Tesi sul tema "Interface de contact"
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1
Bonari, Jacopo. "Novel interface discretisation methods for contact mechanics". Thesis, IMT Alti Studi Lucca, 2021. http://e-theses.imtlucca.it/326/1/Bonari_phdthesis.pdf.
Abstract (sommario):
This thesis’ main scope is the presentation of two different
methodologies for the analysis of contact problems involving morphologically complex or rough surfaces. Both approaches rely on the Finite Element Method (FEM) as the
chosen computational framework. They hinge on the definition of an interface finite element used to model the space encompassed by two solids incontact. This kind of interface element is shared with the field of non-linear fracture
mechanics, employed for the simulation of non-linear crack
growth according to Cohesive Zone Model (CZM). Here, for
the first time, the formulation is extensively applied to contact mechanics. With no further modifications, the interface
element is suited for the solution of contact problems involving smooth and conformal interfaces, exploiting a node-to node
approach and a penalty formulation for the enforcement
of the contact constraints. The element is enriched with specific characteristics that allow for the solution of rough contact problems yet maintaining a very simple mesh discretisation, both using a single-scale and a multiscale approach. In
the single-scale approach, a novel methodology is exploited
that considers an equivalent flat interface and accounts for
the actual geometry by a suitable correction of the standard
normal gap. In the multi-scale approach, the Boundary Element Method (BEM) is exploited for solving, at a micro-scale,
the normal contact problem of a rough rigid indenter making contact with an elastic half-space, according to a far-field displacement determined by the deformation imposed at a
macro-scale. The solution in terms of averaged pressure and
mean separation is then passed back to the macro-scale.
2
Quinn, Amy May. "The study of contact phenomena using ultrasound". Thesis, University of Bristol, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271847.
3
Jason, Bronwin Anastasia. "An adaptive user interface model for contact centres". Thesis, Nelson Mandela Metropolitan University, 2008. http://hdl.handle.net/10948/989.
Abstract (sommario):
Contact centres (CC), are the primary interaction point between a company and its customers and these are rapidly expanding in terms of both workforce and economic scope. An important challenge for today's CC solutions is to increase the speed at which CCAs retrieve information to answer customer queries. CCAs, however, differ in their ability to respond to these queries and do not interact with the computer user interface (UI) in the same way as they each have different capabilities, experience and expertise. Studies have provided empirical support that user performance can be increased when the computer UI characteristics match the user skill level. Adaptive user interfaces (AUIs) are the key to creating personalised systems. Their sole task is to provide an interface most suitable to users' needs whilst facilitating the users' varying skill levels. The aim of this research was to develop an AUI model for CCs to support and improve the expertise level of CCAs. A literature review of CCs, user expertise, AUIs and existing AUI models resulted in the proposal of an AUI model for CCs. The proposed AUI model was described in terms of its architecture, component-level and interface design. An AUI prototype was developed as a proof-of-concept of the proposed AUI model. A literature review on existing AUI evaluation approaches resulted in an evaluation strategy for the proposed AUI model. The AUI prototype was evaluated according to the evaluation strategy that was identified. User testing incorporating eye-tracking and a post-test questionnaire was used to determine the usefulness and usability of the AUI prototype. Significant results were found with regards to user satisfaction ratings, the learnability of the AUI prototype and its effectiveness. This dissertation makes an important contribution in the design of an AUI model that supports and improves the expertise level of CCAs. The model could be used to assist the development of CC applications incorporating AUIs. Future research is however needed to evaluate the effect of the proposed AUI model in a larger CC environment.
4
Chevallier, Eddy. "Définition d'indices de qualité du contact glissant métallique : signature électrique de l'état de surface". Amiens, 2014. http://www.theses.fr/2014AMIE0119.
Abstract (sommario):
La thèse concerne la construction d'une phénoménologie du contact glissant basée sur une approche multi-physique du contact. Nous appuyant sur une caractérisation expérimentale très riche du contact électrique glissant, nous avons construit un modèle théorique (de nature probabiliste) et numérique débouchant entre autre sur l'évaluation de la qualité du contact au travers de divers index de qualité combinant les grandeurs pertinentes du contact, toutes accessibles à la mesure. Le modèle prend en compte, outre la mécanique du contact, les composantes déterministes et aléatoires (profils de rugosité) de la géométrie des surfaces mises en jeu. Le développement du modèle numérique peut se faire selon deux stratégies très différentes. La première intègre des caractéristiques de modèles antérieurs de référence (Greenwood-Williamson,. . . ). La seconde offre l'avantage supplémentaire d'une étude des performances du contact en fonction de la nature des matériaux. De notre modèle statistique émerge un nouveau concept, l'entropie de contact, ainsi dénommée en raison de sa grande similitude avec I'entropie usuelle. Apparaissant comme une fonctionnelle de l'état de surface (géométrie, inhomogénéité chimique,. . . ), cette grandeur présente une grande sensibilité aux conditions de contact telles que la vitesse de glissement et la force de plaquage du contact, influençant directement le transfert de signaux électriques à travers le contact. Elle ouvre ainsi la double perspective d'une thermodynamique du contact glissant et de l'optimisation des états de surfaces en vue d'une qualité maitrisée du contact. Nous avons pu par ailleurs lier cette entropie de contact aux propriétés informationnelles des signaux qui transitent à travers le contact, la rendant accessible à la mesureThe thesis is about the construction of a phenomenology of the slippery contact based on a multi- physical approach of the contact. Pressing us on an experimental characterization very rich in the slippery electric contact, we built a theoretical model (of probability nature) and digital technology resulting among others in the evaluation of the quality of the contact through diverse quality index combining the relevant sizes of the contact, quite accessible to the measure. The model takes into account, besides the mechanics of the contact, the determinist and random components (profiles of roughness) of the geometry of surfaces involvements. The development of the digital model can be made according to two very different strategies. The first one joins characteristics of previous reference models (Greenwood-Williamson). The second offer the additional benefit of a study of the performances of the contact according to the nature of materials. Of our statistical model emerges a new concept, the entropy of contact, so called because of its big similarity with the usual entropy. Appearing as a functional of the state of surface (geometry, chemical unhomogeneity), this size presents a big sensibility in the conditions of contact such as the speed of sliding and the strength of tackle of the contact, influencing directly the transfer of electric signals through the contact. It so opens the double perspective of a thermodynamics of the slippery contact and the optimization
5
Singh, Akash. "An intelligent user interface model for contact centre operations". Thesis, Nelson Mandela Metropolitan University, 2007. http://hdl.handle.net/10948/d1011399.
Abstract (sommario):
Contact Centres (CCs) are at the forefront of interaction between an organisation and its customers. Currently, 17 percent of all inbound calls are not resolved on the first call by the first agent attending to that call. This is due to the inability of the contact centre agents (CCAs) to diagnose customer queries and find adequate solutions in an effective and efficient manner. The aim of this research is to develop an intelligent user interface (IUI) model to support and improve CC operations. A literature review of existing IUI architectures, modelbased design and existing CC software together with a field study of CCs has resulted in the design of an IUI model for CCs. The proposed IUI model is described in terms of its architecture, component-level design and interface design. An IUI prototype has been developed as a proof of concept of the proposed IUI model. The IUI prototype was evaluated in order to determine to what extent it supports problem identification and query resolution. User testing, incorporating the use of eye tracking and a post-test questionnaire, was used in order to determine the usability and usefulness of the prototype. The results of this evaluation show that the users were highly satisfied with the task support and query resolution assistance provided by the IUI prototype. This research resulted in the design of an IUI model for the domain of CCs. This model can be used to assist the development of CC applications incorporating IUIs. Use of the proposed IUI model is expected to support and enhance the effectiveness and efficiency of CC operations. Further research is needed to conduct a longitudinal study to determine the impact of IUIs in the CC domain.
6
Nouira, Dorra. "Non-linear interactions between US waves and contact interface". Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0262.
Abstract (sommario):
Les dernières décennies ont été marquées par un intérêt accru pour les non-linéarités dues aux défauts localisés dans les solides (les fissures fermées par exemple) et aux interfaces de contact en général. En conséquence, un certain nombre de méthodes non-linéaires ont été développés pour la détection de ces défauts et caractérisation des interfaces de contact. Cependant, la compréhension des mécanismes physiques liés aux non-linéarités due contact reste limitée. Dans ce cadre, ce travail de thèse vise à étudier l'interaction non-linéaire entre une onde et une interface tout en intégrant plusieurs mécanismes liés au contact, afin de proposer, à terme, une méthode CND efficace pour la caractérisation des interfaces. L'étude de l'évolution du second harmonique pour caractériser ce type de défauts localisés et plus généralement les interfaces de contact sera au coeur de ce travail.L'interaction non-linéaire entre une onde longitudinale et une interface de contact est modélisée en combinant deux approches. L'une est basée sur des méthodes acoustiques et utilisée en traction, tandis que l'autre est basée sur l’analyse vibratoire structurelle et utilisée en compression. La première consiste à modéliser le contact avec une loi RCCM. L'étude propose une analyse détaillée du comportement de l'interface en traction tout en intégrant l'adhérence. Elle permet d'identifier les paramètres clés qui régissent la signature non-linéaire de la loi RCCM et ainsi permet de mieux comprendre la physique derrière cette interaction non-linéaire. La deuxième méthode, utilisée en compression, est basée sur un modèle de rigidité d'interface non-linéaire où la rigidité d'interface est décrite en fonction de la pression de contact nominale. L'étude consiste en une analyse numérique et expérimentale complémentaires de la composante non-linéaire de la réponse dynamique du système due à la présence d'interface de contact. Elle montre que la tendance de la rigidité à faibles pressions a un effet majeur sur la réponse non-linéaire des systèmes avec des interfaces de contact. Enfin, les lois de contact proposées en compression et traction sont combinées en une seule loi pour permettre une meilleure corrélation entre les différents mécanismes de contact en compression et en traction et donc une meilleure caractérisation de la réponse non-linéaire du système. Les résultats numériques sont prometteurs en vue de la caractérisation d'interfaces de contact à partir de la réponse non-linéaire du système excité par une source extérieure et applicables à la détection non-destructive de l’endommagementThe past decades have been marked by a significant increase in research interest in nonlinearities in cracked solids. As a result a number of different nonlinear methods have been developed for damage detection. However, there still limited understanding of physical mechanisms related to the various nonlinearities due to contacts. This thesis is addressed to study the nonlinear interaction between a wave and an interface while taking into account adhesion, in order to, eventually, propose an efficient NDT method for characterization of contact interfaces. The study of the second-harmonic evolution to characterize the damage will be the focus of this work. The nonlinear interaction between a longitudinal wave and a contact interface is considered in one-dimensional medium by using the Finite Elements method.Numerically, the contact interface is modelled by combining two approaches. One is based on acoustic methods and used in traction, while the other one is based on vibration methods and used in compression. The first one, consists in modelling the contact with an RCCM law. The study propose a detailed analysis on the interface behaviour in traction while taking into account the adhesion. It allows identifying the key parameters that govern the nonlinear signature of the RCCM contact law and so better understanding the interaction between a compression wave and a contact interface that exhibits adhesion in traction. The second one, used in compression, is based on a nonlinear interface stiffness model where the stiffness property of the contact interface is described as a function of the nominal contact pressure. The study consists in a complementary numerical and experimental analysis of nonlinear vibrational response due to the contact interface. It shows that the stiffness-pressure trend at lower pressures has a major effect on the nonlinear response of systems with contact interfaces.Finally, in order to exploit the proposed contact law defined in compression and traction, a strategy to identify the interface parameters during the interaction between a wave and an interface is proposed. The numerical results are promising in view of the characterization of contact interfaces
7
MOISELLO, ELISABETTA. "Integrated Interface Circuits for MEMS Contact-less Temperature Sensors". Doctoral thesis, Università degli studi di Pavia, 2020. http://hdl.handle.net/11571/1370177.
Abstract (sommario):
Thermal sensors, exploiting the relation between the thermal radiation emitted by an object and its temperature, as expressed by the Stefan-Boltzmann law, allow realizing contact-less temperature measurements, required in a wide range of applications, ranging from fever measurements to presence detection for security and climate control systems.
With the advent of smart homes and Internet of Things (IoT) and the wide spreading of mobile and wearable devices, the need for low-cost low-power thermal sensors has arisen, therefore moving the focus of the research away from standard bolometers and pyroelectric detectors and towards uncooled infrared (IR) sensors solutions that can be easily integrated. Bolometers and pyroelectric detectors, which are the main types of thermal sensors found nowadays on the market, in fact, do not comply with the low-cost and easy integration specifications.
Integration of thermal sensors is possible through Micro-Electro Mechanical Systems (MEMS) technology, which allows combining on the same substrate or chip both electrical and mechanical structures with dimensions in the micro-meter range, thus providing structures with high thermal isolation and low thermal mass. The micromachining processes that are required to thermally isolate the sensing element from the substrate are versatile and include anisotropic wet etching, dry and wet etching, electrochemical etch stop, or the use of silicon-on-insulator (SOI).
In this scenario, STMicroelectronics has fabricated two different novel thermal sensors, which fulfill the low-cost low-power specifications for smart homes, IoT and mobile and wearable devices, while also being compatible with CMOS processes and thus easily integrated: a polysilicon thermopile and a micromachined CMOS transistor, from now on referred to as TMOS.
During my Ph.D. activity I was involved in a cooperation between the STMicroelectronics Analog MEMS and Sensors R&D group and the University of Pavia, that led to the design of two readout circuits specifically tailored on the sensors characteristics, one for the thermopile sensor and one for the TMOS (developed by the Technion-Israel Institute of Technology), which were integrated in two test-chip prototypes and thoroughly characterized through measurements as stand-alone devices and as a system with the sensor they were designed for.Thermal sensors, exploiting the relation between the thermal radiation emitted by an object and its temperature, as expressed by the Stefan-Boltzmann law, allow realizing contact-less temperature measurements, required in a wide range of applications, ranging from fever measurements to presence detection for security and climate control systems. With the advent of smart homes and Internet of Things (IoT) and the wide spreading of mobile and wearable devices, the need for low-cost low-power thermal sensors has arisen, therefore moving the focus of the research away from standard bolometers and pyroelectric detectors and towards uncooled infrared (IR) sensors solutions that can be easily integrated. Bolometers and pyroelectric detectors, which are the main types of thermal sensors found nowadays on the market, in fact, do not comply with the low-cost and easy integration specifications. Integration of thermal sensors is possible through Micro-Electro Mechanical Systems (MEMS) technology, which allows combining on the same substrate or chip both electrical and mechanical structures with dimensions in the micro-meter range, thus providing structures with high thermal isolation and low thermal mass. The micromachining processes that are required to thermally isolate the sensing element from the substrate are versatile and include anisotropic wet etching, dry and wet etching, electrochemical etch stop, or the use of silicon-on-insulator (SOI). In this scenario, STMicroelectronics has fabricated two different novel thermal sensors, which fulfill the low-cost low-power specifications for smart homes, IoT and mobile and wearable devices, while also being compatible with CMOS processes and thus easily integrated: a polysilicon thermopile and a micromachined CMOS transistor, from now on referred to as TMOS. During my Ph.D. activity I was involved in a cooperation between the STMicroelectronics Analog MEMS and Sensors R&D group and the University of Pavia, that led to the design of two readout circuits specifically tailored on the sensors characteristics, one for the thermopile sensor and one for the TMOS (developed by the Technion-Israel Institute of Technology), which were integrated in two test-chip prototypes and thoroughly characterized through measurements as stand-alone devices and as a system with the sensor they were designed for.
8
Sankar, Gopal Ravi. "An investigation into a natural language interface for contact centers". Thesis, Nelson Mandela Metropolitan University, 2009. http://hdl.handle.net/10948/890.
Abstract (sommario):
Contact centres are the first point of contact between a company and a customer after the purchase of a product or service. These centres make use of contact centre agents to service customer queries. In the past contact centres hired as many agents as they could in order to service customers, which have led to an increase in personnel costs causing contact centres to become costly to run. Automation techniques were introduced to decrease personnel costs and one such technique is the Interactive Voice Response (IVR). The usability of IVR systems is, however, dismal. Customers would rather speak to a contact centre agent than navigate through the menu structure found in these systems. The menu structure has come under scrutiny because it is difficult to use and navigate, is often not aligned to caller usage patterns, and the menu options are long and vague. This research investigated whether a Natural Language Interface (NLI) could alleviate the problems inherent to IVR. NLIs, however, come with their own disadvantages of which the main ones are ambiguity and the loss of context of a conversation. Two prototypes were implemented, one of which resembled an IVR and the other an NLI (using ALICE concepts). An evaluation of two prototypes confirmed the advantages and disadvantages of these concepts in accordance to theory. A Hybrid prototype was proposed with the aid of two models. The model which proposed an NLI using a rule base was chosen for implementation. The Hybrid prototype was then evaluated against the NLI and IVR prototypes to deduce which prototype was the most effective, efficient and satisfying. The evaluation through the aid of descriptive and inferential statistics showed that the Hybrid prototype was the most usable prototype. The evaluation of the Hybrid prototype confirmed that a Hybrid approach could limit the shortcomings of IVR through the elimination of the menu structure found in these systems, thereby allowing users to state their queries in natural language. The incorporated rule base provided the Hybrid system with long term memory, eliminating one of the main disadvantages of NLIs.
9
Rai, Yugal. "In-situ interface chemical characterisation of a boundary lubricated contact". Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/12191/.
Abstract (sommario):
An increasing demand for improved fuel efficiency and more reliable automotive engines has seen a number of approaches made to further improve the tribological performance in automotive engine parts. Engine oil lubricants extend the life of the moving parts operating under different conditions and also preventing any damages to these parts. However, although its applications are beneficial towards the moving parts, the environmental implications of these lubricants are somewhat harmful, leading to stricter regulations against its emissions. Strict emission requirements have led to a greater interest in understanding the tribological performance of these lubricant additives. Hence, in order to develop more environmentally friendly additives, it is necessary to understand the tribochemical mechanism that occur at the lubricated systems. However, to date despite considerable efforts, a model to predict friction coefficient is only limited to elastohydrodynamic and hydrodynamic lubrication systems. Under boundary and mixed lubrication conditions, the friction and wear behaviour of the tribological system are characterised by the surface asperities of real contact and with the formation of thin surface films. Thus, sophisticated and reliable experimental techniques are required to investigate and assess the tribological systems under this conditions. In-situ approaches can greatly enhance our understanding on the progressive developments between the contacting interfaces, including the detailed chemical, structural and physical interactions governing friction and wear. The research focuses on developing a methodology for in situ and real time boundary lubricated surface optical and chemical characterisation with the aid of Raman Spectroscopy. The techniques are developed with the lubricant additive of Molybdenum Dialkyldithiocarbamate (MoDTC) and used to experimentally evaluate the interface phenomena occurring in a bench tribometer. MoDTC under defined tribological conditions forms MoS2 tribofilms which reduces friction. Surface analytical methodology of ex-situ and in-situ analysis is applied for the lubricant additive to understand the tribochemical process occurring at the tribological contacts.
10
Gonzalez, Franck. "Contributions au développement d'une interface haptique à contacts intermittents". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066068/document.
Abstract (sommario):
Les interfaces haptiques permettent à un opérateur d'interagir avec un environnement virtuel ou distant via le sens du toucher.La majorité des interfaces de l'état de l'art restent au contact de l’utilisateur pendant toute la durée de la manipulation. La liaison permanente entre le robot et l’opérateur nuit à la qualité de l’interaction, notamment en réduisant la transparence en espace libre. Ce problème est d’autant plus prégnant dans le cadre des interfaces haptiques dextres.Cette thèse a pour objectif d'étudier la possibilité d'augmenter la transparence et le réalisme de l'interaction à travers le développement d’interfaces à contacts intermittents. Il s’agit de déconnecter le robot de l'utilisateur lorsqu’aucun contact avec l’environnement n’est nécessaire. Un état de l’art des performances de la manipulation humaine, des interfaces haptiques dextres ainsi que des travaux relatifs au contact intermittent, est d’abord présenté. Un effecteur plan pour le contact intermittent est ensuite conçu. Il est installé à l’extrémité distale d'une interface haptique et plusieurs solutions sont envisagées pour sa loi de commande. Les performances de dix utilisateurs sont comparées dans le cadre d'une tâche de détection de contact en utilisant d'une part l'effecteur adapté au contact intermittent, d'autre part une interface haptique classique. L'élaboration d'une interface permettant une interaction plus naturelle avec l'environnement est ensuite initiée par l'élaboration d'une méthodologie de choix des zones de contact de la main à prendre en compte dans la conception d'une interface haptique. Des perspectives sont finalement données quant à l'extension de ces résultats à une interface haptique dextre à contacts intermittentsHaptic interfaces allow an operator to interact with a virtual environment through the sense of touch. Nowadays, most existing interfaces are mechanically connected to the user's hand throughout the simulation. Therefore he or she interacts with the virtual environment by means of a handle. Thus the interaction is neither natural nor intuitive, and the permanent connection between the robot and the operator is the source of perturbations which prevent the interaction from being perfectly transparent and realistic. The goal of this study is to increase transparency as much as possible by disconnecting the robot from the user when s/he is not in contact with the virtual environment, through the design of a dexterous haptic interface allowing for a more natural interaction than with a classical interface taking into account only one contact point. A state-of-the-art of dexterous haptic interfaces and another for intermittent contact devices are first gathered, and the human performances that should be taken into account for the design of a dexterous haptic interface are analysed. A bidirectional end-effector for intermittent contact is then devised. It is set up at the tip of a haptic interface and several solutions are tested for its control. The performances of six users are compared on the context of a contact detection task, first using the intermittent contact end-effector, then using a classical haptic device. A methodology for the choice of the hand contact areas that should be taken into account in the design of a dexterous haptic interface to enhance the naturalness of the interaction is proposed. Finally, some perspectives are given as for the extension of this study for the design of a dexterous encounter-type haptic interface
11
Taphouse, John Harold. "Thermal contact resistance in carbon nanotube forest interfaces". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54853.
Abstract (sommario):
The continued miniaturization and proliferation of electronics is met with significant thermal management challenges. Decreased size, increased power densities, and diverse operating environments challenge the limitations of conventional thermal management schemes and materials. To enable the continuation of these trends thermal interface materials (TIMs) that are used to enhance heat conduction and provide stress relief between adjacent layers in a electronic package must be improved. Forests comprised of nominally vertically aligned carbon nanotubes (CNTs), having outstanding thermal and mechanical properties, are excellent candidates for next-generation thermal interface materials (TIMs). However, despite nearly a decade of research, TIMs based on vertically aligned CNT forests have yet to harness effectively the high thermal conductivity of individual CNTs. One of the key obstacles that has limited the performance of CNT TIMs is the presence of high thermal contact resistances between the CNT free ends and the surfaces comprising the interface. The aim of this research is to better understand the mechanisms by which the thermal contact resistance of CNT forest thermal interfaces can be reduced and to use this understanding towards the design of effective and to scalable processing methods. Contact area and weak bonding between the CNT tips and opposing surface are identified as factors that contribute significantly to the thermal contact resistance. Three strategies are explored that utilize these mechanisms as instruments for reducing the contact resistance; i) liquid softening, ii) bonding with surface modifiers, and iii) bonding with nanoscale polymer coatings. All three strategies are found to reduce the thermal contact resistance at the CNT forest tips to below 1 mm2-K/W, a value to where it is no longer the factor limiting heat conduction in CNT forest TIMs. These strategies are also relatively low-cost and amenable to scaling for production when compared to existing metal-based bonding strategies.
12
Moser, Maximilian Jörg Josef [Verfasser], e Helmut [Akademischer Betreuer] Abels. "Sharp Interface Limits for Diffuse Interface Models with Contact Angle / Maximilian Jörg Josef Moser ; Betreuer: Helmut Abels". Regensburg : Universitätsbibliothek Regensburg, 2021. http://d-nb.info/1225935733/34.
13
Du, Huifeng. "Finite element analysis of adhesive contact interface in continuous 3D printing". Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127164.
Abstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 65-68).
Projection Micro-Stereolithography (P[mu]SLA) is one of the most high-throughput additive manufacturing methods, yet preserving the high-resolution characteristic of light-based polymerization techniques. However, further improvement of fabrication speed and precision is usually hindered by the undesired adhesive forces at the curing interface, which is an inevitable consequence of in situ liquid-to-solid phase transition. To overcome this limitation, a bio-inspired super low adhesive interface has been proposed based on the observation of a slippery water layer on the peristome surface of pitcher plant. This hydrophobic layer provides an effective shield to solid adhesion due to its low adhesive energy, and attracting force between fabricated part and UV curing interface is significantly reduced. The introduction of this new lubrication layer not only remarkably improves the fabrication speed, but also increases the refilling rate of liquid pre-polymer resin.
This ultra-low adhesive interface shows promises for pushing the boundaries of continuous 3D printing into a realm of high-throughput additive manufacturing methods ready for industrial applications. In this thesis, I sought to provide a more comprehensive understanding of the solid-solid interaction at the curing interface of 3D photo-polymerizing systems. The state-of- the-art review of current literature suggested that a surface-based cohesive contact theory from a continuum mechanics perspective was the most appropriate model to establish a connection between interfacial material properties and macroscopic measurement results from experiment. Based on that I analyzed the entire mechanical separation process using finite-element method, and provided a semi-quantitative explanation of the stability of such lubricant-infused nano-cavities against peeling forces.
This research lays the ground for elucidating the physical mechanism behind the general adhesion-separation problem, and framework has been constructed in a more general form to allow for analyzing a wide range of interdisciplinary problems involving the dynamics of anisotropic moving contact lines and the propagation of surface instabilities induced by adhesive contact.
by Huifeng Du.
S.M.
S.M. Massachusetts Institute of Technology, Department of Mechanical Engineering
14
Narayanaswamy, Anand Subramanian. "A Non-Contact Sensor Interface for High-Temperature, MEMS Capacitive Sensors". Case Western Reserve University School of Graduate Studies / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1275675071.
15
Tomobe, Haruka. "Constitutive Models for Root-Soil Contact Interface Considering Hydro-Mechanical Effects". Kyoto University, 2020. http://hdl.handle.net/2433/253327.
Abstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第22491号
農博第2395号
新制||農||1076(附属図書館)
学位論文||R2||N5271(農学部図書室)
京都大学大学院農学研究科地域環境科学専攻
(主査)教授 村上 章, 教授 藤原 正幸, 教授 白岩 立彦
学位規則第4条第1項該当
16
Nguyen, Sébastien Thanh-Lâm. "Dynamique d'une interface en présence d'une singularité de contact solide/fluide". Paris 11, 2005. https://tel.archives-ouvertes.fr/tel-01390365.
Abstract (sommario):
La solution d'un grande nombre de problèmes académiques, embrassant une grande variété de configurations : la cavité entrainée, la ligne de contact mobile, les écoulements thermocapillaires confinés, possède une singularité (discontinuité d'un champ ou d'une de ses dérivées). Il est bien connu que les méthodes spectrales sont très sensibles aux singularités, ce qui se traduit par la présence d'oscillations non-physiques (phénomène de Gibbs) au voisinage de la discontinuité. Pour cette raison, il est nécessaire de remplacer les conditions aux limites singulières par des conditions régulières filtrant explicitement la singularité pour employer ce type d'approximation numérique. Il est moins connu que les méthodes de précision finie (différences finies, volumes finis, éléments finis. . . ), qui permettent l'emploi direct des conditions singulières, introduisent un filtrage passif de la singularité lié à la finesse de résolution spatiale imposée. Des travaux précédents (thèse d'Eric Chénier) ont montré que l'échelle de filtrage pouvait influencer la structure de l'écoulement à l'échelle globale. En partant du principe que la physique est régulière, il devrait exister un mécanisme modifiant le comportement du fluide dans la région où le modèle classique est mis en défaut. On est alors amené à formuler deux questions fondamentales. D'une part, quel est l'ordre de grandeur de la petite échelle à laquelle la physique change ? D'autre part, existe-t'il un modèle macroscopique à même de rendre compte de ces effets locaux dans une simulation numérique du milieu continu ?Cette thèse est une tentative de répondre à ces deux questionsThe research objective of this work is to achieve a physically relevant modeling removing velocity or vorticitysingularities which occur at solid/fluid junctions. These singularities are very common in a number of fluid flows(e. G. Lid-driven cavity corners, laterally heated liquid bridges, moving contact lines). It is well known that spectralmethods are very sensitive to singularities, and exhibit non physical oscillations (Gibbs Phenomenon) in the vicinityof a discontinuity. For this reason, when using such methods, singular boundary conditions have to be replaced by someregular condition obtained by explicitly filtering the discontinuity. It is less known that finite precision methods(e. G. Finite differences, finite volumes, finite elements), though allowing to keep the original conditions, introducesome implicit filter depending on the scale of discretization. In previous work, evidence was brought up that the localscale of filtering can play a determinant role on the global flow structure. It can, for instance, be responsible forsymmetry breaking of the solution in full zone liquid bridges simulations. Assuming that physics is regular, there must exist some mechanism that modifies the fluid's behavior in the region where the classical model fails. Two fundamental questions show up. First, what is the length of the small scale at which physics differs. Second, does there exist somemacroscopic model which can incorporate these local effects in numerical simulations of continuum. This thesis is devoted to address these two questions
17
Ramadan, Dlair. "Ultrasonic reflection technique for measuring contact conditions at the tool chip interface". Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/14371/.
Abstract (sommario):
The measurement of the interface conditions in a cutting tool contact is essential information for performance monitoring and control. In this work, a new method for measurement of interface conditions, based on the reflection of ultrasound, is evaluated for use in turning in both dry and wet cutting conditions. An ultrasonic wave will be partially reflected when it strikes an interface between materials with different acoustic properties. The proportion of the wave reflected depends on the nature of the interface. A transducer was positioned on the underside of a cutting tool insert and a pulse propagated through the insert. The pulse was reflected back at the tool-chip interface and received by the same transducer. The amplitude of the reflected wave was processed in the frequency domain. Reflection coefficient measurements were then used to investigate the tool-chip interface at different machining parameters including cutting speeds, depth of cut and feeds. It was seen clearly that the reflection coefficient increases with increasing cutting speed due to either a reduction in the tool-chip contact area or a decrease in the pressure applied on the rake face cutting tool. While the reflection coefficient decreases with increasing cutting depth and feed due to either an increase in the tool-chip contact area or an increase in the pressure. The results also showed that the reflection coefficient was significantly affected by feed followed by cutting speed whereas the depth of cut had the lowest effect on reflection coefficient. These results were attributed to the affect of tool-chip contact length with the machining parameters, where the depth of cut had the least effect on contact length. When applying the cutting fluid, more energy was reflected back from the tool-chip interface and thus a higher reflection coefficient was recorded than in dry condition and this was due to the lower pressure that was applied on the rake face cutting tool. The use of ultrasound in the monitoring of contact condition at the tool-chip interface is shown to be a viable technique for research and condition monitoring.
18
Verma, Navni. "Development and Demonstration of Thermal Contact Conductance (TCC) Models for Contact Between Metallic Surfaces". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555452213472626.
19
Noureddin, Borna. "A non-contact video-oculograph for tracking gaze in a human computer interface". Thesis, University of British Columbia, 2003. http://hdl.handle.net/2429/42119.
Abstract (sommario):
Video-based eye tracking devices that can detect where a person is looking without
requiring the user to wear anything can be effective components of a human computer
interface. However, issues such as speed, accuracy, cost and case of use have so far
limited the widespread, practical application of existing devices. No pre-existing device
that does not require user contact is able to accurately track the eye (and hence where a
person is looking) in real time in the presence of large head movements.
This thesis attempts to overcome these limitations by presenting a novel design for a
video-oculograph. It is a non-contact (i.e., it does not require the user to wear anything)
human computer interface device, and uses two cameras to maintain accurate, real-time
tracking of a person's eye in the presence of significant head motion. Image analysis
techniques are used to obtain very accurate locations of the pupil and corneal reflection.
All the computations are performed in software and the device only requires simple,
compact optics and electronics attached to the user's computer via a serial port and IEEE
1394 interface, making the device very cost effective.
An implementation of the design to track a user's fixations on a computer monitor is
also evaluated in this thesis. Two methods of estimating the user's point of gaze on a
computer monitor were evaluated. Using functional approximation, the gaze was
estimated to within 5.2% of the monitor's width and 9.6% of the monitor's height. Using
a direct, analytical approach, the gaze was estimated to within 22.0% horizontally and
27.8% vertically. Evidence was found to support further investigation into effective
calibration procedures that would significantly improve the ability of the system to
estimate the user's point of gaze.
The implemented system - called GTD (Gaze Tracking Device) - is capable of
reliably tracking the user's eye in real-time (nine frames per second) in the presence of
natural head movements as fast as 100°/s horizontally and 77°/s vertically. It is able to
track the location of the eye to within 0.758 pixels horizontally and 0.492 pixels
vertically, and is robust to changes in eye colour and shape, ambient lighting and the use
of eyeglasses.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
20
Mokrani, Hacène. "Etude de la condition de liaison thermique à une interface de contact électrothermique". Nantes, 2008. http://www.theses.fr/2008NANT2098.
Abstract (sommario):
Le présent travail porte sur l’étude expérimentale et théorique des paramètres de contact servant à décrire la condition de liaison thermique à une interface de contact solide-solide imparfait, siège d’une dissipation par effet joule. Ces paramètres sont la résistance thermique de contact RTC, le flux généré à l’interface jg et le coefficient de partage du flux généré a. Un banc d’essai a été conçu et réalisé afin d’estimer à partir de mesure thermique RTC et a. Le principe de mesure consiste à déterminer RTC avant le passage du courant. Ensuite après le passage d’un courant de forte intensité sous faible tension, on détermine jg et a en régime permanent. Enfin, les valeurs de RTC et a sont estimés à nouveau de façon simultanée lors du régime transitoire. Les essais ont été menés sur trois couples de matériaux différents. Les tests de reproductibilité démontrent la grande fiabilité du dispositif réalisé. Les résultats expérimentaux montrent que le comportement de RTC est conforme à la littérature. On a pu décelé une certaine similitude dans le comportement entre RTC et la résistance électrique de contact pour les grandes valeurs de pressions de contact. Les valeurs estimées de a se présentent comme étant le rapport de deux résistances thermiques : la résistance thermique du côté le plus résistif sur la résistance globale traversée par la totalité du flux. On entend par résistance du côté le plus résistif la somme de la résistance thermique interne du barreau le moins conducteur auquel est affectée la part a du flux généré et de la moitié de RTC. Cela veut dire qu’il existe un lien de parenté entre a et RTC mais que cela ne fait de a un paramètre intrinsèqueThe topic of the present work is the experimental and theoretical study of contact parameters describing the thermal link condition of an imperfect solid-solid interface, seat of a thermal dissipation by Joule effect. These parameters are the thermal contact resistance RTC, the interfacial heat flux jg and the heat flux partition coefficient a. An experimental device was designed and set-up in order to estimate RTC and a from thermal measurements. The measurement principle consists in determining RTC before delivering the current. Then, with a high current intensity under a low voltage, jg and a are determined in permanent state. Finally, values are simultaneously estimated in transient thermal regim. Experiments were performed on three different couples of materials. Reproducibility test highlights the reliability of the experimental device. Experimental results show that RTC behaviour is consistence with literature. It was revealed that there is a similitude between the thermal contact resistance and the electrical contact resistance for the high values of pressure contact. Finally the behavior of the partition coefficient a was determined. It appears as being the ratio of two thermal resistances: the thermal resistance of the more resistive side over the global resistance crossed by the whole heat flux. The thermal resistance of the more resistive side is the sum of the internal thermal resistance of the less conductive rod, which receive the part a of the heat flux, and the half of the thermal contact resistance. There is then a link between a and RTC, but that does not of a an intrinsic parameter
21
Scheibert, Julien. "Mécanique du contact aux échelles mésoscopiques". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00172935.
Abstract (sommario):
Deux méthodes expérimentales ont été développées pour mesurer, pour une interface multi-contacts élastomère / verre, les champs mécaniques en volume (micro-capteur de force MEMS noyé sous le film élastique) et à l'interface (imagerie de contact par transmission), résolus spatialement à une échelle intermédiaire entre celle du contact apparent et celle des micro-contacts.La mesure MEMS a permis d'obtenir les champs de contrainte sous charge normale et en glissement stationnaire, en très bon accord avec des modèles mécaniques simples. Pour des substrats de rugosité périodique le lien entre spectre des contraintes et topographie de surface a pu être interprété en termes de filtrage spectral, pertinent pour comprendre la perception tactile.
La mesure optique a permis, en analysant la répartition spatiale de l'intensité, d'obtenir le champ de pression de surface. Sa dépendance avec les propriétés de la couche rugueuse a été confrontée au modèle de Greenwood-Tripp. Par suivi des aspérités, le champ de déplacement a été mesuré avec une résolution sub-micronique et a mis en évidence la coexistence de zones glissantes et adhérentes prédite par Cattaneo et Mindlin.
22
Shan, Lei. "Mechanical interactions at the interface of chemical mechanical polishing". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17774.
23
Iverson, Michael Bryan. "Advanced language attrition of Spanish in contact with Brazilian Portuguese". Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3316.
Abstract (sommario):
Language acquisition research frequently concerns itself with linguistic development and result of the acquisition process with respect to a first or subsequent language. For some, it seems tacitly assumed that a first language, once acquired, remains stable, regardless of exposure to and the acquisition of additional language(s) beyond the first one in childhood. Research on language attrition (language loss) questions the validity of this assumption and raises questions that will not only help in describing and explaining the nature of linguistic attrition, but also shed light on the mental (cognitive) representation of human language. The goal of this dissertation is to contribute to the general program of research that investigates possible domains of first language attrition and its cause(s). More specifically, I endeavor to test the predictions and theoretical tenability of the Interface Hypothesis (Sorace and Filiaci 2006) as applied to language attrition (e.g. Tsimpli et al 2004).
The Interface Hypothesis claims that certain linguistic properties, namely those at external interfaces such as the syntax/discourse interface, are especially vulnerable to optionality in language acquisition (see Sorace and Serratrice 2009). For attrition, it predicts that, upon sufficient exposure, linguistic properties that are dependent on interfaces between the linguistic computational system and external domains of cognition (such as pragmatics and discourse structure) are more vulnerable to erosion than those that lie internally to the linguistic system (e.g. syntax/semantic interface) or those that are purely syntactic in nature. Within this framework, attrition is hypothesized to either be due to direct interference from the L2 or due to linguistic processing deficits that are a byproduct of being bilingual. The comprehensive nature of this case study, which tests the L1 grammar of an adult native speaker of Spanish after 25 years of uninterrupted naturalistic exposure to Brazilian Portuguese across the different property types, not only allows for an examination of possible domains of attrition (e.g. external interfaces, internal interfaces, syntax) but also allows for teasing apart of the cause of attrition by combining both untimed and timed methodologies. Although the main focus of this dissertation is to test the limits and explanatory value of the Interface Hypothesis, the data will also be examined in light of other theories such as Paradis' (2004) Activation Threshold Hypothesis and Jakobson's (1940) Regression Hypothesis to determine the extent to which various theories might best explain the data to be obtained.
24
Söderberg, Anders. "On interface modeling emphasis on friction". Licentiate thesis, KTH, Machine Design (Div.), 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3986.
Abstract (sommario):
The general trend toward increased use of computer models and simulations during product development has led to a need for accurate and reliable product models. The function of many products relies on contact interfaces between interacting components. To simulate the behavior of such products, accurate models of both components and interfaces are required. Depending on the purpose of the simulation, interface models of different degrees of complexity are needed. In simulation of very large systems with many interfaces, it might be computationally expensive to integrate detailed models of each individual interface. Condensed models, or abstractions, that describe the interface properties with a minimum of degrees of freedom are therefore required.
This thesis deals with mechanical interfaces with an emphasis on friction. In the four appended papers friction models are discussed in terms of condensed models, as well as in terms of more detailed contact models. The aim is to study how friction can be modeled in behavioral simulation of products and to discuss the convenience and relevance of using different types of friction models as building blocks of a system model in behavioral simulations.
Paper A presents a review of existing condensed friction models for sliding contacts under different running conditions and discusses the models from both simulation and tribological points of view.
In papers B and C a simplified contact model, called the elastic foundation model, is used to model friction in a boundary-lubricated rolling and sliding contact. The model is integrated in a dynamic rigid body model of a mechanical system, the system behavior is simulated, and the result is compared with experimental results.
Paper D discusses the application of the elastic foundation model to rough surface contact problems and investigates how the error in the elastic foundation results depends on surface roughness.
25
Shan, Lei. "Fluid pressure distribution at the interface between compliant and hard surfaces". Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/17788.
26
Tachon, Loïc. "Développement d'outils numériques et expérimentaux dédiés à l'étude de l'évaporation en présence de ligne triple". Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10027/document.
Abstract (sommario):
Les travaux réalisés au cours de cette thèse visent à apporter une aide à la compréhension des mécanismes régissant l'évaporation des films liquides. La physique des problèmes à changement de phase avec ligne de contact est gouvernée par des mécanismes agissant au niveau de ces dernières ainsi qu'au niveau des interfaces gaz-liquide. La description géométrique des interfaces est donc un point clef dans cette étude tant d'un point de vue numérique qu'expérimental. Un outil numérique tridimensionnel de suivi d'interface infiniment fine a été créé afin d'anticiper la simulation numérique de ces problèmes. Cet algorithme repose sur une description quadratique de l'interface qui est une surface du maillage. L’ordre de convergence de cette méthode relatif à différentes caractéristiques (courbure, normale, position) de l'interface ainsi que sa qualité conservative ont été étudiés.Parallèlement à cette approche numérique, une technique expérimentale d'inversion optique a été développée. Celle-ci permet la mesure dynamique du profil d'une interface au voisinage de la ligne de contact dans le cadre de fluide très mouillant. Cette méthode, appliquée dans le cadre d'un problème de film en évaporation quasi axisymétrique a permis, dans le cadre d'une expérience simple, une première quantification des flux de chaleur et de masse échangés au niveau de la ligne de contactThe tasks fulfilled during this study aim at providing tools for understanding the mechanisms of liquid film evaporation. Evaporation in the presence of a triple lines is ruled by physical mechanisms acting on these singularities as well as on the gas liquid interfaces. Thus, the interface description, under it numerical as experimental aspects, is a key point of this study. A numerical tridimentionnal sharp interface tracking tool has been developed to be used in further numerical simulation of the evaporation problem. In this algorithm, the interface is described as a quadratic grid surface. Its convergence orders relatively to geometrical parameters of the interface (curvature, normal, position) has been studied.In the mean time, an experimental optical inversion technique has been developed and validated. It allows a dynamic measurement of the interface shape in the vicinity of the triple line of highly wetting fluid. This method has been applied to the case of a quasi axisymetric evaporating film and provides a first quantification of the heat and mass transfers generated by the triple line region
27
Frost, Daniel Wayne. "Study of adsorption of biological and nanoparticle solutions at the solid-liquid interface". Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/411.
28
CHANDER, DIVYAKSH SUBHASH. "Modelling the Physical Human-Exoskeleton Interface". Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2928614.
29
Alemani, Mattia. "Particle emissions from car brakes : The influence of contact conditions on the pad-to-rotor interface". Doctoral thesis, KTH, Tribologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208701.
Abstract (sommario):
Due to their adverse health effects emissions have been regulated for over three decades. Brake wear particulate matter is the most important non-exhaust source, however current knowledge is mainly limited to observational studies. This thesis aims to investigate relations between the brake system contact conditions and the related emissions on a model scale; validate the results on a component level; and understand to what extent they are significant on a full-scale. Paper A investigates the influence of nominal contact pressure on a model scale. Results show that higher pressure corresponds to higher emissions Paper B investigates the influence of the nominal contact pressure, for different friction materials, on a model scale. A temperature threshold, responsible for a relevant emission increase, is identified. Paper C investigates particle characteristics and wear mechanisms for different nominal contact pressures, on a model scale. Results show an enhanced tribo-layer at higher pressure levels. Paper D investigates the influence of brake system conditions on emissions, on a model scale. Results show that frictional power is the most important parameter. A transition temperature independent of the contact condition is identified. Paper E investigates similarities occurring on a component scale and a model scale in terms of emissions. Results show a promising correlation, and the possibility of using a pin-on-disc tribometer for R&D activities. Paper F investigates analogies occurring on a component scale and a model scale, in terms of friction performance, fictional surface and chemical composition. Results show similar phenomena occurring for the two test stands. Paper G analyses real brake system working conditions in a urban environment defining, by means of an inertia dyno bench, the related emissions. Results reveal emission factors compliant to EURO6 and EURO2 regulations, in terms of number and mass, respectively.På grund av deras negativa hälsoeffekter har partikel emissioner reglerats i över tre årtionden. Bromsslitagepartiklar är den viktigaste icke-avgaskällan, men nuvarande kunskaper är huvudsakligen begränsade till observationsstudier. Avhandlingen syftar till att undersöka förhållandena mellan bromssystemets kontaktförhållanden och de relaterade utsläppen på modellskala. Validera resultaten på komponentnivå och förstå i vilken utsträckning de är betydande i full skala. Papper A undersöker påverkan av nominellt kontakttryck i en modellskala. Resultat visar att högre tryck motsvarar högre utsläpp. Papper B undersöker påverkan av det nominella kontakttrycket, för olika friktionsmaterial, i modellskala. En temperaturtröskel, för en emissionsökning identifieras. Papper C undersöker partikelegenskaper och slitagemekanismer för olika nominella kontakttryck, i en modellskala. Resultat visar ett förbättrat triboskikt vid högre trycknivåer. Papper D undersöker påverkan av bromssystemets förhållanden på utsläpp i en modellskala. Resultat visar att friktionskraften är den viktigaste parametern. En övergångstemperatur oberoende av kontaktförhållandet identifieras. Papper E undersöker likheter som uppträder på komponentskala och modellskala när det gäller emissioner. Resultatet visar en lovande korrelation, och möjligheten att använda en pinne-på-skiva-tribometer för FoU-aktiviteter. Papper F undersöker analogier som förekommer på en komponentskala och en modellskala, vad gäller friktionsprestanda, friktionsyta och kemisk sammansättning. Resultat visar liknande fenomen som förekommer för de två testskalorna. Papper G analyserar verkliga bromssystem arbetsförhållanden i en stadsmiljö som definierar, med hjälp av en tröghetsdyno bänk, de relaterade utsläppen. Resultatet visar utsläppsfaktorer som är förenliga med EURO6 och EURO2-reglerna, i fråga om antal respektive massa.
QC 20170808
REBRAKE Project
30
Mansot, Jean-Louis. "Etude des pressions dans un interface sphère-plan en présence d'une couche mince organique". Lyon 1, 1986. http://www.theses.fr/1986LYO10050.
31
Etheredge, Darrell Keith. "MULTIWALL CARBON NANOTUBE ARRAYS FOR THERMAL INTERFACE ENHANCEMENT". UKnowledge, 2012. http://uknowledge.uky.edu/me_etds/3.
Abstract (sommario):
High performance/small package electronics create difficult thermal issues for integrated circuits. Challenges exist at material interfaces due to interfacial contact resistances. Multiwall carbon nanotube (MWCNT) arrays are considered to be excellent candidates for use as thermal interface materials (TIMs) due to outstanding thermal/mechanical properties. In this work, MWCNT array TIMs are analyzed in aluminum and carbon fiber composites via flash diffusivity analysis. The effect of TIM thickness, areal/bulk density, surface cleanliness, and volumetric packing fraction; along with the effect of substrate finish and interfacial contact pressure on thermal performance are analyzed. Trends show the best TIMs possess low thickness, high bulk density and packing fraction, and clean surfaces. Pressure dramatically increases thermal performance after establishing contact, with diminishing returns from additional pressure. Diffusivities approaching 40 mm2/s and 0.65 mm2/s are recorded for aluminum and composite systems. Oxygen plasma etching and high temperature annealing (“Graphitizing”) are investigated as methods to remove amorphous carbon from array surfaces. Graphitized TIMs report diffusivity improvements up to 53.8%. Three methods of incorporating MWCNTs into composites are attempted for thermal/mechanical property enhancement. Conductance calculations show increasing diffusivity without increasing thickness enhances thermal performance in composites. MWCNTs for mechanical property enhancement produce no change, or detrimental effects.
32
Boughnim, Nabil. "Traitement du signal pour la reconnaissance de gestes et application à une interface homme machine sans contact". Ecole centrale de Marseille, 2013. http://www.theses.fr/2013ECDM0004.
33
Fontana, Ilaria. "Interface problems for dam modeling". Thesis, Université de Montpellier (2022-….), 2022. http://www.theses.fr/2022UMONS020.
Abstract (sommario):
Les équipes d’ingénierie ont souvent recours aux simulations numériques par éléments finis pour étudier et analyser le comportement des ouvrages hydrauliques de grande dimension. Pour les ouvrages en béton, les modèles doivent être en mesure de prendre en compte le comportement non-linéaire des discontinuités aux diverses zones d’interfaces localisées en fondation, dans le corps du barrage ou à l’interface entre la structure et la fondation. Il faut non seulement être capable de représenter le comportement mécanique non-linéaire de ces interfaces (rupture, glissement, contact), mais également de prendre en compte l’écoulement hydraulique à travers ces ouvertures.Dans le cadre de cette thèse, nous nous focalisons d’abord sur la question du comportement des interfaces, que nous abordons à travers le modèle des zones cohésives (CZM). Ce dernier, introduit dans divers codes de calcul par éléments finis (avec éléments finis de joint), est une approche pertinente pour décrire la physique des problèmes de fissuration et de frottement au niveau de discontinuités géométriques. Bien que le CZM a été initialement introduit pour prendre en compte que le phénomène de rupture, nous montrons dans cette thèse que son utilisation peut être étendue aux problèmes de glissement en s'appuyant sur le formalisme élasto-plastique éventuellement couplé à l'endommagement. En outre, des lois de comportement hydromécaniques non-linéaires peuvent être introduites pour modéliser la notion d’ouverture de fissure et le couplage avec les lois d’écoulement fluide. Au niveau mécanique, nous travaillons dans le cadre des matériaux standard généralisés (SGM), qui fournit une classe de modèles qui satisfont d’une manière automatique des principes de la thermodynamique tout en possédant des bonnes propriétés mathématiques utiles pour la modélisation numérique robuste. Nous adaptons le formalisme SGM volumique à la description des zones d'interface. Dans cette première partie de la thèse, nous présentons nos développements faites dans l'hypothèse de SGM adaptée aux CZM, capable de reproduire les phénomènes physiques observés expérimentalement : rupture, frottement, adhésion.En pratique, les non-linéarités du comportement des zones d’interface sont dominées par la présence de contact, ce qui engendre des difficultés numériques importantes pour la convergence des calculs par élément fini. Le développement de méthodes numériques efficaces pour le problème de contact est donc une étape clé pour atteindre l’objectif de simulateurs numériques industriels robustes. Récemment, l’utilisation de techniques d’imposition faible des conditions de contact à la Nitsche a été proposée comme moyen pour réduire la complexité numérique. Cette technique présente plusieurs avantages, dont les plus importants pour nos travaux sont: 1) possibilité de gérer une vaste gamme de conditions (glissement avec ou sans frottement, non interpénétration, etc); 2) la technique se prête à une analyse d'erreur a posteriori rigoureuse. Ce schéma basé sur les conditions d’interface faibles représente le point de départ pour l’estimation d’erreur a posteriori par reconstruction équilibrée de la contrainte. Cette analyse est utilisée pour estimer les différentes composantes d’erreur (p.e., spatiale, non-linéaire), et pour mettre en place un algorithme de résolution adaptatif, ainsi que des critères d’arrêt pour les solveurs itératifs et le réglage automatique d’éventuels paramètres numériques.L'objectif principal de la thèse est donc de rendre robuste la simulation numérique par éléments finis des ouvrages présentant des discontinuités géométriques. On aborde cette question sous angle double : d’un côté on revisite les méthodes existantes de représentation de fissuration en travaillant sur la loi de comportement mécanique pour les joints ; de l’autre on introduit une nouvelle méthode a posteriori pour traiter le problème de contact et propose son adaptation pour les modèles d’interfaces génériquesEngineering teams often use finite element numerical simulations for the design, study and analysis of the behavior of large hydraulic structures. For concrete structures, models of increasing complexity must be able to take into account the nonlinear behavior of discontinuities at the various interfaces located in the foundation, in the body of the dam or at the interface between structure and foundation. Besides representing the nonlinear mechanical behavior of these interfaces (rupture, sliding, contact), one should also be able to take into account the hydraulic flow through these openings.In this thesis, we first focus on the topic of interface behavior modeling, which we address through the Cohesive Zone Model (CZM). This model was introduced in various finite element codes (with the joint elements), and it is a relevant approach to describe the physics of cracking and friction problems at the geometrical discontinuities level. Although initially the CZM was introduced to take into account the phenomenon of rupture, we show in this thesis that it can be extended to sliding problems by possibly relying on the elasto-plastic formalism coupled to the damage. In addition, nonlinear hydro-mechanical constitutive relations can be introduced to model the notion of crack opening and the coupling with the laws of fluid flow. At the mechanical level, we work in the Standard Generalized Materials (SGM) framework, which provides a class of models automatically satisfying some thermodynamical principles, while having good mathematical and numerical properties that are useful for robust numerical modeling. We adapt the formalism of volumetric SGM to the interface zones description. In this first part of the thesis, we present our developpements under the hypothesis of SGM adapted to CZM, capable of reproducing the physical phenomena observed experimentally: rupture, friction, adhesion.In practice, nonlinearities of behavior of interface zones are dominated by the presence of contact, which generates significant numerical difficulties for the convergence of finite element computations. The development of efficient numerical methods for the contact problem is thus a key stage for achieving the goal of robust industrial numerical simulators. Recently, the weak enforcement of contact conditions à la Nitsche has been proposed as a mean to reduce numerical complexity. This technique displays several advantages, among which the most important for our work are: 1) it can handle a wide range of conditions (slip with or without friction, no interpenetration, etc.); 2) it lends itself for a rigorous a posteriori error analysis. This scheme based on the weak contact conditions represents in this work the starting point for the a posteriori error estimation via equilibrated stress reconstruction. This analysis is then used to estimate the different error components (e.g., spatial, nonlinear), and to develop an adaptive resolution algorithm, as well as stopping criteria for iterative solvers and the automatic tuning of possible numerical parameters.The main goal of this thesis is thus to make the finite element numerical simulation of structures with geometrical discontinuities robust. We address this question from two angles: on one side, we revisit the existing methods for the crack representation working on the mechanical constitutive relation for joints; on the other, we introduce a new a posteriori method for the contact problem and we propose its adaptation for the generic interface models
34
Seppecher, Pierre. "Etude d'une modelisation des zones capillaires fluides : interfaces et lignes de contact". Phd thesis, Paris 6, 1987. http://tel.archives-ouvertes.fr/tel-00522117.
Abstract (sommario):
Nous donnons une description fine des zones capillaires à l'aide de la théorie du second gradient ce qui permet de clarifier les phénomènes de tension superficielle et de tension de ligne. Nous montrons comment par un processus d'intégration à travers les zones capillaires cellesci peuvent être considérées comme des surfaces ou des lignes géométriques porteuses de propriétés matérielles. Pour obtenir des conditions de bilan physiquement acceptables nous faisons une analyse des ordres de grandeur des termes interfaciaux. Enfin nous utilisons la thermodynamique linéaire des phénomènes irréversibles pour écrire les lois de comportement des interfaces et des lignes de contact
35
Bansal, Dinesh Gur Parshad. "Tribological investigation of electrical contacts". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31749.
Abstract (sommario):
Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010.Committee Chair: Streator, Jeffrey; Committee Member: Blanchet, Thierry; Committee Member: Cowan, Richard; Committee Member: Danyluk, Steven; Committee Member: Neu, Richard; Committee Member: Thadhani, Naresh. Part of the SMARTech Electronic Thesis and Dissertation Collection.
36
Cohen, Celine. "Mécanismes moléculaires de la friction aux interfaces polymères souples". Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00669535.
Abstract (sommario):
En dépit de leur importance pratique considérable, et bien que de nombreuses expériences établissent une corrélation certaine entre les hétérogénéités d'interaction de surface (rugosité ou inhomogénéités chimiques) et les propriétés de friction des surfaces, le rôle de ces interactions sur la friction n'est encore pas bien décrit par les modèles et les expériences existants. Dans ce travail de thèse, nous nous sommes intéressés à l'identification des mécanismes moléculaires de la friction aux interfaces polymères souples. Dans ce contexte, nous avons réalisé deux études complémentaires. La première partie du travail concerne le mouvement d'une ligne triple solide-liquide-vapeur qui se déplace sur une surface solide sous l'effet de différentes forces (gravité, forces capillaires et tensions interfaciales), et en particulier le lien entre le piégeage et le dépiégeage de la ligne triple et l'hystérèse de l'angle de contact. Cette méthode permet de mesurer des angles de contact d'avancée et de reculée avec une précision sans précédent (0,1°)et s'avère être particulièrement sensible aux mécanismes qui tendent à ancrer la ligne triple. Ceci en fait un outil de choix pour étudier la friction liquide/solide. Dans la seconde partie du travail, nous avons cherché à comprendre comment des chaînes de polymère flexibles, fortement ancrées sur une surface solide, dans le régime des fortes densités de greffage affectent la friction entre une telle surface et un élastomère réticulé constitué du même polymère. Nous avons montré que le comportement en friction de cette couche confinée suit exactement le comportement rhéofluidifiant observé pour des couches de fondu de masses molaires équivalentes mais avec un temps de relaxation beaucoup plus long que celui des chaînes en fondu,la reptation n'étant pas permise pour les chaînes ancrées. Enfin, en comparant les résultats obtenus pour des couches greffées chimiquement à une extrémité et des couches fortement adsorbées, ayant par ailleurs les mêmes caractéristiques moléculaires (masse molaire des chaînes et épaisseur de la couche ancrée), nous avons mis en évidence que la friction est remarquablement sensible à l'organisation moléculaire au sein de la couche ancrée.
37
Lebeuf, Martin. "Étude de phénomènes chimiques au contact entre le bloc cathodique et la barre collectrice d'une cellule d'électrolyse d'aluminium". Mémoire, Université de Sherbrooke, 2012. http://hdl.handle.net/11143/6187.
Abstract (sommario):
La production d'aluminium est une industrie importante au Québec. Les propriétés de ce métal le vouent à de multiples usages présents et futurs dans le cadre d'une économie moderne durable. Toutefois, le procédé Hall-Héroult est très énergivore et des progrès demeurent donc nécessaires pour en diminuer les coûts financiers et environnementaux. Parmi les améliorations envisageables de la cellule d'électrolyse se trouve le contact entre la cathode et la barre collectrice, qui doit offrir une faible résistivité au passage du courant électrique. En cours d'opération de la cellule, ce contact a tendance à se dégrader, générant des pertes énergétiques significatives. Les causes de cette dégradation, pouvant provenir de phénomènes chimiques, thermiques, mécaniques et/ou électriques, demeurent mal comprises. Le but du présent projet était donc d'étudier les phénomènes chimiques se produisant au contact bloc-barre de la cellule d'électrolyse Hall-Héroult. En premier lieu, un aspect crucial à considérer est la pénétration du bain électrolytique dans la cathode, car des composés de bain atteignent éventuellement la barre collectrice et peuvent y réagir. À cet effet, une méthode novatrice a été développée afin d'étudier les cathodes et la pénétration du bain dans celles-ci à l'aide de la microtomographie à rayons X. Cette méthode rapide et efficace s'est avérée fort utile dans le projet et à un potentiel important pour l'étude future des cathodes et des phénomènes qui s'y produisent. Ensuite, une cellule d'électrolyse rectangulaire à petite échelle a été développée. Plusieurs phénomènes observés en industrie sur des autopsies de cellules post-opération et rapportés dans la littérature ont été reproduis avec succès à l'aide de cette cellule expérimentale. Puis, des tests sans électrolyse, ciblant l'effet du bain électrolytique sur l'acier, ont aussi été conçus et complétés afin de ségréger l'influence des différents paramètres en jeu. L'analyse des résultats de l'ensemble de ces tests a permis de constater différents phénomènes au contact bloc-barre, dont la présence systématique de NaF et, surtout, de béta-Al[indice inférieur 2]O[indice inférieur 3]. Outre la carburation inévitable de la barre collectrice, la formation d'une couche Fe-Al a aussi été observée, favorisée par une pénétration rapide du bain électrolytique dans la cathode ainsi que par une composition de bain acide en surface de la barre. Cette couche comportait par ailleurs des cristaux de béta-Al[indice inférieur 2]O[indice inférieur 3] pouvant nuire à sa conductivité électrique. Ensuite, à des ratios de bain entre 2.5 et 4.9, une mince couche contenant les éléments Al et N peut se former en surface de la barre. Pour un bain tres basique (> 6.0), c'est plutôt une couche Na [indice inférieur 2] O qui a été observée. En conditions d'électrolyse mais sans une pénétration rapide du bain dans la cathode, du Na a pu carrément pénétrer dans la barre collectrice, préférentiellement avec le carbone. De plus, de la corrosion ainsi que des couches de fer et d'oxyde de fer peuvent se former sur la barre et potentiellement dégrader la qualité du contact électrique. \Pour la suite des travaux, des mesures de résistivité ainsi que l'analyse des échantillons industriels permettraient d'évaluer l'impact de ces phénomènes sur la qualité du contact.
38
Tournaire, Hadrien. "Méthodologie pour génération de modèles réduits dynamiques multiphysiques : application aux open rotors". Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC040/document.
Abstract (sommario):
La conception d’un produit industriel requiert parfois des simulations afin de prédire le comportement du produit en question. En pratique ce type de simulations peut être réalisé en utilisant la méthode des éléments finis, cependant la précision et le niveau de détail souhaité génèrent des modèles difficiles à évaluer. En outre, le caractère itératif présent dans de nombreuses conceptions accentue le ralentissement induit par ces simulations couteuses en temps de calculs. Afin de pallier ce problème, une démarche de réduction de modèle est souhaitée par le partenaire industriel. Les grands axes de travail sur cette méthode sont : la recherche d’une haute compacité, la prise en compte de non-linéarités de grands déplacements et l’évaluation de l’amortissement dans les liaisons du système due au phénomène de contact-frictionThe mechanical design of a system involves many investigations, notably the validation of its structural behaviour over its operating frequency range. This kind of analysis can be numerically performed using the finite element method, however in such a context, the required accuracy and detail level imply models whose significant sizes lead to time consuming simulations. Moreover, the optimization process of such a system may request numerous validation computations that turn out extremely slow the design process. In the framework of this PhD we target a reduction methodology whose main features are: being compact, dealing with non-linear displacement and recovering the damping effects of the model joint due to the contact-friction phenomenon
39
Punnamaraju, Srikoundinya. "Voltage and Photo Induced Effects in Droplet-Interface-Bilayer Lipid Membranes". University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1321648604.
40
Guda, Vamsi Krishna. "Contributions à l'utilisation de cobots comme interfaces haptiques à contact intermittent en réalité virtuelle". Thesis, Ecole centrale de Nantes, 2022. http://www.theses.fr/2022ECDN0033.
Abstract (sommario):
La réalité virtuelle (RV) est de plus en plus utilisée dans des simulations industrielles mais la possibilité de toucher les objets manque rapidement par exemple pour juger de la qualité perçue dans la conception de véhicule automobile. Les interfaces haptiques actuels ne permettent de restituer aisément la notion de texture, l’approche envisagée est donc une interface à contact intermittent. Un cobot vient positionner une surface mobile à l’endroit du contact avec un objet virtuel pour permettre un contact physique avec la main de l’opérateur.Les contributions de cette thèse portent sur plusieurs aspects : le placement du robot, la modélisation de l’opérateur, la gestion du déplacement et de la vitesse du robot et la détection des intentions de l’opérateur. Le placement du robot est choisi pourpermettre d’atteindre les différentes zones de travail et pour assurer une sécurité passive en rendant impossible au robot de heurter la têteet le buste de l’opérateur en position normale de travail, i.e. assis dans un fauteuil. Un modèle de l'utilisateur, incluant un torse et desbras, est conçu et testé pour suivre les mouvements de l'utilisateur en temps réel. L’interaction est possible sur un ensemble de pose prédéfinies que l’utilisateur enchaine comme il le désire. Différentes stratégies sont proposées pour prédire les intentions de l'utilisateur. Les aspects clés de la prédiction sont basés sur la direction du regard et la position de la main de l'utilisateur. Une étudeexpérimentale ainsi que l'analyse qui en découle montrent l’apport de la prise en compte de la direction du regard. L’intérêt d’introduire des points dit « de sécurité » pour éloigner le robot de l’opérateur et permettre des déplacements rapides du robot est mis en évidenceVirtual reality (VR) is evolving and being used in industrial simulations but the possibility to touch objects is missing, for example to judge the perceived quality in the design of a car. The current haptic interfaces do not allow to easily restore the notion of texture, therefore an approach is considered “intermittent contact interface” to achieve this. A cobot positions a mobile surface at the point of contact with a virtual object to allow physical contact with the operator's hand. The contributions of this thesis concern several aspects: the placement of the robot, the modeling of the operator, the management of the displacement and the speed of the robot and the detection of the operator's intentions. The placement of the robot is chosen to allow reaching the different working areas and to ensure passive safety by making it impossible for the robot to hit the head and chest of the operator in a normal working position, i.e. sitting in a chair. A model of the user, including a torso and arms, is designed and tested to follow the user's movements in real time Interaction is possible on a set of predefined poses that the user chains together as desired. Different strategies are proposed to predict the user's intentions. The key aspects of the prediction are based on the gaze direction and the hand position of the user. An experimental study as well as the resulting analysis show the contribution of taking into account the gaze direction. The interest of introducing "safety" points to move the robot away from the operator and allow fast robot movements is highlighted
41
Damazo, Bradley N. "A compliance model of the roller contact interface for a friction drive used on ultra precision machine tools". Thesis, Cranfield University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283256.
42
Loizou, Andreas. "Modelling and simulation of themo-mechanical phenomena at the friction interface of a disc brake.An empirically-based finite element model for the fundamental investigation of factors that influence the interface thermal resistance at the friction interface of a high energy sliding pair in a disc brake". Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5489.
Abstract (sommario):
The fundamental theories of heat generation and transfer at the friction interface of a
brake assume either matching or not matching surface temperatures by having a
varying or uniform heat partition ratio respectively. In the research presented the
behaviour of heat partition has been investigated in a fundamental study based on
experimental measurements of temperature and the associated modelling and
simulation of heat transfer in a brake friction pair. For a disc brake, an important
parameter that was identified from the literature study is the interface tribo-layer
(ITL), which has been modelled as an equivalent thermal resistance value based on its
thickness and thermal conductivity. The interface real contact area was also an
important parameter in this investigation, and it has been found to affect heat
partitioning by adding its own thermal resistance.
A 2-dimensional (2D) coupled-temperature displacement Finite Element (FE) model is
presented, based on which a novel relationship which characterises the total thermal
resistance (or conductance) at the friction interface has been characterised based on
the ITL thermal properties, the contact area, and the contact pressure at the interface.
Using the model the effect of friction material wear on the total thermal resistance (or
conductance) at the friction interface was predicted and a comparison of the Archard
and Arrhenius wear laws in predicting the wear of a resin bonded composite friction
material operating against a cast iron mating surface is presented.
A 3-dimensional (3D) model is also presented. This model has represented a small
scale disc brake test rig which has been used in parallel with the simulation for
validation in a drag braking scenario. Two simulation conditions with different pad
surface states were investigated, the first having a nominally flat surface, and the
second an adjusted (worn) pad surface based on bedding-in data. The Arrhenius wear
model was applied to significance of including wear on the total thermal resistance at
the friction interface over a short brake application.
A sensitivity analysis on the interface thermal conductance, the location of heat
generation, and the magnitude of contact pressure has identified the importance of
each factor in determining the total thermal resistance (or conductance) at the friction
interface during any friction brake application. It is concluded that the heat
partitioning is insensitive on the location of heat generation, and that the most
sensitive parameter is the contact pressure.Institution of Mechanical Engineers (IMechE)
43
Babenko, Maksims. "A Study of Heat Transfer at the Cavity-Polymer Interface in Microinjection Moulding. The effects of processing conditions, cavity surface roughness and polymer physical properties on the heat transfer coefficient". Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/14745.
Abstract (sommario):
This thesis investigates the cooling behaviour of polymers during the microinjection moulding process. The work included bespoke experimental mould design and manufacturing, material characterisation, infra-red temperature measurements, cooling analysis and cooling prediction using commercial simulation software. To measure surface temperature of the polymers, compounding of polypropylene and polystyrene with carbon black masterbatch was performed to make materials opaque for the IR camera. The effects of addition of carbon black masterbatch were analysed using differential scanning calorimetry and Fourier transform infrared spectroscopy. Sapphire windows formed part of the mould wall and allowed thermal measurements using an IR camera. They were laser machined on their inside surfaces to generate a range of finishes and structures. Their topographies were analysed using laser confocal microscope. The surface energy of sapphire windows was measured and compared to typical mould steel, employing a contact angle measurement technique and calculated using Owens-Wendt theory. A heating chamber was designed and manufactured to study spreading of polymer melts on sapphire and steel substrates. A design of experiments approach was taken to investigate the influence of surface finish and the main processing parameters on polymer cooling during microinjection moulding. Cooling curves were obtained over an area of 1.92 by 1.92 mm of the sapphire window. These experiments were conducted on the Battenfeld Microsystem 50 microinjection moulding machine. A simulation study of polymer cooling during the microinjection moulding process was performed using Moldflow software. Particular interest was paid to the effect of the values of the interfacial heat transfer coefficient (HTC) on the simulated cooling predictions. Predicted temperature curves were compared to experimentally obtained temperature distributions, to obtain HTC values valid for the material and processing parameters.
44
Soundararajan, Sujitha. "Seismic Energy Dissipation, Self-Centering, and Settlement of Rocking Foundations: Analysis of Experimental Data with Comparisons to Numerical Modeling". Thesis, North Dakota State University, 2019. https://hdl.handle.net/10365/31711.
Abstract (sommario):
The major objective of this study is to correlate the rocking foundation performance parameters with their capacity parameters and earthquake demand parameters using the results obtained from 142 centrifuge and shaking table experiments. It is found that seismic energy dissipation and permanent settlement of rocking foundations correlate well with rocking coefficient and Arias intensity of the earthquake, whereas the maximum moment and peak rotation of the foundation correlate well with peak ground acceleration. A numerical model, using the contact interface model available in OpenSees, is developed to simulate the performance of rocking foundations, and it is validated using experimental results. Though the numerical model predicts the moment capacity, seismic energy dissipation, and tipping-over stability of rocking foundations reasonably well, the model appears to overpredict the settlement of foundations. Furthermore, a parametric study showed that settlement reduces as initial vertical stiffness increases and is directly proportional to peak ground displacement.
45
Hedroug, Karima. "Influence des chromates sur l'hydratation de la pate de ciment portland, durcissant au contact d'armatures galvanisees". Toulouse 3, 1987. http://www.theses.fr/1987TOU30192.
Abstract (sommario):
Les ions chromates jouent le role d'inhibiteur dans la prise des pates de ciment portland car le zinc, constituant de la derniere couche de galvanisation est dans son domaine de passivation car le ph de la solution est tres faible
46
Loizou, Andreas. "Modelling and simulation of themo-mechanical phenomena at the friction interface of a disc brake : an empirically-based finite element model for the fundamental investigation of factors that influence the interface thermal resistance at the friction interface of a high energy sliding pair in a disc brake". Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5489.
Abstract (sommario):
The fundamental theories of heat generation and transfer at the friction interface of a brake assume either matching or not matching surface temperatures by having a varying or uniform heat partition ratio respectively. In the research presented the behaviour of heat partition has been investigated in a fundamental study based on experimental measurements of temperature and the associated modelling and simulation of heat transfer in a brake friction pair. For a disc brake, an important parameter that was identified from the literature study is the interface tribo-layer (ITL), which has been modelled as an equivalent thermal resistance value based on its thickness and thermal conductivity. The interface real contact area was also an important parameter in this investigation, and it has been found to affect heat partitioning by adding its own thermal resistance. A 2-dimensional (2D) coupled-temperature displacement Finite Element (FE) model is presented, based on which a novel relationship which characterises the total thermal resistance (or conductance) at the friction interface has been characterised based on the ITL thermal properties, the contact area, and the contact pressure at the interface. Using the model the effect of friction material wear on the total thermal resistance (or conductance) at the friction interface was predicted and a comparison of the Archard and Arrhenius wear laws in predicting the wear of a resin bonded composite friction material operating against a cast iron mating surface is presented. A 3-dimensional (3D) model is also presented. This model has represented a small scale disc brake test rig which has been used in parallel with the simulation for validation in a drag braking scenario. Two simulation conditions with different pad surface states were investigated, the first having a nominally flat surface, and the second an adjusted (worn) pad surface based on bedding-in data. The Arrhenius wear model was applied to significance of including wear on the total thermal resistance at the friction interface over a short brake application. A sensitivity analysis on the interface thermal conductance, the location of heat generation, and the magnitude of contact pressure has identified the importance of each factor in determining the total thermal resistance (or conductance) at the friction interface during any friction brake application. It is concluded that the heat partitioning is insensitive on the location of heat generation, and that the most sensitive parameter is the contact pressure.
47
Ashraf, Naveed. "An investigation into the influence of the contact pressure distribution at the friction pair interface on disc brake squeal". Thesis, University of Huddersfield, 2013. http://eprints.hud.ac.uk/id/eprint/19033/.
Abstract (sommario):
The main purpose of this thesis is to investigate the dynamic centre of pressure during a noisy brake application. A novel technique is employed to measure the centre of pressure and contact pressure distribution between the disc/pad interfaces during braking events. The test rig was developed to study the contact pressure distribution between disc/pad interfaces. The caliper and set of pads were modified to measure both static and dynamic centre of pressure during braking events. The brake uses a 12 piston opposed caliper arranged to allow a number of the pistons to be controlled independently using 4 master cylinders. This allows the interface centre of pressure to be adjusted both along the length of the pad and radially. The tests included static pressure measurements with the sensor film between the pad friction face and the disc, the centre of pressure being adjusted using the master cylinders to provide a “system benchmark”. Once the static characteristic behaviour of the modified pad is established, the centre of pressure variation is measured under dynamic conditions. This allows the movement of the centre of pressure to be plotted against brake pressure and rotor speed. Furthermore, a detailed finite element model of a disc brake assembly is developed. Contact analysis was performed to determine the pressure distribution, interfacial contact area and normal contact forces under both frictionless (μ=0) and frictional braking conditions. The effect of varying friction coefficients and the brake hydraulic pressure is also examined. Preliminary finite element results of contact pressure distribution between the disc/pad interfaces were compared with the experimental results, followed by a detailed modal analysis of disc brake to predict the natural frequencies and the mode shapes of disc brake. In addition, a stability analysis of brake assembly is carried out to distinguish the unstable frequencies. Structure modification of disc brake assembly was also investigated to understand the characteristics behaviour of brake system in terms of squeal noise performance. It is established from the results that there is a strong relationship between the interface pressure distribution, the effective centre of pressure and the propensity of the brake to generate noise. It is noticed that the centre of pressure may vary both along the pad and radially during braking which adds to the complex analysis of instability. The finite element results compared well with the experimental results. It is observed that the contact pressure distribution and the magnitude of normal contact forces are much higher towards the leading edge of the pads comparing to the trailing edge. It is also established yet again that with a leading centre of pressure the brake is more prone to noise whereas with a trailing centre of pressure the system is more likely to be stable.
48
Miller, Adam Charles. "Assessment of Alternate Viscoelastic Contact Models for a Bearing Interface between an Axial Piston Pump Swash Plate and Housing". The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1403274866.
49
Robert, de saint vincent Matthieu. "Écoulements microfluidiques pilotés sans contact par une onde laser". Thesis, Bordeaux 1, 2010. http://www.theses.fr/2010BOR14072/document.
Abstract (sommario):
L’effet thermocapillaire (ou Marangoni) est la résultante mécanique d’un gradient de tensioninterfaciale induit par la présence d’un gradient de température sur une interface fluide. Il semanifeste par (i) la migration d’un objet fini (goutte, bulle) immergé, et (ii) une déflexion del’interface. Sa nature interfaciale le rend particulièrement pertinent à petite échelle, notammenten microfluidique diphasique. Ce travail de thèse montre comment un effet thermocapillaireinduit localement par chauffage laser peut être utilisé pour produire des composants optofluidiquesélémentaires (vanne, aiguillage, échantillonneur), et en présente une étude quantitative.La déstabilisation d’un jet microfluidique forcée par laser, conduisant à sa rupture, est égalementprésentée et caractérisée. Cette « boîte à outils » optique fournit ainsi une approche sans contact,pour produire et manipuler des gouttes en microfluidique digitale sans nécessité d’une microfabricationdédiée. Par ailleurs, afin de caractériser sur des temps longs les gouttes produites,et ainsi considérer des populations statistiquement significatives, un dispositif optoélectroniquesimple pour mesurer les gouttes et leur vitesse en temps réel a également été développéThe thermocapillary (or Marangoni) effect is the mechanical result of an interfacial tension gradientinduced by a temperature gradient on a fluid interface. This effect manifests itself byinducing (i) the migration of an immersed finite-size object (droplet, bubble), and (ii) a deflexionof the interface. Due to its interfacial nature, the Marangoni effect is particularly relevantat small length scales, especially in the context of two-phase microfluidics. This thesis aims atapplying the thermocapillary effect locally induced by laser heating, in order to create some basicoptofluidic actuators (valve, switch, sampler). A quantitative study of these actuators is presented.The laser-forced destabilization of a co-flowing microfluidic jet, leading to its breakup,is also investigated. This “optical toolbox” represents a non-contacting, and microfabricationfreeapproach for the production and handling of droplets in digital microfluidics. Moreover, tocharacterize these droplet over long times, thus considering statistically significant populations,a simple optoelectronic device has been developed for measuring the size and velocity of thedroplets in real time
50
Ahmadi, Habiburrahman. "Adhesion evaluation of glass fiber-PDMS interface by means of microdroplet technique". Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/9155.
Abstract (sommario):
Master of ScienceDepartment of Mechanical and Nuclear Engineering
Kevin B. Lease
This research was intended to measure the interfacial shear strength between fiber/ matrix systems and to investigate the relation between structure-mechanical properties and performance of fiber/matrix systems. This work conducted a systematic study on model fiber/matrix systems to enhance the fundamental understanding on how variation of polymeric compositions (and hence, different structures), different curing conditions, and fiber surface treatments influence the interactions between the fiber and matrix. In order to measure the interfacial shear strength of fiber/matrix systems, the microdroplet technique was used. In this technique a polymer droplet was deposited on a fiber in the liquid state. Once the droplet was cured a shear force was applied to the droplet in order to detach the droplet from the fiber. The amount of the force needed to de-bond the droplet was directly related to the strength of the bonds formed between the fiber and matrix during the curing process. In addition, the micro-droplet technique was used to evaluate effects of different crosslinker ratio of fiber/ matrix system and also to see if different curing conditions affect the interfacial shear strength of fiber/ matrix system. Surface treatment was also conducted to evaluate its effects on the interfacial shear strength of the fiber/ matrix system using microdroplet technique. The interfacial shear strength of fiber/ matrix system increased along with the increase of crosslinker ratio to a limiting value, and it decreased as long as the crosslinker ratio increased. Curing condition also caused the interfacial shear strength of fiber/ matrix system to increase when it was cured at higher temperature. Fiber surface treatment exhibited a significant effect to the interfacial shear strength as well as the fiber/ matrix contact angle measurement.