Purpose: The purpose of this study is to evaluate how implant-supported fixed dental prosthesis (FDP) restorations with a cantilever at abutment level resist fatigue by dynamic loading and thermocycling depending on the fixture diameters.   Material and method: The study involved two groups with three specimens in each group, based on the diameter of the fixture, 3.5 or 5.0 mm (D3.5 and D5.0). The specimens consisted of two ASTRA TECH platforms, either 3.5 mm or 5.0 mm, 20°Uni Abutments, and a standardized milled CoCr FDP at abutment level with a cantilever. A mounting jig was designed and 3D printed. The specimens underwent a dynamic fatigue test with thermocycling, 5°C and 55°C, and a 250 N load at a frequency of 1.5 Hz for maximum 6×10⁵ cycles, until the specimen either fractured or displayed visible deformation. Fractured specimens were examined under microscope.    Results: In group D3.5, one specimen survived 600,000 cycles without loosening or fracturing, one displayed screw loosening, and one screw fracturing. In group D5,0, two specimens displayed screw fracturing and one screw/abutment loosening.   Conclusions:  · Implant-supported FDP restorations with a cantilever at abutment level tend to resist fatigue better with a larger fixture diameter than with a smaller fixture diameter. · Fixtures with a diameter of 5.0 mm show higher tendency for screw fracturing and loosening compared to fixtures with 3.5 mm.  · More extensive studies regarding implant-supported FDP restorations with cantilever at abutment level and different fixture diameters are required to confirm the results. / Syfte: Syftet med studien är att utvärdera hur implantat-förankrade bro-konstruktioner på distansnivå med frihängande led motstår utmattning genom dynamisk belastning och termocykling beroende på fixturens diameter.   Material och metod: Totalt framställdes två grupper beroende på fixturens diameter, 3,5 eller 5,0 mm, med tre provkroppar per grupp (D3,5 och D5,0). Provkropparna bestod av två fixturer motsvarande position 34 och 35 och ett frihängande led på 36 med plattformarna ASTRA TECH 3,5×9,0 mm eller 5,0×9,0 mm inkluderat distanser 20° Uni Abutment och standardiserade frästa broar i CoCr på distansnivå. Ett dynamiskt utmattningstest genomfördes med hjälp av tuggsimulator med samtidig termocykling 5°C och 55°C. Belastningen på 250 N applicerades på det frihängande ledet under maximalt 6×105 cykler med 1,5 Hz. Provkropparna kontrollerades visuellt och taktilt var 50 000:e cykel för att undersöka om fraktur, deformation eller påverkan på skruvförband uppstått. De frakturerade provkropparna undersöktes i ljusmikroskop för att analysera frakturytor och eventuella deformationer.   Resultat: I grupp D3,5 klarade en provkropp 600 000 cykler utan att lossna eller frakturera, en fick skruvlossning och en fick skruvfraktur. I grupp D5,0 fick två provkroppar skruvfraktur och en fick skruv-/distanslossning.  Slutsats:  · Implantat-förankrade bro-konstruktioner på distansnivå med frihängande led tenderar att motstå utmattning bättre med mindre fixturdiameter än med större fixturdiameter. · Fixturer med diameter 5,0 mm visar större tendens för skruvfrakturer och skruvlossning jämfört med fixturer med 3,5 mm. · Mer omfattande studier beträffande implantat-förankrade bro-konstruktioner på distansnivå med frihängande led och olika fixturdiametrar krävs för att säkerställa resultaten.

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The objective of this study was to evaluate and develop an understanding of durability of an adhesive bonded system, for application in a future high speed civil transport (HSCT) aircraft structure. The system under study was comprised of Ti-6Al-4V metal adherends and a thermosetting polyimide adhesive, designated as FM-5, supplied by Cytec Engineered Materials, Inc. An approach based on fracture mechanics was employed to assess Ti-6Al-4V/FM-5 bond durability. Initially, wedge tests were utilized to find a durable surface pretreatment for the titanium adherends. Based on an extensive screening study, chromic acid anodization (CAA) was chosen as the standard pretreament for this research project. Double cantilever beam specimens (DCB) were then made and aged at 150° C, 177° C, and 204° C in three different environments; ambient atmospheric air (14.7 psia), and reduced air pressures of 2 psi air (13.8 KPa) and 0.2 psi air (1.38 KPa). Joints were aged for up to 18 months (including several intermediate aging times) in the above environments. The strain energy release rate (G) of the adhesive joints was monitored as a function of exposure time in the different environments. A 40% drop in fracture toughness was noted over the 18 month period, with the greatest degradation observed in samples aged at 204° C in ambient atmospheric air pressure. The loss in adhesive bond performance with time was attibutable to a combination of physical and chemical aging phenomena in the FM-5 resin, and possible degradation of the metal-adhesive interface(s). Several mechanical and material tests, performed on the bonded joints and neat FM-5 resin specimens, confirmed the above statement. It was also noted that physical aging could be "erased" by thermal rejuvenation, partially restoring the toughness of the FM-5 adhesive material. The FM-5 adhesive material displayed good chemical resistance towards organic solvents and other aircraft fluids such as jet fuel and hydraulic fluid. The results from the FM-5 adhesive and its bonded joints were compared and contrasted with VT Ultem and REGULUS polyimide adhesives. The FM-5 adhesive showed the best performance among the three adhesive systems. The effect of mode-mixity on the fracture toughness of the Ti-6Al-4V/FM-5 adhesive bonded system was also evaluated. DCB tests in conjunction with end-notched flexure (ENF) and mixed-mode flexure (MMF) tests, were used to fracture the bonded joints under pure mode I, pure mode II, and a combination of mode I and II loadings. The results showed that the mode I fracture toughness was twice as large as the mode II toughness. This was a rather surprising find, in sharp contrast to what several researchers have observed in the past. Our current understanding is that the crack path selection during the failure process plays a significant role in explaining this anomalous behavior. Finally, failure envelopes were generated for the titanium/FM-5 bonded system, both prior to and following thermal aging. These envelopes could serve as useful tools for engineers designing with Ti-6Al-4V/FM-5 bonds. / Ph. D.

We model the nonlinear dynamics of a cantilever beam with tip mass system subjected to different excitation and exploit the nonlinear behavior to perform sensitivity analysis and propose a parameter identification scheme for nonlinear piezoelectric coefficients. First, the distributed parameter governing equations taking into consideration the nonlinear boundary conditions of a cantilever beam with a tip mass subjected to principal parametric excitation are developed using generalized Hamilton's principle. Using a Galerkin's discretization scheme, the discretized equation for the first mode is developed for simpler representation assuming linear and nonlinear boundary conditions. We solve the distributed parameter and discretized equations separately using the method of multiple scales. We determine that the cantilever beam tip mass system subjected to parametric excitation is highly sensitive to the detuning. Finally, we show that assuming linearized boundary conditions yields the wrong type of bifurcation. Noting the highly sensitive nature of a cantilever beam with tip mass system subjected to parametric excitation to detuning, we perform sensitivity of the response to small variations in elasticity (stiffness), and the tip mass. The governing equation of the first mode is derived, and the method of multiple scales is used to determine the approximate solution based on the order of the expected variations. We demonstrate that the system can be designed so that small variations in either stiffness or tip mass can alter the type of bifurcation. Notably, we show that the response of a system designed for a supercritical bifurcation can change to yield a subcritical bifurcation with small variations in the parameters. Although such a trend is usually undesired, we argue that it can be used to detect small variations induced by fatigue or small mass depositions in sensing applications. Finally, we consider a cantilever beam with tip mass and piezoelectric layer and propose a parameter identification scheme that exploits the vibration response to estimate the nonlinear piezoelectric coefficients. We develop the governing equations of a cantilever beam with tip mass and piezoelectric layer by considering an enthalpy that accounts for quadratic and cubic material nonlinearities. We then use the method of multiple scales to determine the approximate solution of the response to direct excitation. We show that approximate solution and amplitude and phase modulation equations obtained from the method of multiple scales analysis can be matched with numerical simulation of the response to estimate the nonlinear piezoelectric coefficients. / Master of Science

In this thesis, a miniaturized energy harvester system is developed. The energy harvester converts fluid kinetic energy into electrical energy without using any rotating components. The working principle of the energy harvester is based on the so called vortex-induced vibration. Such systems have the potential to provide energy for wireless sensor networks in the field of inline measurements for gas, oil or water transportation systems. The theoretical background of the vortex-induced vibration (VIV) is studied. Based on the studies, a fluid-structure interaction simulation is carried out to optimize the structure of the energy harvester. As result, the conversion efficiency is significantly improved, which is experimentally confirmed. A series of demonstrators are manufactured according to the simulation and optimization results. It is tested on a self-constructed test bench. To further improve the performance, an electromagnetic generator is proposed, and therefore, a multimethod demonstrator realized. The demonstrators are working in air flow already at a velocity of 2 m/s, and reach the maximum efficiency at 3.6 m/s. This performance ranks among the best published results and is discussed in detail. / In der vorliegenden Arbeit wird ein miniaturisiertes Energiegewinnungssystem entwickelt, das unter Verzicht auf rotierende Komponenten kinetische Strömungsenergie in elektrische Energie umwandelt. Die Funktion dieses Wandlers basiert auf der sogenannten wirbelinduzierten Vibration. Derartige Systeme besitzen unter anderem das Potenzial, drahtlose Sensornetzwerke zur Erfassung von Messdaten in Gas-, Öl- oder Wassertransportsystemen mit Energie zu versorgen zu können. In der Arbeit wird der theoretische Hintergrund der wirbelinduzierten Vibration untersucht und darauf basierend werden Fluid-Struktur-Wechselwirkungssimulationen zur Strukturoptimierung durchgeführt in deren Ergebnis eine theoretische Verbesserung der Effizienz des Wandlers um ein Mehrfaches erreicht wird, die auch praktisch bestätigt wird. Unter Berücksichtigung der Simulations- und Optimierungsergebnisse wurden eine Reihe von Demonstratoren gefertigt, die auf einem selbst konstruierten Prüfstand getestet wurden. Zur weiteren Erhöhung der Leistungsfähigkeit des Wandlers wird ein zusätzlicher elektromagnetischer Generator vorgeschlagen und damit ein Multi-Methoden-Demonstrator technisch realisiert. Die Demonstratoren arbeiten in strömender Luft bereits bei Geschwindigkeiten von 2 m/s und erreichen bei 3,6 m/s ihre maximale Effizienz. Die erreichten Ergebnisse ordnen sich im Vergleich mit denen aus entsprechenden Publikationen vorn ein und werden ausführlich diskutiert.

Design of retaining structures depends upon the load which is transferred from backfill soil as well as external loads and also the resisting capacity of the structure. The traditional safety factor approach of the design of retaining structures does not address the variability of soils and loads. The properties of backfill soil are inherently variable and influence the design decisions considerably. A rational procedure for the design of retaining structures needs to explicitly consider variability, as they may cause significant changes in the performance and stability assessment. Reliability based design enables identification and separation of different variabilities in loading and resistance and recommends reliability indices to ensure the margin of safety based on probability theory. Detailed studies in this area are limited and the work presented in the dissertation on the Optimum design of retaining structures under static and seismic conditions: A reliability based approach is an attempt in this direction. This thesis contains ten chapters including Chapter 1 which provides a general introduction regarding the contents of the thesis and Chapter 2 presents a detailed review of literature regarding static and seismic design of retaining structures and highlights the importance of consideration of variability in the optimum design and leads to scope of the investigation. Targeted stability is formulated as optimization problem in the framework of target reliability based design optimization (TRBDO) and presented in Chapter 3. In Chapter 4, TRBDO approach for cantilever sheet pile walls and anchored cantilever sheet pile walls penetrating sandy and clayey soils is developed. Design penetration depth and section modulus for the various anchor pulls are obtained considering the failure criteria (rotational, sliding, and flexural failure modes) as well as variability in the back fill soil properties, soil-steel pile interface friction angle, depth of the water table, total depth of embedment, yield strength of steel, section modulus of sheet pile and anchor pull. The stability of reinforced concrete gravity, cantilever and L-shaped retaining walls in static conditions is examined in the context of reliability based design optimization and results are presented in Chapter 5 considering failure modes viz. overturning, sliding, eccentricity, bearing, shear and moment failures in the base slab and stem of wall. Optimum wall proportions are proposed for different coefficients of variation of friction angle of the backfill soil and cohesion of the foundation soil corresponding to different values of component as well as lower bounds of system reliability indices. Chapter 6 presents an approach to obtain seismic passive resistance behind gravity walls using composite curved rupture surface considering limit equilibrium method of analysis with the pseudo-dynamic approach. The study is extended to obtain the rotational and sliding displacements of gravity retaining walls under passive condition when subjected to sinusoidal nature of earthquake loading. Chapter 7 focuses on the reliability based design of gravity retaining wall when subjected to passive condition during earthquakes. Reliability analysis is performed for two modes of failure namely rotation of the wall about its heel and sliding of the wall on its base are considering variabilities associated with characteristics of earthquake ground motions, geometric proportions of wall, backfill soil and foundation soil properties. The studies reported in Chapter 8 and Chapter 9 present a method to evaluate reliability for external as well as internal stability of reinforced soil structures (RSS) using reliability based design optimization in the framework of pseudo static and pseudo dynamic methods respectively. The optimum length of reinforcement needed to maintain the stability against four modes of failure (sliding, overturning, eccentricity and bearing) by taking into account the variabilities associated with the properties of reinforced backfill, retained backfill, foundation soil, tensile strength and length of the geosynthetic reinforcement by targeting various component and system reliability indices is computed. Finally, Chapter 10 contains the important conclusions, along with scope for further work in the area. It is hoped that the methodology and conclusions presented in this study will be beneficial to the geotechnical engineering community in particular and society as a whole.

Parmi les polytypes les plus connus du carbure de silicium (SiC), le polytype cubique (3C-SiC), est le seul qui peut croitre sur des substrats silicium. L’hétérostructure 3C-SiC/Si est intéressante non seulement pour son faible coût de production mais aussi pour la conception de Systèmes Micro-Electro-Mécaniques (« MEMS »). La valeur élevée du module de Young du 3C-SiC, comparé à celui du silicium, permettrait à des cantilevers submicroniques, fabriqués à partir de films minces de 3C-SiC, de vibrer à ultra-hautes fréquences (>100MHz). Cette haute fréquence de résonance est la clé pour obtenir un système AFM non-contact ultra-sensible et rapide. Cependant, il n’existe pas de cantilever en SiC disponible sur le marché en raison de la difficulté à élaborer des films minces de 3C-SiC de bonne qualité, la technique de synthèse la plus utilisée étant le Dépôt Chimique en phase Vapeur (CVD). La raison première de cette difficulté à obtenir un matériau de bonne qualité réside essentiellement dans l’important désaccord de maille et la différence de dilatation thermique entre le 3C-SiC et Si qui génèrent des défauts cristallins à l’interface et jusqu’à la surface du film de 3C-SiC, la zone la plus défectueuse se localisant auprès de l’interface……. / Among aIl the well known polytypes ofihe silicon carbide (SiC), the cubic polytype (3C-SiC) is the only one that min be grown on silicon substrates. This heterostructure 3C SiC/Si ta interesting not only for its low production cost but also for the design of tise Micro-Electro-Mechanical Systems (MEMS). The high value ofthe Young’s modulis the 3C-SiC, compared to the silicon, allows submicronic cantilevers, fabrmcated from tIse 3C-SiC thin filins, to resonate at ultra-high frequency (>100MHz). The high resonant frequency is the key to obtain s fast, ultra-sensitive non-contact AFM systein.However, there isn’t any SiC cantilevers available on the market because of the difficulty to elaborate gond quality 3C-SiC thin films, with tIse Chemical Vapor Deposition (CVD) technique being tIse most frequently used synthesis technology. Tise first reason of tIse difficulty with the CVD technology to obtain gond quality thin film rests essentially in the important lattice mismatch and the difference in thermal expansion coefficient existing between 3C SiC and Si which generate crystalline defects at the interface and propagating tilI the 3C-SiC filin surface, with the inost defective zone localizing near the interface…….

Le dimensionnement des joints collés est une préoccupation majeure du CNES pour lesapplications spatiales des futurs lanceurs. Pour dimensionner une structure collée, il est nécessaire depouvoir apprécier les caractéristiques mécaniques du joint collé.Dans cette étude, trois adhésifs structuraux ont été sélectionnés (Hysol®EA 9321, Hysol®EA9394 et Hysol EA® 9395). Après leur caractérisation massique, une étude statistique pour mettre enévidence les effets des différents paramètres (vitesse d’essai, géométrie éprouvette, le degré depolymérisation…) a été entreprise.La deuxième étape a pour objectif de fiabiliser l’analyse des essais de fissuration etd’améliorer la compréhension des mécanismes d’endommagement et de propagation de fissure dansles liaisons collées. Trois types d’essai ont été utilisés, à savoir, l’essai Double Cantilever Beam(DCB), pour l’étude du mode I, l’essai End Notched Flexure (ENF), pour le mode II, et l’essai MixedMode Bending (MMB), pour les chargements en mode mixte I/II. Nous avons développé de nouvellesinstrumentations et méthodologies d’analyse. Pour affiner le protocole de test standard, la techniquedite de « backface strain monitoring » a été utilisée. Elle consiste à positionnées des jauges dedéformation sur les surfaces de l’éprouvette de façon à enregistrer l’évolution du signalextensométrique durant la propagation de la fissure. Cette méthode permet une meilleure estimation dela position front de fissure ainsi que l'étude de la répartition des contraintes le long du joint de colle.La corrélation d'images numériques (DIC) a également été utilisée afin de proposer un nouveauprotocole de calibrage de la longueur de fissure et pour comparer un modèle analytique (poutre deTimoshenko sur fondation élastique) avec les résultats expérimentaux. / Adhesive bonding is being strongly considered in space applications CNES as anadvantageous assembly technique for future launchers. Correct design of adhesive joints is of majorconcern. Aerospace adhesives are tough viscoelastic matrices (special epoxy resins) reinforced withnano-, or microparticles. Extended use of adhesive joints in structural applications is limited due to thedifficulties in predicting in-service performance, frequently leading to over-conservative design.Three structural adhesives (Hysol®EA 9321, Hysol®EA 9394 and Hysol®EA 9395) wereselected. After their bulk characterization, statistical studies to highlight effects of different parameterse.g. speed, test piece geometry, degree of polymerization were undertaken.In the second stage, fracture mechanics tests were effected employing: the double cantileverbeam (DCB) configuration (mode I characterisation), the three point bending end-notched flexure(ENF) (mode II) and the mixed-mode bending (MMB) (combined mode I/II loading). Crack growth inbonded joints was investigated in a novel way. To refine standard test protocol, the backface strainmonitoring technique was used. Strain gauges were used to measure the strain on the exposed skin ofthe adherends during crack onset and propagation. This method allows better estimation of the crackfront position as well as fine investigation of the stress distribution along the bondline and in the crackfront vicinity. Digital image correlation (DIC) was also used to compare analytical models, e.g.Timoshenko beam on elastic foundation model with experimental results.