Fiber reinforced polymer (FRP) is a composite material made of fibers that carry tensile loads embedded in a polymeric matrix. Externally bonded FRP retrofits of reinforced concrete elements provide an efficient, economical, and accepted method of mitigating deficiencies related to seismic and blast loads, as well as addressing corrosion-related issues. FRPs retrofits are widely regarded as cost effective as the cost associated with retrofit installation and facility down-time are usually less than similar retrofit systems. Besides issues of bond and anchorage between the FRP and the substrate, the main disadvantage of FRP materials is that they behave in a brittle, linear elastic manner. As a result, strengthening concrete structures with FRP may introduce new and undesirable behaviors that are mitigated by design codes through strict strain limits. Because FRP is designed for very low strain levels to prevent brittle rupture and unpredictable debonding, buildings and bridges are strengthened in such a way that restricts their energy dissipation capacity at the ultimate limit state. This runs counter to the structural design philosophy of new buildings where the design objective is to develop significant plastic deformation to dissipate energy. An ideal composite material for infrastructure strengthening is one that combines the ease of application of FRP rehabilitation systems with the ability of ductile metals to yield under relatively large strains to provide energy dissipation and ensure ductile behavior. Known as a fiber metal laminate (FML), the aerospace industry has successfully developed a composite consisting of thin metal sheets alternatively bonded to epoxy saturated fiber fabric that is widely used to construct aircraft fuselages and wings. Unlike FRP, FML composites possess a well-defined yield point and exhibit inelastic behavior. However, aerospace grade FML composites cannot directly be applied to building and bridges because they: (i) were developed for low-stress fatigue resistance rather than performance near ultimate stress; (ii) are precisely manufactured to unnecessarily tight tolerances by civil construction standards; and (iii) are not economical compared with current FRP strengthening techniques. Therefore, developing a multifunctional civil engineering composite material based on FML theory would unlock opportunities related to plastic design, energy dissipation, and other mechanisms not currently possible with FRP. This dissertation presents a comprehensive study on the use FML jackets to enhance the strength and ductility of concrete cylinders. The confinement effect and failure mechanisms of FML confined concrete were analyzed for a range of experimental parameters, including the effect of the number of layers, the fiber orientation, and fabric architecture of the FML jackets. The experimental program was divided into two phases. The first phase consisted of a series of uniaxial tension coupon tests to investigate how the stacking arrangement of various E-glass fabrics and aluminum sheets could be tuned to control the yield strength, post-yield stiffness, and ductility characteristics of the FML lay-ups. Mechanical roughening of aluminum sheets and the addition of a bond enhancement agent to the resin system was found to enhance the interlayer bonding and splice capacity of metal and fiber layers. The results demonstrated that FML coupons with [±45°] glass fabrics exhibited pseudo-elastic-plastic stress-strain response, while coupons with [0°] and [0°/90°] fabrics exhibited strain hardening after yielding of aluminum layers. Furthermore, the ratio of the relative contribution of composite layers to the total elastic stiffness of the FML composites was found to be a good indicator of the mechanical properties and shape of the uniaxial stress-strain response of the FML lay-ups. An analytical model based on the Rule of Mixtures (ROM) was used to predict the tensile behavior of the FML coupons. The second phase consisted of axial compression testing of concrete cylinders confined by FML jackets to investigate the influence of various lay-up schemes on the strength and ductility of the confined concrete. Cylinders jacketed with FML showed a significant increase in their strength and ductility. The degree of strain-softening response, maximum strength, peak strain, ultimate deformation, and energy dissipation capacity of the FML confined concrete was found to be controlled by the pseudo-ductile stress-strain response of the FML jackets. FML lay-ups which exhibited strain hardening uniaxial behavior tended to produce greater enhancements in confined concrete strength and steeper strain softening response than FML lay-ups which exhibited pseudo-elastic-plastic uniaxial behavior. Furthermore, FML confined concrete showed improved performance, compared to FRP confined concrete, in terms of confined concrete behavior and failure mode. Finally, the project also demonstrated that an in-situ, hand lay-up preparation procedure for FML jackets provided a level of performance and construction tolerance suitable for use in civil infrastructure applications. Although the results of this study encourage the use of FML as a viable substitute to FRP for retrofitting deficient concrete members, further research is recommended on large-scale columns to verify the feasibility of this innovative retrofit technique. / Doctor of Philosophy / Glass fiber fabrics infused with epoxy resin can be wrapped around concrete cylinders to create a form of confinement jacket that enhances the strength and ductility of the concrete. The cured fiber reinforced polymer (FRP) composite will resist the lateral expansion of the cylinder when it is subject to axial compression. The resistance action works in the form of an external confining pressure developed by jacket and applied to the surface of the cylinder. The increase in confinement pressure is proportional to the lateral expansion of the cylinder which creates hoop strains in the jacket material. The FRP jacket will rupture suddenly when the jacket reaches its ultimate strain capacity, causing the confined cylinder to fail in an explosive manner. FRP composites are often used to repair and strengthen structures suffering from performance deficiencies. However, the brittle mode of failure of FRP is undesirable because it can occur suddenly and without warning. An ideal composite for infrastructure strengthening applications is one that combines the ease of application of FRP rehabilitation systems with the ability of ductile metals to yield under large strains to provide energy dissipation and ensure ductile behavior. The objective of this research was to investigate the strength and ductility of concrete cylinders confined by fiber metal laminates (FML), a composite material consisting of thin aluminum sheets alternatively bonded to layers of glass fiber fabrics. Axial compression testing of concrete cylinders confined by FML jackets was performed to investigate the influence of various FML lay-up schemes on the strength and ductility of the confined cylinders. Concrete cylinders jacketed with FML showed a significant increase in strength and ductility. FML lay-ups which exhibited strain hardening uniaxial behavior tended to produce greater enhancements in confined concrete strength and steeper strain softening response than FML lay-ups which exhibited pseudo-elastic-plastic uniaxial behavior. Furthermore, FML confined concrete showed improved performance, compared to FRP confined concrete, in terms of confined concrete behavior and failure mode. Although the results of this study encourage the use of FML as a viable substitute to FRP for retrofitting deficient concrete members, further research is recommended on large-scale columns to verify the feasibility of this innovative retrofit technique.

O presente trabalho é um estudo qualitativo do comportamento mecânico do laminado metal-fibra GLARE-5 2/1, submetido a impacto balístico subsônico em condições que simulam à amplitude térmica em aplicações espaciais. Para isto, os corpos de prova foram submetidos e ao impacto balístico de um projétil cilíndrico e alguns destes foram submetidos ao choque térmico, alternando entre -196 e 100°C. Os danos causados por estes ensaios foram analisados com as técnicas de microscopia óptica e tomografia computadorizada de raios X (X-Ray CT), que permitiram o entendimento dos danos em duas e três dimensões. Comparouse o resultado entre estas técnicas e a influência do ordenamento das amostras no escaneamento deste material. Concluiu-se que a X-Ray CT é uma técnica não destrutiva que proporciona boa informação para o entendimento dos danos internos causados pelo impacto no GLARE, embora não replicou com exatidão os danos observados na microscopia óptica. Além disso, o agrupamento de amostras do GLARE para o escaneamento permitiu melhorar a qualidade das imagens resultantes destes escaneamentos. Os danos mais comuns causados pelo impacto foram delaminações metal-fibra, trincamentos na matriz polimérica e delaminações fibra-fibra, sendo a condição criogênica a que resultou em maior volume de danos. Amostras submetidas ao choque térmico mostraram uma queda de sua temperatura de transição vítrea e ganho na resistência ao impacto. / This is a qualitative study of the mechanical behavior of the metal-fiber laminate GLARE-5 2/1 subjected to subsonic ballistic impact under conditions that simulate thermal amplitude in space applications. For this, the specimens were submitted to the ballistic impact of a cylindrical projectile; some specimens were previously thermal shocked, alternating between - 196 and 100 ° C. The damages caused by these tests were analyzed by optical microscopy and X-ray CT (X-Ray CT), which allows the understanding of damage in two and three dimensions. Were compared the results between these techniques and the influence of the ordering of the samples in the scanning of this material. It was concluded that X-Ray CT is a non-destructive technique that provides good information for understanding the internal damage caused by impact on GLARE, although it did not replicate accurately the damage observed under light microscopy. In addition, GLARE sample collation for scanning has improved the quality of the images resulting from these scans. The most common damages caused by the impact were metal-fiber delamination, cracking in the polymer matrix and fiber-fiber delamination, the cryogenic condition being the result of greater damage. Samples subjected to thermal shock showed a drop in their glass transition temperature and gain in impact resistance.

Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas. / This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.

Aplicações dos laminados híbridos metal-fibra incluem, além da indústria aeronáutica, as indústrias naval e automobilística. Diferentemente do setor aeronáutico, pesquisas sobre impactos mecânicos nas duas outras áreas da mobilidade são freqüentemente limitadas pela disponibilidade de equipamentos laboratoriais, de modo que é desejável o desenvolvimento de procedimentos de baixo custo para a determinação da resistência e tolerância a danos por impacto dos materiais de construção. Neste trabalho, a resistência a danos por impacto transversal do laminado híbrido metal-fibra Glare-5® foi determinada via três diferentes metodologias. A primeira utiliza um aparato sofisticado aparato Laser-Doppler para monitorar a aceleração e desaceleração de um impactador esférico de aço com 5 mm de diâmetro durante o evento do choque mecânico. O segundo método se baseia apenas nos valores de carga (força aplicada) vs. o tempo de impacto para a obtenção da energia absorvida pelo material. O terceiro considera somente os dados da velocidade do impactador, ou projétil, imediatamente antes e após o impacto. Concluiu-se que os valores de energia obtidos segundo as duas primeiras metodologias são similares, com o Laser-Doppler gerando resultados levemente não-conservadores, comprovando assim a possibilidade da derivação da resistência ao impacto do laminado através de um experimento simples e rápido, que utiliza apenas uma célula de carga digital para a monitoração da força aplicada em função do tempo. O terceiro método apresentou resultados substancialmente superiores às duas primeiras metodologias, sendo classificado como inadequado aos propósitos do projeto. Determinou-se que o laminado híbrido Glare-5®; absorve entre 60% e 80% da energia disponibilizada em impactos ditos leves, no intervalo de 1 a 6 Joules. Por fim, comprovou-se que a rigidez do material (módulo de elasticidade) é a propriedade residual (numa base de tolerância a danos) mais clara e consistentemente degradada pelo impacto previamente aplicado ao material. / Applications of hybrid fiber-metal laminates include, besides aeronautical industry, the automotive and naval industries. Unlike aeronautical field, impact research activities in the former areas of mobility industry are frequently limited by available laboratory equipment, so that it would be desirable to develop low-cost procedures to determine impact resistance and tolerance properties of construction materials. In this work, the transversal (trans-thickness) impact resistance and tolerance of hybrid fiber-metal laminate Glare-5® have been determined via three different methodologies. The first one utilizes sophisticated apparatus comprising a Laser-Doppler device to monitor deceleration/re-acceleration of 5 mm-diameter steel-ball impactor during the mechanical shock event. The second approach merely relies on the force (applied load) vs. impact time for determining the absorbed energy during the dynamic process. The third methodology requires only impactor velocity data points, immediately before and after the impact. It has been concluded that the energy values obtained from Laser- Doppler and load cell methods are very similar, with the former method producing slightly non-conservative results, allowing one to rapidly derive the impact resistance of hybrid laminate materials through very simple experimental set-ups employing digital load cells only. The third method presented somewhat higher results as compared to the concurrent techniques, so that it has been considered as inadequate for the research purposes. This study has shown that the fibre-metal laminate Glare absorbs between 60% and 80% of the apported impact energy during light impact events (ranging from 1 to Joules). Last, but not the least, materials stiffness was the most clearly and consistently imparted residual mechanical property (in a damage tolerance basis) due to the previous applied impact loading.

Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas. / This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.

Aplicações dos laminados híbridos metal-fibra incluem, além da indústria aeronáutica, as indústrias naval e automobilística. Diferentemente do setor aeronáutico, pesquisas sobre impactos mecânicos nas duas outras áreas da mobilidade são freqüentemente limitadas pela disponibilidade de equipamentos laboratoriais, de modo que é desejável o desenvolvimento de procedimentos de baixo custo para a determinação da resistência e tolerância a danos por impacto dos materiais de construção. Neste trabalho, a resistência a danos por impacto transversal do laminado híbrido metal-fibra Glare-5® foi determinada via três diferentes metodologias. A primeira utiliza um aparato sofisticado aparato Laser-Doppler para monitorar a aceleração e desaceleração de um impactador esférico de aço com 5 mm de diâmetro durante o evento do choque mecânico. O segundo método se baseia apenas nos valores de carga (força aplicada) vs. o tempo de impacto para a obtenção da energia absorvida pelo material. O terceiro considera somente os dados da velocidade do impactador, ou projétil, imediatamente antes e após o impacto. Concluiu-se que os valores de energia obtidos segundo as duas primeiras metodologias são similares, com o Laser-Doppler gerando resultados levemente não-conservadores, comprovando assim a possibilidade da derivação da resistência ao impacto do laminado através de um experimento simples e rápido, que utiliza apenas uma célula de carga digital para a monitoração da força aplicada em função do tempo. O terceiro método apresentou resultados substancialmente superiores às duas primeiras metodologias, sendo classificado como inadequado aos propósitos do projeto. Determinou-se que o laminado híbrido Glare-5®; absorve entre 60% e 80% da energia disponibilizada em impactos ditos leves, no intervalo de 1 a 6 Joules. Por fim, comprovou-se que a rigidez do material (módulo de elasticidade) é a propriedade residual (numa base de tolerância a danos) mais clara e consistentemente degradada pelo impacto previamente aplicado ao material. / Applications of hybrid fiber-metal laminates include, besides aeronautical industry, the automotive and naval industries. Unlike aeronautical field, impact research activities in the former areas of mobility industry are frequently limited by available laboratory equipment, so that it would be desirable to develop low-cost procedures to determine impact resistance and tolerance properties of construction materials. In this work, the transversal (trans-thickness) impact resistance and tolerance of hybrid fiber-metal laminate Glare-5® have been determined via three different methodologies. The first one utilizes sophisticated apparatus comprising a Laser-Doppler device to monitor deceleration/re-acceleration of 5 mm-diameter steel-ball impactor during the mechanical shock event. The second approach merely relies on the force (applied load) vs. impact time for determining the absorbed energy during the dynamic process. The third methodology requires only impactor velocity data points, immediately before and after the impact. It has been concluded that the energy values obtained from Laser- Doppler and load cell methods are very similar, with the former method producing slightly non-conservative results, allowing one to rapidly derive the impact resistance of hybrid laminate materials through very simple experimental set-ups employing digital load cells only. The third method presented somewhat higher results as compared to the concurrent techniques, so that it has been considered as inadequate for the research purposes. This study has shown that the fibre-metal laminate Glare absorbs between 60% and 80% of the apported impact energy during light impact events (ranging from 1 to Joules). Last, but not the least, materials stiffness was the most clearly and consistently imparted residual mechanical property (in a damage tolerance basis) due to the previous applied impact loading.