In der Zahnmedizin werden endodontische Instrumente aus metallischen und polymeren Werkstoffen zur Desinfektion infizierter Wurzelkanalsysteme eingesetzt. Durch den Einsatz von Polymeren ergeben sich aufgrund ihrer günstigen Werkstoffeigenschaften die Vorzüge einer minimal invasiven Arbeitsweise und einer geringeren Bruchgefahr. Demgegenüber besitzen die eingesetzten metallischen Instrumente durch hochfrequente Oszillationen eine verbesserte Reinigungswirkung. Zur Auslegung optimierter polymerbasierter Instrumente, die zuverlässig reinigen, wird daher eine simulationsbasierte Entwicklungsmethode erarbeitet. Ausgangspunkt hierfür ist die ingenieurwissenschaftliche Analyse der methodischen und experimentellen Grundlagen des Gesamtsystems. Die Beschreibung des instationären Schwingungsverhaltens der Instrumente erfolgt durch dynamische Finite-Elemente-Analysen unter Verwendung eines viskoelastischen Materialmodells. Das dazu erforderliche Materialverhalten des ausgewählten Polymers Polyetheretherketon wird mithilfe eines neu entwickelten Prüfaufbaus charakterisiert. Das erarbeitete Simulationsmodell ermöglicht erstmalig eine Analyse des kontaktmechanischen Verhaltens polymerer Miniaturstrukturen unter hochfrequenter Schwingungsanregung. Im Ergebnis steht mit diesem Modell eine realitätsnahe Beschreibung des Schwingungsverhaltens und der auftretenden Beanspruchungen zur Verfügung. Die gewonnenen Erkenntnisse leisten einen wesentlichen Beitrag zur gezielten, werkstoffgerechten und schwingungsoptimierten Auslegung von zukünftigen zahnmedizinischen Instrumenten zur Wurzelkanalreinigung.:1 Einleitung 1.1 Literaturübersicht 1.2 Problemstellung und Zielsetzung 2 Thermoplastische Polymere für die Anwendung in endodontischen Instrumenten 2.1 Mechanische und technische Anforderungen 2.1.1 Bestimmung einer repräsentativen Wurzelkanalgeometrie 2.1.2 Schwingungstechnik und Aufbau von Reinigungsansätzen 2.1.3 Werkstoffauswahl für Reinigungsansätze 2.1.4 Fertigungstechnologien für Miniaturstrukturen aus PEEK 2.2 Biologische und mechanische Wechselwirkungen 2.2.1 Verhalten gegenüber desinfizierenden Spüllösungen 2.2.2 Tribologie der Wurzelkanalreinigung 3 Analyse des zyklischen Verformungsverhaltens von PEEK 3.1 Phänomenologische Beschreibung des Verformungsverhaltens 3.1.1 Klassifizierung des Materialverhaltens 3.1.2 Elastische Verformung thermoplastischer Polymere 3.1.3 Mechanische Dämpfung 3.2 Experimentelle Untersuchungen 3.2.1 Probekörper 3.2.2 Versuchsaufbau und Durchführung 3.2.3 Voruntersuchungen 3.2.4 Ergebnisse der experimentellen Untersuchungen 4 Modellierung des zyklischen Deformationsverhaltens von PEEK 4.1 Einachsige rheologische viskoelastische Materialmodelle 4.1.1 Allgemeine konstitutive Gleichungen 4.1.2 Einachsige rheologische Grundelemente 4.1.3 Einachsige rheologische Modelle 4.1.4 Vergleich der einachsigen rheologischen Modelle 4.2 Charakterisierung des viskoelastischen Materialverhaltens 4.2.1 Analytische Beschreibung der Balkenschwingung 4.2.2 Resonanzkurvenverfahren 4.2.3 Bestimmung der Materialparameter von PEEK 4.3 Numerische Implementierung eines mehrachsigen Materialmodells 4.3.1 Mehrachsiges Materialmodell 4.3.2 Validierung des implementierten Materialmodells 5 Simulation des Schwingungsverhaltens und experimentelle Verifikation 5.1 Numerische Simulationsmodelle 5.1.1 Geometrische Modelle 5.1.2 Rand- und Anfangsbedingungen 5.1.3 Kontaktmodellierung 5.2 Simulationsergebnisse 5.2.1 Schwingungsverhalten ohne Oberflächenkontakt 5.2.2 Schwingungsverhalten mit Oberflächenkontakt 6 Zusammenfassung Literaturverzeichnis A Experimentelle Voruntersuchungen B Klassische Balkentheorie / In dentistry, endodontic instruments made of metallic and polymer materials are used for the disinfection of infected root canal systems. Due to their beneficial material properties, the use of polymers offers the advantages of a minimally invasive operation and a lower risk of breakage. In contrast, the metallic instruments used have an improved cleaning efficiency due to high-frequency oscillations. A simulation-based development method for the design of optimized polymer-based instruments that clean effectively is therefore being worked out. As starting point, an engineering analysis of the methodological and experimental fundamentals of the overall system has been carried out. The description of the instrument’s transient vibration behavior is performed by dynamic finite element analyses using a viscoelastic material model. The required material behavior of the selected polymer polyetheretherketone is characterized with the aid of a newly developed test setup. The resulting simulation model allows for the first time an analysis of the contact mechanical behavior of polymeric miniaturized structures under high-frequency vibration excitation. As a result, this model provides a realistic description of the vibration behavior and the stresses that occur. The knowledge gained will make a significant contribution to the targeted, material-specific and vibration-optimized design of future dental instruments for root canal irrigation.:1 Einleitung 1.1 Literaturübersicht 1.2 Problemstellung und Zielsetzung 2 Thermoplastische Polymere für die Anwendung in endodontischen Instrumenten 2.1 Mechanische und technische Anforderungen 2.1.1 Bestimmung einer repräsentativen Wurzelkanalgeometrie 2.1.2 Schwingungstechnik und Aufbau von Reinigungsansätzen 2.1.3 Werkstoffauswahl für Reinigungsansätze 2.1.4 Fertigungstechnologien für Miniaturstrukturen aus PEEK 2.2 Biologische und mechanische Wechselwirkungen 2.2.1 Verhalten gegenüber desinfizierenden Spüllösungen 2.2.2 Tribologie der Wurzelkanalreinigung 3 Analyse des zyklischen Verformungsverhaltens von PEEK 3.1 Phänomenologische Beschreibung des Verformungsverhaltens 3.1.1 Klassifizierung des Materialverhaltens 3.1.2 Elastische Verformung thermoplastischer Polymere 3.1.3 Mechanische Dämpfung 3.2 Experimentelle Untersuchungen 3.2.1 Probekörper 3.2.2 Versuchsaufbau und Durchführung 3.2.3 Voruntersuchungen 3.2.4 Ergebnisse der experimentellen Untersuchungen 4 Modellierung des zyklischen Deformationsverhaltens von PEEK 4.1 Einachsige rheologische viskoelastische Materialmodelle 4.1.1 Allgemeine konstitutive Gleichungen 4.1.2 Einachsige rheologische Grundelemente 4.1.3 Einachsige rheologische Modelle 4.1.4 Vergleich der einachsigen rheologischen Modelle 4.2 Charakterisierung des viskoelastischen Materialverhaltens 4.2.1 Analytische Beschreibung der Balkenschwingung 4.2.2 Resonanzkurvenverfahren 4.2.3 Bestimmung der Materialparameter von PEEK 4.3 Numerische Implementierung eines mehrachsigen Materialmodells 4.3.1 Mehrachsiges Materialmodell 4.3.2 Validierung des implementierten Materialmodells 5 Simulation des Schwingungsverhaltens und experimentelle Verifikation 5.1 Numerische Simulationsmodelle 5.1.1 Geometrische Modelle 5.1.2 Rand- und Anfangsbedingungen 5.1.3 Kontaktmodellierung 5.2 Simulationsergebnisse 5.2.1 Schwingungsverhalten ohne Oberflächenkontakt 5.2.2 Schwingungsverhalten mit Oberflächenkontakt 6 Zusammenfassung Literaturverzeichnis A Experimentelle Voruntersuchungen B Klassische Balkentheorie

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Over recent decades, the public tendency toward using the structural composite lumber (SCL), a common composite of wood made of wood strands or veneers glued and compressed together, as structural members (especially the main load bearing members such as beams and columns) has risen considerably. In contrast to the fast-paced market growth of these products, development is slow. The experimental development is gradual and time-consuming and the computational development is even slower. The objective of this project is to introduce appropriate numerical models for limit state analysis of a certain type of SCL material called PSL. Parallel strand lumber (PSL), has mesostructures characterized by the presence of voids that renders the mesostructure highly heterogeneous. In addition to material phase aberrations such as grain angle variations and defects, void heterogeneities play an important role in determining the failure modes and strength of PSL. In this study, virtual void structures were defined to form part of the input to finite element analysis of PSL for the purpose of investigating the sensitivity of strength to the void structure. Assuming the wood phase to be homogeneous and orthotropic, the following 2D and 3D characteristics of voids were investigated: volume fraction, volume, alignment and moments of inertia of voids, as well as second moment properties, lineal path function and chord length functions of the two phase mesostructure. In addition, a method was developed to generate virtual voids in order to simulate PSL and investigate the possible effects of the void distribution on material strength. An experimental program along with a statistical survey was conducted to quantify the mentioned characteristics of the voids in two 133 mm * 133 mm * 610 mm 2.0 E Eastern Species PSL billets. As expected, most of the voids lie on the longitudinal direction of the specimen and have approximately an ellipsoidal shape. Based on this shape data, the characteristics of the ellipsoids which best t the voids were calculated. Using the statistical data of the fitted ellipsoids, a random field of virtual ellipsoid shaped voids to simulate the mesostructure of PSL was generated. In this study, the simulation of PSL material is based on two simplifying assumptions: 1) The wood phase is continuum, homogeneous and orthotropic. While in reality, the wood phase consists of glued wood strands that are heterogeneous due to their mechanical variability and only roughly orthotropic on a macro scale as a result of the varying fiber angle; 2) Voids are the mere source of uncertainty. The linear elastic analysis of carefully defined (in mesostructural aspect) PSL models can be the first step of mechanical study of the material. The effective modulus of elasticity of material in presence of voids and the distribution of conventional, principal and effective stresses considering the effect of volume fraction and shape of the voids are the target of this preliminary study. Linear elastic uniaxial analyses showed good mechanical consistency between the models including actual void shapes and the models including ellipsoidal void representations. Also, they showed that the stress mutliaxiality at the tip of the voids is negligible. The study of mechanics of PSL is incomplete unless the question of material anisotropy is taken into consideration. PSL is brittle in tension and ductile in compression. The material heterogeneity increases the complexity of the problem by affecting the stress distribution in the member. A detailed nonlinear approach has been proposed in order to investigate the mechanical behavior of PSL structural members under different uniaxial loading scenarios. This approach introduces proper constitutive models for the wood phase along with good void generation techniques. In other words, this approach suggests what models should be used for the continuum-assumed wood phase to simulate its brittle behavior in tension and ductile behavior in compression; and moreover, tests the applicability and accuracy of ellipsoidal void representation. The models are calibrated using the results of experiments on PSL material. Because of the brittle behavior, all wood products show significant mechanical dependency to the member's size under tensile loading. Once good constitutive model and mesostructural simulation is found for tensile loading, it is easy to make and analyze PSL models with different sizes and investigate the effect of size on mechanical behavior. The simulation results have been compared to the available results of a previously done experimental study.

For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system. The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features. The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components. / Ett sätt att nå målen med minskade koldioxidutsläpp inom industrin är att producera lättare komponenter. Aluminium-kisel (Al-Si) gjutna legeringar är därför ett bra alternativ då dessa legeringar har ett bra förhållande mellan hållfasthet och vikt, goda korrosionsegenskaper, utmärkt gjutbarhet och är ett återvinningsbart material. En av de största utmaningarna för att producera högpresterande komponenter för kritiska applikationer är variationerna i egenskaper inom dessa komponenter. Orsaken till att inte gjutna Al-Si legeringar andvänds i dessa applikationer är förståelsen av defekter och mikrostruktuella faser påverkar de mekaniska egenskaperna negativt. Koppar (Cu) tillsätts i Al-Si legeringar för att öka de mekaniska egenskaperna vilket ofta nyttjas inom bilindustrin. Hot isostatic pressing (HIP) prosessen är en annan möjlighet att förbättra de mekaniska egenskaperna genom att reducera porositeter i materialet. Studien syftar till att undersöka de mekaniska egenskaperna och sprickinitiering och spricktillväxt i en gjuten legering av Al-7Si-Mg med utmattningstestning i svepelektronmikroskop (SEM) i kombination med electron backscatter diffraction, digital image correlation och focused ion beam (FIB). Mängden Cu i Al-Si legeringen påverkade de statiska mekaniska egenskaperna genom att öka sträckgränsen och brottgränsen. Tillsats av Cu upp till 1.5 vikt.% påverkar inte spricktillväxten märkbart. Däremot förändras beteendet markant vid tillsatser av Cu på mer än 3.0 vikt.% som resulterade i en markant reducering i duktilitet. I det värmebehandlade materialet påverkades de mekaniska egenskaperna av Al-matrisen och mängden intermetalliska faser. Avståndet mellan Cu faserna och Si faserna används för att beskriva spricktillväxten i Al-Si legeringarna. Detta tillsammans med tredimensionell tomografi visade att legeringen med 3.2 vikt.% Cu hade en ökad mängd sprickor i området framför den avancerande sprickan, vilket inte den Cu fria legeringen visade. Al-Si legeringen som utsattes för HIP-processen och värmebehandlingen visade att materialets mikrostruktur i gjutet tillstånd påverkade resultatet. HIP processen slöt porositerena i alla undersökta prover och förbättrade de mekaniska egenskaperna. Dessa resultat kommer kunna användas för att konstruera mer högpresterande komponenter.

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In this thesis, the discharge products formed at the cathode and the performance and cell chemistry of sodium-oxygen batteries have been studied. This was carried out using different NaOTf salt concentrations. The influence of different salt concentrations on sodium-oxygen batteries was investigated since it has been shown that increasing the salt concentration beyond conventional concentrations could result in advantages such as increased stability of the electrolytes towards decomposition, higher thermal stability and lower volatility. An increase in salt concentration has also been shown to influence the electrochemical potential window. The solubility of NaOTf was investigated in two different solvents, DME and diglyme. NaOTf was found to be more soluble in DME compared to diglyme but due to the volatile nature of DME, three different concentrations of NaOTf were prepared with diglyme as solvent. Experimentation involved discharging the batteries to either maximum or limited capacity. The discharge products were examined and characterized using XRD and SEM. The main discharge product was identified as sodium superoxide although sodium peroxide dihydrate was also identified in one battery. A trend of higher capacity and voltage plateaus with higher salt concentration was also found. The influence of trace amounts of water was suggested as one explanation as it works as a catalyst, promoting sodium superoxide cube growth due to improved transportation of superoxide. Another or contributing explanation could be a possible change in donor number with increased salt concentration, resulting in higher solubility and longer lifetime of superoxide, promoting the growth of sodium superoxide cubes.

Ce travail de recherche est dédié à la compréhension des mécanismes physiques de l’érosion de cavitation dans un fluide compressible à l’échelle fondamentale de l’implosion d’une bulle de cavitation. Suite à l’implosion d’une bulle de vapeur à proximité d’une surface solide, des très hautes pressions sont générées. Ces pressions sont considérées responsables de l’endommagement (érosion) des surfaces solides observé dans la plupart des applications. Notre approche numérique démarre avec le développement d’un solveur compressible capable de résoudre les bulles de cavitation au sein du code volumes finis YALES2 en utilisant un simple modèle de mélange homogène des phases fluides. Le solveur est étendu à une approche ALE (Arbitraire Lagrangien Eulérien) dans le but de mener des simulations d’interaction fluide-structure sur un maillage mobile. La réponse du matériau solide est calculée avec le code de calcul éléments finis Cast3M, et nous a permis de mener des simulation avec un couplage d’abord monodirectionnel, ensuite bidirectionnel, entre le fluide et le solide. On compare des résultats obtenus à deux dimensions, puis à trois, avec des observations expérimentales. On discute les chargements de pression estimés, et les réponses de différents matériaux pour des implosions de bulle à des différentes distances de la surface. Enfin, à travers l’utilisation de simulations avec couplage bidirectionnel entre fluide et solide, on identifie l’amortissement des chargements de pression pour les différents matériaux. / This research is devoted to understanding the physical mechanism of cavitation erosion in compressible liquid flows on the fundamental scale of cavitation bubble collapse. As a consequence of collapsing bubbles near solid wall, high pressure impact loads are generated. These pressure loads are believed to be responsible for the erosive damages on solid surface observed in most applications. Our numerical approach begins with the development of a compressible solver capable of resolving the cavitation bubbles in the finite-volume solver YALES2 employing a simplified homogenous mixture model. The solver is extended to Arbitrary Lagrangian-Eulerian formulation to perform fluid structure interaction simulation with moving mesh capabilities. The material response is resolved with the finite element solver Cast3M, which allowed us to perform one-way and two-way coupled simulations between the fluid and solid domains. In the end, we draw comparisons between 2D and 3D vapor bubble collapse dynamics and compare them with experimental observations. The estimated pressure loads on the solid wall and different responses of materials for attached and detached bubble collapses are discussed. Finally, the damping of pressure loads by different materials is identified with two-way coupled fluid-structure interaction.

Este trabalho apresenta duas técnicas de ensaios não-destrutivos por ultra-som realizados em um tanque com água para determinar as constantes elásticas de materiais compostos de fibra de vidro/epóxi. A primeira técnica é a transmissão direta utilizando um par de transdutores. A segunda é a técnica de pulso-eco, utilizando um único transdutor. A água do tanque atua como um acoplante para transferir a energia mecânica do transdutor para a amostra. Como o transdutor não fica em contato direto com a amostra, pode-se garantir um acoplamento constante. O sistema de medição dota de um dispositivo que permite medir a velocidade da onda elástica sob diferentes ângulos de incidência, através da rotação manual da amostra. Devido ao fenômeno de conversão de modos com incidência oblíqua na interface amostra-água, ensaios por ultra-som em tanques com água fornecem as informações necessárias para o cálculo das constantes elásticas em amostras de materiais anisotrópicos, numa dada direção, a partir das medições das velocidades longitudinal e de cisalhamento. Numa dada direção de propagação em um meio anisotrópico, existem três ondas elásticas distintas: uma longitudinal e duas de cisalhamento. Se as constantes elásticas do material são conhecidas, é possível obter as três velocidades em uma dada direção bastando resolver a equação de Christoffel. Invertendo a equação de Christoffel, obtém-se as constantes elásticas a partir das velocidades medidas em uma dada direção. Os experimentos são realizados com amostras de fibra de vidro/epóxi unidirecionais e bidirecionais, utilizando transdutores com freqüências de 0,5 MHz, 1 MHz e 2,25 MHz. Os resultados experimentais obtidos utilizando ambas as técnicas são comparados com um modelo denominado “Regra das Misturas" e com resultados da literatura. / In this work, two ultrasonic non destructive techniques were implemented in a water tank and used to determine the elastic constants of glass-epoxy composites samples. The first is the through-transmission technique implemented with a pair of ultrasonic transducers. The second is the back-reflection technique that uses a single transducer in pulse-eco mode. The water acts as a couplant and transfers the mechanical energy from the transducer to the sample. As the transducer is not in direct contact with the sample, we can guarantee a good coupling with the immersion technique. With the system device, it is possible to measure the velocities of the elastic waves in different angles by manually rotating the sample. Due to wave mode conversion phenomenon at the sample-water interface with oblique incidence, ultrasonic immersion testing provides information to calculate the elastic constants of the specimen by measuring longitudinal and shear wave speeds. There are three different modes of waves, one longitudinal and two shear waves, for any given direction of propagation in an anisotropic medium. If the elastic constants of a medium are known, it is possible to obtain the three wave speeds in particular propagations directions by solving the Christoffel equation. Inverting the Christoffel equation, it is possible to obtain the elastic constants from the measured wave speed in several specific directions of the anisotropic material. Measurements were carried out on unidirectional and bidirectional glass-epoxy composite samples, using transducers with central frequency of 0.5 MHz, 1 MHz, and 2.25 MHz. The experimental results obtained with both techniques are compared with a model denominated “Rule of Mixture" estimation and with the literature.

abstract: Being a remarkably versatile and inexpensive building material, concrete has found tremendous use in development of modern infrastructure and is the most widely used material in the world. Extensive research in the field of concrete has led to the development of a wide array of concretes with applications ranging from building of skyscrapers to paving of highways. These varied applications require special cementitious composites which can satisfy the demand for enhanced functionalities such as high strength, high durability and improved thermal characteristics among others. The current study focuses on the fundamental understanding of such functional composites, from their microstructural design to macro-scale application. More specifically, this study investigates three different categories of functional cementitious composites. First, it discusses the differences between cementitious systems containing interground and blended limestone with and without alumina. The interground systems are found to outperform the blended systems due to differential grinding of limestone. A novel approach to deduce the particle size distribution of limestone and cement in the interground systems is proposed. Secondly, the study delves into the realm of ultra-high performance concrete, a novel material which possesses extremely high compressive-, tensile- and flexural-strength and service life as compared to regular concrete. The study presents a novel first principles-based paradigm to design economical ultra-high performance concretes using locally available materials. In the final part, the study addresses the thermal benefits of a novel type of concrete containing phase change materials. A software package was designed to perform numerical simulations to analyze temperature profiles and thermal stresses in concrete structures containing PCMs. The design of these materials is accompanied by material characterization of cementitious binders. This has been accomplished using techniques that involve measurement of heat evolution (isothermal calorimetry), determination and quantification of reaction products (thermo-gravimetric analysis, x-ray diffraction, micro-indentation, scanning electron microscopy, energy-dispersive x-ray spectroscopy) and evaluation of pore-size distribution (mercury intrusion porosimetry). In addition, macro-scale testing has been carried out to determine compression, flexure and durability response. Numerical simulations have been carried out to understand hydration of cementitious composites, determine optimum particle packing and determine the thermal performance of these composites. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2018