Dissertations / Theses on the topic 'Hydrides – Thermal properties – Testing'

As electronic packages and their thermal solutions become more complex the reliability margins in the thermal solutions diminish and become less tolerant to errors in reliability predictions. The current method of thermally stress testing thermal solutions can be over or under predicting end of life thermal performance. Benefits of accurate testing and modeling are improved silicon yield in manufacturing, improved performance, lower cost thermal solutions, and shortened test times. The current method of thermally stress testing is to place the entire unit in an elevated isothermal temperature and periodically measure thermal performance. Isothermally aging is not an accurate representation of how the unit will be used by the customer and does not capture the thermal gradients and mechanical stresses due to different coefficients of thermal expansion of the materials used in the thermal solution. A new testing system, CITRAM which is an acronym for Constant Interface Temperature Reliability Method, has been developed that uses an electronic test board. The approach captures the thermal and mechanical stresses accurately and improves test time by 20-30% as a result of automation. Through this study a difference in the two methods has been identified and the new CITRAM method should be adopted as current practice.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (leaves 42-43).
A process known as mutational spectrometry allows the detection of both single and multiple mutations that appear to be spontaneous, using a technique known as constant denaturing capillary electrophoresis (CDCE). CDCE requires a region of constant temperature and concentration of denaturant. A massively parallel, fully automated instrument, capable of handling as many as 10,000 DNA samples simultaneously, is suited to this technique. A modular structure of such a mutational spectrometer was designed to remain water-tight, provide an array to hold the capillaries for electrophoretic excitation, and modulate the flow of a heat transfer fluid. Six such modules were manufactured and assembled. As the heat transfer fluid passed through the assembled structure, the natural thermal loss was determined.
by Michael R. Del Zio.
S.B.

Among the many efforts to improve the IC test process are tests that attempt to differentiate between healthy and defective or low reliability ICs by manipulating the operating conditions of the IC being tested. This thesis attempts to improve the common understanding of multiple and targeted temperature testing by evaluating work published on the subject to date and by presenting previously unpublished empirical observations. The empirical observations are made from SCAN and LBIST based MinVDD measurements, Static IDD measurements, as well as parametric measurements of transistor characteristics. The test vehicles used are 0.25μm and 0.18μm CMOS ASICs fabricated by LSI Logic. An IC’s performance is bound by a three dimensional space defined by VDD, frequency, and temperature. A model is presented to explain the boundaries of the performance region in terms of the ability of the IC’s constituent transistors to provide power and the Zero-Temperature-Coefficient (ZTC). Also, it is determined that multiple temperature testing can add new tests to current test suites to improve the resolution between healthy and defective ICs.

This research consists of experimental load tests and numerical simulations of structural steel connections with various filler materials to study the effect of non-steel fillers on the connection strength. Non-steel fillers are used in the steel connections to provide thermal insulation by reducing thermal bridging. Eight specimens having steel and polypropylene filler plates of various thicknesses were tested in the laboratory. The collected data were compared to a Finite Element Analysis (FEA) using ABAQUS to validate the numerical results. After validation, three parametric studies were conducted using ABAQUS to provide insight into general behavior of connections with a variety of fillers that could be used as thermal breaks. In addition, an extreme case of having air gaps instead of alternative fillers was also considered. The Research Council on Structural Connections (RCSC 2014) suggests a reduction in the bolt shear strength when undeveloped fillers with a thickness of more than 0.25 inch are used while using any non-steel material is prohibited due the limited research available. Most research studies have investigated the mechanical behavior of thermal breaks in either end-plate moment connections or slip-critical connections. No data is available for thermal breaks in bearing-type connections up to failure. This research aims to study the effects of filler material properties such as modulus of elasticity and strength on bolt strength, as well as investigate whether the current equation in RCSC 2014 is applicable for alternative filler materials like polypropylene that has less than 0.5% of the steel modulus of elasticity and less than 10% of steel strength.

La littérature scientifique révèle que les résultats in vitro sur les matériaux dentaires ont une faible corrélation avec le comportement clinique. Les tests standardisés aux normes fournissent des informations précieuses et pertinentes sur les propriétés des matériaux dentaires, et permettent aussi de comparer les résultats de différents instituts. Cependant, le développement de nouveaux matériaux à partir de nouvelles formulations chimiques nécessite une amélioration des méthodes d'évaluation. Ce travail de recherche est réalisé dans le but d'approfondir les connaissances sur les méthodes d'évaluation des matériaux dentaires avant insertion dans la cavité buccale. Une grande importance a été donnée au choix des matériaux à tester ; nous nous sommes basés sur les dernières tendances actuelles et les derniers développements de composition de matériaux dentaires. La même importance a été donnée à des méthodes et des techniques d'essai au laboratoire ; leur corrélation avec les résultats cliniques a été mise en évidence. Les modifications apportées à la méthodologie de ces tests ont exploré davantage les aspects cachés des différentes interactions de paramètres. La caractérisation et l'évaluation des matériaux dentaires nécessitaient une meilleure compréhension de l'interaction entre les différentes propriétés pour expliquer le vieillissement des matériaux. Notre travail a consisté à combiner de nombreuses études pour répondre à ce sujet. Les études ont porté sur les propriétés mécaniques et physiques, le composite fibré et Bulk, les matériaux CAM CAD, les adhésifs dentaires, le choc thermique et le cyclage thermique, le bisphénol A. L'objectif final était de développer un simulateur oral qui permettrait la reproduction de différents paramètres chimiques, physiques et mécaniques de l'environnement buccal, permettant ainsi de combler l'écart entre les tests in vitro et in vivo de matériaux dentaires
Scientific literature reveals that in vitro results are poorly correlated to materials clinical behavior. ISO standardized testing provides valuable information about the dental materials properties, and enables result comparison between different institutes. Conversely, new materials chemistry and formulations requires improved methodology and testing methods. Throughout our studies included in this work, the main objective was to reach a more global knowledge of the way dental materials are evaluated before being inserted into the oral cavity. A great deal of emphasis was given to the choice of materials to be tested, and that it would represent the current trends in dental practice and the latest developments in material composition. Equal highlight was given to the choice of testing methodology and laboratory testing techniques and their correlation to the clinical outcome. The modifications made to the methodology of these tests explored further the concealed aspects of different parameter interactions. Dental materials characterization and assessment required more understanding about the interaction between different properties to explain material aging; our work was to combine numerous studies to answer this topic. The studies included mechanical and physical properties, bulk and fiber composite, CAD CAM block materials, dental resin adhesive, thermal shock and thermal cycling, Bisphenol A. The final objective was to develop an oral simulator that would enable the reproduction of different chemical, physical and mechanical parameters of the oral environment, thus permitting to bridge the gap between in vitro and in vivo testing of dental materials

Dissertation (Ph.D.)-- Worcester Polytechnic Institute.
Keywords: temperature measurement; heat flux maps; Cone Calorimeter; three-dimensional heat conduction; fire growth models; retainer frame; ceramic fiberboard; edge effect; one-dimensional heat conduction; heat flux mapping procedure; infrared camera; specimen preparation; edge frame; one-dimensional heat conduction model; thermal properties. Includes bibliographical references (p.202-204).

Ces travaux traitent de l'utilisation de la thermographie infrarouge dans le cadre du contrôle non destructif des ouvrages de génie civil.Une première partie, traite de l’étude des paramètres influençant la mesure in situ, de la capacité de la technique à détecter la variation de propriétés intrinsèques au matériau, et de la détection de délaminations. Les résultats présentés sont issus de mesures expérimentales appuyées par une approche numérique aux éléments finis. Dans un premier temps, une étude sur la capacité de la thermographie infrarouge à détecter des variations de porosité ou de teneur en eau a été réalisée. Dans un second temps, des travaux sont menés sur la détermination des seuils de détection des délaminations en fonction des conditions d’exposition. Ils ont montré un seuil de détection correspondant à un rapport de 2, entre l’extension latérale du défaut et sa profondeur, pour un ensoleillement direct, et à un rapport de 3,3 pour un ouvrage soumis uniquement aux variations de température de l’air. La réalisation d’un suivi temporel combiné à l’étude de l’évolution des gradients temporels de température permet d’améliorer ces seuils de détection. Enfin, une étude originale sur le pontage présent au niveau des délaminations, a montré la prédominance de l’influence de celui‐ci sur la profondeur des délaminations.Une deuxième partie porte sur les travaux réalisés dans le cadre du projet ANR‐SENSO. Ils traitent de la combinaison des résultats issus de différentes techniques de CND dans le cadre plus large de l'amélioration des diagnostics pour la gestion du patrimoine
This thesis focuses on the use of infrared thermography as a tool for non destructive testing ofbuildings. Mainly, the application is on civil engineering projects.The first part includes identifying the parameters that can affect this in situ technique. Thisparticularly deals with the infrared thermography capacity to detect intrinsic property variations, anddelamination detection. Combination of experiments on concrete slabs and numerical simulationsare used. In a first step, a study on the capacity of thermography to detect porosity and watercontent variation was conducted. In a second step a study on the thresholds for detectingdelaminations based on exposure conditions is carried out. As an outcome, the threshold that hasbeen detected corresponds to a ratio of 2 between the lateral extension of the defect and its depthto direct sunlight; while a ratio of 3,3 if it is exposed to air temperature variations. This studysuggests that a time monitoring combined with the study of the evolution of temporal temperaturegradients can improve the detection limits. Finally, an original study showed the predominance ofthe influence of bridging on the depth of delamination.The second part tackles the works carried out during the ANR project SENSO. Results fromdifferent non destructive tools were coupled for the purpose of improving diagnosis in the assetmanagement

Le travail présenté dans ce document vise à mettre en évidence et à comprendre l'effet de la taille nanométrique des renforts sur les propriétés des nanocomposites avec une approche expérimentale. Des nanocomposites de PMMA et particules de silice (15nm, 25nm, 60nm, 150nm et 500nm) de fractions volumiques 2 0/0, 40/0 et 6 0/0 ont été fabriqués. Des analyses multi-échelles (MET et DRX-WAXS) ont montré que les paramètres caractéristiques de la microstructure des nanocomposites varient avec la taille des nanoparticules. En effet, la diminution de la taille des nanoparticules à fraction volumique constante a entrainé une diminution de la distance intermoléculaire. Cette diminution a induit une densification de la matrice et une réduction de la mobilité des chaînes de la matrice. Des essais mécaniques (traction, DMA) ont montré que les modules de Young (E) et de conservation (E') des nanocomposites augmentent avec la diminution de la taille des nanoparticules à fraction volumique constante. Et que l'augmentation de E' est conservée avec l'augmentation de la température. Une augmentation des températures de transition vitreuse (Tg) et de dégradation (Td) a également été observée avec les essais DSC, DMA et ATG. Le modèle de la borne inférieure d'Hashin-Shtrikman étendue aux nanocomposites à renforts sphériques proposé par Brisard a été utilisé. La modélisation des modules élastiques des nanocomposites a montré que pour reproduire les données expérimentales, il faut que d'une part que les modules surfaciques caractérisant l'interface soient dépendants de la taille des nanoparticules. Et d'autre part, tenir compte de l'état de dispersion des nanoparticules
The work presented in this paper aims to highlight and to understand the size effect of nano-reinforcements on nanocomposite properties With an experimental approach. Nanocomposites of PMMA and silica particles With different sizes (15nm, 25nm, 60nm, 150nm and 500nm) and volume fractions (20/0, 4 0/0 and 60/0) were manufactured. Multiscale analysis (MET and DRX-WAXS) have shown that the characteristic parameters of the microstructure of nanocomposites vary With the size of the nanoparticles. Indeed, the decrease in the size of nanoparticles at a given volume fraction implies a decrease of the intermolecular distance. This decrease has induced a densification of the matrix and a decrease of the matrix chain mobility. Mechanical tests (tensile, DMA) have shown that the young (E) and the conservation (E') moduli of the nanocomposites increase With the decrease in the size of the nanoparticles With a constant volume fraction. And the increase of E l is kept when temperature growing. An increase in glass transition (Tg) and degradation temperature (Td) was also observed With the DSC, DMA and ATG tests. Experimental elastic properties of the nanocomposites were used to assess the relevance of size effect micromechanical models, particularly the Hashin-Shtrikman bounds With interface effects proposed by Brisard. The modeling has shown that to reproduce the experimental elastic moduli of nanocomposites, the elastic coefficients of the interface must be dependents on particle sizes. And the state of dispersion of particles must be taken into account

The Bridge House is a steel building structure located in Poly Canyon, a rural area inside the campus of California Polytechnic State University, San Luis Obispo. The Bridge House is a one story steel structure supported on 4 concrete piers with a lateral force resisting system (LFRS) composed of ordinary moment frames in the N-S direction and braced frames in the E-W direction and vertically supported by a pair of trusses. The dynamic response of the Bridge House was investigated by means of system identification through ambient and forced vibration testing. Interesting findings such as diaphragm flexibility, foundation flexibility and frequency shifts due to thermal effects were all found throughout the mode shape mapping process. Nine apparent mode shapes were experimentally identified, N-S and E-W translational, rotational and 6 vertical modes. A computational model was also created and refined through correlation with the modal parameters obtained through FVTs. When compared to the experimental results, the computational model estimated the experimentally determined building period within 8% and 10% for both N-S and E-W translational modes and within 10% for 4 of the vertical modes.

L'arc-fil est un nouveau procédé de fabrication additive utilisant une cellule desoudage robotisée pour la fabrication, couche par couche, de pièces de grandes dimensions. Ilpermet de réaliser des ébauches de pièces unitaires ou de petites séries avec des coûts et desdélais de fabrication réduits. Les premiers développements se sont principalement orientés sur laréalisation de pièces à forte valeur ajoutée en alliage de titane et d’aluminium pour le secteuraéronautique et aérospatial, et intéressent maintenant d’autres secteurs tels que les industriesnavales, pétrolières, ferroviaires et mécaniques utilisant des aciers. Ce travail propose uneméthodologie de sélection des paramètres et des stratégies de dépôts, avec le contrôle final despièces fabriquées. Il porte sur deux matériaux : un acier C-Mn à haute limite d’élasticité(ER100) et un acier inoxydable austénitique (316LSi). Le résultat des caractérisations permetd’établir le lien entre les conditions de fabrication, les dimensions géométriques et les propriétésmicrostructurales et mécaniques des pièces obtenues, ce qui conduit au final à une démarchepermettant de faire évoluer le procédé vers l’industrialisation
Wire-arc additive manufacturing is a new process using a common weldingrobotic cell to build large parts layer by layer. It allows building rough single pieces orsmall series parts with a low cost and a short delay. First developments were done ontitanium and aluminum parts for aeronautic and space applications, but more industriessuch as maritime, oil and gas, railway…are now interested into it. In this work, amethodology is proposed to define suitable process parameters and deposit’s strategies,with the final control of the elaborated parts. Developments are done on both highstrength steel ER100 and austenitic stainless steel 316LSi. The results of theexperimental characterisation enable to show the relations between the manufacturingconditions, the dimensions, the microstructure and the mechanicals properties of theparts, and finally lead to guidelines to evolve the wire-arc additive manufacturingtowards industrialisation

La thermographie infrarouge est une méthode largement employée pour la caractérisation des propriétés thermophysiques des matériaux. L’avènement des diodes laser pratiques, peu onéreuses et aux multiples caractéristiques, étendent les possibilités métrologiques des caméras infrarouges et mettent à disposition un ensemble de nouveaux outils puissants pour la caractérisation thermique et le contrôle non desturctif. Cependant, un lot de nouvelles difficultés doit être surmonté, comme le traitement d’une grande quantité de données bruitées et la faible sensibilité de ces données aux paramètres recherchés. Cela oblige de revisiter les méthodes de traitement du signal existantes, d’adopter de nouveaux outils mathématiques sophistiqués pour la compression de données et le traitement d’informations pertinentes. Les nouvelles stratégies consistent à utiliser des transformations orthogonales du signal comme outils de compression préalable de données, de réduction et maîtrise du bruit de mesure. L’analyse de sensibilité, basée sur l’étude locale des corrélations entre les dérivées partielles du signal expérimental, complète ces nouvelles approches. L'analogie avec la théorie dans l'espace de Fourier a permis d'apporter de nouveaux éléments de réponse pour mieux cerner la «physique» des approches modales.La réponse au point source impulsionnel a été revisitée de manière numérique et expérimentale. En utilisant la séparabilité des champs de température nous avons proposé une nouvelle méthode d'inversion basée sur une double décomposition en valeurs singulières du signal expérimental. Cette méthode par rapport aux précédentes, permet de tenir compte de la diffusion bi ou tridimensionnelle et offre ainsi une meilleure exploitation du contenu spatial des images infrarouges. Des exemples numériques et expérimentaux nous ont permis de valider dans une première approche cette nouvelle méthode d'estimation pour la caractérisation de diffusivités thermiques longitudinales. Des applications dans le domaine du contrôle non destructif des matériaux sont également proposées. Une ancienne problématique qui consiste à retrouver les champs de température initiaux à partir de données bruitées a été abordée sous un nouveau jour. La nécessité de connaitre les diffusivités thermiques du matériau orthotrope et la prise en compte des transferts souvent tridimensionnels sont complexes à gérer. L'application de la double décomposition en valeurs singulières a permis d'obtenir des résultats intéressants compte tenu de la simplicité de la méthode. En effet, les méthodes modales sont basées sur des approches statistiques de traitement d'une grande quantité de données, censément plus robustes quant au bruit de mesure, comme cela a pu être observé
Infrared thermography is a widely used method for characterization of thermophysical properties of materials. The advent of the laser diodes, which are handy, inexpensive, with a broad spectrum of characteristics, extend metrological possibilities of infrared cameras and provide a combination of new powerful tools for thermal characterization and non destructive evaluation. However, this new dynamic has also brought numerous difficulties that must be overcome, such as high volume noisy data processing and low sensitivity to estimated parameters of such data. This requires revisiting the existing methods of signal processing, adopting new sophisticated mathematical tools for data compression and processing of relevant information.New strategies consist in using orthogonal transforms of the signal as a prior data compression tools, which allow noise reduction and control over it. Correlation analysis, based on the local cerrelation study between partial derivatives of the experimental signal, completes these new strategies. A theoretical analogy in Fourier space has been performed in order to better understand the «physical» meaning of modal approaches.The response to the instantaneous point source of heat, has been revisited both numerically and experimentally. By using separable temperature fields, a new inversion technique based on a double singular value decomposition of experimental signal has been introduced. In comparison with previous methods, it takes into account two or three-dimensional heat diffusion and therefore offers a better exploitation of the spatial content of infrared images. Numerical and experimental examples have allowed us to validate in the first approach our new estimation method of longitudinal thermal diffusivities. Non destructive testing applications based on the new technique have also been introduced.An old issue, which consists in determining the initial temperature field from noisy data, has been approached in a new light. The necessity to know the thermal diffusivities of an orthotropic medium and the need to take into account often three-dimensional heat transfer, are complicated issues. The implementation of the double singular value decomposition allowed us to achieve interesting results according to its ease of use. Indeed, modal approaches are statistical methods based on high volume data processing, supposedly robust as to the measurement noise

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy
The cracking of mass and structural concrete due to thermal stress is a major problem in the concrete construction industry. Concrete will crack when the thermal stress exceeds tbe tensile strength of the concrete, Decisions on the type of concrete mix, cooling facilities and construction techniques to be used in the erection of a concrete structure can only be made if the thermal behaviour and strength of the concrete can be predicted during hydration. This thesis describes the development of a low cost, computer controlled, adiabatic calorimeter to determine tlte heat of hydration and a probe to determine the thermal conductivity or concrere samples. The main thrust of this thesis is the development of the thermal conductivity probe which, for the first time, can measure the thermal conductivity of concrete through all stages of hydration. A thermal model was also developed to verify the results, and the use of the calorimeter for temperature matched curing tests is also discussed. Results, obtained from the test procedures described, will provide far more accurate predictions of the temperatures in concrete structures than was possible in the past.
Andrew Chakane 2018

碩士
國立高雄科技大學
土木工程系
107
The research objective was to assess the mechanical properties, shrinkage, thermal expansion and conductivity, and chloride penetration of concrete containing reclaimed asphalt pavement materials. Rich and lean concrete mixtures were blended by water to cementitious materials (w/c) ratio of 0.5 and the RAP materials were replacing both coarse and fine aggregates by 0, 20, 40, 60, 80, and 100-%. The concrete cylinders and specimens were cast and cured in the water tank for 7, 28, 56, and 90 days. The test results demonstrate as follows: the mixing temperatures of all concrete mixtures increased among 24.5 and 26.8, from 20-°C; the unit weight, compressive strength, pulse velocity, and shrinkage decreased, when more percentage of RAP were incorporated; thermal conductivity increased when more percentage of RAP were added. However, thermal conductivity decreased when longer curing time of concrete were given; thermal expansion also increased when more percentage of RAP were blended; lastly, the coulombs or charge pass indicating the chloride penetration increased on 90-day moisture-cured concrete specimens, when more RAP were replaced.

Indiana University-Purdue University Indianapolis (IUPUI)
A constant-volume combustor is used to investigate the ignition initiated by a traversing jet of reactive hot gas, in support of combustion engine applications that include novel wave-rotor constant-volume combustion gas turbines and pre-chamber IC engines. The hot-jet ignition constant-volume combustor rig at the Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) was used for this study. Lean premixed combustible mixture in a rectangular cuboid constant-volume combustor is ignited by a hot-jet traversing at different fixed speeds. The hot jet is issued via a converging nozzle from a cylindrical pre-chamber where partially combusted products of combustion are produced by spark- igniting a rich ethylene-air mixture. The main constant-volume combustor (CVC) chamber uses methane-air, hydrogen-methane-air and ethylene-air mixtures in the lean equivalence ratio range of 0.8 to 0.4. Ignition delay times and ignitability of these combustible mixtures as affected by jet traverse speed, equivalence ratio, and fuel type are investigated in this study.

Indiana University-Purdue University Indianapolis (IUPUI)
Fused deposition modeling (FDM) represents one of the most common techniques for rapid proto-typing in additive manufacturing (AM). This work applies image based thermography to monitor the FDM process in-situ. The nozzle temperature, print speed and print orientation were adjusted during the fabrication process of each specimen. Experimental and numerical analysis were performed on the fabricated specimens. The combination of the layer wise temperature profile plot and temporal plot provide insights for specimens fabricated in x, y and z-axis orientation. For the x-axis orientation build possessing 35 layers, Specimens B16 and B7 printed with nozzle temperature of 225 C and 235 C respectively, and at printing speed of 60 mm/s and 100 mm/s respectively with the former possessing the highest modulus, yield strength, and ultimate tensile strength. For the y-axis orientation build possessing 59 layers, Specimens B23, B14 and B8 printed with nozzle temperature of 215 C, 225 C and 235 C respectively, and at printing speed of 80 mm/s, 80 mm/s and 60 mm/s respectively with the former possessing the highest modulus and yield strength, while the latter the highest ultimate tensile strength. For the z-axis orientation build possessing 1256 layers, Specimens B6, B24 and B9 printed with nozzle temperature of 235 C, 235 C and 235 ➦C respectively, and at printing speed of 80 mm/s, 80 mm/s and 60 mm/s respectively with the former possessing the highest modulus and ultimate tensile strength, while B24 had the highest yield strength and B9 the lowest modulus, yield strength and ultimate tensile strength. The results show that the prints oriented in the y-axis orientation perform relatively better than prints in the x-axis and z-axis orientation.

Indiana University-Purdue University Indianapolis (IUPUI)
Ignition of a combustible mixture by a transient jet of hot reactive gas is important for safety of mines, pre-chamber ignition in IC engines, detonation initiation, and in novel constant-volume combustors. The present work is a numerical study of the hot-jet ignition process in a long constant-volume combustor (CVC) that represents a wave-rotor channel. The mixing of hot jet with cold mixture in the main chamber is first studied using non-reacting simulations. The stationary and traversing hot jets of combustion products from a pre-chamber is injected through a converging nozzle into the main CVC chamber containing a premixed fuel-air mixture. Combustion in a two-dimensional analogue of the CVC chamber is modeled using global reaction mechanisms, skeletal mechanisms, and detailed reaction mechanisms for four hydrocarbon fuels: methane, propane, ethylene, and hydrogen. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Hybrid turbulent-kinetic schemes using some skeletal reaction mechanisms and detailed mechanisms are good predictors of the experimental data. Shock-flame interaction is seen to significantly increase the overall reaction rate due to baroclinic vorticity generation, flame area increase, stirring of non-uniform density regions, the resulting mixing, and shock compression. The less easily ignitable methane mixture is found to show higher ignition delay time compared to slower initial reaction and greater dependence on shock interaction than propane and ethylene. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive. Inclusion of minor radical species in the hot-jet is observed to reduce the ignition delay by 0.2 ms for methane mixture in the main chamber. Reaction pathways analysis shows that ignition delay and combustion progress process are entirely different for hybrid turbulent-kinetic scheme and kinetics-only scheme.

Current research on thermal effects on guideways has addressed many aspects of the behavior of guideways using two-dimensional models. The two-dimensional models are acceptable for existing guideway designs, in which cross sectional shapes are uniform along the length of the guideway. However, three-dimensional models are necessary for a modular design, in which the track structures that interact with Maglev vehicles are made separately and are assembled into the support structure, and in which the cross sectional shapes are not uniform. A three-dimensional numerical model of the thermal environment, in which the effect of partial shading is taken into account, is implemented for the study of guideway behavior under various thermal environments. The numerical model of the thermal environment is calibrated to the experimental results under the thermal environment at Austin, Texas, and is extrapolated to predict the behaviors of guideways under the thermal environment in Las Vegas, Nevada, which is one of the candidate sites for the implementation and deployment of the high speed Maglev transportation system. This study addresses the suitability of a modular steel guideway design under such a thermal environment. Characteristics of the behavior of guideways under various thermal environments are identified, and the behavior of guideways under the effect of partial shading is summarized.
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Indiana University-Purdue University Indianapolis (IUPUI)
Zirconia (ZrO2) is an important ceramic material with a broad range of applications. Due to its high melting temperature, low thermal conductivity, and high-temperature stability, zirconia based ceramics have been widely used for thermal barrier coatings (TBCs). When TBC is exposed to thermal cycling during real applications, the TBC may fail due to several mechanisms: (1) phase transformation into yttrium-rich and yttrium-depleted regions, When the yttrium-rich region produces pure zirconia domains that transform between monoclinic and tetragonal phases upon thermal cycling; and (2) cracking of the coating due to stress induced by erosion. The mechanism of erosion involves gross plastic damage within the TBC, often leading to ceramic loss and/or cracks down to the bond coat. The damage mechanisms are related to service parameters, including TBC material properties, temperature, velocity, particle size, and impact angle. The goal of this thesis is to understand the structural and mechanical properties of the thermal barrier coating material, thus increasing the service lifetime of gas turbine engines. To this end, it is critical to study the fundamental properties and potential failure mechanisms of zirconia. This thesis is focused on investigating the structural and mechanical properties of zirconia. There are mainly two parts studied in this paper, (1) ab initio calculations of thermodynamic properties of both monoclinic and tetragonal phase zirconia, and monoclinic-to-tetragonal phase transformation, and (2) image-based finite element simulation of the indentation process of yttria-stabilized zirconia. In the first part of this study, the structural properties, including lattice parameter, band structure, density of state, as well as elastic constants for both monoclinic and tetragonal zirconia have been computed. The pressure-dependent phase transition between tetragonal (t-ZrO2) and cubic zirconia (c-ZrO2) has been calculated using the density function theory (DFT) method. Phase transformation is defined by the band structure and tetragonal distortion changes. The results predict a transition from a monoclinic structure to a fluorite-type cubic structure at the pressure of 37 GPa. Thermodynamic property calculations of monoclinic zirconia (m-ZrO2) were also carried out. Temperature-dependent heat capacity, entropy, free energy, Debye temperature of monoclinic zirconia, from 0 to 1000 K, were computed, and they compared well with those reported in the literature. Moreover, the atomistic simulations correctly predicted the phase transitions of m-ZrO2 under compressive pressures ranging from 0 to 70 GPa. The phase transition pressures of monoclinic to orthorhombic I (3 GPa), orthorhombic I to orthorhombic II (8 GPa), orthorhombic II to tetragonal (37 GPa), and stable tetragonal phases (37-60 GPa) are in excellent agreement with experimental data. In the second part of this study, the mechanical response of yttria-stabilized zirconia under Rockwell superficial indentation was studied. The microstructure image based finite element method was used to validate the model using a composite cermet material. Then, the finite element model of Rockwell indentation of yttria-stabilized zirconia was developed, and the result was compared with experimental hardness data.

PtNiAl bond coats are diffusion aluminide coatings deposited on superalloy based turbine blades for oxidation resistance and improved adhesion between the substrate and the YSZ thermal barrier coating on top. They are deposited by pack aluminisation, which makes their microstructure inherently graded and heterogeneous as well as replete with a variety of precipitates and second phase particles. The microstructure also continuously evolves during thermal cycling, because of interdiffusion with the substrate and the continuous loss of Al to the thermally grown oxide scale on top. During service, the bond coats are exposed to impact, thermal expansion mismatch, thermo-mechanical fatigue and inter-diffusion accompanied by phase transformation, which become leading causes of their failure. The bond coats being B2 crystal structures are known to be brittle at room temperature, due to which they are expected to fail during cooling, although they undergo plastic relaxation by creep above the BDTT. Little attention has been paid to the mechanical response of the bond coats, while a number of studies focus on optimizing their composition for oxidation resistance. The fracture properties of these coatings, in particular, are not very well understood due to the several different length scales of their complex microstructure playing a part. In this context, there is an interest in determination of the fracture toughness of bond coats under different loading and temperature conditions. In the present work, the fracture properties of bond coats is measured with micron-scale resolution using edge notched doubly clamped microbeam structures positioned at individual zones of the graded bond coat, subjected to bending. In order to extract the stress intensity factor for this new configuration and to determine the stress distribution and stability of this geometry under different loading conditions, extended finite element analysis (XFEM) is carried out. After establishing the microbeam geometry as a viable fracture toughness testing configuration, the contribution of different microstructural variables to toughening at room temperature is studied using SEM based in-situ testing. Since the exact composition and structure of the coating depends principally on the elements constituting the matrix-Pt, Ni and Al content, which themselves depend on the deposition parameters, we have examined in detail, coatings aluminised at different temperatures (increasing coating thickness), varying Al content in the pack mixture and starting Pt thicknesses during electro-deposition. These parameters are by no means exhaustive and there is wide scope to investigate the effect of other processing variables as well as their synergistic effects on the mechanical behavior of these coatings. Following this, the high temperature fracture behavior of the stand-alone coatings in tension is also studied to determine their brittle to ductile transition mechanism in the presence of a notch. While this covers the average behavior of the entire coating cross-section, such a study is important to establish the BDTT unambiguously since there are chances of under-estimation of these temperatures in the absence of a notch. Also free¬standing coatings without the underlying substrate offer respite from residual stresses influencing the results of such tests. The present study essentially consists of two distinct parts, one focused on the development of the testing technique to cover multiple length scales of any graded thin film or coating and the other on the determination of fracture properties of the bond coat using these methods. The thesis reads in the following way: Chapter 1 gives an introduction to the diffusion aluminised bond coats, with a focus on the failure mechanisms associated with them while underlying the need for small scale testing in these systems. The conditions driving failure in bond coats can be vast and varied and it is extremely difficult to pin-point a single important cause and also to develop predictive capabilities regarding their failure. This is described as the motivation for the present work, with an objective of finding the variation in fracture toughness values for PtNiAl bond coats of different coating thicknesses and Pt content across the temperature range spanning the BDTT of the sample. Chapter 2 describes in detail all the available literature on thermal barrier coatings in general, and diffusion aluminide bond coats in particular, while specifically highlighting its mechanical response to loads during service. The deposition parameters during pack aluminizing and the graded microstructure which develops as a consequence of the diffusion process are described. The material’s microstructure dictates its properties, but there has been limited work on the mechanical behavior of the coatings themselves due to the difficulty in preparation and testing of free-standing films of the same. Since the base matrix is that of β¬NiAl, and there has been extensive work reported on bulk NiAl in the literature, which is discussed next. This would serve as a benchmark for comparison with the properties of the bond coats themselves, which are expected to respond differently due to their continuously evolving and complex microstructure. A summary of the known mechanical properties of the coatings themselves is given next along with the failure mechanisms that have been proposed. Since the study deals with fracture properties, a short introduction of linear elastic fracture mechanics follows before elaborating on the various small scale fracture testing geometries that have been developed. There are specific differences between testing geometries, stress states as well as in the instrumentation between small scale and bulk fracture toughness tests, which are highlighted. Since these configurations are material and device specific, each group has worked out its own instrument capabilities and mechanics required to extract the mechanical properties of interest from these testing techniques. Due to these differences in addition to the differences in the size scales of the samples tested, the reported properties show a wide variation. Lack of standards add to the difficulty in interpretation of the data; moreover add to the controversy on whether a size effect exists for fracture, as it does for strength. All the non-standard small scale testing configurations require modeling and simulation to extract the desired properties from them, and the present study applies the XFEM to determine the stress distribution and calculate the stress intensity factors corresponding to the fracture loads recorded from experiments. An introduction to the XFEM method is given in the last part. Chapter 3 gives all the experimental and simulation procedures that were carried out in the present work. Since the bond coat properties need to be compared with their bulk counterparts, both the samples are characterized. The exact material compositions chosen for the study were plain NiAl, 2PtAl and 5PtAl among the pack aluminized coatings and bulk arc-melted PtNiAl samples with varying concentrations of Ni and Pt which matched the bond coat matrix compositions. The choice of the three coatings was made depending on the previously known information regarding their microstructure. The deposition conditions, temperature and times of annealing are listed, followed by a brief summary of the general characterization techniques used to study the microstructure of the bond coats before and after fracture testing. Since the micro-beams under bending were fabricated using a focused ion beam, and the micro-tensile specimen were machined by electro-discharge machining, both the micro-machining procedures are described. At such small length scales, conventional testing methods cannot be used and several modifications were incorporated to the testing geometries which are described in the next section which covers two principal fracture testing methods-microbeam bending and mini-tensile testing, along with the advantages and limitations of each. Modeling is an indispensable tool for determining stress distributions in such new geometric configurations involving material property variations, and details of the exact XFEM procedure that was implemented in ABAQUS is given in the last part of this chapter. Chapter 4 summarises the microstructure and indentation properties of the bond coat and bulk NiAl samples characterised using X-ray diffraction, electron microscopy and nanoindentation. XRD was used for phase identification, texture and determination of lattice parameters of the specimen, which confirmed β-NiAl (with no texture) as the matrix with the lattice parameter varying as a function of composition. The SEM-EPMA combination was used for probing the compositional and microstructural gradients, grain size and precipitate distribution across the coating cross-sections. The bond coat was found to have 4 distinct zones with the Ni:Al ratio gradually rising across its thickness. In addition to this, the four zones had very different grain sizes, precipitate type and distributions. Hardness and modulus values were reported from nanoindentation measurements across the coating thickness over a temperature range from 25 to 400˚C and were seen to follow the composition gradients in different ways based on the effect of the off-stoichiometric defects on these properties. The hardness was found to be a minimum for the zone with stoichiometric composition, as was the case in the bulk sample, while the modulus dropped continuously with increasing Ni content in the matrix. These are important to develop a one-to-one correlation with the fracture properties and to understand the micro-mechanisms of the same. Chapter 5 gets on with the specifics of the testing geometry. Since most of the variables of the testing technique were studied using simulation procedures, a large part of this chapter deals with the results from the modeling technique using XFEM. The XFEM is introduced in detail and its applicability in modeling of cracks and discontinuities and advantages over conventional FEM are explained. The material properties are taken from the nanoindentation data and the modeling assumes linear elastic fracture mechanics. As a validation measurement, a conventional three point beam is modeled in bending and the results compared with analytical solutions of the same. The three point beam bending geometry is also used as a benchmark to study the stability of the new geometry, now with fixed boundaries in place of a free ends. This is followed by the results from the modeling for different variables like mesh density, notch root radius, loading offsets, beam dimensions and crack length (a)/specimen width (W) ratios where both the stress distribution as well as KI are captured in 3-D for stationary cracks while crack trajectories are obtained for propagating cracks. The notch root radius is seen to not affect KI below ~300 nm and such notch radii are easily machinable in the FIB at lower currents. The crack trajectory from the experiments is seen to follow the direction of maximum tangential stress, which is also modeled very well in the XFEM. The contribution of KII to the measured stress intensity factor with increasing offsets is also calculated from the model. Stable cracking is seen for the clamped beam geometry, with KI dropping off beyond a critical a/W ratio. This was true even for a model assuming homogeneous, elastic properties with a flat R-curve under load control. This makes the clamped beam structure require higher loads for continued propagation of cracks. This critical ratio is dimension dependent, making a shorter thicker beam stable in comparison to a longer, slender one. This is unusual, especially in comparison to the three point bend geometry which shows stable cracking only in displacement control, specifically for large a/W ratios alone. Also superimposition of the load-displacement curves from simulations with those of experiments gives a good-fit. The experimental results are shown next to back¬up the claims made on geometric stability of such clamped structures. Digital Image Correlation is introduced as a means for direct measurement of crack opening displacements (COD) and fracture toughness without the aid of KI formulations. This also served as a cross¬check on the assumptions of linear elastic fracture mechanics (LEFM) made in the simulation and a good correlation is seen between the CODs measured experimentally and that obtained from the FEM analysis. Fracture toughness measurements of brittle materials with known KIC values, like fused silica glass and single crystal Si film from this proposed geometry are reported as additional validation of this geometry. Further the capabilities of in-situ testing using this geometry to measure R-curve and fatigue properties along with the initiation KIC values are shown via results from monotonic and cyclic loading under different conditions. Chapter 6 returns to address bond coat fracture at room temperature, which is the main objective of the present study. Fracture toughness is evaluated both ex-situ and in-situ, using clamped microbeam bending experiments across individual zones of the 5PtAl bond coat and for different initial Pt contents in the zone 2. KIC is seen to rise sharply with increasing Ni content of the matrix in the former case, from 5 to 15 MPam1/2 which is attributed to the change in defect chemistry with changing stoichiometry. Al rich NiAl is found to be more brittle due to vacancy hardening while Ni rich NiAl is known to increase the metallic character of the NiAl bond. Both Ni rich and Pt rich (Pt,Ni)Al give higher toughnesses among the coatings studied while the crack trajectories and toughening mechanisms distinctly depend on the precipitate morphology in individual zones. Alloying additions are seen to add to the complexity of the fracture behavior of bond coats by strengthening the matrix or by improving its ductility. Micro-kinking, grain boundary and precipitate bridging are seen in the crack wake as contributing factors to partial closure of the crack on unload. The influence of each of the microstructural variable on the fracture mode is dissected in detail before coming to an overall conclusion. The microbeams show controlled, stable cracking, which enable following of the crack trajectories across micron-length scales and make R-curve measurements possible. Both 2PtAl and 5PtAl compositions show a rising R-curve within the length scale of an individual microbeam tested. Size and geometric effects on real vs apparent R-curve behavior are discussed at the end of the chapter. Chapter 7 addresses a different area of high temperature fracture of bond coats, which becomes relevant in terms of determination of brittle to ductile transition temperature (BDTT) in notched specimen and in evaluating topography after failure across this temperature range. This set of tests is designed to measure fracture toughness and study the fracture mode along the temperature scale to exactly identify the BDTT for a given bond coat composition and strain rate, below which the coating undergoes brittle catastrophic fracture and beyond which it creeps and relaxes plastically at very low stresses. Notched free¬standing bond coat specimens are pulled in uni-axial tension to fracture and the stress at failure is used to calculate the average fracture toughness of the bond coat. The stress-strain curve shows linear elastic behavior upto the BDTT of the bond coat as expected, beyond which it becomes increasingly plastic. The KIC is seen to rise marginally upto 750˚C beyond which it showed a significant increase, from which the BDTT was calculated to be ~775˚C for notched samples. The KIC is not reported beyond the BDTT due to irrelevance of LEFM after macroscopic plasticity sets in. Fracture mode is seen to change from transgranular cleavage below the BDTT to void coalescence and ductile rupture beyond it. The experimental challenges, differences in the through thickness KIC’s obtained from tensile tests vis a vi bend tests (due to changing stress states and size scales), as well as mechanisms of ductile to brittle transition in the context of previously available literature are discussed. Chapter 8 gives the closure and important conclusions from the present work. It summarises the key results from the testing technique and highlights the proposed mechanisms which bring about a rising fracture toughness with both increasing Ni:Al ratio across the bond coat cross-section and across individual micro-beams themselves. Some new techniques and geometries which can be adopted for fracture property determination, on which work was initiated but not complete, are also proposed. The last part of the chapter deals with the future implications of the results found and some open threads and challenges on bond coat optimisiation for different properties, which are yet to be dealt with.