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Dissertations / Theses on the topic 'Stick-slip friction'
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Манько, Наталія Миколаївна, Наталья Николаевна Манько, and Nataliia Mykolaivna Manko. "Stick-slip mode of boundary friction." Thesis, Сумський державний університет, 2013. http://essuir.sumdu.edu.ua/handle/123456789/33545.
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The study of the boundary friction processes that develop in nanosized tribosystems has drawn active interest of many researchers. One of the perspective directions is the investigation of the friction of atomically smooth solid surfaces in the presence of an ultrathin film of a homogeneous lubricant between them. The interest is partially due to the applied significance of these systems, as they are used in increasing frequency to design precise devices and instruments.
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Tariku, Fitsum. "Simulation of dynamic mechanical systems with stick-slip friction." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0011/MQ38415.pdf.
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Wu-Bavouzet, Fangnien. "Friction sur surfaces à plots." Paris 6, 2008. http://www.theses.fr/2008PA066383.
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L'objet de cette thèse est l'adhésion et la friction de lentilles millimétriques d'élastomères sur un substrat décoré de plots micrométriques de hauteur variable. A cette fin, nous avons utilisé un AFM géant permettante mesurer les forces normales et tangentielles appliquées à la lentille et d'observer le contact. Il permet d'explorer des vitesses de glissement de l'ordre de 100 µm/s, et des forces de l'ordre de 10-3 N. Nous avons observé deux types de contact selon la hauteur h des plots : intime (h<hc) et posé (h>hc). Les régimes de glissement observés dépendent de la dureté de l'élastomère : avec une lentille dure (module d'Young E ~ 1 MPa), on observe du glissement stable, tandis qu'on met en évidence des ondes de Schallamach et de stick-slip avec des lentilles molles (E ~ 0. 1 MPa). Dans les deux cas, nous avons étudié la force de friction, l'aire de contact et la contrainte tangentielle en fonction de la hauteur des plots, de la vitesse de glissement, et de la force normale.
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Manko, N. N., and I. A. Lyashenko. "Stochastic Oscillations at Stick-Slip Motion in the Boundary Friction Regime." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35148.
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In this paper, the further development of the synergetic model describing the ultrathin lubricant film state
clamped between two atomically smooth solid surfaces operating under boundary friction mode has been done
based on the Lorentz model for the approximation of a viscoelastic medium. In all cases, the phase portraits have
been built. It has been found that the friction surfaces' temperature increasing leads to the growth of stochasticity
in the investigated system. In the phase plane the stochastic oscillation mode can be described as a strange attractor.
Also, the behavior of two different types of tribosystems were described using current model. The first
was the system with the unidirectional shear of the surfaces and, and the second was the system under an alternating
external effect. Obtained results agree qualitatively with known experimental data.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35148
5
Boone, Jacob Dee. "Design, Construction and Evaluation of Universal Friction Tester." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/307.
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AN ABSTRACT OF THE THESIS OF Jacob Boone, for the Master of Science degree in Mechanical Engineering, presented on 10/28/2010, at Southern Illinois University Carbondale. TITLE: DESIGN, CONSTRUCTION, AND EVALUTAION OF UNIVERSAL FRICTION TESTER MAJOR PROFESSOR: Dr. Peter Filip Many different types of friction testers are currently available for testing specific frictional applications. Of these machines very few have versatility, and of the ones that do, the amount of versatility is limited. Since friction is a property specific to each system, all operating parameters need to match the specific application as closely as possible in order to obtain accurate data. This requires many research facilities to have several specific friction testers in order to provide the necessary testing capabilities. The goal of this project was to design a Universal Friction Tester (UFT) with enough versatility to reproduce most types of sliding friction situations. This was accomplished by providing a wide range of testing capabilities through the use of interchangeable system components. Results show that the UFT provides quality data over its entire operating range. It was shown that normal pressure, sliding speed, temperature and system stiffness all have drastic effects on frictional performance. By using a borosilicate glass disc, the friction surface was viewed in-situ during testing. This allowed insights into true surface temperature and contact area. In conclusion, the UFT can successfully take the place of several friction testers and thus provide many friction research capabilities while requiring fewer resources. The wide range of testing capabilities will allow the UFT to be used as a research tool for many types of advanced friction studies. Some of these may include true surface temperatures, true contact area, influence of conditions on stick-slip phenomenon, and thermo-elastic instabilities.
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Lyashenko, I. A., Олексій Віталійович Хоменко, Алексей Витальевич Хоменко, et al. "Hysteresis Phenomena in the Stick-Slip Motion at the Boundary Friction Mode." Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35072.
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The tribological system is considered, which consists of two atomically smooth solid surfaces separated
by an ultrathin lubricant film. The thermodynamic model based on the Landau theory of phase transitions
is built, which describes behavior of this system in the boundary friction mode. The free energy density for
an ultrathin lubricant film is given in the form of expansion into series by the powers of order parameter
that is reduced to the shear modulus of lubricant. The kinetics of the system is studied on the basis of
model describing first-order phase transitions between kinetic modes of friction. It is shown that in the
presence of spring between the external drive and block the width of temperature hysteresis increases versus
fixed coupling.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35072
7
Suetti, André Garcia Lima. "Estudo do fenômeno "stick-slip" aplicado às vibrações de freios automotivos." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265209.
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Orientador: Robson Pederiva<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-19T13:48:38Z (GMT). No. of bitstreams: 1
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Previous issue date: 2011<br>Resumo: O interesse da indústria automobilística em projetar freios menos ruidosos vem incentivando pesquisas na área de acústica e vibração. A compreensão de um dos principais fenômenos de excitação de vibração em sistemas com atrito, o stick-slip, é de grande importância para o aprofundamento desses estudos, que muitas vezes não consideram uma fonte de excitação bem definida e realimentada, recorrendo a excitações impulsivas ou com frequências aleatórias. O stick-slip é uma vibração auto-excitada que pode ocorrer em um corpo fixo que se atrita com outro corpo que está em movimento, fundamentada na diferença entre o coeficiente de atrito estático e dinâmico. Tendo em vista a aplicação da excitação por stick-slip em vibrações em sistemas de freio, equacionamentos analíticos são propostos nesse trabalho tendo a dificuldade incrementada gradualmente. Um estudo dos efeitos do amortecimento em sistemas com stick-slip é também proposto, apresentando um comportamento que difere de sistemas mecânicos sem realimentação. Com o objetivo de se avaliar esses métodos, realizam-se simulações numéricas e um experimento, que se utiliza de materiais de atrito e disco empregados em freios. Os resultados demonstram a compatibilidade das simulações numéricas e os dados obtidos experimentalmente, o que comprova que os métodos podem ser usados na simulação do problema<br>Abstract: Interest of the automotive industry in designing quieter brakes has encouraged the researches in the fields of acoustics and vibration. Understanding one of the main phenomena of vibration excitation in systems with friction, stick-slip, is crucial to a deeper study. Many a time these studies do not consider a well-defined and fed back source, falling back on impulsive and random excitations. The stick -slip is a self-excited vibration that may occur when a static body rubs against a dynamic one. It is based on the difference between the static and dynamic friction coefficients. Considering the stick-slip excitation in the braking system vibration, analytical equations with continuous incremental difficulties are proposed herein. A study of the effects of damping in stick -slip systems is also proposed, presenting a kind of behavior that is different from that of mechanical systems without feedback. In order to evaluate these methods, an experimental or sometimes numerical simulation is conducted using friction material and discs used in braking systems. The results are in agreement with the experimental data, proving that the methods can be used in simulations of problems<br>Mestrado<br>Mecanica dos Sólidos e Projeto Mecanico<br>Mestre em Engenharia Mecânica
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Busse, Leif [Verfasser]. "Investigation, prediction and control of rubber friction and stick-slip : experiment, simulation, application / Leif Busse." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2013. http://d-nb.info/1032719249/34.
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Aubry, Jérôme. "Séismes au laboratoire : friction, plasticité et bilan énergétique." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEE053.
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Au sein de la lithosphère, la transition entre déformations fragile et plastique des roches s’effectue dans le régime semicassant. Comprendre le comportement des failles naturelles dans le régime semi-cassant est fondamental puisque d’importants séismes nucléent à la base de la zone sismogénique, à des conditions de pression et température proches de celles de la transition fragile-plastique. Pendant un séisme, l’énergie élastique accumulée lors de la période intersismique est dissipée au sein de l’interface de glissement par des processus frictionnels et de fracture, le reste étant relâché sous forme d’ondes sismiques. Ce budget énergétique est influencé par la déformation des surfaces de failles pendant des glissements lents à rapides, et plus particulièrement par des processus de chauffage, invisibles aux yeux de la sismologie. Afin d’étudier la déformation semi-cassante des roches et le budget énergétique des séismes, nous avons effectué des expériences de reproduction de séismes au laboratoire, en conditions triaxiales, à l’aide de failles expérimentales de différentes lithologies. Nous avons étudié l’influence de la pression, de la vitesse de déformation, de la température et de la rugosité sur la stabilité des failles le long de la transition fragile-plastique et exploré la dynamique des séismes au laboratoire en mesurant la quantité de chaleur produite sur une faille durant un cycle sismique. Deux conclusions principales émanent de ces travaux. D’abord, les séismes au laboratoire peuvent se déclencher au sein de roches déformées plastiquement dans le régime semi-cassant. Les glissements observés sont majoritairement contrôlés par la rugosité de la faille. Pour finir, lors d’un cycle sismique, les failles opèrent une transition depuis un stade avec de multiples aspérités radiant peu d’énergie, à un stade où elles évoluent comme une aspérité unique, radiant un maximum d’énergie<br>In the lithosphere, the transition from brittle to plastic rock deformation corresponds to the semi-brittle regime. Understand how natural faults behave in the semi-brittle regime is fundamental to explain why large earthquakes generally nucleate at the base of the seismogenic zone, found at pressure and temperature conditions close to the predicted brittle-plastic transition. During an earthquake, part of the released elastic strain energy stored during the interseismic period is dissipated within a fault slip zone by frictional and fracturing processes, the rest being radiated away via elastic waves. This energy balance is influenced by the deformation of fault surfaces during slow or fast sliding, especially by frictional heating processes which could not be resolved by seismology. To investigate semi-brittle deformation and the energy balance of natural earthquakes, we performed laboratory earthquakes in triaxial conditions on experimental faults of various lithologies. We studied the influence of the confining pressure, axial loading rates, temperature and fault roughness on fault stability across the brittle-plastic transition and investigate the dynamics of laboratory earthquakes by measuring frictional heat dissipated during the propagation of shear instabilities. The main conclusions are twofold. First, laboratory earthquakes may nucleate on inherited fault interfaces at brittle-plastic transition conditions and fault slip behavior is mainly influenced by roughness. Second, we conclude that during sliding, faults exhibit a transition from a weak stage with multiple strong asperities and little overall radiation, to a highly radiative stage during which the fault behaves as a single strong asperity
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Di, Bartolomeo Mariano, and Bartolomeo Mariano Di. "Wave generation and propagation at tribological interfaces." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00715732.
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This thesis is addressed to the understanding of the mechanisms at the origin of the contact wave fields at frictional interfaces and its relationship with the local characteristics of the surfaces in contact, as well as with the global dynamics and macroscopic frictional behaviour of the system. The aim of this work is to provide insights on the generation and propagation of the waves through the contact both to avoid instabilities and to control their effect on friction. The work is organized in two main parts. The first part presents the development of a non-linear finite element analysis in large transformations of the dynamic rupture at the interface with contact friction separating two bodies (isotropic and elastic) without relative motion. A rupture is considered when an initially sticking zone shifts in sliding state. The properties of the obtained ruptures are analyzed for a flat interface between dissimilar materials in function of the nucleation energy; then the effect of the interface roughness is analyzed. The differentiated rupture inside the asperities and the conditions for coupling and uncoupling between the waves radiating in the two bodies have been also investigated. In the second part, the analysis deals with the sliding onset between two bodies in contact. The sliding between two bodies made of different isotropic elastic materials and separated by a frictional interface is simulated. The evolution along the time of the global normal and tangential forces is analyzed, relating it to the local phenomena occurring at the interface. This part tries to investigate how micro-slips at the interface, acting as distributed ruptures, trigger the macro-slips between the two bodies. The interaction between local and global dynamics is also studied. Finally a numerical parameter space study is carried out, as a function of several system parameters (contact law, friction coefficient, material damping, normal load, translational velocity and regularization time). The results show the key role of the micro-slips and precursors (detectable wave propagations that occur at tangential global force well below the critical value expected by the friction law) in triggering the macro-slip between the two bodies. Depending on their distribution and magnitude the evolution of the contact forces passes from stick-slip-like behaviour to continuous sliding. The local dynamics at the contact (wave and rupture propagation) is linked to the global behaviour of the system (stick-slip, continuous sliding, induced vibrations); the effect of the contact and system parameters on the transfer of vibrational energy between the sliding contact and the system is investigated. The numerical results obtained by the two parts of the work show a good agreement with experimental results in literature.
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KONDEPUDI, RAMABALARAJENDRASESH. "NUMERICAL ANALYSIS OF LUMPED PARAMETER DYNAMIC SYSTEMS WITH FRICTION." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1083622496.
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Gandhi, Satish. "Study of Friction Effects on System Dynamics using Low-Order Lumped-Parameter Models." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1029423191.
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Tonazzi, Davide. "Macroscopic frictional contact scenarios and local contact dynamics : At the origins of “macroscopic stick-slip”, mode coupling instabilities and stable continuous sliding." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0110/document.
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Le comportement local au contact et son interaction avec la dynamique globale du système sont à l'origine d’innombrables problèmes de contact concernant plusieurs disciplines telles que la tribologie, la géophysique, la mécanique de vibration ou la mécanique de la rupture. Lorsque deux corps élastiques sont en mouvement relatif avec une interface de frottement, des vibrations induites se produisent dans le système. Dans un point de vue macroscopique, le scénario macroscopique de stick-slip survenant pendant le mouvement relatif est caractérisé par la chute soudaine de la force de frottement (état de glissement), séparées par des périodes d'accumulation d'énergie élastique (état d’adhérence). Autrement, une instabilité dynamique se produit quand un mode de vibration du système mécanique devient instable en raison des forces de frottement. Ces types d'instabilités, générées par des forces de frottement, ont été principalement objet de publies traitant de problèmes spécifiques dans différents domaines. Dans ce contexte, des analyses expérimentales et numériques ont été ici mis en place pour comprendre comme le comportement de l'interface locale affecte la réponse macroscopique du système et vice-versa, au cours de scénarios d'instabilité. Les scénarios macroscopiques (instabilité de « stick-slip macroscopique », instabilité modale, glissement continu stable), survenant entre deux milieux élastiques simples en mouvement relatif, ont été étudiés numériquement et expérimentalement. Un dispositif expérimental dédié (TRIBOWAVE) a été développé et a permis de reproduire et examiner les différents scénarios de frottement dans des conditions aux limites bien contrôlées. Les mêmes scénarios de frottement ont été reproduits par des simulations numériques transitoires. Une loi de frottement en fonction du temps d’adhérence (stick) a été définie à partir des essais expérimentaux. La loi de frottement obtenue a été mise en œuvre dans le modèle numérique, conduisant à une validation quantitative des scénarios de frottement par les expériences. Les simulations transitoires non linéaires, l’analyse aux valeurs propres complexes et les tests expérimentaux ont permis de dessiner des cartes de scénarios d'instabilité en fonction des paramètres clés du système. Validé par la comparaison avec les mesures des signaux expérimentaux globaux (forces, accélérations / vitesse), le modèle numérique a permis d'étudier le couplage entre le comportement du contact local (distribution de l'état du contact, propagation des ondes et des ruptures, précurseurs) et la réponse dynamique du système au cours du « stick-slip macroscopique », de l’instabilité due au couplage modale et du glissement continu stable. La compréhension du couplage entre le contact et la dynamique des systèmes apportera de nouvelles améliorations sur le contrôle des instabilités de contact et les problèmes d'usure connexes<br>Local contact behavior and its interaction with the global dynamics of the system are at the origin of innumerable contact issues concerning several different disciplines like tribology, geophysics, vibration mechanics or fracture mechanics. When two elastic media are in relative motion with a frictional interface, friction induced vibrations arise into the system. By a macroscopic point of view, the “macroscopic stick-slip” scenario occurring during relative motion is characterized by sudden friction force drops (sliding state) along the time, separated by periods of elastic energy accumulation (stick state). Instead, the mode dynamic instability occurs when a vibration mode of the mechanical system becomes unstable, due to frictional contact forces. This kind of instabilities, generated by frictional forces, have been mainly object of papers dealing with specific issues in different domains. In this context, experimental and numerical analyses have been focused here on understanding how the local interface behavior affects the macroscopic frictional response of the system, and, conversely, during instability scenarios. The macroscopic frictional scenarios (macroscopic stick-slip instability, mode coupling instability, stable continuous sliding) arising between two simple elastic media in relative motion have been investigated numerically and experimentally. A newer experimental setup (TRIBOWAVE) has been developed and it allowed to reproduce and to investigate the different scenarios under well-controlled boundary conditions. The same frictional scenarios have been reproduced by transient numerical simulations. A dedicated friction law as a function of adherence (sticking) time has been recovered by means of experimental tests. The obtained friction law has been implemented in the numerical model, leading to a quantitative validation of the simulated scenarios by the experiments. Nonlinear transient simulations, complex eigenvalue analyses and experimental tests allowed for drawing instability maps as a function of system key parameters. The numerical model, validated by the comparison with the experimental global measurements (forces, accelerations/velocity), allowed for investigating the coupling between the local contact behavior (contact status distribution, wave and rupture propagation, precursors) and the system dynamic response during macroscopic stick-slip instability, mode coupling instability and stable continuous sliding. The understanding of the coupling between contact and system dynamics will bring to further improvements on the control of contact instabilities and related wear issues
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Ghezzi, Ilaria. "Tribological and vibro-acoustic behaviour of a lubricated contact subjected to the stick-slip phenomenon : The case of the spring-brake system." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI116.
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Les travaux de thèse proposent une approche complémentaire, combinant analyses dynamiques et tribologiques, au problème de stick-slip d’un contact graissé, dans un frein mécanique à ressort. L’instabilité de stick-slip est le résultat du couplage entre la réponse dynamique du système mécanique (frein) et la réponse locale du contact lubrifié à l’interface de freinage. La réponse locale du contact graissé a d’abord été caractérisée par des tests expérimentaux effectués sur tribomètre. Ensuite, les conditions qui conduisent à l'instabilité ont pu être investiguées en détail, à l’aide d’un modèle numérique a paramètres concentres du système complet. Ce modèle simule le comportement dynamique global du système de freinage mécanique. En entrées, il prend les paramètres propres au fonctionnement et à la conception du frein, ainsi que les courbes de frottement locales. En sortie, le poids de chacun des paramètres sur la génération du stick-slip a donc pu être analysé. Enfin, une étude expérimentale de l’influence des différents composants de la lubrification (DLC et graisse) sur le comportement du contact frottant lubrifié a été réalisée. Dépendante de l’épaississant, de l’huile et des additifs, la rhéologie complexe de la graisse est un point clé pour comprendre l'apparition du stick-slip. En effet si la lubrification est traditionnellement censée réduire les pertes par frottement, elle peut malgré tout participer à l’apparition d’instabilités. La compréhension des conditions pour lesquelles un système est prédisposé au phénomène de stick-slip peut permettre de prévenir l'apparition de telles instabilités et des nuisances qu’elles engendrent. Néanmoins, en présence de contacts lubrifiés, la littérature n’y consacre que peu de travaux. C’est dans ce contexte que l’analyse multi-approches présentée dans cette thèse permet de contribuer à la compréhension de l’apparition des instabilités de frottement dans les contacts lubrifiés avec graisse, en apportant également des éléments de solution dans le cas d’une application spécifique<br>The thesis works propose a complementary approach, combining dynamic and tribological analyzes, to the stick-slip problem of a greased contact, in a mechanical spring brake. Stick-slip instability is the result of the coupling between the dynamic response of the mechanical system (brake) and the local response of the lubricated contact at the brake interface. The local response of the greased contact was first characterized by experimental tests performed on a tribometer. Then, the conditions which lead to instability have been investigated in detail, using a numerical lumped model of the complete system. This model simulates the overall dynamic behavior of the mechanical braking system. As inputs, it takes the parameters specific to the operation and design of the brake, as well as the local frictional behavior obtained experimentally. At the output, the influence of each of the parameters on the generation of the stick-slip has been therefore analyzed. Finally, an experimental study of the influence of the different lubricant components (DLC and grease) on the behavior of the lubricated frictional contact has been carried out. Dependent on thickener, oil and additives, the complex rheology of grease is a key point for the understanding of the stick-slip appearance. Indeed, if lubrication is traditionally supposed to reduce friction losses, it can also participate in the appearance of instabilities. Understanding the conditions for which a system is predisposed to the stick-slip phenomenon can help prevent the appearance of such instabilities and the nuisance they cause. However, in the presence of lubricated contacts, the literature shows a lack of informations. It is in this context that the multi-approach analysis presented in this thesis makes it possible to contribute to the understanding of the appearance of friction instabilities in contacts lubricated with grease, by also providing elements of solution in the case of a specific application
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Hamouda, Karim. "Bronze-Steel Friction Characteristics under the Lubrication of Modified Water/Glycerol Mixtures." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65217.
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Increasing environmental awareness has driven a lot of research to look into various environmentally friendly lubricants which can replace more conventional mineral oil based lubricants. This is true in particular for marine and hydropower applications where the risk of lubricant leakage can be damaging to the local environment. Glycerol is an organic compound produced as a byproduct when producing Biodiesel. It is environmentally friendly and has been used by the pharmaceutical and food industries for a long time. Recent research has shown that glycerol has very good tribological properties and can be used as a lubricant in some applications. However, its high viscosity and high static friction are disadvantageous and needs improvement. The purpose of this study is to investigate possible surface active environmentally adapted additives in glycerol and water solutions. 14 additives have been selected for testing and were tested in a pin-on-disc start-stop friction test to see their effect on the static and dynamic friction coefficients. From these 14 additives two were selected due to their superior performance and were further studied. The effect of concentration of water and additive in glycerol was also investigated using the same test conditions. A phosphor based additive has been found to be the best performing.
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Tambe, Nikhil S. "Nanotribological investigations of materials, coatings and lubricants for nanotechnology applications at high sliding velocities." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1109949835.
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Nguyen, Thi Thu Tra. "Dynamic instabilities of model granular materials." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSET007/document.
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Cette thèse étudie les instabilités dynamiques des milieux granulaires modèles saturés à l’aide d’un appareil triaxial classique. Les instabilités englobent la liquéfaction et les effondrements en compression isotrope drainée, les frottements saccadés en compression triaxiale drainée. Ces instabilités apparaissent spontanément à des contraintes effectives de confinement imprévisibles. Elles sont accompagnées de très rapides et très fortes surpressions interstitielles, malgré un drainage approprié; ce que ne présentent pas les milieux granulaires naturels. En compression isotrope drainée (consolidation), des effondrements locaux naissent instantanément. En compression triaxiale drainée, on observe de larges frottements saccadés quasi-périodiques caractérisés par des déformations volumiques et axiales contractantes. De temps en temps, ces effondrements et frottements saccadés locaux peuvent se développer en liquéfaction menant à une destruction complète de la structure granulaire. Les données à haute résolution temporelle issues de ce travail ont permis la découverte d’une nouvelle famille de liquéfaction dynamique et statique. L’étude des émissions acoustiques passives a permis l’identification de signature spectrale caractéristique. Pour les frottements saccadés, la phase de glissement peut être interprétée comme une consolidation dynamique, limitée par l’unique surface en dessous de la ligne critique de rupture dans le plan des contraintes effectives. La séquence temporelle précise des événements exclut que la pression interstitielle soit la cause principale des instabilités. Cependant, le rôle important de la surpression interstitielle est démontré dans des relations quantitatives entre les incréments de contraintes, et de déformations et l’éphémère surpression interstitielle stabilisée développée pendant la phase de glissement. Cela montre finalement la nature quasi-déterministique de ces instabilités dynamiques. Ces relations empiriques sont basées uniquement sur l’amplitude maximale de l’accélération verticale de très courte durée et sont gouvernées indépendamment par la pression de confinement et par l’indice des vides. La similarité de la surpression interstitielle entre différentes instabilités suggère fortement quelques mécanismes similaires de déclenchement, probablement à partir de ré-arrangements de la micro-structure granulaire<br>This thesis reports a laboratory study on the dynamic instabilities of model saturated granular material using a triaxial apparatus. The term instability consists of isotropic collapse and liquefaction under isotropic compression and of stick-slip under triaxial compression in drained condition. The instabilities spontaneously occur at unpredictable effective stress with unexpected buildup of excess pore pressure irrespective of fully drained condition, contrasting with the instability-free behaviour of natural granular materials. In isotropic compression, instantaneous local collapse happens and in triaxial compression, very large and quasi-periodic stick-slip occurs with sudden volumetric compaction and axial contraction. Sometimes, these local failures (collapse and stick-slip) can develop into total liquefaction failure, destroying completely the granular structure. High time-resolved data permit the discovery of a new family of dynamic and static liquefaction. Passive acoustic measurements allow the identification of typical spectral signature. For stick-slip phenomenon, the slip phase with constant duration of stress drop can be interpreted as dynamic consolidation at constant deviatoric stress, limited by a unique boundary inside the critical state line in the effective stress plane. The precise temporal sequence of mechanical measurements excludes the generated pore pressure as the main cause of the instabilities. However, the role of pore pressure is emphasised by consistent quantitative relations between the amplitude of incremental stresses, incremental strains and the ephemeral stabilised excess pore pressure developed during the dynamic event, leading to the quasi-deterministic nature of granular instabilities. These empirical relations are based only on the short-lived maximum vertical acceleration and governed separately by the confining pressure and the initial void ratio. The similarity of pore pressure evolution for different kinds of instability strongly suggests some common speculative triggering mechanisms, probably originated from different rearrangements of the granular micro-structure
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Elmaian, Alex. "Méthodologies de simulation des bruits automobiles induits par le frottement." Phd thesis, Université du Maine, 2013. http://tel.archives-ouvertes.fr/tel-00839253.
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Les bruits automobiles induits par le frottement sont à l'origine de nombreuses plaintes clients et occasionnent des coûts de garantie considérables pour les constructeurs automobiles. Les objectifs de la thèse consistent à comprendre la physique à l'origine de ces bruits et proposer des méthodologies de simulation afin de les éradiquer. Un système générique est tout d'abord étudié. Ce système discret met en jeu un contact entre deux masses et une loi de frottement de Coulomb présentant une discontinuité à vitesse relative nulle. Des calculs de valeurs propres complexes de ce système linéarisé autour de sa position d'équilibre glissant sont menés et montrent la présence d'instabilités par flottement voire par divergence. Les simulations temporelles montrent quant à elles que les non-linéarités de contact permettent de stabiliser les niveaux vibratoires en cas d'instabilité selon quatre régimes distincts. De plus, malgré ses trois degrés de liberté, ce système est capable de reproduire les mécanismes de stick-slip, sprag-slip et couplage modal ainsi que les bruits de crissement, grincement et craquement rencontrés sur les systèmes automobiles. Des études paramétriques sont également présentées et mettent en avant des bifurcations de Hopf ainsi que l'effet déstabilisant potentiellement induit par l'amortissement. Des méthodologies permettant de catégoriser les réponses en termes de bruit et de mécanisme sont par la suite proposées. Les occurrences et risques de ces derniers sont alors analysés et des tendances sont dégagées. Enfin, la relation entre les bruits et les mécanismes est établie. L'attention est ensuite portée sur un système automobile particulier. Afin d'étudier son comportement crissant, les analyses de stabilité et les simulations temporelles sont désormais menées sur des modèles éléments-finis. Les simulations temporelles permettent d'observer l'établissement de vibrations auto-entretenues et d'identifier, parmi tous les modes instables prédits lors des analyses de stabilité, celui qui est réellement à l'origine de l'instabilité. L'effet du coefficient de frottement sur les motifs de coalescence et les cycles limites est également investigué. Le risque de crissement est ensuite évalué pour des conditions d'utilisation variées du système. La méthodologie, basée sur des analyses de stabilité, permet de retrouver les principaux constats expérimentaux obtenus sur banc d'essai. Le rôle des géométries et des matériaux constituant le système est également discuté. Enfin, une solution permettant de réduire de façon significative le risque de crissement est proposée.
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Moldenhauer, Patrick. "Modellierung und Simulation der Dynamik und des Kontakts von Reifenprofilblöcken." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-38439.
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Die Kontaktverhältnisse zwischen Reifen und Fahrbahn bestimmen die maximal übertragbaren Beschleunigungs-, Brems- und Seitenkräfte des Fahrzeugs und sind daher für die Fahrsicherheit von großer Bedeutung. In dieser Arbeit wird ein Modell zur numerisch effizienten Simulation der hochfrequenten Dynamik einzelner Reifenprofilblöcke entwickelt. Der vorgestellte Modellansatz nutzt einerseits die Vorteile der Finite-Elemente-Methode, welche die Bauteilstruktur detailliert auflösen kann, bei der jedoch lange Rechenzeiten in Kauf genommen werden. Andererseits profitiert der vorgestellte Modellansatz von den Vorteilen stark vereinfachter Mehrkörpersysteme, welche die Berechnung der hochfrequenten Dynamik und akustischer Phänomene erlauben, jedoch strukturdynamische Effekte und das Kontaktverhalten in der Bodenaufstandsfläche des Reifens nur begrenzt abbilden können. Das hier vorgestellte Modell berücksichtigt in einem modularen Ansatz die Effekte der Strukturdynamik, der lokalen Reibwertcharakteristik, der nichtlinearen Wechselwirkungen durch den Kontakt mit der rauen Fahrbahnoberfläche und des lokalen Verschleißes. Die erforderlichen Modellparameter werden durch geeignete Experimente bestimmt. Ein Schwerpunkt der Arbeit liegt in der Untersuchung reibungsselbsterregter Profilblockschwingungen bei Variation der Modell- und Prozessparameter. Zur realistischen Betrachtung des Reifenprofilblockverhaltens erfolgt eine Erweiterung des Modells um eine Abrollkinematik, die tiefere Einblicke in die dynamischen Vorgänge in der Bodenaufstandsfläche des Reifens ermöglicht. Diese Simulationen lassen eine Zuordnung der aus der Literatur bekannten zeitlichen Abfolge von Einlaufphase, Haftphase, Gleitphase und Ausschnappphase zu. Es zeigen sich bei bestimmten Kombinationen aus Fahrzeuggeschwindigkeit und Schlupfwert ausgeprägte Stick-Slip-Schwingungen im akustisch relevanten Frequenzbereich. Das Modell erlaubt die Untersuchung des Einflusses der Profilblockgeometrie, der Materialparameter, der Fahrbahneigenschaften sowie der Betriebszustände auf den resultierenden Reibwert, auf das lokale Verschleißverhalten sowie auf das Auftreten hochfrequenter reibungsselbsterregter Schwingungen. Somit ermöglicht das Modell ein vertieftes Verständnis der Vorgänge im Reifen-Fahrbahn-Kontakt und der auftretenden Wechselwirkungen zwischen Struktur- und Kontaktmechanik. Es kann eine Basis für zukünftige Optimierungen des Profilblocks zur Verbesserung wesentlicher Reifeneigenschaften wie Kraftschlussverhalten, Verschleiß und Akustik bilden<br>The contact conditions between tyre and road are responsible for the maximum acceleration, braking and side forces of a vehicle. Therefore, they have a large impact on the driving safety. Within this work a numerically efficient model for the simulation of the high-frequency dynamics of single tyre tread blocks is developed. The presented modelling approach benefits the advantage of the finite element method to resolve the component structure in detail. However, a long computation time is accepted for these finite element models. Moreover, the presented modelling approach makes use of the advantage of simplified multibody systems to calculate the high-frequency dynamics and acoustic phenomena. However, structural effects and the contact behaviour in the tyre contact patch can be covered only to a minor degree. The model treated here considers the effects of structural dynamics, the local friction characteristic, the non-linear interaction due to the contact with the rough road surface and local wear. The required model parameters are determined by appropriate experiments. One focus of this work is the investigation of self-excited tread block vibrations under variation of the model and process parameters. In order to realistically investigate the tread block behaviour the model is extended with regard to rolling kinematics which provides a deeper insight into the dynamic processes in the tyre contact patch. The corresponding simulations allow the allocation of the run-in phase, sticking phase, sliding phase and snap-out which is reported in the literature. For certain combinations of vehicle velocity and slip value pronounced stick-slip vibrations occur within the acoustically relevant frequency range. The model enables to study the influence of the tread block geometry, the material properties, the road surface characteristics and the operating conditions on the resulting tread block friction coefficient, local tread block wear and the occurrence of high-frequency self-excited vibrations. The simulation results provide a distinct understanding of the processes in the tyre/road contact and the interactions between structural mechanics and contact mechanics. They can be a basis for future tread block optimisations with respect to essential tyre properties such as traction, wear and acoustic phenomena
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Di, Bartolomeo Mariano. "Wave generation and propagation at tribological interfaces." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0144/document.
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L’objectif de cette thèse est d’approfondir la connaissance sur la génération et la propagation des ondes à travers l’interface de contact afin de contrôler leurs effets sur le frottement, contrôler les instabilités et réduire les phénomènes d'usure. Le travail est organisé en deux parties principales. La première partie est axée sur une analyse non-linéaire par éléments finis en grandes transformations; la rupture dynamique à l’interface de contact avec frottement, qui sépare deux corps (isotropes et élastiques) en condition de pré-charge statique, est simulée. On définit comme étant une rupture une zone, initialement en adhérence, qui change son état en devenant glissante. Les propriétés des ruptures sont analysées pour une surface plane entre deux matériaux différents en fonction de l’énergie de nucléation; l’effet de la rugosité de surface est ensuite analysée. En outre, la rupture "cumulatives" dans les aspérités et les conditions pour le couplage ou le non-couplage entre les ondes qui se propagent dans les deux corps sont étudiées. Dans la deuxième partie, l'amorçage du glissement entre deux corps en contact constitués de matériaux différents et séparés par une interface avec frottement, est simulée. L’évolution, en fonction du temps, des forces globales (normale et tangentielle) a été mise en relation avec les phénomènes locaux qui se déroulent à l’interface. L'analyse montre comment les micro-slips à l'interface, en agissant comme ruptures localisées, déclenchent les macro-slips entre les deux corps. L'interaction entre les dynamiques locale du contact et globale du système a été aussi étudiée. Enfin, une analyse paramétrique est menée en fonction de plusieurs paramètres (loi de contact, coefficient de frottement, amortissement matériau, charge normale, etc.). Les résultats mettent en avant le rôle-clé des micro-slips et des précurseurs (propagations d'ondes détectables qui ont lieu pour des valeurs de la force tangentielle globale inférieures à la valeur prévue par la loi de frottement) dans l'amorçage du macro-slip entre les deux corps. En fonction de leur distribution et de leur intensité, l'évolution des forces de contact change en passant d'un comportement de type stick-slip à un glissement continu. La dynamique locale au contact (propagation des ondes et ruptures) a été reliée au comportement global du système (stick-slip, glissement continu, vibrations induites); l'effet des paramètres du contact et du système sur le transfert d'énergie vibrationnelle entre le contact glissant et le système a également été examinée: en fonction de leurs valeurs, on peut avoir différentes modalités d'excitation du système (par une distribution de micro-slips ou par des macro-slips) et différentes processus de propagation et dissipation d'énergie. Les résultats numériques obtenus dans les deux parties de la thèse sont cohérents avec les résultats expérimentaux de la littérature<br>This thesis is addressed to the understanding of the mechanisms at the origin of the contact wave fields at frictional interfaces and its relationship with the local characteristics of the surfaces in contact, as well as with the global dynamics and macroscopic frictional behaviour of the system. The aim of this work is to provide insights on the generation and propagation of the waves through the contact both to avoid instabilities and to control their effect on friction. The work is organized in two main parts. The first part presents the development of a non-linear finite element analysis in large transformations of the dynamic rupture at the interface with contact friction separating two bodies (isotropic and elastic) without relative motion. A rupture is considered when an initially sticking zone shifts in sliding state. The properties of the obtained ruptures are analyzed for a flat interface between dissimilar materials in function of the nucleation energy; then the effect of the interface roughness is analyzed. The differentiated rupture inside the asperities and the conditions for coupling and uncoupling between the waves radiating in the two bodies have been also investigated. In the second part, the analysis deals with the sliding onset between two bodies in contact. The sliding between two bodies made of different isotropic elastic materials and separated by a frictional interface is simulated. The evolution along the time of the global normal and tangential forces is analyzed, relating it to the local phenomena occurring at the interface. This part tries to investigate how micro-slips at the interface, acting as distributed ruptures, trigger the macro-slips between the two bodies. The interaction between local and global dynamics is also studied. Finally a numerical parameter space study is carried out, as a function of several system parameters (contact law, friction coefficient, material damping, normal load, translational velocity and regularization time). The results show the key role of the micro-slips and precursors (detectable wave propagations that occur at tangential global force well below the critical value expected by the friction law) in triggering the macro-slip between the two bodies. Depending on their distribution and magnitude the evolution of the contact forces passes from stick-slip-like behaviour to continuous sliding. The local dynamics at the contact (wave and rupture propagation) is linked to the global behaviour of the system (stick-slip, continuous sliding, induced vibrations); the effect of the contact and system parameters on the transfer of vibrational energy between the sliding contact and the system is investigated. The numerical results obtained by the two parts of the work show a good agreement with experimental results in literature
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Craciun, Andra. "AFM force spectroscopies of surfaces and supported plasmonic nanoparticules." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAE039/document.
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Dans ce travail de thèse, le microscope à force atomique (AFM) a été utilisé comme outil de manipulation de haute précision pour construire des nanostructures plasmoniques avec des géométries définies et un réglage précis de la distance interparticulaire et également comme technique de spectroscopie d'absorption. Différentes études concernant les phénomènes pertinents pour la manipulation des nanoparticules et émergeant à l'interface substrat-nanoparticules, ont été réalisées. Des expériences de frottement menées sur diverses surfaces d'oxydes ont révélé un nouveau mécanisme de frottement à l’échelle nanométrique, expliqué par un modèle de potentiel d'interaction de type Lennard-Jones modifié. Les propriétés de frottement et d'adhésion de CTAB adsorbé sur silice sont également présentées. Des nano-bâtonnets d'or fonctionnalisés par du CTAB ont été manipulés par AFM afin de construire des nanostructures plasmoniques. La dernière partie de la thèse présente les efforts expérimentaux et théoriques pour démontrer la faisabilité de l'utilisation d'un AFM comme une technique de spectroscopie optoélectronique à base de force<br>In this thesis work the atomic force microscope (AFM) was employed first as a high precision manipulation tool for building plasmonic nanostructures with defined geometries and precise tuning of interparticle distance and second as an absorption spectroscopy technique. Different studies regarding phenomena emerging at sample nanoparticle interface relevant for nanoparticle manipulation were performed. Friction experiments conducted on various oxide surfaces revealed a novel nanoscale stick slip friction mechanism, explained by a modified Lennard-Jones-like interaction potential model. Frictional and adhesion properties of CTAB adsorbed on silica are also reported. CTAB functionalized gold nanorods were used for building specific plasmonic particulate nanostructures. The final part of the thesis presents experimental and theoretical efforts to demonstrate the feasibility of using an AFM as a force-based optoelectronic spectroscopy technique
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Ляшенко, Яків Олександрович, Яков Александрович Ляшенко та Yakiv Oleksandrovych Liashenko. "Фазовые переходы между кинетическими режимами граничного трения". Thesis, Сумский государственный университет, 2016. http://essuir.sumdu.edu.ua/handle/123456789/46497.
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У дисертацiї побудовано теорiю тертя атомарно-гладких твердих поверхонь, роздiлених межовим мастилом, плавлення i тверднення якого подано як фазовi переходи першого або другого роду. Описано переривчастий режим руху та ефекти пам’ятi, пов’язанi з релаксацiйними процесами. При врахуваннi залежностi ефективної в’язкостi вiд температури i градiєнта швидкостi описано статичну силу тертя. Можливий випадок, коли по площi контакту iснує доменна структура з рiдиноподiбними i твердоподiбними дiлянками. При просторово неоднорiдному розподiлi параметра порядку мастило швидко набуває однорiдного стану. При врахуваннi пружностi контактуючих поверхонь фронт плавлення поширюється вiд межi контакту до центра системи. Побудовано модель наноструктуруючого вигладжування, описано автоколивальний режим, що має мiсце в експериментах. При пiдвищеннi зовнiшнього навантаження
фазовий перехiд першого роду стає неперервним фазовим переходом другого роду. Побудовано нерiвноважну термодинамiчну модель, що враховує передавання енергiї вiд мастила, яке розiгрiвається за рахунок виконання роботи, до поверхонь тертя. Описано тертя мiж зернами у фрагментованому металi у надпластичному станi.<br>В диссертации разработана теория граничного трения между атомарногладкими твердыми поверхностями, разделенными ультратонким слоем смазки. Плавление и затвердевание смазки представлены как фазовые переходы первого либо второго рода. Найдены аналитические выражения критических температур и скоростей, при которых происходят плавление и затвердевание.
На примере простого механического аналога трибологической системы показано, что смазка в процессе трения либо всегда твердоподобна, либо находится в жидкоподобном состоянии, либо реализуются периодические переходы плавление/затвердевание. Рассмотрена трибологическая система, состоящая из контактирующих блоков, один из которых закреплен между двумя пружинами, а другой приводится в непрерывное периодическое движение. Установлено, что для псевдопластических жидкостей с ростом температуры упругие напряжения и сила трения уменьшаются. Проведен учет универсальной зависимости вязкости высокомолекулярных алканов (смазок) от температуры и градиента скорости. Описаны особенности ”стоп-старт“- экспериментов, когда система останавливается на определенное время, а затем продолжает движение. При низких температурах реализуется квазистатическая сила трения, что позволяет объяснить экспериментально наблюдаемые ”эффекты памяти“. Учет линейного слагаемого в разложении свободной энергии, возникающего за счет наличия электрического поля в случае дипольных смазочных молекул при их упорядочении в процессе трения, также позволяет описать статическую силу трения. Рассмотрено поведение смазки, зажатой между шероховатыми поверхностями. При этом по площади контакта присутствуют жидкоподобные и твердоподобные области. В пространственно неоднородном случае, для описания которого проведен учет градиентного слагаемого в разложении свободной энергии, смазка быстро релаксирует к однородному состоянию. Проведено моделирование с учетом упругих свойств контактирующих тел и показано, что плавление начинается на внешней границе контакта и распространяется внутрь к центру системы. Волна плавления сопровождается волной затвердевания. Проведено моделирование процесса наноструктурирующего выглаживания на основе динамической модели, описывающей движение индентора и
учитывающей упругое и пластическое деформирование поверхностного слоя под действием внешней силы. В широком диапазоне параметров реализуется автоколебательный режим, наблюдаемый в экспериментах по выглаживанию цилиндра с просверленным углублением. Построена термодинамическая модель, явным образом учитывающая влияние внешней нагрузки. Показано, что увеличение давления приводит к вынужденному упорядочению и затвердеванию смазки. Рассмотрены симметричное и несимметричное разложения свободной энергии по степеням параметра порядка. В случае симметричного разложения упорядоченное состояние смазки отвечают нулевому значению избыточного объема, что соответствует кристаллическому состоянию при отсутствии структурных дефектов. Такая ситуация реализуется для систем, в которых смазочный слой состоит из квазисферических молекул, способных образовывать упорядоченные структуры. В случае несимметричного потенциала ненулевое значение параметра избыточного объема отвечает как жидкоподобной, так и твердоподобной смазке. Такое описание справедливо для смазочных материалов, выполненных на основе полимерных цепных молекул, которые неспособны полностью упорядочиваться при низких температурах либо больших нагрузках на поверхности трения. Модель показывает появление длинных кинетических участков на зависимости силы трения от времени с увеличением скорости сдвига, что наблюдается во многих экспериментах.
Предложена неравновесная термодинамическая модель, учитывающая процессы теплопроводности, что позволяет представить затвердевание смазки за счет отдачи тепла поверхностям трения. Выделено две подсистемы: неравновесную, получающую теплоту при совершении над системой работы, и равновесную, в которую переходит эта теплота в результате внутренних процессов. Разработанная теория граничного трения применена к описанию процессов, происходящих в твердом теле при его интенсивном нагружении в режиме сверхпластичности. При этом рассматривается известная модель скольжения по границам зерен, где граница зерна представляет ультратонкую смазку, разделяющую соседние зерна. Рассмотрена кинетика процесса на основе системы, состоящей из двух трущихся кристаллических тел. Полученные в диссертации результаты качественно совпадают с экспериментальными данными
других авторов.<br>In thesis a theory of friction of atomically smooth solid surfaces separated by boundary lubricant is constructed, whose melting and solidification are presented as the first- or second-order phase transitions. Stick-slip motion mode and memory effects associated with relaxation processes are described. Taking into account the effective viscosity dependence on the temperature and velocity gradient the static friction force is construed. The case when the contact area has domain structure with liquid- and solid-like sections is possible. At spatially inhomogeneous distribution of the order parameter lubricant quickly becomes homogeneous. When considering the elasticity of contact surfaces the front of melting extends from the boundary of the contact to the center of system. Nanostructuring burnishing model is proposed and auto-oscillatory mode is revealed which takes place in experiments. With external load increasing the firstorder phase transition transforms into continuous second-order phase transition. Nonequilibrium thermodynamic model is built that takes into account the transfer of energy from lubricant, that is heated due to the work execution, to the friction surfaces. Friction between the grains in fragmented superplastic metal is described
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Lundberg, Oskar. "On the influence of surface roughness on rolling contact forces." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193935.
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Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.<br><p>QC 20161013</p><br>Centre for Eco2 Vehicle Design
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Oberhardt, Tobias. "A micromechanical model for the nonlinearity of microcracks in random distributions and their effect on higher harmonic Rayleigh wave generation." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54365.
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This research investigates the modeling of randomly distributed surface-breaking microcracks and their effects on higher harmonic generation in Rayleigh surface waves. The modeling is based on micromechanical considerations of rough surface contact. The nonlinear behavior of a single microcrack is described by a hyperelastic effective stress-strain relationship. Finite element simulations of nonlinear wave propagation in a solid with distributed microcracks are performed. The evolution of fundamental and second harmonic amplitudes along the propagation distance is studied and the acoustic nonlinearity parameter is calculated. The results show that the nonlinearity parameter increases with crack density and root mean square roughness of the crack faces. While, for a dilute concentration of microcracks, the increase in acoustic nonlinearity is proportional to the crack density, this is not valid for higher crack densities, as the microcracks start to interact. Finally, it is shown that odd higher harmonic generation in Rayleigh surface waves due to sliding crack faces introduces a friction nonlinearity.
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Smith, Jonathan Hurndall. "Stick-slip vibration and is constitutive laws." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304168.
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Meurk, Anders. "Force measurements using scanning probe microscopy : Applications to advanced powder processing." Doctoral thesis, Stockholm, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3023.
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Манько, Наталія Миколаївна, Наталья Николаевна Манько та Nataliia Mykolaivna Manko. "Синергетическое представление прерывистого режима граничного трения". Thesis, СумГУ, 2015. http://essuir.sumdu.edu.ua/handle/123456789/39766.
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Дисертацію присвячено дослідженню процесів межового тертя в рамках моделі нанорозмірної трибологічної системи, а також аналізу процесу зсувного плавлення в твердих тілах. Описано поведінку трибологічних систем двох типів – при зсуві верхньої поверхні тертя в одному напрямку та при зовнішньому знакозмінному впливі. Встановлено, що залежно від температури та параметрів мастила може встановлюватись як режим загасаючих коливань, так і автоколивальний режим, представлений у вигляді дивного атрактора. Проведено врахування просторової неоднорідності напружень, деформації та температури мастильного шару. При врахуванні неоднорідного розподілу напружень по площині контакту показано, що в процесі тертя утворюється доменна структура з двома типами доменів. При врахуванні деформаційного дефекту модуля зсуву проаналізовано вплив адитивних флуктуацій напружень, деформації і температури на процес плавлення мастильного матеріалу. Розглянуто модель зсувного плавлення при врахуванні адитивних шумів основних параметрів і проведено аналіз впливу інтенсивності шумів на характер поведінки системи. Показано, що зі зменшенням інтенсивності шуму параметра порядку мультифрактальна поведінка ряду посилюється.<br>Диссертация посвящена исследованию процессов граничного трения в рамках модели наноразмерной трибологической системы, а также анализу процессов сдвигового плавления в твердых телах. Исследовано плавление ультратонкой пленки смазки, зажатой между двумя атомарно-гладкими твердыми поверхностями при их взаимном перемещении в рамках модели Лоренца. Описано поведение трибологических систем двух типов – при сдвиге верхней трущейся поверхности в одном направлении и при внешнем знакопеременном воздействии. Проведено аналитическое описание процессов, происходящих в результате самоорганизации полей сдвиговых напряжений и деформации, а также температуры смазочного слоя. Установлено, что в зависимости от температуры и параметров смазки может осуществляться как режим затухающих колебаний, так и автоколебательный режим, представленный на фазовой плоскости в виде странного аттрактора. Показано, что на поведение системы критическим образом влияют начальные условия. Проведен математический анализ синергетической модели с целью объяснения возникновения различных режимов работы системы при изменении основных параметров. Тип функционирования трибологической системы описан в соответствии с характером устойчивости особых точек. Исследован пространственно неоднородный случай в рамках модели наноразмерной трибологической системы. При реализации численной процедуры решения одномерного дифференциального уравнения в частных производных, позволяющей проследить эволюцию трибологической системы, получено и описано распределение напряжений по толщине смазки. Прослежена зависимость стационарного состояния от температуры и показано, что с ростом температуры увеличивается относительная скорость сдвига трущихся поверхностей. Проведен учет пространственной неоднородности напряжений, деформации и температуры смазочного слоя. Рассмотрено движение трущихся поверхностей во взаимно противоположных направлениях с одинаковыми скоростями, а также ситуация, когда нижняя поверхность жестко закреплена, а верхняя сдвигается с фиксированной скоростью. Учет пространственного распределения параметров позволяет описать нетривиальное неньютоновское поведение эффективной сдвиговой вязкости смазочного материала. Проведен анализ влияния температуры поверхностей и вязкости материала на стационарный режим трения. При описании неоднородного распределения напряжений по плоскости контакта показано, что в процессе трения образуется доменная структура с двумя типами доменов. Выяснено, что в ходе эволюции система стремится к однородному состоянию, в котором по всей плоскости контакта реализуется одно и то же значение сдвиговых напряжений, задающее относительную скорость движения трущихся блоков. При учете деформационного дефекта модуля сдвига проанализировано влияние аддитивных флуктуаций напряжений, деформации и температуры на процесс плавления смазочного материала. Исследовано влияние параметров системы на фазовую диаграмму, где интенсивность шума температуры и температура поверхностей трения определяют области сухого, жидкостного и прерывистого трения. Построены зависимости эффективного потенциала и распределения вероятностей от величины напряжений, вид которых определяет режим трения. Также исследуется влияние деформационного дефекта модуля сдвига смазочного материала на характер самоподобного поведения временных рядов напряжений при наличии в системе аддитивных некоррелированных флуктуаций. Рассмотрена модель сдвигового плавления при учете аддитивных шумов основных параметров и проведен анализ влияния интенсивности шумов на характер поведения системы. Подробно рассмотрена ситуация, когда интенсивность шума параметра порядка является малой величиной. Характерной особенностью временных зависимостей параметра порядка является наличие в ограниченном диапазоне степенного вида функции распределения, и, как следствие, временной ряд является самоподобным. С помощью метода мультифрактального флуктуационного анализа для всех рассматриваемых случаев рассчитаны зависимости модифицированного показателя Херста от параметра деформации и показано, что с уменьшением интенсивности шума параметра порядка мультифрактальное поведение ряда усиливается.<br>The thesis is devoted to study of the boundary friction processes within the framework of the nanoscale tribological system model, as well as to analysis of shear melting in solid state. The behavior of two types of tribological systems has been described: during the displacement of the upper friction surface in one direction and under the external alternating influence. It has been determined that both the mode of damped oscillations and auto-oscillating mode, presented in the form of a strange attractor, may be established dependending on the temperature and parameters of the lubricant. The spatial inhomogeneity of the stress, strain and temperature of the lubricant layer has been considered. While considering the heterogeneous distribution of stresses in the plane of the contact, it has been shown that the domain structure with two types of domains appears in the friction process. The influence of the additive fluctuations of stress, strain and temperature on the melting process of lubricating material has been analyzed considering the deformation defect of shear modulus. The shear melting model considering the additive noise of the main parameters has been studied, and the impact of the noise intensity on the system behavior has been analyzed. It has been shown that decrease of intensity of the order parameter noise increases the multifractal behavior of the series.
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Renard, Yves. "Modélisation des instabilités liées au frottement sec des solides élastiques, aspects théoriques et numériques." Phd thesis, Université Joseph Fourier (Grenoble), 1998. http://tel.archives-ouvertes.fr/tel-00004903.
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Ce travail comporte deux parties. La première partie est une étude bibliographique sur la modélisation du frottement sec et sur les différentes lois de frottement qui ont été introduites pour rendre compte des instabilités du mouvement des solides soumis à la friction sèche. La deuxième partie est une étude théorique et numérique d'un problème modèle dynamique où une lois de type Coulomb avec coefficient de frottement dépendant de la vitesse de glissement est appliquée à un solide élastique. Le cadre des inclusions différentielles est introduit pour traiter rigoureusement les modèles à nombre fini de degré de liberté et à pression de contact imposée. Ce cadre sert ensuite à l'analyse en détail d'un problème unidimensionnel d'une couche élastique glissant avec frottement sur une fondation rigide plane. On montre l'existence et l'unicité de la solution lorsque le coefficient de frottement est croissant, mais lorsque celui-ci comporte au moins une portion décroissante, ce qui est le cas dans la plupart des modélisation, on montre que le problème admet en général une infinité de solutions. Cela amène à considerer un critère de choix de solution appelé critère de retard maximal. Par ailleurs, on introduit une condition de frottement perturbée qui consiste en l'ajout d'une masse de surface et qui redonne aussi l'unicité de la solution. On montre le lien entre le critère de retard maximal et cette condition perturbée. On présente aussi des schémas numériques, des résultats de stabilité et de convergence, ainsi que des expériences numériques. On donne enfin des perspectives pour les problèmes en dimension deux ou trois. On présente des simulations numériques significatives, obtenues à l'aide d'un schéma numérique basé sur une méthode de type directions alternées, et sur la perturbation par une masse de surface.
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Hamiti, Karim. "Etude et mise en oeuvre de lois de commande numériques sur un actionneur électropneumatique avec frottements." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10130.
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Le travail presente dans cette these est devolu a la realisation d'un actionneur electro-pneumatique a commande numerique. La reflexion conduite dans ce domaine avait un double objectif: ? d'une part, l'etude du systeme dans l'optique d'une commande par micro-controleur. Ceci nous a permis de revoir un ensemble de solutions possibles et d'en choisir la plus adequate, tout en gardant a l'esprit l'aspect implementation et le cahier des charges assigne. ? d'autre part, de tester experimentalement des algorithmes de commande lineaire robustes, sur un systeme electro-pneumatique fortement non lineaire. Cependant, nous avons constate que la presence du frottement de collage dans la partie mecanique du banc, a des consequences nefastes sur les performances statiques de l'asservissement. Pour resoudre ce probleme, nous avons propose une solution aisee a implementer, tout en conservant la methode de synthese du regulateur par placement de poles aussi bien que la structure du pid. Enfin, a la vue des resultats experimentaux, nous concluons que l'application des lois de commande lineaires basees sur une modelisation entree-sortie convient pour les verins pneumatiques de petites courses
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Sayed, Baraa Al. "Comportement dynamique des ensembles tournants de turbomachines : Maîtrise des effets des dispositifs de liaisonnement amortisseurs." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0022/document.
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La fatigue à nombre de cycles élevé (HCF) est un mode de défaillance courant et dangereux pour les aubages de turbomachines. Elle est induite par les efforts dynamiques élevés générés lors de résonances présentes dans la plage de fonctionnement de ces machines. Les dispositifs amortisseurs basés sur l’utilisation du frottement sec, tels que les nageoires ou les frotteurs sous-plateformes, permettent de réduire les amplitudes vibratoires, voire de repousser les fréquences de résonance hors des zones de fonctionnement. Cependant la conception de ces dispositifs reste encore largement basée sur l’empirisme et ils peuvent être la source d’un effet de désaccordage potentiellement nuisible. L’objectif ici est de développer des modélisations adaptées au traitement du problème de vibration des aubages en présence de frottement sec, ceci afin de mieux maîtriser les comportements physiques mis en jeu et donc, de mieux maîtriser leur processus de conception. Plusieurs modélisations numériques sont testées et confrontées à des résultats de référence. Une comparaison entre procédures de résolution temporelle et fréquentielle est menée et montre l’efficacité des méthodes fréquentielles. La méthode fréquentielle de la balance harmonique à plusieurs harmoniques est adaptée au problème et exploitée dans le cadre d’une étude énergétique. Cette étude conduit à une meilleure compréhension des phénomènes mis en jeu lors de l’aplatissement des pics en fonctionnement ; elle permet de démontrer que l’alternance des états de contact glissant et bloqué est à l’origine de cet aplatissement et non la dissipation d’énergie comme souvent avancé dans la littérature. Enfin, la méthode est exploitée pour décrire le comportement des disques aubés désaccordés. La méthode de Monte Carlo est utilisée pour obtenir les caractéristiques statistiques de la réponse forcée d’un système discret, en tenant compte des variations stochastiques des paramètres du contact notamment, la charge normale, la raideur du contact et le coefficient de frottement. Les résultats obtenus permettent de mieux comprendre les effets de la nature variable de ces paramètres fondamentaux sur la dynamique d’ensemble du système non linéaire<br>Fatigue with high number of cycles (HCF) is a current and dangerous mode of failure for the blades of turbo shaft engines. It is induced by the high dynamic stresses generated at resonance in the operating range of these machines. The rubbing devices based on use of dry friction, such as shrouds or under-platform dampers, make it possible to reduce the vibratory amplitudes, to even push back the resonance frequencies out of the operation zones. However the design of these devices remains still largely based on empiricism and they can be the source of a potentially harmful effect of mistuning. The goal is to develop adapted modelling for the treatment of blades vibration problem in the presence of dry friction, this in order to better control the concerned physical behaviours and thus, to better control their process of design. Several numerical modelling are tested and confronted with reference results. A comparison between procedures of time and frequency domains resolution is carried out and shows the effectiveness of frequential methods. The frequential method of the Harmonic Balance including several harmonics is adapted to the problem and is used within an energy study. This study leads to a better comprehension of the phenomena of peaks flattening and it shows that the alternation of the states of slipping and sticking contact is the real cause of this flattening and not energy dissipation like often advanced in the literature. Lastly, the method is exploited to describe the behaviour of mistuned bladed disks. The Monte Carlo method is used to obtain the statistical characteristics of the forced response for a lumped system, by taking account of the stochastic variations of parameters in the contact, specifically the normal load, the stiffness of the contact and the coefficient of friction. Results obtained make it possible to better include/understand the effects of the variable nature of these fundamental parameters on dynamics of nonlinear system
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Pavelec, Jiří. "Vývoj lineárního posuvu pro UHV STM/AFM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229812.
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The aim of this diploma thesis is to develop a linear positioning stage for Ultra High Vacuum (UHV) environment. Simple prototypes of the linear positioning stage were designed and incorporated as part of a multiaxis sample manipulator for a UHV Scanning Tunneling Microscopy / Atomic Force Microscopy (STM/AFM). Different types of position encoders and linear guideways are discussed. Implementation of the homodyne interferometer as an optimization tool for a slip-stick based linear stage is described. Scalar diffraction theory is used to model the diffraction grating optical position encoder behavior.
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Заскока, Антон Миколайович, Антон Николаевич Заскока та Anton Mykolaiovych Zaskoka. "Фазові переходи в ультратонких твердоподібних плівках мастила при межовому терті". Thesis, Вид-во СумДУ, 2015. http://essuir.sumdu.edu.ua/handle/123456789/43321.
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Дисертацію присвячено дослідженню процесів межового тертя в рамках термодинамічної моделі плавлення ультратонкого мастила, затиснутого між двома атомарно-гладкими твердими поверхнями. Описано поведінку двох простих механічних аналогів трибологічних систем – при зсуві верхньої поверхні тертя в одному напрямку та при зовнішньому знакозмінному впливі. Установлено, що залежно від керуючих параметрів мастила можуть реалізуватись режими сухого, переривчастого та рідинного тертя.
Проведена модифікація термодинамічного потенціалу, яка дала змогу описати фазові переходи першого роду в системі. Показано, що наявність пружньої взаємодії між блоком та зовнішнім приводом суттєво змінює гістерезис на залежності сили тертя від температури та швидкості зсуву.
Проведено врахування універсальної залежності в’язкості неньютонівського мастила від температури та градієнта швидкості. При цьому досліджено властивості мастила при низьких температурах і швидкостях зсуву. За допомогою врахування залежності в’язкості від температури та градієнта швидкості вдалося описати квазістатичну компоненту сили тертя. Змодельовано ефекти пам’яті межового мастила.
Проведено подальшу модифікацію термодинамічного потенціалу, а саме враховано лінійний доданок в розвиненні вільної енергії. Розраховано критичні значення плавлення і тверднення мастила в цьому випадку для фазових переходів першого та другого родів. Знайдено співвідношення між параметрами розкладення при яких в системі реалізується фазовий перехід першого роду, і при яких – другого. Отримані результати розрахунку якісно співпадають з експериментальними даними інших авторів.<br>Диссертация посвящена исследованию процессов граничного трения в рамках термодинамической модели плавления ультратонкой пленки смазки, зажатой между двумя атомарно-гладкими твердыми поверхностями. Плавление и затвердевание смазки описываются как фазовые переходы первого и второго рода. Описано поведение двух механических аналогов трибологических систем – при сдвиге верхней поверхности в одну сторону и при внешнем знакопеременном воздействии. Показано, что в зависимости от параметров системы возможна реализация режимов сухого, прерывистого и жидкостного трения. Выяснено, что увеличение температуры смазки и/или скорости сдвига приводит к уменьшению максимальных значений силы трения. Изучено влияние коэффициента пропорциональности между вязкостью и скоростью сдвига, коэффициента жесткости пружины, циклической частоты, различных типов смазок (псевдопластических, дилатантных и ньютоновских) на поведение трибологических систем.
Анализ термодинамического потенциала позволил выделить критические значения температур плавления и затвердевания смазки, которые совпадают при реализации в системе фазового перехода второго рода, и различны при протекании фазового перехода первого рода. Установлено, что ширина гистерезиса по температуре значительно увеличивается при наличии пружины между блоком и внешним приводом. Гистерезис по скорости сдвига в таком случае отсутствует.
Проведен учет универсальной зависимости вязкости полимерных смазок от температуры и градиента скорости. Эта зависимость показывает, что логарифм эффективной вязкости пропорционален логарифму скорости сдвига. Коэффициент пропорциональности изменяет свое значение от 1 в твердоподобном состоянии до 0 в жидкоподобном (ньютоновская жидкость). При этом исследованы свойства смазки при низких температурах и скоростях сдвига. Построена трехмерная зависимость силы трения от температуры и скорости сдвига. С помощью учета зависимости вязкости от температуры и градиента скорости удалось описать квазистатическую компоненту силы трения. Построена зависимость силы трения от времени при продолжительной остановке внешнего привода. Смоделированы эффекты памяти граничной смазки, которые проявляются в том, что поведение системы в последующий момент времени зависит от предыдущего состояния. Изучено поведение при различных значениях внешней нагрузки. Построены зависимости для параметров смазок, состоящих из алканов различной длины, продемонстрированы и объяснены отличия для различных типов смазок.
Проведена дальнейшая модификация термодинамического потенциала путем учета линейного слагаемого в разложении свободной энергии по степеням параметра порядка. Рассчитаны критические значения температуры и скоростей плавления и затвердевания смазки в этом случае для фазовых переходов первого и второго рода. Найдено соотношение между параметрами разложения при которых в системе реализуется фазовый переход первого либо второго рода. Показано, что расплавленному состоянию смазки может отвечать ненулевое значение параметра порядка. Такой вид потенциала дал возможность описать квазистатическую силу трения базируясь на новом подходе. На его основе изучено поведение трибологической системы при различных временах остановки внешнего привода для различных времен релаксации параметра порядка. Полученные результаты расчета качественно совпадают с экспериментальными данными других авторов.<br>The thesis is devoted to the boundary friction processes investigation using thermodynamic model of ultrathin lubricant melting, which is grabbed between two atomically-smooth solid surfaces. The behavior of two simple mechanical analogues of tribological systems have been described: during the shearing of upper block in one direction and during the external periodical influence. It has been found out that depending on lubricant control parameters, regimes of dry, interrupted and sliding friction can be realized.
Further thermodynamical potential modification allows us to describe first-order phase transition in the system. The presence of the elastic connection between block and external drive significantly changes temperature and shear velocity hysteresis’s.
The universal dependence of viscosity of lubricant on temperature and velocity gradient has been took into consideration. Herewith, the lubricant characteristics have been investigated at the low temperatures and low shear velocities. The guasi-static friction force was described using the viscosity dependence.
The further thermodynamic potential modification has been performed. For this purpose, the linear term was added in the free energy expansion into series. The critical values of lubricant melting and solidification were calculated for the phase transitions of the first- and second-order. The relation was found between expansion parameters for which first- or second-order phase transition are realized in the system. Obtained results qualitatively coincide with experimental data.
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Асмолова, Лариса Валериевна. "Улучшение динамики электромеханических систем в условиях срывных фрикционных автоколебаний". Thesis, НТУ "ХПИ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/18481.
Full textAbstract:
Диссертация на соискание ученой степени кандидата технических наук по специальности 05.09.03 – электротехнические комплексы и системы. – Национальный технический университет "Харьковский политехнический институт", Харьков, 2015.
Диссертация посвящена определению путей улучшения динамики электро-механических систем (ЭМС) за счет устранения срывных фрикционных автоколебаний (АКФ) методами регулируемого электропривода. Получены аналитические соотношения для определения условия существования срывных АКФ в разомкнутых одномассовой и двухмассовой ЭМС с характеристикой трения, учитывающей скачкообразное снижение коэффициента трения в момент пуска, позволяющие определить области, где срывные АКФ не существуют. Показано, что срывные АКФ проявляются не только в двухмассовой системе с упругой связью, но и теоретически возможны в одномассовой ЭМС вследствие наличия в ней электромагнитной инерционности. Разработаны компьютерные модели характеристики трения, учитывающие различие коэффициентов трения покоя и начала движения, линеаризованные на характерных участках и дополненные логическим блоком, обеспечивающего состояние покоя рабочего органа с учетом увеличения коэффи-циента трения покоя от продолжительности неподвижного контакта. Доказана их адекватность путем сопоставления формы, амплитуды, периода и критической скорости срывных АКФ с параметрами, полученными при проведении физического и компьютерного экспериментов. Оценено влияние параметров разомкнутой двухмассовой ЭМС и алгоритмов пуска электропривода на величину амплитуды, периода срывных АКФ и критической скорости. Показано, что параметрическим методом не обеспечивается расширение области, в которой срывные АКФ отсутствуют, то есть не приводит к улучшению динамики ЭМС. Доказано, что, несмотря на высокие демпфирующие способности ЭМС с типовыми обратными связями по основным координатам, модальным управлением, со структурой подчиненного регулирования координат с различными настройками регуляторов скорости и тока, не устраняют срывных АКФ на скоростях ниже критической скорости разомкнутой системы. Показана возможность существенного снижения критической скорости по сравнению с критической скоростью разомкнутой системы применением в двухмассовой ЭМС интеллектуального управления в виде прямонаправленной нейронной сети и релейного регулятора, работающего в скользящем режиме. Позволяют расширить в области малых скоростей скольжения область, в которой срывные АКФ отсутствуют.<br>The dissertation for the degree of technical sciences candidate, specialty 05.09.03 – electrical complexes and systems. – NTU "KhPI". – Kharkiv, 2015. The dissertation is devoted to determining ways of machine and mechanism dy-namics improvement based on stick-slip frictional self-oscillations suppression by means of regulated electric drive. Conditions of stick-slip frictional self-oscillations ex-istence in open-loop one- and two-mass electromechanical systems (EMS) are specified for the friction characteristic that takes into account step decrease of the friction coeffi-cient at the starting moment, as applied to a cutting machine axial electric drive. Friction characteristic computer models are developed for low-speed runs with consideration of the rheological factor, their adequacy proved by comparison with physical and computa-tional experiment parameters. Action of two-mass EMS factors on the system motion characteristics under low-speed runs is estimated to determine a parametric means of the critical speed reduction, inefficiency of this control tool shown. A two-mass EMS with the typical basic-coordinates feedback, modal control and a various-setting subordinate-regulation structure is found unable to noticeably reduce the critical speed. A two-mass intellectual-control EMS with a feedforward perceptron network and a sliding relay regulator is researched. Computer simulation has verified the effect of significant criti-cal speed reduction and stick-slip frictional self-oscillations elimination resulted from an integral-error relay regulator application.
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Асмолова, Лариса Валеріївна. "Поліпшення динаміки електромеханічних систем в умовах зривних фрикційних автоколивань". Thesis, НТУ "ХПІ", 2015. http://repository.kpi.kharkov.ua/handle/KhPI-Press/18480.
Full textAbstract:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.09.03 – електротехнічні комплекси та системи. – Національний технічний університет "Харківський політехнічний інститут", Харків, 2015.
Дисертація присвячена визначенню шляхів поліпшення динаміки електро-механічних систем (ЕМС) за рахунок усунення зривних автоколивань фрикційних (АКФ) методами регульованого електроприводу. Отримано аналітичні співвідношення умов існування зривних АКФ в одномасовій і двомасовій ЕМС, що визначають області, де АКФ відсутні. Досліджені математичні моделі одномасової та двомасової розімкнених та замкнених ЕМС з характеристикою тертя, яка лінеаризована на характерних ділянках і доповнена логічним блоком для забезпечення стану спокою виконавчого органу. Доведено на основі моделі двомасової розімкненої ЕМС з характеристикою тертя, що зміна її параметрів і алгоритмів пуску електроприводу не розширюють області, де зривні АКФ відсутні. Використання в ЕМС типових зворотних зв'язків і підпорядкованого регулювання з стандартними й відомими налаштуваннями контурів не усувають зривних АКФ на швидкостях нижче за критичну швидкість розімкненої системи. Застосування нейрорегулятора та релейного регулятора забезпечують усунення зривних АКФ на швидкостях, суттєво менших за критичну швидкість розімкненої системи.<br>The dissertation for the degree of technical sciences candidate, specialty 05.09.03 – electrical complexes and systems. – NTU "KhPI". – Kharkiv, 2015.
The dissertation is devoted to determining ways of machine and mechanism dy-namics improvement based on stick-slip frictional self-oscillations suppression by means of regulated electric drive. Conditions of stick-slip frictional self-oscillations ex-istence in open-loop one- and two-mass electromechanical systems (EMS) are specified for the friction characteristic that takes into account step decrease of the friction coeffi-cient at the starting moment, as applied to a cutting machine axial electric drive. Friction characteristic computer models are developed for low-speed runs with consideration of the rheological factor, their adequacy proved by comparison with physical and computa-tional experiment parameters. Action of two-mass EMS factors on the system motion characteristics under low-speed runs is estimated to determine a parametric means of the critical speed reduction, inefficiency of this control tool shown. A two-mass EMS with the typical basic-coordinates feedback, modal control and a various-setting subordinate-regulation structure is found unable to noticeably reduce the critical speed. A two-mass intellectual-control EMS with a feedforward perceptron network and a sliding relay regulator is researched. Computer simulation has verified the effect of significant criti-cal speed reduction and stick-slip frictional self-oscillations elimination resulted from an integral-error relay regulator application.
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LI, JUNSHAN. "The Development of Semi-Analytical Solutions for 3-D Contact Problems." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092069082.
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Tataryn, Peter D. "Modelling and compensation of stick-slip friction for robot arm control." 1996. http://hdl.handle.net/1993/19358.
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Hong, Hsia Jeng, and 夏正宏. "The Influence of the Friction Models on the Stick-Slip Motion." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/25088777141646266977.
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Papangelo, Antonio. "Stick-slip transition and dynamic cyclic response of friction damped systems." Doctoral thesis, 2017. http://hdl.handle.net/11589/99179.
Full textAbstract:
This thesis is subdivided into two parts: in the first we analyze the transition from static to dynamic friction with some emphasis on the implication of using more refined friction laws (with respect to the simple Coulomb model) while in the second part we study the cyclic response of dynamical systems that experience friction. Particularly, in the first part we will take inspiration from some recent experiments from the group of Prof. Fineberg to tackle some partial slip contact problems, with the idea in mind of providing analytical models that can, in some extent, interpreter some of the numerous experimental evidences that came from the direct observation of the sliding phenomena. In the chapters 1-2 a brief introduction of the equations that govern the contact of elastic bodies and the experimental test rig used in the experiments is presented. In chapter 3 the partial slip problem of a flat square-ended punch pressed against an half-plane and tangentially loaded above the contact interface is studied, then a FEM of the Prof. Fineberg experimental test rig will be proposed to avoid the hypothesis of half-plane elasticity, with good agreement between numerical and experimental results. In chapter 4 the implications of using a slip weakening friction law instead of the classical Coulomb law are discussed and an energetic criterion for slip inception is derived, which we will call "Griffith friction model". In chapter 5, using this "Griffith friction", the partial slip problem for different plane geometries (power law punches and sinusoidal profile) is solved.
In the second part of the thesis we will focus our attention on the dynamic response of mechanical systems subjected to friction. In chapter 7 a very simple model of structure subjected to dry friction is studied, constituted by a single degree of freedom system subjected to a periodical tangential excitation and a (possibly) varying normal load. First we compare the quasi-static solution with the dynamic solution in the limit of very low excitation frequency, then we study (in the bounded regime) how the peak displacement and dissipation is related to the phase shift between the normal and the tangential load. In chapter 8 the dynamical behavior of a mass-spring-viscous damper structure linked to a massless Coulomb damper is studied with attention to the regime that minimize the vibration amplitude of the mass. Finally in chapter 9, we study a friction-excited nonlinear oscillator chain, where a polynomial nonlinearity is introduced in the system. We focus our attention on the multiplicity of solutions that are proven to exist in certain parameter rangeS which leads to a bifurcation pattern similar to the snaking bifurcations. In the end conclusions and possible developments of the present work are proposed.
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Owen, William Scott. "An investigation into the reduction of stick-slip friction in hydraulic actuators." Thesis, 2001. http://hdl.handle.net/2429/11786.
Full textAbstract:
The stick-slip friction phenomenon occurs during the switch from static to dynamic friction.
Static friction is the force that opposes the sliding motion of an object at rest. Dynamic friction
is the force that opposes the sliding motion of a moving object. Thus, near zero velocity, there is
a switch from static to dynamic friction. Generally, static friction is greater than dynamic
friction. In order to move an object the applied force must exceed the static friction. Once
movement starts the friction force typically decreases as it switches to dynamic friction.
However, if the applied force is still at the original magnitude, then the sudden increase in the
resultant forces results in an increase in the object's acceleration; namely a jerky motion.
In a similar manner, when an object is brought to rest the sudden increase in friction, as the
switch from dynamic to static friction occurs, results in an abrupt and premature stopping of the
object. Because of the rapidly changing and inconsistent nature of the friction force at low
velocities, accurate and repeatable position control is difficult to achieve. In some cases the
actuator position controller can reach a limit cycle (hunting effect).
Friction compensation at low speeds has traditionally been approached through various control
techniques. This work presents an alternative solution, namely, friction avoidance. By rotating
the piston and rod, the Stribeck region of the friction - velocity curve is avoided and the axial
friction opposing the piston movement is approximately linearized. As a result, simpler, linear
control techniques at low speeds may then be utilized. Simulation and experimental results are
presented to validate this approach and identify the operating limits for the rotational velocity.
The experimental results validate the model.
The results show that by rotating the piston, the friction is reduced and the Stribeck curve is
eliminated. As the rotational velocity is increased the static friction from the axial motion
approaches the static friction of the rotational motion. In order to eliminate the Stribeck curve,
the rotating velocity must be located outside the range of the Stribeck area of the rotating friction
- rotating velocity curve and into the full fluid lubrication regime.
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Kuo, Ter-Ming, and 郭德明. "Fuzzy Control of One-Dimensional Precision Mechanical Systems with Stick-Slip Friction." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/88081792251847330898.
Full textAbstract:
碩士<br>國立中興大學<br>機械工程研究所<br>81<br>This study considers the application of fuzzy control to rigid
and flexible mechanical systems with stick-slip friction in
order that the systems have precise positioning and trajectory-
following performance. The design of a fuzzy control system
need not fully rely on the mathematical model of the plant.
Usually, control engineers design the fuzzy control rules based
only on the heuristic knowledge about the plant. Thus it is
very suitable for the control of complex or highly uncertain
systems. This thesis first introduces the fuzzy control theory
and friction theory, then considers a fuzzy controller with
"two input-one output" and "three input-one output"
respectively, for the rigid and flexible mechanical systems,
and chooses suitably the membership functions and fuzzy control
rules for generating the suitable control signals to achieve
the control purposes. And the computer simulation results show
that the proposed fuzzy controllers have very good performances
and precision for the positioning and track- ing of the systems
considered. In the precise positioning of rigid systems, this
thesis also considers the comparison between the perfor- mances
of the fuzzy control strategy and those of the traditional
nonlinear friction compensation. The computer simulation
results also show that the performances of the fuzzy control
case are better.
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Zhang, Zhen Hou, and 張振厚. "PD and fuzzy logic control for flexible-joint manipulators with stick-slip friction." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/23892085077625934838.
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M, Wen S., and 溫恕民. "Adaptive Fuzzy Control Using Back-Propagation for Mechanical Systems with Stick-Slip Friction." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/50753793944016736093.
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Baleri, Mudlagiri. "Stick-slip friction and rotational vibration under large contact areas and uneven distributed loads." Thesis, 2000. http://hdl.handle.net/2429/10546.
Full textAbstract:
The proposed research is aimed at the analysis of stick-slip frictional phenomenon
when large contact areas are involved and, due to the physical structure of the system, high
uneven contact loads are generated. The study will look at both mechanistic and tribological
aspects of the problem. The main objective of the research is to achieve a better
understanding of the phenomenon based on experimental observations and to develop a
mathematical representation under realistic conditions.
A non-linear finite element model has been developed using ANSYS to obtain an
understanding of the contact pressure distribution at the interface of contact of large surfaces
due to the applied loads. A mathematical model of this distribution has been derived based on
the results of the ANSYS solution. The friction torque acting at the contact surface has then
been estimated by integrating elemental friction torque over the entire plate area.
The LuGre friction model for the localized contacts has been extended for large
contact areas using an integration approach. The simulations have been carried out using
Simulink to understand the dynamic behavior of the integrated LuGre model as well as to
assess the effect of various system parameters on the stick-slip vibrations.
A test rig has been designed and fabricated to re-construct the realistic situations that
occur in large robots and excavators for example. The instrumentation, signal processing,
data acquisition and analysis have subsequently been carried out. The experiments have been
conducted to investigate the effect of various parameters such as total load, loading
configuration, speed, and spring stiffness on the stick-slip vibrations.
The simulations using proposed integrated LuGre model are found to be in good
agreement with the experimental results. The experiments have revealed that with all other
parameters being same, the stick-slip vibrations are more likely to occur under concentrated
loading as compared to distributed loading for the same total load.
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高聰賢. "On Stick-Slip and Surface Friction Under the Effects of Contact Time and Loading Rate." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/89825854307760140707.
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碩士<br>國立中興大學<br>機械工程研究所<br>83<br>When two contact surfaces move in a relatively low velocity, there occurs a discontinuous movement, known as stick-slip motion, due to the presence of friction force. An experimental apparatus is constructed to measure the functional relation of static friction coefficient and stick time under different tangential loading rate while two contact surfaces are in dry or boundary lubricated conditions. The function thus obtained is used in theoretical analysis to describe stick-slip phenomenon. the experimental resultsshow that the diagrams of μ－ts and μs－F relations are S type and reverse S type, respectively. It means that static friction coefficient approaches constant value as stick time or tangential loading rate tends to larger or smaller value. Among these two bounds is an area that μs varies moderately. These experimental results are confirmed by other investigator's research. The model of the dynamic friction coefficient verse speed reveals as a function of exponential type in the present sliding pairs. It's also found that the static friction coefficient is inversely proportional to the surface contact pressure. Stick-slip motion oscillates stably int he region of constant maximum static friction while several abnormal oscillations are found before stick-slip motion goes to steady state for the case where μs locates in the varying region. Moreover, both the experimental and numerical results show that the frequency of stick-slip motion increases with driving speed and approaches the natural frequency of the system.
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Lin, Wen Yuan, and 林文源. "Sliding friction and stick-slip motion of two contact surfaces in dry and lubricated conditions." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/59045238725290396262.
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GHEZZI, ILARIA. "Tribological and vibro-acoustic behaviour of a lubricated contact subjected to the stick-slip phenomenon: the case of the spring-brake system." Doctoral thesis, 2020. http://hdl.handle.net/11573/1506719.
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The main objective of the PhD thesis is the analysis of stick-slip phenomena in lubricated contacts, by merging the physical, experimental and numerical points of view and proposing a novel methodological approach, applied here to an industrial case. Nowadays, in the field of applied mechanics and tribology, one of the most important challenges is the ability to predict and reduce surface damages, failure of machine components and undesirable frictional and dynamic characteristics. In particular, the appearance of friction-induced vibrations at the contact is hardly controllable and can result in high local contact pressure, elevated stresses, system oscillations, discontinuous motion and premature failure]. Understanding the conditions for which the system is more predisposed to the stick-slip phenomenon may allow preventing the appearance of such instabilities, and the related vibrations and noise emission. Friction-Induced Vibrations are a phenomenon that engages multiple scientific challenges, due to the complexity of their physics. Focusing the attention on stick-slip phenomena, these are generally characterized by a saw-tooth displacement-time evolution. Each change in the contact parameters influences directly the dynamic and frictional response of the system, due to the mutual influence of the local scale (contact) and the system scale (macroscopic frictional and vibrational response). Moreover, the presence of a lubricant, and in particular of grease, at the contact interface, increases the complexity of the phenomenon, from both a tribological and dynamic point of view. Lubricated systems are supposed to reduce the frictional losses and wear, but they can also collaborate in the appearance of dynamic contact instabilities, due to the friction-velocity characteristics when passing from boundary to mixed contact regimes. The complex rheology of a grease, function of both the matrix, additive and oil responses, becomes then a key point for the occurrence and evolution of stick-slip. Despite the great importance of this phenomenon, from both scientific and industrial points of view, a lack emerges into the literature about stick-slip of lubricated interfaces. The few works are manly focused on molecular dynamics simulations and numerical modelling of the dynamical response of the system. The different role of the grease components, during the sliding, is nowadays still not clear. Nevertheless, the complex rheology of a grease, function of both the thickener, the base oil and the additives, is a key point for understanding and controlling the occurrence and evolution of stick-slip. Moreover, a general approach is needed to account for the coupling between the local phenomena (e.g. lubricated contact response) and the system dynamic response. Aiming to improve the understanding of stick-slip in lubricated contacts, the present Ph.D. work proposes a novel methodological approach to the stick-slip problem of a lubricated contact, referring to a real industrial case, in order to deploy the obtained results in a more realistic and detailed manner. The subject of the investigation is a mechanical brake used in tubular electric actuators, which can present frictional instabilities originated at the lubricated contact between the two main brake components. The methodology used is twofold: i) on one hand, experimental tests are carried out to understand the local frictional response of the lubricated contact; ii) on the other hand, a lumped model is created in order to simulate and analyse the system dynamic response. Introducing the information about the local lubricated contact behaviour (friction law), achieved experimentally, into the numerical model, it is possible to investigate the parameters for which the system is more predisposed to the stick-slip phenomenon and recreate a representative scenario of its appearance. Particular attention has been placed on the analysis of the lubricant rheology, dealing with different types of lubricants and regimes of lubrication, with both oils and greases. The frictional response has been thus related to the different contributions of the grease components (i.e. thickener, base oil and additives) on the rheology at the interface. The obtained local information has been then integrated in the lumped model to evaluate the unstable dynamic response of the entire system (i.e. the stick-slip phenomena) and identify the lubrication parameters that most influence its appearance. The numerical analysis had the dual objective of understanding the role of the local contact response in the system instability and investigating the stick-slip occurrence as a function of the key system parameters. The obtained results allowed to identify the lubrication components, and the respective friction-velocity curves, more favourable for the stick-slip occurrence. Combining the grease rheology evolutions with the stick-slip dynamic response represents a further challenge in both the domains of research. The Ph.D. thesis has been developed in collaboration between the Sapienza University of Rome, Department of Mechanical and Aerospace Engineering (Rome, Italy), the Institut National des Sciences Appliquées (INSA) of Lyon, laboratory LaMCoS (Lyon, France), and the company SOMFY S.A. (Cluses, France).
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TONAZZI, DAVIDE. "Macroscopic frictional contact scenarios and local contact dynamics: at the origins of “macroscopic stick-slip”, mode coupling instabilities and stable continuous sliding." Doctoral thesis, 2014. http://hdl.handle.net/11573/863973.
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Local contact behavior and its interaction with the global dynamics of the system are at the origin of innumerable contact issues concerning several different disciplines like tribology, geophysics, vibration mechanics or fracture mechanics.
When two elastic media are in relative motion with a frictional interface, friction induced vibrations arise into the system. By a macroscopic point of view, the “macroscopic stick-slip” scenario occurring during relative motion is characterized by sudden friction force drops (sliding state) along the time, separated by periods of elastic energy accumulation (stick state). Instead, the mode dynamic instability occurs when a vibration mode of the mechanical system becomes unstable, due to frictional contact forces. This kind of instabilities, generated by frictional forces, have been mainly object of papers dealing with specific issues in different domains such as brake squeal, hip endoprosthesis squeaking, wheel-rail vibrations, earthquakes, etc.
In this context, experimental and numerical analyses have been focused here on understanding how the local interface behavior affects the macroscopic frictional response of the system, and, conversely, during instability scenarios.
The macroscopic frictional scenarios (macroscopic stick-slip instability, mode coupling instability, stable continuous sliding) arising between two simple elastic media in relative motion have been investigated numerically and experimentally. A newer experimental setup (TRIBOWAVE) has been developed and it allowed to reproduce and to investigate the different scenarios under well-controlled boundary conditions.
The same frictional scenarios have been reproduced by transient numerical simulations. A dedicated friction law as a function of adherence (sticking) time has been recovered by means of experimental tests. The obtained friction law has been implemented in the numerical model, leading to a quantitative validation of the simulated scenarios by the experiments.
Nonlinear transient simulations, complex eigenvalue analyses and experimental tests allowed for drawing instability maps as a function of system key parameters.
The numerical model, validated by the comparison with the experimental global measurements (forces, accelerations/velocity), allowed for investigating the coupling between the local contact behavior (contact status distribution, wave and rupture propagation, precursors) and the system dynamic response during macroscopic stick-slip instability, mode coupling instability and stable continuous sliding.
The understanding of the coupling between contact and system dynamics will bring to further improvements on the control of contact instabilities and related wear issues.
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DI, BARTOLOMEO MARIANO. "Wave generation and propagation at tribological interfaces." Doctoral thesis, 2011. http://hdl.handle.net/11573/917655.
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Wave generation and propagation at contact interfaces is a relevant issue in mechanics because they affect directly a large number of mechanical systems involving either static or sliding frictional parts. Contact dynamics is at the origin of friction induced vibrations, acoustical instabilities, surface damage, wear and fatigue failures [IBRA 94][AKAY 02] Propagating waves at the interface can be exploited for controlling the global friction features of the contact.
Beside classical experiments, numerical analysis on dry contacts in sliding state has been one of the mayor topic in recent literature to which a relevant number of important papers have been dedicated ([RENO 11] and reference therein), due also to the fact that it is a substantial subject of interest for researchers working on many different domains, from dynamics to tribology and geophysics.
At the origin of the phenomena cited above there is the wave generation and propagation at the frictional contact interface. Moreover when the two materials in contact are different, the dynamics of the phenomenon increases in complexity due to the so-called "bimaterial" effect ([WEER 80][ADA 95][BEN 01] and reference therein).
This thesis is addressed to the understanding of the mechanisms at the origin of the contact wave fields and its relationship with the local characteristics of the surfaces in contact, as well as with the global dynamics and macroscopic frictional behaviour of the system. The aim of this work is to provide insights on the generation and propagation of the waves through the contact both to avoid instabilities and to control their effect on friction. The work is organized in two main parts.
The first part presents the development of a non-linear finite element analysis in large transformations of the dynamic rupture at the interface with contact friction separating two bodies (isotropic and elastic) without relative motion. A rupture is considered when an initially sticking zone shifts in sliding state. The properties of the obtained ruptures are analyzed for a flat interface between dissimilar materials in function of the nucleation energy; then the effect of the interface roughness is analyzed. The differentiated rupture inside the asperities and the conditions for coupling and uncoupling between the waves radiating in the two bodies have been also investigated.
In the second part, the analysis deals with the sliding onset between two bodies in contact. The sliding between two bodies made of different isotropic elastic materials and separated by a frictional interface is simulated. The evolution along the time of the global normal and tangential forces is analyzed, relating it to the local phenomena occurring at the interface. This part tries to investigate how micro-slips at the interface, acting as distributed ruptures, trigger the macro-slips between the two bodies. The interaction between local and global dynamics is also studied. Finally a numerical parameter space study is carried out, as a function of several system parameters (contact law, friction coefficient, material damping, normal load, translational velocity and regularization time).
The results show the key role of the micro-slips and precursors (detectable wave propagations that occur at tangential global force well below the critical value expected by the friction law) in triggering the macro-slip between the two bodies. Depending on their distribution and magnitude the evolution of the contact forces passes from stick-slip-like behaviour to continuous sliding. The local dynamics at the contact (wave and rupture propagation) is linked to the global behaviour of the system (stick-slip, continuous sliding, induced vibrations); the effect of the contact and system parameters on the transfer of vibrational energy between the sliding contact and the system is investigated.
The numerical results obtained by the two parts of the work show a good agreement with experimental results in literature.
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Többens, Alexander. "Dynamik und Bifurkationsverhalten eines getriebenen Oszillators mit frei aufliegender Dämpfermasse." Doctoral thesis, 2011. http://hdl.handle.net/11858/00-1735-0000-0006-B4F4-4.
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