To see the other types of publications on this topic, follow the link: Contante.
Dissertations / Theses on the topic 'Contante'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Contante.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
CANNAROLI, SIMONE. "L'antiriciclaggio e le indagini fiscali." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/1366.
Full textAbstract:
La tesi si propone di mettere in luce i punti di contatto e di reciproca interazione fra la disciplina dell’antiriciclaggio e le indagini fiscali, evidenziandone i punti di forza e le criticità. Viene evidenziato come delle misure pensate per prevenire comportamenti criminali e per la tutela del sistema finanziario nel suo complesso possano influenzare significativamente - seppur indirettamente - le dinamiche dell’accertamento tributario. La grande mole di informazioni raggiunta e gestita nell’ambito delle procedure antiriciclaggio, infatti, può essere incrociata con gli altri dati di natura fiscale già a disposizione dell’amministrazione finanziaria offrendo un riscontro sulla veridicità della documentazione contabile e commerciale di un’impresa o sul tenore di vita palesato da una persona fisica. A questo si aggiunge il grande supporto offerto dalle disposizioni in tema di limitazione dell’uso del contante che, convogliando la maggior parte delle transazioni finanziarie in canali tracciati, contribuiscono a rendere visibile ciò che avrebbe potuto rimanere “sommerso”, esercitando anche un forte impatto psicologico in termini di deterrenza, attraverso la diffusione di una generale sensazione di controllabilità. Ciò nonostante, è certamente un errore attribuire all’antiriciclaggio una diretta valenza fiscale. Le tasse si pagano su ciò che si vede, e tracciare i trasferimenti contribuisce a rendere visibili i passaggi di “moneta”, ma nulla dice in merito alla ragione economica per cui questi siano avvenuti. Proprio per superare questo limite si è cercato di imporre ad una vasta categoria di soggetti (finanziari e professionali) uno specifico obbligo di collaborazione attiva, un onere di approfondimento “economico sostanziale” dell’operazione finanziaria e di segnalazione di quelle “sospette”. Ma sull’attendibilità di tali approfondimenti e sulla completezza delle informazioni a cui i collaboratori dello Stato possono accedere il dibattito è aperto, in fondo non si tratta né di organi di polizia, né di soggetti con particolari potestà “investigative”, si tratta solo di soggetti che devono intervistare dei loro clienti e registrarne le risposte. Spesso, peraltro, sarà proprio l’“intervistatore” a consigliare (in veste di consulente di fiducia) le risposte da fornire. Ma l’antiriciclaggio non è solo segnalazione, è soprattutto patrimonio informativo e cultura della trasparenza e della responsabilità (che si vorrebbe diffondere in tutti gli operatori economici e finanziari).The dissertation aims to highlight the points of contact and mutual interaction between the discipline of anti-money laundering and tax investigations, especially underlining the strengths and weaknesses. It will be shown that measures designed to prevent criminal behavior and meant to protect the financial system as a whole can influence significantly - though indirectly - the dynamics of the assessment of taxation. In fact, the large amount of information collected and managed within the ambit of anti-money laundering rules and regulations can be cross-checked with further fiscal data already available for revenues authorities, in order to achieve a financial and commercial feedback on the accuracy of records in relation to an enterprise or with reference to the standards of living of an individual. Not to mention the great support given by the provisions concerning restrictions on the use of cash money that - conveying most of the financial transactions through predetermined channels - help to reveal what could have stayed "hidden"; furthermore, they exert a great influence in terms of psychological deterrence thanks to the dissemination of a general feeling of controllability. Nevertheless, it is certainly a mistake to attribute to anti-money laundering a direct fiscal value. Taxes are paid on what is apparent and, if on one hand tracing the transfers helps to make visible the money transfers themselves, on the other it says nothing about the economic reason why they occur. In order to get around this limit, it was made compulsory for a wide group of people both, financially and professionally speaking, to be actively cooperative; that is to say that they now have to develop a “substantial economic role” with reference to the financial operation and, at the same time, they are also asked to report of those that are considered "suspicious". It has to be said that the debate is open in relation to the reliability of such investigations and information completeness, to which State employees can have access. In the end, we are coping with neither police force nor subjects equipped with special powers of "investigation". It is only a matter of individuals which have to interview their clients and record their answers. And it will be just the 'interviewer' who -as a trustworthy advisor- will recommend what answer is to be given. But anti-money laundering is not just reporting, it is -first and foremost- informative heritage and culture of transparency and accountability (which would be desirable to spread among all economic and financial operators).
2
Bande, Gianluca. "Formes de contact généralisé, couples de contact et couples contacto-symplectiques." Mulhouse, 2000. http://www.theses.fr/2000MULH0621.
Full textAbstract:
On introduit trois types de structures géométriques nouvelles sur des variétés différentiables : formes de contact généralisé, couples de contact et couples contacto-symplectiques. Une forme de contact généralisé sur M est une 2k + 1-forme ω telle que ω∧dω soit une forme volume. Plusieurs exemples sont construits et on donne un critère local qui permet de montrer que tous ces exemples ne sont pas triviaux dans le sens qu'ils ne sont pas de la forme α ∧ dαk (où α est une forme de contact). Un couple de contact sur M est un couple (α, β) de formes de Pfaff de classe constante 2k + 1 et 2h + 1 respectivement et telles que la forme α ∧ dαk ∧ β ∧ dβh soit une forme volume. Chacune de ces formes détermine un feuilletage caractéristique dont les feuilles sont des variétés de contact. Ces feuilletages sont transverses et supplémentaires. La géométrie de tels objets est très riche car on peut naturellement leur associer deux champs de Reeb qui commutent, deux types de courbes de Legendre et deux crochets de Poisson. D'une manière similaire on définit un couple contacto-symplectique. Pour les deux dernières structure on démontre qu'il y a un unique modèle local et on construit plusieurs exemples non triviaux dans les groupes de Lie et dans les fibrés principaux en tores. Comme conséquence de la théorie des couples contacto-symplectiques on construit des exemples de champs de vecteurs (sur des variétés de contact) sans transversale fermée et qui ne sont le champ de Reeb d'aucune forme de contact. Ce qui répond à un célèbre problème de Reeb.
3
Parel, Kurien Stephen. "An analysis of contact stiffness and frictional receding contacts." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:3c29863a-b0cf-4870-851d-261be72f457f.
Full textAbstract:
The tangential contact stiffness for ground Ti-6Al-4V surfaces is measured to linearly decrease with the application of tangential load. At the beginning of the application of tangential load, for ground surfaces, the ratio of the tangential contact stiffness to the normal contact stiffness is seen to be approximately half the Mindlin ratio. This is consistent with many other published experimental studies. Measurements of normal contact stiffness for ground surfaces conform to a model that posits a linear relationship between normal contact stiffness and normal load. An equivalent surface roughness parameter is defined for two surfaces in contact; and the normal contact stiffness for ground surfaces is observed to be inversely proportional to this parameter. Single asperity models were constructed to simulate the effect of different frictional laws and plasticity on the tangential displacement of an asperity contact. Further, multi-asperity modelling showed the effect of different normal load distributions on the tangential behaviour of interfaces. In addition, normal contact stiffness was modelled for a grid of asperities taking into account asperity interactions. A receding contact problem for which the required form of the distributed dislocations is bounded-bounded was solved. Then, a fundamental 2D frictional receding contact problem involving a homogeneous linear elastic infinite layer pressed by a line load onto a half-plane of the same material was analysed. This was done by the insertion of preformed distributed dislocations (or eigenstrains), which take into account the correct form of the separation of the interface at points away from the area of loading, along with corrective bounded-bounded distributions. The general method of solution was further refined and adapted to solve three other receding contact problems. The solutions demonstrated the robustness and applicability of this new procedure.
4
Alshahrany, Shaya. "Rolling contact fatigue in heavily loaded gear transmission contacts." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/90422/.
Full textAbstract:
This thesis examines the influence of asperities such as found on the teeth of gears and discs, and failure mechanisms associated with rough surface Elastohydrodynamic Lubrication (EHL). The principal outcomes of the research provide a good insight into fatigue life, residual stress effects, damage prediction and surface contact failures. In particular, the study is intended to provide understanding into the residual stress distribution resulting from plastic deformation of surface asperities in the running in process. The residual stress is then added to the asperity elastic stress distribution and examined in detail to see the effects on fatigue damage and fatigue life. So, a theoretical model has been developed to assist design against the residual stress effect and surface contact fatigue, such as micropitting. The technique used in the study starts with developing an elastic plastic model of the rough surface by using the Abaqus Finite Element analysis software package. This is a nonlinear problem and ranges of applied loads have been applied to the as-manufactured surfaces causing the asperity features to experience varying degrees of plastic deformation. The pre and post running roughness profiles are studied in order to assess the level of plastic deformation actually occurring at significant surface asperity features by aligning the pre and post running profiles. This results in a new technique that has helped to identify the level of plastic deformation occurring in the practice, and also to make a comparison with FEA contact analysis for the same asperity features to identify the appropriate residual stress field. The residual stress field associated with the plastic deformation was extracted and evaluated. The extracted residual stress field was transferred to a form that facilitated IV inclusion in stress evaluation code to obtain the stress history for the material subject to loading in an EHL contact. The research carried out considers surface fatigue analysis with and without a residual stress field, so as to establish the influence of asperity plastic deformation on the fatigue properties of the surface. All the work is based on numerical simulation of surface fatigue failure in EHL situations and carried out numerically. The procedure can be applied quickly and gives the opportunity to apply several models and investigate the influence of all the model parameters on material deformation and fatigue life.
5
Moraes, Marta Bueno de. "Estudo teórico de característica elétrica de contato schottky não íntimo metal-isolante amorfo e estrutura metal-isolante-metal." Universidade de São Paulo, 1989. http://www.teses.usp.br/teses/disponiveis/54/54132/tde-16012008-104334/.
Full textAbstract:
No presente trabalho foi desenvolvida uma teoria de característica elétrica da estrutura metal-isolante-metal considerando uma camada fina de óxido entre o metal e o isolante, sendo o óxido um outro isolante de banda de energia proibida mais larga. Foi considerada uma distribuição energética uniforme de estados de impurezas à interface óxido-isolante. Estudamos a distribuição real do potencial na região de carga espacial usando a equação de Poisson. Através desta distribuição obtemos a relação entre o potencial de contato e a carga positiva na região de depleção e assim a característica capacitância-voltagem da estrutura. Este tipo de característica é útil para se calcular as características corrente em função do potencial e corrente em função do tempo para um dado potencial e deste modo é importante para o entendimento das estruturas MIM e MOIM.In this work we have developed a theory of electric characteristic of the metal-oxide-insulator-metal structure, considering a thin film of oxide between metal and insulator; the oxide is another insulator of wider forbidden energy gap. A uniform energy distribution of impurity states at the oxide-insulator interface was considered. W e have studied the actual distribution of potential in the region of spatial charge using the Poisson equation. With this distribution we obtain the relation between the contact potential and the charge in the depletion region and then the characteristic potential - capacitance of t his structure. This type of characteristic is useful to calculate the characteristic current - potential, and current-time at a given potential . In this manner it is important to the understanding of MIM and MOIM structures.
6
Li, Sheng. "Lubrication And Contact Fatigue Models For Roller And Gear Contacts." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1234822355.
Full text
7
Balcombe, Robbie. "A study of rolling contact fatigue cracks in lubricated contacts." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9848.
Full textAbstract:
A novel method for coupling fluid pressure and crack deformation for the purpose of analysing rolling contact fatigue (RCF) cracks in lubricated, hydrodynamic and elastohydrodynamic, contacts is presented. The model addresses some of the simplifying assumptions applied to existing models presented in the literature such as: (i) using an imposed fluid pressure gradient inside the crack, (ii) using an imposed fluid pressure at the crack mouth, and (iii) adopting a surface contact pressure, Hertzian or EHL, that does not account for the fluid flow in and out of the crack during loading. The model has been used to model the effect of lubricant/crack interaction in various RCF configurations as the rolling element passes over the pre-formed crack; which has direct application to bearings and rail/wheel contacts. The results of the simulations performed with the fully-coupled fluid/solid solver developed by the author suggest that the cracked component/lubricant interaction contributes significantly to accelerate the rate of surface breaking crack growth in rolling element bearings and wheel/rail type contacts. It is shown through simulations that the lubricant works as a catalyst inside the crack to convert the compressive contact load into a crack opening, tensile fatigue mechanism, through the effect of fluid pressurisation inside the crack. The results obtained using such a model suggest that the opening associated with the fluid action within the crack induces large mode I stress intensity factors. This has been shown to be the principal factor that promotes and influences the rate of rolling contact fatigue crack growth in lubricated contacts. In addition to the modelling work, an experimental method of analysing RCF cracks in real time has been developed. The technique is based on laser induced fluorescence that allows the penetration of the fluid within the crack to be observed. Though the method would require development to be used to provide results that could be used for quantitative comparisons with crack models, some encouraging preliminary results have been obtained: the technique has been shown to be suitable for measuring, at least qualitatively, the real time evolution of the film thickness in RCF cracks.
8
Almeida, Fabio Cardoso. "Análise das forças de contato e comportamento dinâmico de rodeiro ferroviário." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-05092006-113355/.
Full textAbstract:
Sistemas dinâmicos ferroviários são modelados levando-se em consideração as forças de contato roda trilho. As equações de movimento são fortemente influenciadas pela determinação dessas forças, o que requer o conhecimento da mecânica de contato, ferramenta imprescindível na previsão do comportamento de uma composição ferroviária. O rodeiro é responsável por receber as excitações na forma de irregularidades e imperfeições da via e transferi-la para a suspensão primária. A proposta dessa dissertação consiste em realizar simulações no domínio do tempo, da resposta do comportamento dinâmico do rodeiro ferroviário de 2 graus de liberdade. O modelo matemático equivalente é desenvolvido. A rigidez de contato e a conicidade são linearizados em torno de um ponto de operação, próximo ao centro da via. É apresentada a influência da velocidade na estabilidade para o modelo linearizado e para a conicidade variando de 0.1 a 1.0. Os respectivos modos de vibrar também são apresentados. Em seguida, o modelo matemático não linear do rodeiro ferroviário é gerado por software especializado na criação de sistemas de multicorpos, VAMPIRE, que permite a criação das equações de movimento através da topologia do sistema. O modelo é criado seguindo a proposta do benchmarck apresentada pela International Association of Vehicle System Dynamics (IAVSD). O rodeiro recebe uma força lateral crescente que se estabiliza em 20kN. O rodeiro é excitado com a aplicação de outra força lateral a uma taxa de 50kN/s até o descarrilamento. As forças longitudinais, laterais que aparecem no contato, o ângulo do plano de contato, ângulo de yaw e afastamento lateral são comparados com o benchmarck e outros autores.Railway dynamics systems are modeled regarding the creep forces between wheel-rail. The equations of movement are strongly influenced by these forces, what requests the knowledge of the theory in mechanical of contact, necessary tool to foresee the behavior of a railway vehicle. The wheelset is responsible by receiving the perturbations of irregularities and transfer them to the primary suspension. A railway vehicle is composed by primary and secondary suspensions. The proposal is based on performing simulations in the time domain, dynamic mresponse of a railway wheelset of two degrees of freedom. The mathematical model is developed. The stiffness of contact and conicity are linearized around an operation point, near to track center. The influence of speed is determined to linearized model and to a range of 0.1 to 1.0 in the conicity. The eigenvectors are presented. In the following, the non linear model of the wheelset is generated using a specialized package of multi body system, VAMPIRE. The package creates equations of movement after the generation of the topology. The non linear mathematical model are defined by the benchmark proposed by International Association of Vehicle System Dynamics (IAVSD). The wheelset is submitted to 20kN at the rail level. In a second case, the wheelset is submitted to a rate of 50kN/s of lateral force until derailing. The determined longitudinal and lateral forces on contact, yaw angle and displacement of the center of gravity of the wheelset, contact angle are compared with the benchmark results and other authors.
9
Orujova, Ulviyya. "Préstamos directos e indirectos del turco en el léxico español y función de las lenguas transmisoras." Doctoral thesis, Universitat Autònoma de Barcelona, 2018. http://hdl.handle.net/10803/666851.
Full textAbstract:
El tema de la presente tesis es La vinculación turca respecto al léxico español y la función de las lenguas transmisoras, cuyo contenido está estructurado en siete apartados: introducción, estado de la cuestión, metodología, análisis, conclusión, bibliografía y apéndice.
La investigación trata de las palabras tomadas del turco que existen en la lengua española, las que también denominamos “turquismos”. Hoy en día no se distingue mucho la diferencia entre turquismo y arabismo. Uno de los propósitos de esta tesis es demostrar que este tipo de préstamos son de procedencia distinta. El objetivo principal, sin embargo, es el de intentar justificar, a partir de los datos que hemos recogido y analizado, que la lengua turca también debe considerarse en la historia del léxico del español.
Hasta estos momentos, se ha demostrado ampliamente la influencia de los musulmanes de origen árabe en la península ibérica, pero los árabes no fueron los únicos islamitas que se relacionaron con la Península; los turcos también lo hicieron desde diferentes puntos de vista durante largo tiempo, aunque de forma más indirecta. Es evidente que cualquier contacto entre naciones conlleva el intercambio de palabras, y, por esta razón, en el léxico español han aparecido préstamos directos e indirectos de procedencia turca, aunque no sean demasiados si los comparamos con el número de arabismos. Existen también lenguas transmisoras a través de las cuales han llegado al español determinados turquismos. Son el francés, el italiano, el ruso, el árabe, el inglés, entre otras. En la presente investigación se analizan todos los procesos de transmisión de estas voces, se demuestran las áreas semánticas de las que forman parte y su frecuencia de uso en el lenguaje español. Algunos de los ejemplos del corpus son: fez, sultán, horda, turbante, café, hurra, yogur, chamerluco, tabor, corbacho, zapato, tulipán, caftán, atamán, bajá, etc. Algunos de ellos tienen incluso derivados creados en el propio español, que también se han incluido en el corpus de esta investigación.
El número total de los préstamos del turco, directos e indirectos, que se ha extraído de fuentes lexicográficas para la elaboración de la presente tesis doctoral, es 130. Entre las distintas palabras, se observa que los sustantivos (82% de todo el corpus) son más frecuentes que los adjetivos u otras partículas. Esto no es de extrañar, ya que los sustantivos son más numerosos que el resto de palabras por tener el rasgo de nombrar todo tipo de objetos entre otros conceptos.
La importancia de este trabajo está determinada por el hecho de que sus resultados puedan ser utilizados en estudios posteriores para resolver problemas en este ámbito del origen de las palabras. Es un trabajo importante porque el estudio de la influencia del turco es innovadora y está poco estudiada. Esta tesis puede tener un papel importante en el contexto del léxico español para que su temática pueda desarrollarse de un modo más profundo que hasta el momento.The theme of the thesis is Direct and indirect Turkish loanwords on the vocabulary of the Spanish language and the function of intermediary languages. It consists of seven sections: introduction, objective, methodology, analysis, conclusion, bibliography and appendix. The research deals with a linguistic analysis of foreign words borrowed from Turkish that are widely used in the Spanish language, which we also call “turquismos”. Today the difference between “turquismo” and “arabismo” has not been thoroughly investigated. One of the objectives of the thesis is to demonstrate the evidence of this type of loanwords originated from different sources. Based on the selected and analyzed materials, we have made an attempt to prove that the Turkish language has left its traces in the Spanish lexicon during the historical periods of the language and its society. Until now, the influence of Arabian muslims in the Iberian Peninsula has been amply demonstrated, but the Arabs were not the only Islamists who were related to the Peninsula; the Turks also did it from different points of view for a long time, although in a more indirect way. It is evident that any contact between the nations involves the exchange of words, and for that reason, direct and indirect loans of Turkish origin have appeared in the Spanish lexicon, although not too many, if we compare them with the number of Arabisms. There are also intermediary languages through which certain Turkish loanwords were integrated in the Spanish vocabulary. They are French, Italian, Russian, Arabic, English and some others. All the transmission processes of these words, their semantic fields and the frequency of their usage in the Spanish language are analyzed. Some examples of the corpus are: fez, sultán, horda, turbante, café, hurra, yogur, chamerluco, tabor, corbacho, zapato, tulipán, caftán, atamán, bajá, etc. Some of them even have derivatives formed in Spanish itself, which have also been included in the corpus of this research. The total number of direct and indirect Turkish loanwords, which has been selected from lexicographical sources for the doctoral thesis, is 130. It has been observed that the nouns (82% of the whole corpus) are more frequent than adjectives or other parts of the speech. It is not surprising that nouns are more numerous than the rest of the words as they have the feature of naming all kinds of things and objects among other concepts. The theoretical importance of this research is determined by the fact that its results can be used in later studies to solve linguistic problems in the field of etymology of vocabulary units. Its practical significance lies in the study of the influence of the Turkish languages which is innovative. The thesis can have an important role in the context of the Spanish lexicon so that its subject can be developed extensively in the future.
10
Everitt, Carl-Magnus. "Initiation of rolling contact fatigue from asperities in elastohydrodynamic lubricated contacts." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222371.
Full textAbstract:
Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly. In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line. In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum.Rullande kontakter förekommer i många applikationer, till exempel i lager och mellan kugghjulständer. Både lager och kugghjul utsätts ofta för höga laster vilket gör att dess ytor löper stor risk att utmattas, vilket kallas rullande kontaktutmattning. Denna studie fokuserar på pitting, även kallat spalling, vilket är en typ av rullande kontaktutmattning där en utmattninsspricka växer fram som får delar av ytan att ramla av. För att få en bättre förståelse varför pittingskador uppkommer har noggranna simuleringar utförts av rullande kontakter. Kontakten mellan två tänder på kugghjul i en lastbilsretarder har används som underlag då många pittingskador påträffats på dem. För att minska friktionen och nötningen i kontakten mellan kuggtänderna användes smörjmedel. De höga lasterna lastbilsretardern utsattes för deformerade kuggarnas ytor elastiskt samtidigt de kraftigt ökade viskositeten hos smörjmedlet. Dessa förhållanden gör att kontakten kallas för elastohydrodynamiskt smord, vilket på engelska förkortas till EHL. I Artikel A undersöktes om små ytojämnheter kan orsaka ytinitierade pittingskador. Eftersom skadan påträffats i friktionslösa kontakter, så som vid rullcirkeln på de undersökta kugghjulen, är det viktigt att teorierna som förklarar uppkomsten inte är beroende av friktion. Undersökningen fokuserade därför på förhållandena vid rullcirkeln. Slutsatsen från arbetet var att små ytojämnheter, av samma storleksordning som ytojämnheterna på de undersökta kugghjulen, är tillräckligt stora för att orsaka utmattningsskador. I Artikel B undersöktes varför det är vanligare att pitts initieras i dedendum än addendum på drivande kugghjul. Kontakten på båda sidorna om rullcirkeln slirar svagt åt olika håll. Att kontakten slirar skapar friktion som är motriktad rullriktningen i dedendum vilket ökar risken för pittingskador. För att undersöka varför dessa förhållanden ökar risken för skador fördjupades analysen av kontakten genom att inkludera temperaturfältet. Simuleringarna visade att temperaturen ökar genom kontakten vilket orsakar en asymmetrisk spänningsfördelning. Denna asymmetriska spänningsfördelning gör att ytojämnheter i dedendum är troligare att orsaka skador än ytojämnheter i addendum.
QC 20180213
11
Almeida, Lia Ramadoss Ramesh. "Experimental and theoretical investigation of contact resistance and reliability of lateral contact type ohmic MEMS relays." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Theses/ALMEIDA_LIA_13.pdf.
Full text
12
Ciobotarescu, Simona. "Synthesis, molecular modeling and photochromic behaviour of polysiloxanes containing azo-groups with different geometries." Thesis, Angers, 2020. http://bu.univ-angers.fr/Contact.
Full textAbstract:
La présente thèse représente une étude complexe des azopolysiloxanes photosensibles et rejoint les techniques théoriques et expérimentales. Le thème tourne autour du phénomène de transport de masse des azopolymères induit par la photoisomérisation des azobenzènes. La conversion transt – cis de l'azobenzène et de ses dérivés est un processus réversible actionné par la lumière, qui permet le réarrangement de la matière environnante au niveau nano et micro. Cette propriété est exploitée pour fabriquer des réseaux de relief de surface (SRG) avec caractéristiques géométriques specifiques. Les présentes études visent à comprendre ce mécanisme complexe, sujet à une grande controverse parmi les différents groupes de recherche. Les paramètres qui contrôlent le processus sont traités et analysés. L'étude expérimentale comprend la synthèse et la caractérisation de quatre azopolysiloxanes qui sont ensuite analysés pour leur capacité d'obtenir des SRG. Le comportement photochromique est évalué par des expériments d'irradiation à différentes intensités lumineuses, en présence ou l'absence d'une lumière d'assistance qui devrait intensifier l'isomérisation. La simulation informatique se concentre sur la diffusion des molécules dans le système: une molécule de type azobenzène (moteur moléculaire) diluée dans le milieu hôte. Des calculs de modélisation moléculaire sont effectués pour des moteurs de différentes longueurs et avec différents temps d'isomérisation (isomérisation rapide ou lente) afin de définir la relation entre ces paramètres et la diffusion. Fournir des informations expérimentales et théoriques sur les azopolymères, est trop important pour comprendre la formation de SRGThe herein thesis represents a complex study of photosensitive azopolysiloxanes and rejoins both theoretical and experimental techniques. The theme revolves around the azopolymer’s mass transport phenomenon induced by the photoisomerization of azobenzenes. Trans- to cis conversion of azobenzene and its derivatives is a reversible light actuated process that enables the rearrangement of surrounding matter at nano and micro level. This property is exploited to fabricate surface relief gratings (SRG) with certain geometrical features. The present studies are directed to comprehension of this complex mechanism, subject to great controversial among different research groups. The parameters that control the process are addressed and analyzed. Experimental study comprises the synthesis and characterization of four azopolysiloxanes which are then analyzed for the capacity to obtain SRG. Photochromic behaviour is evaluated through irradiation experiments at different light intensity, in the presence or absence of an assistance light that supposedly intensifies isomerization. Computer simulation focuses on diffusion of the molecules in the system: one azobenzene – like molecule (molecular motor) diluted in the host medium. Molecular modeling calculations are performed for motors with different lengths and with various isomerization times (fast or slow isomerization) in order to define the relation between these parameters and diffusion. Providing experimental and theoretical info on azopolymers is part of the SRG formation insight
13
Debray, Kévin. "Phylogenomics of the genus Rosa : hybridization and polyploidy as factors for diversification." Thesis, Angers, 2020. http://bu.univ-angers.fr/Contact.
Full textAbstract:
Le genre Rosa comprend 150-200 espèces bien réparties sur l'hémisphère nord et présente une histoire évolutive complexe. L'hybridation et la polyploïdie sont des forces évolutives majeures chez Rosa bien que ces deux processus ont à peine été pris en compte dans les dernières phylogénies. Avec la récente acquisition de génomes complets et le développement de techniques de séquençage à haut débit, l'objectif de cette thèse était de développer un cadre phylogénomique général pour résoudre les relations phylogénétiques au sein de groupes taxonomiques larges et complexes constitués de taxons proches comme chez Rosa. L'exploitation de génomes complets disponibles publiquement a permis d'extraire 1856 courtes séquences orthologues en simple copie (SCOTags) d'intérêt phylogénétique. Quatre-vingt-douze SCOTags du génome nucléaire et quatre SCOTags du génome chloroplastique ont été ciblé chez 126 espèces en utilisant des PCR mircrofluidiques et du séquençage d'amplicons. La quantité importante de données générées par le séquençage a permis d'estimer le niveau de ploïdie de chaque accession et d'assembler des séquences alléliques qui ont plus tard servi à tracer l'origine hybride de certains taxons. Une approche par étapes a été développée pour progressivement dévoiler les patterns réticulés chez Rosa. Des phylogénies nucléaires et chloroplastiques robustes ont été obtenues ainsi que des scenarios d'hybridation détaillés pour plusieurs spécimens. Enfin, le pouvoir de résolution de marqueurs microsatellite a été étudié pour délimiter des espèces très proches. De nombreux groupes taxonomiques larges et complexes peuvent désormais être étudiés en utilisant cette approche progressiveThe genus Rosa comprises 150-200 species well distributed in the northern hemisphere and has a complex evolutionary history. Hybridization and polyploidy are major evolutionary forces in Rosa although both processes have hardly been taken into account in recent phylogenies. With the recent acquisition of complete genomes and the development of high-throughput sequencing techniques, the aim of this thesis was to develop a general phylogenomic framework to resolve phylogenetic relationships within large and complex taxonomic groups consisting of close taxa, as in Rosa. The exploitation of publicly available complete genomes made it possible to extract 1856 short orthologue sequences in single copy (SCOTags) of phylogenetic interest. Ninety-two SCOTags from the nuclear genome and four SCOTags from the chloroplast genome were targeted in 126 species using mircrofluidic PCR and amplicon sequencing. The large amount of data generated by sequencing made it possible to estimate the ploidy level of each accession and to assemble allelic sequences that were later used to trace the hybrid origin of certain taxa. A stepwise approach wasThe genus Rosa comprises 150-200 species well distributed in the northern hemisphere and has a complex evolutionary history. developed to progressively reveal the reticulated patterns in Rosa. Robust nuclear and chloroplastic phylogenies were obtained as well as detailed hybridization scenarios for several specimens. Finally, the resolving power of microsatellite markers was studied to delineate closely related species. Many large and complex taxonomic groups can now be studied using this stepwise approach
14
Ali, Sakina. "Rôle des vésicules extracellulaires dans la pathogenèse de la résistance à l’insuline dans le syndrome métabolique LPS-enriched small extracellular vesicles from metabolic syndrome patients trigger endothelial dysfunction by activation of TLR4." Thesis, Angers, 2020. http://bu.univ-angers.fr/Contact.
Full textAbstract:
Le syndrome métabolique (SMet) est un ensemble de troubles métaboliques associés à une dysfonction endothéliale et à une résistance à l’insuline. Grâce à leur cargaison qu’ils peuvent transférer d’une cellule à l’autre, les vésicules extracellulaires (VEs), incluant les grandes (lEVs) et les petites (sEVs) vésicules sont impliquées dans différentes voies de communication intercellulaire. Parmi toutes les recherches menées sur les VEs, l’étude de leur implication dans la physiopathologie des maladies métaboliques a mis en évidence de nombreuses communications intercellulaires délétères pour le système vasculaire et pour la signalisation de l’insuline. Les objectifs de mon projet de thèse étaient de caractériser les sEVs circulants de patients SMet et non-SMet, d’évaluer leur effet métabolique sur la fonction endothéliale et enfin d’analyser l’effet des lEVs et des sEVs sur les cellules et tissus cibles de l’insuline. Premièrement, nous avons montré que la concentration circulante des sEVs étaient positivement corrélées avec les critères du SMet, notamment l’obésité viscérale, l’hypertension, la résistance à l’insuline et la dyslipidémie. Nous avons montré que les SMet-sEVs, enrichies en LPS, sont impliqués dans le développement d’une dysfonction endothéliale via l’activation de la voie de signalisation de TLR4. Deuxièmement, nous avons démontré que les deux sous-types de VEs peuvent induire une résistance à l’insuline dans les organes périphériques via des mécanismes moléculaires différents. Ces résultats ont permis de mettre en évidence les voies moléculaires par lesquelles les VEs participent aux altérations métaboliques associées à la dysfonction endothéliale et à la résistance à l’insuline pendant le MetSMetabolic syndrome (MetS),characterized by interconnecting metabolic disorders, is associated with endothelium dysfunction and insulin resistance. Thanks to their ability to transfer their cargo to recipient cells, extracellular vesicles (EVs), including large(lEVs) and small (sEVs) vesicles are involved indifferent intercellular communication pathways. Among the research conducted on EVs, the study of their involvement in the pathophysiology of metabolic diseases have highlighted numerous intercellular communication that are deleterious for the vascular system and for insulin pathways. My thesis project aims were to characterize circulating EVs from non-MetS and MetSpatients, to evaluate their metabolic effect on endothelial function, and to analyze lEVs andsEVs effects on insulin target cells and tissues. First, we shown that circulating concentration of sEVs were positively correlated with MetS criteriain cluding visceral obesity, hypertension, insulin resistance and dyslipidemia. We have shown that MetS sEVs, enriched with LPS, are involved in the development of endothelial dysfunction through the activation of the TLR4 signaling pathway. Second, we demonstrated that both subtype of EVs can induce insulin resistance in peripheral tissues via different molecular mechanisms.These results allow understanding the molecular pathways by which EVs participate in metabolic alterations associated with endothelial dysfunctions and insulin resistance during MetS
15
Ashoka, Sahadevan Suchithra. "Anilate-based molecular building blocks for metal-organic frameworks and molecular conductors Conducting Anilate-Based Mixed-Valence Fe(II)Fe(III) Coordination Polymer: Small-Polaron Hopping Model for Oxalate-Type Fe(II)Fe(III) 2D Networks Nanosheets of Two-Dimensional Neutral Coordination Polymers Based on Near-Infrared-Emitting Lanthanides and a Chlorocyananilate Ligand." Thesis, Angers, 2019. http://bu.univ-angers.fr/Contact.
Full textAbstract:
Ce travail porte sur la synthèse et la caractérisation de matériaux moléculaires fonctionnels basés sur la molécule anilate et présentant des propriétés de conductivité, de magnétisme et de luminescence. Les anilates sont des dérivés de la 2,5-dihydroxy-1,4-benzoquinone substitués en positions 3 et 6 par une variété d’éléments (H, F, Cl, Br, I, CN, etc). Parmi eux, le seul composé hétérosubstitué ClCNAn2- a été choisi pour préparer une nouvelle famille de polymères de coordination bidimensionnels (PC 2D) avec des métaux de transition ou des ions lanthanides : i) un PC à valence mixte FeIIFeIII, de formule [TAG][FeIIFeIII(ClCNAn)3], contient pour la première fois le cation triaminoguanidinium dans un réseau de coordination.ii) Des PC basés sur le ligand ClCNAn2- et des ions lanthanides émettant dans le proche infrarouge (YbIII, NdIII, ErIII). Ces composés ont été exfoliés en monocouches, et des études de photoluminescence ont été menées à la fois sur les cristaux et les monocouches. iii) Une famille de PC hétéroleptiques basés sur des ions lanthanides et sur deux types de ligands pontants, le ligand ClCNAn2- et des ligands de type carboxylates (DOBDC et F4-BDC). iv) Une famille de PC basés sur des ions DyIII ont été préparés afin d’étudier leur propriétés magnétiques. v) Finalement, la capacité des ligands anilates à se combiner à des conducteurs moléculaires basés sur le BEDT-TTF a été démontrée à travers la synthèse et l’électrocristallisation de semiconducteurs organiques et de conducteurs magnétiques hybrides avec l’anion [Fe(ClCNAn)3]3-This work reports on the design, synthesis and characterization of novel anilate-based functional molecular materials showing luminescent, magnetic and/or conducting properties. The family of anilate ligands comprises several derivatives obtained by introducing various substituents (H, F, Cl, Br, I, CN, etc.) at the 3 and 6 positions of the common 2,5-dihydroxy-1,4-benzoquinone framework. Among the anilate ligands, the only known heterosubstituted anilate with Cl/CN substituents at the 3,6 positions, ClCNAn2-, have been selected for preparing a novel family of 2D layered coordination polymers (2D CP) with both 3d metal ions and 4f lanthanide ions, through a general and straightforward synthetic strategy. i) Mixed-valence FeIIFeIII 2D CP, formulated as [TAG][FeIIFeIII(ClCNAn)3], containing, the tris(amino)-guanidinium (TAG) cation for the first time in such 2D networks has been synthesized and thoroughly characterized. ii) 2D CPs based on NIR-emitting lanthanides (YbIII, NdIII, ErIII) and the ClCNAn2- ligand, have been prepared and characterized. These layered compounds were exfoliated to nanosheets, by sonication-assisted solution synthesis. Time-resolved photoluminescence studies performed on both the bulk and nanosheets are also highlighted. iii) Novel family of heteroleptic 2D CPs based on NIR-emitting lanthanides and mixed ligands (ClCNAn2- and carboxylate ligands (DOBDC and F4-BDC)), were prepared and characterized. vi) Novel family of 2D CPs based on DyIII and ClCNAn2- were prepared in order to investigate their magnetic properties. v) Furthermore, the ability of anilate ligands to work as components of BEDT-TTF- based molecular conductors have been demonstrated through the synthesis, via electrocrystallization technique. vi) П-d hybrid multifunctional paramagnetic molecular conductors BEDT-TTF and [Fe(ClCNAn)3]3-) were also studied
16
Rajan, Naveen Mukund. "Experimental study of the effect of a contact conditioner on sliding electrical contacts." Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1546.
Full textAbstract:
This thesis documents research carried over the past two years, aimed at studying the tribology of sliding contacts subjected to high densities of current of the order is 422 --917A/mm2. The overall aim was the development of an experimental test bed for evaluating the effect of different solid lubricant conditioners on sliding electrical contacts. The experimental configuration consists of a flat ended copper tip pressed in contact with a flat copper disc. The copper plate is mounted on a spindle of a lathe which is operated at 550rpm, whereas the copper tip is mounted on a shaft which is instrumented with force sensing piezos to measure the forces during the test. A weak spring is used to compensate for wear of the tip during the experiment. The interface is subjected to high current densities of the order of 422 and 917A/mm2 to evaluate the effect of solid conditioner as contrast with the surface behavior when no interface lubrication was used. The key outputs of the experiments are a) Friction coefficient, b) Contact resistance, c) Amount of material transfer, d) number of passes to failure and e) Wear rate. Two types of tests, namely circular and spiral tests were carried out. The current density of 422A/mm2 would result in softening of the interface whereas current density of 917A/mm2 results in melting of the interface. In terms of contact voltages it is noted that Cu-Cu interface softens at 0.12V and melts at 0.43V. It has been noted that pre-application of SLIC leads to increase of contact resistance by approximately 20% when the interface is loaded statically. When the interface is tested for contact resistance, there is a significant effect of oxide layer on the surface of the plates. When contact resistance is measured these oxide layers contribute significantly, and increase the contact resistance substantially.Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering
"December 2007."
17
Rajan, Naveen Mukund Madhavan Viswanathan. "Experimental study of the effect of a contact conditioner on sliding electrical contacts /." Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1546.
Full text
18
McNeal, Cedric J. "Barrel wear reduction in rail guns : the effects of known and controlled rail spacing on low voltage electrical contact and the hard chrome plating of copper-tungsten rail and pure copper rails /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FMcNeal.pdf.
Full textAbstract:
Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2003.Thesis advisor(s): William B. Maier II, Richard Harkins. Includes bibliographical references (p. 45-46). Also available online.
19
Anisetti, Anusha. "On the Thermal and Contact Fatigue Behavior of Gear Contacts under Tribo-dynamic Condition." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright149363918488722.
Full text
20
Praquin, Jérôme. "Étude des revêtements et des paramètres de fonctionnement électrique, climatique et mécanique sur la conduction et la commutation de faibles courants des contacts électriques de type membrane." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S094.
Full textAbstract:
L'objet de la présente étude est d'étudier, de comprendre et de maîtriser les différentes propriétés électriques de contacts électriques constitués de membranes souples en carbone, qui commutent sur des pistes métalliques d'un circuit imprimé. Ces contacts sont de plus en plus utilisés dans l'automobile car ils possèdent des propriétés mécaniques intéressantes vis-à-vis du ressenti de l'utilisateur, tout en permettant une bonne durée de vie. Dans un premier temps, les paramètres électriques et mécaniques de ces contacts sont caractérisés, les phénomènes de commutation sur divers type de charges sont étudiés et l'influence de contaminants et de la corrosion sur la conduction électrique sont examinés. L'évolution des résistances d'isolement en présence d'humidité est quantifiée. Dans un second temps, une approche de fiabilité est réalisée : l'évolution des paramètres électriques et mécaniques de ces contacts est étudiée lorsqu'ils sont soumis à des stress environnementaux, en particulier la chaleur humide. Les principaux modes d'endommagement sont étudiés. Nous montrons en particulier que les défaillances mécaniques proviennent essentiellement du polymère, et les défaillances électriques proviennent plutôt du circuit imprimé. L'influence d'un revêtement doré côté circuit imprimé, pour différentes épaisseurs, est également étudiée. Notre travail se poursuit par une étude un peu plus fondamentale sur les phénomènes de commutation en présence de matériaux en carbone. Au cours de ce travail novateur, les signatures optiques sont examinées lors de la coupure du courant. Un phénomène baptisé « glowing » est mis en évidence ; les limites en courant et en tension entre « glowing » et arcage électrique sont données, et les phénomènes comparés par rapport aux phénomènes de commutation dans les contacts de type métal – métal. L'étude se termine par un bilan synthétique concernant l'utilisation de contacts comprenant une pastille en carbone, avec leurs avantages et leurs limitationsThe purpose of this study is to explore, understand and master the different electrical properties of electrical contacts made of flexible carbon membranes, which switch on metal tracks on a printed circuit board. These contacts are increasingly used in the automobile because they have interesting mechanical properties for the user, while providing a good reliability. At first, the electrical and mechanical parameters of these contacts are characterized, the switching phenomena on various types of loads are studied and the influence of contaminants and corrosion on the electrical conduction is examined. The evolution of insulation resistance in the presence of moisture is quantified. In a second step, an approach to reliability is achieved: the evolution of electrical and mechanical parameters of these contacts is studied when subjected to environmental stresses, especially moist and heat. The main types of damage are considered. We show in particular that mechanical failures come mainly from polymer and electrical failures from the PCB. The influence of a gold-plated printed for different thicknesses system side, is also studied. Our work continues with a slightly more fundamental study on switching phenomena in the presence of carbon materials. In this pioneering work, the optical signatures are discussed at the current break. A phenomenon called "glowing" is highlighted; limits current and voltage between "glowing" and electrical arcing are given, and compared with respect to the phenomena switching phenomena in metal contacts - type metal. The study concludes with a summary review on the use of contacts comprising a carbon pill, with their advantages and limitations
21
van, der Linden Franciscus [Verfasser]. "Gear contact modeling for system simulations and experimental investigation of gear contacts / Franciscus van der Linden." München : Verlag Dr. Hut, 2017. http://d-nb.info/1128467631/34.
Full text
22
Brunetti, Jacopo. "Mechanical energy balance of frictional contacts : From surface to solid energy dissipation in contact dynamic instabilities." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0118/document.
Full textAbstract:
Chaque fois que se produit un mouvement relatif entre deux systèmes, avec une interface à contact sec, le contact frottant induit des vibrations. La dynamique locale au contact (ruptures et la génération d'ondes) se couple avec la dynamique du système, donnant origine à des vibrations et affectant le comportement frictionnel macroscopique du système. Dans cette thèse, afin de développer une approche globale pour l'investigation des phénomènes multi-physiques, l'énergie a été utilisée comme une caractéristique physique universelle du couplage. La formulation de un bilan énergétique mécanique est utilisé pour identifier deux termes dissipatifs différents, i.e. la dissipation par amortissement matériel/système et la dissipation au contact. Les flux d'énergie, provenant des surfaces en contact et dus aux vibrations induites par frottement, excitent la réponse dynamique du système et, vice versa, l'influence de la réponse dynamique du système sur la dissipation d'énergie locale à l'interface de contact affecte les phénomènes tribologiques connexes. Dans cette thèse, les vibrations induites par le frottement ont été analysées en utilisant: l'approche par éléments finis pour étudier, par l'analyse des flux d'énergie, le couplage entre le contact et la dynamique du système; l'approche expérimentale pour valider les résultats numériques et observer l'influence des phénomènes pas encore inclus dans les modèles numériques; une approche avec une modèle à paramètres concentrés pour évaluer rapidement les effets des paramètres du système. L'analyse numérique par le modèle éléments finis 2D permet une répartition de l’énergie introduite dans le système mécanique entre les deux termes dissipatifs (amortissement matériau et contact), au cours de la réponse transitoire aussi bien en conditions stables qu’instables. En particulier, les vibrations induites par frottement modifient la capacité globale du système à absorber et dissiper l’énergie; une estimation de la puissance dissipée au contact, sans prendre en compte le comportement dynamique du système (flux d’énergie par les vibrations induites par frottement) peut conduire à des erreurs significatives dans la quantification de l’énergie dissipée au contact, ce qui affecte directement plusieurs phénomènes tribologiques. Les mesures expérimentales de crissement montrent comment les mêmes modes instables sont reproduits soit expérimentalement soit numériquement, validant l’utilisation de la simulation 2D transitoires pour l’analyse des vibrations instables induites par le frottement. L’équilibre énergétique a été utilisé sur le modèle à paramétrés concentrés, pour approcher le problème de la surestimation d’instabilité, qui est caractéristique d’une analyse des valeurs propres complexes. Un nouvel indice d’instabilité (MAI) a été défini, par des considérations énergétiques, pour comparer les différents modes instables et pour sélectionner le mode qui devient effectivement instable pendant le crissementWhenever relative motion between two system components occurs, through a dry contact interface, vibrations are induced by the frictional contact. The local dynamics at the contact (ruptures and wave generation) couples with the system dynamics, giving origin to vibrations and affecting the macroscopic frictional behavior of the system. In this thesis, in order to develop an overall approach to the investigation of the multi-physic phenomenon, the energy has been pointed out as a coupling physical characteristic among the several phenomena at the different scales. The formulation of a mechanical energy balance is used for distinguishing between two different dissipative terms, i.e. the dissipation by material/system damping and the dissipation at the contact. The energy flows coming from the frictional surfaces, by friction induced vibrations, excites the dynamic response of the system, and vice versa the influence of the system dynamic response on the local energy dissipation at the contact interface affects the related tribological phenomena. The friction-induced vibrations have been analyzed using three different approaches: the finite element approach, to investigate the coupling between the contact and system dynamics by the analysis of the energy flows; the experimental approach to validate the numerical results and observe the influence of phenomena not still included into the numerical model; a lumped parameter model approach to quickly investigate the effects of the system parameters. The numerical analysis by the 2D finite element model allowed investigating the repartition of the energy introduced into the mechanical system between the two dissipative terms (material damping and contact) during both stable and unstable friction-induced vibrations. In particular, it has been shown how the friction-induced vibrations modify the overall capacity of the system to absorb and dissipate energy; an estimation of the power dissipated at the contact, without considering the dynamic behavior of the system (energy flows by friction induced vibrations) can lead to significant error in the quantification of the dissipated energy at the contact, which affects directly several tribological phenomena. The experimental squeal measurements show how the same unstable modes are recovered both experimentally and numerically, validating the use of the 2D transient simulations for the reproduction of the unstable friction-induced vibrations. Once the energy balance formulated, it has been used on the lumped model to approach the instability over-prediction issue characteristic of the complex eigenvalue analysis. By energy considerations, a newer instability index (MAI) has been defined to compare the different unstable modes and to select the mode that becomes effectively unstable during the transient response. The Modal Absorption Index allows quantifying the capability of each mode to exchange energy with the external environment
23
Neves, Julio Cesar Klein das. "Desenvolvimento de um equipamento para ensaio de fadiga de contato esfera sobre plano e sua aplicação na caracterização de ferros fundidos com matrizes de elevada dureza." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-11122006-131939/.
Full textAbstract:
Esse trabalho descreve o projeto e construção de um equipamento destinado ao estudo de fadiga de contato de rolamento e sua posterior aplicação na caracterização de ferros fundidos. O trabalho foi iniciado com a utilização de um equipamento previamente existente no Laboratório de Fenômenos de Superfície da EPUSP, a máquina I. Esse equipamento era baseado na substituição das pistas externas de um rolamento axial de esferas por corpos de prova na forma de arruelas. Ensaios preliminares mostraram que a máquina I apresentava limitações, a principal delas era não ser capaz de reproduzir integralmente o movimento de rolamento, havendo uma relação desconhecida rolamento/deslizamento no decorrer do ensaio. Com base nas dificuldades operacionais da máquina I, uma segunda máquina, também baseada em um rolamento axial, foi projetada e construída. Ensaios preliminares mostraram que o novo equipamento reproduzia mecanismos de falha por fadiga de contato de rolamento. A etapa seguinte então foi utilizar a máquina II no estudo de fadiga de contato de rolamento de dois tipos de ferro fundido com matrizes de levada dureza, um cinzento e um nodular, os quais foram testados em duas condições: com e sem pré-tensionamento e analisados segundo a estatística de Weibull. Um aço também foi ensaiado como referência. A pré-tensão foi aplicada com uma ferramenta bi-partida e modelada por elementos finitos. Foram realizados ensaios lubrificados, com a aplicação de uma pressão máxima de contato de 3,6 GPa e conduzidos até a falha dos materiais por lascamento da superfície de rolamento. Em todas as condições de ensaio o ferro fundido nodular se mostrou muito superior ao ferro cinzento. Enquanto esse último que apresentou resultados similares na condição com e sem pré-tensão, o ferro fundido nodular teve a sua curva de distribuição de falhas significativamente alterada pela aplicação de tensão externa. Uma heterogeneidade na distribuição do tamanho de nódulos de grafita fez com que as falhas ocorressem sempre na mesma região do corpo-deprova evidenciando a sensibilidade do ensaio a variáveis microestruturais.This work presents design and construction of an equipment for rolling contact fatigue studying and its use to cast irons analysis. Firstly it was used an equipment available at Surface Phenomena Laboratory, in São Paulo University, which was called machine I. The design of the system followed the well-known architecture where races of a thrust ball bearing are substituted by washers made with the material under investigation. Preliminary tests have shown that the first machine had severe limitations, but the most important was lack of ability to reproduce rolling contact fatigue mechanisms. An unknown sliding/rolling ratio always took place in its work. Then a second machine was designed and assembled. Sets up tests have shown typical mechanisms of rolling contact fatigue. The next step was to use the new machine to study two types of cast irons, a gray iron and a ductile iron, under two test conditions: with and without pre-stress. Also a steel specimen was tested as a reference. Results were subjected to Weibull analysis. A device was developed for pre-stress application, and the specimen/device system was modeled by finite elements analysis. Tests were carried out till failure, under lubrication, and with maximum contact pressure of 3.6 GPa. Ductile cast iron behavior was superior to gray iron in all tests. Gray iron specimens with and without pre-stress presented very similar results. On the other hand, ductile iron probability failure curve was strongly affected by pre-stress. An unexpected heterogeneity on graphite nodules size distribution promoted failures on just one region, which is an evidence of test sensitivity to micro structural changes.
24
Porras, Vazquez Alberto. "Lubricant starvation in elastohydrodynamic large-size spinning contacts." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI109.
Full textAbstract:
Cette thèse est dédiée à l'étude des contacts pivotants de grandes dimensions situés à l'interface entre l'extrémité du rouleau et le collet de la bague des roulement. L'objectif principal de l'étude est d'évaluer l'influence de la sous-alimentation sur la distribution d'épaisseur de film du contact et d'analyser comment le pivotement pourrait affecter ce mécanisme. En raison de son importance dans la fiabilité et la performance du roulement, l'accent est mis sur l'épaisseur de film minimale locale située dans la région de faible vitesse de la zone de contact. Pour résoudre ce problème, une double approche numérique-expérimentale est proposée. La distribution de l'épaisseur de film des contacts pivotants est étudiée numériquement à l’aide d'un modèle d'éléments finis préalablement validé par deux bancs d'essai dédiés: Jerotrib et Tribogyr. La simulation de différentes conditions opératoires, cinématiques, géométriques et de lubrification permet d'écrire une expression analytique pour prédire l'épaisseur critique du film précédent. En même temps, de nouvelles techniques pour induire et contrôler expérimentalement la sous-alimentation au contact sont mises en œuvre dans les deux bancs d'essai et leurs résultats sont comparés à ceux de la simulation. Il est démontré que les effets du pivotement et de la sous-alimentation s’additionnent, de sorte que la distribution de l’épaisseur de film du contact pivotant reste asymétrique mais tend à une distribution plus hertzienne, et donc plus mince, lors de la limitation de l’alimentation en huile en amont de l’entrée du contactThis thesis is dedicated to the study of large-size spinning contacts located at the interface between the roller-end and the flange in rolling-element bearings. The main goal of the study is to evaluate the influence of lubricant starvation on the film thickness distribution of the contact and analyze how spinning might affect this mechanism. Due to its importance in the reliability and performance of the bearing, the focus is set of the local minimum film thickness found at the low velocity region of the contact area. To tackle this problem, a dual numerical-experimental approach is proposed. The film thickness distribution of spinning contacts is investigated numerically by means of a finite element model previously validated by two dedicated test rigs: Jerotrib and Tribogyr. The simulation of different operating, kinematic, geometric and lubrication conditions enables to write an analytic expression for predicting the aforementioned critical film thickness. At the same time, novel techniques to experimentally induce and control starvation in the contact are implemented into both test rigs and their results are contrasted with those of the simulation. It is demonstrated that the effects of spinning and starvation add up, so that the film thickness distribution of the spinning contact remains asymmetric but tends to a more Hertzian, and therefore thinner, distribution when limiting the oil supply upstream of the contact’s inlet
25
Bruel, Paulo Eduardo Nunes. "Abordagem analítica e caracterização de contato entre superfícies." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-06122006-003830/.
Full textAbstract:
Pode-se definir o tato através da capacidade de um corpo sentir o contato, localizá-lo, reconhecer a forma e a rugosidade da superfície impactante. Normalmente, não se encontram estruturas analíticas adequadas para descrever o fenômeno. Neste trabalho, pretende-se determinar a localização dos pontos de contato entre dois corpos através da análise dos sinais resultantes das vibrações causadas pelo contato, além de estimar a geometria da superfície do objeto impactante. A descrição qualitativa do impacto é obtida através da análise de uma série de funções matemáticas que geram uma base ortogonal adequada para este tipo de evento. Assim, o contato não é considerado através de uma modelagem física tradicional, mas pela descrição das ondas geradas pelas tensões e deformações superficiais, incorporando a interação de múltiplos pontos vinculados e procedimentos de contagem estatística. Com a metodologia para estudo de impacto experimental, é efetuada a construção qualitativa do espectro de deslocamento de uma placa simplesmente apoiada sujeita à aplicação de esforços distribuídos.The tact may be defined as the capacity of a body to locate the contact on its surface, to recognize shape of the contacting surface as well as the superficial rugosity. Usually analytical models are not able to describe the phenomenon properly. This work, proposes an approach for the contact form location between two bodies using the resultant signals analysis of the vibrations caused for the contact. In this way it is determined the target surface geometry. The qualitative description of the impact is obtained through the analysis of mathematical series that generate orthogonal basis for this sort of event. Thus, the contact is not considered through a traditional physical modeling, but by the description of the waves generated for the superficial stress and strain, incorporating the interaction of multiple entailed points and procedures of counting statistics. With a methodology for study of theoretical impact, the quantitative construction of the specter of displacement of a subject plate to the application of distributed strains is effected.
26
Ndiaye, Serigne Ndiaga. "Ultimate behavior of confined fluids under very high pressure and shear stress." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI104/document.
Full textAbstract:
L’étude du frottement dans les contacts lubrifiés fortement chargés est un sujet complexe. En effet, le frottement dépend fortement du comportement rhéologique du lubrifiant dans le centre du contact et, celui-ci n'est pas bien connu à pression et taux de cisaillement élevé. Diverses méthodes expérimentales ont été développées pour expliquer le comportement plateau dans les courbes de frottement, associé à l’existence d’une contrainte limite de cisaillement, mais aucune d'elles n'a fourni une image complète des mécanismes réels impliqués. Dans la continuité de ces efforts, des études sont présentées dans ce mémoire. Le premier défi dans ce travail est d'effectuer des mesures de frottement dans des conditions isothermes nominales, ce qui signifie que même si des effets thermiques doivent se produire dans toute mesure de frottement, il est possible de les minimiser et de rendre les résultats insensibles à une faible dissipation d'énergie dans le volume expérimental d'intérêt. La minimisation de l’échauffement du lubrifiant aide à se focaliser sur l’origine mécanique de la contrainte limite de cisaillement et de mieux caractériser sa dépendance à la pression et à la température. C'est pourquoi, tout d'abord, une série d'expériences a été réalisée sur deux lubrifiants, un diester pur (benzyl benzoate) et une huile minérale de turbine (Shell T9) avec des vitesses d'entraînement variables. Cela nous permet d'abord d'observer directement l'influence des effets thermiques sur les valeurs de la contrainte limite de cisaillement et ensuite, de déterminer les conditions expérimentales qui limitent ces effets tout en assurant un régime en film complet. Le deuxième objectif est de caractériser le comportement en frottement des lubrifiants sous conditions isothermes nominales et sur une large gamme de pression (jusqu'à 3 GPa) et de température (jusqu’à 80°C) afin d'établir un nouveau modèle découplé permettant de décrire la dépendance à la température et à la pression de la contrainte limite sous fortes charges. Enfin, l'étude se focalise sur la compréhension du comportement microscopique des lubrifiants dans des conditions extrêmes de cisaillement et de pression. Des mesures in situ de spectroscopie Raman et Brillouin ont été également effectuées sous conditions statiques, afin d'étudier le changement de phase du lubrifiantFriction in highly loaded lubricated contacts is a complex issue. Indeed, it highly depends on the lubricant rheological behaviour in the Hertzian region, which is not well known under such high pressure and high shear stress. Various experimental methods have been developed to explain the plateau-like behaviour in friction curves referred to as the limiting shear stress (LSS), but none of them provided a full picture of the real mechanisms involved. In a continuation of these efforts, some investigations are presented in this manuscript. The first challenge in this work is to carry out friction measurements under nominal isothermal conditions, meaning that even if thermal effects must occur in any friction measurement, it is possible to minimize them and to make the results almost insensitive to a weak energy dissipation within the experimental volume of interest. Minimizing shear heating of the lubricant help us to focus on the mechanical origin of the LSS and to better characterize its dependence to pressure and temperature. That’s why, first of all, a series of experiments was performed on two lubricants, a pure diester fluid (benzyl benzoate), and a commercial turbine mineral oil (Shell T9) with varying entrainment velocities. This allow us first to directly observe the influence of the lubricant shear heating on the LSS values and then to determine the experimental conditions which limit this thermal effect while ensuring a full film regime. The second objective is to characterize the frictional behavior of both lubricants under nominal isothermal conditions and over a wide range of pressure (up to 3 GPa) and temperature (up to 80°C) in order to establish a new uncoupled model to describe the temperature and pressure dependence of the limiting shear stress under highly loaded conditions. Finally, the study focuses on the understanding of the microscopic behavior of lubricants under extreme shear and pressure conditions. In situ Raman and Brillouin spectroscopy investigations were also conducted under static conditions, in order to study the lubricant phase changes under various pressure and temperature conditions
27
Serrano, Zapata Maribel. "Disponibilidad léxica en la provincia de Lleida: estudio comparado de dos lenguas en contacto." Doctoral thesis, Universitat de Lleida, 2014. http://hdl.handle.net/10803/285008.
Full textAbstract:
La presente tesis doctoral se enmarca dentro de la disponibilidad léxica y se adscribe al Proyecto Panhispánico de Estudio del Léxico Disponible. Nuestra aportación concreta supone el estudio del léxico disponible en la provincia de Lleida en las dos lenguas oficiales de la misma: el castellano y el catalán. Partiendo de una sola muestra compuesta por 240 informantes, hemos analizado la incidencia que tienen en cada corpus tanto las distintas variables lingüísticas, esto es los centros de interés, como las variables sociales. Además se ha comparado la productividad de los informantes en las dos lenguas y se han descrito las principales tendencias de cada subgrupo social con relación a la producción del castellano y del catalán. Del mismo modo, se ha analizado la influencia mutua de los dos idiomas, esto es, en qué medida el léxico disponible del castellano, o el del catalán, contiene elementos de la otra lengua y qué peso alcanzan dichas unidades en el conjunto total de los datos.La present tesi doctoral s'emmarca dins de la disponibilitat lèxica i s'adscriu al Projecte Panhispànic d’Estudi del Lèxic Disponible. La nostra aportació concreta consisteix en l'estudi del lèxic disponible a la província de Lleida en les dues llengües oficials: el castellà i el català. Les nostres dades es basen en una única mostra de 240 informants i hem analitzat la incidència que tenen en cada corpus tant les diferents variables lingüístiques, és a dir, els centres d'interès, com les variables socials. A més, s'ha comparat la productivitat dels informants en les dues llengües i s'han descrit les principals tendències de cada subgrup social en relació amb la producció del castellà i del català. De la mateixa manera, s'ha analitzat la influència mútua dels dos idiomes, és a dir, en quina mesura el lèxic disponible del castellà, o el del català, conté elements de l'altra llengua i quin pes tenen aquestes unitats en el conjunt total de les dades.
This thesis is part of the lexical availability and it is attached to the Pan-Hispanic Project of Research of Available Lexicon. Our specific contribution has consisted of researching the available lexicon in the Spanish province of Lleida in the two official languages: Spanish and Catalan. Taking into account a single sample of 240 informants, the influence of the different linguistic variables (areas of interests and sociolinguistic variables) on both linguistic corpora has been analysed. In addition, the productivity of the informants in both languages has been compared, and the main trends of each social subgroup in relation with to their productions in Spanish and Catalan has been described. In the same way, the mutual influence of both languages has been analysed, that is: to what extent the available lexicon of one language contains elements of the other language, and what weight do such units have in the overall data.
28
Silva, Alysson Alexander Naves. "Simulação numérica de escoamentos bidimensionais com superfícies livres e linhas de contato dinâmicas." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-22062010-145307/.
Full textAbstract:
Um método lagrangeano-euleriano arbitrário para a resolução de escoamentos dominados por tensão superficial é apresentado neste trabalho. Tais escoamentos são importantes em muitas aplicações, especialmente em canais capilares que frequentemente aparecem em escoamentos em microescala. A resolução deste tipo de escoamento apresenta vários desafios que são abordados neste trabalho. O escoamento é resolvido somente para a fase líquida, com condições de contorno apropriadas para a superfície livre que delimita o líquido e o gás, que é representada por arestas e vértices da malha computacional. Esta se move e se deforma, sendo que sua qualidade é mantida sob controle para não degradar a solução numérica. As equações de Navier-Stokes são discretizadas pelo método de elementos finitos em um referencial arbitrário. O método de incorporação dos efeitos de tensão superficial e linha de contato é explicado em detalhes. Validações comprovam a precisão do método proposto, com comparações através de soluções pseudo-analíticas para casos simples. Finalmente alguns resultados sobre escoamentos em capilares são apresentadosAn arbitrary lagrangian-eulerian finite element method to solve surface tension dominated flows is presented. Such flows are important in many applications, particularly in capillary channels, that appear in microscale flows. The resolution of such flows presents several challenges that are addressed in this work. The flow is solved only in the liquid phase, and proper boundary conditions are applied on the free-surface, bounding the liquid and gas, which is explicitly represented by vertices and edges of the computational mesh. The mesh is moved and deformed, but its quality is kept under control in order to control errors in the numerical solution. The Navier-Stokes equations are discretized by standard Galerkin finite element method in an arbitrary reference. Details of the computation of surface tension and contact line effects are presented. The methodology is validated for a number of simple test cases against known pseudo-analytical solutions, and numerical results are presented, showing the robustness and accuracy of the methodology. Finally, some results about surface-tension-driven flows in capillaries are presented
29
Votsios, Vasilis. "Contact mechanics and impact dynamics of non-conforming elastic and viscoelastic semi-infinite or thin bonded layered solids." Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/11815.
Full textAbstract:
The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.
30
Grégoire, Isaac. "Analyse du coefficient de frottement sur les contacts lubrifiés et impact sur le grippage : Application aux transmissions par engrenages aéronautiques." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI100.
Full textAbstract:
Le développement de nouvelles technologies permettant d’obtenir des procédés de fabrication novateurs, de même que l’utilisation de nouveaux matériaux et lubrifiants, ont rendu possible une amélioration globale de l’efficacité des systèmes mécaniques et la résolution de nombreuses défaillances. Néanmoins, certains types de détérioration comme le grippage restent difficiles à appréhender car ils résultent de nombreux paramètres connexes tels que le régime de lubrification, la température du contact et le coefficient de frottement. Le grippage est un phénomène qui apparait de manière brutale et qui se caractérise par des arrachements et des transferts de matières entre les surfaces en contact pouvant aller jusqu’à la destruction complète du système. Ce dernier est généralement associé à une mauvaise dissipation des calories entrainant des températures de contact élevées. De nombreux critères basés sur la dissipation d’énergie dans le contact ont été établis sans pour autant que l’un d’eux ne soit unanimement reconnu par la communauté scientifique. La première partie de cette étude a consisté à caractériser le comportement en frottement d’un couple matériau-lubrifiant grâce à l’utilisation d’une machine bi-disque. En parallèle, une modélisation thermique de ce banc d’essais a été réalisée en utilisant la méthode des réseaux thermiques. Les corrélations entre les formules analytiques et les mesures expérimentales ont permis d’aboutir à l’établissement d’une loi de frottement liant conditions de contact et température de masse des éprouvettes. Il a aussi pu être démontré que la température de masse des disques pouvait être considérablement différente de la température d’injection du lubrifiant en fonction des conditions opératoires. Ce résultat permet une analyse nouvelle des critères de grippage dont la plupart assimilent la température des éprouvettes à celle d’injection du lubrifiant. Malgré cela, les différents essais de grippage réalisés montrent que l’unique considération de la température de contact pour établir un critère de grippage s’avère insuffisanteThe development of new technologies, which allow innovative manufacturing processes, as well as the use of new materials and lubricants have led to an overall improvement of mechanical systems efficiency and reliability. However some failures, like scuffing, remain difficult to understand since they depend on many related parameters such as the lubrication regime, the contact temperature and the friction coefficient. Scuffing is a critical damage that appears suddenly and which is characterised by local welds and scratches between the sliding surfaces. It can lead to complete destruction of the mechanical system. This phenomenon is in general related to poor heat dissipation and overheating resulting in high contact temperature. Numerous studies were conducted in order to establish a scuffing criterion based on energetic approach. But none of them is unanimously recognized by the scientific community. The first part of this study consisted in characterizing the frictional behaviour of a given couple of lubricant and material thanks to the use of a twin-disc machine. In a second part, a thermal modelling of this test bench has been realised using the thermal network methodology. Correlations between analytical formulas and experimental measurements allowed to establish a friction law relating contact conditions and disc bulk temperature. It has also been demonstrated that the disc bulk temperature could be considerably different from the lubricant injection temperature depending on the operating conditions. This result allows a new interpretation of existing scuffing criteria, which for most of them consider the disc temperature to equal the oil temperature. Despite this analysis, the scuffing experiments performed reveal that accounting solely for the contact temperature is not sufficient to establish a reliable scuffing criterion
31
Ng, Sophia. "Five year tuberculosis risk in institutional contacts an evaluation from a territory wide mass contact screening program /." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41711713.
Full text
32
Morgan, Brent A. "The nature of the metal-semiconductor contact : evidence of spatially variant energy barriers in metal-semiconductor contacts /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952669.
Full text
33
Neto, Dorival Piedade. "Sobre estratégias de resolução numérica de problemas de contato." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-14072009-165646/.
Full textAbstract:
Os problemas de contato representam uma classe de problemas da mecânica dos sólidos para a qual a não-linearidade é introduzida pela alteração das condições de contorno, as quais só podem ser determinadas no decorrer do processo de resolução. O presente trabalho trata dos problemas de contato abordando aspectos de sua formulação e implementação numérica. Apresentam-se, em particular, as formulações de dois diferentes tipos de elemento de contato revendo-se, mais detalhadamente, o tratamento numérico das restrições decorrentes de contato. Algumas estratégias para resolução computacional desta classe de problemas, consistindo em técnicas de otimização, foram implementadas num programa computacional de elementos finitos e avaliadas comparativamente por meio de exemplos numéricos com diferentes graus de complexidade.Contact problems represent a class of solid mechanics problems for which the nonlinear behavior is caused by the change of the boundary conditions during the solution process. The present work treats contact problems observing aspects of its formulation and numerical implementation. Specifically, the formulation for two different contact elements is presented, analyzing, in details, the numerical formulation that results from the contact. Some strategies for the computational solution of this class of problems, given by optimization techniques, were implemented in a finite element computational program and were compared and evaluated by numerical examples with different levels of complexity.
34
Kounoudji, Komla Apelete. ""Intimité tribologique" des contacts d'un assemblage boulonné. Contrôle du serrage, du dévissage, ...des assemblages d'aéro-structures et conséquences sur leur conception." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI055/document.
Full textAbstract:
Depuis l'utilisation des boulons au XVème siècle pour assembler deux pièces, les assemblages boulonnés posent des questions quant à la compréhension de leur fonctionnement et de leurs défaillances, telles que la variation de la tension de serrage entrainant, le desserrage, le dévissage, la perte d'étanchéité, l'initialisation de fissures, ... Pour comprendre leur fonctionnement, une méthodologie d'analyse tribologique a été mise en place, permettant de démonter un assemblage boulonné sans le desserrer, afin de ne pas modifier les conditions de contact lors du desserrage. Ainsi, toutes les interfaces d'assemblages (‘‘filets’’ écrou/vis et ‘‘autres que filets’’) formant des triplets tribologiques, ont été étudiées durant les trois phases de leur cycle de vie (fabrication, serrage, service) par le biais de cas-tests de matériaux différents. Un dialogue interactif entre les expérimentations (corrélations d'images, expertises) et la simulation numérique (Eléments Finis, Eléments Discrets) a permis de dégager des interprétations, notamment concernant les trois phases. Lors de la fabrication, le roulage des vis engendre des transformations tribologiques superficielles au niveau des sous-surfaces des filets formés. Le cœur des vis (noyau) restant non-déformé, ce procédé crée ainsi une différence de microstructure au sein de ces vis, ce qui est une source d'altération de leurs propriétés en fatigue. Lors du serrage, il se forme à l'interface ‘‘filets’’ une mixture de troisièmes corps ‘‘sec-solide’’, accommodant la vitesse entre la vis et l'écrou. Cette mixture résulte d'une réactivité entre une graisse utilisée pour le serrage et des particules, détachées d'un revêtement appliqué sur les filets d'écrous et/ou de vis. En fin de serrage, une partie de la mixture reste piégée entre les filets, jouant le rôle de maintien de la tension de serrage. Dans ces conditions, il apparaît que le frottement varie en fonction de la rhéologie de la mixture, conditionnant la variation de la tension de serrage. En service, des instabilités de contact (glissement, décollement, ...) ont été identifiées au niveau des interfaces. Ces instabilités engendrent dans les interfaces ‘‘autres que filets’’ la formation d'un troisième corps oxydé. Ce dernier constitue un surplus de matière qui peut entrainer l'augmentation des contraintes mécaniques dans les assemblages. A l'interface ‘‘filets’’ écrou/vis, il a été constaté que si la mixture de troisièmes corps piégée en serrage n'est pas cohésive, elle est extrudée des contacts, initialisant la perte de la tension de serrage. A partir de ces interprétations, des interactions entre plusieurs circuits tribologiques conduisent à converger vers un scénario de fonctionnement des assemblages boulonnés, permettant de solutionner leurs défaillances par la re-conception (mise en place de gorge de décharge, ...)Since the use of bolts in the fifteenth century to assemble two parts, the bolted assemblies have the interrogations according to the understanding of their operating and failures occurring, such as the variation of the clamping force leading to, self-loosening, loss of sealing performance, cracks initialization, ... In order to understand their operating, a methodology focused on tribological approach was established, enabling to disassemble a bolted assembly without loosen its, allowing to not change the contact conditions during loosening. So, all the bolted assemblies interfaces (nut/screw ‘‘threads’’ and ‘‘others than threads’’) constituting tribological triplets, have been studied according to the three stages of their full life-cycle (manufacturing, tightening and service) using configurations of different materials. An interactive dialogue between the experiments (fields measuring by digital images correlation, tribological analysis) and the numerical simulation (Finite Element Method, Discrete Element Method) has led to interpretations about the three stages. During the manufacturing, the rolling of screws generates tribological superficial transformations in subsurfaces of machined threads. Contrariwise, inside the volume of these machined screws, there is no tribological transformation. So, this manufacturing process creates a difference of microstructure in these screws, that could be a source of their fatigue properties destruction. During the tightening, it produces at ‘‘threads’’ interface a ‘‘dry-solid’’ mixture of third bodies, accommodating the speed jump between the screw and the nut. This mixture is the result of a reactivity between a grease used for bolted tightening and the particles, detached by plastic flow from a coating initially applied on the threads of nuts and/or bolts. At the end of the process, a part of the mixture remains trapped in the threads, playing the role of maintaining the clamping force. In these conditions, it appears that the friction varies depending of the rheology of the mixture, conditioning the variation of the clamping force. In service, contact instabilities (slip, peeling off, ...) have been identified in the interfaces. These instabilities lead to the formation of an oxidized third body in ‘‘others than threads’’ interfaces. This oxidized third body represents a surplus of material and can increase mechanical stresses in the assemblies. In the nut/screw ‘‘threads’’ interface, it was found that if the mixture of third bodies trapped during the tightening stage is not cohesive, it is extruded, initializing the loss of clamping force. Based on the findings, the interactions between multiple tribological circuits lead to converge to a scenario of bolted assemblies operating, allowing to solve their failures by re-designing (create discharge grooves, ...)
35
Tomanik, Antonio Eduardo Meirelles. "Modelamento do desgaste por deslizamento em anéis de pistão de motores de combustão interna." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-08122004-203125/.
Full textAbstract:
O desgaste de anéis de pistão e cilindro foi modelado através de um programa computacional que calcula as pressões hidrodinâmicas e de contato rugoso agindo nas superficies deslizantes de contato. Os valores previstos de desgaste são comparados com um ensaio em dinamometro de um motor diesel.The wear of piston rings and cylinder liner was modelled through a computer code that calculates the hydrodynamic and roughness contact pressures acting in the contact surfaces. The predicted wear is compared with a 750 hours dynamometer test of a medium duty diesel engine
36
Oliveira, Sônia Paiva de. "Acessibilidade ao exame de contato de hanseníase na Estratégia de Saúde da Família em Cuiabá, Mato Grosso - Brasil." Dissertação apresentada ao Programa de Pós-Graduação do Instituto de Saúde Coletiva, como requisito parcial para a obtenção do título de mestre em Saúde Coletiva, 2013. http://www.repositorio.ufba.br/ri/handle/ri/13132.
Full textAbstract:
Submitted by Maria Creuza Silva (mariakreuza@yahoo.com.br) on 2013-10-07T18:46:13Z
No. of bitstreams: 1
DISS MP SONIA Oliveira. 2013.pdf: 675880 bytes, checksum: b7f05c68c10fe78b12b556c14ecdd4ce (MD5)Approved for entry into archive by Maria Creuza Silva(mariakreuza@yahoo.com.br) on 2013-10-07T18:47:49Z (GMT) No. of bitstreams: 1 DISS MP SONIA Oliveira. 2013.pdf: 675880 bytes, checksum: b7f05c68c10fe78b12b556c14ecdd4ce (MD5)
Made available in DSpace on 2013-10-07T18:47:49Z (GMT). No. of bitstreams: 1 DISS MP SONIA Oliveira. 2013.pdf: 675880 bytes, checksum: b7f05c68c10fe78b12b556c14ecdd4ce (MD5) Previous issue date: 2013
A hanseníase ainda é um sério problema de saúde pública em alguns países do mundo, entre eles o Brasil, que ocupa o segundo lugar em número de casos absolutos no mundo. O estado de Mato Grosso ocupou, em 2011, o primeiro lugar em número de casos novos detectados entre os 27 estados da federação, estando sua capital Cuiabá em situação de hiperendemicidade pelos parâmetros do Ministério da Saúde. O objetivo desse estudo foi analisar a acessibilidade ao exame de contato de hanseníase na Estratégia de Saúde da Família no município de Cuiabá/MT. Na primeira etapa do estudo foi realizada a avaliabilidade do PECH/MT, constatando-se que o mesmo encontra-se implantado adequadamente. Identificou-se que entre os aspectos deficientes na condução das ações do programa está a dificuldade em realizar exames de contatos dos pacientes com hanseníase, revelando a existência de problemas de acessibilidade aos serviços de saúde. A avaliação da acessibilidade foi conduzida através de estudo de caso em duas unidades de saúde da família, por meio de análise documental, observação sistemática e entrevistas semiestruturadas com informantes-chave. O Projeto foi aprovado pelo Comitê de Ética em Pesquisa (CEP) do Instituto de Saúde Coletiva - ISC/UFBA, e os entrevistados assinaram Termo de Consentimento Livre e Esclarecido. A análise da acessibilidade foi realizada em duas dimensões, no âmbito da organização do sistema e dos serviços de saúde. Na primeira dimensão, a avaliação demonstrou que o município encontra-se em situação insatisfatória, evidenciado pela inexistência de plano com ações e metas específicas para o desenvolvimento das ações, falta de garantia de acesso ao serviço de saúde e de insumos para o exame. Na segunda dimensão, observou-se que as unidades foram consideradas de situação intermediária (USF1) e insatisfatória (USF2), indicando a existência de dificuldades quanto à: centralização da realização do exame de baciloscopia, no LACEC; ausência de atividades educativas e falta de sistematização na marcação de consultas. Recomenda-se a composição de equipe de trabalho para coordenar as ações e a proposição de uma política de capacitação contínua de recursos humanos voltados para hanseníase. Deve atentar para a implantação do terceiro turno nas unidades de saúde para atender a demanda de trabalhadores e para o aumento do número de ACS, indispensáveis na busca ativa de casos novos, de contatos faltosos e ações educativas; bem como rever a normatização do MS quanto ao exame dos contatos, pois não está baseado em evidências científicas.
Salvador
37
Dahlberg, Johan. "A numerical and experimental investigation on surface and sub-surface initiation of contact fatigue cracks at cylindrical contacts /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3887.
Full text
38
楊貴永 and Kwai-wing Yeung. "Elastic-plastic analysis of rolling elliptical contacts and the effects of axial superimposed stresses on rolling contact fatiguefailure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31231032.
Full text
39
Strubel, Vincent. "Particle entrapment in EHD contacts - Aerospace applications." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI098/document.
Full textAbstract:
Une lubrification suffisante est essentielle au bon fonctionnement des mécanismes et/ou composants comme par exemple les paliers à roulement. Par contre, les lubrifiants contiennent souvent des débris d’usure ou des polluants extérieurs. Ces particules micrométriques peuvent pénétrer des contacts d’épaisseur inférieure au micromètre induisant des empruntes ou indents pouvant conduire à des endommagements irréversibles pour les surfaces en contact. L’objet de ce travail est l’étude du piégeage de polluants solides à l’aide de particules sphériques d’acier, d’un point de vue théorique, numérique et expérimental. Dans un premier temps, une étude phénoménologique a été proposée à l’aide d’une nouvelle méthode expérimentale basée sur la technique PIV combinée à un tribomètre bille/disque. Les trajectoires des polluants à l’entrée du contact ont pu ainsi être identifiées. En parallèle, un modèle numérique d’écoulement du lubrifiant a été développé pour permettre l’évaluation des conditions menant au piégeage ou non de particules. Finalement, des expériences sur une machine bi-disques en conditions de lubrification polluée contrôlée ont permis de valider les tendances observées pour le piégeage. Une première série de résultats a montré que le piégeage de contaminants est fortement dépendant du profil de vitesse du lubrifiant. Un taux de piégeage très hétérogène a été observé sur des contacts avec une ellipticité transverse à l’écoulement variable. De manière surprenante, malgré une augmentation de la largeur de contact, une forte diminution du nombre de particules piégées a été observée dans des contacts elliptiques. Il a été démontré que cette diminution pouvait être imputée à la présence d’importants reflux de lubrifiant dans les contacts elliptiques larges. L’étude de contacts hybrides, nitrure de silicium–acier, a montré une bonne résistance à l’indentation du nitrure de silicium. Il est à noter que les contacts hybrides présentent des niveaux de piégeage similaire à un contact tout acierContact lubrication is essential in a wide range of mechanical systems like rolling element bearings (REBs). A minimum quantity of clean lubricant all along the bearing life is necessary but difficult to ensure. In fact, lubricants contain inevitably wear debris or external particles, like dust. Carried by the lubricant in the vicinity of elastohydrodynamic (EHD) contacts, particles can be entrapped with disastrous consequences for contacting surfaces. Entrapment of micrometric particles in submicrometric contacting gaps means irreversible damages for the surfaces. Damages weaken the surfaces and reduce significantly the REBs lifetime. The goal of this work is to analyze the critical particle entrainments in the contact inlet. Entrapment of steel spherical particles was investigated from the numerical and experimental point of view. Firstly, the phenomenology of entrapment was explored with a new experimental method based on Particle Image Velocimetry (PIV) technique installed on a tribometer. It enabled the evaluation of velocity profiles in the contact inlet and the tracking of particles within EHD contacts. Secondly, a numerical modelling of the inlet flow for EHD contacts, including the particle tracking, was developed. Finally, tests on a twin-disc machine with a controlled level of well-defined contamination were conducted to validate previous conclusions. A first set of results showed that particle entrapment is highly dependent on the lubricant velocity profile. Depending on contact geometry, from point to wide elliptical contacts, different entrapment probability were revealed. Surprisingly, increasing contact width with wide elliptical contacts leads to a drop of entrapped particles. It was demonstrated that this phenomenon is due to backflows occurring upstream from these contacts. Introducing a hybrid pair of contacting materials (silicon nitride–steel), dents on the surfaces due to entrapped particles were explored. It has been confirmed that silicon nitride surface offers a real ability to resist to indentation. It was also noticed that the entrapment probability for silicon nitride–steel contacts is equivalent to a steel–steel one
40
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.
Full textAbstract:
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 spécifiqueThe 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
41
Marques, Débora Maria Mitter. "Estudo do contato entre sólidos metálicos por meio de simulações de dinâmica molecular." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-29062012-153859/.
Full textAbstract:
Neste trabalho, a relação entre a adesão e o grau de desordem de superfícies em contato é estudada por meio de simulações por dinâmica molecular. O sistema em estudo é composto por um indentador cilíndrico rígido e um bloco deformável. Um reservatório térmico é colocado logo abaixo do bloco, de forma a manter o sistema a temperatura ambiente. Os sólidos são feitos do mesmo material e são modelados por intermédio do potencial genérico de Lennard-Jones. A adesão entre as superfícies é variada gradualmente por meio da variação do raio de corte do potencial que descreve a interação entre as superfícies indentador-bloco. Cada simulação se inicia com um recozimento, após o qual são realizadas as simulações de contato propriamente ditas, até que ocorra penetração de 1,7 raios atômicos. A força normal, a energia potencial, a temperatura e a energia cinética são acompanhadas ao longo do processo. Os resultados reforçam a importância da adesão no jump-to-contact, estando este fenômeno relacionado à geração de defeitos cristalinos. Há indícios de que a distribuição da carga, bem como a dissipação de energia, seja influenciada pela adesão na interface. Mostra-se que a desordem apresentada pelos átomos do bloco é proporcional à contribuição da adesão.In this work, the relationship between adhesion and the degree of disorder of surfaces in contact is studied by means of molecular dynamics simulations. The system consists of a rigid cylindrical indenter and a deformable block. A heat reservoir is placed just below the block, in order to maintain the system at room temperature. Both solids are made of the same material and are modeled through the generic Lennard-Jones potential. Adhesion between the surfaces is gradually varied by varying the cut-off radius of the potential describing the interaction between the indenter surface and the block. Each contact simulation is preceeded by an annealing step, and is conducted until the penetration reaches 1.7 atomic radii. The normal force, the potential energy, kinetic energy and temperature are monitored throughout the process. The results reinforce the importance of adhesion in the phenomenon of jump-to-contact, which is also related to the generation of crystalline defects. The results indicate that the load distribution and power dissipation is influenced by the adhesion at the interface. It is shown that the disorder presented by the atoms of the block is proportional to the contribution of adhesion.
42
Yeung, Kwai-wing. "Elastic-plastic analysis of rolling elliptical contacts and the effects of axial superimposed stresses on rolling contact fatigue failure /." [Hong Kong] : University of Hong Kong, 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12333669.
Full text
43
Fuentes, Adrien Miguel. "Étude expérimentale et numérique de l'assemblage du matériau de contact Ag-SnO2 (88/12) par procédé résistif." Lorient, 2010. http://www.theses.fr/2010LORIS210.
Full textAbstract:
Cette étude est réalisée dans le cadre d’une convention CIFRE en collaboration avec Schneider-Electric et le Laboratoire d’Ingénierie des MATériaux de Bretagne (LIMATB). Elle a pour principal objet d’optimiser l’assemblage du matériau de contact (MDC) Ag-SnO2 88/12 (%m) sur son support cuivre par procédé résistif. Une double approche expérimentale et numérique a permis de réaliser les essais d’assemblage sur des machines à courants conventionnels, et de mettre au point un modèle numérique intégrant les principaux phénomènes physique, électrique et thermique. Schneider-Electric a mis au point et industrialisé un protocole pour assembler le MDC sur le support par brasage résistif en utilisant deux matériaux intermédiaires (une sous-couche argent directement intégré au MDC lors de l’élaboration et une brasure Cu-Ag-P). Il s’agit d’optimiser cette configuration de référence (ASC-AB) en limitant au maximum les matériaux intermédiaires, tout en conservant une qualité de liaison optimum. Trois configurations d’assemblages ont été considérées pour réduire au maximum les matériaux intermédiaires : la première, la plus intéressante au plan économique, sans sous couche argent et sans brasure (SSC-SB), la seconde sans sous couche argent et avec brasure (SSC-AB), et la dernière avec sous couche argent et sans brasure (ASC-SB). Des observations fines microstructurales des liaisons réalisées sur chaque configuration et différents tests d’expertise mécanique et d’endurance électrique pour qualifier les liaisons obtenues, ont permis de montrer que seul l’assemblage ASC-SB était équivalent à la référence ASC-AB. Pour les deux autres configurations, l’absence de la sous-couche argent sur le MDC se traduit par des mécanismes d’enrichissement en SnO2 à l’interface MDC-support qui favorise la fragilité de la liaison. L’effort au niveau du modèle Electrocinétique-Thermique retenu a surtout porté sur la modélisation des conditions interfaciales. Deux approches ont été proposées pour modéliser les phénomènes électrothermiques au niveau des interfaces statiques et dissipatives présentes dans les assemblages : un modèle macroscopique à paramètres surfaciques et un modèle mésoscopique à paramètres volumiques avec des couches de contact. Une importante campagne de caractérisation des propriétés physiques du MDC et des résistances de contact électrique et thermique en fonction de la pression et de la température a permis de compléter le jeu de données d’entrée du modèle. L’opération d’assemblage par soudage résistif de la configuration ASC-SB a été simulée numériquement à l’aide du logiciel aux éléments finis Sysweld™. Des cinétiques thermiques mesurées dans le MDC et le support ont permis de valider le modèle. Dans le cas de la configuration ASC-SB, le modèle a permis de révéler le rôle essentiel d’initiateur joué par les résistances de contact électrique (RCE) aux interfaces électrode/MDC et rivet/électrodeThis study is realised in the framework of a CIFRE agreement in cooperation with Schneider-Electric and the research laboratory, “Laboratoire d’Ingénierie des MATériaux de Bretagne” (LIMATB). The principal subject of this study is to improve the resistance welding process of a Contact Material (CM) Ag-SnO2 88/12 (%w) to a copper support. A double approach, based on experimental and numerical methods, made it possible to carry out welding tests with a conventional current system and permitted us to develop a numerical model which integrates the principal physical, electrical and thermal phenomena. Schneider-Electric has developed and industrialized a protocol to join the CM by resistance brazing technology, with the use of two intermediate materials (a fine silver layer directly integrated in the CM during its elaboration and an interfacial brazing alloy Cu-Ag-P). The aim of this study is to improve this reference configuration (WSL-WBA) [with silver layer-with brazing alloy] by limiting the intermediate materials while maintaining the welding quality. Three configurations have been considered to reduce the intermediate materials: the first, the most economically valuable without silver layer and interfacial brazing alloy (NSL-NBA), the second without silver layer and with an interfacial brazing alloy (NSL-WBA) and the last with silver layer and without interfacial brazing alloy (WSL-NBA). Some fine microstructure observations and various mechanical and electrical endurance expertise tests for the realised bonds of every configuration have made it possible to show that only the WSL-NBA assembling was equivalent to the reference WSL-WBA. For the other two configurations, the absence of the silver layer on the CM involves enrichment mechanisms in SnO2 at the CM-support interface favours the fragility of the bond. The effort for the retained Electrokinetic-Thermal model has focused on the modelling of the interfacial conditions. Two approaches have been proposed for modelling the electrothermal phenomena at the static dissipative interfaces presents in assemblies: a macroscopic model with surfaces parameters and a mesoscopic model with volumes parameters and contacts layers. A consequent campaign of characterisation of physical properties and electrical and thermal contact resistances depending on the pressure and the temperature has permitted to complete the input data of the model. The resistance welding operation of the WSL-NBA configuration has been simulated with the help of the Sysweld™ finite elements software. Thermals kinetics measured in the CM and the support have permitted to validate the model. In the case of the WSL-NBA configuration, the model has permitted to reveal the essential role of ignition played by the electrical contact resistances (ECR) at the electrode/CM and rivet/electrode interfaces
44
Silvestre, Marilene Chaves. "Avaliação da dermatite de contato alérgica ao níquel através da técnica de imuno-histoquímica." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/5/5133/tde-09082017-103915/.
Full textAbstract:
A dermatite de contato alérgica (DCA) ao íon níquel (Ni2+) é uma dermatose inflamatória frequente nos países industrializados. Envolve a ativação de células T específicas ao Ni2+, seguida da proliferação e indução de um perfil misto de citocinas, tanto pró-inflamatórias quanto reguladoras, sugerindo que vários subtipos de células T (helper - Th e citotóxica - Tc) estão envolvidos na resposta imune. Este estudo teve como objetivo a análise das citocinas TNF-alfa, INF-y, IL-2, IL-4, IL-10, IL-13, IL-17 e IL-23 pela técnica de imuno-histoquímica, para tentar identificar a prevalência de um ou mais subtipos de células T (Th/Tc), nos eczemas crônico e agudo de pacientes com DCA ao Ni2+. Avaliamos 20 pacientes (17 mulheres e 3 homens, com idade mediana de 46 anos) apresentando eczema crônico, pelo contato cotidiano do paciente com o Ni2+. Foram coletadas duas biópsias de pele em cada um dos 20 pacientes, a primeira no local do eczema crônico ao Ni2+, antes da aplicação do teste de contato (TC); e a segunda no local do eczema agudo, provocado pelo TC com o sulfato de níquel, 48 horas após sua fixação, nas leituras positivo forte (++) ou positivo muito forte (+++). Foram 160 amostras de eczema agudo e 160 de eczema crônico, perfazendo um total de 320 amostras. Apenas três amostras foram excluídas devido a algum tipo de falha técnica, como, por exemplo, o descolamento dos cortes de pele da lâmina. Para a análise dos dados utilizou-se o software estatístico STATA versão 13. As amostras coradas revelaram resultados positivos para as oito citocinas estudadas, e estas apresentaram valores heterogêneos. Esta heterogeneidade foi medida pelo coeficiente de variação, indicando a variabilidade do conjunto dos dados obtidos. O TNF-alfa, IFN-y, IL-4, IL-13 e IL-17 tiveram prevalência maior no eczema crônico do que no eczema agudo, a IL-2 e IL-23 apresentaram maior prevalência no eczema agudo, em comparação com o eczema crônico e a IL-10 apresentou prevalência similar tanto no eczema agudo quanto no crônico, porém, estas prevalências foram muito baixas, em ambos os eczemas. O TNF-alfa foi a citocina que mais prevaleceu no eczema crônico e a IL-2 foi a mais prevalente no eczema agudo. Porém, estas prevalências foram estatisticamente significantes apenas para a IL-4 e IL-13. Verificamos, nos eczemas crônico e agudo, a presença de um perfil misto de citocinas dos subtipos de células T (Th/Tc), sugerindo que as respostas imunes são expressas ao mesmo tempo. Entretanto, são necessários mais estudos para uma compreensão mais ampla sobre o perfil das citocinas na DCA ao Ni2+, o que poderia levar a novas abordagens terapêuticasAllergic contact dermatitis (ACD) to nickel (Ni+2) is a inflammatory dermatosis, common in industrialized countries. It involves the activation of nickel-specific T cells, followed by the proliferation and induction of a mixed profile of both proinflammatory and regulatory cytokines, suggesting that several T cell subtypes (helper - Th and cytotoxic - Tc) are involved in the immune response. This study aimed to analyze the cytokines TNF-alfa, INF-y, IL-2, IL-4, IL-10, IL-13, IL-17 and IL-23 using the immunohistochemistry technique in order to try to identify the prevalence of one or more T cell subtypes (Th/Tc) in the chronic and acute eczema of patients with ACD to Ni+2. We evaluated 20 patients (17 women and 3 men, median age of 46 years) with chronic eczema, by the patient\'s daily contact with Ni+2. Two skin biopsies were collected in each of the 20 patients, the first at the site of the chronic eczema to Ni+2, prior to the application of the contact test (CT); and the second at the site of acute eczema caused by CT with nickel sulphate, 48 hours after its fixation in the strong positive (++) or very strong positive (+++) readings. There were 160 samples of acute eczema and 160 of chronic eczema, a total of 320 samples. Only three samples were excluded due to some kind of technical failure, such as detachment of the skin cuts from the microscope slide. Statistical software STATA version 13 was used to analyze the data. The stained samples showed positive results for the eight cytokines studied, and these presented heterogeneous values. This heterogeneity was measured by the coefficient of variation, indicating the variability of the data set obtained. TNF-alfa, IFN-y, IL-4, IL-13 and IL-17 had a higher prevalence in chronic eczema than in acute eczema, IL-2 and IL-23 were more prevalent in acute eczema compared to chronic eczema and IL-10 presented similar prevalence in both acute and chronic eczema, however, a very low prevalence in both eczema. TNF-alfa was the most prevalent cytokine in chronic eczema and IL-2 was the most prevalent in acute eczema. However, these prevalences were statistically significant only for IL-4 and IL-13. In chronic and acute eczema, we observed the presence of a mixed cytokine profile of the T cell subtypes (Th/Tc), suggesting that immune responses are expressed at the same time. However, further studies are needed for a broader understanding of the cytokine profile in ACD to Ni+2, which could lead to new therapeutic approaches
45
Bhaskaran, Madhu, and madhu bhaskaran@gmail com. "Synthesis and Characterisation of Silicide Thin Films for Evaluation of Specific Contact Resistivity of Multi-layered Silicon-based Ohmic Contacts." RMIT University. Electrical and Computer Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090429.144556.
Full textAbstract:
Electrical contacts to devices which pose low resistance continue to be of interest as the dimensions of devices decrease and nanotechnology demands better means of creating electrical access. Continued improvement in the performance of ohmic contacts requires techniques to better characterise and quantify the performance of such contacts. In order to study and estimate the resistance of such contacts or the resistance posed by the interface(s) in such contacts, accurate test structures and evaluation techniques need to be used. The resistance posed by an interface is quantified using its specific contact resistivity (SCR), which is denoted using âc (units: £[cm2). Cross Kelvin resistor (CKR) test structures have been used for the measurement of low values of SCR. A simplified approach to this problem of SCR evaluation (developed previously at RMIT University) using the CKR test structures with varying contact sizes was used and during this work was shown to be accurate for the estimation of low values (less than10-8 £[cm2) of SCR. The silicides of interest in this study were titanium silicide (TiSi2) and nickel silicide (NiSi). These thin films are known for their low resistivity and low barrier heights to both n-type and p-type silicon. The research involved thin film formation and substantial materials characterisation of these thin films. The silicide thin films were formed by vacuum annealing metal thin films on silicon substrates. Silicide thin films formed from metal films deposited by DC magnetron sputtering and electron beam evaporation were compared. The composition, crystallographic orientation, and morphology of these thin films were studied using spectroscopy (AES, SIMS, RBS, in situ Raman spectroscopy), diffraction (Bragg-Brentano and glancing angle XRD, RHEED), and microscopy techniques (TEM, SEM, and AFM). TiSi2 and NiSi thin films were also found to be suitable for microsystems fabrication due to their ability to withstand wet etching of silicon using potassium hydroxide. The SCR of aluminium-titanium silicide ohmic contacts was evaluated to be as low as 6 x 10-10 Çcm2, which is the lowest reported for any two- layer single-interface contact. Characterisation of ohmic contacts comprising of aluminium, nickel silicide, and doped silicon (with shallow implants) were also carried out using the same technique. SCR values as low as 5.0 x 10-9 Çcm2 for contacts to antimony-doped silicon and 3.5 x 10-9 £[cm2 to boron-doped silicon were evaluated.
46
Nonato, Fábio 1985. "Modelo dinamico para o contato em mancais de elementos rolantes sujeito a lubrificação elastohidrodinamica." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263812.
Full textAbstract:
Orientador: Katia Lucchesi CavalcaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
Made available in DSpace on 2018-08-14T16:47:29Z (GMT). No. of bitstreams: 1 Nonato_Fabio_M.pdf: 2576321 bytes, checksum: 620be5d1e8be22816a88e01fd2596425 (MD5) Previous issue date: 2009
Resumo: Com a necessidade da diminuição do tempo de projeto, a utilização de modelos computacionais para simulação de componentes mecânicos se torna rota obrigatória para se evitar excessivos testes físicos. Com base nesta premissa, se torna necessário estudar a dinâmica de componentes anteriormente considerados rígidos, como mancais de elementos rolantes, e assim conhecer sua influência sobre o sistema completo. Assim, utilizando um modelo por diferenças finitas em múltiplos níveis, foi avaliada a condição de lubrificação no contato em rolamentos sujeitos a lubrificação Elastohidrodinâmica (EHD) transiente. Desta forma foi possível caracterizar dinamicamente o contato, aproximando o filme de óleo a um conjunto de mola e amortecedor não lineares. Portanto introduz-se um elo flexível ao mancal, possibilitando a sua análise dinâmica como parte do sistema.
Abstract: With the need of time reduction on mechanical projects, the use of computational models for the analysis of mechanical components becomes mandatory in order to avoid excessive physical tests. Based on this assumption, is necessary to study the dynamic of previously assumed rigid components, as the rolling elements bearings, and thus knowing its influence on the complete system. Utilizing a multi-level finite difference method, the lubrication condition on the contact in bearings under Elastohydrodynamic (EHD) transient lubrication was evaluated. Therefore the dynamic characterization of the contact was possible, adjusting the oil film to a nonlinear spring-damper set. Hence a flexible joint is introduced in the bearing, making it possible its dynamic analyses as part of the system.
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
47
Brisolari, André. "Estudo da molhabilidade em madeiras tropicais ou de reflorestamento por medidas de ângulo de contato e de permeabilidade." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-17062009-145256/.
Full textAbstract:
Este trabalho tem por objetivo estudar a molhabilidade e a permeabilidade para quatro espécies de madeiras tropicais (Pinus elliottii, Araucaria angustifolia, Eucalyptus grandis e Eucalyptus citriodora). A molhabilidade é um parâmetro importante para a caracterização de diferentes espécies de madeira e, portanto, depende de fatores como o estado de limpeza da superfície da madeira, orientação das fibras, tipo de amostra (alburno ou cerne), secagem, tratamentos térmicos e químicos, rugosidade superficial, etc. Primeiramente, investigamos a molhabilidade para as quatro espécies tropicais por medida de ângulo de contato aparente para diferentes solventes na superfície da madeira As amostras foram tratadas termicamente no intervalo 100 200º C, por 8h e foi utilizado o método da gota séssil e um goniômeto. Os valores dos ângulos de contato foram maiores para as amostras submetidas aos tratamentos térmicos, indicando um aumento no caráter hidrofóbico da madeira. A técnica de ângulo de contato não foi eficiente para tratamentos térmicos superiores a 200º C, devido a sua degradação. No experimento de permeabilidade foi utilizado um fluxo de ar através das amostras com poros fechados e abertos. Foi verificado um acréscimo de 82 % na vazão para as situações de poros abertos no Eucalyptus citriodora. Nossos resultados permitem detectar mudanças consideráveis na molhabilidade e permeabilidade da madeira, sendo informações valiosas para a conservação e utilização destas madeiras.This work aims to study wettability and permeability for tropical wood species (Pinus elliotti, Araucaria angustifolia, Eucalyptus grandis and Eucalyptus citriodora).The adhesive wettability is an important parameter for characterizing different wood species and depends on factors such as cleaning state of the wood surface, orientation of the wood fibers, type of sample (sapwood or heartwood), drying, thermal and chemical treatments, surface roughness, etc. First, we investigated the wettability of the four tropical wood species by measuring the apparent contact angles of different solvents on the wood surfaces. The samples were heat treated from 100 to 200 °C for 8 h, and the contact angles measured by the sessile drop method with a home-made goniometer. For samples heat-treated below 200 °C, higher values of contact angles were obtained, indicating a hydrophobic character for thermal treated woods. After this temperature, the wood degradation took place. For permeability experiments, a flow of air was used for wood samples with closed and open pores. An increase of 82% in flow was verified for open pores woods such as Eucalyptus citriodora. Our results allowed us to detect considerable changes on wood wettability and permeability and that are powerful information for conservation and use of these woods.
48
Tsuji, Monique Cotarelli. "Dermatites de contato em indivíduos expostos a alisantes capilares contendo formaldeído identificados por reação química." Botucatu, 2020. http://hdl.handle.net/11449/192407.
Full textAbstract:
Orientador: Jaime Olbrich NetoResumo: Os cabelos são um importante componente de identidade social e sedução, favorece o mercado de cosméticos, notadamente o capilar, que busca inovações e novidades destinadas a obter um resultado desejado. Mulheres e homens dão importância para a saúde e aparência dos mesmos, empenhando cuidados que vão além dos habituais de higiene. A procura pelo cabelo ideal expõe a riscos de doenças, tanto os profissionais dos salões de beleza e como seus clientes. São doenças ocupacionais, em muitos casos, negligenciadas. Entre estes riscos encontra-se a dermatite de contato. No Brasil, a chamada escova progressiva é a mais conhecida e utilizada para alisamento. Neste processo o uso de formaldeído (FA) em concentrações não permitidas tem sido prática comum, expondo cabeleireiros e clientes a risco de doenças relacionadas ao contato com FA. O FA é permitido na concentração de até 0,2% como conservante de produtos. O presente estudo objetivou avaliar indivíduos expostos ao FA ao realizarem alisamento capilar, se estavam sensibilizados ao FA. Para identificar FA em produtos de alisamento capilar, usado pelos cabeleireiros participantes desta pesquisa, utilizou-se um kit comercialmente disponível. Foram incluídos profissionais expostos ao FA, clientes (esporadicamente expostos) e indivíduos nunca expostos. Foram realizados patch teste com a bateria brasileira para dermatite de contato, e um participante apresentou teste cutâneo positivo para formol, onze para bicromato de potássio e oito para s... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Hair is an important component of social identity and seduction, it favors the cosmetics market, notably the capillary, which seeks innovations and novelties designed to obtain a desired result. Women and men give importance to their health and appearance, engaging in care that goes beyond the usual hygiene. The search for the ideal hair exposes the risks of diseases, both the professionals of the beauty salons and their clients. Occupational diseases that are, in many cases, neglected. Contact dermatites is one of the risks. In Brazil, the so-called brazilian hair straightening is the preferred for straightening. In this process, the use of formaldehyde (FA) in unallowed concentrations has been common practice, exposing hairdressers and clients to the risk of diseases related to contact with FA. At a concentration of up to 0.2%, as a p preservative, FA is permitted. The present study aimed to evaluate individuals exposed to FA when performing hair straightening, and if they were sensitized to FA. To identify FA in hair straightening products, used by hairdressers participating in this research, a commercially available kit was used. Professionals exposed to the FA, clients (sporadically exposed) and individuals never exposed were included. Patch tests were performed with the Brazilian battery for contact dermatitis, and one participant presented a positive skin test for formaldehyde, eleven for potassium bichromate and eight for nickel sulfate. Clinical symptoms were more se... (Complete abstract click electronic access below)
Mestre
49
Illamola, i. Gómez Cristina. "Contacto de lenguas y la expresión de la posterioridad temporal en el español de Cataluña." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/292244.
Full textAbstract:
Varios estudios realizados en las últimas décadas del siglo XX y las primeras del XXI demuestran que el futuro simple en español (cantaré) está en pleno retroceso en Hispanoamérica y en el resto de zonas peninsulares para la expresión de eventos prospectivos frente a la forma perifrástica IR A + INFINITIVO (voy a cantar). Algunos estudios que lo reafirman son los de Miró y Pineda, 1990; Gómez Manzano, 1992; Almeida y Díaz, 1998; Troya Déniz, 1998; Sedano, 2006; Melis 2006. No obstante, en los territorios de habla catalana se considera que, respecto del español general (peninsular y americano), la tendencia es inversa: la estructura perifrástica es menos productiva que la sintética (Ramírez-Parra y Blas Arroyo, 2000; Buzón García, 2013, en áreas de la Comunidad Valenciana, e Illamola, 2008 y 2013, en zonas de Cataluña).
La tesis doctoral que se presenta tiene como objetivos principales analizar, por un lado, la distribución de la forma sintética –RÉ y de la construcción perifrástica IR A + INFINITIVO en contextos prospectivos para comprobar en qué medida sigue la tendencia señalada para el español general. Y, por otro, estudiar esta variación en el marco de los fenómenos de contacto de lenguas, en tanto que se examina a partir de un corpus de producciones orales escolares de informantes bilingües castellano-catalán, entre 11 y 16 años, de dos municipios de Cataluña —Mataró y Manlleu— y en dos momentos temporales distintos —cuando cursaban 6º de primaria y, cuatro años más tarde, cuando cursaban 4º de la ESO.
Concretamente, se quiere constatar la influencia del catalán en la producción de enunciados con referencia temporal prospectiva en castellano, expresados mediante una u otra forma. Si bien en catalán existe la perífrasis ANAR A + INFINITIVO, esta no acepta el valor de futuridad y mantiene el valor etimológico de movimiento y de finalidad. En cambio, en castellano, sí es posible dicho valor (y otros modales), dado el diferente grado de gramaticalización que presenta esa estructura en esta lengua.
Por lo tanto, se considera que la imposibilidad que presenta el catalán para formular enunciados prospectivos mediante la construcción perifrástica con el verbo IR repercute en el empleo que hacen los informantes de una u otra forma de expresión en castellano. Así, aquellos individuos cuya lengua inicial sea el catalán producen mayor número de formas sintéticas y, por contra, aquellos informantes cuya lengua inicial es el castellano emplean formas analíticas en mayor medida.
Se parte, por tanto, de la hipótesis de que la lengua inicial de los informantes es uno de los factores que inciden en el uso de una u otra variante para la expresión de futuro. Ahora bien, además de las variables clásicas que emplea la sociolingüística variacionista (sexo, edad), se incluyen como posibles condicionantes de este particular empleo nuevas variables independientes que permiten examinar más de cerca este fenómeno y las prácticas lingüísticas de los individuos; a saber: uso de castellano en el seno familiar, empleo de castellano en las interacciones entre amigos, competencia oral declarada y consumo de programas televisivos en castellano y en catalán. Todas estas variables inciden en los usos y prácticas lingüísticos de los individuos y, en consecuencia, condicionan en mayor o menor medida el empleo del futuro simple de indicativo y la perífrasis.
En conclusión, en esta tesis se constata, en primer lugar, que los individuos analizados emplean de forma profusa la forma sintética, de modo que la tendencia es contraria a la constatada en otras zonas castellanohablantes monolingües y que puede hablarse de un fenómeno de convergencia lingüística, donde el sistema del castellano se está acercando paulatinamente al del catalán. Y, en segundo lugar, que el factor que de forma significativa condiciona el uso de la forma perifrástica es el sexo, aunque se observan correlaciones entre el empleo de IR A + INFINITIVO y la lengua inicial, la competencia oral declarada en castellano y el consumo televisivo: cuanto mayor es la presencia de castellano en estas esferas, mayor es la producción de FA.Several studies in the last decades of the 20th and early 21st century show that, in Latin America and the rest of the Iberian Peninsula, there is a clear decline in the use of the future simple (cantaré) to express prospective events; the periphrastic construction IR A +INFINITIVO (voy a cantar) prevailing over it (Miró & Pineda, 1990; Gómez Manzano, 1992; Almeida & Diaz, 1998; Troy Déniz, 1998; Sedano, 2006; Melis 2006). However, in the Catalan-speaking territories it is considered that, in contrast to general Spanish (Peninsular and American), the tendency is the opposite: the periphrastic structure is less productive than the synthetic (Ramirez-Parra & Blas Arroyo, 2000; Buzón García, 2013, in Valencia, and Illamola, 2008, 2013 in Catalonia). The first aim of this doctoral thesis is to analyze, on the one hand, the distribution of the synthetic form (futuro simple) and the periphrastic construction (IR A + INFINITIVO) in prospective contexts, in order to see to what extent the described tendency for general Spanish remains. And, on the other hand, to study this variation in the context of language contact phenomena, by means of an oral corpus of 11-16 year old Spanish-Catalan individuals, from two cities in Catalonia —Mataró and Manlleu—, and at two different moments: during 6th grade and, four years later, when they were in 4th grade of ESO. It is assumed, therefore, that the L1 of the informants is one of the factors that influences the use of one or other variant for expressing the future. Now, apart from the classic variables used by variationist studies (sex, age), we include new independent variables as potential determinants of this particular use in order to better understand this phenomenon; namely use of Spanish in the family, use of Spanish in interactions between friends, declared oral competence and the consumption of TV programs in Spanish and Catalan. All these variables affect the uses and linguistic practices of individuals and, consequently, determine to a greater or lesser extent the use of simple future indicative and periphrastic construction. In conclusion, this thesis finds, first, that the individuals analyzed used the FS to a high degree, demonstrating that the tendency is clearly the opposite to that found in monolingual Spanish areas. Therefore, we can consider it a phenomenon of linguistic convergence where the Spanish linguistic system is gradually approaching that of Catalan. And, second, that the factor that most significantly affects the use of the periphrastic construction is sex, although there is a correlation between the use of IR A + INFINITIVO and L1, declared oral competence in Spanish and TV programs in Spanish: the higher the presence of Spanish in these areas, the greater the production of FA.
50
Duan, FangFang. "Numerical tribology of the wheel-rail contact : Application to corrugation defect." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0019/document.
Full textAbstract:
Depuis plus d'un siècle, l’usure ondulatoire représente un des problèmes de maintenance les plus important pour les réseaux ferroviaires. Celle-ci est à l’origine d’émissions sonores incommodantes pour le voisinage et de vibrations structurelles pouvant réduire la durée de vie des infrastructures et matériels ferroviaires. Ce phénomène périodique présent à la surface des rails est intimement lié à la dynamique du contact roue-rail qui résulte des paramètres régissant le frottement, la dynamique du train et de la voie… Afin de mieux appréhender les conditions menant à l’apparition de l’usure ondulation, un modèle numérique a été proposé pour compenser l’impossibilité d’instrumenter localement et de façon fiable un contact roue-rail dynamiquement. Tout d'abord, un outil approprié a été choisi pour modéliser la dynamique du contact roue-rail afin de reproduire numérique de l’usure ondulatoire des voies rectilignes. Le code d'éléments finis dynamique implicite Abaqus a été choisi pour instrumenter numériquement localement le contact roue-rail. Ainsi, tant l'origine que l'évolution de l’usure ondulatoire dans des phases transitoires (accélération / décélération) sont étudiées. Une étude de sensibilité a été menée pour mettre en évidence la sensibilité de l’usure ondulatoire apparaissant dans des conditions transitoires au passage d’une ou plusieurs roues ainsi que d’un défaut géométrique présent à la surface du rail. Des conditions dynamiques locales d’adhérence-glissement (stick-slip), liées à la dynamique de la roue et du rail couplés par le contact, est identifié comme origine de l’usure ondulatoire des voies rectilignes dans des conditions transitoires. Deuxièmement, les résultats obtenues avec le modèles précédent ont mis en évidence une décroissance de l’amplitude de l’usure ondulatoire reproduire numérique en fonction du nombre de roue passant sur le rail. Ce résultat semble être en contradiction avec les observations de rails réels. Ce problème est lié à la difficulté de gérer la dynamique de contact, et tout particulièrement dans le cas où il y a des impacts locaux, dans les modèles éléments finis classiques tels que ceux implémentés dans Abaqus. Pour palier ce problème, une méthode de masser redistribuée a été implémentée dans Abaqus et utilisée sur le cas précédent. Les résultats montrent un accroissement plus réaliste de l’usure ondulatoire en fonction du nombre de rouesFor more than a century, rail corrugation has been exposed as one of the most serious problems experienced in railway networks. It also comes with a series of problems for maintenance, such as rolling noises and structural vibrations that can reduce lifetime of both train and track. This periodical phenomenon on rail surface is closely linked to wheel-rail contact dynamic, which depends on friction, train dynamics… To better understand corrugation birth conditions, a numerical model is suggested to complement the experimental limitations and to instrument a wheel-rail contact both locally and dynamically. At first, an appropriate tool was chosen to create the dynamic wheel-rail contact model to reproduce straight-track corrugation, also called “short-pitch” corrugation. The implicit dynamic finite element code Abaqus was chosen to investigate the dynamic local contact conditions. Both the origin and the evolution of straight-track corrugation under transient conditions (acceleration / deceleration) are studied. The parametrical sensibility of corrugation is thus investigated both with single/multiple wheel passing(s) and with geometric defect. A stick-slip phenomenon, linked to both wheel and rail dynamics coupled through the contact, is identified as the root of straight-track corrugation under transient conditions. Secondly, results obtained with the previous model have highlighted a quick decrease of corrugation amplitude with the increase of wheel passings over the rail. This last result seems to be in contradiction with reality. This problem comes from the difficulty to reliably manage contact dynamics, and particularly with local impacts, with the use of classical finite element models such as the one implemented in Abaqus. To compensate for this lack, a mass redistribution method is implemented in Abaqus and used with the previous case. The results show a more realistic corrugation growth according to the number of wheel passings