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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When a high voltage cable is transported throughout factory it is affected by sidewall pressure in cable bends between the roller supports and the cable. The problem is when the sidewall pressure is too high it will deform the cable which can have a negative impact on the conductivity of the cable. The roller supports can also get damaged because of fatigue. These negative consequences are the subject to exploration by implementing known analytical solution of contact mechanics developed by Hertz together with finite element analysis and experimental testing.   Two possible methods of measuring the radial force is studied to be able adjust the roller supports positions to reduce the sidewall pressure on the cable. The first one is to use the pressure film to determine the radial force. The second one is to by measuring the compression in cable to thereafter translate it to radial force by having the relation between compression and radial force for the specific cable.   Two different types of high voltage cables, a direct current (DC) cable and an alternating current (AC) cable is studied by using finite element method and experimental tests to see the relation between the compression and radial force in the cable. Also in these experimental tests the pressure films are used and evaluated to see if this measuring technique combined with Hertzian’s theory make it possible determining the radial force.   For the method of using the pressure films to determine the radial force the result shows it is difficult to translate the pressure from the films to radial force for a high voltage because of the cable’s armouring wires. The conclusion about these the pressure films is that they are good to use to describe the compression and can be used as relative measurement between the rollers but not for determine the radial force.   The result shows it is a possible to describe relation between compression and radial force for a high voltage cable and use this information to determine the radial force by measuring the compression. But the conclusion is that it is ineffective and less accurate way of measuring the radial force.   These results from this thesis are important for further research within the area and they help creating a greater understanding of sidewall pressure related problems in cables.

Nous proposons dans ce manuscrit une nouvelle méthode pour prendre en compte l’effet du gradient en Fretting-fatigue. Les champs mécaniques présents à proximité du front de contact sont décrits à travers des facteurs d’intensité non locaux. L’objectif est d’aboutir à une description du champ de vitesse sous la forme d’une somme de termes exprimés chacun comme le produit d’un facteur d’intensité (Is, Ia, Ic), qui dépend des chargements macroscopiques appliqués à l’ensemble et d’une fonction de forme (ds, da, dc), qui est liée à la géométrie locale du contact. Cette description est obtenue à travers un processus non intrusif de post-processing des résultats obtenus avec des calculs à éléments finis. De plus, elle a été pensée pour être implémentée dans un contexte industriel. En pratique, pour chaque chargement macroscopique et pour chaque géométrie, il est possible de calculer un ensemble de facteurs d’intensité non locaux qui permettent de décrire les champs mécaniques locaux près du front de contact. Cette description non locale a l’avantage d’être (i) indépendante de la géométrie du contact employé et (ii) utilisable dans des modèles à éléments finis utilisés dans l’industrie qui sont caractérisés par des maillages plus grossiers par rapport à ceux utilisés pour étudier le fretting-fatigue dans des milieux académiques. Une étude est menée pour vérifier que les facteurs d’intensité non locaux peuvent être utilisés pour transposer les résultats expérimentaux d’une géométrie à une autre. / In this manuscript a new method to describe the stress gradient effect in fretting-fatigue is proposed. It is based on the description of the mechanical fields arising close to the contact edges through nonlocal intensity factors. For this purpose, the kinetic field around the contact ends is partitioned into a summation of multiple terms, each one expressed as the product between intensity factors, Is, Ia, Ic, depending on the macroscopic loads applied to the mechanical assembly, and spatial reference fields, ds, da, dc, depending on the local geometry of the part. This description is obtained through nonintrusive post-processing of FE computation and is conceived in order to be easily implementable in the industrial context. As a matter of fact, for any given macroscopic load and geometry, a set of nonlocal intensity factors is computed that permits to characterize the mechanical fields close to the contact edges. Such nonlocal description has the advantage of being (i) geometry independent so that the nonlocal intensity factors can be used to compare laboratory test with real-scale industrial assembly, (ii) applicable to industrial FE models usually characterized by rougher meshes compared to the ones used to describe fretting-fatigue in the academic context. The procedure is applied to fretting-fatigue test data in order to verify whether the nonlocal intensity factors can be used to transpose experimental results to different contact geometries from the one in which they have been obtained.

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