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1
Erdem, Melek Esra. "Failure Analysis Of Thick Composites." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615605/index.pdf.
Full textAbstract:
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.
2
Carrasco-Munoz, Y. Guerra Jacinto. "Design exploration methodology for ultra thick laminated composites." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/8289.
Full textAbstract:
Existing test and analytical methods (theoretical and numerical) are normally restricted to thin laminate components, which cannot accurately represent the 3D stress state behaviour of the so called Ultra Thick Laminates (UTL) structures. Thus, it is necessary to expand the scope of application of the current numerical methods to accurately predict the out-of-plane delamination failure associated with these types of structures (mainly due to the transverse shear stresses and interlaminar stresses).
The overall objective of this work is to address the following research objectives:
• To assess the functionality, advantages and limitations of different solid element formulations, including layered solid elements that are available in commercial Finite Element codes, applied to the mechanical response prediction of UTL composite components (thicknesses up to 30 mm are considered).
• To perform a design exploration and optimisation of constant thickness UTL composite component in terms of the orientation of a varying and repeatable stacking sequence of an eight ply Non-Crimped Fabric, in order to assess the design implications on performance.
In order to achieve the above stated objectives a standard, flexible and expandable FE based design exploration methodology (at a ply level) for UTL composite components is proposed, which considers a commercial FE tool (ANSYS), and a data management system and optimisation tool (ISIGHT), through the use of layered solid elements (SOLID186 and SOLID191, 20-node layered solid elements). Application of manufacturing design rules (for reducing the number of feasible stacking sequences to be evaluated) is also considered, in order to reduce the computational cost of such a study, as well as to present a practical solution from the manufacturing point of view.
Initially, in-plane and out-of-plane capabilities of various layered element formulations and modelling strategies where evaluated for thin and thick laminate applications against known analytic solutions (CLT, etc), in order to understand the key parameters and the accuracy limitations of each formulation. This led to practical recommendations for pre and post processing of thick laminate FE models, such as for the number of layered solid elements required as a function of the thickness of the UTL component to effectively predict the magnitude and variation in transverse shear stress across the thickness.
The application of this research was demonstrated on the design exploration and performance optimisation of a UTL composite specimen (with constant thickness) under a 3-point bending test (linear static analysis), for which experimental results were available. The individual ply orientations are the design variables considered, and the performance was assessed through the vertical displacement of the component and the maximum transverse shear stress value.
This exploration of the design space did identify other possible configurations that may have a better performance than the baseline (Biax), considering only the maximum transverse shear stress values as directly responsible for the delamination failure. However, these improved designs may present a higher number of plies failed or a higher failure index (Tsai-Wu failure criteria). Further experimental studies are required to further explore the design space, but this work represents the starting point and possible approaches for development of robustness and weight optimisation of UTL composites are proposed.
3
Small, Peter D. (Peter David). "Ultrasonic wave propagation in thick, layered composites containing degraded interfaces." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33585.
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Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references.
The ultrasonic wave propagation of thick, layered composites containing degraded bonds is investigated. A theoretical one-dimensional model of three attenuative viscoelastic layers containing two imperfect interfaces is introduced. Elastic material properties and measured 'values of ultrasonic phase velocity and attenuation are used to represent E-glass and vinyl ester resin fiber-reinforced plastic (FRP) laminate, syntactic foam, and resin putty materials in the model. The ultrasonic phase velocity in all three materials is shown to be essentially constant in the range of 1.0 to 5.0 megahertz (MHz). The attenuation in all three materials is constant or slightly increasing in the range 1.0 to 3.0 MHz. Numerical simulation of the model via the mass- spring-dashpot lattice model reveals the importance of the input signal shape, wave speed, and layer thickness on obtaining non-overlapping, distinct return signals in pulse-echo ultrasonic nondestructive evaluation. The effect of the interface contact quality on the reflection and transmission coefficients of degraded interfaces is observed in both the simulated and theoretical results.
by Peter D. Small.
S.M.
Nav.E.
4
Breen, Charles Edward Pitt. "Impact damage in thick carbon fibre reinforced plastic laminated composites." Thesis, University of Bristol, 2007. http://hdl.handle.net/1983/426d2091-43e8-4d4a-ae7a-b0ded8dea0e2.
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5
Saboktakin, Rizi Abbasali. "Integrity assessment of preforms and thick textile reinforced composites for aerospace applications." Mémoire, École de technologie supérieure, 2013. http://espace.etsmtl.ca/1267/1/SABOKTAKIN_RIZI_Abbasali.pdf.
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Les composites à renforts textiles 3D, contenant des fibres dans le plan et dans la direction de l'épaisseur, offrent certains avantages par rapport aux composites à renforts textiles 2D. Ces avantages comprennent une grande résistance à la délamination et une meilleure tolérance à l'endommagement. La plupart des textiles 3D ont été développés pour des pièces destinées à l'industrie aérospatiale telles que des panneaux d'ailes, des trains d'atterrissage, des tuyères de fusée et la capsule Orion. Cette thèse vise à évaluer l'intégrité structurelle des textiles composites en combinant des techniques d'inspection destructives et non destructives. Dans la première partie de la thèse, des techniques non destructives, y compris les rayons-X (CT) et des techniques basées sur les ultrasons (UT), ont été développées pour détecter les défauts importants comme la rupture des fibres et le désalignement des tissus. La deuxième partie porte sur l'étude de l'influence des défauts de fabrication qui se produisent dans les processus d’ touffetage sur les performances mécaniques.
Des résultats expérimentaux ont montré que tomographie rayons-X facilite la détection et la caractérisation de ces deux défauts de fabrication, ainsi que de l'architecture des tissus. En outre, la modélisation méso-échelle d'un composite tissé en 2D a été réalisée avec succès pour l'analyse de l'influence du défaut de rupture des fibres et de l'architecture des fibres de propagation de l'onde. Les résultats expérimentaux montrent que le touffetage des préforme limite ou élimine le mouvement de leurs fils. En plus, la touffetage par des fils de haute résistance à la traction peut améliorer celle de leurs préforme 3D. La touffe d’un préforme fait augmenter la force de compactage des fibres. À cet effet, cette méthode est nécessaire pour augmenter le volume des fibres de plus de 50 % en comparaison d'un préforme non touffeté. La résistance à la déformation d'une préforme est influencée par l’opération de touffetage. En effet, une préforme touffetée est plus résistance à la déformation qu’une préforme non touffetée. La variation de la géométrie de la préforme a été mesurée par balayage laser. En outre, la capacité CT a été étudiée en tant que moyen pour reconnaître les formes et les emplacements des vides dans les matériaux composites. La résistance à la traction des composites avec un touffetage transversale a eu moins de réduction de que celle avec touffetage longitudinal. Les tests de fatigue à haute vitesse de déformation montrent que les composites touffetés ont une durée de vie inférieure à celle des composite non touffetés. L’opération de touffetage permet d'améliorer les propriétés mécaniques des panneaux sandwichs à noyau en nid d'abeilles sollicités en compression locale et en flexion trois points. Les dommages sont souvent initiés dans les régions riches en résine qui entourent le renfort de touffetage. L'acceptation primaire de l’utilisation des composites touffetés 3D dans les structures aérospatiales est très dépendantes de l'exactitude et de la fiabilité des données expérimentales pour identifier le degré auquel les renforts améliorent ou dégradent les propriétés mécaniques. Dans cette thèse, la corrélation entre les préformes touffues, les propriétés des composites et leurs modifications dues au touffetage sont traités pour une configuration spécifique. Les données expérimentales sont présentées à la fois sur un taux faible et à haut débit statique et des forces de fatigue à différents niveaux de contrainte. L'examen microstructural est effectué en utilisant la microscopie à haute résolution et les techniques de CT. Les résultats de cette thèse contribuent à l'enquête sur la tolérance d'intégrité et de dommage dans les matériaux composites tuftés 3D en vue d'une certification pour l'utilisation dans les futurs avions de transport. Cependant, la certification des composites tuftés pour les applications aérospatiales est toujours problématique en raison de l'absence de techniques d'évaluation non destructive fiables pour leur inspection et les facteurs de fabrication peuvent influencer considérablement leur performance, il s'agit d'un problème important auquel on doit s’attaquer dans le domaine de composite pour l’aérospatial.
6
Gorris, Thibault. "Application de la méthode Thick Level Set à l'étude des composites stratifiés." Ecole Centrale de Nantes, 2012. http://www.theses.fr/2012ECDN0050.
Full textAbstract:
Cette étude considère l’endommagement des composites stratifiés par une méthode proposant la propagation d’un front de levelset épais (TLS : Thick LevelSet). Un modèle élements finis est généralisé pour étudier l’ensemble des dommages dans un composite : fissuration transverse dans la couche 90, délaminage en pointe de fissure et délaminage entre les deux couches. La génération de nouvelles fissures est contrôlée à l’aide du taux de restitution d’énergie locale Y. L’étude porte sur l’espacement critique entre plusieurs fissures au sein de stratifié verre/époxy, carbone/époxy. Le travail de thèse étudié dans ce manuscrit propose donc d’appliquer et d’améliorer une nouvelle méthode de modélisation de l’endommagement des composites stratifiés avec différents empilements. Les travaux portent plus particulièrement dans des empilements 0 et 90 du fait de la limitation au cas 2D. L’objectif est ici de déterminer les outils nécessaires à la description discrète de la microfissuration transverse et du délaminage, puis d’en identifier les différents paramètres ainsi que leur influence pour enfin valider le travail par la comparaison avec des résultats expérimentaux obtenus dans la littérature. L’étude aborde également la fissuration dans les plis de peauThis work presents a study of damage in cross-ply laminates by a new thick levelset (TLS) approach. A generalised finite element model is developped to study the various kinds of damage in a composite : transverse cracking in the 90 layer, delamination at crack-tip and at the interface between plies. Generation of new cracks is controlled by the local energy release rate Y. With this model, we can predict critical crack spacing in glass/epoxy or carbon/epoxy laminates. Various stacking sequences are considered, but we focus on cross-ply (0 and 90 orientation) laminates models. We determine the var-ious modeling elements necessary to a discrete description of transverse micro-cracking and delamination, identify necessary parameters and check their influence, finally validat-ing our work by comparaison with results from literature
7
Bin, Ahmad Sobri Sharizal. "Mechanical and laser drilling of thick carbon fibre reinforced polymer composites (CFRP)." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/mechanical-and-laser-drilling-of-thick-carbon-fibre-reinforced-polymer-composites-cfrp(e5c5182e-a8b2-49c9-bceb-bd7ba9342eb1).html.
Full textAbstract:
Carbon fibre reinforced polymer, or CFRP composite materials, play an increasingly important role in modern manufacturing. They are widely used in aerospace, and their use is currently spreading to other industries where high strength-to-weight ratios are required. However, machining of composites is still a challenging task and often hampered by poor quality. Despite the extensive research that was conducted on the machining of composite materials over the last few years, mechanical drilling still suffers from delamination, fibre pull-out and poor surface finish, whereas laser cutting produces microstructured defects and a taper problem. This thesis reports on the drilling of CFRP composites by demonstrating the possibility of drilling small diameter holes (i.e. 8mm) into 25.4mm thick carbon fibre reinforced polymer composites (CFRPs) using mechanical drilling and laser drilling as stand-alone processes and as a sequential combination. The research involved four main phases of experimental testing. The first part of Phase 1 involved!preliminary experiments of drilling thick CFRP to identify the most suitable drilling strategy. Three mechanical drilling strategies conducted in the same parameter by using a 2-flute uncoated WC twist drill that was assessed with respect to feasibility of drilling thick CFRP. The results showed that the single-step strategy was the most feasible strategy to drill thick CFRP compared to 2- and 4-peck drilling strategies. The second part of Phase 1 concerned the influence of speed-feed combinations on hole quality by utilising three twist drills with different materials and geometries in both an uncoated and coated condition. The results indicated that a significant increase in peel-up delamination was found with increasing feed rate. In contrast, using a constant feed rate but increasing the spindle speed seemed to reduce peel-up delamination. Furthermore, the hole entry for 2-flute uncoated WC drill bits was an uncommon study finding because most of the previous researchers experienced more damages at the hole exit and their investigation focused on the hole exit only. Currently, implementation of laser technology in cutting and drilling composites is becoming popular as an alternative solution. Various experiments were conducted with the goal of identifying the effects of machining parameters on key output measures (i.e. heat affected zone (HAZ), hole depth and other damages) in drilling of 25.4 mm thick CFRP by using a fibre laser. Phase 2 involved a number of machining parameters selected to identify the potential of a fibre laser in drilling thick CFRP composites (i.e. laser power, scanning speed, focal point plane position (FPP), assisted-gas type and gas pressure). The results proved that a fibre laser could penetrate thick CFRP to a 22mm depth only. Moreover, the spiral trepanning strategy was able to penetrate 80% out of the total thickness of the CFRP in continuous wave (CW) mode, whereas the modulated laser beam (i.e. laser pulse mode) can penetrate 67% only. This result was a major recorded breakthrough because previous research attempts cut up to 5mm only. Laser power proved to be the most influential factor for hole depth in laser drilling of thick CFRP when the spiral trepanning strategy was applied. Machining trials were conducted in Phase 3 by using a 16kW fibre laser in modulated pulsed laser mode. In this phase, laser power of more than 1kW was attempted to cut the whole thickness of CFRP composites in CW mode, but it was unsuccessful. However, a new parameter was discovered (i.e. the cooling time between passes in modulated pulsed mode), which proved a considerable reduction of HAZ when the higher cooling time was imposed. Finally, phase 4 involved the experiments of sequential laser-mechanical drilling. A 1kW fibre laser was selected as a pre-drilling or initial step and followed by mechanical drilling as the final step. The sequential drilling method successfully reduced thrust force and torque for mechanical drilling by an overall average of 61%, resulting in high productivity and decreasing the thermal and mechanical stresses in the cutting tool and, in turn, promoting higher tool life. The highest delamination factor (Fda) ratio was experienced by the sequential laser 8mm â mechanical 8mm for both tools (i.e. 2- and 3-flute uncoated tungsten carbide) and laser pre-drilling strategies (i.e. single- and double-side). Thus, a novel laser-mechanical sequential drilling technique was developed, evaluated and tested in the drilling of thick CFRP composites; this is the first time ever in drilling thick CFRP (i.e. 25.4mm).
8
Dogra, Jasween. "The development of a new compression test specimen design for thick laminate composites." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7121.
Full textAbstract:
A new specimen design for determining the compression strength of thick unidirectional laminate composites has been developed using finite element simulations and validated by experimental testing. The computational models included parts of the testing fixture. The materials used for experiments were carbon fibre/epoxy T300/914 from Hexcel Composites and IM7/8552. An understanding has been developed to explain why, using the standard, parallel sided design, for testing specimens in compression and using the ICSTM fixture, specimens using a laminate thicker than 2 mm do not fail in an acceptable way. Initially, simulation and experimental parametric studies were carried out to investigate the effects of loading and design conditions on the fixture and specimen in order to change the stress distribution in the 2 mm thick, parallel sided, 10 mm x 10 mm gauge section specimen. In addition, in order to optimise the specimen itself, different adhesives for bonding end tabs to the laminate were investigated, as were the end tab design and material used in their manufacture. Subsequent simulations showed that the use of an extended and waisted gauge length of either circular or s-shaped profile both caused thick laminate specimens to fail close to the centre of the gauge length. The predicted strength being similar to that measured for a 2 mm thick, parallel sided specimen using the optimised design. Experimental compression strength data from thick laminate specimens with the circular and s-shaped profiles machined into the gauge section validated the finite element results; the strengths achieved being almost identical to those for the 2mm thick laminates. Results from the analysis of the standard design and some preliminary work on the waisted design were presented at a conference [52]. Results for further work on the waisted design and experimental details have been reported in [51] and [75].
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Vel, Senthil S. "Analytical Solutions for the Deformation of Anisotropic Elastic and Piezothermoelastic Laminated Plates." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30003.
Full textAbstract:
The Eshelby-Stroh formalism is used to analyze the generalized plane strain quasistatic deformations of an anisotropic, linear elastic laminated plate.The formulation admits any set of boundary conditions on the edges and long faces of the laminate. Each lamina may be generally anisotropic with as many as 21 independent elastic constants. The three dimensional governing differential equations are satisfied at every point of the body.The boundary conditions and interface continuity conditions are satisfied in the sense of a Fourier series. Results are presented for three sample problems to illustrate the versatility of the method.
The solution methodology is generalized to study the deformation of finite rectangular plates subjected to arbitrary boundary conditions. The effect of truncation of the series on the accuracy of the solution is carefully examined. Results are presented for thick plates with two opposite edges simply supported and the other two subjected to eight different boundary conditions. The results are compared with three different plate theories.The solution exhibits boundary layers at the edges except when they are simply supported. Results are presented in tabular form for different sets of edge boundary conditions to facilitate comparisons with predictions from various plate theories and finite element formulations.
The Eshelby-Stroh formalism is also extended to study the generalized plane deformations of piezothermoelastic laminated plates. The method is capable of analyzing laminated plates with embedded piezothermoelastic patches. Results are presented for a thermoelastic problem and laminated elastic plates with piezothermoelastic lamina attached to its top surface. When a PZT actuator patch is attached to an elastic cantilever substrate, it is observed that the transverse shear stress and transverse normal stress are very large at the corners of the PZT-substrate interface.
This dissertation is organized in the form of three self-contained chapters each of which will be submitted for possible publication in a journal.Ph. D.
10
Nunes, Stephanie Gonçalves. "Processamento por infusão a vácuo de compósitos espessos aramida/epóxi e análise do desempenho sob impacto." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/180659.
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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.
11
Ma, Wei. "Fracture toughness characterization of thin Ti/SiC composites." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/9324.
Full textAbstract:
Titanium based alloys reinforced uniaxially with silicon carbide fibres (Ti/SiC)
are advanced and innovative materials for aerospace vehicles. To avoid
potential problems, these new materials should be extensively tested and
analyzed before application.
This research focuses on experimental fracture toughness study on 0.5 mm
thick Ti/SiC composite materials for aerospace applications. The fracture
toughness tests are mainly based on BS 7448 with some modifications for
transversely isotropic behaviour of the composite materials.
By loading on specimens in the direction perpendicular to the fibre axis, three
critical values of fracture toughness parameters characterizing fracture
resistance of material, plane strain fracture toughness [Plane strain fracture toughness
}, critical crack tip
opening displacement [Critical crack tip opening displacement
] and critical J-integral [Critical at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
]are measured for two
kinds of titanium alloy specimens and three kinds of Ti/SiC composites
specimens.
The values of [Provisional value of Plane strain fracture toughness
] obtained from the fracture toughness tests are not valid [Plane strain fracture toughness
]
for these materials, since the thickness of specimens is insufficient to satisfy the
minimum thickness criterion; however, the results could be used as particular
critical fracture toughness parameter for 0.5 mm thick structures of the materials.
The valid values of [Critical J at the onset of brittle crack extension or pop-in when
Δa is less than 0.2 mm.
] and [Critical crack tip opening displacement
] could be used as fracture toughness
parameters for all thickness of structures of the materials. The results also show
that: fracture toughness of the titanium alloys decreases dramatically after being
unidirectional reinforced with SiC fibre, which is mainly triggered by poor
fibre/matrix bonding condition. Moreover, Ti-Al3-V2.5 reinforced with 25%
volume fraction SiC fibre performs better than the other two composites in
fracture resistance.
12
Rojek, Jan. "Effect of voids in thick-walled pressure vessels : Experimental observations and numerical modelling." Thesis, Université Paris sciences et lettres, 2020. http://www.theses.fr/2020UPSLM015.
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Dans cette thèse, on analyse l'effet de la porosité sur le comportement mécanique d'un matériau composite à fibres de carbone utilisé dans le cadre d'applications à hautes performances. Les réservoirs hyperbare destinés au stockage de l'hydrogène en sont un exemple. Du fait de leur fabrication par enroulement filamentaire, ces structures à parois épaisses présentent des taux de porosité parfois très élevés. La conséquence de telles porosités sur la durabilité des réservoirs et plus largement sur des structures composites chargées de manière multi-axiale est très peu documentée. Les travaux présentés ici s'inscrivent par ailleurs dans le développement d'un modèle existant à MINES ParisTech et ayant fait ses preuves pour prédire la résistance de composites unidirectionnels. Il s'agit ici de perfectionner ce modèle en intégrant de nouveaux facteurs comme les porosités. Des observations (tomographie aux rayons X et microscopie optique) d'un réservoir sont réalisées afin de caractériser les vides et leur distribution au sein de la structure. En parallèle, une étude expérimentale est conduite sur des éprouvettes à différents taux de porosité. La résistance de ces éprouvettes, chargées simultanément en traction longitudinale et compression transverse, est évaluée grace à un système expérimental spécialement conçu. A des échelles encore plus fines, des essais sont réalisés sur des échantillons d'époxy entaillés pour caractériser la croissance des cavités microscopiques et le comportement mécanique de la résine sous un état des contraintes multi-axial. Toutes ces données expérimentales sont ensuite exploitées et intégrées dans le modèle numérique afin de simuler le comportement à rupture d'un réservoir à parois épaissesThe topic of this thesis is the influence of voids on the mechanical properties of carbon fibre reinforced polymers used in high performance applications, such as pressure vessels for hydrogen storage. Manufactured through filament winding, these thick-walled structures can show a significant void content. The effect of these voids on the strength of pressure vessels and, more in general, on the strength of composite structures subjected to multiaxial loads, is not thoroughly understood. The work presented in this thesis is carried out in the context of an existing model of tensile failure of unidirectional composites developed at MINES ParisTech. The objective of the work presented here is to take into account additional factors, such as void content. X-ray tomography and optical microscopy observations are carried out to characterize voids in a carbon-epoxy pressure vessel. In another experimental study, mechanical tests are performed on carbon-epoxy specimens with different levels of void content. The influence of a biaxial load (longitudinal tension and through-thickness compression) is evaluated using a custom-designed experimental setup.At the microscopic scale, tests on notched epoxy specimens are carried out to investigate microscopic void growth and the mechanical behaviour of the resin under a multiaxial stress state. Finally, a numerical approach to modelling failure of a thick-walled cylinder is proposed in the framework of the multiscale fibre break model, taking into account the experimental observations
13
Pilato, Aurélie. "Caractérisation des structures composites bobinées épaisses, application à l’étude du comportement de réservoirs de stockage d’hydrogène." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14397/document.
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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 réelleThis 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
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McKeon, Peter. "A fundamental study to enable ultrasonic structural health monitoring of a thick-walled composite over-wrapped pressure vessel." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54308.
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A structural health monitoring system is desired to monitor the integrity of cylindrical, multi-layer carbon over-wrapped pressure vessels intended to house hydrogen at high pressures. In order to develop the system based on ultrasonic guided wave technology, the interaction between ultrasonic guided waves and defect types of interest must be understood. Finite element models in two and three dimensions are developed to predict guided wave motion in the reservoirs. Key parameters are optimized including frequency range, excited modes, detected modes, and transducer dimensions. A novel baseline subtraction technique in the frequency wavenumber domain is presented to increase lower level detection limits. Some experiments are carried out to corroborate the findings in the finite element environment.
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Agogué, Romain. "Analyse expérimentale et numérique de la fabrication de pièces composites par le procédé RTM." Phd thesis, Université d'Orléans, 2011. http://tel.archives-ouvertes.fr/tel-00628046.
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Cette thèse s'intéresse à la fabrication de pièces composites par le procédé Resin Transfert Molding (ou RTM), appliquée à des tubes de protection thermiques. Plus particulièrement, cette thèse vise à démontrer la faisabilité d'utiliser ce procédé pour la fabrication cette pièce complexe. La phase d'imprégnation de préformes sèches est plus particulièrement étudiée. Après mise en oeuvre, cette pièce peut présenter des défauts tels que de la porosité ou des déplacements de plis constituant la préforme. L'objectif de cette thèse est donc de comprendre l'origine de ces défauts et de minimiser voire de d'empêcher leur apparition. Pour cela, une démarche expérimentale a été mise en place. Celle ci comprend la réalisation d'un pilote de laboratoire permettant d'appliquer différentes conditions d'imprégnation aux préformes considérées. La perméabilité des renforts considérés a aussi été évaluée à différentes échelles grâce à l'utilisation de moyen dédiés à l'échelle macroscopique (banc de perméabilité planaire et transverse), et grâce à l'utilisation d'un code de calcul se basant sur des images de tomographie synchrotron à l'échelle microscopique. Enfin, une analyse de la qualité des prototypes réalisés a été menée en suivant des procédures mises en place lors de ce projet et les résultats analysés et mis en relation avec les conditions de mise en oeuvre. Cette approche expérimentale est couplée aux simulations numériques de la phase d'imprégnation que nous avons aussi mise en oeuvre au cours de cette thèse. Par l'utilisation combinée de la simulation numérique et des essais expérimentaux, nous avons défini des critères estimant le risque d'apparition des défauts. Ces critères ont montré leur efficacité sur les solutions innovantes que nous avons proposées puisque répondant aux exigences du cahier des charges industriel.
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Ait, Laasri Hicham. "Étude et élaboration de matériaux ferroélectriques sans plomb pour le stockage de l'énergie électrique." Thesis, Littoral, 2018. http://www.theses.fr/2018DUNK0528/document.
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Les matériaux ferroélectriques présentant une permittivité diélectrique élevée et de faibles pertes diélectriques présentent un grand intérêt pour la réalisation de condensateurs et le stockage de l'énergie électrique. Les propriétés structurales et diélectriques influencent les paramètres ferroélectriques tels que la polarisation maximale du matériau Pm et la polarisation rémanente Pr sous l'effet d'un champ électrique appliqué Em. Ce mémoire propose d'étudier les propriétés structurales, diélectriques et ferroélectriques des céramiques dérivées de BaTiO₃ (BT) et SrTiO₃ (ST) ainsi que des films épais PVDF pur et composites tels que PVDF/BT et PVDF/BZT. Les céramiques ont été synthétisées par la méthode de la réaction solide et le procédé sol-gel. La substitution dans les sites-A ou les sites-B du matériau BaTiO₃ avec des cations tels que Ca ²⁺, Sr²⁺ and Zr⁴⁺ réduit la densité d'énergie électrique stockée Wd et augmente l'efficacité de stockage énergétique η. La céramique BaZr₀.₅Ti₀.₅O₃ (BZT0.5) présente l'efficacité de stockage énergétique la plus élevée (η=75%). La substitution dans les sites-A du matériau SrTiO₃ avec 40% de cations Ca²⁺ diminue la permittivité diélectrique (ε'∽200), mais cette permittivité est cependant plus stable sur une large gamme de fréquence [100 Hz-1 GHz]. La céramique Sr₀.₆Ca₀.₄TiO₃ préparée par voie sol-gel présente la densité d'énergie électrique stockée la plus élevée (Wd=0.149 J/cm³) sous l'action d'un champ électrique maximal élevé (Em=105 kV/cm). Les films épais à base de polymère PVDF ont été synthétisés par Spin-Coating. La permittivité diélectrique des films épais PVDF pur augmente avec l'apaisseur du film. L'incorporation de particules BT et BZT0.15 dans la matrice polymère PVDF augmente la permittivité diélectrique des films composites PVDF/BT (ε'=32 pour 30% de particules BT) et PVDF/BZT0.15 (ε'=32 pour15% de particules BZT)Ferroelectric materials with a high dielectric permittivity and low dielectric losses are very attractive for the realization of capacitors and for electrical energy storage. To improve the electrical energy density Wd, the structural and dielectric properties influence the ferroelectric parameters such as the maximum polarization Pm and the remanent polarization Pr under an applied electric field Em. This manuscript proposes to study the structural, dielectric and ferroelectric properties of ceramics derived from BaTiO₃ (BT) and SrTiO₃ (ST) as well as pure PVDF thick films and composites such as PVDF/BT and PVDF/BZT. The ceramics were synthesized by the solid state reaction reaction route and the sol-gel process. The subsitution in the A-sites or B-sites of the BaTiO₃ material with cations such Ca²⁺, Sr²⁺ and Zr⁴⁺ reduces the electrical energy density Wd and increases the energy storage efficiency η. The ceramic BaZr₀.₅Ti₀.₅O₃ (BZT0.5) has the highest energy storage efficiency (η=75%). The substitution in the A-sites of SrTiO₃ material with 40% of Ca²⁺ cations reduces the dielectric permittivity (ε'∽200), but is more stable over a wide frequency range [100 Hz -1 GHZ]. The Sr₀.₆Ca₀.₄TiO₃ ceramic prepared by sol-gel process has the highest electrical energy density (Wd = 0.149 J/cm³) under an electrical field Em = 105 kV/cm. The PVDF thick films were synthesized by Spin-Coating. The dielectric permittivity of pure PVDF thick films increases when increasing the thickness. The addition of BT and BTZ0.15 particles in the PVDF polymer matrix increases the dielectric permittivity of the composite PVDF/BT thick films (ε'=32 for 30% of BT particles) and PVDF/BZT0.15 ones (ε'=32 for 15% of BZT particles)
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Chee, Clinton Yat Kuan. "STATIC SHAPE CONTROL OF LAMINATED COMPOSITE PLATE SMART STRUCTURE USING PIEZOELECTRIC ACTUATORS ©." Thesis, The University of Sydney, 2000. http://hdl.handle.net/2123/709.
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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.
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El-Hajjar, Rani Fayez. "Experimental study and analytical modeling of translayer fracture in pultruded FRP composites." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-03152004-230942/unrestricted/elhajjar%5Frani%5Ff%5F200405%5Fphd.pdf.
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Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2004.Dr. Zureick, Abdul-Hamid, Committee Member; Dr. White, Donald, Committee Member; Dr. Saxena, Ashok, Committee Member; Dr. Jacobs, Laurence, Committee Member; Dr. Haj-Ali, Rami, Committee Chair; Dr. Armanios, Erian, Committee Member. Vita. Includes bibliographical references (leaves 164-172).
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Zulu, Andrew Wisdom. "Thick Composite Properties and Testing Methods." Thesis, KTH, Lättkonstruktioner, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-243885.
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In most application to date reinforced carbon fiber composites have been used in relatively smaller thickness, less than 10mm thick and essentially for carrying in-plane loads. As a result, design and testing procedures were developed which reflected the need to understand the in-plane response of the material. recently, engineers and designers have begun to use reinforced carbon fiber composites in thicker sections, where an understanding of the through-thickness response is of para-mount importance in designing reliable structures, particularly where the through-thickness strength has a controlling influence on the overall structural strength of the component. In this thesis tests will be done on carbon fiber non-crimp fabric (NCF) which will be loaded in compression and shear and elastic moduli and strength will be evaluated. In characterizing the through-thickness mechanical properties of a composite, the objective is to produce a state of stress in the test specimen which is uniform and will repeatedly measure the true properties with accuracy. In this study, specimens were machined from two blocks of thick (~20 mm) laminates of glass/epoxy and NCF carbon fiber infused with vinylester and tested in compression, and shear.
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Chang, Jin-Der. "Theory of thick, laminated composite shallow shells /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487779914824542.
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Chee, Clinton Yat Kuan. "STATIC SHAPE CONTROL OF LAMINATED COMPOSITE PLATE SMART STRUCTURE USING PIEZOELECTRIC ACTUATORS �." University of Sydney. Aeronautical Engineering, 2000. http://hdl.handle.net/2123/709.
Full textAbstract:
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.
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Hellweg, H. B. "Non-linear failure simulation of thick composite structures." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496330.
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Hufenbach, W., M. Gude, B. Zhou, and L. Kroll. "Stress and failure analysis of thick-walled conical composite rotors." Sage, 2004. https://publish.fid-move.qucosa.de/id/qucosa%3A38442.
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The high specific strength and stiffness of composite materials, as well as the possibility of creating a load-adapted property profile of them are ideally suited for the design of high-speed lightweight rotors. With respect to a load-adapted reinforcement structure of composite rotors, the rotor geometry has a significant influence on the optimum fibre orientation. In the case of conical rotors—the structural behaviour is strongly influenced by centrifugally induced bending effects in the rotor structure, which cause complex three-dimensional stress states in combination with the ordinary tangential and radial stresses. For analysis of the resulting complex stress states, an analytical method has been developed and verified numerically as well as experimentally. The novel method presented here is the basis for a realistic failure analysis and, in particular, serves as an efficient tool for extensive parameter studies and optimizations within the design process.
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Breivik, Nicole L. "Compression of thick laminated composite beams with initial impact-like damage." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09052009-040529/.
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Alon, Yair. "Analysis of thick composite plates using higher order three dimensional finite elements." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA243188.
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Thesis (M.S. in Aeronautical Engineering and Aeronautics and Astronautics Engineers Degree)--Naval Postgraduate School, December 1990.Thesis Advisor(s): Kolar, Ramesh. Second Reader: Lindsey, G. H. "December 1990." Description based on title screen as viewed on March 30, 2010. DTIC Descriptor(s): Thickness, stability, composite materials, laminates, theory, elastic properties, orientation(direction), composite structures, three dimensional, solutions(general), integration, plates, anisotropy, isotropism, convergence, thinness, behavior, nonlinear analysis, static tests, formulas(mathematics), lagrangian functions, fibers DTIC Identifier(s): Laminates, plates, structural response, composite structures, finite element analysis, nonlinear analysis, stress strain relations, theses, displacement, buckling, interpolation. Author(s) subject terms: Finite element, nonlinear analysis, plate bending thick plates, laminated composites, buckling, constant arc length three dimensional element Includes bibliographical references (p. 87-88). Also available in print.
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Brown, Timothy L. "Influence of layer waviness on the hydrostatic response of thick composite cylinders." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09192009-040247/.
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Kim, Hyungkeun. "Process engineering of thick dielectric films by Chemically Bonded Composite Sol-Gel." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31084.
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This research explores new processing methods to decrease residual stress in ceramic films on metallic substrates, and thus to prevent large-scale cracking in the films. The system of particular concern is alumina-based ceramic coating on aluminum alloy, wherein coefficient of thermal expansion (CTE) of the ceramic is about 3x smaller than that of the alloy. The specific goal was to achieve relatively thick (~0.2mm) and substantially low density of cracks in dielectric films of alumina-based ceramic on aluminum alloy AA5052, by Chemically Bonded Composite Sol-Gel (CB-CSG) process. The principal strategies undertaken in the materials process engineering involved: (i) multi-layer film deposition - to introduce the intermediate steps of stress relaxation; (ii) composite sol-gel slurries with bi-modal particle size distribution - to decrease the overall process temperature, and to decrease film strain during thermal treatment as well as to increase the density and stability of the slurries; (iii) chemical bonding of the film through phosphating - to further decrease the process temperature to the level of 300°C; and (iv) introduction of organic-phase (citric acid) derived bond coats at the interface between the AA5052 substrate and the ceramic coating -to achieve residual stress relaxation through viscoelastic deformation of the bond coat.
The coatings were processed through spray deposition of consecutive -40 µm thick layers, heat-treated at 300°C for 10 min after each deposition. Two size fractions of alumina powders (average size of 0.5 µm of "fine" and 3 µm of "coarse") were used in formulation of the Composite Sol-Gel (CSG) slurry, and the fine/coarse particle content was optimized based on slurry viscosity and stability, as well as properties of the final coating. The coatings were characterized for microstructure, residual stresses and dielectric strength, as a function
of the process parameters. The most important finding of this work is that it is possible to deposit thick ceramic films on aluminum alloy substrates, if all four processing strategies listed above are implemented simultaneously. In particular, the citric acid - derived organo-ceramic bond coats seem to play an important role in relaxing residual stresses resulting from differential thermal contraction and expansion.
It is concluded that the viscoelastically deforming organo-ceramic bond coat helps to relax residual stresses in the coating layers due to differential thermal contraction/expansion, and thus allows deposition of films of up to 200 µm thickness. Dielectric strength of the CB-CSG alumina coated AA5052 aluminum reached a maximum of 15±1 kV/mm for the first layer, and subsequently decreased to 10.5±1 kV/mm. It is believed that this decrease in the dielectric strength after the first layer is caused by increased density of cracks in the coating, as evidenced by decrease of the residual stress in the coatings.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Roberge, Jean-François. "Fatigue evaluation of thick monolithic aluminum structures repaired using composite bonded doublers." Mémoire, Université de Sherbrooke, 2001. http://savoirs.usherbrooke.ca/handle/11143/1295.
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The composite repair of metallic aircraft structures is a proven technology used in many repair applications on both military and commercial aircraft. Composite bonded repairs to metallic aircraft structures are generally used for fatigue enhancement, crack patching, as well as in different kinds of damage repairs. A classical research approach has been adopted for the project. A literature review has been conducted to become acquainted with the crack initiation and crack growth prediction methods in composite bonded repair situations and to gather experimental data for validation purposes. Test data generated by DERA and the USAF has been used to evaluate crack growth and crack initiation analysis tools. Both classical and FEA based fatigue analysis have been evaluated for accuracy. From the evaluation, a list of deficiencies has been developed, and a new methodology proposed to improve the fatigue life prediction for thick cracked aluminum structures. The new methodology provides a good compromise between accuracy and complexity in the analysis of bonded repair designs. A new set of data was generated, due to the lack of experimental crack growth data available for typical CF18 materials and spectrum loading. The proposed methodology has been evaluated against existing and new test data generated for the project. The designed test coupons had a centre section of 6.35 mm (0.25 inch) of thickness and were made of 7050-T7451 Aluminum. Coupon testing was realized using spectrum loading representative of CF-18 usage. This project has been realized in collaboration with the Canadian Department of National Defence (DND), Martec Limited and the Université de Sherbrooke"--Résumé abrégé par UMI
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Mahajan, Amit. "Fabrication of composite thick films of BaLa4Ti4O15 and Ba4Nd9.33Ti18O54 by electrophoretic deposition." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2306.
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Mestrado em Ciência e Engenharia de MateriaisAs comunicações sem fios experimentaram um crescimento excepcional nas últimas décadas e que se prevê que continue nos próximos anos (Capítulo 1, Referêcia 3) Com este crescimento há uma procura crescente de dispositivos de menores dimensões e mais versáteis, do que os actualmente existentes, que permitam maiores níveis de integração, possibilidade de operação a altas frequências e produção a custos reduzidos. Actualmente existe também a necessidade de desenvolver materiais com permitividade dieléctrica relativa (εr) entre 40 - 80, baixas perdas dieléctricas e coeficiente de temperatura da frequência de ressonância (tf) próximo de zero. Actividades de investigação e desenvolvimento para explorar a utilização de tecnologias de fabrico de filmes finos e espessos para substituir os materiais cerâmicos em uso corrente, estão actualmente em curso. Neste contexto, foi explorada no presente trabalho a fabricação de filmes espessos por deposição electroforética (EPD) do composto BaLa4Ti4O15 (BLT), cuja selecção se relaciona com as óptimas propriedades que apresenta para aplicação às frequências das microondas. Foi igualmente tentada a preparação de filmes espessos compósitos de BaLa4Ti4O15 (BLT) - Ba4Nd9.33Ti18O54 (BNT) para preenchimento do intervalo existente em termos de materiais com permitividades dieléctricas 40-80. A escolha da deposição electroforética de entre os vários processos de fabricação de filmes espessos prende-se com as características únicas desta técnica, nomedamente, elevada flexibilidade e simplicidade para aplicação a vários materiais e combinação de materiais, possibilidade de aplicação a uma gama variada de formas e estruturas tridimensionais complexas, densas e porosas e a capacidade de ser utilizada à escala industrial a baixos custos. Neste trabalho foi seguida uma aproximação sistemática para a fabricação dos filmes espessos compósitos pr EPD. Primeiramente procedeu-se à síntese de pós monofásicos de BLT e BNT pelo processo convencional de reacção no estado sólido e a sua pureza foi confirmada por análises de Difracção de Raios X. O tamanho e distribuição de tamanho e a morfologia dos pós de BLT e BNT foram caracterizados por recurso a técnicas de determinação de tamanho de partícula e microscopia electrónica de varrimento. De seguida foram preparadas suspensões dos pós de BNT e BLT em diferentes meios suspensores, como água, etanol e trietanolamina. Ao mesmo tempo, foi estudada a estabilidade das suspensões por análises de tamanho de partícula e medidas de transmitância de luz UV. As suspensões com estabilidade optimizada foram utilizadas para deposição de filmes espessos, em meio básico e meio ácido e foram estudadas as variáveis de processamento, como espessura, massa do depósito, corrente eléctrica em função do tempo e voltagem. Foi também discutido o efeito do passo de prensagem isostática, após deposição, na morfologia e densidade dos filmes e também na sua resposta dieléctrica. Filmes de BLT de 10 mm de espessura depositados sobre folhas de platina e sinterizados a 1600ºC/1h exibem εr = 58, TCεr +30ppm/ºC e perda dieléctrica de 0.002 a 1 MHz. Como termo de comparação foram preparados cerâmicos de BLT. Foi feita a caracterização estrutural, microestrutural e dieléctrica de filmes e cerâmicos de BLT, sinterizados entre 1400ºC e 1600ºC. Filmes espessos compósitos de BNT/BLT e BLT/BNT foram preparados com sucesso por EPD. Através da combinação de camadas de BLT e BNT foram preparados filmes espessos compósitos de 30 μm com εr ~71, TCεr ~-16ppm/ºC e perda dieléctrica de a 1 MHz. Estes resultados são de particular relevância visto que combinam a possibilidade de preparar filmes espessos com propriedades desenhadas para aplicações a frequências elevadas e das microondas com a capacidade de diminuir o tamanho do dispositivo. Embora preliminares estes resultados abrem novas oportunidades tecnológicas, que deverão ser mais exploradas ABSTRACT: Wireless communications have experienced an exceptional growth in the last decades and similar growth is expected for next coming years, according to the ABI analysis [Chapter 1, Reference 3]. With this growth there is an increase demand for the production of devices of smaller dimensions and more flexible than the current in use ones, with increased integration, possibility of operation at high frequencies and produced with reduced costs. There is also a present demand to develop materials with relative permittivity (εr) between 40 - 80, low loss and near zero temperature coefficient of resonant frequency (tf). Research activities to exploit thin and thick film technologies to replace the bulk ceramics are currently underway. Within this context, in this work, the fabrication of thick films by electrophoretic deposition of the tertiary compound BaLa4Ti4O15 (BLT) was exploited, because of the optimal properties for microwave applications of BLT. Simultaneously, the preparation of BaLa4Ti4O15 (BLT) - Ba4Nd9.33Ti18O54 (BNT) composite thick films was attempted to fill the permittivity gap of 40-80 as describe above. The choice of electrophoretic deposition (EPD) technique over other thick film processing techniques is obvious because of its unique features, such as the high flexibility and simplicity for application with various materials and combinations of materials, and on a wide range of shapes and 3D complex and porous structures, and its ability to be scaled-up to the fabrication of large product volumes and sizes at low costs. A systematic approach was used to fabricate the composite thick films. Firstly, BLT and BNT powders were prepared by solid state reaction synthesis and the phase purity of the powders was confirmed by XRD. The size and morphology of the powders were assessed by particle size analysis and scanning electron microscopy. BNT and BLT suspensions were prepared in different suspension media such as water, ethanol and acetone. The pH of the suspension was varied by dilute nitric acid and triethanolamine. Concomitantly the stability of the suspensions was characterised by particle size analysis and UV transmittance measurements. Stable suspensions were used for the deposition of particles in acidic and basic conditions, and the processing parameters such as thickness, deposit weight, current as a function of time and voltage were studied. The effect of iso static pressing and film thickness on the properties and morphology was also discussed. 10 mm thick BLT films on platinum foils and sintered at 1600ºC/1h exhibit εr = 58, TCεr +30ppm/ºC and loss tangent 0.002 at 1 MHz. As a comparison tool, BLT ceramics were prepared as well. Films and ceramics were sintered between 1400ºC to 1600ºC and their morphology and dielectric response assessed. BNT/BLT and BLT/BNT composite thick films were successfully prepared by electrophoretic deposition. By the combination of BLT and BNT layers a 30 μm composite thick film with εr ~71, TCεr ~-16ppm/ºC and loss tangent of 0.002 at 1 MHz were prepared. These results are of particular relevance since they combine the possibility to prepare thick films with tailored properties for high frequency and microwave properties with the aptitude to decrease the device size. Although preliminary these results open further technological opportunities, that should be more explored
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Roberge, Jean-François. "Fatigue evaluation of thick monolithic aluminum structures repaired using composite bonded doublers." [S.l. : s.n.], 2001.
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Wang, Bing. "Duration-of-load and creep effects in thick MPB strand based wood composite." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23906.
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British Columbia (BC) is in the midst of the largest outbreak of the Mountain Pine Beetle (MPB) ever recorded in western Canada. Technologies capable of converting stained lumber into market acceptable products are urgently required to reduce the impact of the growing volume of MPB killed lumber on the profitability of forestry in BC.
New, thick MPB strand-based structural composite products can be produced and help absorb a large volume of MPB wood. With appropriate mechanical properties, such products can be used as beams, headers, and columns in the low-rise commercial, multi-family residential and single family residential markets.
This work was focused on the duration-load and creep behaviour of thick MPB strand-based wood composite. The beam specimens were made in the Timber Engineering and Applied Mechanics Laboratory at UBC. A series of tests were conducted on the matched groups to investigate the creep-rupture behaviour. These investigations comprised of ramp load tests at three loading rates, long-term constant load tests at two stress levels and cyclic bending tests at six stress levels.
A damage accumulation model was developed to study the creep-rupture behaviour. This model stipulates that the rate of damage growth is given in terms of the current strain rate and the previously accumulated damage, and a 5-parameter rheological model is applied to describe the viscoelastic constitutive relationship to represent the time-dependent strain, while the damage accumulation law acts as the failure criterion. The results of the long-term constant load tests were then interpreted by means of the creep-rupture model which had been shown to be able to represent the time-dependent deflection and time-to-failure data for different stress levels. The predictions of the model were verified using results from ramp load tests at different loading rates and results from cyclic loading tests at different stress levels. The creep-rupture model incorporates the short term strength of the material, the load history and predicts the deflection history as well as the time-to-failure. As it is a probabilistic model, it allows its incorporation into a time-reliability study of wood composites’ applications.
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Chung, Chang-Bum. "Compressive behavior of thick composite shells : benchmark solutions for loss of stabilty and hygroscopic effects." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/13406.
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Rameau, Jean-Michel. "Multi-axial damage and failure models for thick composite lugs under static and cyclic loading." Thesis, KTH, Lättkonstruktioner, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185174.
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The thesis deals with quasi-static and fatigue simulations of thick composite lugs subjected to three-dimensional stress states. This includes damage prediction of hybrid laminates made of GRFP and CRFP containing unidirectional and woven fabric plies.Focus lies on the development of a progressive damage model in fatigue which accounts for sti˙ness and strength degra-dations. Two methods based on Puck’s failure criterion are proposed to predict failure of unidirectional plies: one for plane stress analysis and and the other which takes out-of-plane damage into account.Virtual testing in FEM is conducted in quasi-static and fatigue analysis on thick composite lugs subjected to uni-axial loading. Damage, strength and life predictions are then compared with experimental results to validate the numerical models under investigations.In der vorliegenden Arbeit wird die Berechnung der Festig-keit von dickwandigen Lochleibungslaminaten im Faserver-bundwerksto˙en unter dreidimensionalen Spannungszustän-den untersucht. Nichtlineare Materialverhalten von Hybrid-laminaten in CFK und GFK werden für Unidirektionalfa-serlagen und Gewebelagen berücksichtigt.Der Schwerpunkt liegt auf der Entwicklung von progressi-ven Versagensmodellen unter der Berüsichtigung von Rest-festigkeit und Reststeifigkeit des Materials. Zwei Modelli-erungsmethoden nach Puck-Kriterium zur Vorhersage des Versagens in UD-Lagen werden vorgeschlagen: eine Degra-dierungstechnik für ebene Spannungszustände und ein me-hrachsiges Modell.Numerische Simulationen mit der Finite-Elemente-Methode werden in Statik- und Ermüdungsanalyse an dickwandigen Lochleibungslaminaten unter einachsiger Belastung durch-geführt. Beschädigungen, Festigkeiten und Ermüdungsle-bensdauer werden dann mit experimentiellen Daten ver-glichen, um die numerischen Methoden zu validieren.
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Al-Ghothani, Ali M. "A unified approach to the dynamics of bending and extension of moderately thick laminated composite plates /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487266691094416.
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George, E. R. "A method for the ply-level elastic characterization of composite materials using thick tubular angle-ply specimens." Thesis, Virginia Tech, 1993. http://hdl.handle.net/10919/42959.
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Accurate mechanical properties are critical to the design and use of composite material structures. Due to the available processing methods, the properties of ceramic matrix materials are especially sensitive to the geometry of the component and how it is made. A method is presented by which the ply-level elastic properties of a composite material can be obtained for a common structure; a thick, laminated tube. The mechanical and thermal response of the tubes is modeled by a planar cylindrical elasticity solution. Properties are determined from surface strain measurements of a thick tube subject to axial, torsional, pressure, and thermal loads. All elastic properties (including thermal expansion coefficients) can be obtained except the out-of-plane shear moduli (G13, G23) which are not involved in the planar elasticity solution employed. The ply-level properties are estimated by inversion of the elasticity solution in terms of the global strain measurements. A Least Squares optimization approach is used for the inversion of the elasticity solution. Application of the method for a filament wound aluminum oxide-aluminum oxide tube is presented. Advantages and limitations of the method are identified.
Master of Science
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Gagnon, Paul. "Notched strength analysis of tensile specimens taken from a thick, filament-wound graphite/epoxy pressure vessel." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/101373.
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An experimental analysis of specimens taken from a thick, filament-wound composite material pressure vessel (cylinder) was performed by testing tensile coupons with various semi-elliptical surface notches. The strength of specimens with small notches was found to be notch insensitive. The strength of specimens with larger notches depended on the size of the notch.
The fracture toughness of the laminate was found by applying a general fracture-toughness parameter approach. Using this value, several approaches were employed to predict failure loads. The accuracy of the approaches depended on the size of the notches. In general, the linear-elastic fracture mechanics method overpredicted the failure strength of specimens with intermediate sized notches, but predicted failure strength accurately for specimens with large notches. A strength of materials approach accurately predicted notched strength only for specimens with small notches. Notched strength was more accurately predicted for all notch sizes using an empirical approach, with the notch area used to predict failure instead of the notch depth, which was used in the linear-elastic fracture mechanics and strength of materials approaches.M.S.
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Kouri, Jeffrey Victor. "Improved finite element analysis of thick laminated composite plates by the predictor corrector technique and approximation of C[superscript]1 continuity with a new least squares element." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/20762.
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Hall, Benjamin L. "Finite element and analytical analysis of cracks in thick stiffened plates repaired with a single–sided composite patch." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/42638.
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Approved for public release; distribution is unlimitedThe purpose of this thesis was to investigate crack growth behavior in thick stiffened aluminum plates repaired with a single-sided composite patch. A model was developed using finite element analysis that extracted the mode I strain energy release rate (SERR) with use of the Virtual Crack Closure Technique. The dimensions and spacing of the stiffeners were varied to determine their effect on reducing the SERR. This model was also compared to an unstiffened model and one without a composite patch. A tensile load and a bending moment were both applied to the model for various configurations. These results were then used to develop an analytical model that can be used to predict the effectiveness of a patched surface.
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Bombardier, Yan. "Prediction of the shape of fatigue cracks propagating in thick monolithic aluminium structures repaired using composite bonded doublers." Mémoire, Université de Sherbrooke, 2004. http://savoirs.usherbrooke.ca/handle/11143/1417.
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Developed in the 1970's, the composite bonded repair technology has been proven to be an efficient and reliable method for use on metallic aircraft structures. The purpose of this method is to slow or arrest crack growth, and thus, prolong the life of the structure. The technology has been successfully used in repair applications on both military and civil aircraft for fatigue enhancement and crack patching. However, the installation of composite bonded repairs on aircraft must satisfy their damage tolerance requirements to ensure the safe operation of the aircraft. To meet these requirements, reliable crack growth prediction models are one of the tools required to assess the safety of the repaired structures without the need for long and expensive test programs. Thus, accurate prediction tools are the key that will help this technology to be integrated in structural integrity programs by the aeronautical industry. In 2001, Martec Limited performed a research study intended to survey the available crack initiation and crack growth prediction tools for fatigue life evaluation of thick aluminium structures repaired using composite bonded doublers. The approach developed by Martec provided accurate crack growth predictions for the case of double-sided repairs, but did not provided the same level of accuracy for the single-sided repair configurations. It was therefore recommended by Martec to investigate the influence of crack shape on the crack growth predictions to achieve more accurate predictions for single-sided repair configurations. Consequently, a new systematic crack growth prediction methodology, based on 3D finite element methods, was developed for thick structures repaired using composite bonded doublers. The methodology considers effects specific to bonded composite repairs, such as the effect of thermal residual strains caused by the curing process, the effect of out-of-plane bending, and the crack shape. The methodology was tested using three different experimental tests found in literature. The experimental crack shapes and crack growth data were compared with numerical results. Good agreement between experimental and numerical crack growth predictions was obtained and the gain in accuracy acquired by including the shape of the crack was demonstrated. As part of a collaborative program on fatigue prediction of bonded repairs, Martec Limited has initiated this research project in collaboration with the Department of National Defence (DND), the Chief of Research And Development (CRAD), and Sherbrooke University. This project was conducted at Martec, under the auspices of the partnership program for masters and doctoral studies in the workplace of Sherbrooke University.
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Philobos, Mahera S. "Benchmark elasticity solution for the buckling of thick composite cylindrical shells under axial compression and combined external pressure and axial compression." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19549.
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Marchetti, Fabien. "Modelling and characterisation of anisotropic multilayered plates on a wide frequency range." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI130.
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Le présent travail de thèse traite de la modélisation vibratoire et de la caractérisation dynamique de matériaux multicouches anisotropes. Dans le premier chapitre, une classification de quelques modèles analytiques de multicouche et techniques de caractérisation expérimentales de structures planes est établie sous la forme d'une synthèse bibliographique. Elle regroupe les récents résultats publiés autour du sujet. Le second chapitre propose une extension d'un modèle équivalent de multicouche au cas des structures anisotropes. Ce modèle décrit les premières courbes de dispersion de la structure et tient compte des phénomènes de cisaillement pouvant agir sur le mode de flexion en hautes fréquences. Le principal avantage du modèle réside dans sa simplicité et sa rapidité grâce à son nombre de variables cinématiques indépendant du nombre de couches. Les caractéristiques du multicouche sont définies par les 5 rigidités de flexion d'une plaque équivalente mince qui est comparée à ce dernier. L'extension de modèle est validée à l'aide d'une étude expérimentale réalisée sur des plaques composites en fibres de carbone. Un intérêt tout particulier est porté sur la modélisation de l'amortissement structurel. Une définition énergétique du facteur de perte, décrite par une formulation spatiale et temporelle de l'atténuation, est comparée à une définition équivalente. Une nouvelle définition de la formulation spatiale est proposée dans le cas de structures très amorties et est comparée aux résultats de la littérature. Dans le troisième chapitre, la technique de caractérisation RIC est étendue au cas des structures anisotropes. Cette méthode inverse s'appuie sur l'analyse du champ de déplacement de la structure et possède, grâce à son aspect local, des atouts non négligeables pour des applications industrielles. La méthodologie est tout d'abord présentée pour l'identification de sources (objectif initial de la méthode) et est ensuite adaptée à la caractérisation. Plusieurs applications numériques et expérimentales sont présentées afin de valider cette extension. Enfin, le quatrième chapitre porte sur la caractérisation expérimentale d'un sandwich en nids d'abeille sur une large bande fréquentielle (1 à 300 kHz). Le comportement dynamique complexe de cette structure épaisse est décrit au travers des résultats prometteurs fournis par les simulations de notre modèle et les estimations de RIC. Ces résultats sont également comparés à ceux d'un modèle de référence et d'autres méthodes de caractérisationThis PhD thesis concerns the modelling and the dynamic characterisation of anisotropic multilayered structures. In the first chapter, a classification of some analytical models and experimental methods of characterisation is presented in the form of a bibliographical synthesis where the main published results are gathered. The second chapter introduces an extension of an equivalent model of multilayered structures to the case of anisotropic materials. This model describes the first dispersion curves of the structure and considers the shear phenomena that can affect the bending mode in high frequencies. The main advantage of the model lies in its simplicity and rapidity thanks to a number of kinematic variables independent of the number of layers. The characteristics of the multilayer are defined by the 5 flexural rigidities of a thin equivalent plate which is compared to the multilayer. The results of the model are validated by means of an experimental study on carbon fiber composite plates. A particular interest is dedicated to the modelling of structural damping. An energetic loss factor, based on a temporal and spatial definition of the attenuation, is compared to an equivalent one. A new definition of the spatial attenuation is suggested for high damped structures and is compared to literature. In the third chapter, the methodology of the characterisation technique CFAT is adapted for anisotropic plates. This inverse method is based on the displacement field analysis of the structure and has, by means of its local aspect, relevant advantages for industrial applications. This adaptation is, as a first step, introduced for the identification of sources (initial objective of the method) and applied, in a second step, for the characterisation. Several numerical and experimental applications are presented to validate the results of the method. Finally, the fourth chapter deals with the experimental characterisation of a honey comb sandwich on a high frequency range (1 to 300 kHz). The complex dynamic behaviour of this thick structure is described through the promissing results given by the simulations of our model and the estimations of RIC. These results are also compared to the ones of a reference model and other characterisation methods
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Hetznecker, Alexander. "Untersuchung der gassensitiven Eigenschaften von SnO2/NASICON-Kompositen." Doctoral thesis, [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975219723.
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Shen, WanLin, and 沈婉琳. "Manufacturing Simulations and Processing Optimizations for Thick Composites." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/87306267383562935701.
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碩士大葉大學
工業工程與科技管理學系
95
In this research, the manufacturing parameter in curing cycle will be simulated. In the simulation, all of the middle laminates will be found the fact that the resulting temperature is lag and the laminate’s consolidation is nearly perfect. In compress, follow the increasing temperature the viscosity will be changed. Due to the changing, the pressure will load on fiber from resin. After that, the curing cycle will be finished. The conventional thermosetting composite material present temperature lags, degree of cure un-uniform, and consolidation uncompleted in manufacturing process. Therefore, the difference between the middle and boundary laminate’s temperature is large. When the temperature keeps increase with steady pressure, the resin pressure, composite thickness, and degree of cure will be changed. Since the temperature’s difference between the middle and boundary laminate’s is large, the product’s quality will present instability. In this study, the software, MATLAB and ANSYS, can get temperature’s results and compare them. The consolidation behavior of laminate is analyzed with Crank-Nicholson of finite difference method. Conclude these results, there is three conclusions can be gotten: the change of thickness, the temperature distribution and cure of middle laminate. Finally, through GA, the optimization’s design will be obtained.
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Hojjati, Mehdi. "Curing of thick thermosetting composites : experiment, simulation, and scaling." Thesis, 1994. http://spectrum.library.concordia.ca/2890/1/NN97580.pdf.
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Jiang, Yijun. "A novel method for the manufacturing of thick composites." Thesis, 2004. http://spectrum.library.concordia.ca/7875/1/MQ91053.pdf.
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Due to the nature of exothermic reaction and high thermal resistance, processing thick-sectioned composites can be very difficult. Instead of expensive and time consuming trial and error methods, pre-catalyzing fabric technique applied to the hand lay-up process is very effective to decrease exothermal peak dramatically. By applying the peroxide catalyst to the fabric, this technique can slow down the polymerization reaction rate and subsequently reduce the internal temperature during curing. In this study, two kinds of pre-catalyzing methods were developed: one used polystyrene as the catalyst binder; another used epoxy resin as the binder. The experimental results indicate that the pre-catalyzing method using polystyrene as the binder can control the peak exothermic temperature to be under 30{493}C, and the method using epoxy binder can limit that temperature to be below 39{493}C. Latter method has shorter curing time than former one. Both methods can reduce the temperature gradient greatly. The degree of cure for both methods can be more than 87% with low exothermic temperature after the cure, and the laminate is rigid enough with this degree of cure to be used for further post cure. The degree of cure can be improved to be higher than 97% by leaving the samples for more than five weeks in ambient temperature. Compared with polystyrene binder which made the interlaminar shear strength decrease by 12.8%, the epoxy resin binder has the better characteristic not to exhibit this decrease, and the short beam shear tests show no degradation of ILSS.
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Lin, Yung-kun, and 林永崑. "Processing and compressive behavior of thick carbon/epoxy composites." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/29116061555960428162.
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博士逢甲大學
機械與航空工程研究所博士班
97
The key manufacturing technology of thick laminated composites was developed in this study. A pressure rolling machine was designed and employed to remove air possibly trapped in between plies. This device can reduce the negative influence of the artificially stacking prepreg quality, assure tested specimens of stability and consistency, and increase experimental accuracy. The carbon fiber/epoxy laminated composites with different materials, thickness, and stacking sequence were formed by autoclave. To apply the compressive load, an end-supported, end-loaded fixture of adjustable nonconstrained length was designed and used. This fixture allows researchers to in-situ monitor fracture evolution of thick composites in compression. The compression tests for the specimens of carbon fiber composites of the T-300 woven fabric and the TC-35 cross-ply were carried out. The growth of cracks was monitored and recorded in real-time by picture and video cameras. The compressive fracture behavior of these thick laminated composites under various test conditions was investigated. The topics of fracture behavior include the variety of loading curves, the tendency of stiffness and strength, the failure mode, the fracture evolution, the crack onset and development, the relation between fracture evolution and stress-strain curves, and stiffness loss. Furthermore, this study develops some empirical models to predict the compressive strength of thick laminated composites based on the compressive strength of general laminated composites. In T-300 woven fabric carbon fiber specimens, when the nonconstrained length of specimens with end-supported is lower than the critical test length, its loading curve shows a postfailure portion. The major failure modes are kind-bands and delamination. When the nonconstrained length is higher than the critical test length, the loading curve doesn’t have the postfailure portion. The buckling becomes the major failure mode. As the nonconstrained length is further increasing, the buckling failure mode is more obvious. Moreover, the stiffness and strength are all decreased as the nonconstrained length increases. In 160 cross-plies TC-35 carbon fiber specimens with different stacking sequences, the numbers of 0° and 90° layers are both 80, but the compressive behavior is changed as different stacking sequences. It shows that the stacking sequence is an important parameter influencing the compressive behavior. Furthermore, the empirical relationship between the compressive strength and the NLI (Number of Laminar Interface) of specimen follows the exponential equation distribution. For both supported and nonsupported specimens, the compressive strength increases as the NLI increases. The supported specimens have higher stiffness and strength than the nonsupported counterparts because of the Poisson’s effect. From the fracture evolution observation, the crack triggering can be in the form of transverse shear crack due to microbuckling and fiber splitting. Later the failure mode transforms into fiber kinking due to the shear crack slip. Delamination occurs at the interface of 0° and 90° laminae. Finally, the 90° laminae fail due to the cracks caused by shear slipping or buckling. The number of transverse shear cracks increases as the NLI increases. The specimen formed a Y shaped configuration failure consisting of two symmetric crack paths and delamination.
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Small, Peter D. "Ultrasonic wave propagation in thick, layered composites containing degraded interfaces." Thesis, 2005. http://hdl.handle.net/10945/24361.
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CIVINSThe ultrasonic wave propagation of thick, layered composites containing degraded bonds is investigated. A theoretical one-dimensional model of three attenuative viscoelastic layers containing two imperfect interfaces is introduced. Elastic material properties and measured values of ultrasonic phase velocity and attenuation are used to represent E-glass and vinyl ester resin fiber-reinforced plastic (FRP) laminate, syntactic foam, and resin putty materials in the model. The ultrasonic phase velocity in all three materials is shown to be essentially constant in the range of 1.0 to 5.0 megahertz (MHz). The attenuation in all three materials is constant or slightly increasing in the range 1.0 to 3.0 MHz. Numerical simulation of the model via the mass-spring-dashpot lattice model reveals the importance of the input signal shape, wave speed, and layer thickness on obtaining non-overlapping, distinct return signals in pulse-echo ultrasonic nondestructive evaluation. The effect of the interface contact quality on the reflection and transmission coefficients of degraded interfaces is observed in both the simulated and theoretical results.
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Rowghanian, Pooya. "Improvement of Temperature Distribution across Thick Thermoset Composites Using Carbon Nanotubes." Thesis, 2012. http://spectrum.library.concordia.ca/973983/1/Rowghanian_MASc_S2012.pdf.
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The effect of adding carbon nanotubes (CNT) into epoxy on the temperature gradient in thick thermoset composites was studied and presented. Addition of CNT increases the thermal diffusivity of the resin and reduces the curing reaction speed. The latter slows down the rate of energy liberation, while the former helps to dissipate faster the released heat in the exothermic reaction. The results showed that the addition of up to 1 wt% CNT can reduce the difference between temperatures at the center and at the surface of 1.5-inch thick column of epoxy by 41%. Measured variations of heat capacity and thermal diffusivity by changes in both temperature and carbon nanotube contents as well as the empirically-evaluated cure kinetics of epoxy were used in a transient one-dimensional heat transfer finite difference model to determine the temperature distribution across thickness during the cure. Good agreement was obtained between calculated and experimental trends.
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Sun, Esther Mei. "Modeling and simulation of thermomechanical behavior of thick fiber reinforced thermoset composites." 1996. http://catalog.hathitrust.org/api/volumes/oclc/35953208.html.
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Ameen, Maqsood Mohammed. "Analysis of Thick Laminated Composite Beams using Variational Asymptotic Method." Thesis, 2016. http://etd.iisc.ernet.in/2005/3720.
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An asymptotically-exact methodology is presented for obtaining the cross-sectional stiffness matrix of a pre-twisted, moderately-thick beam having rectangular cross sections and made of transversely isotropic material. The beam is modelled with-out assumptions from 3-D elasticity. The strain energy of the beam is computed making use of the constitutive law and the kinematical relations derived with the inclusion of geometrical nonlinearities and initial twist. Large displacements and rotations are allowed, but small strain is assumed. The Variational Asymptotic Method (VAM) is used to minimize the energy functional, thereby reducing the cross section to a point on the reference line with appropriate properties, yielding a 1-D constitutive law. In this method as applied herein, the 2-D cross-sectional analysis is performed asymptotically by taking advantage of a material small parameter and two geometric small parameters. 3-D strain components are derived using kinematics and arranged as orders of the small parameters. Warping functions are obtained by the minimisation of strain energy subject to certain set of constraints that renders the 1-D strain measures well-defined. Closed-form expressions are derived for the 3-D non-linear warping and stress fields. The model is capable of predicting interlaminar and transverse shear stresses accurately up to first order.