ABSTRACT CONTACT MECHANICS OF GRADED MATERIALS WITH TWODIMENSIONAL MATERIAL PROPERTY VARIATIONS G&ouml / kay, Kemal M.S., Department of Mechanical Engineering Supervisor: Asst. Prof. Dr. Serkan Dag September 2005, 62 pages Ceramic layers used as protective coatings in tribological applications are known to be prone to cracking and debonding due to their brittle nature. Recent experiments with functionally graded ceramics however show that these material systems are particularly useful in enhancing the resistance of a surface to tribological damage. This improved behavior is attributed to the influence of the material property gradation on the stress distribution that develops at the contacting surfaces. The main interest in the present study is in the contact mechanics of a functionally graded surface with a two &ndash / dimensional spatial variation in the modulus of elasticity. Poisson&rsquo / s ratio is assumed to be constant due to its insignificant effect on the contact stress distribution [30]. In the formulation of the problem it is assumed that the functionally graded surface is in frictional sliding contact with a rigid flat stamp. Using elasticity theory and semi-infinite plane approximation for the graded medium, the problem is reduced to a singular integral equation of the second kind. Integral equation is solved numerically by expanding the unknown contact stress distribution into a series of Jacobi polynomials and using suitable collocation points. The developed method is validated by providing comparisons to a closed form solution derived for homogeneous materials. Main numerical results consist of the effects of the material nonhomogeneity parameters, coefficient of friction and stamp size and location on the contact stress distribution.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 189-198).

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Rick Neu; Committee Member: Itzhak Green; Committee Member: Jeffrey Streator

This Thesis develops a mathematical model for predicting the thermal response in the surgical drilling of bone. The model accounts for the bone, chip and drill bit interactions by providing a detailed account of events within a cylindrical control volume enveloping the drill, the cut bone chip within the drill bit flute and the solid bone. Lumped parameter approach divides the control volume into a number of cells and cells within the sub-volumes representing the drill solid, the bone chip and the bone solid are allowed to interact. The contact mechanics of rough surfaces is used to model chip-flute and chip-bone frictional interaction. In this way not only the quantification of friction due to sliding contact of chip-flute and chip-bone rough surface contact are treated, but also the contact thermal resistances between the rubbing surfaces are included in the model. A mixed combination of constant and adaptive mesh is employed to permit the simulation of the heat transfer as the drill bit penetrates deeper into the bone during a drilling process. Using the model the effect of various parameters on the temperature rise in bone, drill and the chip are investigated. It is found that maximum temperature within the bone occurs at the location adjacent to the corner of the drill-tip and drill body. The results of the model are found to agree favorably with the experimental measurements reported in the existing literature on surgical drilling.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Kevin B. Lease / The overall goal of this study was to assess the effects of surface chemistry on adhesion of polymeric systems underwater. The adhesion is quantified by the thermodynamic work of adhesion (W) when two surfaces are approached and the energy release rate (G) when the surfaces are separated. For some polymeric systems there is a difference between W and G, referred to as adhesion hysteresis. For this study an experimental approach based upon Johnson-Kendall-Roberts (JKR) theory of contact mechanics was utilized to evaluate how surface chemistry affects the adhesion behavior (both W and adhesion hysteresis) in the presence of water. The interfacial interactions were also studied in air and contrasted to those obtained underwater. To accomplish the overall goal of this research, this study was divided into two phases where smooth model surfaces with disparate surface chemistries were used. The model surfaces in the first part included poly(dimethysiloxane) (PDMS), glass surfaces chemically functionalized to display hydrophilic to medium to hydrophobic characteristics, and thin films of wood-based biopolymers. The functionalities used to modify glass surfaces included polyethylene oxide (PEO) with hydrophilic nature; amine, carbomethoxy, and mercapto (thiol) with intermediate characteristics; cyclohexyl, fluorocarbon, and methyl with hydrophobic behavior. In addition to these surfaces, flat PDMS and clean glass surfaces were also used for means of comparison. The wood-derived polymers included two different cellulose types (natural cellulose and regenerated cellulose) as well as one lignin surface (from hardwood milled lignin). These surfaces were probed with native PDMS hemispheres, which are hydrophobic. The results showed that in air the value of W for all model surfaces was independent of the surface chemistry, except fluorocarbon which was lower. Underwater W was significantly affected by the surface hydrophilicity/ hydrophobicity. The adhesion hysteresis both in air and underwater was significantly dependent on the structure of the probed surface. For the second phase PDMS hemispheres were chemically modified with amine functionality to probe model surfaces with hydrophilic and intermediate behavior. These surfaces included glass surfaces functionalized with PEO and amine as well as PDMS sheets that were functionalized with amine. Native PDMS flat surfaces were also used for means of comparison. The results showed that for the selected surfaces both W and hysteresis were affected by the surface chemistry in both media.

Orientador: Alberto Luiz Serpa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-13T06:24:20Z (GMT). No. of bitstreams: 1 Mirisola_MarceloHenriqueBizarro_M.pdf: 3557658 bytes, checksum: 1d84aceed33a91925d0d85bf045308af (MD5) Previous issue date: 2009 / Resumo: Nesta dissertação é abordado o tema otimização estrutural em componentes sob efeito de contato. O objetivo é otimizar a distribuição das pressões de contato atuantes no olhal menor de uma biela. Para alcançar este objetivo, são apresentadas técnicas de otimização estrutural baseada no método dos elementos finitos, são estudados conceitos relacionados a problemas de otimização e problemas de contato, e é explorado o acoplamento entre problemas de otimização e de contato. O software de elementos finitos ANSYS 10.0 é aplicado em problemas de otimização, em problemas de contato, e em problemas de otimização com contato. O foco do trabalho é mantido nas técnicas de otimização paramétrica e de forma. Este trabalho propõe um método combinando os dois métodos de otimização presentes no modulo Design optimization do ANSYS. Os resultados mostram que o método combinado proposto é capaz de evitar pontos de mínimo local e apresenta uma boa relação entre a qualidade dos resultados e o "custo computacional". Também é proposta uma técnica de parametrização baseada na posição dos nós da malha de elementos finitos. Esta técnica apresenta a vantagem de não necessitar de um modelo em elementos finitos parametrizados da estrutura que se deseja otimizar. Exemplos de validação são apresentados e um modelo aproximado do problema das pressões de contato atuantes no olhal menor de uma biela é criado e otimizado, atingindo uma redução de 45% da máxima pressão de contato. / Abstract: This dissertation deals with the issue of structural optimization of components under contact effects. The aim is to optimize the contact pressure distribution acting in the connecting-rod small end. To achieve this goal, techniques of structural optimization based on the finite element method are presented, the basis of optimization and contact problems are briefly reviewed and the coupling of these problems is explored. The finite element software ANSYS 10.0 is applied in optimization problems, contact problems, and optimization problems with contact. The focus of the work is parametric and shape optimization techniques. This work proposes a method coupling the two-optimization methods within the Design optimization module of ANSYS. The results show that the proposed combined method is able to avoid local minima and achieve a good relation between the quality of results and the computational cost. It is also proposed a parameterization technique based on the node positions in the finite element mesh. This technique has the advantage of not needing a parameterized finite element model of the structure to be optimized. Examples for validation purposes are presented and an approximated model of the problem of the contact pressure distribution acting in the connecting-rod small end is designed and optimized, reaching a reduction of 45% in the maximum contact pressure. / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Orientadores: Alberto Luiz Serpa, Marco Lúcio Bittencourt / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-22T23:15:11Z (GMT). No. of bitstreams: 1 Dias_AllanPatrickCordeiro_M.pdf: 5620368 bytes, checksum: a856aa1d97161e81d35fc5c6fd68d91a (MD5) Previous issue date: 2013 / Resumo: No presente trabalho, apresenta-se um elemento de contato com alta ordem de interpolação, construído a partir do método mortar de decomposição de domínios discretizados. O alvo de estudo é a verificação da acurácia da solução com o aumento da ordem de interpolação do elemento em problemas bidimensionais de contato com grandes deformações, atrito sem considerar efeitos termomecânicos. São apresentadas soluções para alguns problemas clássicos da literatura de contato. Os resultados obtidos, de uma forma geral, tanto para pequenas como para grandes deformações, mostram que a alta ordem de interpolação pode ser considerada uma interessante estratégia para ganho de precisão na solução deste tipo de problemas, quando o foco em análise é o estudo das tensões e esforços gerados pelo contato / Abstract: This work presents a high-order mortar finite element for frictional contact problems considering finite deformations without thermomechanics effects. The aim of this work is to increase the accuracy of the solution in the contact region with the application of p-FEM high-order method. The results for both small and large strains shows that the high order interpolations can be considered an interesting strategy in this kind of problems, when the analysis is focused on the study of stresses and reactions generated by contact / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Le bruit de frottement de deux surfaces rugueuses est dû à la vibration verticale engendrée par les impacts inter-aspérités de deux solides glissants. Il relève de la physique des interfaces multicontact dont les propriétés sont encore largement méconnues. L'objet de cette thèse est de comprendre les mécanismes de transfert d'énergie et de génération des vibrations à l'œuvre à l'interface entre deux surfaces rugueuses en glissement relatif. Ces interfaces présentent des spots de contact qui se renouvellent très rapidement mais dont la physique statistique reste à découvrir. Un outil numérique est spécialement développé pour étudier efficacement ce phénomène aux échelles microscopique et macroscopique. Les simulations sont effectuées à l'aide de centres de calcul haute performance à Lyon. Elles ont mené aux conclusions suivantes. Le niveau de la vibration Lv (dB) est une fonction croissante du logarithme de la rugosité de surface Ra et de la vitesse de glissement V, ce qui est en accord avec les résultats expérimentaux issus de la littérature. De plus, grâce à cet outil numérique, on a pu analyser précisément les chocs entre surfaces définis à partir de l'évolution temporelle de la force de contact. Leur durée est de l'ordre de 0.1 ms, la force maximale de contact peut atteindre 100 fois le poids propre du solide glissant, et le nombre de chocs est de l'ordre de 10000 par seconde pour une surface de l'ordre de 4 cm2. Les chocs sont donc des excitations transitoires brèves mais nombreuses et intenses. Ces chocs se comportent comme les sources d'énergie vibratoire qui sont responsables d'un transfert d'énergie à l'interface. C'est en effet la transformation de l'énergie cinétique du mouvement solide glissant en énergie vibratoire qui est responsable du bruit de frottement. / The friction noise between two rough surfaces is caused by the vertical vibration generated by inter-asperity impacts of sliding solids. This phenomenon involves the physics of multicontact interfaces, a field which is largely unknown. The purpose of this thesis is to understand the mechanisms of noise generation and the energy transfer process between two rough surfaces in sliding contact. The contact spots in the interface are rapidly renewed during the movement in a random fashion but their statistical properties remain to be discovered. A numerical tool is developed in order to efficiently study this phenomenon at both macroscopic and microscopie scales. The simulations are carried out thanks to the high performance computing centre in Lyon. This study leads to the following conclusions. The vibration level Lv (dB) is an increasing logarithm function of surface roughness Ra and sliding velocity V. This statement is consistent with experimental results available in the literature. Moreover, we can analyze precisely the asperity shocks which are defined from the time evolution of the contact force. The shock duration is of the order of 0.1 ms, the maximal contact force can reach to 100 times the weight of sliding solid, and the shock rate is of the order of 10000 for a surface of 4 cm2 . The asperity shocks are transient excitations, brief but abundant and intensive. These shocks behave like vibrational energy sources and are responsible of the energy transfer in the interface. This is the transformation process of kinetic energy to vibrational energy which is responsible of friction noises.

In Chapter 1, a brief introduction of nanoindentation and finite element method is presented. General procedures have been developed based on FEM modeling of nanoindentation data to obtain the mechanical properties of thin films. Selected FEM models are illustrated in detail. In Chapter 2, nanoindentation test is simulated using finite element method based on contact mechanics approach. The relationship between load and indentation depth is obtained. The numerical results show good agreement with experimental data. It is shown that FEM is an effective tool for simulation of nanoindentation tests of metallic films. However, limitations caused by simplification of models and assumptions should not be neglected. In Chapter 3, finite element method is used to analyze bonded repair structure of aluminum plates with Multiple Site Damage (MSD). A 2-D 3-layer technique is used to deal with the damage area. A typical aluminum plate with multiple collinear twin cracks is taken as an example. The effects of relative position of two cracks, patch size, and patch thickness on stress intensity factors are studied in detail. The results reveal that the stress intensity factors at the tips of collinear twin cracks can be reduced greatly through bonded composite repair. In order to increase the performance of the patch repair, the adhesive properties, the patch length and thickness must be optimized. In Chapter 4, finite element method is used for thermo-mechanical analysis of porous coatings in steel micro channels used for catalysis. Thermal stresses in the coating due to temperature changes are obtained. The effects of micro channel geometry on thermal stresses are studied in detail. The results reveal that in order to increase the mechanical performance of the coatings, film thickness and profile geometry must be optimized. Chapter 5 summarizes major results and outlines future work.

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