L’objectif de cette thèse est d’approfondir la connaissance sur la génération et la propagation des ondes à travers l’interface de contact afin de contrôler leurs effets sur le frottement, contrôler les instabilités et réduire les phénomènes d'usure. Le travail est organisé en deux parties principales. La première partie est axée sur une analyse non-linéaire par éléments finis en grandes transformations; la rupture dynamique à l’interface de contact avec frottement, qui sépare deux corps (isotropes et élastiques) en condition de pré-charge statique, est simulée. On définit comme étant une rupture une zone, initialement en adhérence, qui change son état en devenant glissante. Les propriétés des ruptures sont analysées pour une surface plane entre deux matériaux différents en fonction de l’énergie de nucléation; l’effet de la rugosité de surface est ensuite analysée. En outre, la rupture "cumulatives" dans les aspérités et les conditions pour le couplage ou le non-couplage entre les ondes qui se propagent dans les deux corps sont étudiées. Dans la deuxième partie, l'amorçage du glissement entre deux corps en contact constitués de matériaux différents et séparés par une interface avec frottement, est simulée. L’évolution, en fonction du temps, des forces globales (normale et tangentielle) a été mise en relation avec les phénomènes locaux qui se déroulent à l’interface. L'analyse montre comment les micro-slips à l'interface, en agissant comme ruptures localisées, déclenchent les macro-slips entre les deux corps. L'interaction entre les dynamiques locale du contact et globale du système a été aussi étudiée. Enfin, une analyse paramétrique est menée en fonction de plusieurs paramètres (loi de contact, coefficient de frottement, amortissement matériau, charge normale, etc.). Les résultats mettent en avant le rôle-clé des micro-slips et des précurseurs (propagations d'ondes détectables qui ont lieu pour des valeurs de la force tangentielle globale inférieures à la valeur prévue par la loi de frottement) dans l'amorçage du macro-slip entre les deux corps. En fonction de leur distribution et de leur intensité, l'évolution des forces de contact change en passant d'un comportement de type stick-slip à un glissement continu. La dynamique locale au contact (propagation des ondes et ruptures) a été reliée au comportement global du système (stick-slip, glissement continu, vibrations induites); l'effet des paramètres du contact et du système sur le transfert d'énergie vibrationnelle entre le contact glissant et le système a également été examinée: en fonction de leurs valeurs, on peut avoir différentes modalités d'excitation du système (par une distribution de micro-slips ou par des macro-slips) et différentes processus de propagation et dissipation d'énergie. Les résultats numériques obtenus dans les deux parties de la thèse sont cohérents avec les résultats expérimentaux de la littérature. / 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.

This study describes the personal experience of heath care workers after a needle stick injury. The process of enquiry is embedded in a post modernistic ecosystemic perspective to elicit common themes in the health care workers’ (HCW) experiences of a Needle stick injury (NSI). Themes that emerged related mainly to the participants experience after having had a NSI. In the HCW environment HIV/AIDS is very well known disease. It is ironic that the HCW system at large is in denial regarding the dangers which the HCW’s face on a day to day basis working in a ‘mine field’ where every patient is a potential life threat to the HCW. From an ecosystemic stance one can clearly see the ecological principle at play. The HCW system seems to be stuck in a negative feedback process as the status quo is maintained by the defence/coping mechanisms. Adaptation seems to be limited. This inability to compensate leads to the disillusionment of the HCW who has to use ‘acceptable’ defence/coping mechanisms to deal with the trauma of being threatened by HIV/AIDS. The researcher found it constructive to use psychodynamic language, as defence mechanisms are psychodynamic concepts, to describe the process of the HCW system. As Keeney (1983) said that we are not surrounded, in a world of opposition, but rather in a realm of both/and dichotomies. The one cannot exit without, nor be discarded for, the other. Therefore, it could be suggested that an understanding of both systems and psychodynamic concepts may be a helpful tool in understanding and describing the processes of human interaction within an ecosystemic framework. / Dissertation (MA (Counselling Psychology))--University of Pretoria, 2007. / Psychology / unrestricted

This thesis highlights generic aspects of contact angle hysteresis and stick-slip motion,encountered in most practical wetting situations.First, we study the scaling relation between the heterogeneity strength and the amplitudeof the contact angle hysteresis it induces in the model configuration of a chemicallyheterogeneous microchannel. A key parameter which determines the qualitativefeatures is the heterogeneity wavelength. In particular, we identify a near-thresholdbehavior where the quadratic scaling between the heterogeneity amplitude and the resultinghysteresis, already known for a dilute system of wetting defects, is explainedby the closeness to the threshold, and a macroscopic limit without observable stick-slipwhere this scaling is linear.In the second part, we adapt the description to the configuration of a meniscusaround a wavy fibre. This adaptation brings the generic results of the first part in thereach of experiments. A comparison with experiments is achieved at the level of theindividual topography-induced jumps.In the third part, we expand the formulation to treat the quasi-steady interface shapecontact line dynamics and study how the the presence of stick-slip motion at the observableor unobservable scale modifies the scaling relation between the contact linevelocity and contact angle. We recover the known result that the scaling exponent dependson the nature of the externally controlled parameter, identify the causes of thisdependency in the corresponding static limits, and predict the disappearance of this dependencyabove a critical velocity which decreases with the heterogeneity wavelength.Finally, we show trough examples how the modelling framework which permitscapturing contact angle hysteresis and stick-slip motion in a minimalistic way can beadopted to treat configurations with a finite amount of contact points, or the 3D problemof a drop with a deformed contact line. We discuss the arising configuration-specificeffects, also in configurations of biomimetic interest. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Introduktion Operationssjuksköterskor handhar dagligen vassa instrument och har ett nära samarbete med operatören. Det finns risk för stick- och skärskador, varför flera utarbetade preventiva metoder finns att tillgå. Instrumenteringen av vassa instrument ska vara effektiv och säker. Handhavandet kräver kunskap och ställer krav på operationssjuksköterskan. Syfte Syftet med studien var att beskriva operationssjuksköterskors upplevelser av det intraoperativa handhavandet av vassa instrument. Metod Kvalitativ metod med induktiv ansats och individuella semistrukturerade intervjuer. Data analyserades genom manifest och latent innehållsanalys. Resultat Sju underkategorier, tre huvudkategorier samt ett övergripande tema framkom. Operationssjuksköterskorna var trygga i sin roll och arbetade med lugnt och fokuserat förhållningssätt utifrån personligt utformade arbetssätt för att bevara kontrollen. Säkert handhavande hos operatören upplevdes respektfullt och operationssjuksköterskorna anpassade sig och sade ifrån när riskfyllt handhavande observerades. Vid stick- och skärskada var professionellt handlande med bevarad aseptik angeläget. En viss rädsla för blodburen smitta fanns, men de såg samtidigt stick- och skärskador som en del av vardagen i deras arbetsmiljö. Slutsats Operationssjuksköterskorna var trygga i handhavandet av vassa instrument vilket gav dem förmåga till att anpassa sig. Konsekvent användande av personligt utformade arbetssätt upplevdes säkert och bidrog till kontroll. Stick- och skärskadepreventiva metoder användes i synnerhet vid känd blodburen smitta då rädsla förelåg att drabbas av smitta. / Introduction Theatre nurses manages sharp instruments and works closely with the surgeon. There is a risk of sharps injury and several developed preventative methods are avaliable. Instrumentation of sharp instruments must be effective and safe. The management requires knowledge and puts demands on the theatre nurse. Aim To describe the theatre nurses’ experiences of the intraoperative management of sharp instruments. Method Qualitative method with an inductive approach and individual semi-structured interviews. Data was analyzed with manifest and latent content analysis. Results Seven subcategories, three main categories and one covering theme. Theatre nurses were confident in their role and worked with a calm and focused approach with own personal designed work routines to maintain control. Safe management by the surgeon led to feelings of respect towards the theatre nurses and they adapted and reprimanded the surgeon when hazardous management was observed. In case of sharps injury, professional managing with remained asepsis was important. There was some level of fear towards bloodborne pathogen, but at the same time they saw sharp injuries as a common occurrence in their work environment. Conclusion Theatre nurses were confident in the management of sharp instruments which gave them the ability to adapt. Consistent use of personal designed work routines was percieved as safe and contributed to control. Preventative methods against sharps injury were especially used in care of patients with known bloodbourne pathogene as there was a fear of being infected.

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An experimental technique for conducting low speed impact of adhesively bonded automotive composite joints is presented. Based on the use of a modified drop tower, mode I, II, and mixed mode values for critical energy release rate were determined for a composite/epoxy system and used to create a fracture failure envelope. Because load measurements become erratic and unreliable at higher test rates, displacement-based relationships were used to quantify these energy release rates. Displacement data was collected with an imaging system that utilized edge detection to determine displacement profiles, end displacements, and opening displacements where applicable. Because of the resolution of the image-based approach used, determining crack length experimentally was extremely difficult. As a result, numerical methods were developed to objectively determine the crack length based on the available experimental data in mode I, II, and mixed mode I/II configurations. This numerical method uses a nonlinear fit to determine mode I crack lengths and a theoretical model based on cubic equations for mode II and mixed-mode I/II, where the coefficients of the equations are determined by using both boundary and transition conditions that are a result of the test setup. A double cantilever beam (DCB) geometry was chosen to collect mode I data, an end-loaded split (ELS) geometry was used for mode II, and a single leg bend (SLB) geometry was used for mixed-mode I/II. These geometries were used to determine the fracture characteristics of adhesively bonded automotive composites to create fracture failure envelopes as well as provide mode I, II, and mixed-mode I/II data to be used in finite element models. The chosen adhesive exhibited unstable, stick-slip crack growth, which resulted in very few data points being collected from each static DCB specimen as well as drastic drops in energy release rate between initiation and arrest points. Unstable growth also created issues in dynamic testing, as data points surrounding these "stick-slip" events were lost due to the insufficient sampling rate of the available imaging system. Issues also arose with differences between thick and thin composite adherend specimens. These differences could result from additional curing in thick adherend composite specimens due to the adherends retaining heat. DSC testing was conducted on uncured adhesive using a 2, 5, and 10 minute hold at the cure temperature, and significant additional curing was observed between the two and five minute cures. Due to the difference in relative stiffness between the 12 and 36 ply composite, the local loading rate at the crack tip was lower in the 12 ply adherends, possibly allowing for a larger plastic zone and thus a higher energy release rate. As a result, tests were conducted on 36 ply composite specimens at rates of 1 mm/min and 0.1 mm/min to determine if there were loading rate effects. This testing showed that higher initiation energy relase rates were found at the lower test rate, thus reinforcing the local loading rate theory. Due to issues with plastic deformation in aluminum adherends, mode II and mixed-mode I/II data were collected using only composite adherends. Only one data point was collected per specimen as the crack propagated directly into the composite after initiating from the precrack, thus multiple tests were conducted to collect sufficient data for constructing a failure envelope. Once mode I, II and mixed-mode I/II fracture data was collected, a fracture failure envelope was created. This failure envelope, combined with a predetermined factor of safety, could provide some of the necessary tools for design with this adhesive/composite system. / Master of Science

[pt] Nesta tese, a teoria das hastes de Cosserat é revisitada e aplicada à dinâmica de coluna de perfuração. O objetivo é estudar o comportamento dessas estruturas dentro de poços de petróleo curvos. Para atingir este objetivo, um modelo estrutural determinístico é construído onde as tubos de perfuração (drill-pipes) e o conjunto de fundo (bottom hole assembly) são considerados como uma estrutura unidimensional de Cosserat. Em seguida, é desenvolvida uma estratégia para tratar o contato lateral em poços com configuração curvilínea. Depois disso, o problema de contorno livre é tratado mediante uma estratégia que considera como a condição de borda evolui à medida que a estrutura de perfuração avança. Isto é feito mediante uma formulação de interação broca-rocha que deve considerar a dinâmica de corte. Para isso, uma equação extra, de advecção, é resolvida junto com as equações de movimento de Cosserat. Em seguida, alguns casos de aplicação são apresentados. Numa primeira instancia, alguns elementos do problema são avaliados separadamente. Seguidamente, eles são integrados e analisados de forma conjunta. Por exemplo, primeiramente uma coluna de perfuração sem contato de fundo (off-bottom) é simulada, ou seja, sem contato broca-rocha, para estudar o comportamento e a implementação da estratégia para o contato lateral. Aqui também são calibrados alguns dos parâmetros do modelo de atrito. Em seguida, a estratégia para contabilizar o corte na rocha é implementada em um modelo 2-DOF de baixa dimensão e em um semi-discreto onde a dinâmica de torção é modelada como uma equação de onda. Os resultados mostram que o uso de abordagens contínuas resulta mais apropriade que aquelas onde se utilizam modelos de baixa dimensãom, particularmente quando são consideradas colunas longas, e quando há interesse em analisar não apenas o comportamento da broca, mas também o comportamento do sistema mecânico ao longo dos tubos de perfuração. Isso é reforçado por outro exemplo onde a dinâmica de corte é combinada com a formulação de Cosserat. Observações semelhantes do ponto de vista qualitativo são encontradas. Resumindo os resultados obtidos, as diferenças nas previsões dadas pelos modelos de baixa dimensão e o de unidimensional de Cosserat justificam o desenvolvimento e aplicação da abordagem com esta formulação em estruturas de perfuração. Finalmente, a modo de introduzir outro aspecto importante em colunas de perfuração e que pode ser uma linha de pesquisa para continuar o trabalho, a variabilidades presente em elementos como rocha, inclui-se um caso de aplicação considerando um poço horizontal e um campo estocástico de atrito. / [en] In this thesis, the theory of Cosserat rods is applied to the dynamics of drill-strings. The main objective is to evaluate the behaviour of these strings when they move within curved wells. To achieve this goal, a deterministic structural model is constructed, where the drill-pipes and the bottom hole assembly are taken as a Cosserat rod. Next, a strategy to deal with the lateral contact in curved well configurations is developed. After that, the free boundary problem is assessed: while drilling, the boundary changes due to cutting, modifying the position of the soil and, consequently, changing the bit-rock interaction forces. For this reason, a bit-rock model that can account for the cutting dynamics is adopted, in which an extra advection equation is solved together with the equations of motion of the Cosserat rod. Next, application cases are provided. First, some effects included in the model are tested in isolation, such as the lateral friction, the lateral contact, and the cutting. After that, they are all combined. In the first analysis, an off-bottom string is simulated, i.e. without contact at the bit. This allows testing the formulation associated with the lateral contact. Also, the calibration of the lateral friction parameters is made. Following that, the strategy to account for the cutting at the bit is implemented in a low-dimensional 2-DOF model, and in a semi-discrete model with a continuous wave equation for the torsional dynamics. The results show that the use of continuous approaches is more appropriate than low-dimensional models. Especially when long columns are considered, and when there is interest in understanding not only the behaviour at the bit but also along drill-pipes. This finding is reinforced by another application where the cutting dynamics are combined with the Cosserat rod formulation. Again, similar observations from a qualitative point of view are found. Overall, the differences in the results between the lumped low-dimensional models and the continuous Cosserat rod justify the development and application of the Cosserat approach to drilling structures. Finally, an introductory stochastic analysis concerning the variability of the rock is presented as an introduction to a future line of research, where stochasticity is included. / [es] En esta tesis, la teoria de Cosserat para elementos unidimensionales es revisitada y aplicada a la simulación de columnas de perforación. El objetivo es estudiar el comportamiento de estas estructuras en pozos de geometría curva. Para alcanzar este objetivo se construye un modelo determinístico. En este modelo, los caños de perforación (drill-pipes) y el conjunto de fondo (bottom hole assembly) son modelados como una estructura unidimensional de Cosserat. Seguidamente, una estrategia para tratar con el contacto lateral en pozos curvos es desarrollada. Luego, el problema de frontera libre es estudiado: durante la perforación, la condición de borde cambia debido al cambio del perfil altimétrico del terreno, alterando su posición y consecuentemente las fuerzas asociadas a la interacción broca-roca. Por esta razón, se decide utilizar un modelo de interacción broca-roca que tiene en cuenta la dinámica del corte. En este abordaje una ecuación extra, la ecuación de advección, es resuelta en forma acoplada con las ecuaciones del movimiento de la estructura de Cosserat. Algunos ejemplos de aplicación son presentados. En una primera instancia, algunos de los elementos del problema son estudiados en forma aislada. Luego combinados en un modelo completo. Por ejemplo, el caso de una columna sin contacto de fondo (off-bottom) es tratado para evaluar el comportamiento y la implementación de la estrategia mencionada para detectar el contacto lateral. Además, se efectúa la calibración de alguno de los parámetros relacionados con la fricción lateral. Luego, la estrategia para considerar el corte en la punta es implementada en un modelo de 2-DOF, y en otro semi-discreto donde se considera un modelo de ecuación de onda para la dinámica torsional. Los resultados muestran que el uso de formulaciones continuas es más apropiado que aquellas formulaciones donde se utilizan modelos de dimensiones reducidas, particularmente cuando se estudia columnas largas donde el interés se centra en entender no solo el comportamiento de la broca sino también a lo largo de la tubería. Este resultado es reforzado por otro caso de aplicación en donde se combina la dinámica de corte con un modelo de Cosserat. Observaciones similares son vistas en el comportamiento cualitativo de la solución. En resumen, las diferencias observadas en los diferentes ejemplos de aplicación entre los modelos de dimensiones reducidas y el modelo continuo de Cosserat justifican el desarrollo y la aplicación de la teoría de Cosserat a estructuras de perforación. Finalmente, dado que uno de los objetivos planteados también es considerar la variabilidad en algunos elementos como ser las propiedades de la roca, un caso de aplicación considerando un pozo horizontal es mostrado.

This research investigates the modeling of randomly distributed surface-breaking microcracks and their effects on higher harmonic generation in Rayleigh surface waves. The modeling is based on micromechanical considerations of rough surface contact. The nonlinear behavior of a single microcrack is described by a hyperelastic effective stress-strain relationship. Finite element simulations of nonlinear wave propagation in a solid with distributed microcracks are performed. The evolution of fundamental and second harmonic amplitudes along the propagation distance is studied and the acoustic nonlinearity parameter is calculated. The results show that the nonlinearity parameter increases with crack density and root mean square roughness of the crack faces. While, for a dilute concentration of microcracks, the increase in acoustic nonlinearity is proportional to the crack density, this is not valid for higher crack densities, as the microcracks start to interact. Finally, it is shown that odd higher harmonic generation in Rayleigh surface waves due to sliding crack faces introduces a friction nonlinearity.