Academic literature on the topic 'Hybrid Composite Plate'

Cette thèse porte sur le développement d'un traducteur ultrasonore multi-élément capacitif à couplage air (MEACUT) et son utilisation dans le domaine du contrôle non destructif (CND) de matériaux. Un modèle est employé pour simuler numériquement ce traducteur, et pour optimiser sa conception. Un prototype est ensuite fabriqué, puis caractérisé expérimentalement pour quantifier ses performances. Son originalité réside dans le fait qu'il possède une large bande passante en fréquence, tout en offrant la possibilité d'une focalisation variable. Ce prototype est alors employé pour la détection d'un endommagement causé par impact, dans une plaque composite. Il est clairement constaté que la résolution spatiale du procédé d'inspection employé (C-scan) est fortement améliorée grâce aux performances techniques du MEACUT. Enfin, un modèle hybride 3D est développé pour simuler, rapidement et intégralement, ce procédé de CND. Le très bon accord obtenu entre prédictions numériques et mesures expérimentales laisse présager que cet outil de simulation pourra servir à mettre au point d'autres expérimentations de CND, qui pourront à leur tour exploiter les performances du MEACUT<br>This thesis focuses on the development of a Multi-Element Air-coupled Capacitive Ultrasonic Transducer (MEACUT) and its use in the field of non-destructive testing (NDT) of materials. A numerical model is used to simulate the translator, and to optimize its design. A prototype is then built and experimentally characterized to quantify its performance. Its originality lies in the fact that it has a broad frequency bandwidth while offering the possibility of a dynamic focusing. This prototype is then used for the detection of damage caused by impact, in a composite plate. It is clearly found that the spatial resolution of the inspection process employed (C-scan) is greatly improved thanks to the technical performance MEACUT. Finally, a 3D hybrid model is developed to simulate quickly and fully, the process of NDT. The good agreement obtained between numerical predictions and experimental measurements suggests that this simulation tool can be used to develop other NDT experiments, which may in turn exploit the performance of MEACUT

Delamination is a frequent cause of failure in laminated structures, particularly under compressive loads. The presence of delaminations in composite laminates reduces their overall stiffness. In addition, delaminations tend to grow rapidly under postbuckling loads, causing further reductions in the structural strength and leading ultimately to a sudden structural failure. Recently, many studies have been carried out to investigate the effects of delaminations on the buckling and vibration behaviour of composite structures. Finite element analysis is often used to perform these due to its ability to model complex geometries, loading and boundary conditions, but this comes at a high computational cost. The exact strip method provides an efficient alternative approach using an exact dynamic stiffness matrix based on a continuous distribution of stiffness and mass over the structure, so avoiding the discretization to nodal points that is implicit in finite element analysis. However due to its prismatic requirements, the exact strip method can model damaged plates directly only if the damaged region extends along the whole length of the plate. This thesis introduces a novel combination of exact strip and finite element analysis which can be used to model more complex cases of damaged plates. Comparisons with pure finite element analysis and a previous technique based on the exact strip method demonstrate the capability and efficiency of this hybrid method for a range of isotropic and composite plates.

Das Forschungsvorhaben liefert einen Beitrag zum Schweißen von Gleich- und Mischmaterialverbindungen aus Naturfaserverstärkten Kunststoffen (NFK) sowie deren Verarbeitung im Compoundieren und Spritzguss. Es wurde holzfasergefülltes (WPC) und flachsfasergefülltes (FFC) Polypropylen (PP) mit unterschiedlichen Füllgraden verwendet. Der Einsatz synthetisch-organsicher Fasern (PET-Fasern) im Compound zielte darauf ab, besonders die Schlagzähigkeit zu verbessern. Im Bereich des Urformens wurden Aussagen zur Verarbeitbarkeit, zu rezepturabhängigen Kurz- und Langzeiteigenschaften sowie Aussagen zur Dauergebrauchsfähigkeit erarbeitet. Die Anwendbarkeit der Fügeverfahren Heizelement- (HE-Schweißen) und Vibrationsschweißen (VIB-Schweißen) konnte für Gleich- und Mischmaterialverbindungen sowohl ohne als auch mit angepasster Energieeinbringung nachgewiesen werden. In diesem Zusammenhang können Aussagen zur Rezepturabhängigkeit, Verfahrensführung, Parameterauswahl, Prüfkriterien sowie den technischen Grenzen der Schweißverbindung unter kurzzeitmechanischer Beanspruchung getroffen werden. Weiterhin wird ein Beitrag zur Dauergebrauchsfähigkeit unter UV-Globalbewitterung und thermischer Alterung sowie zu langzeitmechanischen Eigenschaften von NFK-Schweißverbindungen geliefert.

Tese de Doutoramento em Engenharia Civil<br>This research work deals with development of a novel retrofitting element for RC structures designated as “Hybrid Composite Plate (HCP)”. This prefabricated element is composed of a thin strain hardening cementitious composite (SHCC) plate reinforced with either near surface mounted CFRP (NSM-CFRP) laminates, designated as HCP(L), or externally bonded CFRP (EB-CFRP) sheets, designated as HCP(S). From the materialstructural point of view, this system benefits from the high ductility of SHCC and the high tensile strength of CFRP in retrofitting of RC structures. HCP is essentially tailored to be significantly free of the shortcomings identified in the most advanced available retrofitting techniques, such as textile reinforced mortar (TRM) and conventional FRP systems. Furthermore, it is possible to attach this proposed system to the RC members by means of either adhesive, chemical anchors or a combination thereof. The investigation carried out is mainly dedicated to the development of HCP and assessment of its structural efficiency for upgrading/repairing RC members with a variety of retrofitting demands. In this framework, series of experimental tests are executed to assess HCP retrofitting efficiency for upgrading shear, flexural and energy dissipation capacity of RC members. Results of these experimental tests confirmed HCP’s high potential for retrofitting RC structures. An analytical approach is presented to estimate the ultimate flexural capacity of the beams with an HCP attached to their soffit, which is further complemented with a numerical strategy to predict the load-deflection response of such retrofitted beams. The proposed analytical and numerical approaches accurately predict the flexural capacity and load-deflection response, of flexurally strengthened beams using HCP. Finally, adopting a combination of experimental tests and finite element modelling, recommendations for an optimized HCP(L) and its connection with concrete are provided. The local bond stress-slip models at the interface of CFRP-SHCC and interface of HCP(L)- concrete are determined. Based on results obtained, equations correlating the pull force capacity of the HCP(L) to the CFRP-SHCC bond length for CFRP laminates with two different axial stiffness are derived.<br>Esta tese apresenta a investigação realizada para o desenvolvimento de um novo elemento visando o reforço de estruturas de betão armado (BA) designado por Hybrid Composite Plate (HCP). Este elemento consiste num painel pré-fabricado composto por uma fina camada de material de matriz cimentícia apresentando comportamento de endurecimento em tração ( SHCC) reforçada laminados de matriz polimérica reforçada com fibras de carbono (CFRP) inseridos à superfície (Near Surface Mounted), designado por HCP(L), ou com manta de CFRP aplicada segundo a técnica de colagem exterior (externally bonded, EB-CFRP), designadas por HCP(S). Do ponto de vista estrutural, este sistema beneficia da alta ductilidade do SHCC e da elevada resistência à tração do CFRP no reforço de estruturas de BA. O HCP afigura-se como uma solução apropriada essencialmente por não apresentar as deficiências identificadas nas técnicas mais avançadas de reforço estrutural atualmente disponíveis, tais como TRM (Textile Reinforced Mortar) e sistemas FRP (Fiber Reinforced Polymer). O sistema proposto permite uma ligação aos elementos de BA através de resina epóxi, ancoragem química ou uma combinação entre estes. A investigação realizada foi dedicada ao desenvolvimento do HCP e avaliação da sua eficiência estrutural para melhorar ou reparar elementos de BA para uma variedade de exigências de reforço. Com este objetivo, uma série de ensaios foram realizados para avaliar a eficiência do reforço do HCP ao corte, flexão e capacidade de dissipação de energia de elementos de BA. Uma formulação analítica foi desenvolvida para estimar a resistência à flexão de vigas de BA reforçadas com HCP ligado à sua face inferior. Esta abordagem foi completada com um modelo numérico para prever a resposta carga-deformação destas vigas. A formulação analítica e o modelo numérica propostos previram com precisão, respetivamente, a capacidade de flexão e a resposta carga-deformação de vigas reforçadas com HCP. Finalmente, com base na combinação de resultados de ensaios experimentais e modelos de elementos finitos, são fornecidas recomendações para a otimização do HCP(L) e a sua ligação ao betão. Para a caracterização das interfaces CFRP-SHCC betão-HCP(L) foram determinadas leis tensão versus deslizamento. Com base nos resultados obtidos, apresentamse as equações que relacionam a capacidade de carga à tração do HCP(L) com o comprimento de ligação do CFRP-SHCC composto por camadas de CFRP dotadas de rigidez distinta.<br>Fundação para a Ciência e a Tecnologia (FCT) SFRH/BD/65663/2009.<br>Fundação para a Ciência e a Tecnologia (FCT) PTDC/ECM/114511/2009

博士<br>中原大學<br>化學研究所<br>97<br>Abstract This dissertation divided into two parts. The preparation of polyimide nanocomposite hollow fiber includes two kinds of additive, plate clay or spherical silica, is the first part. The preparation of polyvinyl alcohol and polyacrylonitrile plate nanocomposite membrane contain silver nanoparticle is the second part. Silver nitrite converts into silver nanoparticle by using in-situ photochemical reduction and direct chemical reduction. In this research, the structure and performance of a series of organic-inorganic hybrid materials will be investigated. In the first part, casting solution contains polyimide, NMP, and nanoparticle (flat clay or spherical silica) was used to prepare asymmetric polyimide nanocomposite hollow fiber membrane. The effect of additives on the morphology, membrane formation mechanisum, mechanical properties, and pervaporation performance of the asymmetric polyimide nanocomposite hollow fiber membrane was investigated. The results revealed that the addition of nano-filler in the spinning solution and increasing the filler amount can promote the formation of macrovoids in nonocomposite hollow fiber membrane. Otherwise, the exchange rate between the solvent and nonsolvent during the membrane formation process increases resulting in an asymmetric PI hollow fiber membrane with a wider wall thickness. The material composition will affect the thermal stability, mechanical strength and the separation performance of vapor permeation of aqueous ethanol solution. The elongation at break, strength at break, and work of rupture increase with nano-filler is a unique phenomenum different than general polymer. Moreover, water contact angle increasing presents self-clearing performance. The second part, a series of nano-scale silver polymer composite films were prepared from polyvinyl alcohol silver ions chelate aqueous solution. Silver ions transfer to silver by in-situ photochemical reduction using UV-irradiation. Other way, polyacrylonitrile silver ions chelate in N,N-dimethylformamide (DMF) will change into silver by direct chemical reduction. The reduction of silver ion in nano-composite films were confirmed by UV/vis optical absorption, Fourier-transformation infrared spectroscopy (FTIR), SEM-mapping, and X-ray diffraction (XRD). The surface morphology of nano-scale silver polymer composite films were investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The amount of nano-scale silver in polymer composite films will affect the thermal stability, contact angle and antibacterial activities. In this study, we found that the structural morphology of PVA-Ag+ chelate films change vastly due to the changes in loading amount. However, silver nano-particles produced by in situ reduction UV-irradiation shown particles on the surface of PVA films. The surface morphology of PVA-Ag0 and PAN-Ag0 membrane is similar. PVA-Ag+ is effective prohibite the growth of Escherichia coli and Staphylococus aureus in 0.5 wt% silver nitrite loading. PVA-Ag0 and PAN-Ag0 films are effective in prohibiting the growth of Escherichia col. Furthermore, we demonstrated that the hybrid composite films have good hydrophobic characterization owing to the presence of nano-scale silver. From DSC experimental results, the glass transition (Tg) and melting temperatures decreases with increasing AgNO3 loading owing to destroy of the crystalline.

Dissertação de Mestrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.<br>The traditional carbon fibre-reinforced composites offer excellent mechanical properties while having a low density, which makes them an ideal solution for the applications where weight is a major concern. The self-reinforced composites (SRC’s) consist of polymer fibres reinforcing a matrix made from the same material. In fact, it is by partially melting the fibres that the matrix is created. This type of composites provide a high toughness but lack the high stiffness and strength needed in structural applications. Hybrid composites are a combination of at least two types of fibres in a matrix. By hybridizing self-reinforced polypropylene (SRPP) with unidirectional (UD) carbon fibre reinforced polypropylene (CFRPP), it is expected to combine properties of both composite types. The goal is to have a stiff and strong composite while maintaining a high toughness. This thesis aims to understand how the material properties of a hybrid composite influence the flexural properties in a corrugated plate. The flexural properties of hybrid composites have been studied but always in flat surfaces. Also, the low compressive properties of polymer fibres make it difficult to capture the flexural properties. By using this type of surface, the flexural properties should not be as highly dependent on the position of the carbon fibre (CF) laminae in relation to the neutral plane as they are for flat laminates. Experimental work has been performed to understand the dependence of the flexural properties of hybrid composite materials on the carbon fibre volume fraction (Vf) and position. The experimental work was supported by a numerical modelling study. This study established preliminary knowledge needed for further developments of the model. In combination with the experimental work, the limitations of the current model are pointed out. The achievement of a more advanced model in the future, that can predict the behaviour of these hybrid composite materials when subjected to bending, is possible. The main conclusions of this work were that the stiffness of a corrugated hybrid composite plate is not influenced by the position of the UD CFRPP layers. This property only changes with the CF Vf. The maximum flexural load and displacement at this point are also influenced by the CF content and by the thickness of the UD CFRPP layers. The other work we ever did together. Without the experience of working with him, there would be a lot of things I would not have learned. To Carlos Lavoura and José Canhola, my mentors in my rowing experience. They were the ones who guided me throughout ten years of rowing, making me a better athlete and a better person. For giving me the will to never give up on my goals and dreams, thank you.<br>Os tradicionais materiais compósitos reforçados com fibras de carbono oferecem excelentes propriedades mecânicas enquanto mantêm uma baixa densidade, o que faz deles uma solução ideal para aplicações nas quais o peso é um fator a considerar. Os materiais compósitos auto-reforçados consistem em fibras poliméricas que reforçam uma matriz do mesmo material. De fato, é ao fundir parcialmente as fibras que se obtém a matriz. Este tipo de materiais compósitos proporciona uma elevada tenacidade mas não tem a alta rigidez e resistência mecânica necessária em aplicações estruturais. Os materiais compósitos híbridos resultam da combinação de dois tipos de fibras numa matriz. Ao hibridizar polipropileno auto-reforçado com polipropileno reforçado com fibras de carbono unidirecionais, é esperada a combinação das propriedades dos dois tipos de compósitos. O objetivo é que se tenha um compósito rígido e resistente enquanto se mantém uma alta tenacidade. Esta dissertação tem como objetivo a compreensão de como as propriedades materiais de um compósito híbrido influenciam as propriedades à flexão numa placa enrugada. As propriedades à flexão de compósitos híbridos já foram estudadas, mas sempre em superfícies planas. Além disso, as fracas propriedades compressivas das fibras poliméricas tornam difícil capturar as propriedades à flexão destas. Ao usar este tipo de superfície, as propriedades à flexão não deverão ser tão dependentes da posição das camadas de fibras de carbono em relação ao plano neutro como se verifica para laminados. O trabalho experimental foi realizado para entender a dependência das propriedades à flexão de um material compósito híbrido com a variação da fração volúmica e posição das fibras de carbono. O trabalho experimental foi suportado por um estudo de modelação numérica. Este estudo estabeleceu conhecimentos preliminares necessários para desenvolvimentos futuros do modelo. Em combinação com o trabalho experimental, as limitações do modelo atual são enunciadas. O desenvolvimento de um modelo mais avançado no futuro, que possa prever o comportamento destes materiais compósitos híbridos quando sujeitos a flexão, é possível. As principais conclusões deste trabalho são que a rigidez dos compósitos híbridos em placas enrugadas não é influenciada pela posição das camadas de fibras de carbono. Esta propriedade apenas varia com a fração volúmica de fibras de carbono. A carga de flexão máxima e deslocamento também são influenciados pelo conteúdo de fibras de carbono e pela espessura das camadas de fibras de carbono unidirecionais. O trabalho de modelação confirmou o comportamento da rigidez mas o modelo não é capaz de prever as outras propriedades. Ainda é possivel fazer um grande desenvolvimento do modelo.

碩士<br>國立臺北科技大學<br>機電整合研究所<br>99<br>The structural components of composite materials are often subjected to elevated temperatures during their service life. In such circumstances, high thermally induced compressive stresses will be developed in the constrained composite plates and consequently will lead to buckling; and thus significantly degrade their performance. So, thermal buckling and stability characteristics are one of the major design criteria for composite laminated plates for their optimal usage. In order to fully exploit their strength, an accurate prediction of their buckling load carrying capacity is essential. In the present work, the Hamilton’s energy principle is used to governing partial differential equations of hybrid composite plate in a general state of non-uniform initial stresses includes thermal effects are formulated from Mindlin plate theory. The Galerkin method is used to reduce the governing partial differential equations to ordinary differential equations. Thermal buckling is presented for hybrid composite plates under thermal loading and arbitrary initial stresses. Two types of thermal loadings, namely; uniform temperature rise and linear temperature rise are considered. The critical buckling temperatures, vibration frequency and buckling load are obtained from the linear eigenvalue problems. The effects of various parameters for hybrid composite plates will be studied. The analysis results show that the thickness ratio and initial stress has a great impact to the critical temperature parameter of the hybrid composite plates. The ratio of has an apparent influence on natural frequency and buckling load. And buckling load is also affected by thickness ratio.