Dissertations / Theses on the topic 'Fracture Stability'

Physical vapor deposited hard coatings comprised of cubic (c) transition metal (TM)-Al-N, and (TM)-Si-N are the current work horse materials for a large number of metal cutting and wear resistant applicatíons to light against the extreme conditions of temperature and stress simultaneously. In spite of a high degree of sophisticatíon in terms of material choice and microstructural design, a lower fracture resistance and limited thermal stability of the coatings remains a technological challenge in the field. The lower fracture resistance ofthe coating is an inherent material property. Limited thermal stability in the TM-Al-N system is associated with the transformation of metastable c -AIN to its stable wurtzite (w)-AIN phase ata temperature above 900 oC resulting an undesirable hardness drop. The current work shows how to overcome these challenges by manipulaling the coating material at different length scales, i.e. microstructure, crystal and interface structure, and alloy design. The endeavor of multiscale materials design is achieved by converging a deeper material and process knowledge to result specific structural modification over multiple length scales by alloying transition metal nitrides with AIN and SiNxs following. Microstructure variation is achieved in ZrN coating by alloying it with SiNx, where the surface segregated SiNx breaks down the columnar structure and evolves a self-organized nanocomposite structure with a hardness variation from 37 ±2 GPa to 26 ±1 GPa. The indentation induced fracture studies reveal crack deflection for the colum nar coating, likely a long the coiumn boundaries. The crack deflection olfers additional energy dissipative mechanisms that make the columnar structured coating more fracture resistant, which is not the case fur the nanocomposite coating in spite of its lower hardness. Crystal structure of AIN is variad between stable wurtzite structure to metastable cubic structure in the ZrAIN alloy by adapting a mullilayer structure and tuning the layerthickness. The multilayer consisting c-AIN layer shows a hardness of 34 ±1 GPa anda twofold enhancement in the critica! force to cause an indentation induced surface crack compared to the multilayer containing w-AIN in spite of a lower hardness for the later case. The higher fracture resistance is discovered to be ca u sed by stress- induced transformation of /IJN from its metastable cubic structure to its thermodynamically stable wurtzite structure associated with a molar volume expansion of20% that builds up local compressive stress zones delay;ng the onset and propagation of the cracks. This is in fact the first experím en tal data point for the stress-induced transfurmation toughening in a hard coatíng. The current work also demonstrates a concept of im proving the thermal stabilíty ofTM-Al-N by m odifying the interface structure between w-AIN and c-TMN. A popular belief in the field is that AIN in lis stable wurtzite structure is detrimental to coating hardness, and hence the curren! material design strategy Is to force AIN in metas table cubic phase that confines the application temperature (- 900 oC). In contrast, here it is shown that the w-AIN offers a high hardness provided if it is grown (semi-)coherent to c-TMN. This is experimentally shown for lhe multilayer system ofTiN/ZrAIN. The interface structure between the c-TiN, c-ZrN and w-AIN is transformed from incoherent to (semi-)coherent structure bytuning the growth conditions under a favorable crystallographic template. Furthennore, the low energy(semi-) coherent interface structure between w-AIN and c- TiN, c- ZrN display a high thermal stability, causing a high and more stable hardness up to an annealing temperature of 1150 oC with a value of34± 1.5 GPa. This value is 50 % higher comparad to the state-of-the-art monolithic and multilayered Ti-/IJ -N and Zr-Al-N coating containing incoherent w-AIN. Finally, an entropy based alloy design concept is explorad to form a thermodynamic<br>Los recubrimientos duros formados por metales de transición (TM) cúbicos -AlN, y -SiN depositados mediante fase de vapor (CVD) son materiales extensamente utilizados en gran número de aplicaciones de corte y de desgaste bajo condiciones extremas de temperatura y solicitaciones mecánicas. A pesar de un alto grado de sofisticación en cuanto a la selección del material y el diseño microestructural, la baja resistencia a la fractura y la limitada estabilidad térmica sigue siendo un importante reto tecnológico. La variación microestructural en los recubrimientos de ZrN se controla mediante la aleación con SiNx, ya que la segregación superficial de SiNx rompe la estructura columnar y evoluciona a un nanocompuesto autoorganizado con una dureza de entre 37 ±2 GPa y 26 ±1 GPa. Las grietas producidas por indentación muestran la existencia de deflexión de grieta, lo que proporciona un mecanismo de disipación de energía adicional, haciendo de este material más resistente a la generación de grieta.La estructura cristalina del recubrimiento de AlN se varía entre la fase estable wurtzita y la fase cúbica estable ZrAlN mediante el control de la estructura y el espesor de la arquitectura multicapa. El recubrimiento multicapa formado por la fase c-AlN presenta una dureza de 34 ±1 GPa y una resistencia a la generación de grietas por indentación dos veces mayor comparado con el recubrimiento multicapa formado por w-AlN, aunque éste presente una dureza menor. La mayor resistencia a fractura está causada por la transformación inducida por tensión de AlN desde la fase cúbica metaestable a la fase wurtzita termodinámicamente estable acompañada de una expansión molar del 20%, resultando en una generación de tensiones compresivas que retarda la generación y propagación de grietas. Esta es la primera vez que se reporta la existencia de transformación catalizada por tensión en recubrimientos duros. En esta tesis también se demuestra el concepto de mejorar la estabilidad térmica de los recubrimientos basados en TM-Al-N mediante la modificación de la estructura interfacial entre las fases w-AlN y c-TMN. En general la existencia de AlN en su fase estable wurtzita puede ser detrimental para la dureza, y por lo tanto se suele depositar el material en la fase cúbica, lo que limita la temperatura de utilización (~ 900 oC). Esta dureza es un 50%mayor de la dureza reportada para recubrimientos monolíticos y multicapas de Ti-Al-N y Zr-Al-N que contengan fase incoherente de w-AlN. Finalmente, el concepto de aleaciones de alta entropía se utiliza para depositar una solución sólida termodinámicamente estable del sistema TM-Al-N que presenta una entalpía de mezcla positiva. Elementos de aleación multi-principales de (AlTiVCrNb)N se utilizan para formar una solución sólida cúbica . La alta entropía configuracional en la mezcla es mayor que la entalpía, por lo que se espera una formación de solución sólida estabilizada a temperaturas mayores de 1000K. Sin embargo, a temperaturas elevadas, la optimización entre la minimización de la energía de interacción y la maximización del desorden configuracional causa la precipitación de AlN en su estructura wurtzita estable, y la solución sólida cúbica está únicamente confinada entre TiN, CrN , VN y NbN que tienen baja entalpía de mezcla. En resumen, esta tesis presenta soluciones tecnológica a dos retos importantes en el campo. Se consigue una mejora significativa en la resistencia a fractura en los recubrimientos mediante la selección de materiales y el diseño microestructural mediante mecanismos de deflexión de grieta y transformación de fase asistida por tensión. Así mismo, se aumenta la estabilidad térmica de recubrimientos TM-Al-N mediante una nueva microestructura consistente en c-TMN y w-AlN termodinámicamente estable con una estructura interfacial (semi-)coherente de baja energía.

When a patient is diagnosed with various spinal injuries, deformities, or advanced degeneration, it is commonly suggested that he/she undergoes surgery for spinal fusion. Most current procedures in spinal fusion restrict mobility in one or multiple levels of the spine so that, over time, new bone will grow between the levels creating a single motionless unit of bone. The bilateral pedicle screw system (BPSS) has long been considered to be the "gold standard" in spinal fusion. However, for patients with osteoporosis, adequate fixation within the bone-screw interface has continuously been difficult to achieve or has come with high risk of other forms of catastrophic damage. Reflecting this, a new pedicle screw design was developed and evaluated against current standard pedicle screws commonly used in spinal surgery. All screw designs were also tested with a common cement augmentation technique surrounding the circumference of the screw. All tests measured pullout strength, stiffness, energy to failure, toughness, and the amount of destruction to the surrounding synthetic bone. While the newly designed pedicle screw failed to produce significantly stronger pullout forces in comparison to the standard screws, it did show evidence of a longer lasting residual axial resistance and a safer mode of failure than the standard screw, hinting that the design may benefit individuals who experience screw pullout and are awaiting reinstrumentation.

This work included two separate studies; the common theme in each was the use of mode-I fracture testing to evaluate wood adhesion. In the first study, mode-I fracture testing was used to compare the thermal stability of polyurethane (PUR) and resorcinol-formaldehyde (RF) wood adhesives. Bonded specimens for both adhesives were subjected to prolonged thermal exposure, and fracture testing was subsequently conducted after re-equilibration to standard test conditions. It was found that both PUR and RF suffered a significant fracture energy loss after heat treatment, and that RF was more thermally stable than PUR, as expected. However, both adhesives suffered significant thermal degradation, and fracture testing did not distinguish the RF system as being clearly superior to PUR. Dynamic mechanical analysis (DMA) was also used to analyze and compare the thermal softening of PUR and RF in terms of the decline in storage modulus. DMA results indicated that PUR specimens suffered greater stiffness loss due to simple thermal softening. Because fracture testing indicated that both adhesives suffered significant degradation, the DMA results suggested that the generally superior fire resistance of RF adhesives is born from greater high temperature stiffness; whereas the more compliant PUR suffers greater immediate softening during thermal exposure. In other words, both systems suffer from thermal degradation, but the more highly cross-linked RF system suffers less thermal softening and therefore maintains a greater load carrying capacity during fire exposure. In the second study, mode-I fracture testing was used to test the effects of wood surface thermal deactivation (surface energy reduction) on the adhesion between southern pine wood (Pinus spp.) and polyethylene (PE). Pine specimens were progressively surface deactivated by 185°C heat treatments for periods of 5, 15, and 60 minutes. Control and deactivated pine laminae were subsequently hotpressed/bonded using PE film as the adhesive. Mode-I fracture testing was conducted under the assumption of linear elasticity, however load/displacement test curves suffered from a severe degree of nonlinearity believed to be caused by PE bridging behind the advancing crack tip. Instead of applying a nonlinear data analysis, a standard linear elastic analysis was conducted and deemed acceptable for comparative purposes within this study. Under dry conditions (unweathered specimens), 5 and 15 minute thermal treatments resulted in progressively worse adhesion (lower fracture energies) when compared to control surfaces; but the 60 minute heat treatment improved adhesion relative to 5 and 15 minute treatments, and showed a trend of improving adhesion as surface deactivation became more extreme. Simulated-weather resistance was also studied and it was determined that the highest degree of surface deactivation slightly improved weather durability in comparison to control surfaces. Overall, the findings here were similar to those in a previously published work- thermal deactivation of wood surfaces shows promise as a method to improve adhesion between wood and nonpolar polyolefins.<br>Master of Science

Background: We performed a biomechanical comparison of 2 methods for operative stabilization of pronation-abduction stage III ankle fractures; group 1: Anterior-posterior lag screws fixing the posterior tibial fragment and lateral fibula plating (LSLFP) versus group 2: locked plate fixation of the posterior tibial fragment and posterior antiglide plate fixation of the fibula (LPFP). Methods: Seven pairs of fresh-frozen osteoligamentous lower leg specimens (2 male, and 5 female donors) were used for the biomechanical testing. Bone mineral density (BMD) of each specimen was assessed by means of dual-energy x-ray absorptiometry. After open transection of the deltoid ligament, an osteotomy model of pronation abduction stage III ankle fracture was created. Specimens were systematically assigned to LSLFP (group 1, left ankles) or LPPFP (group 2, right ankles). After surgery, all specimens were evaluated via CT to verify reduction and fixation. Axial load was then applied onto each specimen using a servohydraulic testing machine starting from 0 N (Zwick/Roell, Ulm, Germany) at a speed of 10 N/s with the foot fixed in a 10 degrees pronation and 15 degrees dorsiflexion position. Construct stiffness, yield, and ultimate strength were measured and dislocation patterns were documented with a high-speed camera. The normal distribution of all data was analyzed using Shapiro-Wilk test. The group comparison was performed using paired Student t test. Statistical significance was assumed at a P value of .05. Results: All specimens had BMD values consistent with osteoporosis. BMD values did not differ between the left and right ankles of the same pair (P = .762). The mean BMD values between feet of men (0.603 g/cm²) and women (0.329 g/cm²) were statistically different (P = .005). The ultimate strength for LSLFP (group 1) with 1139 ± 669 N and LPPFP (group 2) with 2008 ± 943 N was statistically different (P = .036) as well as the yield in LSLFP (group 1) 812 ± 452 N and LPPFD (group 2) 1292 ± 625 N (P = .016). Construct stiffness trended to be higher in group 2 (179 ± 100 kNn) compared to group 1 (127 ± 73 kN/m) but this difference was not statistically significant (P = .120). BMD correlated with bone-construct failure. Conclusion: Fixation of the posterior tibial edge with a posterolateral locking plate resulted in higher biomechanical stability than anterior-posterior lag screw fixation in an osteoporotic pronation-abduction fracture model. Clinical Relevance: The clinical implication of this biomechanical study is that the posterior antiglide plating might be advantageous in patients with osteoporotic pronation abduction stage III ankle fracture.

Abstract Isolated lateral malleolar supination-external rotation (SER) -type ankle fractures without incongruity on the standard radiographs can be either stable or unstable depending on the status of the deep deltoid ligament. Neither clinical signs of injury on the medial aspect of the ankle nor the displacement of fibular fracture on mortise radiographs seem to predict stability. Therefore, stress testing has been adopted in clinical use. No “gold standard” method exists but the manual external rotation (ER) stress test is the most extensively studied. The ER stress test has some disadvantages, and other methods—such as gravity stress radiography and magnetic resonance imaging—have been suggested instead. However, the evidence to support the use of these methods is still insufficient. The aims of this dissertation were to assess the roles of (1) morphological factors from standard radiographs of 286 patients, (2) clinical findings on the medial side of the ankle and gravity stress radiography of 79 patients, and (3) MRI of 61 patients in evaluating the stability of the ankle mortise in patients with unimalleolar SER-type fractures with no talar shift on standard radiographs. The ER stress test result was considered to be the reference for stability throughout these studies. We found that a fracture line width &lt; 2 mm in lateral radiographs, only two fracture fragments, and female sex are independent factors predicting a stable ankle mortise. Neither clinical signs on the medial side of the ankle nor gravity stress radiography alone predict the stability of the ankle mortise accurately. According to our MRI findings, total tears of the deep deltoid ligaments are rare, and partial tears are common in this this patient group. The reliability of the MRI assessment is only moderate. In conclusion, patients with non-comminuted fractures and &lt; 2 mm displacement on lateral radiographs have stable ankle mortises and need no further stress testing. The gravity stress radiography is an accurate test for the evaluation of the ankle mortise stability only if the clinical signs indicate a similar result with the gravity stress radiographs. The use of MRI provides no additional benefit compared to ER stress testing for stability evaluation of an SER-type ankle fracture<br>Tiivistelmä Supinaatio-ulkokiertomekanismilla syntyneet isoloidut ulkokehräsluun murtumat ilman röntgenkuvassa näkyvää telaluun siirtymää voivat olla joko vakaita tai epävakaita nilkan sisemmän nivelsiteen syvän lehden tilasta riippuen. Kliinisessä tutkimuksessa todettujen nilkan sisäreunan vamman merkkien tai röntgenkuvauksella todettavan ulkokehräsluun murtuman virheasennon ei ole osoitettu ennustavan nivelhaarukan mahdollista epävakautta, joten nilkkaa kuormittaen tehtäviä röntgenkuvauksia on otettu kliiniseen käyttöön. Mikään näistä kuvausmenetelmistä ei ole niin sanottu kultainen standardi, mutta ulkokiertovääntötestiä (ER-testi) on tutkittu laajimmin. ER-testin käyttöön liittyy kuitenkin ongelmia, joiden vuoksi niin sanottua painovoimakuvausta tai muun muassa magneettikuvausta (MRI) on ehdotettu käytettäväksi sen sijaan. Näiden menetelmien käyttöä tukeva tieteellinen näyttö on kuitenkin vielä riittämätöntä. Tämän väitöskirjatyön tarkoituksena oli tutkia (1) 286 potilaan tavallisista kuormittamattomista röntgenkuvista morfologisten tekijöiden, (2) 79 potilaan nilkan sisäreunan kliinisen tutkimuksen ja painovoimakuvauksen sekä (3) 61 potilaalla MRI:n merkitystä ja tarkkuutta arvioitaessa supinaatio-ulkokiertomekanismilla syntyneiden ulkokehräsluun murtumien vakautta. ER-testin tulosta käytettiin referenssinä nivelhaarukan vakaudelle kaikissa osatöissä. Sivukuvasta mitattuna ulkokehräsluun murtuman leveys &lt; 2 mm, vain kahden kappaleen murtuma ja naissukupuoli ovat itsenäisiä vakaata nivelhaarukkaa ennustavia tekijöitä. Kliininen tutkimus tai painovoimakuvaus eivät yksinään pysty ennustamaan nivelhaarukan vakautta riittävän tarkasti. MRI:n perusteella sisemmän nivelsiteen syvän lehden täydelliset repeämät ovat tässä vammatyypissä harvinaisia mutta osittaiset repeämät ovat hyvin tavallisia huolimatta ER-testin tuloksesta. MRI:n tulkinnan luotettavuus on ainoastaan kohtalainen. Yhteenvetona voidaan todeta, että ilman ilmeistä telaluun siirtymää röntgenkuvassa yksinkertaiset supinaatio-ulkokiertomekanismilla syntyneet ulkokehräsluun murtumat ovat vakaita eikä nivelhaarukan vakauden testaaminen ole tarpeen, jos murtumaraon leveys sivukuvassa on &lt; 2 mm. Painovoimakuvaus on luotettava, mikäli sen tulos on sama ulkoisten vamman merkkien kanssa. Magneettikuvauksesta ei ole hyötyä arvioitaessa tämän nilkkamurtumatyypin vakautta

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>O estudo de estabilidade do poço visa minimizar eventos indesejáveis, decorrente de um peso de fluido inadequado. No desenvolvimento do projeto de estabilidade mecânica do poço são definidos limites de pressões, onde o valor de pressão máxima aceitável é fornecido pelo gradiente de fratura. Diversos modelos são propostos na literatura a fim de estimar o valor do gradiente de fratura e a base para todos eles consiste numa precisa determinação do modelo geomecânico. Para esse trabalho foi realizado uma pesquisa bibliográfica dos principais modelos propostos para a determinação do gradiente de fratura, comparando resultados obtidos pela simulação de cada modelo com valores reais de pressão de quebra obtidos in-situ. Identificou-se a influência da escolha desse modelo no resultado da Janela Operacional, as principais práticas disponíveis para se determinar o modelo geomecânico e a sua importância no resultado final do valor de gradiente de fratura. Para a análise comparativa os modelos propostos foram divididos em dois grupos definidos como Tensão Mínima e Tensão tangencial. A solução poroelástica apresentada por Detournay e Cheng (1988) foi a que mais se aproximou dos valores reais de pressão de quebra obtidos insitu. Um maior conhecimento a respeito do modelo adotado para o gradiente de fratura é fundamental no processo de otimização de um projeto de estabilidade de poço de petróleo, podendo transformar projetos inviáveis operacionalmente em viáveis.<br>The study of wellbore stability aims to minimize undesirable events, due to a inappropriate weight of fluid The wellbore stability analysis defines limits pressures, where the maximum value pressure acceptable is provided by fracture gradient. Several models have been proposed in the literature to estimate the value of the fracture gradient and the basis for all they are the good determination of the geomechanical model. In this work a research in the literature was performed for the determination of different fracture gradient models, comparing results obtained by the simulation of each model with real values of fracture pressure, obtained in-situ. It was noticed the impact in the result of the Operational Window due to the assumptions from the different fracture gradients models. It was also evaluated the main practices available to determine the geomechanical model and its importance in the final result for the value of the fracture gradient. For comparative analysis, the proposed models were divided into two groups defined as Minimum Stress and Hoop Stress. The solution presented by Detournay and Cheng (1988),was the closest to the real values for fracture gradient obtained in-situ. Increased knowledge about the model adopted for the fracture gradient is fundamental in the process of optimizing the Operational Window.

Objective: To measure the fracture toughness, surface area and volume of a conventional Bis-GMA based resin composite (Filtek Supreme), experimental oxirane/acrylate based resin composite (OASys), and ormocer-based resin composite (Admira) at baseline (control) and after a 15-day exposure to a Streptococcus mutans based biofilm or 30 days storage in water. Methods. A 25 x 5 x 2.8 mm stainless-steel mold with 2.5 mm single edge notch at the center was used, following ASTM standards [E399-90], to fabricate 135 specimens (n=15) and distributed into nine groups based on composite material and aging conditions. For the baseline group, specimens were fabricated and then tested after 24hours storage in water. For the biofilm challenge, specimens were randomly placed in a six well tissue culture plate and kept at 37o C with bacterial growth media (Brain Heart Infusion (BHI); Streptococcus mutans) changed daily for 15 days. BHI medium was supplemented with 0.5% sucrose to promote the establishment of a biofilm for the initial 24 hours. For the water storage challenge, specimens were kept for 30 days in 5 ml of deionized distilled autoclaved water at 37o C and was changed every seven days. Three specimens from each experimental group were randomly selected for μCT evaluation by scanning the specimens before and after the proposed challenge. Fracture toughness (KIc) testing was carried out using a universal test with a load cell capacity of 500 N using three-point bending with 20mm spam at a cross-head speed of 0.5 mm/min. Results. Filtek and Admira mean baseline toughness (KIc) was significantly higher than that observed for water and biofilm challenges. OASys mean fracture toughness values in water were significantly higher than the baseline. Toughness values for OASys in biofilm were not statistically different when compared to either water or baseline. One-way repeated measures statistical test was used, which showed no significant change in volume or surface area regardless of the materials tested or the challenges used (p>0.05). Conclusion. The fracture toughness of the commercially available resin composite materials (Filtek Supreme Ultra, Admira Fusion) was negatively affected by the environmental challenges of 15 days of biofilm challenge and by 30 days of water storage. The experimental composite (OASys) showed a different pattern than the commercially available composite, with an increase in fracture toughness after being stored in water. The μCT evaluation method allowed for physical evaluation without affecting the specimens.

Les simulations numériques des fissures fragiles par les modèles d’endommagement à gradient deviennent main- tenant très répandues. Les résultats théoriques et numériques montrent que dans le cadre de l’existence d’une pre-fissure la propagation suit le critère de Griffith. Alors que pour le problème à une dimension la nucléation de la fissure se fait à la contrainte critique, cette dernière propriété dimensionne le paramètre de longueur interne.Dans ce travail, on s’attarde sur le phénomène de nucléation de fissures pour les géométries communément rencontrées et qui ne présentent pas de solutions analytiques. On montre que pour une entaille en U- et V- l’initiation de la fissure varie continument entre la solution prédite par la contrainte critique et celle par la ténacité du matériau. Une série de vérifications et de validations sur diffèrent matériaux est réalisée pour les deux géométries considérées. On s’intéresse ensuite à un défaut elliptique dans un domaine infini ou très élancé pour illustrer la capacité du modèle à prendre en compte les effets d’échelles des matériaux et des structures.Dans un deuxième temps, ce modèle est étendu à la fracturation hydraulique. Une première phase de vérification du modèle est effectuée en stimulant une pré-fissure seule par l’injection d’une quantité donnée de fluide. Ensuite on étudie la simulation d’un réseau parallèle de fissures. Les résultats obtenus montrent qu’il a qu’une seule fissure qui se propage et que ce type de configuration minimise mieux l’énergie la propagation d’un réseau de fractures. Le dernier exemple se concentre sur la stabilité des fissures dans le cadre d’une expérience d’éclatement à pression imposée pour l’industrie pétrolière. Cette expérience d’éclatement de la roche est réalisée en laboratoire afin de simuler les conditions de confinement retrouvées lors des forages.La dernière partie de ce travail se concentre sur la rupture ductile en couplant le modèle à champ de phase avec les modèles de plasticité parfaite. Grâce à l’approche variationnelle du problème on décrit l’implantation numérique retenue pour le calcul parallèle. Les simulations réalisées montrent que pour une géométrie légèrement entaillée la phénoménologie des fissures ductiles comme par exemple la nucléation et la propagation sont en concordances avec ceux reportées dans la littérature<br>Phase-field models, sometimes referred to as gradient damage, are widely used methods for the numerical simulation of crack propagation in brittle materials. Theoretical results and numerical evidences show that they can predict the propagation of a pre-existing crack according to Griffith’s criterion. For a one- dimensional problem, it has been shown that they can predict nucleation upon a critical stress, provided that the regularization parameter is identified with the material’s internal characteristic length.In this work, we draw on numerical simulations to study crack nucleation in commonly encountered geometries for which closed-form solutions are not available. We use U- and V-notches to show that the nucleation load varies smoothly from the one predicted by a strength criterion to the one of a toughness criterion when the strength of the stress concentration or singularity varies. We present validation and verification of numerical simulations for both types of geometries. We consider the problem of an elliptic cavity in an infinite or elongated domain to show that variational phase field models properly account for structural and material size effects.In a second movement, this model is extended to hydraulic fracturing. We present a validation of the model by simulating a single fracture in a large domain subject to a control amount of fluid. Then we study an infinite network of pressurized parallel cracks. Results show that the stimulation of a single fracture is the best energy minimizer compared to multi-fracking case. The last example focuses on fracturing stability regimes using linear elastic fracture mechanics for pressure driven fractures in an experimental geometry used in petroleum industry which replicates a situation encountered downhole with a borehole called burst experiment.The last part of this work focuses on ductile fracture by coupling phase-field models with perfect plasticity. Based on the variational structure of the problem we give a numerical implementation of the coupled model for parallel computing. Simulation results of a mild notch specimens are in agreement with the phenomenology of ductile fracture such that nucleation and propagation commonly reported in the literature

Background: Open reduction and internal fixation with a plate is deemed to represent the gold standard of surgical treatment for displaced intra-articular calcaneal fractures. Standard plate fixation is usually placed through an extended lateral approach with high risk for wound complications. Minimally invasive techniques might avoid wound complications but provide limited construct stability. Therefore, 2 different types of locking nails were developed to allow for minimally invasive technique with sufficient stability. The aim of this study was to quantify primary stability of minimally invasive calcaneal interlocking nail systems in comparison to a variable-angle interlocking plate. Material and Methods: After quantitative CT analysis, a standardized Sanders type IIB fracture model was created in 21 fresh-frozen cadavers. For osteosynthesis, 2 different interlocking nail systems (C-Nail; Medin, Nov. Město n. Moravě, Czech Republic; Calcanail; FH Orthopedics SAS; Heimsbrunn, France) as well as a polyaxial interlocking plate (Rimbus; Intercus GmbH; Rudolstadt, Germany) were used. Biomechanical testing consisted of a dynamic load sequence (preload 20 N, 1000 N up to 2500 N, stepwise increase of 100 N every 100 cycles, 0.5 mm/s) and a load to failure sequence (max. load 5000 N, 0.5 mm/s). Interfragmentary movement was detected via a 3-D optical measurement system. Boehler angle was measured after osteosynthesis and after failure occurred. Results: No significant difference regarding load to failure, stiffness, Boehler angle, or interfragmentary motion was found between the different fixation systems. A ignificant difference was found with the dynamic failure testing sequence where 87.5% of the Calcanail implants failed in contrast to 14% of the C-Nail group (P < .01) and 66% of the Rimbus plate. The highest load to failure was observed for the C-Nail. Boehler angle showed physiologic range with all implants before and after the biomechanical tests. Conclusion: Both minimally invasive interlocking nail systems displayed a high primary stability that was not inferior to an interlocking plate. Clinical relevance: Based on our results, both interlocking nails appear to represent a viable option for treating displaced intra-articular calcaneal fractures.

Theoretical strength of solids is defined as the ultimate strength beyond which plastic deformation, fracture, or decohesion would occur. Understanding the microscopic origin from quantum mechanics and thermoelastic formulation is of great importance to mechanical properties and engineering design of various solids. While quite a few theory models have been made in the past century by several generations of scientists, including Frankel and Born, a general and convincing framework has not been fully established. We study this issue from three respects: (1) Unify various elastic stability criteria for solids that determine an upper bound of theoretical strength; (2) with ab initio method, we test the elastic stability conditions of crystal Au. The phenomenon of bifurcation is observed: under hydrostatic expansion, the rhombohedral modulus reaches zero first of all; while under uniaxial tensile stress, the tetragonal shear modulus first reaches zero; (3) propose a nonlinear theoretical formulation of stability criterion. As an analytic method, this scheme is quite simple, in the mean time, it saves computation resource.

This thesis investigated the effect of the modification of bone fracture fixation stiffness on the progression of healing. It was hypothesised that fixation stiffness would correlate with callus size, with lower stiffness fixation causing larger callus growth. It was further proposed that subsequent stiffening of this condition at set times would draw benefit from the larger callus, resulting in improved healing. Analyses involved computational and experimental rat models. It was demonstrated that changes in fracture fixation can result in varied tissue growth, with future investigation broaching applications into clinical fracture scenarios.

The aim of this thesis is to describe behavior of cracks in layered polymer materials. Quasi-brittle fracture (through the initiation and subsequent crack propagation mechanism) under low stresses is the most common mode of failure of polymer materials. In this case plastic deformations are localized in the vinicity of the crack tip and linear elastic fracture mechanics description of the crack behavior can be used. The knowledge of fracture parameters change during the crack propagation in multilayer body is a key point for establishing of the maximum load and consequently for the assessment of the residua lifetime. In contrast to homogeneous bodies the estimation of stress intensity factors for multilayer (composite) structure is numerically more elaborated and the fracture mechanics approach is complicated by the existence of interfaces between single layers, where material parameters are changed by a step. Special attention is paid to the configuration of a crack growing close to the material interface and along the interface. For the crack with tip on the material interface the effective values of stress intensity factor based on the crack stability criteria are estimated. It is shown that under special conditions (depending mainly on the elastic mismatch of materials) the existence of material interface has positive influence on the lifetime of the multilayered structure.

In the range of linear elastic fracture mechanics, the conditions for critical loading assessment of structures made of two dissimilar materials are usually based on the assumptions of prevailing normal mode of loading. The same assumption is usually applied to the stability criterion of bi-material notches. However, in engineering practice there are cases of loading and failure closed to the shear mode. The aim of the work is the assumption of the stability criterion of bi-material notches subjected to combination of normal and shear loading. The FEM model of the bi-material notch under combination of normal and shear loading mode is created and solved and evaluated as well.

Made available in DSpace on 2014-12-17T14:57:54Z (GMT). No. of bitstreams: 1 RaimundoNBF_TESE_1-104.pdf: 5288172 bytes, checksum: 0543c551bb4ef0aded2a4c286f66043d (MD5) Previous issue date: 2012-09-28<br>The application of composite materials and in particular the fiber-reinforced plastics (FRP) has gradually conquered space from the so called conventional materials. However, challenges have arisen when their application occurs in equipment and mechanical structures which will be exposed to harsh environmental conditions, especially when there is the influence of environmental degradation due to temperature, UV radiation and moisture in the mechanical performance of these structures, causing irreversible structural damage such as loss of dimensional stability, interfacial degradation, loss of mass, loss of structural properties and changes in the damage mechanism. In this context, the objective of this thesis is the development of a process for monitoring and modeling structural degradation, and the study of the physical and mechanical properties in FRP when in the presence of adverse environmental conditions (ageing). The mechanism of ageing is characterized by controlled environmental conditions of heated steam and ultraviolet radiation. For the research, it was necessary to develop three polymer composites. The first was a lamina of polyester resin reinforced with a short glass-E fiber mat (representing the layer exposed to ageing), and the other two were laminates, both of seven layers of reinforcement, one being made up only of short fibers of glass-E, and the other a hybrid type reinforced with fibers of glass-E/ fibers of curaua. It should be noted that the two laminates have the lamina of short glass-E fibers as a layer of the ageing process incidence. The specimens were removed from the composites mentioned and submitted to environmental ageing accelerated by an ageing chamber. To study the monitoring and modeling of degradation, the ageing cycles to which the lamina was exposed were: alternating cycles of UV radiation and heated steam, a cycle only of UV radiation and a cycle only of heated steam, for a period defined by norm. The laminates have already undergone only the alternating cycle of UV and heated steam. At the end of the exposure period the specimens were subjected to a structural stability assessment by means of the developed measurement of thickness variation technique (MTVT) and the measurement of mass variation technique (MMVT). Then they were subjected to the mechanical tests of uniaxial tension for the lamina and all the laminates, besides the bending test on three points for the laminates. This study was followed by characterization of the fracture and the surface degradation. Finally, a model was developed for the composites called Ageing Zone Diagram (AZD) for monitoring and predicting the tensile strength after the ageing processes. From the results it was observed that the process of degradation occurs Abstract Raimundo Nonato Barbosa Felipe xiv differently for each composite studied, although all were affected in certain way and that the most aggressive ageing process was that of UV radiation, and that the hybrid laminated fibers of glass-E/curaua composite was most affected in its mechanical properties<br>A aplica??o dos materiais comp?sitos e em particular os pl?sticos refor?ados por fibras (PRF) tem conquistado espa?o, gradativamente, dos materiais ditos convencionais, por?m desafios t?m sido colocados quando sua aplica??o ocorre em equipamentos e estruturas mec?nicas que ficar?o expostos a condi??es ambientais adversas, principalmente quando se tem a influ?ncia da degrada??o ambiental do tipo temperatura, radia??o UV e umidade, no desempenho mec?nico dessas estruturas, ocasionando danos estruturais irrevers?veis tais como: perda de estabilidade dimensional, degrada??o interfacial, perda de massa, perda das propriedades estruturais e altera??es no mecanismo de dano. Neste contexto a presente tese tem como objetivo o desenvolvimento de um processo de monitoramento e modelagem da degrada??o estrutural, e o estudo das propriedades f?sicas e mec?nicas, em PRF quando em presen?a de condi??es ambientais adversas (envelhecimento). O mecanismo de envelhecimento ? caracterizado por condi??es ambientais controladas de vapor aquecido e de radia??o ultravioleta. Para a pesquisa foi desenvolvido tr?s comp?sitos polim?ricos, o primeiro uma l?mina de resina poli?ster refor?ado com manta de fibras curtas de vidro-E (representando a camada exposta ao envelhecimento) e dois laminados, ambos de sete camadas de refor?o, sendo um constitu?do s? com manta de fibras curtas de vidro-E, e o outro do tipo h?brido refor?ado com fibras de vidro-E/fibras de curau?. Ressalta-se que os dois laminados t?m a l?mina de fibras curtas de vidro-E como camada de incid?ncia do processo de envelhecimento. Os corpos de provas (CP s) foram retirados dos comp?sitos citados e submetidos ao envelhecimento ambiental acelerado atrav?s da c?mara de envelhecimento. Para o estudo do monitoramento e modelagem da degrada??o, os ciclos de envelhecimento a que foram expostos ? l?mina foram: ciclos alternados de radia??o UV e vapor aquecido, ciclo somente de radia??o UV e o ciclo somente de vapor aquecido, por um per?odo definido em norma. J? os laminados foram submetidos a apenas ao ciclo alternado de UV e vapor aquecido. Ao t?rmino do per?odo de exposi??o os CP s foram submetidos ? avalia??o da estabilidade estrutural mediante a t?cnica desenvolvida de medi??o de varia??o de espessura (TMVE) e a t?cnica de media??o de varia??o de massa (TMVM). Em seguida os mesmos foram submetidos aos ensaios mec?nicos de tra??o uniaxial para a l?mina e todos os laminados, al?m do ensaio de flex?o em tr?s pontos para os laminados. Esse estudo foi seguido da caracteriza??o da fratura e da degrada??o superficial. Por fim, foi desenvolvido um modelo para os Resumo Raimundo Nonato Barbosa Felipe xii comp?sitos denominado de Diagrama da Zona de Envelhecimento (DZE) para o monitoramento e predi??o da resist?ncia mec?nica ? tra??o ap?s os processos de envelhecimento. Ao t?rmino das an?lises foi observado que o processo de degrada??o se d? de forma diferente para cada comp?sito pesquisado, no entanto todos foram afetados, o processo de envelhecimento mais agressivo foi o de radia??o UV, e que o comp?sito que foi mais afetado em suas propriedades mec?nicas foi o laminado h?brido de fibras de vidro-E/curau?

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>O presente trabalho apresenta aplicações das técnicas de Relaxação Dinâmica e Análise Limite ao estudo da estabilidade de maciços rochosos fraturados. O maciço é modelado como um meio descontínuo formado por blocos rígidos com deformação concentrada nas juntas. A técnica de Relaxação Dinâmica é usada para a solução do problema de equilíbrio resultante, através do programa BLOCO. As expressões desenvolvidas para a matriz de rigidez tangente, usando o modelo de Barton & Bandis, foram implementadas no programa BLOCO. Exemplos para a validação do algoritmo são apresentados. A partir do trabalho de Faria (1992), foi implementado um procedimento automatizado e otimizado para a solução do problema de Análise Limite em um meio formado por blocos rígidos. O procedimento desenvolvido permitiu a solução de problemas de porte relatados na literatura.<br>This work presents some applications of the Dynamic Relaxation and Limit Analysis techniques, to the study of the stability of fractured rock masses. Rock mass is modeled as a discontinuum formed by rigid blocks with deformable joints. Dynamic Relaxation was applied to solve the resulting equilibrium problem, using the program BLOCO. Expressions obtained for tangent stiffness matrix, derived from Barton & Bandis model, were implemented into the BLOCO program. In order to extend Faria`s (1992) work, an automatic and optimized procedure, to solve the Limit Analysis problem of a media formed by rigid blocks was implemented. The developed procedure was applied to the study of relatively large dimensions problems, reported in the literature.<br>Este trabajo presenta aplicaciones de las técnicas de Relajación Dinámica y Análisis Límite al estudio de la estabilidad de macizos rocosos fracturados. EL macizo es modelado como un medio discontinuo formado por bloques rígidos con deformación concentrada en las juntas. La técnica de Relajación Dinámica se utiliza para resolver el problema de equilíbrio resultante, a través del programa BLOQUE. Las expresiones desarrolladas para la matriz de rígidez tangente, usando el modelo de Barton & Bandis, se implementaron en el programa BLOQUE. Se presentan algunos ejemplos para la evaluación del algoritmo. A partir del trabajo de Faria (1992), fue implementado un procedimiento automatizado y optimizado para la solución del problema de Análisis Límite en un medio formado por bloques rígidos. El procedimiento desarrollado permitió resolver problemas de porte relatados en la literatura.

Made available in DSpace on 2014-12-17T14:57:54Z (GMT). No. of bitstreams: 1 RenataCTSF_TESE_1-81.pdf: 4666386 bytes, checksum: 75d1cdda6a2cab121f77f0774f7de4e7 (MD5) Previous issue date: 2012-09-14<br>There are a number of damaging mechanisms that various materials can suffer in service. However, when working with polymer composite materials, this is something that requires analysis, especially when exposed to adverse environmental conditions. Thus, the objective of the present thesis is the study of the direct influence of environmental aging and the form of hybridization of the reinforcement woven on the structural stability, surfacedegradation and fracture process of polymer composites laminates. For this, the development of two polymer composite laminates was necessary, where one of them was reinforced with a bi-directional woven with hybrid strandsofkevlar-49/glass-Efibers, and the other also with a bi-directionalwoven, however with weft and warpformed of alternating strandsof Kevlar-49 fibers and glass-E fiber The reinforcementwoven are industrially manufactured. Both laminates use a polyester resin as a matrixand are made up of four layers each. All laminates were industrially prepared by the hand lay-up method of manufacturing. To do this, test specimens were manufactured of the respective laminates and submitted to environmental aging accelerated through the aging chamber. They were exposed to alternating cycles of UV radiation and moisture (heated steam) for a standard defined period. At the end of the exposure period the specimens were subjected to mechanical tests of uniaxial tensile and bending in three points and to the characterizationsof the fracture and surface deterioration. In addition, they were submitted to a structural degradation assessment by the measurement of mass variation technique (MMVT) and the measurement of thickness variation technique (MTVT), this last technique being developed in this thesis. At the end of the analysis it was observed that the form of hybridization of the reinforcement woven and the aging process directly influence with losses or gain in mechanical properties, with losses in the structural degradation and in the formation and propagation of damage mechanism of the developedcomposite laminates<br>S?o v?rios os mecanismos de danos que os diversos materiais podem sofrer em servi?o. No entanto, ao se trabalhar com os materiais comp?sitos polim?ricos isso ? algo que necessita de an?lises principalmente quando expostos a condi??es ambientais adversas. Logo, a respectiva tese objetiva o estudo da influ?ncia direta do envelhecimento ambiental e da forma de hibridiza??o dos tecidos de refor?o no comportamento mec?nico, degrada??o estrutural (dimensional e de massa) de laminados comp?sitos polim?ricos. Para tanto se fez necess?rio o desenvolvimento de dois laminados comp?sitos polim?ricos, onde um deles ? refor?ado com um tecido bidirecional com mecha h?brida de fibras de kevlar-49/vidro-E e o outro com um tecido tamb?m bidirecional, por?m com trama e urdume formadas com mechas alternadas de fibras kevlar-49 e fibras de vidro-E. Os tecidos de refor?o s?o de fabrica??o industrial. Ambos os laminados utilizam como matriz a resina de poli?ster, sendo constitu?dos de quatro camadas cada. Todos os laminados foram confeccionados industrialmente pelo m?todo de fabrica??o handlay-up. Desta forma, foram fabricados corpos de provas (CP s) dos respectivos laminados e submetidos ao envelhecimento ambiental acelerado atrav?s da c?mara de envelhecimento. Os mesmos foram expostos aos ciclos alternados de radia??o UV e umidade (vapor aquecido) por um per?odo definido em norma. Ao t?rmino do per?odo de exposi??o os CP s foram submetidos aos ensaios mec?nicos de tra??o uniaxial e flex?o em tr?s pontos e ?s caracteriza??es da fratura e da deteriora??o superficial. Al?m disso, foram submetidos ? avalia??o da degrada??o estrutural mediante a t?cnica de media??o de varia??o de massa (TMVM) e a t?cnica de medi??o de varia??o de espessura (TMVE), sendo essa ?ltima desenvolvida nesta tese. Ao t?rmino das an?lises foi observado que a forma de hibridiza??o dos tecidos de refor?o e o processo de envelhecimento influenciam diretamente, seja com perdas ou ganho naspropriedades mec?nicas, com perdas na degrada??o estrutural e na forma??o e propaga??o do mecanismo de dano dos laminados comp?sitos desenvolvidos

La stabilité des excavations dans les roches fracturées est influencée, entre autres, par le régime structural, qui est inhérent à la roche. Divers outils sont disponibles pour les analyses de stabilité, mais la qualité des résultats dépend considérablement des données d’entrée disponibles et des outils utilisés. Dans ce mémoire, deux études de cas sont présentées, qui étudient l'influence de la représentation de données structurales sur l'analyse de stabilité. La première étude de cas traite de la stabilité d'une pente de roche le long d'une route près de Fleurimont, qui a subi des effondrements de dièdre. L’objectif était de découvrir si les effondrements pourraient avoir été prédits et d'évaluer la probabilité de la rupture de dièdre le long de la pente. Plusieurs analyses d'équilibre limite ont été effectuées, y compris une analyse déterministe rétrospective de deux ruptures de dièdres, et une analyse probabiliste des dièdres individuels. De plus, une analyse probabiliste de système de joints a été effectuée en utilisant les modèles 3D de système de joints, qui ont été générés avec des données de terrain. Les données nécessaires pour les analyses ont été recueillies sur place. Les résultats d’analyse rétrospective ont indiqué l'instabilité potentielle des dièdres observés, et les approches probabilistes ont confirmé l'occurrence des effondrements de dièdre le long de la pente, mais ils ont également démontré que la probabilité d'effondrements semblables est faible. Les résultats ont démontré qu'une analyse de données exhaustive en utilisant plusieurs outils d'analyse est requise pour obtenir une évaluation fiable du comportement de la roche. La deuxième étude de cas discute de la stabilité des galeries à la mine souterraine LaRonde de l'Agnico Eagle, qui sont concernées par de grandes déformations à cause de la convergence des parois. L'analyse de la convergence observée s'est concentrée sur la génération d'une série de modèles numériques 2D selon la méthode des éléments finis, visant à reproduire le mécanisme d'effondrement et les déformations résultantes. La foliation in situ a été reproduite par des joints, qui ont été introduits explicitement dans le modèle. Les données structurales requises ont été rassemblées sur place. Les modèles ont été calibrés avec les données de convergence disponibles. Les résultats de modélisation numérique ont atteint une bonne concordance avec les observations sur place. Les deux profils caractéristiques observés et l’ordre de grandeur des déformations mesurées ont pu être reproduits. Il a été démontré que le modèle numérique appliqué est un outil utile pour modéliser les conditions complexes observées à la mine. Plus d'expériences de validation devraient être effectuées, mais la méthode peut potentiellement être employée pour élaborer de meilleures stratégies pour les travaux de développement minier dans des conditions semblables. Les deux études de cas ont démontré l'influence de la représentation des données structurales sur l'analyse de données. En outre il a été montré que le choix des outils d'analyse influence les résultats obtenus.<br>La stabilité des excavations dans les roches fracturées est influencée, entre autres, par le régime structural, qui est inhérent à la roche. Divers outils sont disponibles pour les analyses de stabilité, mais la qualité des résultats dépend considérablement des données d’entrée disponibles et des outils utilisés. Dans ce mémoire, deux études de cas sont présentées, qui étudient l'influence de la représentation de données structurales sur l'analyse de stabilité. La première étude de cas traite de la stabilité d'une pente de roche le long d'une route près de Fleurimont, qui a subi des effondrements de dièdre. L’objectif était de découvrir si les effondrements pourraient avoir été prédits et d'évaluer la probabilité de la rupture de dièdre le long de la pente. Plusieurs analyses d'équilibre limite ont été effectuées, y compris une analyse déterministe rétrospective de deux ruptures de dièdres, et une analyse probabiliste des dièdres individuels. De plus, une analyse probabiliste de système de joints a été effectuée en utilisant les modèles 3D de système de joints, qui ont été générés avec des données de terrain. Les données nécessaires pour les analyses ont été recueillies sur place. Les résultats d’analyse rétrospective ont indiqué l'instabilité potentielle des dièdres observés, et les approches probabilistes ont confirmé l'occurrence des effondrements de dièdre le long de la pente, mais ils ont également démontré que la probabilité d'effondrements semblables est faible. Les résultats ont démontré qu'une analyse de données exhaustive en utilisant plusieurs outils d'analyse est requise pour obtenir une évaluation fiable du comportement de la roche. La deuxième étude de cas discute de la stabilité des galeries à la mine souterraine LaRonde de l'Agnico Eagle, qui sont concernées par de grandes déformations à cause de la convergence des parois. L'analyse de la convergence observée s'est concentrée sur la génération d'une série de modèles numériques 2D selon la méthode des éléments finis, visant à reproduire le mécanisme d'effondrement et les déformations résultantes. La foliation in situ a été reproduite par des joints, qui ont été introduits explicitement dans le modèle. Les données structurales requises ont été rassemblées sur place. Les modèles ont été calibrés avec les données de convergence disponibles. Les résultats de modélisation numérique ont atteint une bonne concordance avec les observations sur place. Les deux profils caractéristiques observés et l’ordre de grandeur des déformations mesurées ont pu être reproduits. Il a été démontré que le modèle numérique appliqué est un outil utile pour modéliser les conditions complexes observées à la mine. Plus d'expériences de validation devraient être effectuées, mais la méthode peut potentiellement être employée pour élaborer de meilleures stratégies pour les travaux de développement minier dans des conditions semblables. Les deux études de cas ont démontré l'influence de la représentation des données structurales sur l'analyse de données. En outre il a été montré que le choix des outils d'analyse influence les résultats obtenus.<br>The stability of excavations in fractured rock is influenced among others by the structural order inherent in the rock mass. Various analysis tools are available for stability analysis, but the quality of results depends considerably on the available analysis data and the tools used. In this thesis two case studies of excavations in fractured rock are presented that investigate the influence of structural data representation on the stability analysis. The first case study focused on the stability of a rock slope along a road cut near Fleurimont that has experienced wedge failures. The aim was to find out, if the failures could have been predicted, and to evaluate the probability of wedge failures along the slope. Different limit equilibrium wedge analyses were carried out, including a deterministic back-analysis of two wedge failures and a probabilistic analysis of individual wedges. Furthermore a probabilistic joint system analysis was carried out using 3D joint system models generated out of field data. As part of this work the required analysis data was collected on site. The back-analysis results suggested potential instability of the observed wedges, and the probabilistic approaches confirmed the occurrence of wedge failures along the slope, but also indicated the only low probability for these failures. The results demonstrated that a comprehensive data analysis using various analysis tools is required to reach a reliable assessment of the rock behaviour. The second case study discusses the stability of drifts at Agnico Eagle’s LaRonde underground mine that are affected by large deformations due to rock squeezing. The analysis of the observed drift convergence focused on the generation of a series of numerical 2D finite element models, aiming to reproduce failure mechanism and resulting deformations. The in situ foliation was reproduced by explicitly introducing joints into the model. The required structural data was collected on site. As reference data for the model calibration available convergence data was used. The modelling results reached a good agreement with the observations on site. Both observed characteristic deformation profiles as well as measured deformation magnitudes could be adequately reproduced. It could be demonstrated that the applied numerical model is a useful tool to model the complex squeezing ground conditions observed at the mine. More validation experiments should be carried out, but the method can potentially be used to develop better mine development strategies in similar conditions. Both case studies demonstrated the influence of structural data representation on the data analysis. Furthermore it could be shown that the choice of analysis tools influences the obtained results.<br>The stability of excavations in fractured rock is influenced among others by the structural order inherent in the rock mass. Various analysis tools are available for stability analysis, but the quality of results depends considerably on the available analysis data and the tools used. In this thesis two case studies of excavations in fractured rock are presented that investigate the influence of structural data representation on the stability analysis. The first case study focused on the stability of a rock slope along a road cut near Fleurimont that has experienced wedge failures. The aim was to find out, if the failures could have been predicted, and to evaluate the probability of wedge failures along the slope. Different limit equilibrium wedge analyses were carried out, including a deterministic back-analysis of two wedge failures and a probabilistic analysis of individual wedges. Furthermore a probabilistic joint system analysis was carried out using 3D joint system models generated out of field data. As part of this work the required analysis data was collected on site. The back-analysis results suggested potential instability of the observed wedges, and the probabilistic approaches confirmed the occurrence of wedge failures along the slope, but also indicated the only low probability for these failures. The results demonstrated that a comprehensive data analysis using various analysis tools is required to reach a reliable assessment of the rock behaviour. The second case study discusses the stability of drifts at Agnico Eagle’s LaRonde underground mine that are affected by large deformations due to rock squeezing. The analysis of the observed drift convergence focused on the generation of a series of numerical 2D finite element models, aiming to reproduce failure mechanism and resulting deformations. The in situ foliation was reproduced by explicitly introducing joints into the model. The required structural data was collected on site. As reference data for the model calibration available convergence data was used. The modelling results reached a good agreement with the observations on site. Both observed characteristic deformation profiles as well as measured deformation magnitudes could be adequately reproduced. It could be demonstrated that the applied numerical model is a useful tool to model the complex squeezing ground conditions observed at the mine. More validation experiments should be carried out, but the method can potentially be used to develop better mine development strategies in similar conditions. Both case studies demonstrated the influence of structural data representation on the data analysis. Furthermore it could be shown that the choice of analysis tools influences the obtained results.

La stabilité des exploitations à ciel ouvert (mines ou carrières) excavées dans des massifs rocheux dépend de leur géométrie, des caractéristiques géométriques de la fracturation (orientation et espacement) du massif et des caractéristiques mécaniques du massif et des discontinuités. L'évaluation du risque d'instabilité rocheuse dépend de la quantité et la qualité des informations disponibles sur le massif rocheux et des méthodes d'analyse mises en œuvre pour évaluer le comportement mécanique de l'assemblage de blocs rocheux. Différents sites de talus naturels, d'excavation routière et de carrières et mines à ciel ouvert présentés dans le mémoire montrent que les informations connues peuvent beaucoup varier d'un site à l'autre. Les étapes de collecte et de synthèse des données, puis de modélisation afin d'analyser la stabilité d'une pente rocheuse conduisent à des incertitudes. Le mémoire traite plus particulièrement de l'influence des incertitudes géométriques et différentes méthodes de regroupement des fractures en familles sont explorées. La combinaison du travail proposé par différents auteurs conduit à une nouvelle méthode nommée PSMY. Cette méthode ainsi que la méthode spectrale ont été programmées sous l'environnement Mathematica et les résultats sont comparés à des regroupements "manuels" réalisé avec le logiciel DIPS. Les méthodes de regroupement sont présentées selon le pourcentage d'orientations classé par la méthode. L’orientation et l’espacement des familles de fractures sont ajustées à des lois statistiques. Les paramètres statistiques sont comparés en fonction de la méthode regroupement. Ces paramètres influencent la construction d'un modèle géométrique du massif rocheux appelé DFN (Discrete Fracture Network). L'influence des regroupements sur l'analyse de stabilité est étudiée à partir de modélisation stochastiques à l'équilibre limite utilisant les logiciels SWEDGE et RESOBLOK. Ces logiciels ne prennent pas en compte les mêmes incertitudes et en sortie ils fournissent des indicateurs de stabilité différents. Une analyse de sensibilité des indicateurs (nombre de blocs instables, volume moyen du bloc instable, volume total instable) aux méthodes de regroupement et aux orientations de talus est réalisée. Une analyse de variance permet de préciser l'influence de ces deux facteurs. Une évaluation de l’état de stabilité global du massif, en fonction de la cohésion et de l'angle de frottement est proposée. L'influence de la méthode de modélisation est évoquée en comparant des calculs tridimensionnels à l'équilibre limite et des modélisations bidimensionnel et tridimensionnels en éléments discrets rigides ou déformables. Un couplage entre le logiciel RESOBLOK (équilibre limite) et LMGC90 (éléments discrets) permet de comparer les analyses pour une même géométrie. Pour le cas de la déviation d'Ax-les-Thermes et certaines configurations géométriques instables l’influence des paramètres de modèles sur stabilité du talus est testée. Plusieurs variantes sont comparées. La simulation d’une excavation en 3D multi phases est réalisée et l’indice de mobilisation est étudié pour comparer les divers types de contacts dans LMGC90 par rapport à l’éventuel glissement des blocs dans les étapes successives<br>The stability of open-cast operations (mines or quarries), excavated in rock mass depends on their geometry, the geometrical characteristics of the rock mass fractures (orientation and spacing) and the mechanical characteristics of the rock mass and the discontinuities. The assessment of the rock instability risk depends on the quantity and quality of the available information on the rock mass and the analysis methods used for the evaluation of the mechanical behavior of the rock block collection. Different sites of natural rock slopes, of road cuts, and of open-cast mines and quarries, described in the present document, show that the known information can vary a lot from one site to the other. The steps of data gathering and analysis, then the modelling step used to analyze the stability of the rock slope, lead to uncertainties. The present work deals in particular with the influence of the geometrical uncertainties, and the different clustering methods, to define families of fractures, are examined. The combination of works suggested by several authors leads to a new method called PSMY. This method, together with the spectral method, was coded in the Mathematica platform, and the obtained results are compared with "hand-made" clusters, done with the DIPS software. The clustering methods are presented according to the ratio of classified orientations. The orientation and spacing of fracture families are fitted by statistical law. The statistical parameters are compared according to the clustering method used. These parameters have an influence on the construction of the rock mass geometrical model, called DFN (Discrete Fracture Network). The influence of the clusters on the stability analysis is studied from the stochastic models based on the limit equilibrium analysis, in the SWEDGE and RESOBLOK software. These programs do not take into account the same uncertainties, and as a result, they give different stability indicators. A sensitivity analysis of these indicators (number of unstable blocks, average volume of unstable blocks, and total volume of unstable blocks) versus the clustering methods used, and the orientation of the slopes, is carried out. A variance analysis allows an evaluation of the influence of these factors. The assessment of the global stability condition of the rock mass, depending on the cohesion and the friction angle, is proposed. The influence of the modeling method is analyzed by comparing 3D calculations using the limit equilibrium calculations, and 2D and 3D models using discrete rigid and deformable blocks. A coupling between RESOBLOK (limit equilibrium) and LMGC90 (discrete elements) allows the comparison of results on the same original geometry. For the case of Ax-les-Thermes road-cut, and for various unstable geometries, the influence of the model parameters is tested. Several cases are compared. The 3D simulation of an excavation, at different steps, is performed, and the mobilization index is studied, in order to compare several types of contacts, within the LMGC model, in relation to the possible sliding of blocks, at those different steps

This dissertation is to obtain an overall understanding of the crack path selection in adhesively bonded joints. Using Dow Chemical epoxy resin DER 331® with various levels of rubber concentration as an adhesive, and aluminum 6061-T6 alloy with different surface pretreatments as the adherends, both symmetric and asymmetric double cantilever beam (DCB) specimens are prepared and tested under mixed mode fracture conditions in this study. Post-failure analyses conducted on the failure surfaces indicate that the failure tends to be more interfacial as the mode II component in the fracture increases whereas more advanced surface preparation techniques can prevent failure at the interface. Through mechanically stretching the DCB specimens uniaxially until the adherends are plastically deformed, various levels of T-stress are achieved in the specimens. Test results of the specimens with various T-stresses demonstrate that the directional stability of cracks in adhesive bonds depends on the T-stress level. Cracks tend to be directionally stable when the T-stress is compressive whereas directionally unstable when the T-stress is tensile. However, the direction of crack propagation is mostly stabilized when more than 3% mode II fracture component is present in the loading regardless of the T-stress levels in the specimens. Since the fracture sequences in adhesive bonds are closely related to the energy balance in the system, an energy balance model is developed to predict the directional stability of cracks and the results are consistent with the experimental observations. Using the finite element method, the T-stress is shown to be closely related to the specimen geometry, indicating a specimen geometry dependence of the directional stability of cracks. This prediction is verified through testing DCB specimens with various adherend and adhesives thicknesses. By testing the specimens under both quasi-static and low-speed impact conditions, and using a high-speed camera to monitor the fracture sequence, the influences of the debond rate on the locus of failure and the directional stability of cracks are investigated. Post-failure analyses suggest that the failure tends to be more interfacial when the debond rate is low and tends to be more cohesive when the debond rate is high. However, this rate dependence of the locus of failure is greatly reduced when more advanced surface preparation techniques are used in preparing the specimens. The post-failure analyses also reveal that cracks tend to be more directionally unstable as the debond rate increases. Finally, employing interface mechanics and extending the criteria for the direction of crack propagation to adhesively bonded joints, the crack trajectories for directionally unstable cracks are predicted and the results are consistent with the overall features of the crack paths observed experimentally.<br>Ph. D.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>A estabilidade de poços de petróleo é convencionalmente analisada empregando soluções analíticas que não são adequadas para modelagem de meios fraturados, devido a suposições de meio continuo. Esta dissertação tem como objetivo principal desenvolver uma metodologia computacional para geração de janela operacional utilizando uma solução numérica, adequada para meios fraturados. No trabalho foi escolhido o software UDEC (Universal Distinct Element Code), que é baseado no método dos elementos discretos (MED). Este método considera o maciço rochoso como a união de blocos de rocha intactos, unidos pelas fraturas e cujo comportamento físico para cada elemento pode ser analisado individualmente. A modelagem computacional no UDEC foi realizada mediante uma analise hidromecânica acoplada. Esta modelagem permitiu avaliar a influencia de alguns mecanismos que governam a estabilidade de poços, como: as tensões in situ, a poropressão e a orientação, espaçamento e persistência das famílias de fraturas. Os resultados numéricos mostram o efeito das fraturas na orientação e magnitude das tensões, além da magnitude da poropressão resultando em cálculos dos limites de colapso inferior e fratura superior da rocha mais realistas.<br>The stability of oil wells is conventionally analyzed using analytical solutions that are often not suitable for modeling fractured media due to assumptions of continuous medium. This work has as main objective to develop a computational method for generating mud window using a numerical solution, suitable for fractured media. The software chosen for this work was the UDEC (Universal Distinct Element Code), which is based on discrete element method (DEM). This method considers the rock mass as the union of blocks of intact rock jointed by fractures, and whose physical behavior for each element can be analyzed individually. Computational modeling in UDEC was carried out in a coupled hydromechanical analysis. This modeling allowed to evaluate the influences of some of the mechanisms that govern the stability of wells, as in situ stresses, pore pressure and orientation, spacing and persistence of families of fractures. Numerical results show the effect of fracture orientation and magnitude of the stresses, besides the magnitude of the pore pressure resulting in more realistic calculations of lower collapse and upper fracture of the rock mass.

Coal seams are unconventional subsurface formations that host methane and are weaker (relative to conventional subsurface) formations. Coal seams are prone to coal fines generation within the fractured porous space throughout the life of the reservoir. These coal fines damage the permeability, deliverability and productivity of coal seams. Furthermore, the coal fines mobility/blockage in the hydraulically induced fractures and proppant packs negatively impacts the proppant conductivity. In this work, a comprehensive study has been conducted to augment the understanding of coal fines and their behaviour within porous and proppant pack systems. Systematic experiments were conducted to address the coal fines by developing various approaches presented in this work. The approaches adopted to achieve the study objectives were: i) streaming zeta potential on coal and sandstone, ii) nano-treated proppant surface modification for coal fines adsorption, and iii) coal fines mobility/attachment in the proppant packs. One of the electrokinetic parameters that is crucial in releasing/mobilising coal fines is coal’s zeta potential. The coal surface is generally hydrophobic and possesses negative zeta potential. Researchers have used the electrophoretic zeta potential technique to indicate charge identification of coal particles, denoting repulsion or attraction of the particle. In chapter 3, a robust study investigates streaming zeta potential measurements of an in-situ sub-bituminous coal core saturated with saline water of 0.1, 0.3 and 0.6 mol.dm-3 NaCl salinities. Thus, the novel study determines the charge carried by percolating fluid when passing through coal rock. The zeta potential is directly proportional to saline water salinity. The trends found in the research were consistent with reported zeta potential measured using other techniques, while the magnitude varied. The findings reported in the study apply to subsurface coal seams at salinity up to 0.6 mol.dm-3 NaCl. Coal seams are hydraulically fractured for commercial production, and sand-based proppants occupy the fractured space. Before understanding the electrokinetics of coal fines, the behaviour of these sand-based proppants should be determined. Sand-based proppants are predominantly silica, and so are sandstones. Furthermore, the selection of sandstone was further motivated by two reasons, i) for comparison and benchmarking, and ii) correlation with coals (as sandstone and coal both are negatively charged). The research presented in chapter 4 considered clay-rich (i.e. clay ≥ 5 wt.%) sandstones for the first time (as coal can have clay ingredients). Specifically, streaming potential measurements were conducted on Bandera Grey sandstone (clay-rich and -poor) saturated with saline water in pressurised environments. Additionally, the streaming potential was determined at identical conditions for the effect of two surfactants, sodium dodecylbenzene sulfonate (SDBS) and cetrimonium bromide (CTAB), at concentrations of 0.01 and 0.1 wt. % on the clay-poor sample. Moreover, a comparison of electrophoretic and streaming zeta potentials was conducted. Accordingly, the work analyses the effects of mineralogy and surfactants within this process. Clay-rich sandstone possessed lower zeta-potentials than clay-poor sandstone at the two tested salinities. SDBS reduced zeta-potential and yielded higher repulsive forces rendering the rock more hydrophilic. Additionally, electrophoretic zeta-potentials were higher when compared to streaming zeta-potentials. Mechanisms for the observed phenomena are also provided. Following the observations from the two studies, proppant column experiments with glass bead proppant and high volatile bituminous were conducted and are presented in chapter 5. One of the approaches to handling coal fines is its dispersal within the aqueous suspension. Proppant column experiments were conducted to test various schemes. It was found that coal zeta potential using SDBS reaches a maximum, and regardless of the pH, it effectively delivers the maximum output of coal fines in the effluent. Thus, a 0.001 wt.% SDBS could effectively disperse coal fines suspension through proppant packs. Nano-treated proppant surface modification was developed to investigate coal fines mobility/attachment within the proppant packs. Succinctly, four (alumina, magnesia, silica and zirconia) nanoparticles (NPs) were adsorbed onto synthetic porous media (glass bead) using a robust pseudo-continuous fixed-bed (PCFB) adsorption method in work presented in chapter 6. A wide range of salinity (0 to 10.5 wt.% NaCl), temperature (298.15 to 348.15 K), NPs loading (0.01 to 0.2 wt.%), and injection rate (1 to 50 mL.min-1) were tested. Results showed that PCFB adsorption of NPs with higher specific surface area resulted in faster adsorption (adsorbed in ~25 mins) with > 99% immobilisation of NPs on the proppant pack. Adsorption kinetics showed reasonable conformity with the pseudo-first-order model, where isothermal adsorption followed the Sips model. The adsorption capacity of magnesia NPs (specific surface area 50 to 80 m2.g-1, 7 wt.% NaCl) at 298.15 K was higher than silica NPs. Accordingly, the newly developed PCFB method can be used for onsite treatment of proppants with nanoparticles, which can then be injected into a fractured formation to achieve multiple objectives such as fines fixation, wettability alteration and sand control. In this work, another study explored the application of nano-treated proppant packs on the adsorption of coal fines, presented in chapter 7. In this study, the objective was to identify silica nano-formulations (0 – 0.1 wt.%), and coal fines concentration of 0.1 to 1 wt.% were examined to determine the fixation of coal fines within the glass bead synthetic proppant pack. The quantitative results showed that the proppant pack with nanoparticle treatment strongly affects the fixation ability of coal fines. The non-NP treated pack yielded 30% adsorption, whilst the NP treated pack yielded 74% adsorption. It was noted that greater adsorption is also related to the higher zeta potential of silica NPs (i.e. nearer to iso-electric point). A set of laboratory experiments on industrial-grade proppants was conducted as the definitive work, presented in chapter 8. The work involved sensitivity experiments as a function of coal rank, pH, salinity, and surfactants. These conductivity results were compared with established analytical models to interpret the mechanistic coal-proppant interaction in the presence of an electrolyte. It was found that fines dispersion and its mobility within the proppant pack is easier at high pH, low salinity, temperature, anionic surfactants, and lower concentration of coal fines. However, fines mobility is reduced at neutral pH, high salinity, temperature, and cationic surfactants.

Residual dysfunction after a fracture of the distal radius is most often mild but may give rise to significant impairment especially in the younger active population. The symptoms often manifest around the distal ulna when loading the hand or rotating the forearm. In this region are found articular and soft tissue connections running from the distal ulna to the distal radius as well as to the ulnar side of the carpus. The aims of this thesis were to investigate the effects of distal radius fractures on the structures about the distal ulna and to what extent malunion and ulnar soft tissue lesions affect function. Both patients and cadaver specimens were used in the five different studies. In a retrospective study of 17 malunited distal radius fractures supination impairment improved significantly by correction of the skeletal malunion. This highlights the importance of distal radioulnar joint congruity for forearm rotation in a subset of cases. The pathomechanisms of injury to the triangular fibrocartilage complex (TFCC) were studied. In a cadaveric distal radius fracture model different restraining properties and injury patterns were investigated. Similar patterns of injury were then observed in 20 patients with a displaced distal radius fracture. It was found that a TFCC injury can be expected with dorsal displacement of the distal radius fragment of 32o or more from the anatomically correct position. The distribution of a TFCC injury apparently differs depending on the size of an associated ulnar styloid fracture. In cases of an intact ulnar styloid or a concomitant tip fracture (Type 1) the first stage of injury seems to be extensor carpi ulnaris subsheath separation from the distal ulna and the dorsal radioulnar ligament. Thereafter follows a disruption of the deep insertions into the fovea of the ulna starting from the palmar and extending dorsally and radially. An extensive injury can be detected with a novel non-invasive test called the ‘bald ulnar head test’, which is performed under anaesthesia. Diagnosis of an acute TFCC injury is difficult using non-invasive methods. In a prospective study of 48 patients, CT scanning to detect pathologic subluxation was found to be of little use in both acute and chronic cases, and is therefore not endorsed on this indication. A radioulnar stress test, which in previous studies has correlated well to a deep TFCC injury, was found to be highly reliable but not to correspond with significant disability in self-administered questionnaires of functional outcome two years or more after injury. This indicates that the subset of patients possibly benefiting from acute repair must be identified by other means.

This Ph.D. thesis was written under the supervision of Assoc. Prof. Luboš Náhlík, Ph.D. and Assoc. Prof. Pavel Hutař, Ph.D. Thesis is focused mainly on application of generalized linear elastic fracture mechanics, which allows description of crack behaviour propagating from general singular stress concentrators, such as material interfaces or sharp V-notches, and verification of validity of used fracture criteria. The obtained results were used in the next part of the thesis, which deals with the issue of crack propagating in ceramic composites, where the stress distribution field is strongly influenced by the existence of material interface and presence of residual stresses, that arise during manufacturing process of composite.

Ce travail de thèse propose un modèle numérique complet pour l'écoulement transitoire des eaux souterraines dans les milieux poreux et fracturés et son application sur l’analyse de la stabilité des pentes sous l’effet d’une diminution du niveau de l’eau dans un réservoir. L’écouement de l’eau dans les milieux fracturés est complexe, en raison de la présence d'un grand nombre de fractures et de fortes variations dans les propriétés géométriques et hydrauliques de ces milieux.La thèse est organisée en six chapitres.Le premier chapitre pésente les problèmes abordés et les objectifs de la thèse. Le 2nd chapitre présente une synthèse des analyses numériques de l'écoulement dans les milieux fracturés et de ses effets sur la stabilité des pentes. Le 3ème chapitre présente le développment d’un modèle numérique d'écoulement transitoire saturé dans des milieux fracturés avec une surface libre en utilisant la méthode des éléments composites (CEM). Le 4ème chapitre présente un modèle numérique d'écoulement transitoire à saturation variable, dans les milieux fracturés à l'aide du CEM.Le 5ème chapitre présente une étude de la stabilité des pentes sous l’effet de variation des paramètres hydrauliques et de résistance des sols, et da géométrie des pentes.Le 6ème chapitre présente une étude paramétrique de l'influence des caractéristiques de fracture sur l'écoulement transitoire et la stabilité d’une pente soumise à des conditions de diminution<br>This thesis presents a comprehensive numerical method for analyzing transient groundwater flow in porous and fractured media and its application to the analysis of the stability of soil and rock slopes subjected to transient groundwater flow induced by reservoir drawdown conditions. Compared to that of porous media, the analysis of flow in fractured media is relatively complex, due to the presence of a large number of fractures and strong variations in geometric and hydraulic properties.The thesis is organized in six chapters. Chapter 1 presents the issues to be addressed and the thesis objectives. Chapter 2 discusses basic theories related to the numerical analysis of groundwater flow in fractured media and its effects on slope stability.Chapter 3 develops the numerical model of transient, saturated flow in fractured media with a free surface using the composite element method (CEM). Chapter 4 presents the numerical model of transient, variably-saturated flow in fractured media using the CEM.Chapter 5 includes an investigation of the stability of homogeneous soil slopes under drawdown conditions, depending on the drawdown rate, hydraulic and strength parameters of soils, and slope geometry.The last chapter presents a parametric study on the influence of fracture characteristics on transient flow and stability of layered rock slope subjected to drawdown conditions

Le travail de recherche a pour objectif la realisation du logiciel degres destine a la prevision de la geometrie de la fosse d'une mine a ciel ouvert et la detection des risques de rupture. Il a ete mis en oeuvre sur le site de la "grande decouverte" de carmaux (tarn - france)

Depuis plus d'une vingtaine d'années une attention toute particulière est portée sur l'étude de réseaux électriques afin d'améliorer leur dimensionnement, leur qualité, leur sécurité et leurs performances. En effet, ces réseaux deviennent de plus en plus complexes avec l'apparition de nouvelles sources d'énergie de nature diverse et l'augmentation de dispositifs d'électronique de puissance qui servent d'interfaces de connexion ou de dispositifs de contrôle. Ces évolutions engendrent de nombreux problèmes d'analyse et de dimensionnement des réseaux électriques modernes. Pour les résoudre, nous proposons une démarche originale de modélisation et d'analyse basée sur les systèmes d'ordre non entier. Elle peut s'appliquer soit aux réseaux électriques, soit à leurs composants (machines électriques, piles à combustibles, charges, etc. ). Plus précisément, le premier objectif de ce mémoire est l'application de la théorie fractale à la modélisation dynamique des systèmes électriques afin d'obtenir des modèles de connaissance plus précis et d'ordre réduit. On tâchera notamment de mettre en évidence les liens qui existent entre géométrie fractale des systèmes électriques, performances fréquentielles et modélisation d'ordre non entier. Le deuxième objectif est l'application des modèles d'ordre non entier aux études de stabilité classiquement menées sur les systèmes électriques<br>Since twenty years, a particular attention is focused on the study of electrical networks to improve their design, their quality and safety and at least their performance. Indeed, these electrical networks become more complex with the emergence of new sources of energy of various kinds and the rise of electronic devices which connect or control devices. These changes lead to numerous issues of analysis and design of modern electrical power networks. To solve them, the authors propose an original approach of modelling and analysis based on non-integer order systems. This approach can be applied to global power networks or to one of their components (e. G. Electrical machines, fuel cell, loads). More specifically, the first aim of this PhD concerns the application of fractal theory to the dynamic modelling of electrical systems in order to obtain knowledge models which are more accurate and of reduced order. Then, this report highlights the links between fractal geometry of electrical systems, frequency performance and non-integer order modelling. The second objective is the application of non-integer order models to stability studies of electrical systems

Depuis plus d'une vingtaine d'années une attention toute particulière est portée sur l'étude de réseaux électriques afin d'améliorer leur dimensionnement, leur qualité, leur sécurité et leurs performances. En effet, ces réseaux deviennent de plus en plus complexes avec l'apparition de nouvelles sources d'énergie de nature diverse et l'augmentation de dispositifs d'électronique de puissance qui servent d'interfaces de connexion ou de dispositifs de contrôle. Ces évolutions engendrent de nombreux problèmes d'analyse et de dimensionnement des réseaux électriques modernes. Pour les résoudre, nous proposons une démarche originale de modélisation et d'analyse basée sur les systèmes d'ordre non entier. Elle peut s'appliquer soit aux réseaux électriques, soit à leurs composants (machines électriques, piles à combustibles, charges, etc.). Plus précisément, le premier objectif de ce mémoire est l'application de la théorie fractale à la modélisation dynamique des systèmes électriques afin d'obtenir des modèles de connaissance plus précis et d'ordre réduit. On tâchera notamment de mettre en évidence les liens qui existent entre géométrie fractale des systèmes électriques, performances fréquentielles et modélisation d'ordre non entier. Le deuxième objectif est l'application des modèles d'ordre non entier aux études de stabilité classiquement menées sur les systèmes électriques.

Le comportement mécanique des massifs rocheux fracturés est énormément et quelquefois dramatiquement, affecté par le comportement des discontinuités présentes dans les massifs. L'influence des discontinuités sur le comportement mécanique des masses rocheuses a été démontrée par de nombreuses études expérimentales et numériques. Les joints sont à l’origine des ruptures ou instabilités observées dans les structures du génie civil et leur comportement dépend de nombreux facteurs. Par conséquent, les modèles de comportement des discontinuités et les paramètres associés jouent un rôle essentiel dans les applications des techniques numériques. Un programme permettant de déterminer les paramètres des lois constitutives des discontinuités ainsi que les critères de rupture en cisaillement, à partir des données d'essais en laboratoire, a été mis au point. Saeb et Amadei ont développé un modèle analytique, incrémental et non linéaire de comportement des joints rocheux. Base sur la formulation des auteurs, nous avons généralisé le comportement des joints rocheux à des sollicitations cycliques dans la direction normale et avec changement de direction de sollicitations dans la direction tangente au joint. Les deux modèles ont été implantés dans le code de calcul des éléments distincts UDEC. Une vérification des modèles ainsi qu'une étude paramétrique ont été réalisées sur des géométries simples (y compris les deux lois linéaires de UDEC). Trois exemples d'application à l'étude de l'influence des lois sur la stabilité des ouvrages ont été traités. Les deux premiers étudient l'influence des lois de comportement sur la stabilité d'ouvrages à plusieurs profondeurs ainsi que l'influence de la rigidité du milieu entourant les fractures. Une comparaison entre les résultats de la modélisation (selon les lois constitutives et certains paramètres qu'elles font intervenir dans leur mise en œuvre) et les mesures in situ constituent le troisième exemple

La déformation due au fluage d'un massif rocheux autour d'un tunnel a été rencontrée fréquemment. Ce phénomène est évident où il y a des tunnels creusés dans la roche tendre, des masses rocheuses faible et fortement cisaillées, ou des massifs rocheux soumis à des contraintes in-situ élevées. La déformation due au fluage se produit fréquemment au moment d’excavation des tunnels longs où il y a des failles et des zones fracturées et cisaillées. Ce phénomène peut causer différents dommages sur des systèmes de soutènement en raison de la déformation excessive et des effondrements. La déformation excessive impose une ré-excavation de la section du tunnel, qui monte le coût supplémentaire, la durée de la réalisation du projet et le risque de la sécurité sur le projet. En plus, comme la stabilité de terrain est dans un état critique durant la ré-excavation, une petite négligence peut conduire à une grande caverne. Bien que la déformation de fluage est commune dans un massif rocheux à une faible résistance dans un tunnel très profond, mais ce phénomène a été observé dans des tunnels peu profonds. Une bonne compréhension des déformations causées par une excavation souterraine requiert la connaissance de l'interaction roche-support et l'interprétation des données de terrain. Auparavant, l’objet principal de la surveillance effectuée durant la construction du tunnel était des mesures de la pression au terrain imposé sur le revêtement du tunnel. Mais aujourd’hui, les méthodes modernes de construction de tunnel se concentrent sur la surveillance des déplacements pendant et après la construction. Afin de déterminer des déformations dans les tunnels, Panet et Sulem ont supposé que "Le tunnel a une section transversale circulaire et le milieu est homogène et isotrope, aussi le tunnel est suffisamment profond pour considérer que la distribution des contraintes est homogène". Mais dans le cas quasi réel, la distribution de la contrainte autour du tunnel est hétérogène et anisotrope. Dans cette étude, pour la modification des équations Panet et Sulem, certaines équations sont proposées en cas de matériau hétérogène et anisotrope pour généraliser le problème. La galerie de force motrice Seymareh a été considérée comme l’étude de cas. Celle-ci est une partie du conduit d’eau dans le projet de centrale électrique du barrage Seymareh. Ce projet est situé à l'ouest de l'Iran. Les données de surveillance de la galerie de force motrice sont collectées au moment de l’excavation du tunnel, et sont comparées avec les résultats de la modélisation numérique et de la solution analytique. Cette comparaison montre que les résultats des données expérimentales obtenues par la surveillance sont très proches des résultats de la solution analytique, mais il y a une différence entre les deux et la modélisation numérique. Il était prévisible, car l’effet d’autres activités comme l’excavation des tunnels verticaux n’est pas prise en compte dans l’analyse numérique et aussi dans la solution analytique. Il est évident que les autres activités comme l’excavation des tunnels verticaux et l'excavation du tunnel principal vers deux directions opposées, peuvent affecter sur les résultats de la surveillance. D'autre part, les données initiales utilisées dans l'analyse numérique et la solution analytique ne sont pas tout à fait exactes, car elles sont obtenues en tant que représentatives du massif rocheux de la région, mais pas pour une section particulière. Toutefois, le but de cette étude est le développement d'une solution analytique de la déformation dans les tunnels sur les conditions générales et la poursuite de cette étude pourra être plus développée.<br>The creep deformation of a rock mass around a tunnel has been encountered frequently. It is particularly common in tunnels excavated in soft rock, heavily sheared weak rock masses or rock masses subjected to high in-situ stresses. Creep deformation in fault and shear fractured zones are one of the frequently encountered difficulties in long tunnel construction, which tend to cause failure of supporting systems due to excessive deformation and cavern. Excessive deformation would necessitate re-mining of the tunnel cross section, thus imposing impacts such as extra cost, extended time schedule and safety risk on the project. Furthermore, as the ground stability is in critical condition during re-mining, the slightest negligence would lead to major cavern. Although creep deformation is common to extremely poor rock mass under high overburden in a tunnel alignment, but however this phenomenon is not limited to tunnels with high overburden. A good understanding of the deformations caused by an underground excavation requires simultaneously knowledge of the rock-support interaction and interpretation of field data. Formerly, the main purpose of the monitoring carried out during tunnel construction was to measure the ground pressures acting on the tunnel lining. Modern tunneling practice emphasizes the monitoring of the displacements occurring during and after the construction. Panet and Sulem for determining of deformations in tunnels have assumed that "The tunnel has a circular cross section and around the tunnel, the rock is homogeneous and isotropic and also the tunnel is deep enough to consider that the stress distribution is homogenous". But in almost real cases, the stresses distribution around the tunnel is not homogeneous and isotropic. In this study, for modification of the Panet and Sulem equations, some equations are proposed in case of nonhomogeneous and anisotropic for generalizing of the problem. Seymareh power tunnel which is considered as a case study is a part of the powerhouse waterways system of the Seymareh dam and hydroelectric power plant project. The project is located in west of Iran. The monitoring data of power tunnel which are collected during excavation of tunnel is compared with the results of numerical modelling and analytical solution results as well as. The results obtained from comparison show although the field data, which are collected through the monitoring, are very close to the analytical solution results (approximately), but there is a significant difference between both of them and numerical modelling results. It was predictable; because the influence of the other activities such as excavation of shaft and surge tank in the numerical analysis and also analytical solution are not considered. It is obvious that other activities such as excavation of shaft and surge tank and also excavation of mean tunnel from other direction which were under operation at the same time can effect on the results of monitoring. On the other hand, the initial data which are used in numerical analysis and analytical solution are not quite accurate; because they are extracted as a representative of the rock mass of region, not for a particular section. However the goal of this study is development of analytical solution of deformation in tunnels on general conditions and pursuit of the study could be leaded to more development in this field.

In Sweden the encapsulated nuclear waste will be surrounded by compacted bentonite in the granitic host rock. In contact with water-bearing fractures the bentonite barrier may release montmorillonite colloids that may be further transported in groundwater. If large amounts of material are eroded from the barrier, the buffer functionality can be compromised. Furthermore, in the scenario of a leaking canister, strongly sorbing radionuclides, can be transported by montmorillonite colloids towards the biosphere. This thesis addresses the effects of groundwater chemistry on the generation, stability, sorption and transport of montmorillonite colloids in water bearing rock fractures. To be able to predict quantities of montmorillonite colloids released from the bentonite barrier in contact with groundwater of varying salinity, generation and sedimentation test were performed. The aim is first to gain understanding on the processes involved in colloid generation from the bentonite barrier. Secondly it is to test if concentration gradients of montmorillonite colloids outside the barrier determined by simple sedimentation experiments are comparable to generation tests. Identical final concentrations and colloid size distributions were achieved in both types of tests. Colloid stability is strongly correlated to the groundwater chemistry. The impact of pH, ionic strength and temperature was studied. Aggregation kinetics experiments revealed that for colloid aggregation rate increased with increasing ionic strength. The aggregation rate decreased with increasing pH. The temperature effect on montmorillonite colloid stability is pH-dependent. At pH≤4, the rate constant for colloid aggregation increased with increasing temperature, regardless of ionic strength. At pH≥10, the aggregation rate constant decreased with increasing temperature. In the intermediate pH interval, the aggregation rate constant decreased with increasing temperature except at the highest ionic strength, where it increased. The relationship between the rate constant and the ionic strength allowed the critical coagulation concentration (CCC) for Na- and Ca-montmorillonite to be determined. In order to distinguish the contribution of physical filtration and sorption to colloid retention in transport, the different retention mechanisms were quantified. Sorption on different representative minerals in granite fractures was measured for latex colloids (50, 100, 200 nm) and montmorillonite colloids as a function of ionic strength and pH. Despite of the negative charge in mineral surfaces and colloids, sorption was detected. The sorption is correlated to the mineral point of zero charge and the zeta potential of the colloids, and increases with increasing ionic strength and decreasing pH. In transport experiments with latex colloids in columns packed with fracture filling material, the retention by sorption could clearly be seen. In particular at low flow rates, when the contact time for colloids with the mineral surfaces were the longest, sorption contributed to retention of the transport significantly. The retention of latex colloids appeared to be irreversible in contrary to the reversible montmorillonite colloid retention. Generation, stability and sorption of the montmorillonite colloids are controlled by electrostatic forces; hence, the results were in qualitative agreement with DLVO.

De récentes expérimentations réalisées sur des sites réels, ont permis de mettre en évidence la complexité du comportement de groupe de pieux dans une pente instable. On fait le point sur les méthodes existantes et on approfondit l'étude du mécanisme du comportement du sol au voisinage d'une rangée de pieux en se limitant au phénomène d'interaction sol-pieu. Apres étude bibliographique du phénomène donnant lieu à la programmation de deux des méthodes les plus significatives, on réalise deux approches en déformation: modélisation en continuum élastique permettant de prendre en compte une géométrie de maillage des pieux quelconques et d'appliquer au groupe une sollicitation en déplacement très générale, modélisation s'appuyant sur la méthode des éléments finis et sur un modèle bidimensionnel horizontal simulant l'écoulement du sol entre une rangée de pieux. Comparaison de diverses méthodes.

La stabilité à court terme et à long terme sont deux aspects importants dans l'analyse de la stabilité des pentes. L'objectif de cette étude est de proposer des modèles numériques pour simuler le comportement mécanique à court terme et à long terme de la matrice rocheuse et joints rocheux. Pour la matrice rocheuse, un modèle élasto- endommagement qui prend les deux situations, de compression et de traction en compte est utilisé. Un paramètre est introduit pour mettre l'accent sur l'influence de la pression de confinement. Et puis un modèle de fluage de la matrice rocheuse qui compte le paramètre de dommages comme une variable dépendant du temps est proposé. Les résultats des simulations montrent un exact accord avec les résultats expérimentaux. Généralement, joints rocheux sont la partie la plus fragile dans les structures rocheuses. Pour joints rocheux, l'aspérité de la surface commune est représentée par un paramètre JRC. Ce paramètre est lié à l'angle de frottement, et donc affecte la rigidité en cisaillement de joint. Dans ce travail, un modèle constitutif est employé sur la base de cette théorie présentée, et le paramètre JRC est proposé comme une variable dépendante du temps, ce qui représente la dégradation de l’aspérité avec le passage du temps. Une simulation est réalisée et vérifiée que ce modèle est capable de décrire les phénomènes de fluage. Extended finite element method (XFEM) est introduit et appliqué dans le modèle de joint de décrire exactement l'état réel des joints. Une simulation d'une structure complexe est effectuée à la fin pour vérifier la capacité de simuler de ces modèles<br>Short-term and long-term stability are two important aspects in analyzing slope stability. The objective of this study is to propose the numerical models to simulate the short and long-term mechanical behaviour of rock matrix and rock joint. For rock matrix, one elasto-damage model which takes both the compressive and tensile situations into account is employed. One parameter is introduced to emphasize the influence of confining pressures. And then one creep model for rock matrix which considering the damage parameter as a time-dependent variable is proposed. The simulation results show great agreement with experimental results. Generally, rock joints are the most fragile part in rock structures. For rock joint, the asperity of joint surface is represented by a parameter JRC. This parameter is related to the friction angle, and then affects the shear stiffness of joint. In this work, a constitutive model is employed based on this theory, and then the parameter JRC is proposed to be a time-dependent variable, which represents the graduate degradation of joint asperity with time passage. One simulation is performed and verified that this model is capable to describe creep phenomena. The extended finite element (XFEM) theory is introduced and applied in the joint model to exactly describe the real condition of joint. A simulation of one complicated structure is performed at last to verify the simulating ability of these models