This thesis includes the study of the mechanical performance of two different types of fibers reinforced hybrid composites. Two kinds of fibers, natural fiber (flax) and synthetic fiber (E-glass), are used to reinforce epoxy resin. To evaluate the effective properties of the hybrid composites, a micromechanical analysis of the structure genome (SG) of a unidirectional fiber hybrid composites is performed using nite element analysis (FEA). Both fibers are assumed to be circular and packed in a hexagonal pattern. The effects of varying volume fractions and fiber locations, of the two fibers, on the elastic properties of the hybrid composites are studied using FEA. Rule of hybrid mixtures (RoHM) and Halpin-Tsai equations, which are analytical equations, are used as a preliminary prediction of the elastic constants of the hybrid composites. Then, the comparison is made between FEA and analytical results. The predicted elastic constants through numerical homogenization are in good a agreement with analytical results. The effect of changing fiber locations on the tensile strength of hybrid composite is investigated using tensile tests. Impact strength of single fiber composites and ax/glass fiber hybrid composites, in which various stacking sequences of ax and glass fibers are used, are obtained using Charpy impact tests. Moisture absorption test was performed by immersing single fiber composites and various stacking sequences of hybrid composites in deionized water at room temperature for a week. To investigate the effect of water absorption on the tensile properties of composite, tensile test was done on various stacking sequences of the hybrid composite. FEA and analytical equations showed that Young's and shear moduli increased and the axial Poison's ratio decreased linearly with the glass fiber content. Also, FEA showed that changing fiber locations have no effect on the effective properties of the hybrid composite. However, changing fiber stacking sequences showed a significant effect on tensile strength, impact strength, and water absorption properties of the hybrid composites. It was concluded that better design of the hybrid composite was achieved when glass fibers placed on the extreme positions and flax fibers in the middle. Positive hybrid effect is achieved from hybridization of E-glass fiber with flax fiber.

This dissertation demonstrates the first of its kind distributed magnetic field sensor based on a fiber optic distributed acoustic sensing (DAS) scheme. Ferromagnetic nickel and Metglas® were dispersed internally within a fiber optic preform and then drawn on an in-house fiber optic draw tower to lengths in the kilometers. Due to the close proximity of the ferromagnetic metals and fiber optic core, the magnetostrictive strain response of the ferromagnetic materials when exposed to a magnetic field would perturbate within the fiber cladding and transfer that strain, internally, to the fiber optic core. Strain resulting from the magnetostrictive effect allows the DAS based sensor to accurately translate strain into readable magnetic field data. Due to the high sensitivity seen in this sensor design, multiparameter sources, acoustic and magnetic fields, were tested and validated and a three dimensional magnetic-field vector sensor was proposed. Numerical analysis of the novel sensor design was first implemented using COMSOL Multiphysics, where inputs such as magnetostrictive element shape, size, distance, and number were first investigated. Upon optimizing system constraints, the sensor design was further modified such that single mode operation was consistent across multiple fiber draws while retaining high strain transfer from the ferromagnetic elements to the fiber optic core. Ferromagnetic material selection was evaluated as a function of the saturation magnetostriction constants and a total of 4 modules were used to fully characterize the complex physics involved in this sensor design. All fabrication and testing were performed in-house using a full scale 3-story fiber draw tower and custom environmental testing stations to imitate naturally occurring events such as magnetic or acoustic point sources. A unique stacking method was used to embed ferromagnetic nickel and Metglas® into a fiber optic preform which when combined with a custom fiber draw process resulted in consistent multi-material fibers drawn to lengths of 1-km. In-house testing facilities included different types of electromagnetic generators, in addition to a soil test bed, and an outdoor test bed which allowed 100 meters of fiber to be tested simultaneously. All tested sensors demonstrated high strain transfer capabilities on the order of 0.01-10 μϵ depending on the materials used, ferromagnetic rod number, and core to metal spacing. Due to the sensitivity of the system the difference between AC and DC was distinct, and directional magnetostriction was studied. Transverse and longitudinal magnetic wave propagation was controlled through a solenoid and rectangular Helmholtz coil, both built in-house. A three-dimensional magnetic field vector sensor was proposed due to the success of the magnetic field sensor, and a design was proposed and initially tested to validate direction as a function of field strength and distance. To summarize, this dissertation explores the first fully distributed magnetic field sensor using DAS based techniques and one of the first multi-material fiber draw processes which can produce consistent single mode fiber up to 1-km. Due to extensive FEA modeling, multiple iterations of the magnetic sensor were fully characterized and an equation describing the relationship between sensor design and strain transfer has been created and validated experimentally. Multi-parameter tests including acoustic and magnetic fields were implemented and an algorithm was developed to separate the mixed signals. Finally, a test was performed to demonstrate the feasibility of sensing magnetic fields directionally. Cumulative results demonstrate a high-quality sensor alternative to current designs which may surpass other magnetic sensors due to innate multi-parameter capabilities, in addition to the inexpensive production cost and extremely long operating lengths. / Doctor of Philosophy / This dissertation demonstrates the first of its kind distributed magnetic field sensor based on a fiber optic distributed acoustic sensing (DAS) scheme. Ferromagnetic nickel and Metglas® were dispersed internally within a fiber optic preform and then drawn on an in-house fiber optic draw tower to lengths in the kilometers. Due to the close proximity of the ferromagnetic metals and fiber optic core, the magnetostrictive strain response of the ferromagnetic materials when exposed to a magnetic field would perturbate within the fiber cladding and transfer that strain, internally, to the fiber optic core. Strain resulting from the magnetostrictive effect allows the DAS based sensor to accurately translate strain into readable magnetic field data. Due to the high sensitivity seen in this sensor design, multiparameter sources, acoustic and magnetic fields, were tested and validated and a three dimensional magnetic-field vector sensor was proposed. Numerical evaluation of the sensing structure was perused before experimental testing using COMSOL Multiphysics. Experimental and numerical evaluations were compared and showed a high degree of certainty which allowed expedited design modifications. Sensor characterization included scanning electron microscopy, and electron diffraction spectroscopy, which provided insight into material composition and fiber polishing quality. Due to the high-quality results attained in the combined acoustic and magnetic field tests, a final design was proposed to gather magnetic field data as a vector, showing both magnitude and direction. The 3D magnetic field vector sensor was partially validated based on a test which compared intensity with distance and a design and methodology was proposed to fully test and characterize this design. To summarize, a novel magnetic field sensor, capable of multi-parameter sensing, was proposed and tested experimentally and numerically resulting in a robust and highly sensitive design. The work presented here provides some of the first insights into multi-material fiber fabrication, an equation which provides an estimated relationship between magnetostrictive strain transfer onto a fiber optic core and the perceived DAS based sensor results, as well as a first of its kind multi-parameter distributed acoustic and magnetic field sensor.

Injection molded short fiber reinforced composites have generated commercial interest in the manufacturing of lightweight parts used in semi-structural applications. Predicting these materials’ fiber orientation with quantitative accuracy is crucial for technological advancement, but the task is difficult because of the effect of inter-particle interactions at high concentrations of fiber found in parts of commercial interest. A complete sample preparation procedure was developed to obtain optical micrographs with optimal definition of elliptical and non-elliptical footprint borders. Two novel aspects in this procedure were the use of tridimensional markers to identify specific locations for analysis and the use of controlled-etching to produce small shadows where fibers recede into the matrix. These images were used to measure fiber orientation with a customized image analysis tool. This tool contains several modifications that we introduced in the method of ellipses which allow us to determine tridimensional fiber orientation and to obtain measurements in regions with fast changes in orientation. The tool uses the location of the shadow to eliminate the ambiguity problem in orientation and characterizes non-elliptical footprints to obtain the orientation in small sampling areas. Cavitywise measurements in two thin center-gated disks showed the existence of an asymmetric profile of orientation at the gate and an orientation profile that washed out gradually at the entry region until disappearing at about 32 gap widths. This data was used to assess the prediction of cavitywise orientation using a delay model for fiber orientation with model parameters obtained from rheometrical experiments. Model predictions combining slip correction and experimentally determined orientation at the gate are in agreement with experimental data for the core layers near the end-of-fill region. Radialwise measurements of orientation at the shell, transition and core layer, and microtextural description of the advancing front are included in this dissertation. The analysis and assessment of the radial evolution of fiber orientation and advancing front based on comparing the experimental data with simulation results are under ongoing investigation. / Ph. D.

Leaf springs are a part of the suspension system attached between the axle and the chassis of the vehicle to support weight and provide shock absorbing capacity of the vehicle. For more than half a century the leaf springs are being made of steel which increases the weight of the vehicle and is prone to rusting and failure. The current study explores the feasibility of composite leaf spring to reduce weight by designing, manufacturing and testing the leaf spring for the required load cases. An off the shelf leaf spring of Ford F-150 is chosen for making of composite hybrid spring prototype. The composite hybrid prototype was made by replacing all the leaves with glass fiber unidirectional laminate except the first leaf. Fatigue tests are then done on steel and composite hybrid leaf spring to observe the failure locations and mechanism if any. High frequency fatigue tests were then done on composite beams with varying aspect ratio in a displacement-controlled mode to observe fatigue location and mechanism of just glass fiber composite laminate. It was observed that specimens with low aspect ratio failed from crack propagation initiated from stress concentrations at the loading tip in 3-point cyclic flexure test and shear forces played a dominant role in propagation of crack. Specimens with high aspect ratio under the same loading did not fail in cyclic loading and preserved the same stiffness as before the cyclic loading. The preliminary fatigue results for high aspect ratio composite beams predict a promising future for multi-leaf composite springs.

Le présent travail de thèse se consacre au développement d'un nouveau modèle micromécanique pour les composites en thermoplastique renforcé par des fibres de verre courtes. L'objectif est notamment la modélisation du comportement visco-endommageable en fatigue du PA66-GF30. Ce matériau, particulièrement utilisé dans l'industrie automobile, est sujet à une microstructure spécifique issue du procédé de moulage par injection. L'approche multi-échelles développée consiste en une méthode de Mori-Tanaka modifiée, appliquée à des renforts avec enrobage et prenant en compte l'évolution de l'endommagement à l'échelle microscopique. La description des mécanismes d'endommagement se base sur une investigation expérimentale poussée préalablement menée au sein de l'équipe. Des scénarios d'endommagement ont été proposés et incluent trois processus locaux différents : la décohésion de l'interface, la microfissuration de la matrice et les ruptures de fibres. Ceux-ci sont spécialement affectés par la microstructure. L'approche développée intègre ces cinétiques d'endommagement ainsi que la viscoélasticité non-linéaire de la matrice et la distribution d'orientation des inclusions due au procédé de fabrication. Chaque mécanisme d'endommagement est modélisé par une loi d'évolution basée sur les contraintes locales calculées à l'échelle microscopique. La loi constitutive finale, à l'échelle du volume élémentaire représentatif, est implémentée dans une bibliothèque scientifique en C++, SMART+, et est conçue pour être compatible avec une analyse de structures par éléments finis. L'identification du modèle est réalisée par rétro-ingénierie, en tirant profit de résultats expérimentaux multi-échelles, dont notamment des tests in-situ au MEB ainsi qu'une analyse qualitative et quantitative par μCT. / The current work focuses on a new micromechanical high cycle fatigue visco-damage model for short glass fiber reinforced thermoplastic composites, namely: PA66/GF30. This material, extensively used for automotive applications, has a specific microstructure which is induced by the injection process. The multi-scale developed approach is a modified Mori-Tanaka method that includes coated reinforcements and the evolution of micro-scale damage processes. Their description is based on the experimental investigations of damage mechanisms previously performed by the team. Damage chronologies have been proposed involving three different local degradation processes: fiber-matrix interface debonding/coating degradation, matrix microcracking and fiber breakage. Their occurrence strongly depends on the microstructure. The developed model integrates these damage kinetics and accounts for the complex matrix viscoelasticity and the reinforcement orientation distributions induced by the process. Each damage mechanism is introduced through an evolution law involving local stress fields computed at the microscale. The developed constitutive law at the representative volume element scale is implemented into a C++ scientific library, SMART+, and is designed to work with Finite Element Methods. The model identification is performed via reverse engineering, taking advantage of the multiscale experimental results: in-situ SEM tests as well as quantitative and qualitative μCT investigations.

Os compósitos são materiais formados por duas fases de diferentes propriedades químicas e físicas, sendo uma matriz e um reforço, que apresentam alta rigidez, melhores respostas à fadiga sob cargas cíclicas, leveza e resistência mecânica, o que os torna viáveis para substituir materiais nobres e de custo elevado, com diversas aplicações na aeronáutica, nos esportes, na indústria bélica e principalmente na construção civil. Além disso, os compósitos podem ser obtidos a partir da incorporação de resíduos em sua composição, solucionando problemas como o descarte irregular. Com o intuito de contribuir nessa área de conhecimento o presente estudo propôs o desenvolvimento de um compósito em forma de placas poliméricas a partir da incorporação do agregado reciclado de poliuretana termofixa reciclado à resina vegetal de mamona e à mantas de fibra de vidro. Para isso, o trabalho estabeleceu uma metodologia na qual o resíduo industrial de poliuretana termofixa é transformado em agregado reciclado, a partir de processos de corte e moagem, caracterização e classificação segundo as normas NBR 10.004 a 10.007 (ABNT, 2004). Na sequência, com o auxílio de uma prensa térmica, foi possível confeccionar as placas poliméricas e caracterizálas quanto às suas propriedades mecânicas (tração, flexão, punção), físicas (absorção em água, inchamento, densidade e dureza), térmicas (condutividade térmica) e quanto ao seu potencial de durabilidade (resistência ao impacto, à abrasão superficial, ao ataque químico, à exposição ao ultravioleta e às intempéries, resistividade elétrica e flamabilidade). Os resultados obtidos por meio dos ensaios realizados apontaram que os parâmetros ensaiados comportaram-se como materiais semelhantes àqueles utilizados na construção civil, o que possibilita a utilização do material desenvolvido nesta pesquisa em aplicações por este setor. / This study proposes the development of a composite material in the form of polymer slabs. The material is created from the incorporation of recycled thermoset polyurethane to castor oil resin and glass fiber mats. Composite materials are formed by two phases with different chemical and physical properties. One phase is a matrix, and the other a reinforcement. These materials are highly stiff, light, have mechanical strength and present better responses to fatigue under cyclic loads. These properties make them a substitute for noble materials, being eligible for uses in aviation, sports, the arms industry and, specially, civil construction. Furthermore, composites may be obtained by the incorporation of residue, solving problems of waste disposal. In the procedures undertaken, the industrial waste of thermoset polyurethane is transformed into a recycled aggregate, achieved by the cutting, grinding, characterization and classification in compliance to the ABNT standards (NBR 10.004 to10.007). Afterwards, with the use of a thermal press, it was possible to produce the slabs and characterize them according to the following properties: mechanical (tensile strength, and puncture), physical (water absorption, swelling and stiffness), thermal (conductivity) and the potential durability (resistance to impact, abrasion, chemical attack. ultraviolet and weather exposure, electrical resistance, and flammability). The test results indicated that the composite behaves similarly to materials used in civil construction, which enables its use in the area.

Preparos para retentores intra-radiculares mais conservadores evitam desgaste desnecessário da estrutura dentinária, requer menos cimento e podem melhorar a retenção adesiva do pino. Assim o objetivo deste estudo foi avaliar a espessura de cimento ea resistência adesiva de pinos de fibra de vidro cônicos em preparo para retentor intra-radicular realizados com uma ponta ultrassônica desenvolvida. Trinta incisivos laterais superiores foram preparados com limas reciprocantes Wave One Gold (Dentsply Sirona, Ballaigues, Suiça) e aleatoriamente divididos em 2 grupos (n=15) de acordo com a técnica de preparo para pino: grupo US foram preparados com uma ponta ultrassônica desenvolvida, e grupo WP (controle) com a broca recomendada pelo fabricante do pino. Os pinos de fibra de vidro cônicos WhitePost DC 0.5 (FGM, Joinville, SC, Brasil) foram cimentados utilizando cimento resinoso dual nos terços cervical e médio do canal radicular. Isto posto, todos os espécimes foram seccionados transversalmente em três seções (cervical, média e apical do pino) para análise da área de cimento resinoso ao redor do pino que foi calculada através do programa AutoCAD, em seguida, para avaliar a resistência adesiva, o teste de cisalhamento por extrusão foi aplicado através de uma maquina de ensaio universal numa velocidade média de 0.5 mm/min até o deslocamento do conjunto restaurador intra-radicular e o tipo de falha avaliado por estereomicroscopia. A comparação entre grupos e entre terços da área de cimento e resistência adesiva foram analisadas pelo teste t independente e Anova com Tukey; e os tipos de falha entre os grupos por Mann-Whitney, todos com nível de significância de 5%. No grupo ultrassônico foi observado a menor quantidade de cimento (p<0.05) e a resistência adesiva nos diferentes grupos e terços se manifestou maior somente no terço apical do grupo ultrassônico (p<0.05). Falha adesiva entre cimento e dentina foi a mais prevalente do terço cervical e apical do grupo US e cervical de grupo WP. Falha adesiva entre cimento e pino foi a mais prevalente nos demais terços. Conclui-se que o preparo para retentor com a ponta ultrassônica desenvolvida requer menor quantidade de cimento e influencia na melhor resistência de união no terço apical do pino de fibra de vidro. / Conservative post space preparations for intra-radicular retainers prevent unnecessary desgaste of the dentin structure, require less cement and improve bond strength of the post. The aim of this study was to evaluate the influence of resin cement thickness and bond strength of prefabricated glass fiber circular postin post space preparations with an ultrasonic tip developed. Thirtymaxillarylateral incisors were prepared with Wave One Gold reciprocating files (Dentsply Sirona, Ballaigues, Switzerland) and randomly divided into 2 groups (n=15) according to the post preparation technique: gruoup US was prepared with an ultrasonic tip developed and group WP (control) with the drill recommended by the post fabricant. Every glass fiber posts WhitePost DC 0.5 (FGM, Joinville, SC, Brazil) was cemented using dual polymerizing resin cement in the cervical and middle thirdof the root canal. After that, every specimen was sectioned transversally into three sections(cervical, middle and apical of the post) and the resin cement thickness area was calculated with AutoCAD program, the bond strength test was done with an universal testing machineat medium velocity 0.5 mm/min and the failure pattern after the test was analyzed with stereomicroscopy. Datas obtained were analyzed statistically using Student\'s t-Test, ANOVA,andTukey\'s test. The comparison of failure modes between the groups in the different thirds was done using Mann-Whitney test, All of those at a 5% significance. Ultrasonic group presented thinnest layer of cement in all thirds (p<0,05), which also obtained a higher bond strength only in apical third (p<0,05). Adhesive failurebetween cement and dentinwas the most prevalent of the cervical and apical third of G1 and cervical of G2.Adhesive failure between cement and post was the most prevalent in the others thirds. It can be concluded that the postpreparation with the ultrasonic tip developed provides a smaller thickness of resin cement that influenced thebond strength in the apical third of the glass fiber post.

Este estudo avaliou, in vitro, a influência da radioterapia na resistência de união (RU) e na interface adesiva entre diferentes cimentos resinosos e dentina radicular. Sessenta caninos superiores foram distribuídos em 2 grupos (n=30) de acordo com a irradiação: não irradiados e irradiados. Os dentes do grupo irradiado foram submetidos à radioterapia com raios-X de 6 MV em frações de 2 Gy, com 30 ciclos, perfazendo 60 Gy. Os dentes foram seccionados para obtenção de raízes com 16 mm de comprimento, sendo realizado em seguida o preparo biomecânico com instrumento Reciproc R50 e obturação pela técnica de condensação lateral com cimento a base resina epóxica. Cada grupo foi subdividido de acordo com o cimento resinoso utilizado para a cimentação dos pinos de fibra de vidro (n=10): RelyX U200; Panavia F 2.0; RelyX ARC. Os pinos foram submetidos a tratamento de superfície com ácido fluorídrico 10% e cimentados de acordo com as recomendações de cada fabricante. Após a cimentação dos pinos, os dentes foram seccionados transversalmente em slices de 1 mm de espessura, obtendo-se 3 slices de cada terço da raiz. Os slices mais cervicais de cada terço foram utilizados para avaliar a RU, por meio do teste de push-out com velocidade de 0,5 mm/min, e posterior análise do padrão de falha em estereomicroscópio. Os slices mais apicais de cada terço foram selecionados para análise da interface cimento/dentina em MEV com aumentos de 100, 1000, 2000 e 4000X. Os dados de RU e adaptação da interface cimento/dentina foram submetidos à análise estatística pelos testes de ANOVA e Tukey, e Kruskal-Wallis e Duns, respectivamente. Os espécimes irradiados apresentaram menores valores de RU (8,23&plusmn;4,26) comparados aos dentes não irradiados (11,88&plusmn;6,42) (p<0,00001). Quanto aos cimentos resinosos, o RelyX U200 apresentou maiores valores na RU (15,17&plusmn;5,89) comparado aos cimentos RelyX ARC (7,68&plusmn;4,22) (p<0,0001) e Panavia F 2.0 (7,32&plusmn;2,71) (p<0,0001). O terço cervical apresentou maiores valores de RU (13,08&plusmn;6,10) comparado aos terços médio (9,72&plusmn;5,03) e apical (7,38&plusmn;4,53) (p<0,0001). O padrão de falhas mostrou ocorrência de falhas coesivas na dentina para os espécimes irradiados. Na análise da interface cimendo/dentina por MEV, observou-se maior desadaptação nos dentes submetidos à radioterapia. Em relação aos cimentos resinosos, foi observada maior adaptação com RelyX U200 e RelyX ARC comparados à Panavia F 2.0. Na análise qualitativa em MEV observou-se presença de fraturas e microfraturas na dentina radicular e menor presença de fibras colágenas em dentes irradiados. Para o cimento resinoso RelyX U200 e Panavia F 2.0 observou-se interface justaposta do cimento com a dentina radicular em dentes irradiados e não irradiados, sendo que para o cimento resinoso RelyX ARC foi observada formação de camada híbrida e tags de maneira similar para dentes irradiados e não irradiados. Concluiu-se que a radioterapia resultou na redução da resistência de união e na maior desadaptação da interface cimento resinoso/dentina radicular e que o cimento resinoso autoadesivo se apresentou como melhor alternativa para cimentação de pinos de fibra de vidro em dentes irradiados. / This in vitro study, evaluated the influency of radiotherapy on bond strength (BS) and adhesive interface between different resin cements and root dentin. Sixty maxillary canines were selected and distributed into two groups (n = 30) according to the irradiation protocol: non-irradiated and irradiated. The irradiated group were submitted to X-ray radiotherapy of 6 MV in fractions of 2 Gy, with 30 cycles, until complete 60 Gy. The teeth were sectioned to obtain 16 mm of root length, followed by biomechanical preparation with R50 reciproc instrument and obturation using the lateral condensation technique with epoxy resin-based sealer. Then, each group was subdivided according to the resin cement used for the glass fiber post cementation (n = 10): RelyX U200, Panavia F 2.0 and RelyX ARC. The posts were submitted to surface treatment with 10% hydrofluoric acid, and then cemented according to the manufacturer instructions. After the posts cementation, the teeth were sectioned transversely into 1 mm thick slices, and 3 slices were obtained from each root third. The most cervical slice of each third was used to evaluate the BS by the push-out test at 0.5 mm/min of velocity and the failure pattern was analyzed using stereomicroscopy. The most apical slice of each third was selected for SEM analysis, which were prepared and metalized. The dentin/cement interface analysis was performed at the following magnification: 100, 1000, 2000 and 4000X. The BS data and dentin/cement interface adaptation were submitted to statistical analysis by ANOVA, Tukey and Kruskal-Wallis, and Duns tests respectively. The irradiated specimens had lower BS values (8.23 &plusmn; 4.26) compared to non-irradiated group (11.88 &plusmn; 6.42) (p <0.00001). Regarding the resin cements, the RelyX U200 showed the higher values in BS (15.17 &plusmn; 5.89) compared to RelyX ARC (7.68 &plusmn; 4.22) and Panavia F 2.0 (7 , 32 &plusmn; 2.71) (p <0.0001). In addition, the cervical third presented higher BS values (13.08 &plusmn; 6.10) when compared to the middle (9.72 &plusmn; 5.03) and apical (7.38 &plusmn; 4.53) thirds (p <0.0001). The failure pattern showed cohesive failures in root dentin of the irradiated specimens. In the SEM dentin/cement interface analysis, a greater misadaptation was observed for the teeth submitted to radiotherapy. Regarding the resin cements, a better adaptation was observed for the RelyX U200 and RelyX ARC compared to the Panavia F 2.0. In the SEM qualitative analysis of the irradiated teeth, was possible to observe the presence of fractures and microfractures in the root dentin and a small number of collagen fibers. The resin cements RelyX U200 and Panavia F 2.0 showed a juxtaposed interface of the cement with the root dentin in irradiated and non-irradiated teeth, being that for the RelyX ARC cement the presence of hybrid layer and tags was similar for irradiated and non-irradiated groups. It was concluded that the radiotherapy promoted reduction of the bond strength and increase the gaps in the dentin/resin cement interface and the self-adhesive resin cement is the best alternative for glass fiber posts cementation in irradiated teeth.

Preparos para retentores intra-radiculares mais conservadores evitam desgaste desnecessário da estrutura dentinária, requer menos cimento e podem melhorar a retenção adesiva do pino. Assim o objetivo deste estudo foi avaliar a espessura de cimento ea resistência adesiva de pinos de fibra de vidro cônicos em preparo para retentor intra-radicular realizados com uma ponta ultrassônica desenvolvida. Trinta incisivos laterais superiores foram preparados com limas reciprocantes Wave One Gold (Dentsply Sirona, Ballaigues, Suiça) e aleatoriamente divididos em 2 grupos (n=15) de acordo com a técnica de preparo para pino: grupo US foram preparados com uma ponta ultrassônica desenvolvida, e grupo WP (controle) com a broca recomendada pelo fabricante do pino. Os pinos de fibra de vidro cônicos WhitePost DC 0.5 (FGM, Joinville, SC, Brasil) foram cimentados utilizando cimento resinoso dual nos terços cervical e médio do canal radicular. Isto posto, todos os espécimes foram seccionados transversalmente em três seções (cervical, média e apical do pino) para análise da área de cimento resinoso ao redor do pino que foi calculada através do programa AutoCAD, em seguida, para avaliar a resistência adesiva, o teste de cisalhamento por extrusão foi aplicado através de uma maquina de ensaio universal numa velocidade média de 0.5 mm/min até o deslocamento do conjunto restaurador intra-radicular e o tipo de falha avaliado por estereomicroscopia. A comparação entre grupos e entre terços da área de cimento e resistência adesiva foram analisadas pelo teste t independente e Anova com Tukey; e os tipos de falha entre os grupos por Mann-Whitney, todos com nível de significância de 5%. No grupo ultrassônico foi observado a menor quantidade de cimento (p<0.05) e a resistência adesiva nos diferentes grupos e terços se manifestou maior somente no terço apical do grupo ultrassônico (p<0.05). Falha adesiva entre cimento e dentina foi a mais prevalente do terço cervical e apical do grupo US e cervical de grupo WP. Falha adesiva entre cimento e pino foi a mais prevalente nos demais terços. Conclui-se que o preparo para retentor com a ponta ultrassônica desenvolvida requer menor quantidade de cimento e influencia na melhor resistência de união no terço apical do pino de fibra de vidro. / Conservative post space preparations for intra-radicular retainers prevent unnecessary desgaste of the dentin structure, require less cement and improve bond strength of the post. The aim of this study was to evaluate the influence of resin cement thickness and bond strength of prefabricated glass fiber circular postin post space preparations with an ultrasonic tip developed. Thirtymaxillarylateral incisors were prepared with Wave One Gold reciprocating files (Dentsply Sirona, Ballaigues, Switzerland) and randomly divided into 2 groups (n=15) according to the post preparation technique: gruoup US was prepared with an ultrasonic tip developed and group WP (control) with the drill recommended by the post fabricant. Every glass fiber posts WhitePost DC 0.5 (FGM, Joinville, SC, Brazil) was cemented using dual polymerizing resin cement in the cervical and middle thirdof the root canal. After that, every specimen was sectioned transversally into three sections(cervical, middle and apical of the post) and the resin cement thickness area was calculated with AutoCAD program, the bond strength test was done with an universal testing machineat medium velocity 0.5 mm/min and the failure pattern after the test was analyzed with stereomicroscopy. Datas obtained were analyzed statistically using Student\'s t-Test, ANOVA,andTukey\'s test. The comparison of failure modes between the groups in the different thirds was done using Mann-Whitney test, All of those at a 5% significance. Ultrasonic group presented thinnest layer of cement in all thirds (p<0,05), which also obtained a higher bond strength only in apical third (p<0,05). Adhesive failurebetween cement and dentinwas the most prevalent of the cervical and apical third of G1 and cervical of G2.Adhesive failure between cement and post was the most prevalent in the others thirds. It can be concluded that the postpreparation with the ultrasonic tip developed provides a smaller thickness of resin cement that influenced thebond strength in the apical third of the glass fiber post.

[pt] Este trabalho tem como objetivo investigar o desempenho de colunas com seção I em polímeros reforçados com fibra de vidro (pGFRP) submetidas a cargas de compressão concêntricas de curta duração. Uma revisão bibliográfica acerca das teorias existentes é apresentada, incluindo os conceitos básicos de instabilidade, teoria de flambagem global e local, modos de falha de colunas perfeitas, bem como o comportamento de colunas reais. Um programa experimental foi conduzido, incluindo a caracterização dos materiais. Vinte e nova colunas – com três diferentes seções I e diferentes tipos de resina, propriedades mecânicas, bem como comprimentos – foram testadas. Do ponto de vista global, as colunas foram biengastadas. As placas constituintes, por sua vez, foram testadas com três diferentes condições de contorno: biengastadas (CC), biapoiadas (SS) e simplesmente em contato com as chapas de base da máquina de compressão (CB). Foi observado que a condição de contorno CB – a mais adotada em estudos anteriores -, se aproxima mais de um engaste do que de uma condição simplesmente apoiada. A distribuição não linear de deformações elásticas ao longo da seção também foi investigada. Finalmente, recomendações para um ensaio de flambagem local apropriado foram propostas. / [en] This work aims to investigate the performance of pultruded glass fiber reinforced polymer (pGFRP) I-section columns subject to short term concentric compression. A review of existing theories is presented, including the instability concepts, global and local buckling theories, perfect columns failure modes and the behavior of real columns. An experimental program including material characterization was conducted. Twenty-nine stubs – with three different I-sections geometries, having distinct flange width-to-section depth ratios (bf/d = 0.5; 0.75 and 1.0), mechanical properties, overall lengths and matrices – were tested. In a global point of view, the columns were fixed at both ends. The constituent plates, on the other hand, were tested with different end-conditions: clamped (CC), simply supported (SS) and simply in contact with base plates of the universal machine (CB). The third analyzed boundary condition, which is the most adopted in previous studies, was concluded to be closer to a clamped end-condition. The non-linear elastic strains distribution throughout the cross-section was also investigated. Finally, guideline recommendations for successful local buckling tests were proposed.