Cette étude traite de la prise en compte du gradient de contrainte et du frottement pour calculer l'amorçage de fissures en fatigue. On s'intéresse notamment au dimensionnement d'une manille en Inconel 718 munie de bagues en Inconel 718montées avec interférence. Pour cela, on réalise des essais de fretting et de fatigue pour étudier les conditions d'amorçage de fissures en présence de gradient de contrainte et de frottement. Les résultats expérimentaux mettent en évidence l'effet du gradient des contraintes sur l'amorçage de fissures et justifient la prise en compte du gradient pour le dimensionnement en fatigue des structures. A travers ces essais balayant une gamme de gradient de contrainte étendue, on confirme que la présence d'un gradient de contrainte retarde l'amorçage de fissures. Les avantages et les inconvénients de plusieurs approches de fatigue multiaxiale intégrant le gradient de contrainte sont étudiés. De cette analyse, une proposition est faite permettant de décrire au mieux les résultats expérimentaux de fatigue et de fretting. Cette approche s'appuie sur l'utilisation d'une fonction de poids dépendant du gradient de la pression hydrostatique. Cette approche est similaire à des approches mises en oeuvre sur d'autres problématiques de fatigue ce qui permet de dégager quelques points de convergence pour traiter le problème du gradient de contrainte en fatigue. Un essai de fatigue sur une manille munie d'une bague montée avec interférence est réalisé. L'effet du gradient de contrainte sur l'amorçage de fissures dans ce système est trop faible pour que l'utilisation d'une approche intégrant l'effet de gradient soit pertinente. Cette observation est cohérente avec les résultats expérimentaux précédents obtenus dans cette étude. L'inconel 718 apparaît donc comme un matériau peu sensible à l'effet de gradient de contrainte. Une approche de fatigue multiaxiale de type Crossland permet une description raisonnable de la durée de vie du système. Une analyse numérique montre que la tenue en fatigue du système est peu sensible au coefficient de frottement alors que l'interférence a un impact beaucoup plus important.

Fretting and wear are recurrent problems in the field of aeronautics. Contacts the blade / disk at the compressor or high-pressure turbine aircraft engines, for example, are subjected to high stresses at high temperatures. The challenge for manufacturers is to maximize the lifetime of these components and be able to predict crack initiation. To improve handling parts, coatings are used to protect them. Materials and their mechanical properties have a direct impact on the contact and the lifetime. The choice of materials, number of layers, the thickness of the order are therefore essential. By their composition (fibers, single crystals), elaboration (extrusion) or their mode of deposition, the hypothesis to consider homogeneous isotropic materials is too simplistic. Anisotropy is an important parameter to take into account in the design. Composite materials are increasingly used in the aeronautic. In this context, this thesis aims to study the behavior of anisotropic homogeneous materials, focusing on the influence of the main parameters mechanical characteristics of a material to better understand their effects. We focus on the Young's modulus (or modulus of elasticity), the module Coulomb (or shear modulus) and the Poisson's ratio, and values ​​in different directions. As expected, the Young's modulus in the direction normal to the contact plays an important role in determining the pressure profile. However, the influence of Young modulus in the plane tangent to the contact is not to neglect it also alters the shape of the contact area. The orientation of the material with respect to the contact is therefore a parameter to take into consideration, it can directly reduce or enhance the effect of Young's modulus in a direction privileged. The module Coulomb and Poisson's ratio were also analyzed. As a result they significantly affect the contact. These results are confirmed in the case of a coated solid, unlike the effects of coating and substrate can compensate. The impact properties of the coating will be even more important than it is thick. The scale of the contact relative to the materials used is also important on the pressure profiles. A comparison between the model anisotropic homogeneous and isotropic heterogeneous model have been performed. At mesoscopic scale, the composite is composed of a matrix with fibers that induce pressure peaks while at the macroscopic level, the composite material is seen as a homogeneous material, the pressure profiles are smoothed.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: David. L. McDowell; Committee Member: Min Zhou; Committee Member: Naresh N. Thadhani; Committee Member: Rami M. Haj-Ali; Committee Member: Richard W. Neu.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Fretting wear results in the loss of fit and tolerance at contact interfaces. The aerospace and aircraft industry is severely impacted by fretting wear and fretting fatigue that frequently occurs in turbo machinery and riveted structural connections. There have been numerous studies, investigating the fretting phenomenon for these aerospace applications. Literature available in regard to fretting wear encountered in these aerospace applications is limited. This study is therefore aimed at investigating the fretting wear encountered in aerospace application. An in-house fretting test apparatus was specially designed and developed in order to perform the fretting wear experiments. Ti-6Al-4V and Al7075-T6 are the two aerospace materials that were tested using the fretting test apparatus. An extensive experimental study was conducted in order to investigate the effect of the normal force on the fretting wear and friction behaviour of the two aerospace materials. The most severe of these experiments were identified and then repeated for up to 106 fretting cycles. Additional fretting wear experiments were also conducted between the two aerospace materials and cemented carbides, since the carbides are currently being utilized as coatings in some aerospace contacts that are prone to fretting induced damage. The experimental study revealed that a decrease in the normal force resulted in an increase in the severity of the fretting wear of both aerospace materials. The additional fretting wear experiments involving carbide-metal contact couples found that Ti-6Al-4V and Al7075-T6 were prone to adhesive wear. / AFRIKAANSE OPSOMMING: Knaagslytasie veroorsaak materiaalverlies by die kontakoppervlakke. Die lugvaart industrie is erg geraak deur knaagslytasie en knaaguitputting wat dikwels voorkom in turbo-enjin toepassings en strukturele verbindings. Daar was al talle studies gedoen oor die effek van knaag op lugvaart toepassings. Literatuur met betrekking tot knaagslytasie in lugvaart toepassings is egter beperk. Hierdie studie was dus gemik daarop om knaagslytasie in sekere lugvaart toepassings te ondersoek. Tydens die studie is ʼn toetsopstelling ontwerp en ontwikkel om knaagslytasie eksperimente uit te voer. Ti-6Al-4V en Al7075-T6 is die twee lugvaartmateriale wat ondersoek is met behulp van die toetsopstelling. ʼn Omvattende eksperimentele studie is gedoen om die effek van die normaal krag op knaagslytasie en die wrywings gedrag van die lugvaartmateriale te ondersoek. Die eksperimente wat die ergste slytasie en hoogste wrywing getoon het, is herhaal vir 106 siklusse. Bykomende knaag eksperimente was ook tussen die twee lugvaartmateriale en sekere karbiede gedoen, aangesien karbiede tans as deklae in sommige lugvaart kontakte gebruik word. Die eksperimentele studie het getoon dat 'n afname in die normale krag gelei het tot 'n toename in wrywing vir beide lugvaartmateriale. Die bykomende knaagslytasie eksperimente op karbied metaal pare het getoon dat Ti-6Al-4V en Al7075-T6twee lugvaart materiale nie in staat was om enige van die karbide te beskadig nie. Die lug-en Ruimte-materiaal aan die ander kant ervaar het kwaadaardige dra.

Made available in DSpace on 2016-06-02T19:11:45Z (GMT). No. of bitstreams: 1 DissRL.pdf: 4606587 bytes, checksum: 0964a2f543c4356671aec314cf14a445 (MD5) Previous issue date: 2005-10-24 / Diversas linhas aéreas de transmissão de energia elétrica (LTs) foram construídas numa época em que o Brasil dispunha de pouca tecnologia para o desenvolvimento dos projetos e construção. Com isso, os projetos eram baseados em normas estrangeiras, que prescreviam distâncias entre os condutores elétricos e o solo abaixo dos valores hoje recomendados pela norma brasileira. Uma das alternativas para a correção do problema de cabos baixos é a reforma da linha de transmissão, quando pode ser empregado o processo de retracionamento para alteamento dos cabos CAA (Condutores de Alumínio com Alma de Aço). Este trabalho tem como objetivo, o estudo da influência do grampo de suspensão (fadiga e "fretting" - desgaste por atrito entre os fios do condutor e o grampo de suspensão) em determinadas propriedades mecânicas dos condutores usados, visto que esse ponto do condutor é deslocado para fora do grampo de suspensão quando da aplicação do retracionamento, além de ficar submetido a um valor de carregamento mecânico mais elevado. Esses estudos englobam a realização de ensaios de tração e vibração, além de análises metalográficas em amostras de cabos condutores completos usados (regiões dentro e fora do grampo de suspensão) e em condutores novos sem uso. Os resultados obtidos do ensaio de tração indicaram que, para os cabos estudados, não há uma influência direta da região do grampo nas propriedades mecânicas estáticas, como a carga de ruptura e alongamento percentual. Com relação ao ensaio de vibração, todas as amostras de cabos não apresentaram qualquer tipo de fratura, o que levou o ensaio a ser realizado até 10.000.000 de ciclos. As análises microestruturais mostraram a presença de marcas de fretting na parte da camada mais externa e interna dos condutores, mas apenas com danos muito superficiais. Dessa forma, pode-se concluir que, para o condutor estudado é possível a utilização do processo de retracionamento para a reforma da linha de transmissão.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-08-10T11:35:31Z No. of bitstreams: 1 RobertoKleciusMendoncaFernandes_TESE.pdf: 9615422 bytes, checksum: cd708447bea2bf643fce86924f5bbab0 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-08-11T10:55:04Z (GMT) No. of bitstreams: 1 RobertoKleciusMendoncaFernandes_TESE.pdf: 9615422 bytes, checksum: cd708447bea2bf643fce86924f5bbab0 (MD5) / Made available in DSpace on 2017-08-11T10:55:04Z (GMT). No. of bitstreams: 1 RobertoKleciusMendoncaFernandes_TESE.pdf: 9615422 bytes, checksum: cd708447bea2bf643fce86924f5bbab0 (MD5) Previous issue date: 2017-05-15 / O mancal seco ? um elemento estrutural presente na maioria dos sistemas mec?nicos das ind?strias dos setores eletrodom?sticos, agropecu?rios, aeroespacial, aeron?utico e automotivo. Este trabalho d? continuidade a uma linha de pesquisa iniciada no Grupo de Estudos de Tribologia e Integridade Estrutural (GET) da Universidade Federal do Rio Grande do Norte (UFRN) e tem o objetivo de investigar tribologicamente comp?sitos polim?ricos com matriz de politetrafluoretileno (PTFE) e carga de rejeito de scheelita para aplica??o em mancais secos, visando reduzir custo e aumentar a vida em servi?o destes elementos. O rejeito de scheelita, origin?rio da extra??o da scheelita utilizada para produ??o do tungst?nio, ? um res?duo mineral composto de ?xidos, como os de sil?cio, c?lcio, alum?nio, ferro, magn?sio, tungst?nio, dentre outros. O rejeito de scheelita foi caracterizado na condi??o como adquirido, atrav?s de an?lises de MEV e EDS, e peneirado para tamanho de part?cula inferior a 45 ?m. O PTFE foi analisado por DRX. PTFE e rejeito de scheelita foram misturados mecanicamente, moldados por compress?o a quente, num molde projetado envolto por uma resist?ncia el?trica, atrav?s de uma prensa hidr?ulica. Investigou-se o desempenho tribol?gico dos comp?sitos submetidos a cargas (1) em movimento linear alternado (reciprocating) e (2) com indenta??es repetidas. As superf?cies novas e ensaiadas foram analisadas por Microscopia de For?a At?mica (AFM) no que concerne aos par?metros de rugosidade peri?dica e n?o peri?dica. Verificou-se que a varia??o no teor de rejeito de scheelita e a frequ?ncia do movimento alternado influenciaram no desempenho tribol?gico e na resist?ncia do comp?sito, relacionados ao coeficiente de atrito, ? rugosidade, ao desgaste e ? indenta??o. Os comp?sitos polim?ricos desenvolvidos e ensaiados demonstraram se constituir em novos materiais adequados para aplica??o de mancais secos, notadamente o comp?sito com 80% de PTFE e 20% de rejeito de scheelita que, mostrando-se como de melhor desempenho tribol?gico, apresenta-se como uma alternativa vi?vel e de custo mais baixo que o PTFE puro. / Dry rubbing journal bearing is a structural part that is present in the most of mechanical systems of industries from home appliances, agricultural, aerospace, aeronautic and automotive sectors. This work gives continuity to a research started in Group of Studies in Tribology and Structural Integrity (GET) at Federal University of Rio Grande do Norte (UFRN) and has objective to investigate, tribologically, a scheelite tailings- filled PTFE composites to dry rubbing journal bearings application, to reduce cost and extend life service of this parts. The tailing of scheelite, obtained from scheelite mining to produce tungsten, is a mineral spoilage composed of oxides, as a silicon oxides, calcium, aluminum, iron, magnesium, tungsten and others. The tailing of scheelite was analyzed as acquired through SEM and EDS analysis, and sieved to get a particle size less than 45 ?m. PTFE was analyzed through XRD. PTFE and scheelite tailings was mechanically mixed, hot compression molding in a designed mold involved by a electrical resistance and compressed by a hydraulic press. It was investigated tribological performance of composites subject to loads (1) in reciprocating movement and (2) repeated indentations. The new and tested surfaces were analyzed through Atomic Force Microscope (AFM) to collect periodic and non periodic roughness parameters. It was verified that scheelite tailing content and frequency of reciprocating influenced tribological performance and strength of composites, related to coefficient of friction, roughness, wear and indentation. The developed and tested polymeric composites showed to constitute a new materials suitable to dry rubbing journal bearings applications, notably 80% of PTFE and 20% scheelite tailing composite content that was the best tribological performance composite and being introduced as a viable alternative and lower cost than pure PTFE.

A number of investigators have reported enhancement in oxidation and wear resistant of carbon-carbon composites (CCC) in the presence of protective coating layers. However, application of a surface and subsurface coating system that can preserve its oxidation and wear resistance along with maintaining lubricity at high temperature remains unsolved. To this end, thermodynamically stable protective oxides (ZnO/Al2O3/ZrO2) have been deposited by atomic layer deposition (ALD) to infiltrate porous CCC and graphite foams in order to improve the thermal stability and wear resistance in low and high speed sliding contacts. Characterization of microstructural evolution was achieved by using energy dispersive x-ray spectroscopy (EDS) mapping in scanning electron microscope (SEM) coupled with focused ion beam (FIB), x-ray tomography, high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and X-ray diffraction (XRD). Evaluation of the tribological properties of CCC coated with abovementioned ALD thin films were performed by employing low speed pure sliding tribometer and a high speed/frequency reciprocating rig to simulate the fretting wear behavior at ambient temperature and elevated temperatures of 400°C.It was determined with x-ray tomography imaging and EDS mapping that ALD ZnO/Al2O3/ZrO2 nanolaminates and baseline ZrO2 coatings exhibited excellent conformality and pore-filling capabilities down to ~100 μm and 1.5 mm in the porous CCC and graphite foam, respectively, which were dependent on the exposure time of the ALD precursors. XRD and HRTEM determined the crystalline phases of {0002} textured ZnO (wurtzite), amorphous Al2O3, and {101}-tetragonal ZrO2. Significant improvements up to ~65% in the sliding and fretting wear factors were determined for the nanolaminates in comparison to the uncoated CCC. A tribochemical sliding-induced mechanically mixed layer (MML) was found to be responsible for these improvements. HRTEM confirmed the presence of a high density of ZnO shear-induced basal stacking faults inside the wear tracks responsible for intrafilm shear velocity accommodation that mitigated friction and wear.

The purpose of this study is to determine whether chlorinated polymers such as polyvinylchloride (PVC) and polyvinylidenechloride (PVDC) degrade in a fretting interface. Polymer coated 52100 steel balls are fretted against a polished 1045 steel plate for 30 minutes in air and nitrogen at 25-30 percent and greater than 95 percent relative humidity. ESCA analysis is used to determine interface chemistry and help conclude that the color formation observed in the polymer coating is due to polymer degradation. Additional tests of thermally stabilized PVC on a steel plate supported this theory and aided in understanding the polymers performance in the interface. Experiments with the “pure” PVC on a glass plate showed that iron at the interface can initiate and catalyzes the polymer degradation. The effects of the different atmospheres, as well as the effect of humidity is also presented. / M.S.

A fundamental study was conducted to investigate the ability of thin polymeric coatings to prevent metallic contact and fretting corrosion in steel-on-steel systems. Ten polymer types were chosen for study: polymethylmethacrylate (PMMA), polytetrafluoroethylene (PTFE), polyimide (PI), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyvinyl chloride (PVC), low-density polyethylene (LOPE), high-density polyethylene (HDPE), polysulfone (PSO) and polystyrene (PS). These polymers were applied as thin films to a steel disk which was in turn fretted by a normally-loaded steel sphere. The experimental investigation consisted of two phases. In the first phase, the lives of the ten polymer types were evaluated over a range of normal loads from 11.1 to 44.5 N. In the second phase, optical and electron microscopy were used to document the fretting process at the sphere-film interface as a function of time. / Master of Science

Thin polymeric coatings have been applied to metal surfaces to prevent and/or prolong the onset of fretting corrosion, but the properties that make a polymeric coating effective and the means by which a coating fails are unknown. The purpose of this study was to determine the effect of molecular weight, casting solvent, and amplitude of motion on the life of thin (25 ~m nominal) polystyrene coatings. Narrow molecular weight distribution polystyrene coatings ranging from <Mw>=19,400 to <Mw>=1,460,000 were applied to UNS G10450 steel disks with toluene and MEK as casting solvents. The coatings were fretted against UNS G52100 steel balls at 20 Hz under 22.3 N normal load. Amplitudes of motion ranged from 100 ~m to 500 ~m. Coating life and friction force were measured. Coatings of <Mw>=207,700 showed maximum life at all amplitudes. Friction remained constant for all tests, and increasing amplitude decreased life. Toluene-cast coatings had slightly shorter lives and more coating racks than MEK-cast coatings. Toluene-cast coatings below <Mw>=53,700 cracked severely during solvent removal and were not tested. / Master of Science