Em aplicações que requerem solicitações de impacto, compósitos de matriz polimérica reforçados com fibra de aramida se destacam, principalmente em relação aos metais, devido a propriedades como alta resistência e rigidez específicas, que dão origem a sistemas mais leves e de alta performance. Quando voltados para aplicações de impacto, principalmente a alta velocidade, tais compósitos são, em sua maioria, moldados por compressão ou autoclave, a partir de pré-impregnados. No entanto, tais combinações de processamentos e matéria-prima acarretam em estruturas de elevado custo, tornando a infusão a vácuo uma opção atrativa, além de permitir a obtenção de peças grandes e complexas, dimensionalmente acuradas e partes integradas. Porém, a obtenção de um compósito espesso reforçado por fibra de aramida com elevado desempenho ao impacto por tal método de fabricação ainda é um desafio. Neste contexto, este trabalho aborda o efeito da espessura no processamento por infusão a vácuo de compósitos aramida/epóxi e seu desempenho em aplicações que requerem solicitações de impacto (baixa e alta velocidade) Para isso, foram produzidos compósitos com 5, 8, 13, 18, 23 e 28 camadas de aramida e caracterizados por ultrassom C-scan, microscopia ótica, densidade, teor de constituintes, testes mecânicos (flexão, short beam e indentação quase-estática) e cargas de impacto de baixa e alta velocidade (drop-weight e balístico). Todos os compósitos apresentaram boa homogeneidade na distribuição da matriz ao longo do reforço, com um teor de fibra de ≈60%, e valores de resistência short beam elevados (17,3 - 23,6 MPa). A performance sob impacto (baixa e alta velocidade) foi comparável à de compósitos fabricados por compressão ou autoclave, tendo os compósitos a partir de 18 camadas resistido ao projétil 9 mm Luger FMJ e o de 28 camadas resistido ao projétil .357 Magnum FMJ, podendo ser classificados como nível FB2 e FB3, respectivamente, de acordo com a norma europeia EN 1522. Portanto, o processamento de infusão a vácuo mostrou ser uma alternativa adequada para produzir compósitos espessos de aramida/epóxi (até 12 mm), substituindo rotas de processamento mais caras. / In applications that require impact solicitations, polymer matrix composites reinforced with aramid fiber stand out, especially in relation to metals, due to properties such as high specific strength and stiffness, which give rise to lighter and high-performance systems. When used for impact applications, especially at high speed, such composites are mostly molded by compression or autoclaved, from prepregs. However, such combinations of processing and raw material lead to high cost structures, making vacuum infusion an attractive option, as well as allowing the production of large, complex, dimensionally accurate and integrated parts. Nonetheless, obtaining a thick composite reinforced by aramid fiber with high impact performance by such manufacturing method is still a challenge. In this context, this work addresses the effect of the thickness in the vacuum infusion processing of aramid/epoxy composites and its performance in applications that require impact solicitations (low and high speed) For this, composites with 5, 8, 13, 18, 23 and 28 layers of aramid were produced and characterized by ultrasonic C-scan, optical microscopy, density, constituent content, mechanical tests (flexion, short beam and quasi-static indentation) and low- and high-speed impact loads (drop-weight and ballistic). All composites presented good homogeneity in the matrix scattering along the reinforcement, with a fiber content of ≈ 60%, and high short beam resistance values (17.3 - 23.6 MPa). The performance under impact (low and high speed) was comparable to that of composites processed by compression or autoclave, the composites with 18 layers resisted to the 9 mm Luger FMJ projectile and the one with 28 layers resisted to the .357 Magnum FMJ projectile, being classified as level FB2 and FB3, respectively, according to the European standard EN 1522. In summary, vacuum infusion processing proved to be a suitable alternative to produce thick aramid/epoxy composites (up to 12 mm), replacing more expensive processing routes.

Em aplicações que requerem solicitações de impacto, compósitos de matriz polimérica reforçados com fibra de aramida se destacam, principalmente em relação aos metais, devido a propriedades como alta resistência e rigidez específicas, que dão origem a sistemas mais leves e de alta performance. Quando voltados para aplicações de impacto, principalmente a alta velocidade, tais compósitos são, em sua maioria, moldados por compressão ou autoclave, a partir de pré-impregnados. No entanto, tais combinações de processamentos e matéria-prima acarretam em estruturas de elevado custo, tornando a infusão a vácuo uma opção atrativa, além de permitir a obtenção de peças grandes e complexas, dimensionalmente acuradas e partes integradas. Porém, a obtenção de um compósito espesso reforçado por fibra de aramida com elevado desempenho ao impacto por tal método de fabricação ainda é um desafio. Neste contexto, este trabalho aborda o efeito da espessura no processamento por infusão a vácuo de compósitos aramida/epóxi e seu desempenho em aplicações que requerem solicitações de impacto (baixa e alta velocidade) Para isso, foram produzidos compósitos com 5, 8, 13, 18, 23 e 28 camadas de aramida e caracterizados por ultrassom C-scan, microscopia ótica, densidade, teor de constituintes, testes mecânicos (flexão, short beam e indentação quase-estática) e cargas de impacto de baixa e alta velocidade (drop-weight e balístico). Todos os compósitos apresentaram boa homogeneidade na distribuição da matriz ao longo do reforço, com um teor de fibra de ≈60%, e valores de resistência short beam elevados (17,3 - 23,6 MPa). A performance sob impacto (baixa e alta velocidade) foi comparável à de compósitos fabricados por compressão ou autoclave, tendo os compósitos a partir de 18 camadas resistido ao projétil 9 mm Luger FMJ e o de 28 camadas resistido ao projétil .357 Magnum FMJ, podendo ser classificados como nível FB2 e FB3, respectivamente, de acordo com a norma europeia EN 1522. Portanto, o processamento de infusão a vácuo mostrou ser uma alternativa adequada para produzir compósitos espessos de aramida/epóxi (até 12 mm), substituindo rotas de processamento mais caras. / In applications that require impact solicitations, polymer matrix composites reinforced with aramid fiber stand out, especially in relation to metals, due to properties such as high specific strength and stiffness, which give rise to lighter and high-performance systems. When used for impact applications, especially at high speed, such composites are mostly molded by compression or autoclaved, from prepregs. However, such combinations of processing and raw material lead to high cost structures, making vacuum infusion an attractive option, as well as allowing the production of large, complex, dimensionally accurate and integrated parts. Nonetheless, obtaining a thick composite reinforced by aramid fiber with high impact performance by such manufacturing method is still a challenge. In this context, this work addresses the effect of the thickness in the vacuum infusion processing of aramid/epoxy composites and its performance in applications that require impact solicitations (low and high speed) For this, composites with 5, 8, 13, 18, 23 and 28 layers of aramid were produced and characterized by ultrasonic C-scan, optical microscopy, density, constituent content, mechanical tests (flexion, short beam and quasi-static indentation) and low- and high-speed impact loads (drop-weight and ballistic). All composites presented good homogeneity in the matrix scattering along the reinforcement, with a fiber content of ≈ 60%, and high short beam resistance values (17.3 - 23.6 MPa). The performance under impact (low and high speed) was comparable to that of composites processed by compression or autoclave, the composites with 18 layers resisted to the 9 mm Luger FMJ projectile and the one with 28 layers resisted to the .357 Magnum FMJ projectile, being classified as level FB2 and FB3, respectively, according to the European standard EN 1522. In summary, vacuum infusion processing proved to be a suitable alternative to produce thick aramid/epoxy composites (up to 12 mm), replacing more expensive processing routes.

Em aplicações que requerem solicitações de impacto, compósitos de matriz polimérica reforçados com fibra de aramida se destacam, principalmente em relação aos metais, devido a propriedades como alta resistência e rigidez específicas, que dão origem a sistemas mais leves e de alta performance. Quando voltados para aplicações de impacto, principalmente a alta velocidade, tais compósitos são, em sua maioria, moldados por compressão ou autoclave, a partir de pré-impregnados. No entanto, tais combinações de processamentos e matéria-prima acarretam em estruturas de elevado custo, tornando a infusão a vácuo uma opção atrativa, além de permitir a obtenção de peças grandes e complexas, dimensionalmente acuradas e partes integradas. Porém, a obtenção de um compósito espesso reforçado por fibra de aramida com elevado desempenho ao impacto por tal método de fabricação ainda é um desafio. Neste contexto, este trabalho aborda o efeito da espessura no processamento por infusão a vácuo de compósitos aramida/epóxi e seu desempenho em aplicações que requerem solicitações de impacto (baixa e alta velocidade) Para isso, foram produzidos compósitos com 5, 8, 13, 18, 23 e 28 camadas de aramida e caracterizados por ultrassom C-scan, microscopia ótica, densidade, teor de constituintes, testes mecânicos (flexão, short beam e indentação quase-estática) e cargas de impacto de baixa e alta velocidade (drop-weight e balístico). Todos os compósitos apresentaram boa homogeneidade na distribuição da matriz ao longo do reforço, com um teor de fibra de ≈60%, e valores de resistência short beam elevados (17,3 - 23,6 MPa). A performance sob impacto (baixa e alta velocidade) foi comparável à de compósitos fabricados por compressão ou autoclave, tendo os compósitos a partir de 18 camadas resistido ao projétil 9 mm Luger FMJ e o de 28 camadas resistido ao projétil .357 Magnum FMJ, podendo ser classificados como nível FB2 e FB3, respectivamente, de acordo com a norma europeia EN 1522. Portanto, o processamento de infusão a vácuo mostrou ser uma alternativa adequada para produzir compósitos espessos de aramida/epóxi (até 12 mm), substituindo rotas de processamento mais caras. / In applications that require impact solicitations, polymer matrix composites reinforced with aramid fiber stand out, especially in relation to metals, due to properties such as high specific strength and stiffness, which give rise to lighter and high-performance systems. When used for impact applications, especially at high speed, such composites are mostly molded by compression or autoclaved, from prepregs. However, such combinations of processing and raw material lead to high cost structures, making vacuum infusion an attractive option, as well as allowing the production of large, complex, dimensionally accurate and integrated parts. Nonetheless, obtaining a thick composite reinforced by aramid fiber with high impact performance by such manufacturing method is still a challenge. In this context, this work addresses the effect of the thickness in the vacuum infusion processing of aramid/epoxy composites and its performance in applications that require impact solicitations (low and high speed) For this, composites with 5, 8, 13, 18, 23 and 28 layers of aramid were produced and characterized by ultrasonic C-scan, optical microscopy, density, constituent content, mechanical tests (flexion, short beam and quasi-static indentation) and low- and high-speed impact loads (drop-weight and ballistic). All composites presented good homogeneity in the matrix scattering along the reinforcement, with a fiber content of ≈ 60%, and high short beam resistance values (17.3 - 23.6 MPa). The performance under impact (low and high speed) was comparable to that of composites processed by compression or autoclave, the composites with 18 layers resisted to the 9 mm Luger FMJ projectile and the one with 28 layers resisted to the .357 Magnum FMJ projectile, being classified as level FB2 and FB3, respectively, according to the European standard EN 1522. In summary, vacuum infusion processing proved to be a suitable alternative to produce thick aramid/epoxy composites (up to 12 mm), replacing more expensive processing routes.

A three-dimensional finite element model is constructed to predict the failure of a hybrid and thick laminate containing bolted joints. The results of the simulation are compared with test results. The simulation comprises two main challenging steps. Firstly, for a realistic model, a 3D model is established with geometric nonlinearities and contact is takeninto account. The laminated composite model is constructed by 3D layered elements. The effect of different number of elements through the thickness is investigated. The failure prediction is the second part of the simulation study. Solutions with and without progressive failure approach are obtained and the effect of progressive failure analysis for an optimum simulation of failure is discussed. The most appropriate failure criteria to predict the failure of a thick composite structure is also investigated by considering various failure criteria. By comparing the test results with the ones found from the finite element analyses, the validity of the developed model and the chosen failure criteria are discussed.

Ce travail de thèse s'est déroulé dans le cadre du programme H2E (Horizon Hydrogène Énergie) piloté par Air Liquide et en partenariat industriel avec Composites Aquitaine. Le stockage d’hydrogène sous forme gazeuse impose que les réservoirs bobinés en composite carbone/époxy utilisés résistent à des pressions internes en service allant de 350 à 700bar.L’état de l’art montre que le procédé d’enroulement filamentaire et son application à des épaisseurs de matériaux composites importantes peuvent générer des variations, dans l’épaisseur, des contraintes résiduelles d’origine thermique, de la teneur en fibres et en porosités et de l’épaisseur des couches. Ces hétérogénéités peuvent alors être à l’origine de modifications des propriétés mécaniques du composite. Notre travail s’est donc appuyé sur la caractérisation physico-chimique à l’échelle des constituants (mesure de températures, nano-indentation, analyse d’images et microtomographie) ainsi que la caractérisation mécanique à l’échelle de la couche de référence mais également à l’échelle de la structure (essais plans spécifiques sur éprouvettes bobinés et essais hors-plan).Les hétérogénéités de la matière ainsi identifiées sur le réservoir ont été intégrées dans un modèle de calcul analytique permettant d'étudier leurs influences sur sa pression d'éclatement. La conception d'un essai de mise sous pression interne d'un anneau a par ailleurs permis de vérifier le comportement mécanique de la structure réelle. / This PhD work was conducted in the H2E (Horizon Hydrogen Energy) program coordinated by Air Liquide and with the industrial partnership of Composites Aquitaine. The hydrogen storage under gaseous form needs the filament-wound carbon/epoxy composite vessels used to resist to service pressures between 350 to 700bar.The influences of the process and of the thickness of the structure on its mechanical behaviour were determined by precise bibliographic work and were supposed to generate thermal residual stresses and also to be responsible of variations in the thickness and fibre content of the plies. These heterogeneities could modify the mechanical properties of the composite material. Our work focuses, first of all, on the physical chemistry characterization at the constituents scale (temperature measurement, nano-indentation, image analysis and microtomography) and then on the mechanical characterization of the reference ply and also of the structure (dedicated tests on filament-wound samples and out-of-plane tests).The material heterogeneities identified on the vessel were integrated in an analytical calculation model to study their influences on its burst pressure. The development of an internal pressure test allows us to verify the global mechanical behaviour of the real structure.

The application of static shape control was investigated in this thesis particularly for a composite plate configuration using piezoelectric actuators. A new electro-mechanically coupled mathematical model was developed for the analysis and is based on a third order displacement field coupled with a layerwise electric potential concept. This formulation, TODL, is then implemented into a finite element program. The mathematical model represents an improvement over existing formulations used to model intelligent structures using piezoelectric materials as actuators and sensors. The reason is TODL does not only account for the electro-mechanical coupling within the adaptive material, it also accounts for the full structural coupling in the entire structure due to the piezoelectric material being attached to the host structure. The other significant improvement of TODL is that it is applicable to structures which are relatively thick whereas existing models are based on thin beam / plate theories. Consequently, transverse shearing effects are automatically accounted for in TODL and unlike first order shear deformation theories, shear correction factors are not required. The second major section of this thesis uses the TODL formulation in static shape control. Shape control is defined here as the determination of shape control parameters, including actuation voltage and actuator orientation configuration, such that the structure that is activated using these parameters will conform as close as possible to the desired shape. Several shape control strategies and consequently algorithms were developed here. Initial investigations in shape control has revealed many interesting issues which have been used in later investigations to improve shape controllability and also led to the development of improved algorithms. For instance, the use of discrete actuator patches has led to greater shape controllability and the use of slopes and curvatures as additional control criteria have resulted in significant reduction in internal stresses. The significance of optimizing actuator orientation and its relation to piezoelectric anisotropy in improving shape controllability has also been presented. Thus the major facets of shape control has been brought together and the algorithms developed here represent a comprehensive strategy to perform static shape control.

The application of static shape control was investigated in this thesis particularly for a composite plate configuration using piezoelectric actuators. A new electro-mechanically coupled mathematical model was developed for the analysis and is based on a third order displacement field coupled with a layerwise electric potential concept. This formulation, TODL, is then implemented into a finite element program. The mathematical model represents an improvement over existing formulations used to model intelligent structures using piezoelectric materials as actuators and sensors. The reason is TODL does not only account for the electro-mechanical coupling within the adaptive material, it also accounts for the full structural coupling in the entire structure due to the piezoelectric material being attached to the host structure. The other significant improvement of TODL is that it is applicable to structures which are relatively thick whereas existing models are based on thin beam / plate theories. Consequently, transverse shearing effects are automatically accounted for in TODL and unlike first order shear deformation theories, shear correction factors are not required. The second major section of this thesis uses the TODL formulation in static shape control. Shape control is defined here as the determination of shape control parameters, including actuation voltage and actuator orientation configuration, such that the structure that is activated using these parameters will conform as close as possible to the desired shape. Several shape control strategies and consequently algorithms were developed here. Initial investigations in shape control has revealed many interesting issues which have been used in later investigations to improve shape controllability and also led to the development of improved algorithms. For instance, the use of discrete actuator patches has led to greater shape controllability and the use of slopes and curvatures as additional control criteria have resulted in significant reduction in internal stresses. The significance of optimizing actuator orientation and its relation to piezoelectric anisotropy in improving shape controllability has also been presented. Thus the major facets of shape control has been brought together and the algorithms developed here represent a comprehensive strategy to perform static shape control.