Previous studies show that the Piezoelectric-Driven Stick-Slip (PDSS) actuator is a promising device in many micropositioning and micromanipulation applications, where positioning with a long range and a high resolution is required. However, research in this area is still in its early stage and many issues remain to be addressed. One key issue is the representation of the dynamic displacement of the end-effector. It is known that such factors as the dynamics of piezoelectric actuator (PEA) and the presliding friction involved can significantly contribute to the displacement dynamics. Although this has been widely accepted, specific quantitative relationship between the aforementioned factors and the displacement dynamics has rarely been defined. The aim of this research is to develop a model to represent the displacement of the end-effecter of the PDSS actuators, in which both the presliding friction and the PEA dynamics are addressed. <p>In order to represent the presliding friction, the models reported in literatures, including Dahl model [Olsson, et al., 1998], Reset Integrator model [Haessig and Friedland 1991], LuGre model [Canudas de Wit et al., 1995] and Elastoplastic model [Dupont et al., 2002] were reviewed and examined; and the LuGre model was chosen to be used because of its efficiency and simple formulation. On the other hand, a linear second order dynamic system model was employed to represent the combination of a PEA and its driven mechanism. On the basis of the pre-sliding friction model and the linearized PEA dynamics model, a model representative of the end-effector displacement of the PDSS actuator model was developed. <p>In order to validate experimentally the developed PDSS model, a displacement measuring and data acquisition experiment system was established and a prototype was developed based on dSPACE and Simulink. On the prototyped actuator, two experiments were designed and conducted to identify the parameters involved in the model. One experiment is for the determination of the parameters of the second order system for the dynamics of the combination of a PEA and its driven mechanism; and other one is for the determination of the parameters of the chosen friction model. The identified parameters were then employed in the developed PDSS model to simulate the displacements and the results were compared with the experimental results that were obtained under the same operating conditions as the simulation. The comparison suggests that the model developed in this study is promising for the end-effector displacement of the PDSS actuator.

Piezoelectric actuators (PEA) hold the most promise for precision positioning applications due to their capability of producing extremely small displacements down to 10 pm (1 pm = 10-12 m) as well as their high stiffness and force output. The piezoelectric-driven stick-slip (PDSS) actuator, working on the friction-inertia concept, has the capacity of accomplishing an unlimited range of motion. It also holds the promises of simple configuration and low cost. On the other hand, the PDSS actuator has a relatively low efficiency and low loading capability, which greatly limits its applications. The purpose of this research is to improve the performance of the PDSS actuators by employing specially-designed working surfaces.<p> The working surfaces, referred as anisotropic friction (AF) surfaces in this study, can provide different friction forces depending on the direction of relative motion of the two surfaces, and are used in this research to accomplish the aforementioned purpose. To fabricate such surfaces, two nanostructure technologies are employed: hot filament chemical vapour deposition (HFCVD) and ion beam etching (IBE). The HFCVD is used to deposit diamond on silicon substrates; and the IBE is used to etch the diamond crystalloid with a certain angle with respect to the coating surface to obtain an unsymmetrical-triangle microstructure. <p> A PDSS actuator prototype containing the AF surfaces was developed in this study to verify the function of the AF surfaces and characterize the performance of PDSS actuators. The designed surfaces were mounted on the prototype; and the improvement in performance was characterized by conducting a set of experiments with both the normal isotropic friction (IF) surfaces and the AF surfaces, respectively. The results illustrate that the PDSS actuator with the AF surface has a higher efficiency and improved loading capability compared to the one with the IF surfaces.<p> A model was also developed to represent the displacement of the novel PDSS actuator. The dynamics of the PEA and the platform were approximated by using a second order dynamic system. The pre-sliding friction behaviour involved was investigated by modifying the LuGre friction model, in which six parameters (Note that three parameters are used in the LuGre model) were employed to represent the anisotropic friction. By combining the PEA mechanism model, the modified friction model, and the dynamics of end-effector, a model for the PDSS actuator with the AF surface was developed. The model with the identified parameters was simulated in MATLAB Simulink and the simulation results obtained were compared to the experimental results to verify the model. The comparison suggests that the model developed in this study is promising to represent the displacement of the novel PDSS actuators with AF surfaces.

This thesis is addressed to the understanding of the mechanisms at the origin of the contact wave fields at frictional interfaces and its relationship with the local characteristics of the surfaces in contact, as well as with the global dynamics and macroscopic frictional behaviour of the system. The aim of this work is to provide insights on the generation and propagation of the waves through the contact both to avoid instabilities and to control their effect on friction. The work is organized in two main parts. The first part presents the development of a non-linear finite element analysis in large transformations of the dynamic rupture at the interface with contact friction separating two bodies (isotropic and elastic) without relative motion. A rupture is considered when an initially sticking zone shifts in sliding state. The properties of the obtained ruptures are analyzed for a flat interface between dissimilar materials in function of the nucleation energy; then the effect of the interface roughness is analyzed. The differentiated rupture inside the asperities and the conditions for coupling and uncoupling between the waves radiating in the two bodies have been also investigated. In the second part, the analysis deals with the sliding onset between two bodies in contact. The sliding between two bodies made of different isotropic elastic materials and separated by a frictional interface is simulated. The evolution along the time of the global normal and tangential forces is analyzed, relating it to the local phenomena occurring at the interface. This part tries to investigate how micro-slips at the interface, acting as distributed ruptures, trigger the macro-slips between the two bodies. The interaction between local and global dynamics is also studied. Finally a numerical parameter space study is carried out, as a function of several system parameters (contact law, friction coefficient, material damping, normal load, translational velocity and regularization time). The results show the key role of the micro-slips and precursors (detectable wave propagations that occur at tangential global force well below the critical value expected by the friction law) in triggering the macro-slip between the two bodies. Depending on their distribution and magnitude the evolution of the contact forces passes from stick-slip-like behaviour to continuous sliding. The local dynamics at the contact (wave and rupture propagation) is linked to the global behaviour of the system (stick-slip, continuous sliding, induced vibrations); the effect of the contact and system parameters on the transfer of vibrational energy between the sliding contact and the system is investigated. The numerical results obtained by the two parts of the work show a good agreement with experimental results in literature.

Les pieds d'aubes de soufflantes de turboréacteurs font face à des sollicitations de type fretting. Il en résulte deux types d'endommagements: (i) l'amorçage et la propagation de fissures, (ii) l'usure des surfaces en contact. OBJECTIF: Afin de fournir les outils permettant de répondre à la problématique industrielle, une méthode semi-analytique permettant de traiter des problèmes de contacts élasto-plastiques revêtus et/ou hétérogènes est développé à partir d'éléments existants et de solutions analytiques et numériques novatrices. METHODE: La structure est simplifiée en supposant un contact entre deux massifs élastiques semi-infinis. Des solutions analytiques donnant pour: + les contributions élémentaires de chargements normaux et tangentiels constants sur une surface rectangulaire + les contributions élémentaires de déformations plastiques supposées constantes sur un volume parallélépipédique + les contributions élémentaires de déformations d'incompatibilité liées à un problème hétérogène (inclusions, revêtements, endommagement,...) supposées constantes sur un volume parallélépipédique. >> les déplacements en surface ou les contraintes dans le volume. Les déplacements en surface ou les contraintes dans le volume sont alors exprimés en utilisant des produits de convolution discrets entre des coefficients d'influence et la source surfacique (chargements en surface) ou volumique (déformations plastiques ou d'incompatibilité). Le problème normal et le problème tangentiel en glissement total ou en glissement partiel peuvent alors être résolus, en prenant en compte les effets plastiques et hétérogènes. L'algorithme d'optimisation sous contrainte utilisé (contact elastique) est celui développé par L.Gallego tandis que la base du solver plastique utilisé a été développé par C. Jacq (contact elasto-plastique sans frottement) RESULTATS: De nouvelles solutions analytiques sont obtenues pour le calcul des déplacements résiduels tangentiels.

Nos sistemas de freio automotivo, o principal componente que determina seu desempenho é o material de fricção, pois um bom material de fricção deve garantir estabilidade no atrito em diferentes condições de uso, além de possuir resistência à corrosão, longa vida útil, baixa taxa de desgaste, boa relação custo versus desempenho e baixo ruído. Desde que o conforto dos veículos tornou-se um fator importante para indicar sua qualidade, eliminar ou reduzir os ruídos e vibrações de seus componentes passou a ser uma vantagem competitiva no mercado automotivo, e, o problema de ruído nos sistemas de freios vem sendo um dos maiores causadores de reclamações de clientes nos últimos anos. O ruído de freio é na maioria das vezes o resultado de uma vibração auto excitada induzida pela fricção ou uma instabilidade dinâmica do sistema de freio. O processo de stick-slip é um típico exemplo de oscilação induzida por atrito, observada em baixas velocidades de deslizamento e geralmente resulta em vibrações, que geram ruídos graves e rangidos. Com o objetivo de verificar a viabilidade da utilização das medições de vibração durante a ocorrência do fenômeno do stick-slip para a caracterização de materiais de fricção utilizando um tribômetro, foram preparados seis materiais de fricção produzidos pela empresa Fras-le, fabricante de materiais de fricção para freios automotivos. Os ensaios foram realizados no Laboratório de Tribologia (Latrib) da Escola de Engenharia da Universidade Federal do Rio Grande do Sul (UFRGS). No tribômetro utilizado nos ensaios foi instalado um acelerômetro sobre o suporte onde é fixada a pastilha do material de fricção a ser ensaiado. Vários ensaios foram realizados, cada um sob ação de força normal e velocidade de giro do disco constantes. Os resultados dos ensaios demonstraram que o tribômetro apresenta excelente desempenho para caracterização de materiais de fricção, possibilitando o desenvolvimento de novos materiais a partir de ensaios realizados neste equipamento. A avaliação da resposta da aceleração da vibração obtida nos ensaios demonstrou que a resposta da vibração é dependente dos diversos parâmetros medidos, como deslocamento, velocidade e variação de torque, e para melhor prever a propensão de um determinado material em apresentar vibração de stick-slip deve-se levar em consideração, além da variação de torque, o torque máximo de cada ciclo de stick-slip. Além disso, o uso do acelerômetro para avaliação de ensaios de stick-slip mostrou-se viável e seu uso deve ser estimulado em trabalhos futuros. / In automotive brake systems, the main component that determines their performance is the friction material, because good friction material must ensure stability in friction under different conditions of use, as well as corrosion resistance, long life, low wear rate, good relation between cost and performance, and low noise. Since the comfort of vehicles has become important factor to indicate its quality, eliminate or reduce the noise and vibration of its components has become a competitive advantage in the automotive market, and the problem of noise in brake systems has been a cause of customer complaints in recent years. The brake noise is most often the result of a self-excited vibration induced friction or dynamic instability of the brake system. The stick-slip phenomenon is a typical example of oscillation induced by friction observed at low sliding speeds and generally results in vibrations which generate noise. In order to check the feasibility of using vibration measurements during the occurrence of the stick-slip phenomenon in the characterization of friction materials using a tribometer, were prepared six friction materials produced by the company Fras-le, manufacturer of friction materials for automotive brake. The tests were performed in the Laboratory of Tribology (Latrib) of the School of Engineering at Federal University of Rio Grande do Sul (UFRGS). In tribometer used for testing an accelerometer was installed on the support of the pad of friction material to be tested. Several tests were conducted, each under constant normal force and speed of rotation of the disk. The test results showed that the tribometer shows excellent performance for characterization of friction materials, enabling the development of new materials from tests performed on this equipment. The evaluation of the response of vibration acceleration obtained in the tests demonstrated that the response of vibration is dependent on various measured parameters, such as displacement, velocity and torque variation, and to better predict the propensity of a material to present vibration stickslip must take into account both the variation of torque and the maximum torque of each cycle of stick-slip. Furthermore, the use of accelerometer for assessing stick-slip tests was viable and its use should be encouraged in future work.

Nos sistemas de freio automotivo, o principal componente que determina seu desempenho é o material de fricção, pois um bom material de fricção deve garantir estabilidade no atrito em diferentes condições de uso, além de possuir resistência à corrosão, longa vida útil, baixa taxa de desgaste, boa relação custo versus desempenho e baixo ruído. Desde que o conforto dos veículos tornou-se um fator importante para indicar sua qualidade, eliminar ou reduzir os ruídos e vibrações de seus componentes passou a ser uma vantagem competitiva no mercado automotivo, e, o problema de ruído nos sistemas de freios vem sendo um dos maiores causadores de reclamações de clientes nos últimos anos. O ruído de freio é na maioria das vezes o resultado de uma vibração auto excitada induzida pela fricção ou uma instabilidade dinâmica do sistema de freio. O processo de stick-slip é um típico exemplo de oscilação induzida por atrito, observada em baixas velocidades de deslizamento e geralmente resulta em vibrações, que geram ruídos graves e rangidos. Com o objetivo de verificar a viabilidade da utilização das medições de vibração durante a ocorrência do fenômeno do stick-slip para a caracterização de materiais de fricção utilizando um tribômetro, foram preparados seis materiais de fricção produzidos pela empresa Fras-le, fabricante de materiais de fricção para freios automotivos. Os ensaios foram realizados no Laboratório de Tribologia (Latrib) da Escola de Engenharia da Universidade Federal do Rio Grande do Sul (UFRGS). No tribômetro utilizado nos ensaios foi instalado um acelerômetro sobre o suporte onde é fixada a pastilha do material de fricção a ser ensaiado. Vários ensaios foram realizados, cada um sob ação de força normal e velocidade de giro do disco constantes. Os resultados dos ensaios demonstraram que o tribômetro apresenta excelente desempenho para caracterização de materiais de fricção, possibilitando o desenvolvimento de novos materiais a partir de ensaios realizados neste equipamento. A avaliação da resposta da aceleração da vibração obtida nos ensaios demonstrou que a resposta da vibração é dependente dos diversos parâmetros medidos, como deslocamento, velocidade e variação de torque, e para melhor prever a propensão de um determinado material em apresentar vibração de stick-slip deve-se levar em consideração, além da variação de torque, o torque máximo de cada ciclo de stick-slip. Além disso, o uso do acelerômetro para avaliação de ensaios de stick-slip mostrou-se viável e seu uso deve ser estimulado em trabalhos futuros. / In automotive brake systems, the main component that determines their performance is the friction material, because good friction material must ensure stability in friction under different conditions of use, as well as corrosion resistance, long life, low wear rate, good relation between cost and performance, and low noise. Since the comfort of vehicles has become important factor to indicate its quality, eliminate or reduce the noise and vibration of its components has become a competitive advantage in the automotive market, and the problem of noise in brake systems has been a cause of customer complaints in recent years. The brake noise is most often the result of a self-excited vibration induced friction or dynamic instability of the brake system. The stick-slip phenomenon is a typical example of oscillation induced by friction observed at low sliding speeds and generally results in vibrations which generate noise. In order to check the feasibility of using vibration measurements during the occurrence of the stick-slip phenomenon in the characterization of friction materials using a tribometer, were prepared six friction materials produced by the company Fras-le, manufacturer of friction materials for automotive brake. The tests were performed in the Laboratory of Tribology (Latrib) of the School of Engineering at Federal University of Rio Grande do Sul (UFRGS). In tribometer used for testing an accelerometer was installed on the support of the pad of friction material to be tested. Several tests were conducted, each under constant normal force and speed of rotation of the disk. The test results showed that the tribometer shows excellent performance for characterization of friction materials, enabling the development of new materials from tests performed on this equipment. The evaluation of the response of vibration acceleration obtained in the tests demonstrated that the response of vibration is dependent on various measured parameters, such as displacement, velocity and torque variation, and to better predict the propensity of a material to present vibration stickslip must take into account both the variation of torque and the maximum torque of each cycle of stick-slip. Furthermore, the use of accelerometer for assessing stick-slip tests was viable and its use should be encouraged in future work.

Nos sistemas de freio automotivo, o principal componente que determina seu desempenho é o material de fricção, pois um bom material de fricção deve garantir estabilidade no atrito em diferentes condições de uso, além de possuir resistência à corrosão, longa vida útil, baixa taxa de desgaste, boa relação custo versus desempenho e baixo ruído. Desde que o conforto dos veículos tornou-se um fator importante para indicar sua qualidade, eliminar ou reduzir os ruídos e vibrações de seus componentes passou a ser uma vantagem competitiva no mercado automotivo, e, o problema de ruído nos sistemas de freios vem sendo um dos maiores causadores de reclamações de clientes nos últimos anos. O ruído de freio é na maioria das vezes o resultado de uma vibração auto excitada induzida pela fricção ou uma instabilidade dinâmica do sistema de freio. O processo de stick-slip é um típico exemplo de oscilação induzida por atrito, observada em baixas velocidades de deslizamento e geralmente resulta em vibrações, que geram ruídos graves e rangidos. Com o objetivo de verificar a viabilidade da utilização das medições de vibração durante a ocorrência do fenômeno do stick-slip para a caracterização de materiais de fricção utilizando um tribômetro, foram preparados seis materiais de fricção produzidos pela empresa Fras-le, fabricante de materiais de fricção para freios automotivos. Os ensaios foram realizados no Laboratório de Tribologia (Latrib) da Escola de Engenharia da Universidade Federal do Rio Grande do Sul (UFRGS). No tribômetro utilizado nos ensaios foi instalado um acelerômetro sobre o suporte onde é fixada a pastilha do material de fricção a ser ensaiado. Vários ensaios foram realizados, cada um sob ação de força normal e velocidade de giro do disco constantes. Os resultados dos ensaios demonstraram que o tribômetro apresenta excelente desempenho para caracterização de materiais de fricção, possibilitando o desenvolvimento de novos materiais a partir de ensaios realizados neste equipamento. A avaliação da resposta da aceleração da vibração obtida nos ensaios demonstrou que a resposta da vibração é dependente dos diversos parâmetros medidos, como deslocamento, velocidade e variação de torque, e para melhor prever a propensão de um determinado material em apresentar vibração de stick-slip deve-se levar em consideração, além da variação de torque, o torque máximo de cada ciclo de stick-slip. Além disso, o uso do acelerômetro para avaliação de ensaios de stick-slip mostrou-se viável e seu uso deve ser estimulado em trabalhos futuros. / In automotive brake systems, the main component that determines their performance is the friction material, because good friction material must ensure stability in friction under different conditions of use, as well as corrosion resistance, long life, low wear rate, good relation between cost and performance, and low noise. Since the comfort of vehicles has become important factor to indicate its quality, eliminate or reduce the noise and vibration of its components has become a competitive advantage in the automotive market, and the problem of noise in brake systems has been a cause of customer complaints in recent years. The brake noise is most often the result of a self-excited vibration induced friction or dynamic instability of the brake system. The stick-slip phenomenon is a typical example of oscillation induced by friction observed at low sliding speeds and generally results in vibrations which generate noise. In order to check the feasibility of using vibration measurements during the occurrence of the stick-slip phenomenon in the characterization of friction materials using a tribometer, were prepared six friction materials produced by the company Fras-le, manufacturer of friction materials for automotive brake. The tests were performed in the Laboratory of Tribology (Latrib) of the School of Engineering at Federal University of Rio Grande do Sul (UFRGS). In tribometer used for testing an accelerometer was installed on the support of the pad of friction material to be tested. Several tests were conducted, each under constant normal force and speed of rotation of the disk. The test results showed that the tribometer shows excellent performance for characterization of friction materials, enabling the development of new materials from tests performed on this equipment. The evaluation of the response of vibration acceleration obtained in the tests demonstrated that the response of vibration is dependent on various measured parameters, such as displacement, velocity and torque variation, and to better predict the propensity of a material to present vibration stickslip must take into account both the variation of torque and the maximum torque of each cycle of stick-slip. Furthermore, the use of accelerometer for assessing stick-slip tests was viable and its use should be encouraged in future work.

No description available.

No description available.

The failure of oil well drillstrings due to torsional and longitudinal stresses caused by stick-slip phenomena during the drilling operation causes great expense to industry. Due to the complicated and harsh drilling environment, modelling of the drillstring becomes an essential requirement in studies. Currently, this is achieved by modelling the drillstring as a torsional lumped model (which ignores the length of the drillstring) for real-time measurement and control. In this thesis, a distributed-lumped model including the effects of drillstring length was developed to represent the drillstring, and was used to simulate stick-slip vibration. The model was developed with increasing levels of detail and the resultant models were validated against typical measured signals from the published literature. The stick-slip model describes the friction model that exists between the cutting tool and the rock. Based on theoretical analysis and mathematical formulation an efficient and adaptable model was created which was then used in the application of a method of species conserving genetic algorithm (SCGA) to optimise the drilling parameters. In conclusion, it was shown that the distributed-lumped model showed improved detail in predicting the transient response and demonstrated the importance of including the drillstring length. Predicting the response of different parameters along the drillstring is now possible and this showed the significant effect of modelling the drillcollar. The model was shown to better represent real system and was therefore far more suited to use with real time measurements. / Iraqi Government, Ministry of Higher Education and Scientific Research.