Three dimensional (3D) woven composites have attracted the interest of academia and industry thanks to their damage tolerance characteristics and automated fabric manufacturing. Although much research has been conducted to investigate their out-of-plane "through thickness" properties, still their in-plane properties are not fully understood and rely on extensive experimentation. The aim of this work is to study the electromechanical behaviour of three different fibre architectures of 3D woven composites "orthogonal (ORT), layer-to-layer (LTL) and angle interlock (AI)" loaded, in three different orientations "warp (0º), weft (90º) and off-axis (45º)", in quasi-static tension. Stress/strain response is captured as well as damage initiation and evolution up to final failure. The ORT architecture demonstrated a superior behaviour, in the off-axis direction, demonstrated by high strain to failure (~23%) and high translaminar energy absorption (~40 MJ/m3). The z-binder yarns in ORT suppress delamination and allow larger fibre rotation during the fibre "scissoring motion" that enables further strain to be sustained. In-situ electrical resistance variation is monitored using a four-probe technique to correlate the resistance variation with the level of damage induced while loading. Monotonic and cyclic "load/unload" tests are performed to investigate the effect of piezo-resistivity and residual plasticity on resistance variation while damage is captured by X-ray scanning during interrupted tests at predefined load levels. In addition, this study investigates the potential of using 3D woven composites in joint assemblies through open-hole tension and "single fastener double-lap joint" bearing strength tests. 3D woven composites in the off-axis orientation, especially ORT, demonstrate a potential for overcoming some of the major challenges for composite joints' applications which are the pseudo-ductility, stress redistribution away from the notch and notch insensitivity. Finally, the study proposes a micro-mechanics based damage model to simulate the response of 3D orthogonal woven composites loaded in tension. The proposed model differs from classical damage mechanics approaches in which the evolution law is obtained by retrofitting global experimental observations.

Electrical trees are micrometre-size tubular channels of degradation in high voltage polymeric insulation, a precursor to failure of electrical power plant. Hence, electrical trees critically affect the reliability of power systems and the performance of new insulation designs. Imaging laboratory-grown electrical trees has been an important tool for studying how trees develop. Commonly, electrical trees prepared in transparent or translucent polymers are imaged using traditional optical methods. Consequently, most of the analysis has been based on two-dimensional (2D) images of trees, thus, valuable information may be lost. However, electrical trees are complex interconnected structures that require a tree-dimensional (3D) approach for more complete analysis. This thesis investigates a method for imaging and analysis of electrical trees to characterise their 3D structure and provide a platform for further modelling. Laboratory created electrical trees were imaged using X-ray Computed Tomography (XCT) and Serial Block-Face Scanning Electron Microscopy (SBFSEM), 3D imaging techniques that provide sub-micrometre spatial resolution. Virtual replicas of the trees, which are the 3D geometrical models representing the real electrical trees, were generated and new indices to characterise the 3D structure of electrical trees were developed. These parameters were indicative of differences in tree growth and thus, they can be used to investigate patterns and classify the structure of electrical trees. The progression of the tree was analysed using cross-sections of the tree that are orthogonal to the growth: the number of tree channels and area covered by them were measured. The fractal dimension of the tree was calculated from the 3D model and from the 2D projections, the latter being lower for all the tree-type structures studied. Parameters from the skeleton of the tree such as number of nodes, segment length, tortuosity and branch angle were measured. Most of the mean segment lengths ranged 6-13 µm, which is in accordance to the 10µm proposed by various tree-growth models. The capabilities of XCT and SBFSEM imaging techniques were evaluated in their application to electrical trees. Bush and branch trees, including early-growth electrical trees (of length 20-40 µm), were analysed and compared using the comprehensive tool of visualisation and characterisation developed. A two-stage tree-growth experiment was conducted to analyse the progression and development of tree branches using XCT: tree channels after the second stage of growth were wider than after the first, while the fractal dimension remained the same. The capabilities of XCT and SBFSEM were tested for imaging electrical trees in optically-opaque materials such as micro and nano-filled epoxy compounds. The general structure of trees in epoxy filled up to 20 wt% micro-silica was observed using both techniques. The use of a virtual replica as the 3D geometrical model for the simulation of the electric field distribution using Finite Element Analysis (FEA) was preliminary explored. A combination of the imaging techniques is proposed for a more complete structural analysis of trees. It is believed that a great impact towards understanding electrical treeing will be achieved using the 3D technical platform developed in this thesis.

Cone penetration in sands is a complex process: it contains several challenges that geomechanicians face, such as large displacements, large strains, strain localization, and microscale phenomena such as particle crushing and sand fabric evolution. In order to gain a deeper understanding of the penetration process and the mechanisms controlling penetration resistance, capturing these displacement and strain fields and microscale phenomena is necessary. Furthermore, as more sophisticated theoretical models become available for the simulation of the cone penetration problem, the experimental validation of those methods becomes vital.<br><div><br></div><div>This dissertation presents a multiscale study of the cone penetration process in silica sands. The penetration problem is investigated using a combinational approach consisting of calibration chamber experiments, digital image correlation (DIC) analysis, and X-ray computed Tomography (XCT) scans. Three silica sands with different particle characteristics are used in the experimental program. These three sands have similar particle size distributions; however, they differ in particle morphologies and particle strengths. These differences allow a study of the effect of microscale sand properties on the macroscale response of the sands to the cone penetration process. The three silica sands used in this research are fully characterized using laboratory experiments to obtain particle size distributions, particle morphologies, particle crushing strengths, minimum and maximum packing densities, and critical-state friction angles. Subsequently, both dense and medium-dense samples of the three sands are compressed in a uniaxial loading device placed inside an X-ray microscope (XRM) and scanned at multiple stress levels during uniaxial compression. Results from uniaxial compression experiments indicate that: (1) the compressibility of the sands is closely tied to particle morphology and strength, and (2) the anisotropy in the orientations of interparticle contact normals generally increases with axial stress; however, this increase is limited by the occurrence of particle crushing in the sample.<br></div><div><br></div><div>Subsequently, cone penetration experiments are performed under different confinement levels on dense samples of the three sands in aspecial half-cylindrical calibration chamber equipped with DIC capabilities. For each penetration experiment, incremental displacement fields around the cone penetrometer are obtained using DIC analysis, and these incremental displacement fields are further analyzed to compute the incremental strain fields. A novel methodology is developed to obtain the shear-band patterns that develop around the penetrometer automatically. Furthermore, differences in the shear-band patterns in deep and shallow penetration environments are also investigated. Results show that strain fields tend to localize intensely near the penetrometer tip, and the shear bands tend to develop along the inclined face and near the shoulder of the penetrometer. Significant differences in the shear band patterns in deep and shallow penetration environments are also observed.<br></div><div><br></div><div>After each cone penetration experiment, a specially developed agar-impregnation technique is used to collect minimally disturbedsand samples from around the penetrometertip. These agar-impregnated sand samples are scanned in the XRM to obtain 3D tomography data, which are further analyzed to quantify particle crushing around the penetrometer tip. The results show that: (1) for a given sample density, the amount of crushing around the cone penetrometer depends on the confinement and the sand particle characteristics, (2) the level of crushing is not uniform around the penetrometer tip, with more severe crushing observed near the shoulder of the penetrometer, and (3) the regions with more severe particle crushing around the penetrometer approximately overlap with regions of high shear strain and volumetric contraction. A framework is also proposed to obtain the ratio of penetration resistance in more crushable sands to penetration resistance in less crushable sands. Furthermore, a novel resin-impregnation technique is also developed to collect undisturbedsand samples from around the penetrometer tip. The resin-impregnated sand sample collected after one of the penetration experiments is scanned in the XRM to obtain the 3D tomography data, which is then analyzed to obtain the distribution of interparticle contact normal orientations at multiple locations around the penetrometer tip. These analyses indicate that the interparticle contact normals tend to orient themselves with the incremental principal strains around the penetrometer: below the penetrometer tip, the interparticle contact normals orient vertically upwards, while closer to the shoulder of the penetrometer, the interparticle contact normals become more radially inclined.<br></div><div><br></div><div>Data presented in this dissertation on penetration resistance, incremental displacement fields, incremental strain fields, particle crushing, and interparticle contact normal orientations around the cone penetrometer are aimed to be useful to researchers working on the multiscale modeling of penetration processes in granular materials and aid in the further development of our understanding of penetration processes in sands.<br></div>

Asphalt joints are potentially weakest parts of every pavement. Despite of their importance, reliable tools for measuring their mechanical properties for design and performance assessments are still scarce. This is particularly true for cold joints when attaching a new hot pavement to a cold existing one as in case of large patches for pavement repair. In this study, three static fracture testing methods, i.e. indirect tensile test (IDT), direct tension test (DTT) and 4 point bending (4PB), were adapted and used for evaluating different laboratory made joints. The results suggested that joints with inclined interfaces and also the ones with combined interface treatments (preheated and sealed) seemed to show more promising behaviors than the vertical and untreated joints. It was also confirmed that compacting from the hot side towards the joint improved the joint properties due to imposing a different flow pattern as compared to the frequent compaction methods. The latter finding highlighted the importance of asphalt particle rearrangements and flow during the compaction phase as a very little known subject in asphalt industry. Studies on compaction are of special practical importance since they may also contribute to reducing the possibility of over-compaction and aggregate crushing. Therefore, in this study, a new test method, i.e. Flow Test (FT), was developed to simulate the material flow during compaction. Initially, asphalt materials were substituted by geometrically simple model materials to lower the level of complexity for checking the feasibility of the test method as well as modeling purposes. X-ray radiography images were also used for capturing the flow patterns during the test. Results of the FT on model materials showed the capability of the test method to clearly distinguish between specimens with different characteristics. In addition, a simple discrete element model was applied for a better understanding of the test results as a basis for further improvements when studying real mixtures. Then, real mixtures were prepared and tested under the same FT configuration and the results were found to support the findings from the feasibility tests. The test method also showed its potential for capturing flow pattern differences among different mixtures even without using the X-ray. Therefore, the FT was improved as an attempt towards developing a systematic workability test method focusing on the flow of particles at early stages of compaction and was called the Compaction Flow Test (CFT). The CFT was used for testing mixtures with different characteristics to identify the parameters with highest impact on the asphalt particle movements under compaction forces. X-ray investigations during the CFT underlined the reliability of the CFT results. In addition, simple discrete element models were successfully generated to justify some of the CFT results. / <p>QC 20151104</p>

<div>The mechanical behaviors of different kinds of biological tissues, including muscle tissues, cortical bones, cancellous bones and skulls, were studied under various loading conditions to investigate their strain-rate sensitivities and loading-direction dependencies. Specifically, the compressive mechanical behaviors of porcine muscle were studied at quasi-static (<1/s) and intermediate (1/s─10^2/s) strain rates. Both the compressive and tensile mechanical behaviors of human muscle were investigated at quasi-static and intermediate strain rates. The effect of strain-rate and loading-direction on the compressive mechanical behaviors of human frontal skulls, with its entire sandwich structure intact, were also studied at quasi-static, intermediate and high (10^2/s─10^3/s) strain rates. The fracture behaviors of porcine cortical bone and cancellous bone were investigated at both quasi-static (0.01mm/s) and dynamic (~6.1 m/s) loading rates, with the entire failure process visualized, in real-time, using the phase contrast imaging technique. Research effort was also focused on studying the dynamic fracture behaviors, in terms of fracture initiation toughness and crack-growth resistance curve (R-curve), of porcine cortical bone in three loading directions: in-plane transverse, out-of-plane transverse and in-plane longitudinal. A hydraulic material testing system (MTS) was used to load all the biological tissues at quasi-static and intermediate loading rates. Experiments at high loading rates were performed on regular or modified Kolsky bars. Tomography of bone specimens was also performed to help understand their microstructures and obtain the basic material properties before mechanical characterizations. Experimental results found that both porcine muscle and human muscle exhibited non-linear and strain-rate dependent mechanical behaviors in the range from quasi-static (10^(-2)/s─1/s) to intermediate (1/s─10^2/s) loading rates. The porcine muscle showed no significant difference in the stress-strain curve between the along-fiber and transverse-to-fiber orientation, while it was found the human muscle was stiffer and stronger along fiber direction in tension than transverse-to fiber direction in compression. The human frontal skulls exhibited a highly loading-direction dependent mechanical behavior: higher ultimate strength, with an increasing ratio of 2, and higher elastic modulus, with an increasing ratio of 3, were found in tangential loading direction when compared with those in the radial direction. A transition from quasi-ductile to brittle compressive mechanical behaviors of human frontal skulls was also observed as loading rate increased from quasi-static to dynamic, as the elastic modulus was increased by factors of 4 and 2.5 in the radial and tangential loading directions, respectively. Experimental results also suggested that the strength in the radial direction was mainly depended on the diploë porosity while the diploë layer ratio played the predominant role in the tangential direction. For the fracture behaviors of bones, straight-through crack paths were observed in both the in-plane longitudinal cortical bone specimens and cancellous bone specimens, while the cracks were highly tortuous in the in-plane transverse cortical bone specimens. Although the extent of toughening mechanisms at dynamic loading rate was comparatively diminished, crack deflections and twists at osteon cement lines were still observed in the transversely oriented cortical bone specimens at not only quasi-static loading rate but also dynamic loading rate. The locations of fracture initiations were found statistical independent on the bone type, while the propagation direction of incipient crack was significantly dependent on the loading direction in cortical bone and largely varied among different types of bones (cortical bone and cancellous bone). In addition, the crack propagation velocities were dependent on crack extension over the entire crack path for all the three loading directions while the initial velocity for in-plane direction was lower than the other two directions. Both the cortical bone and cancellous bone exhibited higher fracture initiation toughness and steeper R-curves at the quasi-static loading rate than the dynamic loading rate. For cortical bone at a dynamic loading rate (5.4 m/s), the R-curves were steepest, and the crack surfaces were most tortuous in the in-plane transverse direction while highly smooth crack paths and slowly growing R-curves were found in the in-plane longitudinal direction, suggesting an overall transition from brittle to ductile-like fracture behaviors as the osteon orientation varies from in-plane longitudinal to out-of-plane transverse, and to in-plane transverse eventually.</div>

Im Rahmen der vorliegenden Dissertationsschrift „Semi-quantitative röntgentomographische Untersuchungen zur Biodistribution von magnetischen Nanopartikeln in biologischem Gewebe“ wurden tomographische Untersuchungen an biologischen Objekten durchgeführt. Bei diesen Objekten handelt es sich um Gewebeproben nach minimal-invasiven Krebstherapien wie zum Beispiel magnetischem Drug Targeting und magnetischer Wärmebehandlung. Der Erfolg dieser Therapien ist sowohl abhängig von der korrekten Verteilung der magnetischen Nanopartikel als auch von der Tatsache, dass diese in der Zielregion in einer ausreichenden Menge vorhanden sind. Das Vorliegen dieser beiden Voraussetzungen ist in der vorliegenden Arbeit untersucht worden. Dabei lag der Schwerpunkt der Arbeit auf der Quantifizierung von magnetischem Material in unterschiedlichen biologischen Gewebeproben mittels Röntgenmikrocomputertomographie (XµCT). Für diesen Zweck wurde ein Kalibrationssystem mit speziellen Phantomen entwickelt, mit dessen Hilfe eine Nanopartikelkonzentration einem Grauwert voxelweise zugewiesen werden kann. Mit Hilfe der Kalibration kann der Nanopartikelgehalt sowohl in monochromatischen als auch in polychromatischen tomographischen Daten im Vergleich zu magnetorelaxometrischen Ergebnissen mit wenigen Prozent Abweichung ermittelt werden. Trotz Polychromasie und damit einhergehenden Artefakten können 3-dimensionale röntgentomographische Datensätze mit einer geringfügigen Konzentrationsabweichung im Vergleich zur quantitativen Messmethode Magnetorelaxometrie semi-quantitativ ausgewertet werden. / The success of the minimal invasive cancer therapies, called magnetic drug targeting and magnetic heating treatment, depends strongly on the correct distribution of the magnetic nanoparticles on one side. On the other side it depends on the fact that a sufficient amount of magnetic nanoparticles carrying drugs is accumulated in the target region. To study whether these two requirements are fulfilled motivates this PhD thesis „Semi-quantitative X-ray-tomography examinations of biodistribution of magnetic nanoparticles in biological tissues“. The analysis of the distribution of the magnetic nanoparticles in tumours and other tissue examples is realized by means of X-ray-micro computer tomography (XμCT). The work focuses on the quantification of the magnetic nanoparticles in different biological tissue samples by means of XµCT. A calibration of the tomographic devices with adequate phantoms, developed in the frame of this work, opens now the possibility to analyze tomographic data in a semi-quantitative manner. Thus, the nanoparticle concentration can be allocated voxel-wise to the grey values of the three-dimensional tomographic data. With the help of calibration of the tomography equipments used, polychromatic as well as monochromatic three-dimensional representations of objects can be analyzed with regard to the biodistribution of magnetic nanoparticles as well as with regard to their quantity. The semi-quantitative results have been compared with results obtained with a quantitative measurement method magnetorelaxometry (MRX). Thereby a good agreement of the semi-quantitative and quantitative data has been figured out.

Im Rahmen der vorliegenden Dissertationsschrift „Semi-quantitative röntgentomographische Untersuchungen zur Biodistribution von magnetischen Nanopartikeln in biologischem Gewebe“ wurden tomographische Untersuchungen an biologischen Objekten durchgeführt. Bei diesen Objekten handelt es sich um Gewebeproben nach minimal-invasiven Krebstherapien wie zum Beispiel magnetischem Drug Targeting und magnetischer Wärmebehandlung. Der Erfolg dieser Therapien ist sowohl abhängig von der korrekten Verteilung der magnetischen Nanopartikel als auch von der Tatsache, dass diese in der Zielregion in einer ausreichenden Menge vorhanden sind. Das Vorliegen dieser beiden Voraussetzungen ist in der vorliegenden Arbeit untersucht worden. Dabei lag der Schwerpunkt der Arbeit auf der Quantifizierung von magnetischem Material in unterschiedlichen biologischen Gewebeproben mittels Röntgenmikrocomputertomographie (XµCT). Für diesen Zweck wurde ein Kalibrationssystem mit speziellen Phantomen entwickelt, mit dessen Hilfe eine Nanopartikelkonzentration einem Grauwert voxelweise zugewiesen werden kann. Mit Hilfe der Kalibration kann der Nanopartikelgehalt sowohl in monochromatischen als auch in polychromatischen tomographischen Daten im Vergleich zu magnetorelaxometrischen Ergebnissen mit wenigen Prozent Abweichung ermittelt werden. Trotz Polychromasie und damit einhergehenden Artefakten können 3-dimensionale röntgentomographische Datensätze mit einer geringfügigen Konzentrationsabweichung im Vergleich zur quantitativen Messmethode Magnetorelaxometrie semi-quantitativ ausgewertet werden. / The success of the minimal invasive cancer therapies, called magnetic drug targeting and magnetic heating treatment, depends strongly on the correct distribution of the magnetic nanoparticles on one side. On the other side it depends on the fact that a sufficient amount of magnetic nanoparticles carrying drugs is accumulated in the target region. To study whether these two requirements are fulfilled motivates this PhD thesis „Semi-quantitative X-ray-tomography examinations of biodistribution of magnetic nanoparticles in biological tissues“. The analysis of the distribution of the magnetic nanoparticles in tumours and other tissue examples is realized by means of X-ray-micro computer tomography (XμCT). The work focuses on the quantification of the magnetic nanoparticles in different biological tissue samples by means of XµCT. A calibration of the tomographic devices with adequate phantoms, developed in the frame of this work, opens now the possibility to analyze tomographic data in a semi-quantitative manner. Thus, the nanoparticle concentration can be allocated voxel-wise to the grey values of the three-dimensional tomographic data. With the help of calibration of the tomography equipments used, polychromatic as well as monochromatic three-dimensional representations of objects can be analyzed with regard to the biodistribution of magnetic nanoparticles as well as with regard to their quantity. The semi-quantitative results have been compared with results obtained with a quantitative measurement method magnetorelaxometry (MRX). Thereby a good agreement of the semi-quantitative and quantitative data has been figured out.