Accelerated aging of 15 kV Cross-linked Polyethylene (XLPE) and Ethylene Propylene Rubber (EPR) power cables was carried out in the experiments set for the study of this thesis. The degradation of cable insulation under different aging conditions was studied and compared. The study helped to understand the effects of different factors on the aging of XLPE and EPR cable insulation. In the study, degradation of XLPE cable insulation caused by switching impulses was investigated. The deterioration of EPR cable insulation initiated by elevated ac voltage and switching impulses were also studied. Measurements of partial discharge parameters, capacitance, and dissipation factor were analyzed to evaluate the condition of cable insulation during accelerated aging process. Measurement of ac breakdown voltage provided evidence of the cables’ remaining dielectric strength after accelerated aging.

Concentrated solar power systems are expected to be sited in desert locations where the direct normal irradiation is above 1800 kWh/m2.year. These systems include large solar collector assemblies, which account for a significant share of the investment cost. Solarreflectors are the main components of these solar collector assemblies and dust/sand storms may affect their reflectance properties, either by soiling or by surface abrasion. While soiling can be reverted by cleaning, surface abrasion is a non reversible degradation.The aim of this project was to study the accelerated aging of second surface silvered thickglass solar reflectors under simulated sandstorm conditions and develop a multi-parametric model which relates the specular reflectance loss to dust/sand storm parameters: wind velocity, dust concentration and time of exposure. This project focused on the degradation caused by surface abrasion.Sandstorm conditions were simulated in a prototype environmental test chamber. Material samples (6cm x 6cm) were exposed to Arizona coarse test dust. The dust stream impactedthese material samples at a perpendicular angle. Both wind velocity and dust concentrationwere maintained at a stable level for each accelerated aging test. The total exposure time in the test chamber was limited to 1 hour. Each accelerated aging test was interrupted every 4 minutes to measure the specular reflectance of the material sample after cleaning.The accelerated aging test campaign had to be aborted prematurely due to a contamination of the dust concentration sensor. A robust multi-parametric degradation model could thus not be derived. The experimental data showed that the specular reflectance loss decreasedeither linearly or exponentially with exposure time, so that a degradation rate could be defined as a single modeling parameter. A correlation should be derived to relate this degradation rate to control parameters such as wind velocity and dust/sand concentration.The sandstorm chamber design would have to be updated before performing further accelerated aging test campaigns. The design upgrade should improve both the reliability of the test equipment and the repeatability of accelerated aging tests. An outdoor exposure test campaign should be launched in deserts to learn more about the intensity, frequencyand duration of dust/sand storms. This campaign would also serve to correlate the results of outdoor exposure tests with accelerated exposure tests in order to develop a robust service lifetime prediction model for different types of solar reflector materials.

O objetivo deste estudo foi avaliar a estabilidade de cor e opacidade de cinco sistemas cerâmicos glazeados naturalmente e com pintura extrínseca, utilizando os espectrofotômetros Color Guide 45/0 (BYK-Gardner) e Easyshade (Vita), sob influência do envelhecimento artificial acelerado. Foram confeccionados 14 corpos de prova para cada grupo testado de cerâmica - metalocerâmica Ceramco 3 (Dentsply) (grupo 1), cerâmica pura Ceramco 3 (grupo 2), cerâmica pura EX -3 (Noritake) (grupo 3), Vitroceram (Angelus) recoberta com Allceram (Degudent) (grupo 4) e Vitroceram recoberta com Cerabien (Noritake) (grupo 5). Sete corpos de prova de cada grupo cerâmico foram glazeados naturalmente e sete foram submetidos à pintura extrínseca com pigmento Vita Chrom 712. Uma leitura inicial foi realizada em todos os corpos de prova utilizando o espectrofotômetro Color Guide, obtendo valores de opacidade e das coordenadas L*, a*, b* e E*; e utilizando o espectrofotômetro Easyshade, obtendo valores de L*, C*, h* e E*. Após o envelhecimento artificial de 500h, foram realizadas novas leituras nos espectrofotômetros. Os resultados encontrados foram submetidos à análise estatística e concluiu-se que os grupos 2, 3 e 4 foram influenciados estatisticamente pelo envelhecimento artificial acelerado quanto à opacidade; e que o grupo 5 foi o que obteve o pior desempenho de estabilidade de cor (E* = 3,32 - VTCE e E* = 2,68 = VTCEPE) para o espectrofotômetro Color Guide. Com o espectrofotômetro Easyshade os grupos 4 e 5 e as cerâmicas MC, CER, EX foram considerados ineficazes quanto à estabilidade de cor (p<0,05). / The aim of this study was to evaluate the color stability and opacity of five ceramic systems naturally glazed and with extrinsic porcelain colorant, under influence of accelerated aging, using two spectrophotometers Color Guide 45/0 (BYK-Gardner) and Easyshade (Vita) as a tool for color and opacity measurement. Fourteen samples were provided for each tested group of ceramics: metal-ceramic Ceramco3 (Dentsply) (Group 1), Ceramco3 (Group 2), EX3 (Noritake) (Group 3), Vitroceram (Angelus) with Allceram (Degudent) (Group 4) and Vitroceram with Cerabien (Noritake) (Group 5). Seven samples of each group were submitted to extrinsic colorant (Vita Chrom 712) and the other seven were naturally glazed. An initial measurement was performed and the values of opacity, L*, a*, b* and E* were obtained using the Color Guide spectrophotometer, and using Easyshade the values of L*, C*, h* and E* were obtained. After the process of 500h accelerated aging a new measurement was performed for all samples. The results were statistically analyzed and the conclusion was that the opacity of groups 2, 3 and 4 were statistically influenced by the accelerated aging and the group 5 had the worst assessment in color stability (E* = 3,32 - VTCE e E* = 2,68 - VTCEPE) with the Color Guide spectrophotometer. With Easyshade, groups 4 and 5 and MC, CER and EX ceramics were considered ineffective as for color stability (p<0,05).

O objetivo deste estudo foi avaliar a estabilidade de cor e opacidade de cinco sistemas cerâmicos glazeados naturalmente e com pintura extrínseca, utilizando os espectrofotômetros Color Guide 45/0 (BYK-Gardner) e Easyshade (Vita), sob influência do envelhecimento artificial acelerado. Foram confeccionados 14 corpos de prova para cada grupo testado de cerâmica - metalocerâmica Ceramco 3 (Dentsply) (grupo 1), cerâmica pura Ceramco 3 (grupo 2), cerâmica pura EX -3 (Noritake) (grupo 3), Vitroceram (Angelus) recoberta com Allceram (Degudent) (grupo 4) e Vitroceram recoberta com Cerabien (Noritake) (grupo 5). Sete corpos de prova de cada grupo cerâmico foram glazeados naturalmente e sete foram submetidos à pintura extrínseca com pigmento Vita Chrom 712. Uma leitura inicial foi realizada em todos os corpos de prova utilizando o espectrofotômetro Color Guide, obtendo valores de opacidade e das coordenadas L*, a*, b* e E*; e utilizando o espectrofotômetro Easyshade, obtendo valores de L*, C*, h* e E*. Após o envelhecimento artificial de 500h, foram realizadas novas leituras nos espectrofotômetros. Os resultados encontrados foram submetidos à análise estatística e concluiu-se que os grupos 2, 3 e 4 foram influenciados estatisticamente pelo envelhecimento artificial acelerado quanto à opacidade; e que o grupo 5 foi o que obteve o pior desempenho de estabilidade de cor (E* = 3,32 - VTCE e E* = 2,68 = VTCEPE) para o espectrofotômetro Color Guide. Com o espectrofotômetro Easyshade os grupos 4 e 5 e as cerâmicas MC, CER, EX foram considerados ineficazes quanto à estabilidade de cor (p<0,05). / The aim of this study was to evaluate the color stability and opacity of five ceramic systems naturally glazed and with extrinsic porcelain colorant, under influence of accelerated aging, using two spectrophotometers Color Guide 45/0 (BYK-Gardner) and Easyshade (Vita) as a tool for color and opacity measurement. Fourteen samples were provided for each tested group of ceramics: metal-ceramic Ceramco3 (Dentsply) (Group 1), Ceramco3 (Group 2), EX3 (Noritake) (Group 3), Vitroceram (Angelus) with Allceram (Degudent) (Group 4) and Vitroceram with Cerabien (Noritake) (Group 5). Seven samples of each group were submitted to extrinsic colorant (Vita Chrom 712) and the other seven were naturally glazed. An initial measurement was performed and the values of opacity, L*, a*, b* and E* were obtained using the Color Guide spectrophotometer, and using Easyshade the values of L*, C*, h* and E* were obtained. After the process of 500h accelerated aging a new measurement was performed for all samples. The results were statistically analyzed and the conclusion was that the opacity of groups 2, 3 and 4 were statistically influenced by the accelerated aging and the group 5 had the worst assessment in color stability (E* = 3,32 - VTCE e E* = 2,68 - VTCEPE) with the Color Guide spectrophotometer. With Easyshade, groups 4 and 5 and MC, CER and EX ceramics were considered ineffective as for color stability (p<0,05).

Kevlar materials offer excellent tensile and thermal properties but can rapidly degrade under exposure to hot and humid environmental conditions. Currently Kevlar fiber's survival probability comes from a single filament test. Unfortunately, the single filament test is a tedious process and prone to operator bias, leading to inaccurate survival function that does not represent the actual survival function. This research aims to validate the fiber bundle test to replace the single filament test in extracting Kevlar’s survival function. Another important aspect is determining the factors that cause the fiber to lose its properties. This research also aims to determine the factors that degrade Kevlar fibers and those factors’ combined effects on degrading the KM2 fiber. This information is essential for safety factor design when exposure to these environmental factors would cause the Kevlar KM2 to fail prematurely. Results from experimental data and analysis indicate that the fiber bundle test is a good replacement for single filament tests and estimation techniques can determine the bundle Weibull parameters. Furthermore, the survival function for treated fibers is better if the bundle is lubricated. The accelerated aging experiments show that accelerated aging is possible with combined temperature and moisture. Kevlar KM2 bundle conditioned at 270 °C and 150 g water for 3 hours lost over 95% of its breaking strength. This is comparable to Kevlar bundles treated for over 500 hours in 250 °C or treated for over 100 days in 100% relative humidity environment at 80 °C found in literature.

Partial discharge testing is a nondestructive method of identifying possible premature insulation breakdown. Magnet wires are used in various electrical equipment like injection coils, solenoids, small transformers and motors. Winding wires used in high voltage systems are subjected to several stresses during operation, which considerably lowers their lifetime. A prolonged combined effect of these stresses causes aging of the wires, inception of partial discharge activity, and degradation of the organic material in the enamel coating and varnish used by the manufacturer. The tests were conducted for AWG 30 and AWG 31 twisted magnet wire samples. The samples are aged under accelerated conditions of high frequency, temperature, and pulsed voltages. As well as conventional sinusoidal voltages. This thesis is focused on the results of voltage, frequency, and temperature stresses on the magnet wires. The partial discharge inception voltage (PDIV) and breakdown voltages are measured for different twisted wire samples. A software tool is utilized to study these partial discharge patterns. Evaluation of the parameters charge intensity, pulse count, and pulse phase position are presented in 2- and 3-dimensional plots.

Résumé : La technologie des armatures en matériaux composites de polymères renforcés de fibre (PRF) reste relativement récente (moins de 20 ans) et souffre d’une moins bonne réputation en termes de durabilité, ce qui tend à freiner son acceptation par les professionnels du secteur. Les travaux présentés dans ce mémoire ont pour but d’étudier les effets de l’humidité et de l’alcalinité sur les performances mécaniques et thermomécaniques de barres d’armature en PRF. Si de nos jours l’évolution des propriétés des armatures de PRF a été largement étudiée par différents chercheurs, nous n’avons que peu d’informations sur les modes de dégradation qui entrainent ces pertes de performances. Le but des travaux entrepris dans ce mémoire est de trouver des pistes d’investigation pour la compréhension de ces mécanismes de dégradation qui pourraient éventuellement par la suite être reprises dans le cadre de travaux de thèse. Les travaux qui ont été entrepris s’articulent autour de deux projets. Le premier s’intéresse à l’étude du vieillissement accéléré de barres de polymère renforcé de fibres de verre (PRFV) de différents diamètres et soumis à un environnement humide. Le second s’intéresse à l’étude de barres de PRFV et de polymère renforcé de fibres de basalte (PRFB) de même diamètre soumis à un environnement alcalin qui simule le milieu interstitiel du béton. / Abstract : The FRP rebars technology remains relatively recent and suffers from a bad reputation in terms of durability which slows its acceptation among the professionals of the construction field. The aim of the work presented in this essay is to study the effects of moisture and alkalinity on the mechanical and thermo mechanical performances of FRP rebars. Nowadays, the progressions of FRP performances have been widely studied by different researchers but we still have few knowledge about the modes of degradation which lead to performance losses. The final goal of this work is to find investigation trails for the understanding of those degradation mechanisms which could possibly be taken over as part of a thesis work. The work is divided into two projects. The first one is the study of accelerated aging of glass fibers reinforced polymer (GFRP) rebars, of different diameters, conditioned in a moist environment. The second one concerns the behavior of GFRP and basalt fibers reinforced polymer (BFRP) rebars, of same diameter, conditioned in an alkaline environment which simulates the interstitial solution of concrete.

This report aims to increase the scientific knowledge about long-term prospects for the adhesive and adhesive joints for bonding of stainless steels. The effects of water, temperature and chemicals on the adhesive and adhesive joints are investigated. Stainless steel plates are pretreated with a primer and isopropanol, there after joined together with single lap modeling. The strength of the joint is tested with a tensile test and additionally a watertightness test is performed to determine if the joints are watertight. For this project three versions of stainless steels is used and two different technologies of two- part adhesives, silicone and silane-modified polymer and one technology of tape, a double coated acrylic foam tape are tested. The result shows that all the adhesives fails cohesively and that tape fails partly adhesively. Result shows that all tests are affected by water, temperature and chemicals on different levels but tape is affected the most with a minimum of 40% loss in shear strength. Watertightness test shows that aged tape joints are not watertight. The polymer shows no signs of decreasing in shear strength and is watertight, but does become more viscous by aging. The report shows that a possible combination of adhesive and pretreatment that can withstand the effects of water, temperature and chemicals is found. The polymer presents a possibility to bond stainless steel with a simple pretreatment. Tape didn’t pass the test in a suitable way but presents opportunities if a sufficient pretreatment can be found.

L'utilisation de matériaux isolants à base de granulats végétaux est en plein essor notamment pour la réhabilitation du bâti ancien, améliorant ainsi le confort des habitants. Ces matériaux possèdent des propriétés thermiques, hydriques et acoustiques appréciables. Cependant, leur développement est encore limité par le manque d'information sur l'évolution de leurs performances à long terme. Ainsi, l’objectif de cette étude est d’évaluer l’évolution des propriétés fonctionnelles du béton de chanvre, en identifiant les mécanismes de vieillissement lorsque le matériau est exposé à différents types d'environnements. Pour cela, deux bétons de chanvre formulés avec une même chènevotte et deux liants de nature chimique différente sont retenus. L’approche utilisée dans cette étude est pluridisciplinaire (chimique, physico-chimique, microbiologique, microstructurale, acoustique, thermique et mécanique) et multi échelle. L'étude des propriétés chimiques et microstructurales permet de comprendre les variations des propriétés fonctionnelles. Dans un premier temps, la caractérisation initiale des deux formulations a permis de mettre en évidence l’absence d’influence de la nature du liant sur les propriétés fonctionnelles des isolants, ce qui peut être en partie expliqué par des microstructures similaires. Une faible résistance mécanique des matériaux, liée à l'inhibition de la prise des liants en raison de leurs interactions avec les molécules extraites de la chènevotte, a également été mise en évidence. Dans un second temps, les bétons de chanvre ainsi que la chènevotte brute sont soumis à un vieillissement accéléré en imposant des cycles d’humidification/séchage pendant deux ans. Les modifications des performances des matériaux à différentes échéances sont comparées à celles d'échantillons de référence placés à 50% d’humidité relative et une température constante contrôlée. Dans les conditions de référence, aucune variation de propriétés n'est observée. Pour le vieillissement accéléré, les variations de propriétés mises en évidence sont induites par différents paramètres. Dans le cas de la chènevotte brute, l’action des microorganismes et l’adsorption d’eau entrainent une perte de masse et l'ouverture des porosités à l'origine des variations des propriétés acoustiques et hydriques. Pour le béton de chanvre, aucun développement fongique n’est observé en surface du matériau. En revanche, l’action de microorganismes est bien visible à l’intérieur des granulats végétaux, et des mécanismes supplémentaires sont identifiés : les réactions d'hydratation et de carbonatation au sein du liant ainsi que la minéralisation de la chènevotte entrainent des variations de propriétés thermiques, acoustiques et hydriques en modifiant la microstructure des bétons de chanvre. En conclusion, l’absence de variations des propriétés des bétons de chanvre dans les conditions de référence laisse penser que dans un bâtiment réel, leurs propriétés peuvent être stables dans le temps, les pathologies observées étant alors liées à une mise en œuvre défaillante. Pour aller plus loin, les résultats obtenus lors de ce travail devront être validés par une étude in situ qui permettrait d’estimer la durée de vie de ces matériaux / The use of insulating materials based on plant aggregates is growing quickly, especially for the rehabilitation of old buildings, thus improving the comfort of residents. These materials have significant thermal, hydric and acoustic properties. However, their development is still limited by the lack of information on the evolution of their long-term performances. Thus, the objective of this study is to evaluate the evolution of the functional properties of hemp concretes, by identifying the aging mechanisms when the material is exposed to different types of environments. For this aim, two hemp concretes formulated with one type of hemp and two binders with different chemical nature are retained. The approach of this study is multidisciplinary (chemical, physico-chemical, microbiological, microstructural, acoustic, thermal and mechanical) and multi-scale. The study of chemical and microstructural properties allows the understanding of the variations of functional properties. Firstly, the initial characterization of the both hemp concretes made it possible to demonstrate the absence of impact of the nature of the binder on the functional properties of the insulators, which can be partly explained by their similar microstructure. A weak mechanical resistance of the materials was also highlighted, related to the inhibition of the setting of the binders because of their interactions with the molecules extracted from the shiv. Secondly, hemp concretes and bulk shiv hemp are subjected to an accelerated aging by imposing cycles of humidification / drying during two years. The modifications of the material performances at different time scales are compared to reference samples stored at 50% of relative humidity and a constant controlled temperature. Under reference conditions, no variation in properties is observed. For accelerated aging, the variations of properties highlighted are induced by several parameters. In the case of bulk shiv, the action of microorganisms and the adsorption of water lead to a loss of mass and to the opening of porosities, leading to variations in acoustic properties. For hemp concretes, no fungal development is observed on the surface of the material. On the other hand, the action of microorganisms is clearly visible inside the plant aggregates, and additional mechanisms are identified: the hydration and carbonation reactions within the binder as well as the mineralization of the vegetal particles cause variations in thermal, acoustic and hydric properties by modifying the microstructure of hemp concretes.In conclusion, the absence of variations in the properties of hemp concretes in the reference conditions suggests that in a real building, their properties can be stable over time, the observed pathologies then being due to a faulty implementation. To go further, the results obtained during this work have to be validated by an in-situ study to be able to estimate the lifetime of these materials

A proposta desse estudo foi avaliar in vitro a alteração de cor e a rugosidade superficial de três marcas de resinas indiretas de nova geração, após serem submetidas ao processo de envelhecimento artificial acelerado. Foram confeccionados 12 corpos-de-prova (15 mm diâmetro e 2 mm espessura) para as resinas: Artglass (Heraeus Kulzer), Solidex (Shofu), Targis (Ivoclar Vivadent) que receberam acabamento e polimento com discos Sof-Lex - 3M. As primeiras mensurações para o teste de rugosidade e de espectrofotometria colorimétrica foram realizadas, respectivamente, com Rugosímetro Surfcorder SE 1700 (Kosakalab) e Espectrofotômetro PCB 6807 (BYK GARDNER), que utiliza a escala CIE L*a*b* para determinação da cor. As amostras foram submetidas ao processo de envelhecimento artificial acelerado por 384 horas, e após esse período foram novamente submetidas ao processo de leitura de cor e de rugosidade. A estabilidade de cor foi determinada pela diferença (&#916;E) entre coordenadas L*, a* e b* obtidas das amostras antes e após o envelhecimento. Os resultados foram submetidos à ANOVA (Tukey) e mostraram que todas as resinas apresentaram alterações de cor, sem significância estatística (p>0,05). A resina Solidex foi a que apresentou maior valor de alteração de cor (&#916;E = 4,31), e que apresentou um padrão de rugosidade (Ra= 0,079) estatisticamente diferente das resinas Art-Glass (Ra=0,141) e Targis (Ra=0,124) (p<0,001). Conclusão: Todas as resinas apresentaram alteração de cor e aumento de rugosidade após o envelhecimento artificial acelerado. A resina Solidex apresentou a maior alteração de cor e a menor rugosidade após o envelhecimento acelerado. / This study had the aim of assessing in vitro color change and surface roughness of three brands of new generation indirect resins, after being submitted to accelerated aging process. Twelve specimens were constructed (15 mm diameter and 2 mm width) for the resins: Artglass (Heraeus Kulzer), Solidex (Shofu), Targis (Ivoclar Vivadent) which were finished and polished with the disks Sof-Lex - 3M. The first measurements for the roughness and spectrophotometer colorimeter tests were performed, respectively, with the Surfcorder Profilometer SE 1700 (Kosakalab) and Spectrophotometer PCB 6807 (BYK GARDNER), which uses the scale CIE L*a*b* for color determination. The samples were submitted to the accelerated artificial aging process for 384 hours, and then submitted once again to the process of color and roughness reading. Color stability was determined by the difference (&#916;E) between coordinates L*, a*, and b* obtained from the samples before and after aging. The results were submitted to ANOVA (Tukey) and showed that all resins presented color changes with no statistical significance (p>0.05). Solidex resin showed the highest value of color change (&#916;E = 4.31), and a roughness pattern (Ra= 0.079) statistically different from the resins Art-Glass (Ra=0.141) and Targis (Ra=0.124) (p<0,001). Conclusion: All resins showed color change and an increase of roughness after artificial accelerated aging. Solidex resin showed the highest color change and the lowest roughness after accelerated aging.