Strontium pyrophosphate is a promising phosphate that is used widely in the industry as a result of its luminescent, fluorescent, dielectric, semi-conductor, catalyst, magnetic and ion exchange properties. Thermoluminescent dosimetry (TLD) is one of such areas. Recent researches in METU on thermoluminescence property of strontium pyrophosphate showed that strontium pyrophosphate could give enough intensity for radiation dosimetry when doped with oxides of some rare-earth elements. In this study strontium pyrophosphate was synthesized and the product was doped with copper-silver, copper-indium and manganese-praseodymium ions by solid-state reaction. In addition to these processes, characterization and the investigation of thermoluminescence properties of strontium pyrophosphate with and without dopants was conducted. Stoichiometric quantities of strontium carbonate and ammonium dihydrogen phosphate were weighed, mixed and ground by agate mortar. Afterwards, the mixture was heated at 900&amp / #730 / C for 14.5 hours. For doping process, synthesized strontium pyrophosphate and different amounts of copper oxide, indium oxide, silver nitrate, manganese oxide and praseodymium oxide were weighed and powdered together. Then, mixture was heated at 950&amp / #730 / C for 11 hours. For characterization of strontium pyrophosphate samples with and without dopants / X-ray Diffraction (XRD) was implemented. Fourier Transform Infrared Spectroscopy (FTIR) was used to determine whether the bond structures were affected from doping or not. Thermal properties of the samples were investigated with the help of Differential Thermal Analysis (DTA). Morphology of compounds was observed by Scanning Electron Microscope (SEM). Afterwards thermoluminescence (TLD) studies were carried out. XRD pattern of samples showed that the intensity of hkl-310 peak of strontium pyrophosphate increased with the inclusion of metal oxides, however none of the characteristic peaks of metal oxides was observed. Addition of metal oxides caused no change in FTIR meaning that the anionic part of matrix compound, which is strontium pyrophosphate, has structural stability. Thermal analysis and morphological investigation of this material were performed. TLD results were different for each sample, which has different content. The most significant peak, which is suitable for radiation dosimetry was observed at 160&amp / #730 / C in the glow curve with the sample doped with 7% manganese oxide and 1% praseodymium oxide.

A novel material characterization method for magneto-dielectric composite material was proposed. MD materials have been reported as providing new opportunities for effective antenna size reduction in many studies. Since MD materials have to be realized through material synthesis, an accurate measurement method is required to extract them. The proposed method, cavity perturbation technique using substrate integrated waveguide cavity resonator, has been demonstrated through theories, simulations and measurement that it can be used to extract both electric and magnetic properties of the MD composite material effectively. MD materials using cobalt-fluoropolymer have been synthesized and material design guidelines for antenna applications are also provided. The benefits of using MD materials on antenna miniaturization was also demonstrated by comparing the performance of an antenna on MD material to other antennae on high dielectric constant materials and FR-4 material. Through simulations and measurements, the MD material is a promising solution for next generation smartphone or wearable type applications.

Low temperature cracking is a major distress in asphalt pavements. Several test configurations have been introduced to characterize the fracture properties of hot mix (HMA); however, most are considered to be research tools due to the complexity of the test methods or equipment. This dissertation describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be deployed at the Department of Transportation level. The primary advantages of this innovative and yet practical test include: relatively large fracture surface test zone, simplicity of the specimen geometry, widespread availability of the required test equipment, and ability to test laboratory compacted specimens as well as field cores. Numerical modeling was utilized to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. To develop the test procedure, a laboratory study was conducted to determine the optimal test parameters for HMA material. An experimental plan was then developed to evaluate the capability of the test in capturing the variations in the mix properties, asphalt pavement density, asphalt material aging, and test temperature. Five plant-produced HMA mixtures were used in this extensive study, and the results revealed that the IRT fracture test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Furthermore, an analytical model was developed based on the viscoelastic properties of HMA to estimate the maximum allowable crack size for the pavements in the experimental study. This analysis indicated that the low-temperature cracking potential of the asphalt mixtures is highly sensitive to the fracture toughness and brittleness of the HMA material. Additionally, the IRT fracture test data seemed to correlate well with the data from the distress survey which was conducted on the pavements after five years of service. The maximum allowable crack size analysis revealed that a significant improvement could be realized in terms of the pavements performance if the HMA were to be compacted to a higher density. Finally, the IRT fracture test data were compared to the results of the disk-shaped compact [DC(t)] test. The results of the two tests showed a strong correlation; however, the IRT test seemed to be more repeatable.

Bolts and rivets are produced by cold forging technique. A great majority of metal forming companies prefer to use their dexterity rather than science and technology. The main aim of this thesis is to establish an environment for developing technology in bolt production by reducing trial and error. In this thesis finite element method is utilized to model bolt forming for correcting tooling designs, removing production defects and estimating forging forces. Material characterization, precise determination of boundary conditions and verification of numerical results are also investigated. It is shown how efficient the finite element method is for technology development in metal forming industry. Furthermore, two anomalies in extrusion process are presented: The hump and the force hill in extrusion force-displacement curve. Reasons of these two anomalies are studied using finite element simulations and verified by experiments. Thesis also explains reduction methods of three-dimensional problems to axisymmetric models and compares the results.

Cemented carbide containing sub carbide phases, M6C and M12C, known as eta-phase, increases the lifetime milling cutters due to increased resistance to comb cracks. When milling, the inserts much sustain high temperatures, meaning edgeline toughness and thermal fatigue resistance are needed. To obtain this, finer grains and higher binder content are needed. In this study, WC-Co cemented carbides with eta-phase and Cr as well as a higher binder content are investigated. The microstructure is the focus, with parameters such as eta-phase particle size and volume fraction, WC grain size being evaluated. Another part of the study is the investigate the effect of Cr on heat treatment. The addition of Cr in a WC-Co cemented carbide with eta-phase has shown to give rise to smaller eta-phase particle sizes and WC grain size as compared to without Cr. Also, increasing the volume fraction of eta-phase has less influence on WC and eta-phase particle size. Heat treated samples without Cr is shown to increase the coercivity of the samples at 700 degrees Celsius, without change in WC grain size. The effect is also leading to an increase in hardness. But with addition of Cr, the effect seems to diminish.

L’hydroformage de tube nécessite l’emploi d’outillage coûteux et la phase de mise au point utilise intensivement la simulation par éléments finis. Pour ces simulations, il est nécessaire de disposer de données matériaux adaptées dans le domaine plastique. Le comportement des matériaux utilisés en mise en forme dépend du mode de sollicitation. Ainsi, plusieurs essais de caractérisation tels que l’essai de traction et les essais de gonflement de flan et de tube sont traités dans ce travail.On s’intègre dans une démarche pragmatique afin d’offrir des méthodes simples pour une mise en œuvre dans un contexte industriel en limitant le nombre d’essai, une méthode expérimentale de caractérisation simple et une méthode d’analyse des résultats expérimentaux efficace. De plus, on se limite à des modèles matériaux disponibles dans tout type de code de calcul comme la loi d’écrouissage de Swift et le critère de plasticité de Hill 1948.Après une introduction des différents types d’hydroformage et des notions de bases du comportement plastique des matériaux, la mise en œuvre des essais est présentée. On retiendra qu’il existe plusieurs façons de post-traiter les résultats expérimentaux. La méthode classique a été choisie pour l’essai de traction, celle préconisée par Koç et al. est utilisée pour le gonflement de flan et enfin la méthode de Boudeau et Malécot a été adoptée pour le gonflement de tube.À partir des essais effectués sur un acier austénitique inoxydable de type AISI 304, plusieurs courbes d’écrouissages distinctes ont été obtenues. Des simulations numériques ont été menées afin de confronter ces lois de comportement sur la prédiction des profils des flans et des tubes déformés ainsi que sur les distributions d’épaisseur de ceux-ci. Enfin, le matériau ayant été considéré isotrope jusqu’à présent, on s’attache à l’influence de l’anisotropie du matériau dans le cadre de la mise en forme par hydroformage. Pour cela un plan complet est mené.Mots-clés : hydroformage, caractérisation de matériaux, tube, simulation E.F., expérimentation / Tube hydroforming requires the employment of expensive tooling and its industrial development makes an intensive use of finite element simulations. For these simulations, we need plastic material data. The material behavior, in forming, depends on the loading mode. Thus, several characterization tests such as uniaxial tensile test, the bulging test on sheet and tube, are investigated in this work.The works are conducted in the context of a pragmatic approach. The goal is to offer simple methods for implementation in an industrial setting based on a limited number of tests, a simple experimental method and an efficient method for post-processing experimental results. In addition, we limit ourselves to classical material models, available in any FE code, such as the Swift’s hardening law and the Hill 1948 plastic criterion.After the introduction of the different kind of hydroforming and the fundamentals on the plastic behavior of materials, the experimental tests are presented. There are many ways for post-processing the experimental results of these advanced testing methods. The conventional method is chosen for post-processing the experimental results obtained with the tensile test ; for the sheet bulging test, the method recommended by Koç et al. is used and the model proposed by Boudeau and Malécot’s is adopted for tube bulging test.The different tests are carried out on an austenitic stainless steel AISI 304 and, distinct hardening curves are obtained. Numerical simulations of the tests and a tube hydroforming operation are performed with the different hardening law. The FE results are compared; the comparisons are led on the resulting bulged sheet or tube and on the thickness distribution. Finally, the influence of the initial anisotropy in tube hydroforming is studied through a full Design Of Experiences.Keywords: hydroforming, material characterization, tube, F.E. simulation, experiment

Doctor of Philosophy / Department of Chemistry / Takashi Ito / This dissertation describes single-molecule tracking (SMT) measurements for the quantitative characterization of one-dimensional (1D) nanostructures in 200 nm-thick surfactant-templated mesoporous silica (STMS) and cylinder-forming polystyrene-poly(ethylene oxide) diblock copolymer (CF-PS-b-PEO) films with a μm-scale thickness. SMT is advantageous for the characterization of nanomaterials over conventional methods because it permits the simultaneous and quantitative assessment of the nanoscale and microscale morphologies, and mass-transport properties of the materials with a high nanometer-scale resolution under ambient conditions. It offers a unique means for the assessment and evaluation of the μm-scale nanostructure alignment in polymer films induced by vertical spin-coating (for STMS films), directional solution flow and solvent-vapor penetration (SVP) methods (both for CF-PS-b-PEO films), highly crucial for many potential technological applications using the materials. Through this work, we have identified suitable sample preparation conditions (e.g. solvent, temperature or solution flow rate) for obtaining highly-ordered mesoporous and microdomain structures over a long-range (> 5 μm). For the quantitative assessment of the 1D SMT data, orthogonal regression analysis was employed, providing assessment of the in-plane orientation and size of individual nanostructures with nanometer-scale precision. The analysis of the 1D trajectory data allowed the radius (ca. 11 nm) of cylindrical PEO microdomains to be estimated, yielding results consistent with the AFM results (ca. 14 nm). The distribution of the trajectory angles offered the estimation of the average orientation and order of the nanostructures in domains/grains for a μm-wide region of the polymer films, revealing the higher efficiency of SVP in the nanostructure alignment as compared to the spin coating and solution flow approaches. Systematic SMT measurements across the film depth and along lateral mm-scale distances afforded valuable insights into the shear- and solvent-evaporation-based alignment mechanisms induced by solution flow and SVP/spin coating approaches, respectively. Fluorescence recovery after photobleaching (FRAP) measurements in a SVP-aligned CF-PS-b-PEO film permitted the longer-range mass-transport properties to be probed, reflecting the effective continuity of the aligned cylindrical nanostructures over > 100 μm in length. In this dissertation, FRAP and more importantly SMT methods have provided a unique and useful means for the in-depth characterization of morphology and mass-transport characteristics in thin polymer films under ambient conditions, in confined spaces, and with a nanometer-scale resolution.

Doctor of Philosophy / Department of Chemistry / Daniel A. Higgins / This dissertation describes single-molecule tracking (SMT) studies for the quantitative characterization of one-dimensional (1D) nanostructures in surfactant-templated mesoporous silica monoliths prepared within microfluidic channels. Single molecule diffusion of fluorescent probe molecules within the cylindrical mesopores reflects microscopic morphologies and mass-transport properties of the materials with high temporal and spatial resolution. The pore organization and materials order are initially investigated as a function of sol aging prior to loading into the microfluidic channels. Mesopores in these materials are templated by Cetyltrimethylammonium bromide (CTAB). Wide-field fluorescence videos depict 1D motion of the dyes within the individual mesopores. Orthogonal regression analysis of these motions provides a measure of the mesopore orientation. Channels filled prior to gelation of the sol produce monoliths incorporating large monodomains with highly aligned mesopores. In contrast, channels filled close to or after gelation yield monoliths with misaligned pores that are also more disordered. Two-dimensional (2D) small angle X-ray scattering (SAXS) experiments support the results obtained by SMT. These studies help to identify conditions under which highly aligned mesoporous monoliths can be obtained and also demonstrate the utility of SMT for characterization of mesopore order. The non-ionic surfactant Pluronic F127 is also utilized as the structural-directing agent. The diffusive motions of PDI dyes that are uncharged, cationic and anionic are explored by SMT and fluorescence correlation spectroscopy (FCS). The SMT studies for the uncharged dye show development of 1D diffusion along the flow direction while charged dyes exhibit predominant isotropic diffusion, with each of these behaviors becoming more prevalent as a function of aging time after filling of the microfluidic channels. SMT studies from silica-free F127 gels suggest that partitioning plays a important role in governing the diffusion behavior of the PDI dyes within the surfactant-filled mesopores. FCS results exhibit similar mean diffusion coefficients for all three dyes that suggest these dyes diffuse through similar sample regions. These studies demonstrate that the silica pore walls in the mesoporous silica monoliths remain permeable after gelation and that partitioning of solute species to different regions within the pores plays an important role in restricting the dimensionality of their diffusive motion

abstract: There is a concerted effort in developing robust systems health monitoring/management (SHM) technology as a means to reduce the life cycle costs, improve availability, extend life and minimize downtime of various platforms including aerospace and civil infrastructure. The implementation of a robust SHM system requires a collaborative effort in a variety of areas such as sensor development, damage detection and localization, physics based models, and prognosis models for residual useful life (RUL) estimation. Damage localization and prediction is further complicated by geometric, material, loading, and environmental variabilities. Therefore, it is essential to develop robust SHM methodologies by taking into account such uncertainties. In this research, damage localization and RUL estimation of two different physical systems are addressed: (i) fatigue crack propagation in metallic materials under complex multiaxial loading and (ii) temporal scour prediction near bridge piers. With little modifications, the methodologies developed can be applied to other systems. Current practice in fatigue life prediction is based on either physics based modeling or data-driven methods, and is limited to predicting RUL for simple geometries under uniaxial loading conditions. In this research, crack initiation and propagation behavior under uniaxial and complex biaxial fatigue loading is addressed. The crack propagation behavior is studied by performing extensive material characterization and fatigue testing under in-plane biaxial loading, both in-phase and out-of-phase, with different biaxiality ratios. A hybrid prognosis model, which combines machine learning with physics based modeling, is developed to account for the uncertainties in crack propagation and fatigue life prediction due to variabilities in material microstructural characteristics, crack localization information and environmental changes. The methodology iteratively combines localization information with hybrid prognosis models using sequential Bayesian techniques. The results show significant improvements in the localization and prediction accuracy under varying temperature. For civil infrastructure, especially bridges, pier scour is a major failure mechanism. Currently available techniques are developed from a design perspective and provide highly conservative scour estimates. In this research, a fully probabilistic scour prediction methodology is developed using machine learning to accurately predict scour in real-time under varying flow conditions. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2016

abstract: A hybrid molecular dynamics (MD) simulation framework is developed to emulate mechanochemical reaction of mechanophores in epoxy-based nanocomposites. Two different force fields, a classical force field and a bond order based force field are hybridized to mimic the experimental processes from specimen preparation to mechanical loading test. Ultra-violet photodimerization for mechanophore synthesis and epoxy curing for thermoset polymer generation are successfully simulated by developing a numerical covalent bond generation method using the classical force field within the framework. Mechanical loading tests to activate mechanophores are also virtually conducted by deforming the volume of a simulation unit cell. The unit cell deformation leads to covalent bond elongation and subsequent bond breakage, which is captured using the bond order based force field. The outcome of the virtual loading test is used for local work analysis, which enables a quantitative study of mechanophore activation. Through the local work analysis, the onset and evolution of mechanophore activation indicating damage initiation and propagation are estimated; ultimately, the mechanophore sensitivity to external stress is evaluated. The virtual loading tests also provide accurate estimations of mechanical properties such as elastic, shear, bulk modulus, yield strain/strength, and Poisson’s ratio of the system. Experimental studies are performed in conjunction with the simulation work to validate the hybrid MD simulation framework. Less than 2% error in estimations of glass transition temperature (Tg) is observed with experimentally measured Tgs by use of differential scanning calorimetry. Virtual loading tests successfully reproduce the stress-strain curve capturing the effect of mechanophore inclusion on mechanical properties of epoxy polymer; comparable changes in Young’s modulus and yield strength are observed in experiments and simulations. Early damage signal detection, which is identified in experiments by observing increased intensity before the yield strain, is captured in simulations by showing that the critical strain representing the onset of the mechanophore activation occurs before the estimated yield strain. It is anticipated that the experimentally validated hybrid MD framework presented in this dissertation will provide a low-cost alternative to additional experiments that are required for optimizing material design parameters to improve damage sensing capability and mechanical properties. In addition to the study of mechanochemical reaction analysis, an atomistic model of interphase in carbon fiber reinforced composites is developed. Physical entanglement between semi-crystalline carbon fiber surface and polymer matrix is captured by introducing voids in multiple graphene layers, which allow polymer matrix to intertwine with graphene layers. The hybrid MD framework is used with some modifications to estimate interphase properties that include the effect of the physical entanglement. The results are compared with existing carbon fiber surface models that assume that carbon fiber has a crystalline structure and hence are unable to capture the physical entanglement. Results indicate that the current model shows larger stress gradients across the material interphase. These large stress gradients increase the viscoplasticity and damage effects at the interphase. The results are important for improved prediction of the nonlinear response and damage evolution in composite materials. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2017