This thesis present novel non-destructive laboratory test methods to characterize asphalt concrete. The testing is based on frequency response measurements of specimens where resonance frequencies play a key role to derive material properties such as the complex modulus and complex Poisson’s ratio. These material properties are directly related to pavement quality and used in thickness design of pavements. Since conventional cyclic loading is expensive, time consuming and complicated to perform, there has been a growing interest to apply resonance and ultrasonic testing to estimate the material properties of asphalt concrete. Most of these applications have been based on analytical approximations which are limited to characterizing the complex modulus at one frequency per temperature. This is a significant limitation due to the strong frequency dependency of asphalt concrete. In this thesis, numerical methods are applied to develop a methodology based on modal testing of laboratory samples to characterize material properties over a wide frequency and temperature range (i.e. a master curve). The resonance frequency measurements are performed by exciting the specimens using an impact hammer and through a non-contact approach using a speaker. An accelerometer is used to measure the resulting vibration of the specimen. The material properties can be derived from these measurements since resonance frequencies of a solid are a function of the stiffness, mass, dimensions and boundary conditions. The methodology based on modal testing to characterize the material properties has been developed through the work presented in paper I and II, compared to conventional cyclic loading in paper III and IV and used to observe deviations from isotropic linear viscoelastic behavior in paper V. In paper VI, detailed measurements of resonance frequencies have been performed to study the possibility to detect damage and potential healing of asphalt concrete.  The resonance testing are performed at low strain levels (~10^-7) which gives a direct link to surface wave testing of pavements in the field. This enables non-destructive quality control of pavements, since the field measurements are performed at approximately the same frequency range and strain level. / <p>QC 20141117</p>

In this dissertation the work done in the projects KME-410/502 will be presented.The overall objective in these projects is to evaluate and develop tools for designingagainst fatigue in single-crystal nickel-base superalloys in gas turbines. Experimentshave been done on single-crystal nickel-base superalloy specimens in order toinvestigate the mechanical and fatigue behaviour of the material. The constitutivebehaviour has been modelled and veried by FE-simulations of the experiments.Furthermore, the microstructural degradation during long-time ageing has been investigatedwith respect to the material's yield limit. The eect has been includedin the constitutive model by lowering the resulting yield limit. Moreover, the fatiguecrack initiation of a component has been analysed and modelled by using acritical plane approach in combination with a critical distance method. Finally, asan application, the derived single-crystal model was applied to all the individualgrains in a coarse grained specimen to predict the dispersion in fatigue crack initiationlife depending on random grain distributions. This thesis is divided into three parts. In the rst part the theoretical framework,based upon continuum mechanics, crystal plasticity, the critical plane approachand the critical distance method, is derived. This framework is then used in thesecond part, which consists of six included papers. Finally, in the third part, detailsof the used numerical procedures are presented.

[pt] O estudo de materiais inteligentes tem instigado várias aplicações nas mais diversas áreas do conhecimento (da área médica à industria aeroespacial). Os materiais mais utilizados em estruturas inteligentes são as ligas com memória de forma, as cerâmicas piezoelétricas, os materiais magneto-estrictivos e os fluidos eletro- reológicos. Nas últimas décadas, as ligas com memória de forma vêm recebendo atenção especial, sendo utilizadas principalmente como sensores ou atuadores. Existe uma gama de fenômenos associados a estas ligas que podem ser explorados. Visando uma análise mais precisa do comportamento destes materiais, tem se tornado cada vez maior o interesse no desenvolvimento de modelos matemáticos capazes de descrevê-los de maneira adequada, permitindo explorar todo o seu potencial. O objetivo deste trabalho é propor um modelo constitutivo unidimensional que considera quatro variantes de microconstituintes (austenita, martensita induzida por temperatura, martensita induzida por tensão trativa e martensita induzida por tensão compressiva) e diferentes propriedades para cada fase. O efeito das deformações induzidas por temperatura é incluído na formulação. O modelo contempla ainda o efeito das deformações plásticas e o acoplamento entre os fenômenos de plasticidade e transformação de fase. Além disso, são introduzidas modificações na formulação que permitem o alargamento do laço de histerese da curva tensão-deformação, fornecendo resultados mais coerentes com dados experimentais. Por fim, incorpora-se a assimetria no comportamento tração-compressão. A validação do modelo é obtida comparando os resultados numéricos obtidos através do modelo com resultados experimentais encontrados na literatura para ensaios de tração a diferentes temperaturas e para a assimetria no comportamento tração- compressão. / [en] The study of intelligent materials has instigated many applications within the various knowledge areas (from medical field to aerospace industry). The most used materials in intelligent structures are the shape memory alloys (SMA), the piezoelectric ceramics, the magnetostrictive materials and the electrorheological fluids. In the last decades, SMAs have received special attention, being mainly used as sensors or actuators. There is a number of phenomena related to these alloys that can be explored. Aiming a more precise analysis of SMA behavior, the interest on the development of mathematical models capable of describing these phenomena properly has grown, allowing to explore all their potential. The aim of this work is to propose a unidimensional constitutive model which considers four microconstituent variants (austenite, martensite induced by temperature, martensite induced by tensile loading and martensite induced by compressive loading) and different material properties for each phase. The effect of thermal strains is included in the formulation. The model considers the effect of plastic strains and the plastic-phase transformation coupling. Besides, some changes are introduced in the formulation in order to enlarge the stress-strain hysteresis loop, resulting in better agreements with experimental data. Eventually, the tensioncompression asymmetry is incorporated. The model validation is obtained through the comparison between the numerical results given by the model and experimental results found in the literature for tensile tests at different temperatures and for tension- compression asymmetry.

Severe plastic deformation methods are of great interest in industrial forming applications, as they give rise to significant refinement in microstructures and improvements in mechanical and physical properties. In the &ldquo / Equal Channel Angular Extrusion (ECAE)&rdquo / , which is the most common method for production of ultrafine grained bulk samples, very high plastic strains are introduced into the bulk material without any change in cross section. This study is composed of two main parts. Part I focuses on the plastic deformation behavior of Al alloys by modeling ECAE with Msc. Marc finite element software. A series of numerical experiments were carried out for the die angles of 90&deg / , 120&deg / , and 150&deg / , different friction conditions, and different round corners. Besides, the effects of strain hardening characteristics of the material, strain hardening coefficient (K) and exponent (n) of Hollomon&rsquo / s law, on corner gap formation and strain homogeneity in equal channel angular pressing process were investigated quantitatively. The results were compared and verified with those of the upper bound analysis. The numerical results showed that the process performance can be improved by modifying the die corner curvature accordingly, without running time consuming simulations. On the other hand, the aim of Part 3 is to investigate the texture evolution, mechanical response and the corresponding mechanisms, in terms of the flow stress anisotropy and tension-compression asymmetry in the ZK60 Mg alloy. The alloy was processed using ECAE, with different processing routes and temperatures, in order to produce samples with a wider variety of microstructures and crystallographic textures. Several mechanical tests and microstructure examinations were carried out / and the flow stress anisotropy and tension-compression asymmetry of the as-received and processed samples were measured. It was found that the initial texture has a strong effect on the resulting textures / and the textures, combined with the microstructure effect, define the mechanical properties of processed samples. Thus, the tension-compression asymmetry and the flow stress anisotropy variations in the processed samples are attributed to the generated textures and it is possible to control these properties by controlling the processing route and temperature.

The main aim of this thesis is to define material parameters of Chaboche model of plasticity. Adjustment of the parameters has to correspond to the experimental datas. These datas are represented by an uniaxial strain controlled test curve for fewer than two cycles and also by cyclic stress-strain curve. After that, an cyclic tension-compresion test for various parameters of Chaboche´s model of plasticity is simulated in an ANSYS software. Finally, the most suitable configuration of Chaboche´s model of plasticity is used for cylindrical thick-walled body. Cylindrical body represents a simplified model of high-pressure tank of fuel (diesel) – rail in Common Rail system.

In der Arbeit wird das thermo-mechanische Verhalten eines in der optischen Industrie oft verwendeten Klebstoffs zur Klebung opto-mechanischer Bauteile experimentell untersucht und für numerische Anwendungen hinreichend genaue mathematisch und physikalisch geeignet modelliert (Linse, Spiegel, etc.). Durch die Tatsache das diese Klebstoffe bei Raumtemperatur ihre Glasübergangstemperatur besitzen zeigen die Untersuchungen eine äußerst starke Veränderung der Materialeigenschaften über der Temperatur. Hervorzuheben sind die Zug-/Druckasymmetrie des elastischen Modul und die hydrostatisch abhängige Plastizität. Abgerundet werden diese Untersuchungen mit der Ermittlung der temperaturabhängigen thermischen Ausdehnung und des rein mechanisch wirksamen chemischen Schrumpf beim Abbinde-Prozess. Zu Beachten ist dass diese Untersuchungen bei Dehnraten konstanten Experimenten erfolgten. Kriech- bzw. Relaxationseffekte wurde aus dem Umfang dieser Arbeit ausgeschlossen. In erster Linie ist es von Interesse die Basis zu schaffen quasistatische thermisch und mechanische beanspruchte Klebungen untersuchen zu können. Die angesprochenen vernachlässigten Effekte können auf dieser Basis zukünftig untersucht und damit in der Modellierung berücksichtigt werden. Durch die im Rahmen der Arbeit gewonnenen Erkenntnisse werden Empfehlungen zur Auslegung solcher geklebter opto-mechanischer Baugruppen mit Standardmaterialmodellen wie das VON-MISES Plastizitätsmodell gegeben. Zusätzlich wird die Entwicklung eines zukünftigen Materialmodells, dass die genauere Modellierung der zuvor genannten Effekte gestattet, skizziert.:Inhaltsverzeichnis Abkürzungsverzeichnis IV Mathematische Operatoren und Notationen V Symbolverzeichnis VI 1 Einleitung 1.1 Problemstellung und Motivation 1.2 Zielsetzung 1.3 Stand der Technik 1.4 Aufbau von Klebungen und Klebstoffen 1.5 Mechanisches Verhalten von Klebungen 2 Grundlagen der Kontinuumsmechanik 2.1 Deformation und Verzerrung 2.2 Bilanzgleichungen 2.3 Konstitutive Gleichungen 2.3.1 Elastisches Materialverhalten 2.3.2 Invarianten des Spannungstensors und -deviators 2.3.3 Plastizität mit isotroper Verfestigung 2.3.4 Plastizitätsmodell nach VON MISES 2.3.5 Lineares DRUCKER-PRAGER-Modell 2.3.6 Weiterentwickelte DRUCKER-PRAGER-Modelle 2.4 Randwertproblem 2.5 Schwache Form der lokalen Impulsbilanz 3 Experimente zur Materialcharakterisierung 3.1 Uniaxialer Zugversuch 3.1.1 Prüfmaschine und -aufbau 3.1.2 Festlegung der Prüfgeschwindigkeit 3.1.3 Auswertung des Zugversuchs 3.1.4 Temperaturabhängige Zugversuche 3.2 Uniaxialer Druckversuch 3.2.1 Prüfmaschine und Auswertung Inhaltsverzeichnis II 3.2.2 Ergebnisse aus dem Druckversuch 3.3 Dreipunktbiegeversuch 3.3.1 Probenform und Prüfaufbau 3.3.2 Auswertungen beim Dreipunktbiegeversuch 3.3.3 Dehnratenkonstanten Prügeschwindigkeit 3.3.4 Temperaturabhängige Dreipunktbiegeexperimente 3.4 Zugscherversuch für dicke Fügeteile 3.4.1 Prüfmaschine und -aufbau 3.4.2 Probenform und Herstellung 3.4.3 Prüfgeschwindigkeit 3.4.4 Verschiebungsmessung 3.4.5 Auswertungen beim Zugscherversuch 3.4.6 Ergebnisse der Zugscherversuche 3.5 Temperaturabhängiger Ausdehnungskoeffizient 3.6 Messung des chemischen Schrumpfs 3.7 Invariantendarstellung bei Raumtemperatur 3.8 Zusammenfassung der Versuchsergebnisse 4 Simulationen 4.1 Finite-Elemente-Methode 4.1.1 LS-DYNA und MSC.Marc 4.1.2 Nichtlineare Optimierung 4.2 Parameteridentifikation aus den Experimenten 4.2.1 Einachsiger Zugversuch 4.2.2 Einachsiger Druckversuch 4.2.3 Dreipunktbiegeversuch 4.2.4 Zugscherversuch für dicke Fügeteile 5 Demonstratorexperimente und -simulationen 5.1 Zugscherverbund von Überlappungsklebungen 5.2 Demonstrator für chemischen Schrumpf 5.2.1 Einfluss einer reduzierten Klebelänge 5.3 Demonstrator für thermische Ausdehnung 6 Zusammenfassung und Ausblick

Deformation phenomena in shape memory alloys involve stress-, temperature-induced phase transformations and crystallographic variant conversion or reorientation, equivalent to a twinning operation. In near equiatomic NiTi, Ti rich compositions can exist near room temperature as a monoclinic B19' martensitic phase, which when deformed undergoes twinning resulting in strains as large as 8%. Upon heating, the martensite transforms to a cubic B2 austenitic phase, thereby recovering the strain and exhibiting the shape memory effect. Ni rich compositions on the other hand can exist near room temperature in the austenitic phase and undergo a reversible martensitic transformation on application of stress. Associated with this reversible martensitic transformation are macroscopic strains, again as large as 8%, which are also recovered and resulting in superelasticity. This work primarily focuses on neutron diffraction measurements during loading at the Los Alamos Neutron Science Center at Los Alamos National Laboratory. Three phenomena were investigated: First, the phenomena of hysteresis reduction and increase in linearity with increasing plastic deformation in superelastic NiTi. There is usually a hysteresis associated with the forward and reverse transformations in superelastic NiTi which translates to a hysteresis in the stress-strain curve during loading and unloading. This hysteresis is reduced in cold-worked NiTi and the macroscopic stress-strain response is more linear. This work reports on measurements during loading and unloading in plastically deformed (up to 11%) and cycled NiTi. Second, the tension-compression stress-strain asymmetry in martensitic NiTi. This work reports on measurements during tensile and compressive loading of polycrystalline shape-memory martensitic NiTi with no starting texture. Third, a heterogeneous stress-induced phase transformation in superelastic NiTi. Measurements were performed on a NiTi disc specimen loaded laterally in compression and associated with a macroscopically heterogeneous stress state. For the case of superelastic NiTi, the experiments related the macroscopic stress-strain behavior (from an extensometer or an analytical approach) with the texture, phase volume fraction and strain evolution (from neutron diffraction spectra). For the case of shape memory NiTi, the macroscopic connection was made with the texture and strain evolution due to twinning and elastic deformation in martensitic NiTi. In all cases, this work provided for the first time insight into atomic-scale phenomena such as mismatch accommodation and martensite variant selection. The aforementioned technique of neutron diffraction for mechanical characterization was also extended to engineering components and focused mainly on the determination of residual strains. Two samples were investigated and presented in this work; first, a welded INCONEL 718 NASA space shuttle flow liner was studied at 135 K and second, Ti-6Al-4V turbine blade components were investigated for Siemens Westinghouse Power Corporation. Lastly, also reported in this dissertation is a refinement of the methodology established in the author's masters thesis at UCF that used synchrotron x-ray diffraction during loading to study superelastic NiTi. The Los Alamos Neutron Science Center is a national user facility funded by the United States Department of Energy, Office of Basic Energy Sciences, under Contract No. W-7405-ENG-36. The work reported here was made possible by grants to UCF from NASA (NAG3-2751), NSF CAREER (DMR-0239512), Siemens Westinghouse Power Corporation and the Space Research Initiative.

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Neben Reifen, Riemen und Schläuchen zählen speziell auch die Balgwände von Luftfedern zu den Kompositen, da deren weiche Elastomermatrix zur Verstärkung Gewebelagen aus textilen Corden enthält. Diese Verstärkungsträger bestehen aus miteinander verzwirnten Garnen, die ihrerseits einen Zwirn aus polymeren Filamenten darstellen. Luftfederbälge weisen dementsprechend eine hochkomplexe innere Geometrie auf und sind zudem durch stark anisotropes, nichtlineares Materialverhalten gekennzeichnet. Für die strukturmechanische Simulation von Luftfedern mit der Finite-Elemente-Methode (FEM) werden in der vorliegenden Arbeit neuartige, hochauflösende Modelle entwickelt, die diesen Eigenschaften Rechnung tragen. Zunächst wird ein mathematisches Modell formuliert, das die verzwirnte Geometrie von Corden auf allgemeinen räumlichen Bahnkurven beschreibt und mithilfe dessen sich auch die lokale Orientierung der Filamente bestimmen lässt. Zur konstitutiven Modellierung des Filamentmaterials wird zudem ein transversal isotropes, hyperelastisches Materialmodell so modifiziert, dass bei Druckbelastung in Filamentrichtung nur noch die der Regularisierung dienende, isotrope Grundsteifigkeit zum Tragen kommt. Das Geometriemodell der Corde ist die Basis für deren dreidimensionale Abbildung in FE-Netzen von Luftfederbälgen. Als erster Schwerpunkt wird ein auf zyklischer Symmetrie basierendes Streifenmodell entwickelt, das die Cordgeometrie im gesamten Balg vollständig auflöst. Ein besonderes Augenmerk gilt dabei der Generierung konformer Netze, um die Grenzflächen zwischen Matrix und Corden exakt darzustellen. Das Streifenmodell ermöglicht somit detaillierte Analysen zur lokalen Verteilung von Spannungen und Verzerrungen im Inneren der Balgwand. Als zweiter Schwerpunkt wird diese Art der Modellierung auf einen kleinen rechteckigen Ausschnitt der Balgwand übertragen. Dieser Teppich ist als Submodell konzipiert, das Verschiebungen für seine Schnittränder aus einem vereinfachten Globalmodell bezieht und demzufolge die Analyse allgemeiner, nicht axialsymmetrischer Lastfälle möglich macht. Abschließend werden die Modelle anhand einer Rollbalgluftfeder für Busanwendungen eingehend untersucht und einem Praxistest zum Vergleich zweier Konstruktionsvarianten unterzogen. / Tires, belts, hoses and, in particular, air spring bellows are regarded as composites due to layers of reinforcing textile cords that are embedded in a soft elastomer matrix. These cords are produced by twisting yarns which, for their part, represent a twisted structure of polymeric filaments. Hence, air spring bellows feature a highly complex internal geometry as well as strongly anisotropic, nonlinear material behavior. For structural simulations of air springs by means of the finite element method (FEM), new high resolution models are developed here, which reflect all the aforementioned properties. At first, a mathematical model capable of representing the twisted geometry of cords on three-dimensional curves is introduced, which also allows to derive local filament orientations. For the constitutive description of filament material, a transversally isotropic, hyperelastic material model is modified so that only the small isotropic stiffness introduced for regularization remains in case of compressive loads in filament direction. The cord geometry model serves as the basis for their three-dimensional representation in FE meshes of air spring bellows. Firstly, the focus lies on developing a slice model relying on cyclic symmetry, which takes cord geometry into account throughout the entire bellows. Special emphasis is put on building conforming meshes in order to incorporate all material interfaces explicitly. As a result, the slice model allows for detailed analyses of local stress and strain distribution inside the bellows. Secondly, this type of modeling is applied to a rectangular section of the bellows. This carpet is conceived as a submodel acquiring the displacements to be imposed on its cut faces from a simplified global model, and therefore provides the opportunity to analyze general load cases not complying with axial symmetry. Based on a rolling lobe air spring used in bus applications, both models are examined thoroughly and, at last, subjected to a practical test comparing two different designs.

Für die Materialcharakterisierung und Parameteridentifikation von technischen Elastomeren werden homogene Probekörper benötigt. Eine besonders wichtige Beanspruchungsart ist dabei der einachsige Zug/Druck. Für Versuche dieser Art findet die Standard-Hantel Anwendung, die für kombinierte Zug-/Druckversuche geeignet ist. Allerdings lässt sich hier schon bei geringen Druckbelastungen ein inhomogener Messbereich detektieren. Ein Ziel dieser Arbeit besteht in der Entwicklung eines neuen und verbesserten Probekörpers, der für hochpräzise Zug-/Druckversuche geeignet ist. Im Gegensatz zur Standard-Hantel wird der für Messungen zugänglich gemachte homogene Messbereich deutlich verbessert. Darüber hinaus soll der Bereich der maximal erreichbaren Stauchung signifikant erhöht werden. Der Probekörper selbst weist dabei eine verhältnismäßig einfache Hantelgeometrie mit verlängertem Mittelteil auf. Durch ein spezielles Design der Halterungsgeometrie kann sowohl ein homogenes Verzerrungsfeld erreicht als auch eine hohe Knickstabilität gewährleistet werden. Die Grundidee besteht dabei darin, dass der Probekörper mit zunehmender Stauchung immer weiter mit der Halterungsgeometrie in Kontakt tritt und dadurch seine knickgefährdete Länge reduziert wird. Mit Hilfe eines speziellen Halterungsalgorithmus kann eine neue, verbesserte Halterungsgeometrie berechnet werden. Mit dem entwickelten Probekörper-Setup (bestehend aus Hantel- und Halterungsgeometrie) lassen sich dann eine Vielzahl phänomenologischer Eigenschaften von technischen Elastomeren wie Payne- Effekt, Mullins-Effekt, Erholungs- und Relaxationsverhalten vorzugsweise bei extremen Stauchungen (bis zu 70 %) untersuchen. Ein weiteres Ziel dieser Arbeit besteht in der Entwicklung eines Scherprobekörpers zur Realisierung präziser Schermessungen. Das Design soll dabei auf einem flächigen Probekörper (Elastomermatte) beruhen, um Alterungsuntersuchungen, Untersuchungen mit faserverstärkten Materialien und Versuche mit Vorreckungen realisieren zu können. Im Gegensatz zu herkömmlichen Scherprobekörpern soll dabei auf eine stoffschlüssige Verbindung mittels Kleben oder Anvulkanisieren aufgrund von Materialirritationen oder Schrumpf verzichtet werden. Im Rahmen dieser Arbeit wurde diesbezüglich ein spezielles Fixierdesign mit Stiften entwickelt, welches zur Ausbildung nahezu homogener Scherdeformationen führt. Damit lassen sich eine Vielzahl wichtiger Eigenschaften bei einer annähernd homogenen Scherdeformation untersuchen. / Homogeneous test specimens are required for material characterization and model parameter identification. An important kind of loading is uniaxial tension/compression. For this, a standard dumbbell is available for combined tension-compression tests. But even for small compressive strains the standard dumbbell leads to an inhomogeneous stress state in the measuring zone. One aim of this work is the development of a new test specimen, which is suitable for high-precision tension/compression tests. In comparison to the standard dumbbell the homogeneity in the measuring zone is significantly improved. Furthermore, the range of maximal compression is increased substantially. The test specimen itself consists of a slender dumbbell structure. By a special design of the mounting geometry, homogeneous stress and strain fields as well as a high stability can be achieved. For an increasing compression, the test specimen comes into contact with the mounting geometry and the critical length is reduced. By means of dynamic analysis, the mounting geometry was calculated and optimized. This method is a powerful tool for developing new mounting geometries, by taking into account both the stability and the homogeneity characteristic. With the developed specimen-setup (consisting of dumbbell and mounting geometry), the phenomenological characteristics of rubber like Payne effect, Mullins effect, recovery and relaxation behavior can be investigated up to a compressive strain of 70 %. Another aim of this work is the development of a shear specimen, which enables precision shear measurements for large shear values. The design is based on a planar test specimen (rubber mat) in order to enable ageing tests, tests with fibre-reinforced materials and tests with pre-stretching. In contrast to other shear specimens, a material-locking connection by gluing or vulcanizing sould be avoided in consequence of material irritation or shrinkage. For this, a special fixing design was developed, which enables a uniform initiation of shear deformation for different rubber thicknesses. Finally, the new shear specimen enables the investigation of typical rubber properties.