Добірка наукової літератури з теми "Multiscale surface characterization"

Many surface properties are related to their topography. The characteristics of an engineering surface can be recorded as a roughness profile characterized by calculation of roughness parameters. The supposed relevant parameters are used to characterize the surface and to tailor similar surfaces with the same characteristics. The aim of this paper is to propose an alternative method based on information theory to avoid roughness parameters calculation in quantifying the similarity of two roughness profiles. The relevance of this method is emphasized using experimental profiles.

Anisotropy can influence surface function and can be an indication of processing. These influences and indications include friction, wetting, and microwear. This article studies two methods for multiscale quantification and visualization of anisotropy. One uses multiscale curvature tensor analysis and shows anisotropy in horizontal coordinates i.e., topocentric. The other uses multiple bandpass filters (also known as sliding bandpass filters) applied prior to calculating anisotropy parameters, texture aspect ratios (Str) and texture directions (Std), showing anisotropy in horizontal directions only. Topographies were studied on two milled steel surfaces, one convex with an evident large scale, cylindrical form anisotropy, the other nominally flat with smaller scale anisotropies; a µEDMed surface, an example of an isotropic surface; and an additively manufactured surface with pillar-like features. Curvature tensors contain the two principal curvatures, i.e., maximum and minimum curvatures, which are orthogonal, and their directions, at each location. Principal directions are plotted for each calculated location on each surface, at each scale considered. Histograms in horizontal coordinates show altitude and azimuth angles of principal curvatures, elucidating dominant texture directions at each scale. Str and Std do not show vertical components, i.e., altitudes, of anisotropy. Changes of anisotropy with scale categorically failed to be detected by traditional characterization methods used conventionally. These multiscale methods show clearly in several representations that anisotropy changes with scale on actual surface measurements with markedly different anisotropies.

A proper characterization of the multiscale topography of rough surfaces is very crucial for understanding several tribological phenomena. Although the multiscale nature of rough surfaces warrants a scale-independent characterization, conventional techniques use scale-dependent statistical parameters such as the variances of height, slope and curvature which are shown to be functions of the surface magnification. Roughness measurements on surfaces of magnetic tape, smooth and textured magnetic thin film rigid disks, and machined stainless steel surfaces show that their spectra follow a power law behavior. Profiles of such surfaces are, therefore, statistically self-affine which implies that when repeatedly magnified, increasing details of roughness emerge and appear similar to the original profile. This paper uses fractal geometry to characterize the multiscale self-affine topography by scale-independent parameters such as the fractal dimension. These parameters are obtained from the spectra of surface profiles. It was observed that surface processing techniques which produce deterministic texture on the surface result in non-fractal structure whereas those producing random texture yield fractal surfaces. For the magnetic tape surface, statistical parameters such as the r.m.s. peak height and curvature and the mean slope, which are needed in elastic contact models, are found to be scale-dependent. The imperfect contact between two rough surfaces is composed of a large number of contact spots of different sizes. The fractal representation of surfaces shows that the size-distribution of the multiscale contact spots follows a power law and is characterized by the fractal dimension of the surface. The surface spectra and the spot size-distribution follow power laws over several decades of length scales. Therefore, the fractal approach has the potential to predict the behavior of a surface phenomenon at a particular length scale from the observations at other length scales.

Surface gradient characterization by light reflectance (SGCLR) is used for the first time for multiscale curvature calculations and discrimination of worn surfaces on six damaged ceramic–metal composites. Measurements are made using reflectance transformation imaging (RTI). Slope and curvature maps, generated from RTI, are analyzed instead of heights. From multiscale decompositions, bootstrapping, and analysis of variance (ANOVA), a strong correlation (R² = 0.90) is found between the density of furrows of Mehlum curvatures, with a band pass filter at 5.4 µm, present in ceramic grains and their mechanical properties. A strong correlation is found between the mean curvatures of the metal and the ceramics, with a high pass filter at 1286 µm.

The objective of this work is to study the geometric properties of surface topographies of hot-work tool steel created by electric discharge machining (EDM) using motif and multiscale analysis. The richness of these analyses is tested through calculating the strengths of the correlations between discharge energies and resulting surface characterization parameters, focusing on the most representative surface features—craters, and how they change with scale. Surfaces were created by EDM using estimated energies from 150 to 9468 µJ and measured by focus variation microscope. The measured topographies consist of overlapping microcraters, of which the geometry was characterized using three different analysis: conventional with ISO parameters, and motif and multiscale curvature tensor analysis. Motif analysis uses watershed segmentation which allows extraction and geometrically characterization of each crater. Curvature tensor analysis focuses on the characterization of principal curvatures and their function and their evolution with scale. Strong correlations (R2 > 0.9) were observed between craters height, diameter, area and curvature using linear and logarithmic regressions. Conventional areal parameter related to heights dispersion were found to correlate stronger using logarithmic regression. Geometric characterization of process-specific topographic formations is considered to be a natural and intuitive way of analyzing the complexity of studied surfaces. The presented approach allows extraction of information directly relating to the shape and size of topographic features of interest. In the tested conditions, the surface finish is mostly affected and potentially controlled by discharge energy at larger scales which is associated with sizes of fabricated craters.

Le grenaillage de précontrainte est un traitement de surface couramment appliqué dans les secteurs aéronautique, automobile et biomédicale afin d’améliorer les performances mécaniques des pièces. Ce traitement consiste à introduire des contraintes résiduelles de compression en sub-surface. Cependant, les avancées technologiques, accompagnées de l’évolution des matériaux, ont généré de nouvelles demandes en terme de traitement de grenaillage. En particulier, le besoin industriel d’un traitement capable à la fois d’assurer un niveau de performance mécanique suffisant tout en fonctionnalisant la surface se fait ressentir de manière croissante. L’objectif de ce travail est de montrer dans quelle mesure ce besoin peut être comblé par un nouveau traitement appelé tribo-grenaillage. Les deux fonctions visées par le tribo-grenaillage nécessitent une caractérisation des états surfaciques (fonctionnalisation) et sub-surfaciques (contraintes résiduelles) des pièces traitées. Ces états sont le résultat d’interactions mécaniques entre des médias, de nature et de forme différentes, et la surface traitée. L’approche du tribo-grenaillage consiste à contrôler ces interactions et les transferts de texture et d’énergie mis en jeu afin de maitriser la signature fonctionnelle implantée. Par conséquent, une caractérisation multi-échelle de la surface et de la sub-surface de la cible est réalisée simultanément à celle de la surface des médias. Cette étape de caractérisation repose sur l’évaluation d’une surface tribo-grenaillée élémentaire représentative de la texturation globale. Le contrôle et l’optimisation du procédé sont envisagés au travers de la mise en place d’un jumeau numérique alimenté par les données de caractérisation multi-échelle, de modélisation par éléments finis ainsi que celles issues de l’instrumentation du jumeau physique
Shot peening is a surface treatment commonly applied in the aerospace, automotive and biomedical industries to improve the mechanical performance of parts. This treatment consists in introducing residual compressive stresses in the sub-surface. However, technological advances, accompanied by the evolution of materials, have generated new demands in terms of shot peening treatment. In particular, the industrial need for a treatment capable of both ensuring a sufficient level of mechanical performance while functionalizing the surface is increasingly felt. The aim of this work is to show to what extent this need can be met by a new treatment called tribo-peening. The two functions targeted by tribo-peening require a characterization of the surface states (functionalization) and sub-surface (residual stresses) of the treated parts. These states are the result of mechanical interactions between media, of different nature and shape, and the treated surface. The tribo-peening approach consists of controlling these interactions, the texture and energy transfers involved in order to master the implanted functional signature. Therefore, a multi-scale characterization of the target surface and sub-surface is performed simultaneously with that of the media surface. This characterization step is based on the evaluation of tribo-peened surface representative of the overall texturing, the so-called Elementary Representative Areal Surface. The control and optimization of the process are envisaged through the establishment of a digital twin fed with multi-scale characterization data, finite element modeling as well as data from the instrumentation of the physical twin

Cette thèse est un travail prospectif sur la caractérisation multi-échelle de matériaux à gradient de propriétés générés par des traitements de surface de type mécanique (grenaillage à air comprimé ou par ultrasons) ou thermochimique (nitruration, implantation ionique, cémentation basse température). Les apports de plusieurs techniques de caractérisation (microscopie électronique à balayage, spectrométrie, indentation instrumentée, microscopie interférométrique), à différentes échelles, et l'existence possible d'une signature des traitements de surface étudiés sur le matériau ont été examinés. Une analyse multi-échelle des échantillons grenaillés par ultrasons a permis d'établir un lien entre les paramètres procédé et la rugosité du matériau. Une approche originale statistique a été proposée pour déterminer la dureté d'un matériau modifié par un traitement de surface donné sans altérer la surface par une rectification. Elle a permis d'établir un lien entre la rugosité des échantillons grenaillés par ultrasons et leur dureté. Une recherche bibliographique détaillée a été réalisée sur la simulation de l'essai d'indentation instrumentée par éléments finis en étudiant une centaine d'articles afin d'évaluer l'influence des hypothèses des modèles sur leurs résultats. A l'aide d'un modèle éléments finis, la sensibilité des courbes d'indentation à une variation des paramètres matériau a été examinée. Cela a permis de mettre en place une réflexion sur l'identification des propriétés d'un matériau à gradient à l'aide de l'essai d'indentation.

Le rétrécissement continu des dispositifs microélectroniques exige la production des couches nanométriques uniformes et conformes, avec une pureté chimique et des interfaces abruptes. Le dépôt de couche atomique (ALD) est un procédé favorable à la production de tels films. Tirant ses avantages de la nature auto-limitante des réactions, ALD peut permettre un contrôle de l’épaisseur à la monocouche, produisant des films de haute pureté. Bien que l'ALD présente de nombreux avantages, des inconvénients se rencontrent lors du dépôt de films de quelques nanomètres. En particulier, la croissance initiale en îlots et la formation d'une couche interfaciale sont deux de ses limitations principales, en particulier dans le cas du dépôt d’oxyde métallique sur Si. De plus, le dépôt sur des grandes surfaces n'est pas toujours uniforme et dépend du réacteur et des conditions du procédé. Ces inconvénients doivent être supprimés afin de déposer des films d'oxydes sur Si, essentiels pour la production de transistors à effet de champ du futur. Dans cette thèse, l'ALD de Al2O3 de TMA et H2O sur Si est étudiée de manière approfondie, afin de remédier aux inconvénients ci-dessus. L'étude consiste en une approche multi-échelles numérique et expérimentale combinée. Quatre modèles numériques différents ont été développés pour traiter différentes échelles d'espace. Un ensemble de techniques de caractérisation a été utilisé, notamment l'ellipsométrie, XRR, TEM, STEM, EDX, XPS et SIMS. Dans ce cadre, les phénomènes détaillés sont illuminés, ce qui permet de comprendre le processus et l'origine des inconvénients de l'ALD. La compétition entre la désorption et les réactions de surface, s'est avérée être le facteur limitant pour le dépôt à basse température, jusqu'à 200°C. La concentration des sites réactifs en surface limite le dépôt à des températures supérieures à 300°C. Bien que l’ALD soit conçu comme un processus dépendant uniquement de la chimie de surface, l’analyse des phénomènes de transport à l’intérieur du réacteur a montré que la conception du réacteur et du processus peut affecter la distribution des réactifs et la température à l’intérieur du réacteur ALD. L'approche multi-échelles et le couplage entre les différents modèles numériques ont révélé que l'interaction entre les mécanismes de surface et les phénomènes de transport avait un effet sur l'uniformité du dépôt. En utilisant cette approche numérique, il est possible de dériver des conditions optimales garantissant une uniformité du film. Au cours des premières étapes, le dépôt du film est inhibée, ce qui a conduit à un régime de croissance en îlots. L'analyse intégrée a montré que 25 cycles d'ALD sont nécessaires pour déposer un film continu de Al2O3. Au cours de ce régime, l'oxydation interfaciale a conduit à la formation d'une couche d'oxyde interfacial d'environ 2 nm, composée de SiOx, AlOx et SixOyAl, qui altère les propriétés et donc les applications potentielles de la structure déposée. Un prétraitement in situ au plasma N2-NH3 du substrat de Si a été introduit, conduisant à la formation d'une couche de SixNyH sur la surface du substrat. Le prétraitement a augmenté la réactivité de surface, et la période d’inhibition était limitée. Une croissance linéaire est obtenue après 5 cycles. En outre, l'oxydation interfaciale du Si a été réduite, car la couche SixNyH s'est avérée servir de barrière efficace pour la diffusion de l' O et l'oxydation du Si. Le travail présenté dans cette thèse montre la nécessité de telles approches intégrées pour analyser les phénomènes impliqués dans l'ALD. Telles études permettent une compréhension approfondie des mécanismes, afin de proposer des solutions pour lutter contre les inconvénients apparus lors des premières étapes de dépôt. Cela pourrait permettre a l’ ALD de produire des couches minces nanométriques uniformes et conformes de grande pureté avec des interfaces abruptes, capables de répondre aux exigences de l’industrie électronique
The constant shrinking of microelectronic devices requires the production of conformal and uniform nanometric thin films, with a high chemical purity and abrupt interfaces. In this context, Atomic Layer Deposition (ALD) has emerged as a favorable process to produce such films. Drawing its advantages from the self-limiting nature of the surface reactions involved, ALD can yield thickness control down to the monolayer, producing conformal films of high purity. Although ALD has many advantages, drawbacks arise when depositing films of some nanometers. In particular, the initial island growth and the formation of an interfacial oxide layer are two of its main limitations, especially for the case of metal oxide ALD on Si. Moreover, the deposition on large area wafers is not always uniform, and depends on the reactor and process design. These drawbacks need to be suppressed in order to establish ALD as the adequate process for the deposition of high-k gate oxides on Si, essential for the production of field effect transistors of the future. In this thesis, the ALD of Al2O3 from TMA and H2O on Si is thoroughly investigated, in order to tackle the above drawbacks. The investigation consists of a combined multiscale computational and experimental approach. Four different numerical models were developed dealing with different space scales. A complete set of characterization techniques was used, including ellipsometry, XRR, TEM, STEM, EDX, XPS and SIMS. Using this framework, the detailed phenomena involved are illuminated, thus allowing to better understand the process and identify the factors responsible for the drawbacks of ALD. The competition between surface mechanisms, namely desorption and surface reactions, was found to be the limiting factor for deposition at low temperatures, up to 200oC. The concentration of surface reactive sites was found to limit the deposition at higher temperatures up to 300oC. Although ALD is conceived as a process depending only on surface chemistry, the analysis of the transport phenomena inside the ALD chamber showed that the reactor and process design can affect the reactant and temperature distribution inside the ALD reactor. The multiscale approach and the coupling among the different computational models revealed that the interplay between surface mechanisms and transport phenomena affects the film uniformity. Using this computational approach, it was possible to derive optimal process conditions that ensure maximum film uniformity. During the first deposition steps, the film deposition was found to be inhibited, leading to an island growth regime. The integrated analysis showed that 25 cycles are needed in order to deposit a continuous Al2O3 film. During this regime, interfacial oxidation of the Si substrate led to the formation of a ~2 nm interfacial oxide layer, consisting of SiOx, AlOx, and Al-silicates, which degrades the properties and thus the potential applications of the deposited structure. An in situ N2-NH3 plasma pretreatment of the HF-cleaned Si substrate was introduced, leading to a formation of a SixNyH layer on the substrate surface. The pretreatment was found to enhance the surface reactivity, as the inhibition period was restricted and linear ALD growth was obtained even after 5 cycles. Furthermore, interfacial Si oxidation was reduced, as the SixNyH layer was found to serve as an effective barrier for O diffusion and Si oxidation. The work presented in this thesis demonstrates the necessity of such integrated approaches to analyze the detailed phenomena involved in ALD. Such studies help in the thorough understanding of the ALD mechanisms, and consequently in elaborating solutions which restrict the drawbacks arising during the initial deposition steps. This could pave the way for the ALD process to industrially produce uniform and conformal nanometric thin films of high purity and abrupt interfaces, able to answer to the demands of the future electronic industry

The reliable characterization of fatigue behavior and progressive damage of advanced alloys relies on the monitoring and quantification of parameters such as strain localizations as a result of both crystallographic deformation mechanisms and bulk response. To this aim, this article attempts to directly correlate microstructural strain at specific fatigue life to global strain as well as surface roughness in Magnesium alloys. Strain at the grain scale is calculated using Digital Image Correlation (DIC), while surface topography gradients are computed using roughness data at different stages of the fatigue life. The results are further correlated to Electron Back Scatter Diffraction (EBSD) measurements which reveal the profuse and spatially inhomogeneous nature of the crystallographic deformation mechanisms related to yielding and fatigue crack initiation. Emphasis is given on using multimodal NDE data to formulate first a description of the current state of the material subjected to fatigue loading and on identifying conditions that can probabilistically drive the affected by both local and global response, governing degradation process.

Indentation, in addition to the traditional tensile testing, has been widely used for evaluating mechanical properties of hard materials such as metals and bone as well as soft materials like polymer and soft tissues. However, it is difficult to measure the contact area and surface deformation in conventional indentation tests of soft tissue which will bring large errors to the evaluation of the material properties. Also the assumption of isotropic property limited the usage of indentation test in characterizing the nonlinear, anisotropic properties of soft tissue thin film. In this project, 2D and 3D finite element analyses has been carried out to predict hyperelastic material response under indentation and punch tests. A novel indentation test system was developed, which made the direct measurement of local deformation and contact area possible. The apparatus consists of a transparent indenter, a digital microscope, and a computer based control and data acquisition system. The proposed testing system and associated finite element analysis are used to characterize the mechanical properties of multiscale (bulk and thin film) biological tissues.

RF-MEMS devices area complex systems governed by the interaction of a variety of forces, including electrostatics, solid deformation, fluid damping and contact. The performance and reliability of these devices is strongly dependent on device geometry and composition, and also on material microstructure and related properties. In this paper, we consider multiscale simulation of RF MEMS switched. At the device level, we introduce a comprehensive integrated numerical framework to simulate the major governing physics and their interactions. At the micron scale, we develop a mesoscale contact model to describe the history-dependent force-displacement relationships in terms of the surface roughness, the long-range attractive interaction between the two surfaces, and the repulsive interaction between contacting asperities (including elastic and plastic deformation). The inputs to this model are obtained from atomic level simulations and nanoscale surface topography characterization. The mesoscale contact model is integrated in the device-level simulation to predict the pull-in and pull-out behavior of these switches. The uncertainties associated with the simulation are quantified and propagated using a non-intrusive collocation method based on generalized Polynomial Chaos (gPC) expansions. With such a framework, we are able to predict the PDFs of pull-in and pull-out voltage, identify the critical factors that have the most influence on the quantities of interest, and therefore guide resource allocation and risk-informed decision-making.

The objective of this study is to enhance heat transfer process using micro/nano scale channels with surface modifications. An application focus of this study is to design an extremely compact heat-exchanger using single/multi component fluid in miniaturized channels along with surface modifications to achieve higher heat exchange per unit surface area. For the last couple of decades significant progress has been made in characterizing flows in micro channels because of its high surface to volume ratio enhancing heat transfer process. However a centerline question still remains — what should be an optimized size of a miniaturized channel to achieve maximum heat transfer? A lack of theoretical characterization of single or multi component flows in micro to nano scale channels is partially responsible for this setback. Lattice Boltzmann (LB) method, a mesoscopic thermo fluid flow modeling technique, has grown significantly over the last couple of years mainly because of the promise of incorporating mesoscale molecular interaction and also the ability to solve Navier-Stokes equation at the hydrodynamic limit. Moreover, LB method which is based on microscopic models and mesoscopic equations, is considered an attractive numerical alternative for solving multiphase phenomena in a multiscale setup. Also fluid-solid interactions can be implemented conveniently in the LB method without introducing additional complex kernels. At first to address thermo-fluid phenomena over a heated surface Rayleigh-Benard (RB) convection was modeled, and to observe forced flow cavity flow was simulated based on LB method. Some of these results had been compared with literature and documented to have good comparison which showed verification of the current in-house LB simulation codes. After this, effects of surface interaction (hydrophobic and hydrophilic) and miniature cross sections (micro-scale) were calculated using single-component RB convection model. Several results were generated e.g. effects of surface interaction and Knudsen number (Kn) on the average Nusselt number (Nu) in a Rayleigh Benard (RB) convection with hot bottom and cold top surfaces. Results showed higher average heat transfer (Nu) when the bottom surface is hydrophobic and top surface is hydrophilic compared to neutral surface condition in a typical single component RB convection flow over a range of Rayleigh numbers (Ra). Knudsen number (Kn) effect was incorporated to observe the effect of miniature cross section. The average Nu decreased with the increase of Kn i.e. the miniaturization of the channel section from macro-scale to micro-scale also over a range of Rayleigh numbers. However, the number of micro-channels that could be placed in the cross section of a macro-channel increased considerably with increasing Kn. Effect of Kn on the velocity profiles, slip velocities, and maximum velocities were also calculated in a flow between parallel plates. Maximum velocities decreased and slip velocities increased with increasing Kn. Many of these results are in good qualitative comparison with results in literature.

Abstract Surface waves are observed in many situations including natural and engineering applications. Experiments conducted at the Gas Turbine and Transmissions Research Centre (G2TRC) used high speed imaging to observe multiscale wave structures close to an aeroengine ball bearing in a test rig. The dynamic behavior and scale of the waves indicate that these are shear-driven although highly influenced by gravity at low shaft speed. To understand the interactions between gas and liquid phases including momentum and mass transfers, characterization of the observed waves and ligaments was undertaken. Waves were studied at surfaces close to the ball bearing and ligaments were assessed near the cage. Characterization was in terms of frequency and wavelength as functions of speed, flow-rate, bearing axial load and gravity. The assessments confirmed the existence of gravity-capillary waves and capillary waves. Gravity-capillary waves were measured to have a longer mean wavelength on the co-current side of the bearing (gravity and shear acting together) compared to the counter-current side (gravity and shear opposing). Using a published definition of critical wavelength (λcrit), measured wavelengths at 3,000 rpm were 2.56λcrit on the co-current side compared to 1.86λcrit at the countercurrent location. As shaft speed increases, wavelength reduces with transition to capillary waves occurring at around 0.83λcrit. At shaft speeds beyond 5000 rpm, capillary waves were fully visible and the wavelength was obtained as 0.435λcrit. Flow-rate and load did not significantly influence wavelength. Wave frequency was found to be proportional to shaft speed. The gravity-capillary waves had frequencies within the range 13–25 Hz while capillary waves exhibited a frequency well beyond 100 Hz. The frequencies are highly fluctuating with no effect of load and flow rate observed. Ligaments were characterized using Weber number and Stability number. The number of ligaments increased with shaft speed. A correlation for ligament number based on operating conditions is proposed.