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Estudo do desgaste de ferramentas com e sem revestimentos de filmes finos utilizadas em operações de conformação a frio.; Study on the wear behavior of uncoated and thin film coated tools used in cold forming operations.

Mendes, Marco Aurélio Rosso Santana
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 08/10/2009 PT
Relevância na Pesquisa
27.06%
Este trabalho dedica-se ao estudo dos mecanismos de desgaste de ferramentas utilizadas em processos de conformação a frio, como punções e matrizes. O texto se inicia por uma discussão que há na literatura a respeito do esfolamento (tradução da palavra galling) que é o principal ao mecanismo de desgaste encontrado na conformação a frio. Em seguida apresenta-se uma breve análise do desempenho tribológico de punções usados industrialmente em operações de estampagem. Tornos CNC foram utilizados para a realização de alguns ensaios de desgaste por deslizamento, sem repetição de trilha, com materiais normalmente utilizados em conformação a frio. Ferramentas de aço AISI M2 com e sem revestimentos por filmes finos de TiN e AlTiCrN foram deslizadas contra aços AISI 1045. Resultados de força de atrito e observações das superfícies via microscopia foram obtidos para qualificar as diferentes condições ensaiadas. Ambas as condições de ferramentas revestidas apresentaram desempenho tribológico superior à ferramenta sem revestimento e uma inversão de desempenho foi observada entre as ferramentas revestidas: a ferramenta revestida com o filme de AlTiCrN apresentou um melhor desempenho quando a situação de ensaio foi mais branda. Quando os esforços foram mais severos...

Modelagem unidimensional do regime misto de lubrificação aplicada a superfícies texturizadas.; One dimensional modelling of the mixed lubrication regime applied to textured surfaces.

Profito, Francisco José
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/09/2010 PT
Relevância na Pesquisa
27.36%
O presente trabalho aborda a modelagem unidimensional do regime misto de lubrificação para problemas caracterizados por condições genéricas de carga, velocidade e geometria. Tal modelagem foi desenvolvida a partir de modelos clássicos, tais como a equação de Reynolds relacionada com os fenômenos hidrodinâmicos, e as formulações de Greenwood & Williamson e Greenwood & Tripp utilizadas na descrição do contato de asperezas entre superfícies rugosas. A cavitação do fluido lubrificante foi considerada através dos modelos tradicionais de half-Sommerfeld e Swift-Steiber (Reynolds). Com relação à reologia do lubrificante, as possíveis variações de viscosidade devidas ao próprio campo de pressões hidrodinâmicas e às altas taxas de cisalhamento do fluido ("shear-thinning") foram também contempladas na modelagem proposta. Adicionalmente, quatro filtros não convencionais de rugosidade foram propostos e implementados com o objetivo de eliminar as distorções verificadas na definição do plano (ou linha) médio(a) de referência em topografias caracterizadas pela presença de vales profundos, tais como as obtidas após a aplicação da técnica de texturização a laser (LST). A definição adequada desse plano (ou linha) médio(a) de referência é imprescindível para a correta determinação dos parâmetros necessários para a utilização dos modelos de contato de Greenwood a partir das metodologias consideradas neste trabalho. Toda a modelagem unidimensional foi implementada em um programa computacional denominado VTL ("Virtual Tribology Laboratory")...

O design de gemas através dos enfoques: Mineralogia, Tribologia e Design; The gemstone design through the focus: Mineralogy, Tribology and Design

Nadur, Angela Vido
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 24/11/2014 PT
Relevância na Pesquisa
27.06%
Esta tese tem como objetivo descrever o processo de desenvolvimento da gema lapidada, do início até o fim, abordando o comportamento dos minerais colocados em produção e sua aplicação no Design. O mineral gemológico foi submetido a processos mecânicos, comumente utilizados na lapidação de gemas, e analisados através da tribologia. A lapidação de gemas foi desenvolvida através de processos empíricos, em que pode ser descrita pela ciência através de fatores como tempo, velocidade de rotação, carga aplicada e padrões de qualidade de brilho são parâmetros julgados pelo lapidário e avaliados através de padrões visuais. Neste trabalho, destacaram-se parâmetros mineralógicos preponderantes que possibilitaram a otimização da lapidação de gemas, como a relação da orientação cristalográfica com o polimento (dureza, direção de polimento); relação da composição química do mineral com os pós de polimentos e lubrificantes; sua influência na planicidade de superfície; determinação de propriedades ópticas em relação aos ângulos críticos aplicados nas faces do pavilhão, e itens preponderantes que referem-se ao Design de Gemas. Foram utilizados seis conjuntos de minerais gemológicos...

Simulador de desgaste da componente acetabular da prótese de anca

Sobral, João Miguel Antunes
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
POR
Relevância na Pesquisa
17.66%
A tribologia estuda o atrito e o desgaste resultantes da interacção de superfícies em movimento relativo. O desgaste é um dos factores mais relevantes na durabilidade da prótese da anca. O objectivo da investigação referente à tribologia da prótese da anca visa minimizar o atrito e o desgaste do implante e deste modo aumentar o tempo de vida da articulação artificial. Ensaios do tipo pino-em-disco, que permitem a caracterização de materiais relativamente a parâmetros importantes como o coeficiente de atrito, o desgaste e os efeitos da rugosidade dos materiais ou da lubrificação e ensaios simulando as condições in vivo em relação aos componentes da prótese, cabeça femoral e acetábulo, ao ciclo dinâmico aplicado bem como às condições de lubrificação, têm sido utilizados no desenvolvimento tribologico da prótese da anca. Esta dissertação é o resultado da concepção, projecto e fabrico, no contexto actual da tribologia da prótese da anca, de um dispositivo para ensaios de desgaste de componentes acetabulares, destinado à análise comparativa de taxas de desgaste do acetábulo com diferentes pares cabeça femoralacetábulo e da sua variação em função da força aplicada. Após o estudo de várias soluções técnicas optou-se pelo desenvolvimento do dispositivo de ensaios de desgaste de componentes acetabulares de modo a simular as condições in vivo...

Variation in joint fluid composition and its effect on the tribology of replacement joint articulation

Mazzucco, Daniel Clarke, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 286 p.; 24973381 bytes; 24987129 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
27.66%
Polyethylene wear is a significant clinical problem limiting the long-term survival of joint replacement prostheses, particularly in total hip arthroplasty (THA) and total knee arthroplasty (TKA). Although the tribology of joint replacement has consequently become an area of significant research, the effect of joint fluid on lubrication in the replaced joint has been largely overlooked. Several factors that affect the tribology of metal on polyethylene articulation in joint prostheses stem from the fluid lubricating the joint. In particular, the properties and composition of joint fluid likely contribute to fluid film lubrication and boundary lubrication in joint replacements, as they do in natural joints. The primary objective of this thesis is to examine the effect of natural variation in joint fluid composition and properties on friction, lubrication, and wear in joint arthroplasty. To achieve this goal, several parameters relating to the composition and mechanical properties of joint fluid are determined. Steady shear viscosity and linear viscoelastic properties of joint fluid are evaluated as indicators of its mechanical properties. Furthermore, concentrations of the hyaluronic acid, protein, and phospholipid in joint fluid are measured using standard biochemical techniques.; (cont.) The molecular weight of hyaluronic acid is also determined using size exclusion chromatography. These properties and components are evaluated in joint fluid from patients undergoing TKA and from patients undergoing surgical revision of an existing TKA (as well as from other patient groups). Results are considered in the context of previous studies of healthy and diseased synovial fluid. Correlations between and among components and flow properties are determined. Friction tests are performed on articulations between ultra-high molecular weight polyethylene (PE) and cobalt-chromium-molybdenum alloy (Co-Cr)...

Análise tribológica das malhas multifuncionais obtidas por multicamadas; Analysis of the tribology of multi-layened multifunctional knitted fabrics

Aquino, Marcos Silva de
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Mecânica; Tecnologia de Materiais; Projetos Mecânicos; Termociências Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Mecânica; Tecnologia de Materiais; Projetos Mecânicos; Termociências
Tipo: Tese de Doutorado Formato: application/pdf
POR
Relevância na Pesquisa
27.06%
The present work consists in the analysis of tribologycal properties of basic and multifunctional knitted fabrics. This knowledge has fundamental importance for the textile industry since it can quantify, in an objective way, the tactil. The fabrics used were characterized by friction and mechanical tests for determining the viscoelastic region, wear resistance and friction coefficient of the fabrics used. The stress-strain curve was obtained by the method Kawabata, KES-FB1. Wear tests performed with the aid of equipment Martindale. The measurement of friction coefficient, two methods were used and analyzed comparatively. The first was a method already established worldwide known as KES-FB4 and the second was an innovative method called FRICTORQ, developed by the University of Minho. These two methods were compared taking into account the relative motion between the tribologycal pairs are different from each method. While the first motion is translational, the second is rotational. It was formal that the knitted had a multifunctional fabrics tribologycal performance which was better than the basic knitted fabrics, as the viscoelastic region, was laager highlighting a multifunctional structure, with greater wear resistance mainly on the back side of the knitted fabrics and lower friction coefficient. Performing a comparative analysis between two methods used to measure the friction coefficient...

Análise tribológica de um sistema de acionamento alternativo de pigs para a indústria do petróleo

Medeiros, Suelson Diógenes de França
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Mecânica; Tecnologia de Materiais; Projetos Mecânicos; Termociências Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Mecânica; Tecnologia de Materiais; Projetos Mecânicos; Termociências
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
27.06%
It is analyzed through the concepts of tribology and mechanical contact and damage the suggestion of implementing a backup system for traction and passage of Pipeline Inspection Gauge (Pig) from the inside of pipelines. In order to verify the integrity of the pipelines, it is suggested the possibility of displacement of such equipment by pulling wires with steel wires. The physical and mechanical characteristics of this method were verified by accelerated tests in the laboratory in a tribological pair, wire versus a curve 90. It also considered the main mechanisms of wear of a sliding system with and without lubricant, in the absence and presence of contaminants. To try this, It was constructed a test bench able to reproduce a slip system, work on mode back-and-forth ("reciprocation"). It was used two kinds of wires, a galvanized steel and other stainless steel and the results achieved using the two kinds of steel cables were compared. For result comparative means, it was used steel cables with and without coating of Poly Vinyl Chloride (PVC). The wires and the curves of the products were characterized using metallographic analysis, microhardness Vickers tests, X-ray diffraction (XRD), X-Ray Refraction (XRF) and tensile tests. After the experiments were analyzed some parameters that have been measurable...

Sele??o de materiais e an?lise de valor: metodologia balanced scorecard de engenharia da qualidade aplicada ao estudo do desgaste e coroas de perfura??o de uma empresa de sondagem.

Santos, Zirlene Alves da Silva
Fonte: Programa de P?s-Gradua??o em Engenharia de Materiais. Rede Tem?tica em Engenharia de Materiais, Pr?-Reitoria de Pesquisa e P?s-Gradua??o, Universidade Federal de Ouro Preto. Publicador: Programa de P?s-Gradua??o em Engenharia de Materiais. Rede Tem?tica em Engenharia de Materiais, Pr?-Reitoria de Pesquisa e P?s-Gradua??o, Universidade Federal de Ouro Preto.
Tipo: Tese de Doutorado
PT_BR
Relevância na Pesquisa
17.36%
Este estudo aborda o desenvolvimento de uma metodologia que associa gest?o, Engenharia de materiais e Tribologia. Na gest?o a pesquisa teve como enfoque o BSC (Balanced Scorecard) ou medida de desempenho. Trata-se de uma ferramenta de gest?o estrat?gica. Utilizou-se a Engenharia da Qualidade, especificamente o Planejamento de Experimentos para fazer a combina??o de vari?veis e an?lise estat?stica. Na Engenharia de Materiais o estudo focou na sele??o de materiais. Na Tribologia foi pesquisado o desgaste. Para o desenvolvimento da metodologia intitulada BSCEQ utilizou-se primeiramente pesquisa estruturada com especialistas sobre o conhecimento do BSC e a viabilidade da metodologia. Os especialistas s?o das ?reas de minera??o, siderurgia e ind?stria automobil?stica. Com o resultado, foi poss?vel definir os principais indicadores para a metodologia. Com os indicadores definidos, foi poss?vel incorporar ? metodologia a t?cnica estat?stica Planejamento de Experimentos ou DOE (Design Of Experiment). A metodologia foi aplicada ao desgaste de componentes, da ind?stria mineral, especificamente, coroas de perfura??o para soldagem geol?gica. A aplica??o foi realizada inicialmente com a defini??o das perspectivas de uma empresa de perfura??o, ?rea da pesquisa. As perspectivas foram chamadas de entrada e concentravam-se na vis?o financeira...

A Novel Method for Calculating the Frictional Properties of Articular Cartilage Using a Material Testing Machine; Eine neue Methode zur Berechnung der Reibungseigenschaften von Gelenkknorpel unter Einsatz einer Materialprüfmaschine

Mu, Yiping
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
27.66%
Osteoarthritis (OA) is a common degenerative joint disease which causes chronic pain, joint destruction, disability, depression, and social in patients. Many researchers have studied the coefficient of friction of articular cartilage (AC) using a variety of methods, especially with the tribology method. Functional biotribology is a useful way to better understand how and why cartilage becomes osteoarthritis. In this study, a novel biomechanical measurement system was built to determine the friction of a sheep joint performing loaded torsional oscillations between the joint surfaces. A surgical induced OA model was used, which was better to control the size, the depth, and the position of the defect.Four different defect groups were designed for this experiment: no defect group, 16mm 2 defect group, 32 mm 2 defect group, and total defect group. The OA model joints were investigated in an oscillating torsion experiment applied by a material testing machine with 12 successive loading cycles in axial direction. Each sample was tested in four different axial loading conditions: 100N, 200N, 450N and 900N axial forces. This the flow chart of the experiment, there are four defect conditions for one joint. The OA model joints were investigated in an oscillating torsion experiment applied by a material testing machine with 12 successive loading cycles in axial direction. Because this was not a simple model for kinetic friction between plane surfaces moving linearly with respect to each other...

Overview of the In-Space Propulsion (ISP-1) Project

ALLIOT Patrick; VUILLAMY Didier; BEAURAIN Andre; RICCIUS Joerg; ORDONNEAU Gerard; BOZET Jean Luc; BRUCHHAUSEN MATTHIAS; YALAOUI Samir; FORTUNIER Pascal
Fonte: French Association for aeronautics and space Publicador: French Association for aeronautics and space
Tipo: Contributions to Conferences Formato: CD-ROM
ENG
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17.36%
The intent of this publication is to provide an overview of the progress of the ISP1 project over the 2011-2012 period. In the frame of the European FP7 Collaborative Project, Focused Research Project Theme 7, the In-Space Propulsion (ISP-1) project GA# 218849 was initiated in 2009 with the objective of improving the knowledge and the techniques which are necessary for future space missions relying on cryogenic propulsion. The ISP-1 program is structured into five main work packages which deal with various technological issues associated to the development of a Low Thrust Cryogenic Propulsion system. It concentrates on liquid oxygen, liquid hydrogen, and liquid methane propellants. The subject addressed by the work packages are the LOX-methane combustion, the hydrogen embrittlement, the material compatibility and tribology in liquid oxygen, the energy management of low thrust propulsion system, and the development of electrically driven cryogenic turbopumps. The scientific and technological goals assigned to each work package can be summarized as: - LOX/CH4 Combustion studies and test focused on low thrust LOX/CH4 space propulsion with an emphasis on low pressure liquid injection - Compatibility and tribology analysis and tests addressing both technological aspects (Foil bearings in cryogenic conditions ...

Water Drop Tribology of Graphene and Polymer Nanocomposites

Cox, Paris
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
37.36%
Basic physics teaches us that the frictional force (lateral force) needed to move objects on surfaces are proportional to load (normal force) – Amonton’s Laws. In tribology, this force is proportional to contact area, whereas Amonton is just a special case for contact area scaling with load. Such established laws do not seem to apply to small drops on flat, smooth surfaces in which frictional forces have an inverse relation to contact area and have time component prior to movement. Such phenomena can be explained by Shanahan-deGennes were intermolecular forces are considered for a deformed surface. Graphene is a special case where no time component is observed and frictional forces are attributed to its chemical homogeneity and stability. In the second part of this thesis, graphene is considered as nanofiller to build up polymer nanocomposites via Layer by Layer (LbL). Graphene Nanoribbons derived from multi-walled carbon nanotubes (MWCNT) offers a special case for thermoplastic polyurethane nanocomposites in that of thermally activated twisting morphology influences nanocomposite properties. Finally an electric field driven transdermal hydrogel drug delivery device has been demonstrated by just using CNTs, polyvinyl-borax gel and a CNT membrane

Effects of a straight oil on friction at the tool-workmaterial interface in machining

CLAUDIN, Christophe; RECH, Joel; MONDELIN, Alexandre; FROMENTIN, Guillaume
Fonte: ELSEVIER Publicador: ELSEVIER
EN
Relevância na Pesquisa
27.06%
Authors would like to express their gratitude to the TOTAL Company for the furniture of the lubricant.; The quantification of friction coefficient along the tool-workmaterial interface in machining remains an issue in tribology. This paper aims identifying the evolution of friction coefficient for a large range of sliding velocity during the machining of a AISI4140 steel (290 HB) with a TiN coated carbide tool. The influence of a straight oil is investigated compared to a dry sliding situation (dry machining). It has been shown that, in dry machining, friction coefficient decreases with the sliding velocity until reaching a downer limit around 0.2. On the contrary, the presence of a straight oil decreases significantly friction coefficients to a value around 0.1. Additionally, the friction coefficient becomes independent from the sliding velocity. It also been shown that a straight oil is able to penetrate the pin-workmaterial interface even if a very high contact pressure is present (~3 GPa). The penetration duration is very fast, whereas its evacuation duration is much higher and strongly dependant on sliding speeds.

The methodology non–destructive test inspection by ultrasound for predict the beginning of the failure of a material subject to rolling contact fatigue

León, J.C; Pinto, M.A; Romero C, J. E
Fonte: Universidad de Carabobo Publicador: Universidad de Carabobo
Tipo: Artigo de Revista Científica
ES_ES
Relevância na Pesquisa
27.06%
The methodology of inspection of the non-destructive testing by means of ultrasound was proposed and implemented to predict the beginning of the failure of an element under rolling contact fatigue, since it is not counted on norms that specify it. For this purpose a series of instructions appears step by step that are necessary to follow to make a reliable inspection by means of the ultrasound technique, using as foundation that is established in ASME BPVC section V code. An artificial reproduction of the fatigue failure by rolling contact in steel material was used, with the purpose of verifying the feasibility of the developed methodology, in replacement of a fatigue test of contact in tribometer of pending execution. Keywords: ultrasound, rolling contact, fatigue, tribology.

The Tribology of Sliding Elastic Media

Cule, D.; Hwa, T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.06%
The tribology of a sliding elastic continuum in contact with a disordered substrate is investigated analytically and numerically via a bead-spring model. The deterministic dynamics of this system exhibits a depinning transition at a finite driving force, with complex spatial-temporal dynamics including stick-slip events of all sizes. These behaviors can be understood completely by mapping the system to the well-known problem of a directed-path in {\em higher-dimensional } random media.; Comment: Uuencode file: 4 pages, small changes in the previous version

A macro level scientometric analysis of world tribology research output (1998 - 2012)

Elango, Bakthavachalam; Rajendran, Periyaswamy; Bornmann, Lutz
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/10/2014
Relevância na Pesquisa
27.36%
Bibliographic records related to tribology research were extracted from SCOPUS and Web of Science databases for the period of 15 years from 1998 to 2012. Macro-level scientometric indicators such as growth rate, share of international collaborative papers, citations per paper, and share of non-cited papers were employed. Further, the Gini coefficient and Simpson Index of Diversity were used. Two new relative indicators : Relative International Collaboration Rate (RICR) and Relative Growth Index (RGI) are proposed in this study. The performance of top countries contributing more than 1000 papers across the study period was discussed. Contributions and share of continents and countries by income groups were examined. Further research contributions and citation impact of selected country groups such as the Developing Eight Countries (D8), the Association of Southeast Asian Nations (ASEAN), the Union of South American Nations (UNASUR) and the Emerging and Growth-Leading Economies (EAGLEs) countries were analyzed. High levels of interdisciplinarity exist in tribology research. Inequality of distribution between countries is highest for number of publications and citations. Asia outperforms the other world regions and China contributes most of the papers (25%)...

Whole counting vs. whole-normalized counting: A country level comparative study of internationally collaborated papers on Tribology

Elango, B.; Rajendran, P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/10/2014
Relevância na Pesquisa
27.06%
The purpose of this study is to compare the changing behavior of two counting methods (whole counting and whole-normalized counting) and inflation rate at country level research productivity and impact. For this, publication data on tribology research published between 1998 and 2012 from SCOPUS has been used. Only internationally collaborated papers are considered for comparison between two counting methods. The result of correlation tests shows that there is highly correlation in all the four indicators between the two counting methods. However, the result of t-test shows that there is significant difference in the three indicators (paper count, citation count and h-index) between the two counting methods. This study concludes that whole-normalized counting (fractional) is the better choice for publication and citations counting at the country level assessment.; Comment: Submitted to the Current Science

Study of Citation Networks in Tribology Research

Elango, Bakthavachalam; Bornmann, Lutz; Shankar, Subramaniam
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/11/2014
Relevância na Pesquisa
27.36%
CitNetExplorer has been used to study the citation networks among the scientific publications on tribology during the 15 years period from 1998-2012. Three data sets from Web of Science have been analyzed: (1) Core publications of tribology research, (2) publications on nanotribology and (3) publications of Bharat Bhushan (a top-contributor to nanotribology research). Based on this study, some suggestions are made to improve the CitNetExplorer.; Comment: Submitted to the journal Scientometrics

Tribology of thin wetting films between a bubble and a moving solid surface

Karakashev, S. I.; Stoeckelhuber, K. W.; Tsekov, R.; Phan, C. M.; Heinrich, G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.06%
The tribology of a bubble rubbing on a solid surface is studied via interferometry. A unique experimental setup is designed for monitoring the thickness profiles of a wetting film, intercalated between the bubble and hydrophilic glass moving with speed up to 412 um/s. The determination of the 3D film thickness profiles allows us to calculate 3D maps over the wetted surface of the local capillary, disjoining and lift pressures, viscous stress and friction force. In this way the average friction force and the corresponding friction coefficient are obtained. A theoretical model for the dependence of the friction coefficient on the film thickness is developed. The relevant slip coefficient, being a measure for the slip between liquid and solid, is determined as a function of the speed of the solid surface. It is found out that below 170 um/s a friction regime exists which formally resembles dry friction, while at larger speed the friction force between the bubble and solid passes through a maximum. Furthermore, the friction coefficient has a large value at low speed of the solid and reduces substantially with the speed increase.

Fricción y desgaste de baldosas cerámicas de gres de monococcion y de gres porcelanico; Friction and wear of monofired ceramics and porcelainized stoneware tiles

Rincón López, Jesús María; Romero, Maximina; Almendro, M. B.
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 347902 bytes; application/pdf
SPA
Relevância na Pesquisa
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[ES] Se ha sometido una amplia gama de pavimentos cerámicos comercializados de gres porcelánico y de monococción porosa a ensayos de fricción/ abrasión usando un equipo de “pin-on–disk”. Los resultados del coeficiente de fricción se discuten en función de la perfilometría de la huella final resultante y de resultados previos realizados con el método PEI de resistencia a la abrasión profunda. Se obtienen valores de coeficiente de fricción dinámico (μ) entre 0.6- 1.00 para todas las plaquetas investigadas sin que se haya encontrado una correlación directa entre este coeficiente y los valores de la clasificación PEI o incluso de los ensayos de indentación expresados con el índice de fragilidad como la relación B = HV/ KIC . Aun así, las curvas de variación de μ en función de los ciclos de giro, permiten comprobar que existe un fenómeno de abrasión simultánea cuando se usan puntas de alúmina, mostrando un comportamiento diferente según el tipo de plaqueta ensayada. Para sistematizar estos resultados en función del tipo de material considerado, se ha definido un parámetro de abrasión a partir de las curvas: μ - ciclos (expresados en rpm), lo que puede permitir una mejor clasificación de dichos materiales.; [EN] A wide range of ceramic tiles used as pavements of porcelainized stoneware and monofired tiles have been submitted to abrasion tests by using a pin-on–disk tribometer...

The coupled effects of environmental composition, temperature and contact size-scale on the tribology of molybdenum disulfide

Khare, Harmandeep S.
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
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Burris, David L.; Liquid lubricants are precluded in an exceedingly large number of consumer as well as extreme applications as a means to reduce friction and wear at the sliding interface of two bodies. The extraterrestrial environment is one such example of an extreme environment which has motivated the development of advanced solid lubricant materials. Mechanical systems for space require fabrication, assembly, transportation and testing on earth before launch and deployment. Solid lubricants for space are expected to not only operate efficiently in the hard vacuum of space but also withstand interactions with moisture or oxygen during the terrestrial storage, transportation and assembly prior to deployment and launch. Molybdenum disulfide (MoS 2 ) is considered the gold standard in solid lubricants for space due to its excellent tribological properties in ultra-high vacuum. However in the presence of environmental species such as water and oxygen or at elevated temperatures, the lubricity and endurance of MoS 2 is severely limited. Past studies have offered several hypotheses for the breakdown of lubrication of MoS2 under the influence of water and oxygen, although exact mechanisms remain unknown. Furthermore, it is unclear if temperature acts as a driver solely for oxidation or for thermally activated slip and thermally activated desorption as well. The answers to these questions are of fundamental importance to improving the reliability of existing MoS 2 -based solid lubricants for space...