This study aims to gain a fundamental understanding of the physics of triboelectri- cal charging of solid particles and the separation of the charged particles under an exter- nal DC electric field by computer simulations. A condenser model is used to implement charging mechanism and a soft sphere model is used to account for the Hertzian contact mechanics. The governing nondimensional parameters of the problem are identified and a parametric study is performed to investigate their effects on the charging efficiency and separation. The study finds relevance in a host of technologically important processes, such as recycling of plastic wastes, seed cleaning in agricultural industry and separation of coal from impurities in mining.

O meio corporativo, principalmente quando se trata de montadoras automotivas, é carente de conhecimento dos fatores que podem influenciar o processo de união entre pares tribológicos. Quando há um fim específico, como o tema deste trabalho: assegurar níveis de controle capazes de eliminar os riscos de uma vedação deficiente na câmara de combustão com custo mínimo, tal carência é ainda maior. O estudo da tribologia inerente à união entre cabeçote e bloco do motor diesel é fundamental para se compreender a que ponto é possível garantir a melhor estanqueidade possível, especialmente no que esteja relacionado ao processo rotineiro de aperto na linha de produção. Nesse sentido, a investigação proposta neste trabalho tem o claro objetivo de propor melhores condições técnicas de vedação ao caso particular da união entre cabeçote e bloco do motor de forma a eliminar / minimizar qualquer influência externa durante o aparafusamento do par supracitado. Adicionalmente, o conhecimento aqui exposto poderá ser difundido a muitas outras aplicações similares nas quais a fixação aparafusada está atrelada a funções que não apenas de fixação, podendo estas estarem inclusive em outros universos do produto, tais como motores, cabinas, eixos e transmissão. / The automobile corporate field has a lack of knowledge when the subject is related to tightening specific issues, especially regarding tribological studies. When there is a specific goal as this thesis theme: ensure all the control levels to eliminate sealing deficiency risks inside combustion chamber in a low investment cost, the needs are even higher. The tribological study between diesel engine block and its cylinder heads assembly is essential to comprehend what is necessary to have the best possible sealing, mostly when it\'s related to the routine on the assembly tightening process. Thinking on that, this work has the goal to propose the best condition on fastening technique that guarantees the sealing to any superficial topography roughness. Additionally, the acquired knowledge will be spread to other similar applications that are not unequally associated to bolted joints, but also in other vehicle universes, such as engines, cabs, axles and transmissions.

Abstract Despite the large amount of research work in condition based maintenance and condition monitoring methods, there is still a need for more reliable and accurate methods. The clear evidence of that need is the continued dependence on time based maintenance, especially for critical applications such as turbomachinery and airplane engines. The lack of accurate condition monitoring systems could lead to not only the unexpected failures as well as the resulting hazards and repair costs, but also a huge waste of material and time because of unnecessary replacement due to false alarms and unnecessary repair and maintenance. Temperature change is a phenomenon that accompanies every dynamic activity in the universe. However, it has not been adequately exploited for mechanical system condition monitoring. The reason is the slow response of current temperature monitoring systems compared to other condition monitoring methods such as vibration analysis. Many references inferred that the change in temperature is not sensible until approaching the end of the monitored component life and even the whole system life (Kurfess, et al., 2006; Randall, 2011; Patrick, et al., March 7-14, 2009). On the other hand, the most commonly used condition monitoring method, i.e., vibration analysis, is not free from pitfalls. Although vibration analysis has shown success in detecting some bearing faults, for other faults like lubrication problems and gradual wear it is much less effective. Also, it does not give a reliable indication of fault severity for many types of bearing faults. The advancement of thermography as a temperature monitoring tool encourages the reconsideration of temperature monitoring for mechanical system fault detection. In addition to the improved accuracy and responsiveness, it has the advantage of non-contact monitoring which eliminates the need for complex sensor mounting and wiring especially for rotating components. Therefore, in current studies the thermography-based monitoring method is often used either as a distinct method or as a complementary tool to vibration analysis in an integrated condition monitoring system. The main objectives of this study are hence to: 1. Define heat sources in the rolling element bearings and overview two of the most famous bearing temperature calculation methods. 2. Setup a bearing test rig that is equipped with both vibration and temperature monitoring systems. 3. Develop a temperature calculation analytical model for rolling element bearing that include both friction calculation and heat transfer models. The friction calculated by the model will be compared to that calculated using the pre-defined empirical methods. The heat transfer model is used for bearing temperature calculation that will be compared to the experimental measurement using different temperature monitoring devices. 4. Propose a new in-band signal enhancement technique, based on the synchronous averaging technique, Autonomous Time Synchronous Averaging (ATSA) that does not need an angular position measuring device. The proposed method, in addition to the Spectral Kurtosis based band selection, will be used to enhance the bearing envelope analysis. 5. Propose a new method for classification of the bearing faults based on the fault severity and the strength of impulsiveness in vibration signals. It will be used for planning different types of tests using both temperature and vibration methods. 6. Develop and experimentally test a new technique to stimulate the bearing temperature transient condition. The technique is supported by the results of finite element modeling and is used for bearing temperature condition monitoring when the bearing is already running at thermal equilibrium condition.

Nanoindentation is a widely used technique to measure the mechanical properties of films with thickness ranging from nanometers to micrometers. A much better understanding of the contact mechanics is obtained mostly through finite element modeling. The experiments were modeled using the software package Nano SP1 that is based on COSMOSM™ (Structural Research & Analysis Corp, www.cosmosm.com), a finite element code. The fundamental material properties affecting pile-up are the ratio of the effective modulus to yield stress Eeff/σ and the work hardening behavior. Two separate cases of work hardening rates were considered; one with no work hardening rate and other with a linear work hardening rate. Specifically, it is observed that pile up is large only when hf/hmax is close to one and degree of work hardening rate is small. It should also be noted that when hf/hmax < 0.7 very little pile-up is observed no matter what the work-hardening behavior of the material. When pile-up occurs the contact area is greater than that predicted by the experimental methods and both the hardness and modulus are overestimated. In this report the amount by which these properties are overestimated are studied and got to be around 22% approx. Bluntness of the tip often leads to the misinterpretation of the load-displacement data. Further analysis was done in order to find out the amount of deviation from the ideal tip due to tip bluntness. Radius of the tips were also calculated for cubecorner (41.35 nm) and conical indenter (986.05 nm).

Orientador: Katia Lucchesi Cavalca / Dissertação (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

No description available.

No description available.

Adhesion between solid bodies plays a prominent role in a wide variety of situations ranging from tribological applications to dust coagulation initiating the formation of planets. It can be due to various reasons like capillary, electrostatic, van der Waals, and hydrophobic forces. Among these, adhesion due to van der Waals force| which has its origin in permanent or instantaneous electric dipoles present in all atoms and molecules|is of special significance as it is present in all cases. Computational studies on adhesion due to van der Waals force commonly assume it as a surface force due to its short effective range, which is about a few tens of nanometers, in comparison to the length-scales commonly encountered. However, such restrictions are often violated in various important problems. For example, the characteristic dimensions of asperities| which are the smallest roughness elements interacting to cause friction and wear| are usually of nanometer length-scale. In addition, the assumptions inherent in development of surface force model are exact only when the deformations are small. In all such situations, the van der Waals force must be assumed as distributed over the volume. In this work, a computational model is developed by incorporating van der Waals force and short-range repulsion (steric repulsion or Pauli repulsion) as body forces distributed over the volume in a large deformation, static/transient, finite element framework. First the development of the general formulation is discussed, and then it is specialized for various considerations like handling symmetry and interaction between an elastic body and a rigid half-space, which offer significant computational advantages over the general formulation. The applicability of the model is illustrated by using a number of benchmark and practical problems. The comparison of the analysis results and well-established analytical models are provided, which validates our method. As a specific example, the smooth change of interaction force from a thin-rod model to a at-plate model on increasing the cross-sectional areas of two interacting elastic rods is demonstrated. The impact of elastic bodies in presence adhesion, and the associated energy loss is an important concern in studies regarding the origin of friction. Therefore, adhesive impact of elastic rods and spheres is studied using our formulation. Emphasis of the study is on finding the apparent energy loss during impact, which represents the part of energy lost to elastic stress waves remaining in the body after the impact, and hence not available for rebound motion. In case of impact of elastic rods on a rigid half-space, it is shown that the apparent energy loss is a unique function of the tensile strain energy developed in the rod due to van der Waals attraction. A one-dimensional model is developed for this case to determine the energy loss based on the specified problem parameters, which can be used to predict practically relevant phenomena like capture. In case of impact of elastic spheres, which is often correlated with asperity interactions, the energy loss is found to be significant only if adhesion-induced instabilities occur. The behavior shown by rods and spheres are probably at the two extremes with regards to energy loss during impact of elastic bodies in presence of adhesion. Practical use of the formulation is demonstrated by applying it to the study of amplitude variation and phase shifts in tapping-mode atomic force microscopy. Specifically, the advantage of operating the AFM cantilever just below its natural frequency as compared to operating it just above the natural frequency is demonstrated. Bistable behavior, which is the coexistence of two stable vibration modes under exactly same operating conditions, is shown to be severe when the driving frequency is higher than the natural frequency of AFM cantilever even in the absence of adhesion, which can result in spurious contrast-reversal artifacts during imaging. The hysteresis loop associated with the bistable behavior may lead to erroneous conclusions regarding presence of adhesion. Since this model overcomes the limitations of lumped parameter models and the computational models based on surface force approximation, the results can be used for much more realistic interpretation of experimental data. Computational framework developed in this study achieves the capability for analysis of adhesive contact problems directly from van der Waals interaction and steric repulsion. Such a model can be used for revisiting the fundamental problems in contact mechanics, as well as for providing better insights into experimental observations.

Dans un contact pneu/chaussée, le bruit de roulement résulte de l’interaction mécanique entre les aspérités de la chaussée et les pains de la bande de roulement. À l’issue de cette interaction, des forces compressives apparaissent pour repousser les deux corps en contact. Ces forces conduisent à la vibration du pneumatique. Ces vibrations sont à l’origine du bruit rayonné. Le travail de cette thèse s’inscrit dans le cadre de l’évaluation du bruit de roulement. L’objectif est double. Premièrement, il s’agit de comprendre les mécanismes à l’œuvre dans un processus de roulement de deux surfaces rugueuses qui engendrent une vibration puis du bruit. Deuxièmement, on cherche à mettre en évidence l’influence des aspérités de la chaussée sur les forces dynamiques interfaciales et sur le bruit généré. Dans ce contexte, on propose un nouveau modèle 3D de contact dynamique basé sur la décomposition modale de la réponse du pneumatique. Cette nouvelle approche permet de réduire considérablement le temps CPU. Le pneumatique est modélisé par une plaque orthotrope sur fondation élastique. Le problème de contact est résolu par la méthode de pénalité. On a validé ce modèle analytiquement. Cet outil permet de prédire finement ce qui se passe dans la zone de contact. Nous pouvons prédire les forces de contact et les vitesses vibratoires. En outre, il permet de déterminer l’aire de contact et les cartes de pression. À l’échelle locale, les caractéristiques d’un choc sont connues. On est capable de déterminer la force maximale du choc, à partir de l’évolution temporelle de la force de contact, et sa durée mais aussi le pourcentage de temps du choc. / In a tire road contact, the rolling noise results from the mechanical interaction between the asperities of the roadway and the tread pattern. Following this interaction, compressive forces appear to push the two bodies in contact. These forces lead to the vibration of the tyre. These vibrations are the origin of the radiated noise. The work of this thesis falls within the evaluation of rolling noise. The objective is twofold. First, we seek to understanding the mechanisms involved in a rolling process of two rough surfaces that generate vibration and then noise. Second, we aim to show the influence of the road asperities on the interfacial dynamic forces and on the noise generated. In this context, we propose a new 3D model of the dynamic contact based on a modal decomposition of the tyre response. This new approach significantly reduces CPU time. The tyre is modeled by an orthotropic plate on a elastic foundation. The contact problem is solved by the penalty method. This model was validated analytically. This tool allows us to finely predict what happens in the contact area. We can predict contact forces and vibratory velocities. Moreover, it makes it possible to determine the contact area and the pressure maps. At the local scale, the characteristics of a shock are known. We are able not only to determine the maximum force of impact, using time evolution of the contact force, and its duration but also the percentage of shock time.

La simulation de la dynamique des systèmes multicorps avec contact frottant joue un rôle important dans un grand nombre d'applications industrielles.Elle est même devenue une partie importante du développement de nouveaux produits, de la vérification et même de l'optimisation de leur conception pour améliorer les anciens produits.Les travaux présentés dans cette thèse font partie d'une collaboration entre l'équipe BiPoP, équipe de recherche de l'INRIA Grenoble, et Schneider Electric.Le but principal de ces travaux est de comprendre l'influence du jeu dans les articulations, ainsi que l'influence du dimensionnement industriel et les tolérances géométriques sur lecomportement global des liaisons mécaniques. Plus spécifiquement nous avons étudié le mini-disjoncteur C-60 (domaine dans lequel la sécurité humaine doit être garantie), pour répondre à cette demande de robustesse, tout en respectant les tolérances sur les pièces constituant le disjoncteur C-60.Le jeu radial dans les articulations pivot est une source de variabilité dans les conditions initiales du système, mais également dans la dégradation de ses performances.La dégradation du système se présente toujours sous forme de vibrations, de bruit, de forces de réactions très grandes dans les articulations, de mauvaise précision et exactitude de la sortie.Le but est d'étudier l'influence des conditions initiales et le déplacement hors-plan, ainsi que l'effet de polarisation en trois dimensions.Un objectif supplémentaire est de développer un banc d'essai virtuel efficace pour reproduire les mesures obtenues sur un vrai banc d'essai en laboratoire, en utilisant la plateforme logicielle SICONOS qui utilise la méthode NSCD (Non Smooth Contact Dynamic) introduite par J.J. Moreau et M. Jean.Le schéma NSCD a prouvé son efficacité numérique: il est capable de traiter des problèmes de complémentarité, le contact ainsi que les impacts et les lois de frottement multivaluées.Le but est de comprendre quelle est la meilleure description géométrique pour simuler de très petits jeux.L'étude complète est divisée en deux parties. La progression part du cas planaire pour arriver au cas spatial, et la complexité suit le même chemin.Dans le cas planaire, on analyse un mécanisme à quatre barres avec du jeu quand une des articulations est commandée en boucle ouverte, ou par retour d'état linéaire ou non-linéaire(PD, linéarisation par retour d'état, ou commande passive).L'accent est mis sur la quantification de la dégradation des performances quand du jeu est ajouté dans les articulations. On montre alors que les commandes par retour d'état se comportent de façon robuste.Dans le cas spatial, le mécanisme C-60 est analysé précisément pour explorer les possibilités de relaxer les tolérances industrielles sur les pièces sans compromettre ni les performances ni la sécurité. L'influence de l'entrée, du modèle et des incertitudes numériques sur le modèle C-60 est étudiée.L'influence induite par le jeu et le coefficient de frottement dans les articulations sur la performance du produit est étudiée.Pour valider le modèle de simulation, des expériences sont effectuées sur des prototypes d'essai et les résultats sont comparés avec les simulations numériques.Nous avons trouvé une bonne correlation entre les résultats numériques et expérimentaux.L'analyse statistique~(analyse du pire cas, et par des simulations basées sur la méthode de Monte-Carlo) a été réalisée pour trouver la dispersion des conditions fonctionnelles.En plus des variations dimensionnelles, la tolérence aux variations géométriques comme la forme, l'orientation et la position, est analysée.Ce travail de recherche devrait aider les concepteurs à simuler le comportement du système mécanique avec une articulation de révolution imparfaite,depuis l'étape de conception préliminaire jusqu'à la fin de la conception pour avoir une amélioration significative de la planification et du budget. / Dynamic simulation of multibody systems with unilateral contact and friction plays an important role in a wide range of industrial applications. It has become an integral part of new product development, verification/optimization of the design and to enhance the old products.This work is a part of collaboration between the BiPoP research team of INRIA Grenoble and the Schneider Electric company.The main goal of this thesis is to understand the influence of clearances in the revolute joints on the overall behaviour of the linkage mechanisms and specifically on the C-60 miniature circuit breaker where human safety must be guaranteed.In other words, the objective is to address the robustness of the C-60 breaker with respect to the production tolerances, which areexpressed in the form of dimensional and geometrical variations on the parts. These variations are the source of clearance in the joints of the mechanism.The radial clearance in the revolute joints is a source of variability in the initial conditions of the system and also the degradation of the system's performance. The degradation of the system isalways in the form of vibration, noise, very high reaction forces at the joints.The aim is to study the influence of initial conditions and the out-of-plane motion, so the polarization effect in three dimensional case.Another objective is to develop the time efficient virtual test bench to reproduce the measurements of real test bench in the laboratory using the open-source simulation software SICONOS which is based on the NonSmooth Contact Dynamic method (NSCD) introduced by J.J. Moreau and M. Jean.The NSCD scheme is proven to be a quite efficient numerical method, capable of handling complementarity conditions, as well as impacts and set-valued friction laws.The goal is to understand what is the most appropriate geometricdescription which allows to simulate very small clearances.The complete study is divided in two main sections.The progress through these partsgoes from the planar to the spatial case, the complexity follows the same advance.In the planar case, a four-bar mechanism with joint clearance, when one joint is actuated by collocated open-loop or state feedback controllers (PD, statefeedback linearization, passivity-based) is analysed. The focus is put on how much the performancedeteriorates when clearances are added in the joints. It is shown that collocated feedback controllersbehave in a robust way.In the spatial case, the C-60 mechanism is analysed precisely to explore the possibilities to relax the manufacturing tolerances on the parts withoutany compromise on either performance or the human safelyThe influence of the input, model and numerical uncertainties on the C-60 model is studied. The joint-wise influences of the clearance and coefficient of friction on theproduct performance are studied.To validate the simulation model, experiments are carried-out on the prototype samples and the results are compared with the simulations.We found quite good correlation between the virtual and experimental results.A statistical analysis~(worst-case and Monte Carlo simulation) has been carried out to find out the dispersion of the functional conditions.In addition to dimensional variations, the geometrical variations such as form, orientation and position tolerances are also analyzed.This research work shall help the designers to simulate the real time behaviour of the mechanical systems with the imperfect revolutejoint from the pre-design stage till the end of the design, to have good improvement on schedule and budget.