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Moisture ingress and thermal effects on carbon fibre reinforced plastic is a well understood phenomenon. For aircraft structures where safety is paramount this results in the use of worst case material properties, known as HOTAA/ET properties. In reality most structures are not fully saturated and are therefore penalised by using these worst case properties. This project attempts to fully understand the environmental effect on mechanical performance and accurately model a structures exposure to the environment, while still maintaining conservatism, to realise structural weight savings for aircraft. From the literature study it appears that this is the first attempt to link the mechanical property degradation brought about by environment, to classical laminate theory. By modelling individual ply property performance, based on each ply's level of saturation and linking it to a bespoke set of materials properties generated within the project, it is possible to accurately model the mechanical performance of a component. The model and modelling process derived within this project have been successfully validated by structural testing.

Moisture diffusion studies were performed using unidirectional (UD) tape and quasiisotropic (QI) woven 5-harness satin fabric, carbon fibre reinforced (CFR) epoxy composite materials. Firstly the moisture constants, (i.e. diffusion coefficient, D[x], and equilibrium moisture content, M[max]) were experimentally derived at 70°C and 85% relative humidity (%RH), for the two CFR materials. To investigate moisture absorption as a function of %RH test coupons were conditioned to differing equilibrium moisture levels viz., 70°C/60%RH, 70°C/75%RH, 70°C/85%RH, and 70°C/95%RH. Also oven dry (OD) and as-received (AR) tests were performed for baseline comparison. The effect of moisture absorption on the mechanical behaviour was investigated; lamina properties were studied by measuring tension, compression, shear (inter/intralaminar) strength and stiffness of the UD material. This comprehensive set of testing provided quantitative relationships between moisture content and mechanical properties. The quasi-isotropic lay-up was then utilised to investigate multi-directional laminate lay-ups using open hole tension and compression testing. The experimental data showed that the uptake of moisture in both the materials studied was described well by Fick's Second Law and the properties most affected by moisture ingress were matrix-dominated properties. More specifically, the transverse tensile strength, F[t][2] was most affected by the ingress of moisture, with a near 50% reduction in strength when conditioned to equilibrium moisture content at 70°C/95%RH. Such information is a necessary prerequisite if improved design procedures are going to be developed in the future. The initial phase of testing produced mechanical property/moisture relationships that were employed to predict the strength and stiffness of the material containing specific moisture gradients through-the-thickness (TTT). To be able to predict mechanical properties with different moisture distribution, firstly moisture distribution TTT of the material was modelled using an analytical solution to Fick's Second Law. Then moisture content was considered on a ply-by-ply basis TTT of the laminate; reductions were applied to each individual ply property dependent on the moisture content using the experimentally derived relationships, essentially applying environmental knock-down factors (KEKDF'S) to each individual ply. Classical Laminate Analysis (CLA) was then performed using the Max Stress failure criteria in order to predict the overall laminate failure. A second phase of mechanical testing was then performed to validate these predictions. The mechanical property predictions compared well to the experimental data showing similar reductions in strength for a given profile of moisture in the laminate. The predicted strengths also fell within the measured standard deviation of the experimental data in a significant proportion of the results.

Made available in DSpace on 2014-10-09T12:53:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:03Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Os materiais compósitos possibilitam a melhoria das propriedades mecânicas dos materiais associados a menores densidades favorecendo a proteção pessoal, de veículos e aeronaves militares. A poliaramida apresenta como vantagens, melhora nas propriedades mecânicas e térmicas do compósito, elevando o grau de dureza e impacto em desempenho balístico. Porém, as fibras de aramidas apresentam uma superfície química inerte e lisa que dificulta a interação com as resinas termorrígidas, criando consequentemente uma fraca adesão interfacial entre as fibras e a matriz. Assim, o objetivo deste trabalho é o tratamento superficial da fibra de aramida, para melhorar a reatividade da superfície das fibras, e a adesão interfacial entre a fibra e a matriz. Compósitos de aramida e resina éster-vinílica foram preparados por moldagem por compressão, e o tratamento superficial das fibras foi realizado com a ligação C-F e constatado a presença de ~ 2,5% de flúor (em massa) (dado qualitativo). Como resultados, os compósitos contendo fibras tratadas apresentaram menor teor de vazios (0,33 ± 0,36%) em relação aos compósitos de fibras não tratadas (4,67 ± 1,14%). Para os compósitos de fibras tratadas, também foram obtidos resultados inferiores de resistência à tração, resistência ao impacto, fator de amortecimento e fator de adesão, e resultados superiores para módulo de elasticidade, temperatura de transição vítrea, módulo de armazenamento e módulo de perda. Para o teste de Barra Hopkinson, foi observado que os compósitos de aramida tratada tornaram-se mais frágeis à medida que a taxa de deformação foi aumentada, diminuindo a absorção de energia com o aumento da deformação. Concluiu-se que o compósito de fibras tratadas apresentou maior adesão entre fibras e matriz, resultando em menor teor de vazios, maior rigidez, dissipação de energia, menor movimentação nos segmentos de cadeia e maior temperatura de transição vítrea. Porém, o tratamento das fibras tornou o compósito mais frágil, resultando na diminuição das propriedades de resistência ao impacto balístico em relação ao compósitos de fibras não tratadas. / Submitted by Paula Leal (pffleal@ucs.br) on 2017-12-12T13:10:21Z No. of bitstreams: 1 Dissertacao Marilu Wirti.pdf: 4204467 bytes, checksum: 4c10afe3fdb21356992b6ae8bab0ea29 (MD5) / Made available in DSpace on 2017-12-12T13:10:21Z (GMT). No. of bitstreams: 1 Dissertacao Marilu Wirti.pdf: 4204467 bytes, checksum: 4c10afe3fdb21356992b6ae8bab0ea29 (MD5) Previous issue date: 2017 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES. / The use of composite materials enables the improvement of the materials mechanical properties associated with lower densities favoring protection of personnel, military vehicles and aircrafts. The advantages of polyaramid are the improvement of the mechanical and physical properties, and a high degree of hardness and ballistic performance. However, the aramid fibers have an inert and smooth chemical surface, which hinders interaction with the thermosetting resins, resulting in a weak interfacial adhesion between fibers and matrix. Thus, the aim of this study is to perform surface treatment of aramid in order to improve surface reactivity of the fibers to improve interfacial adhesion between fibers and matrix. Aramid Kevlar® and vinyl-ester composites were molded by compression molding, and the fibers surface treatment occurred by the deposition of ~ 2,5% of fluorine (in mass) (qualitative data). The treated fibers composite showed lower voids content (0,33 ± 0,36%) in relation to the untreated fibers composite (4,67 ± 1,14%). Furthermore, inferior results of tensile strength, impact strength, damping factor and adhesion factor were obtained for the treated fibers composite, along with superior results for modulus of elasticity, glass transition temperature, storage modulus and loss modulus. For the Hopkinson Bar test, it was observed that the aramid composites became weaker as the deformation rate was increased, which decreased energy absorption with the increased deformation. It was concluded that the treated fiber composite showed a higher adhesion between fibers and matrix, resulting in lower voids content, higher stiffness, energy dissipation, lower chain segment movement and higher glass transition temperature. However, the treatment of the fibers made the composite more fragile, resulting in the decrease of the properties of resistance to ballistic impact in relation to the composites of untreated fibers.

Os materiais compósitos possibilitam a melhoria das propriedades mecânicas dos materiais associados a menores densidades favorecendo a proteção pessoal, de veículos e aeronaves militares. A poliaramida apresenta como vantagens, melhora nas propriedades mecânicas e térmicas do compósito, elevando o grau de dureza e impacto em desempenho balístico. Porém, as fibras de aramidas apresentam uma superfície química inerte e lisa que dificulta a interação com as resinas termorrígidas, criando consequentemente uma fraca adesão interfacial entre as fibras e a matriz. Assim, o objetivo deste trabalho é o tratamento superficial da fibra de aramida, para melhorar a reatividade da superfície das fibras, e a adesão interfacial entre a fibra e a matriz. Compósitos de aramida e resina éster-vinílica foram preparados por moldagem por compressão, e o tratamento superficial das fibras foi realizado com a ligação C-F e constatado a presença de ~ 2,5% de flúor (em massa) (dado qualitativo). Como resultados, os compósitos contendo fibras tratadas apresentaram menor teor de vazios (0,33 ± 0,36%) em relação aos compósitos de fibras não tratadas (4,67 ± 1,14%). Para os compósitos de fibras tratadas, também foram obtidos resultados inferiores de resistência à tração, resistência ao impacto, fator de amortecimento e fator de adesão, e resultados superiores para módulo de elasticidade, temperatura de transição vítrea, módulo de armazenamento e módulo de perda. Para o teste de Barra Hopkinson, foi observado que os compósitos de aramida tratada tornaram-se mais frágeis à medida que a taxa de deformação foi aumentada, diminuindo a absorção de energia com o aumento da deformação. Concluiu-se que o compósito de fibras tratadas apresentou maior adesão entre fibras e matriz, resultando em menor teor de vazios, maior rigidez, dissipação de energia, menor movimentação nos segmentos de cadeia e maior temperatura de transição vítrea. Porém, o tratamento das fibras tornou o compósito mais frágil, resultando na diminuição das propriedades de resistência ao impacto balístico em relação ao compósitos de fibras não tratadas. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES. / The use of composite materials enables the improvement of the materials mechanical properties associated with lower densities favoring protection of personnel, military vehicles and aircrafts. The advantages of polyaramid are the improvement of the mechanical and physical properties, and a high degree of hardness and ballistic performance. However, the aramid fibers have an inert and smooth chemical surface, which hinders interaction with the thermosetting resins, resulting in a weak interfacial adhesion between fibers and matrix. Thus, the aim of this study is to perform surface treatment of aramid in order to improve surface reactivity of the fibers to improve interfacial adhesion between fibers and matrix. Aramid Kevlar® and vinyl-ester composites were molded by compression molding, and the fibers surface treatment occurred by the deposition of ~ 2,5% of fluorine (in mass) (qualitative data). The treated fibers composite showed lower voids content (0,33 ± 0,36%) in relation to the untreated fibers composite (4,67 ± 1,14%). Furthermore, inferior results of tensile strength, impact strength, damping factor and adhesion factor were obtained for the treated fibers composite, along with superior results for modulus of elasticity, glass transition temperature, storage modulus and loss modulus. For the Hopkinson Bar test, it was observed that the aramid composites became weaker as the deformation rate was increased, which decreased energy absorption with the increased deformation. It was concluded that the treated fiber composite showed a higher adhesion between fibers and matrix, resulting in lower voids content, higher stiffness, energy dissipation, lower chain segment movement and higher glass transition temperature. However, the treatment of the fibers made the composite more fragile, resulting in the decrease of the properties of resistance to ballistic impact in relation to the composites of untreated fibers.

Made available in DSpace on 2014-10-09T12:53:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:03Z (GMT). No. of bitstreams: 0 / Este trabalho tem por objetivo obter propriedades mecânicas de compósitos angle-ply fabricados pelo processo de enrolamento filamentar, na forma de placas com diversas orientações do reforço. As placas foram fabricadas com fibra de carbono e matriz epoxídica e fibra de vidro e matriz epoxídica. Os exemplares para ensaio foram obtidos nas direções de 0°, ±10°, ±20°, ±30°, ±60°, ±70°, ±80° e 90° em relação á direção do equipamento de ensaio, atribuída como sendo 0°. Resultados mostraram que para corpos-de-prova de fibra de cartaono bobinados na direção ±10° a tensão máxima média obtida foi de 855 MPa e o módulo de elasticidade médio de 136 GPa, enquanto que para corpos-de-prova de fibra de carbono bobinados na direção de ±80°, a tensão máxima média foi de 68 MPa e módulo de elasticidade médio de 10 GPa. Os resultados obtidos indicaram que as propriedades mecânicas diminuem acentuadamente a partir da direção de ±10°. Também foram obtidas as frações volumétricas, dureza Barcol e análise térmica das placas fabricadas. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:40:45Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:22Z (GMT). No. of bitstreams: 1 02756.pdf: 6061739 bytes, checksum: 638186919450401c574295b83b6bf8d1 (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP