Consider life testing of J-component series systems that are subjected to stress levels that are steeper than that at normal usage condition. The objective of performing such life tests, commonly known as Accelerated Life Testing (ALT) in the literature, is to collect observations on system failure times within a limited time frame. The accelerated observations are then used to infer on the component and system reliability metrics at usage stress. In this thesis, the existing literature is first extended by considering the general case of K stress variables, as opposed to the usual consideration of a single stress variable. Next, a general model assuming that the component log-lifetimes belong to an arbitrary location-scale family of distributions, is formulated. The location parameters are assumed to depend on the stress variables through a general stress translation function, while the scale parameters are assumed to be independent of the stress variables. This formulation covers the standard lifetime distributions as well as well-known stress translation functions as special cases. Bayesian methodologies are then developed for four special cases of the proposed general model, viz., exponentials, Weibulls with equal shape parameter, Weibulls with distinct shape parameters and log-normals with distinct scale parameters. For exponential and Weibull models, the priors on lifetime parameters are assumed to be log-concave and independent of each other. The resulting univariate conditional posterior of each lifetime parameter given the rest, is shown to be log-concave. This facilitates Gibbs sampling from the joint posterior of lifetime parameters. Propriety of the joint posteriors with Laplacian uniform priors on stress coefficients are also proved under a suitable set of sufficient conditions. For the log-normal model, the observed data is first augmented with log-lifetimes of un-failed components to form complete data. A Gibbs sampling scheme is then developed to generate observations from the joint posterior of lifetime parameters, through the augmented data and a conjugate prior for the complete data. In all four cases, Bayesian predictive inference techniques are used to study component and system reliability metrics at usage stress. Though this thesis mainly deals with Bayesian inference of accelerated data of series systems, maximum likelihood analysis for the log-normal component lifetimes is also performed via an expectation-maximization (EM) algorithm and bootstrap, which are not available in the literature. The last part of this thesis deals with construction of optimal Bayesian designs for accelerated life tests of J-component series systems under Type-I censoring scheme. Optimal ALT plans for a single stress variable are obtained using two different Bayesian D-optimality criteria for exponentially distributed component lives. A detailed sensitivity analysis is carried out to investigate the effect of different planning inputs on the optimal designs as well.

This thesis focuses on the development of a novel polymer based housing for power thyristor devices typically used in long distance high voltage direct current (HVDC) transmission. Power thyristor devices used in HVDC power conversion stations are typically packaged in a hermetically sealed ceramic housing and have demonstrated an excellent history of reliability and performance. However, to avoid increasing the number of thyristors in future higher powered HVDC schemes thyristors having higher power ratings at 8.5 kV and sizes at 125 mm and 150 mm diameters are sought for implementation to achieve higher transmission ratings of, for example, 4000 A at +/- 800 kV. The main disadvantages of such large ceramic-based packages are higher processing cost and weight whilst robustness is also a concern. To overcome these issues, replacing the current ceramic housing with a polymeric material has been investigated in this project. The advantages it is anticipated such packages will provide include lower cost, less weight, robustness, recyclability, etc. However, some challenges it will also offer are: non-hermeticity i.e. polymers are moisture and gas permeable, potentially more complex manufacturing routes, and different electrical, mechanical and thermal properties compared to ceramic materials. The work presented in this thesis was part of a larger project where these challenges have been addressed by developing and testing a prototype polymeric thyristor housing. The prototype is aimed at demonstrating that polymer packages can deliver performance and reliability comparable to, if not better than, current ceramic packages. In this thesis, it is the package development and reliability related studies that are discussed. Because the housings will experience severe electrical stresses and various thermal excursions during their service life, the electrical and thermo-mechanical behaviour of the polymer housing was studied using finite element analysis to gain an understanding of the effects of various design variables and materials properties on performance and the tradeoffs between performance and manufacturability. From these modelling studies, design guidelines have been established for the future development of polymer housings. On the other hand, to identify the physics-of-failure of the prototype that was manufactured as part of the project, accelerated life tests were performed to study its reliability. The knowledge gained from the polymer prototype development was then applied to the design of a larger 125 mm diameter housing using the Taguchi method of experimental design.

Em sistemas modernos de manutenção inteligente a qualidade de uma máquina ou equipamento depende do suporte que é fornecido junto com esse produto, com a confiabilidade e segurança na utilização do mesmo. Estas exigências, por vezes, não são cumpridas e podem estar indisponíveis em algumas máquinas. Este trabalho descreve uma abordagem utilizando sinais de vibração coletados em tempo real com falhas como estudo preliminar para uma abordagem mais profunda como estudo dametodologia de testes de vida acelerado para auxiliar durante a fase de vida operacional permitindo ao fabricante a determinação dos ciclos de vida do produto. A abordagem proposta construída em cima de experiências anteriores em desenvolvimento no projeto Integração de Sistemas Inteligentes de Manutenção e Cadeia de Fornecimento de Peças Sobressalentes. O objetivo deste trabalho é apresentar resultados preliminares analisando a variabilidade das assinaturas de falhas das engrenagens danificadas de maneira a permitir a identificação dos ciclos de vida do produto para partes específicas de um atuador elétrico. / In modern systems of intelligent maintenance the quality of a machine or equipment depends on the support that comes with this product, with the reliability and safety in the use of it. These requirements are sometimes not met and may be unavailable on some machines. This paper describes an approach using vibration signals collected in real-time with faults as a preliminary study for a deeper approach with the study of the methodology of accelerated life tests to assist during the operational life stage allowing the manufacturer the determination of the life cycles of product. The proposed approach built on previous experiences under development in the project Integration of Intelligent Systems of Maintenance and Chain of Supply of Spares. The objective of this work is to present preliminary results analyzing the variability of failure signatures of the damaged gears in order to allow the identification of product life cycles for specific parts of an electric actuator.

The objective of the proposed research is to develop statistical algorithms for controlling failure trends through targeted maintenance of at-risk components. The at-risk components are identified via chronological history and diagnostic data, if available. Utility systems include many thousands (possibly millions) of components with many of them having already exceeded their design lives. Unfortunately, neither the budget nor manufacturing resources exist to allow for the immediate replacement of all these components. On the other hand, the utility cannot tolerate a decrease in reliability or the associated increased costs. To combat this problem, an overall maintenance model has been developed that utilizes all the available historical information (failure rates and population sizes) and diagnostic tools (real-time conditions of each component) to generate a maintenance plan. This plan must be capable of delivering the needed reliability improvements while remaining economical. It consists of three facets each of which addresses one of the critical asset management issues: * Failure Prediction Facet - Statistical algorithm for predicting future failure trends and estimating required numbers of corrective actions to alter these failure trends to desirable levels. Provides planning guidance and expected future performance of the system. * Diagnostic Facet - Development of diagnostic data and techniques for assessing the accuracy and validity of that data. Provides the true effectiveness of the different diagnostic tools that are available. * Economics Facet - Stochastic model of economic benefits that may be obtained from diagnostic directed maintenance programs. Provides the cost model that may be used for budgeting purposes. These facets function together to generate a diagnostic directed maintenance plan whose goal is to provide the best available guidance for maximizing the gains in reliability for the budgetary limits utility engineers must operate within.

Em sistemas modernos de manutenção inteligente a qualidade de uma máquina ou equipamento depende do suporte que é fornecido junto com esse produto, com a confiabilidade e segurança na utilização do mesmo. Estas exigências, por vezes, não são cumpridas e podem estar indisponíveis em algumas máquinas. Este trabalho descreve uma abordagem utilizando sinais de vibração coletados em tempo real com falhas como estudo preliminar para uma abordagem mais profunda como estudo dametodologia de testes de vida acelerado para auxiliar durante a fase de vida operacional permitindo ao fabricante a determinação dos ciclos de vida do produto. A abordagem proposta construída em cima de experiências anteriores em desenvolvimento no projeto Integração de Sistemas Inteligentes de Manutenção e Cadeia de Fornecimento de Peças Sobressalentes. O objetivo deste trabalho é apresentar resultados preliminares analisando a variabilidade das assinaturas de falhas das engrenagens danificadas de maneira a permitir a identificação dos ciclos de vida do produto para partes específicas de um atuador elétrico. / In modern systems of intelligent maintenance the quality of a machine or equipment depends on the support that comes with this product, with the reliability and safety in the use of it. These requirements are sometimes not met and may be unavailable on some machines. This paper describes an approach using vibration signals collected in real-time with faults as a preliminary study for a deeper approach with the study of the methodology of accelerated life tests to assist during the operational life stage allowing the manufacturer the determination of the life cycles of product. The proposed approach built on previous experiences under development in the project Integration of Intelligent Systems of Maintenance and Chain of Supply of Spares. The objective of this work is to present preliminary results analyzing the variability of failure signatures of the damaged gears in order to allow the identification of product life cycles for specific parts of an electric actuator.

Em sistemas modernos de manutenção inteligente a qualidade de uma máquina ou equipamento depende do suporte que é fornecido junto com esse produto, com a confiabilidade e segurança na utilização do mesmo. Estas exigências, por vezes, não são cumpridas e podem estar indisponíveis em algumas máquinas. Este trabalho descreve uma abordagem utilizando sinais de vibração coletados em tempo real com falhas como estudo preliminar para uma abordagem mais profunda como estudo dametodologia de testes de vida acelerado para auxiliar durante a fase de vida operacional permitindo ao fabricante a determinação dos ciclos de vida do produto. A abordagem proposta construída em cima de experiências anteriores em desenvolvimento no projeto Integração de Sistemas Inteligentes de Manutenção e Cadeia de Fornecimento de Peças Sobressalentes. O objetivo deste trabalho é apresentar resultados preliminares analisando a variabilidade das assinaturas de falhas das engrenagens danificadas de maneira a permitir a identificação dos ciclos de vida do produto para partes específicas de um atuador elétrico. / In modern systems of intelligent maintenance the quality of a machine or equipment depends on the support that comes with this product, with the reliability and safety in the use of it. These requirements are sometimes not met and may be unavailable on some machines. This paper describes an approach using vibration signals collected in real-time with faults as a preliminary study for a deeper approach with the study of the methodology of accelerated life tests to assist during the operational life stage allowing the manufacturer the determination of the life cycles of product. The proposed approach built on previous experiences under development in the project Integration of Intelligent Systems of Maintenance and Chain of Supply of Spares. The objective of this work is to present preliminary results analyzing the variability of failure signatures of the damaged gears in order to allow the identification of product life cycles for specific parts of an electric actuator.

En raison de leurs performances en termes de densités énergétiques et de puissance, les batteries Li-ion sont les systèmes de stockage électrique privilégiés pour les nouvelles générations de véhicules électriques. Leur modélisation est indispensable pour fournir une évaluation de leurs performances tout au long de leur durée de vie tout en limitant le nombre d'essais expérimentaux, et ceci dans le but de concevoir des configurations et des gestions optimales des packs batteries pour une application envisagée. Le but de ce travail consiste à proposer un modèle physique capable de prédire le comportement et le vieillissement de la batterie sous différentes conditions. Un modèle simplifié électrochimique et thermique capable de prédire le comportement physicochimique et le vieillissement de batteries Li-ion a été étudié. Une analyse de sensibilité a été menée sur l'ensemble des paramètres du modèle dans différentes conditions afin de mettre en évidence leurs influences sur les sorties du modèle. Sur cette base, une méthode d'identification a été proposée pour préserver une indépendance des résultats de l'identification paramétrique par rapport à la sensibilité des paramètres. Cette méthode a permis d'améliorer les prédictions de vieillissement avec des estimations très proches des résultats expérimentaux. Au-delà des gains en compréhension et prédiction, ce modèle physique ouvre de nouvelles possibilités pour établir des protocoles de vieillissement accélérés. / Due to their high power and energy densities, Li-ion batteries are the leading systems for the new generations of electric vehicles, for which an optimum cell design, management and configuration is essential. Modeling provides tools to perform complex analysis of the performance of Li-ion batteries and reduces the amount of time spent on experimental testing. The aim of our research is to propose a physics-based model that can predict battery behavior and aging under various conditions during the entire lifespan. A simplified electrochemical and thermal model that can predict both physicochemical and aging behaviors of Li-ion batteries has been studied. A sensitivity analysis of all its physical parameters has been performed in order to find out their influence on the model outputs based on simulations under various conditions. The results gave hints on whether a parameter needs particular attention when measured or identified and on the conditions under which it is the most sensitive. A specific simulation profile has been designed for parameters involved in aging equations in order to determine their sensitivity. Finally, a step-wise method has been followed to limit the influence of parameter values when identifying sorne of them. This sensitivity analysis and the subsequent step-wise identification method show very good results, such as a better fitting of the experimental data with simulated cell voltage. Beyond advanced comprehension and prediction, this physical model opens new possibilities to define accelerated aging tests.

Le titanate de baryum dopé (BaTiO3, BT) avec des éléments de terres rares est utilisé comme diélectrique dans la fabrication de condensateurs céramiques multicouches (MLCC). L'oxyde de terres rares le plus couramment utilisé comme dopant dans la formulation commerciale de la poudre BT pour la fabrication de MLCC est Y2O3, car il a des propriétés similaires à celles de l'ajout de Ho2O3, Er2O3 ou Dy2O3 et il est moins coûteux. D'autres additifs, tels que Mn, Mg et Ca contribuent à la répartition globale des défauts électroniques pouvant être générés lorsque les ions dopants sont insérés dans le réseau, tandis que SiO2 est utilisé comme additif de frittage. La structure pérovskite du BT peut héberger une large gamme de dopants pouvant remplacer Ba ou Ti dans le réseau. Aussi, des phases secondaires, notamment celles connues sous le nom de pyrochlores Y2Ti2O7, associées à l'Y2O3 en tant que dopant BT, supposées être á l'origine des mécanismes de défaillance à long terme des MLCC, apparaissent. Le but de ce travail est de caractériser le BT dopé avec différentes concentrations d'Y2O3, en validant son éventuelle contribution à la formation de phases secondaires et en évaluant la fiabilité des MLCC préparées avec ce type de matériaux. Le rôle de Y2O3 a été évalué sur deux types de matières premières, le premier est du BaTiO3 pur (<100 ppm en Y) et le second est une formulation commerciale conçue pour les MLCC connus sous le nom de X7R (-55 °C et 125 °C, ±15 %) qui, entre autres éléments, contient déjà 1% en poids de Y2O3. Des poudres et des céramiques avec différentes concentrations d'Y3+, telles qu'Y2O3, de dopage (1% en poids à 20% en poids) ont été préparées puis traitées thermiquement ou frittées. Le traitement thermique de la poudre a été effectué à l'air, tandis que le frittage de la céramique (poudre compactée à 2 MPa) a été effectué à la fois dans l'air et dans une atmosphère réductrice (1310 °C à l'air pendant 3 h, deux étapes: 1310 °C puis 1150 °C 15 h et une atmosphère réductrice N2, H2, H2O à 1310 °C pendant 3 h). En ce qui concerne l'addition d'Y2O3, la transition de phase de tétragonal à un mélange de tétragonal et de cubique a été observée lorsque la concentration en Y2O3 augmentait dans la poudre traitée thermiquement et dans la céramique correspondante. [...] / Doped barium titanate (BaTiO3, BT) with rare-earth elements (REE) is used as dielectric in the manufacture of multilayer ceramic capacitors (MLCCs). The most common REE oxide employed as dopant in the commercial formulation of BT powder for fabrication of MLCCs is Y2O3, because it results in similar properties than adding Ho2O3, Er2O3 or Dy2O3, and it is less expensive. Other additives, such as Mn, Mg, and Ca contribute to the global distribution of the electronic defects that can be generated when the doping ions are inserted into the lattice, while SiO2 is used as a sintering additive. The perovskite structure of the BT can host a wide range of dopants that can substitute either Ba or Ti in the lattice. There are reports of secondary phases, particularly those known as pyrochlores Y2Ti2O7, related to Y2O3 as BT dopant, that are supposed to be the cause of long term failure mechanisms of MLCC's under nominal operation. The purpose of this work is to characterize BT doped with different concentrations of Y2O3, validating its possible contribution to the formation of secondary phases, and evaluating reliability of MLCCs prepared with this kind of materials. The role of Y2O3 was evaluated on two kinds of raw materials, the first one is pure BaTiO3 (< 100 ppm Y) and the second kind is a commercial formulation designed for MLCCs known as X7R (-55 °C and 125 °C, 15% tolerance) which, among other elements, already contains 1 wt% of Y2O3. Powders and ceramics with different Y3+, as Y2O3, doping concentration (1 wt% up to 20 wt%) were prepared and subsequently thermally treated or sintered, respectively. Heat treatment of powder was conducted on air, while sintering of ceramics (powder compacted at 2 MPa) was carried out both, in air and reducing atmosphere (1310 °C in air for 3 h, two steps: 1310 °C then 1150 °C 15 h, and a reducing atmosphere N2, H2, H2O at 1310 °C for 3 h). Regarding Y2O3 addition, the phase transition from tetragonal to a mixture of tetragonal and cubic was observed as Y2O3 concentration increases in the thermally treated powder and in the corresponding ceramics. [...]

För att verifiera att komponenter håller under en förväntad livslängd kan en Accelererad Livstids Testning (ALT) användas. En av huvudaspekterna som kan förstöra ett ALT-test av plastkomponenter är om kontakttemperaturen överstiger glasövergångstemperaturen. Detta eftersom det förändrar testkomponentens materialegenskaper. För att förhindra att detta inträffar i en ALT byggdes en testrigg medtemperatursensorer för att övervaka kontakttemperaturen. Om kontaktpunkten modifieras med en temperatursensor förändrar det uppbyggnaden av ytan och gör testet ogiltigt. Metoden som används är istället att mäta temperaturen på ytan på testdelen och simulera kontakttemperaturen med en modell baserad på den Finita Elementmetoden. Denna avhandling jämför de två teknikerna Tunn Film RTD och Tunn Termoelement Tråd Typ T i samband med uppbyggnaden av en värmeöverföring FEM-modell. Det undersöktes också vilken teknologi av IR-enpunkts sensor och Tunn Film RTD som har högst prestanda med avseende på fyra kvalitetsparametrar under användning tillsammans med testriggen. Slutsatserna är att Tunn Film RTD och Tunn Termoelement Tråd av Typ T sensorerna båda ger en liknande precision i mätningar för att bygga en användbar FEM-modell. När de används på testriggen presterar Film RTD:n är bättre än IR-sensorn i tre av fyra områden med avseende på de fyra definierade kvalitetsparametrarna. Tunn Film RTD är den rekommenderade teknologin för denna typ av mätning. / To verify that components last for an expected lifetime an Accelerated Life Testing (ALT) can be used. One of the main aspects that can ruin an ALT of plastic components is if the contact temperature rises above the glass transition temperature, since this changes the material properties of the tested component. To prevent this from occurring in a ALT, a test rig was built with temperature sensors to monitor this contact temperature. If the contact point is modified with a temperature sensor, this will change the surface and make the test invalid. The method is instead to couple surface temperature measurements with a Finite Element Model (FEM) to estimate the contact temperature. This thesis compares the two techniques Thin Film RTD and Thin Thermocouple Wire Type T in conjunction with the building of a heat transfer Finite Element Method (FEM)-model. It also investigates which technology of Non Contact IR Single Point sensor or Thin Film RTD have the highest performance in use with the test rig with regard to four quality parameters. The conclusions are that RTD and the Thermocouple Type T sensors both provide equal precision in measurement to build a useful FEM model. In application on the test rig, the Thin Film RTD is better than the Infrared (IR)-sensor in three out of four areas when compared in the four defined quality parameters. Thin Film RTD is the recommended technology in this application.

<p>In this thesis, inferential methods for one-shot device testing data from accelerated life-test are developed. Due to constraints on time and budget, accelerated life-tests are commonly used to induce more failures within a reasonable amount of test-time for obtaining more lifetime information that will be especially useful in reliability analysis. One-shot devices, which can be used only once as they get destroyed immediately after testing, yield observations only on their condition and not on their real lifetimes. So, only binary response data are observed from an one-shot device testing experiment. Since no failure times of units are observed, we use the EM algorithm for determining the maximum likelihood estimates of the model parameters. Also, inference for the reliability at a mission time and the mean lifetime at normal operating conditions are also developed.</p> <p>The thesis proceeds as follows. Chapter 2 considers the exponential distribution with single-stress relationship and develops inferential methods for the model parameters, the reliability and the mean lifetime. The results obtained by the EM algorithm are compared with those obtained from the Bayesian approach. A one-shot device testing data is analyzed by the proposed method and presented as an illustrative example. Next, in Chapter 3, the exponential distribution with multiple-stress relationship is considered and corresponding inferential results are developed. Jackknife technique is described for the bias reduction in the developed estimates. Interval estimation for the reliability and the mean lifetime are also discussed based on observed information matrix, jackknife technique, parametric bootstrap method, and transformation technique. Again, we present an example to illustrate all the inferential methods developed in this chapter. Chapter 4 considers the point and interval estimation for the one-shot device testing data under the Weibull distribution with multiple-stress relationship and illustrates the application of the proposed methods in a study involving the development of tumors in mice with respect to risk factors such as sex, strain of offspring, and dose effects of benzidine dihydrochloride. A Monte Carlo simulation study is also carried out to evaluate the performance of the EM estimates for different levels of reliability and different sample sizes. Chapter 5 describes a general algorithm for the determination of the optimal design of an accelerated life-test plan for one-shot device testing experiment. It is based on the asymptotic variance of the estimated reliability at a specific mission time. A numerical example is presented to illustrate the application of the algorithm. Finally, Chapter 6 presents some concluding remarks and some additional research problems that would be of interest for further study.</p> / Doctor of Philosophy (PhD)