surfaces with 6×108 RGD/mm2 irrespectively of presence of feature and their size. In summary, our data suggest that the size of pyramids predominately control the number of endothelial cells that adhere to the substratum but the average RGD density governs the degree of cell spreading and length of focal adhesion within adherent cells. The data points towards a two-step model of cell adhesion: the initial contact of cells with a substratum may be guided by the topography while the engagement of cell surface receptors is predominately controlled by the surface chemistry

    Multiscale measures of equilibrium on finite dynamic systems

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    DuretĂ© des revĂȘtements : quel modĂšle choisir ?

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    La caractĂ©risation des propriĂ©tĂ©s mĂ©caniques des revĂȘtements, et plus particuliĂšrement de leur duretĂ© est d’une grande importance dans le milieu industriel et fait l’objet de nombreuses Ă©tudes. Le plus souvent, la mesure directe de cette grandeur n’est pas possible, puisque sa valeur est influencĂ©e par les caractĂ©ristiques du substrat sur lequel le revĂȘtement est dĂ©posĂ©. Dans cet article, nous nous proposons d’étudier la robustesse de diffĂ©rents modĂšles utilisĂ©s dans la littĂ©rature, avec prise en compte de l’effet de la force sur la duretĂ© du film et du substrat, pour dĂ©duire la duretĂ© du revĂȘtement de celle du « composite » [revĂȘtement – substrat]. Pour cela, nous avons effectuĂ© des essais sur une piĂšce industrielle en acier, revĂȘtue par un dĂ©pĂŽt de nickel chimique de 55 ”m d’épaisseur. Cette Ă©paisseur est suffisante pour que la duretĂ© du revĂȘtement puisse ĂȘtre mesurĂ©e et comparĂ©e Ă  celle obtenue par les modĂšles. En effectuant des essais sous diffĂ©rentes forces appliquĂ©es, nous avons mesurĂ© expĂ©rimentalement les duretĂ©s « composite » et celles du substrat. À partir des valeurs de duretĂ© du revĂȘtement et du substrat (valeurs considĂ©rĂ©es comme exactes, sans incertitude), nous avons optimisĂ© les coefficients variables de chaque modĂšle pour tracer une duretĂ© composite, en fonction de l’inverse de la diagonale de l’empreinte, la plus proche possible des rĂ©sultats expĂ©rimentaux. Ces courbes sont considĂ©rĂ©es ensuite comme les « courbes expĂ©rimentales » (sans incertitude), sur lesquelles nous Ă©tudions la robustesse des modĂšles. Cette robustesse est d’abord testĂ©e en perturbant les valeurs de duretĂ© « expĂ©rimentales » par un bruit (incertitude due Ă  l’appareil de mesure). Une deuxiĂšme perturbation est Ă©galement introduite en supprimant les donnĂ©es relatives aux plus faibles profondeurs de pĂ©nĂ©tration, afin de dĂ©terminer le domaine expĂ©rimental (profondeur d’indentation sur Ă©paisseur de revĂȘtement) oĂč la prĂ©vision de la duretĂ© du revĂȘtement est possible (il est Ă©vident que si les conditions expĂ©rimentales sont rĂ©unies pour que la duretĂ© du film seul puisse ĂȘtre mesurĂ©e, l’utilisation d’un modĂšle ne s’impose pas). Nous montrons que les modĂšles deviennent moins stables lorsque le nombre de paramĂštres variables augmente, et que le modĂšle de Jönsson et Hogmark donne les meilleures prĂ©visions. Cette mĂ©thode peut ĂȘtre utilisĂ©e pour dĂ©finir les conditions expĂ©rimentales (choix de l’appareil et gamme de forces) qui permettent de mesurer la duretĂ© d’un revĂȘtement en fonction de sa duretĂ© et de son Ă©paisseur prĂ©sumĂ©es

    Analyse des courbes de décharge en nanoindentation dans le cas des polymÚres massifs

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    L'interprĂ©tation des courbes d'indentation est particuliĂšrement difficile dans le cas des polymĂšres en raison de la complexitĂ© de leur comportement mĂ©canique et notamment de leur viscositĂ©. L'analyse des courbes d'indentation montre clairement l'influence de la viscositĂ© par l'enfoncement de la pointe lors du plateau de maintien et par la valeur anormalement Ă©levĂ©e de l'exposant de la loi puissance reprĂ©sentant l'Ă©quation de la courbe de dĂ©charge. En consĂ©quence, la mesure des propriĂ©tĂ©s Ă©lastiques peut ĂȘtre fortement influencĂ©e par le comportement visqueux du matĂ©riau. Pour s'en affranchir et mesurer de maniĂšre fiable le module d'Ă©lasticitĂ© et la duretĂ© du matĂ©riau, il est important d'effectuer des essais avec un protocole d'indentation et des conditions expĂ©rimentales adaptĂ©es. Des essais effectuĂ©s avec un chargement Ă  vitesse de charge/charge constante (F˙/F\dot{F}/F = Cst) suivis d'un plateau de maintien suffisamment long (600 s) et d'une courbe de dĂ©charge Ă  vitesse de dĂ©charge/charge constante ont Ă©tĂ© menĂ©s sur deux polymĂšres amorphes (polycarbonate, polymĂ©thacrylate de mĂ©thyle). En utilisant la mĂ©thode d'Oliver et Pharr et la pente initiale d'un ajustement par une loi puissance de la courbe de dĂ©charge, nous obtenons des valeurs calculĂ©es du module d'Ă©lasticitĂ© apparent, proches de celle dĂ©terminĂ©es par des essais de traction

    L'apport de la science dans l'entraĂźnement sportif : l'exemple de la course de fond

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    International audienceThe purpose of this paper is to analyze the turning machinability of a martensitic steel, according to the cutting speed, and through signal analyses of the morphology of the machined surface. We initially carried out the classification of a large number of parameters of roughness, on the basis of their relevance with regard to cutting speed. The originality of the proposed method lies in the combination of the classical technique of analysis of variance with the statistical technique of resampling of data, called Bootstrap. Another characteristic of the study consists in the addition to the traditional categories of roughness parameters (Amplitude, Frequency, Morphological and Hybrid parameters) to analyze multiscale aspect of surface topography through fractal analysis. According to the analysis carried out, the fractal dimension and the slope of the signal (dz/dx) of the topographical signal of the studied surface appear much more relevant than all the other Euclidian parameters. The fractal dimension and the slope of profile allow us to estimate a critical transition speed between the cutting states by generalized strain hardening and those by localized strain hardening. This parameter is also more relevant than the others, because it allows a good analysis of the influence of cutting speed, within each of the two machining modes. The obtained result is relevant because it provides a practical and inexpensive method for the quality control of the machined surface, to manufacturers and engineering companies, without removing some mechanical part, but only through a direct analysis of the slopes of the profile, with, in particular, the help of a portable instrument. We establish later that the transition between disorder and order of the aspect of the observed profiles is essentially due to an instability, which we analyze by the chaos theory. For that purpose, we propose an original construction of an attractor that presents a fixed point for low cutting speeds. This attractor characterizes, beyond the critical cutting speed, an instability described by a phenomenon of successions of states on the attractor between work hardening by localized shear plastic deformation and softening due to the rise in temperature
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