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Morrisey, Ben. "Vibration Testing of Short Fibre Reinforced Polymer Composites". Thesis, KTH, Lättkonstruktioner, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-261221.
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Applications of short fibre reinforced polymer composites (SFRPCs) have been rapidly increasing and most of the components made of these materials are subjected to cyclic loading. In automotive applications, “under the hood” is the harshest environmental condition for plastic-based materials with temperatures ranging from -40°C to 120°C. Components are subjected to mechanical vibrations primarily as a result of the periodic excitation and the dynamics of the engine firing. It is important, therefore, to design and test the components accurately so as to minimise the risk of component failure during the expected lifetime of the vehicle. Taking this into account, this thesis investigated if the current test methods being used at Scania ensured a valid fatigue testing of engine components made of SFRPCs. An extensive literature review was carried out detailing the work published on SFRPC fatigue to-date and the methods currently used at Scania NMBT were detailed. A series of sine and random vibration tests were then performed to characterise material behaviour in addition to Dynamic Mechanical Analysis and Scanning Electron Microscopy of failed specimens. The results of these, combined with the knowledge gathered in the literature review, resulted in a number of suggestions to adapt the current test methods with the aim of increasing their validity for SFRPCs.
2
Mortazavian, Seyyedvahid. "Fatigue Behavior and Modeling of Short Fiber Reinforced Polymer Composites". University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1437787779.
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Parveen, Bushra. "Fibre Orientation and Breakage in Glass Fibre Reinforced Polymer Composite Systems: Experimental Validation of Models for Injection Mouldings. Validation of Short and Long Fibre Prediction Models within Autodesk Simulation Moldflow Insight 2014". Thesis, University of Bradford, 2014. http://hdl.handle.net/10454/14865.
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End-gated and centre gated mouldings have been assessed with varying thickness and sprue geometries for the centre gate. Alternative image analysis techniques are used to measure the orientation and length of injection moulded short and long fibres composite components. The fibre orientation distribution (FOD) measurements for both geometries have been taken along the flow path. In shear flow the FOD changes along the flow path, however the FOD remains relatively constant during expansion flow. The core width and FOD at the skin within a long glass fibre (LGF) specimen is different in comparison to a short glass fibre (SGF) specimen. Fibre length measurements have been taken from the extrudate, sprue and 2 positions within the centre gate cavity. The size of the sprue has little influence on fibre breakage if the moulding is more than 1 mm thick The SGF FOD prediction models within Autodesk Simulation Moldflow Insight 2014 (ASMI) have been validated against measured SGF data. At present, by default, the models over-predict the < cos2θ > for most geometries. When the coefficients are tailored for each model, drastic improvements are seen in the FOD prediction. The recently developed SGF RSC model accurately predicts the FOD in shear, in a thin geometry, whereas the Folgar-Tucker model predicts the FOD accurately in expansion flow. The measured LGF fibre length distribution (FLD) and FOD have been validated against the LGF prediction models. The LGF models are currently under predicting the breakage and over-predicting < cos2θ >. The breakage prediction improves if measured FLD of the extrudate is input into the model.
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Meslin, Frédéric. "Propriétés rhéologiques des composites fibres courtes à l'état fondu". Cachan, Ecole normale supérieure, 1997. http://www.theses.fr/1997DENS0020.
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Ce travail traite de l'étude des suspensions de particules axisymétriques et rigides dans une matrice fluide. Plus précisément, nous nous sommes intéressés au comportement rhéologique de ces matériaux. Le contexte industriel associe est la mise en forme des thermoplastiques renforces par des fibres courtes. Dans une partie théorique, nous proposons un modèle de comportement, issu d'une approche micromécanique, pour les suspensions de sphéroïdes rigides dans une matrice newtonienne : une loi reliant les contraintes et les taux de déformations macroscopiques, une équation pour décrire le mouvement des particules. Ce modèle de comportement est applicable au cas des solutions en régime semi-dilue. Dans une partie expérimentale, nous proposons d'identifier des paramètres rhéologiques du modèle de comportement. A cet effet, des mesures de viscosité en cisaillement sont présentées, ainsi qu'un nouvel écoulement. Ce dernier écoulement, dit écoulement en croix, doit permettre d'identifier le paramètre rhéologique caractérisant l'anisotropie des suspensions.
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Despringre, Nicolas. "Analyse et modélisation des mécanismes d'endommagement et de déformation en fatigue multiaxiale de matériaux composites : polyamide renforcé par des fibres courtes". Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0058/document.
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Le présent travail de thèse se consacre au développement d'un nouveau modèle micromécanique pour les composites en thermoplastique renforcé par des fibres de verre courtes. L'objectif est notamment la modélisation du comportement visco-endommageable en fatigue du PA66-GF30. Ce matériau, particulièrement utilisé dans l'industrie automobile, est sujet à une microstructure spécifique issue du procédé de moulage par injection. L'approche multi-échelles développée consiste en une méthode de Mori-Tanaka modifiée, appliquée à des renforts avec enrobage et prenant en compte l'évolution de l'endommagement à l'échelle microscopique. La description des mécanismes d'endommagement se base sur une investigation expérimentale poussée préalablement menée au sein de l'équipe. Des scénarios d'endommagement ont été proposés et incluent trois processus locaux différents : la décohésion de l'interface, la microfissuration de la matrice et les ruptures de fibres. Ceux-ci sont spécialement affectés par la microstructure. L'approche développée intègre ces cinétiques d'endommagement ainsi que la viscoélasticité non-linéaire de la matrice et la distribution d'orientation des inclusions due au procédé de fabrication. Chaque mécanisme d'endommagement est modélisé par une loi d'évolution basée sur les contraintes locales calculées à l'échelle microscopique. La loi constitutive finale, à l'échelle du volume élémentaire représentatif, est implémentée dans une bibliothèque scientifique en C++, SMART+, et est conçue pour être compatible avec une analyse de structures par éléments finis. L'identification du modèle est réalisée par rétro-ingénierie, en tirant profit de résultats expérimentaux multi-échelles, dont notamment des tests in-situ au MEB ainsi qu'une analyse qualitative et quantitative par μCTThe current work focuses on a new micromechanical high cycle fatigue visco-damage model for short glass fiber reinforced thermoplastic composites, namely: PA66/GF30. This material, extensively used for automotive applications, has a specific microstructure which is induced by the injection process. The multi-scale developed approach is a modified Mori-Tanaka method that includes coated reinforcements and the evolution of micro-scale damage processes. Their description is based on the experimental investigations of damage mechanisms previously performed by the team. Damage chronologies have been proposed involving three different local degradation processes: fiber-matrix interface debonding/coating degradation, matrix microcracking and fiber breakage. Their occurrence strongly depends on the microstructure. The developed model integrates these damage kinetics and accounts for the complex matrix viscoelasticity and the reinforcement orientation distributions induced by the process. Each damage mechanism is introduced through an evolution law involving local stress fields computed at the microscale. The developed constitutive law at the representative volume element scale is implemented into a C++ scientific library, SMART+, and is designed to work with Finite Element Methods. The model identification is performed via reverse engineering, taking advantage of the multiscale experimental results: in-situ SEM tests as well as quantitative and qualitative μCT investigations
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Jain, Ayush. "Development and Characterization of Multi-scale Polymer Composite Materials for Tribological Applications". Thesis, Luleå tekniska universitet, Maskinelement, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-65241.
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With industries aiming at higher efficiencies, lightweight parts, and easier manufacturability there has been a recent trend of replacing the metallic materials with polymeric materials and its composites. Particularly in the automotive industry, there is a demand of replacing metallic material of bushes and bearings with polymer based materials (PBM). For these heavy performance requirements (as in automobiles), the commonly used industrial polymers like Acetal and Nylon fail to provide good mechanical and tribological performance. High-performance polymer like Polyphenylene Sulfide (PPS) is a relatively newer material and shows a potential of being a PBM alternative for metallic bearings in automobiles if their tribological performance can be improved. One of the ways of improving the tribological performance of the polymer is by the addition of filler material, hence making a polymer composite. In this study, we used Short Carbon Fibre as micro-reinforcement material and Nano-diamonds and Graphene Oxide as nano-reinforcement material to make PPS composites. The varying mechanical and tribological behaviour of PPS composites with different weight percentage of reinforcement materials was investigated. The optimum composition of the reinforcement materials was identified, which resulted in significant improvement in mechanical and tribological properties of the base material.
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Bunpot, Mai-Ngam. "Strength prediction in short fibre-reinforced thermoplastics". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326535.
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Laurencin, Tanguy. "Étude de la rhéologie des suspensions de fibres non-newtoniennes par imagerie et simulation numérique 3D à l'échelle des fibres". Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI013/document.
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Ce travail porte sur la mise en forme des matériaux composites à matrice polymère renforcée par des fibres courtes dont les performances physiques et mécaniques sont directement reliées à la distribution spatiale et à l’orientation des renforts employés. Il se focalise sur l’étude des mécanismes de déformation se produisant au cours de l’écoulement de ces systèmes qui se comportent comme des suspensions de fibres non-newtoniennes. Le problème est abordé par une procédure originale combinant images 3D acquises en temps réel et simulations numériques avancées, réalisées à l’échelle des fibres. Dans le premier cas, des suspensions modèles avec fluide suspensif non-newtonien ont été déformées en compression dans des conditions confinées dans un microtomographe à rayons X synchrotron. Cette technique a permis l’acquisition en temps réel de clichés 3D à forte résolution spatiale de l’écoulement des suspensions. Dans le deuxième cas, un code de calculs éléments finis 3D a été utilisé, celui-ci étant capable de décrire finement des objets immergés dans des fluides non-newtoniens, par des level-sets et des techniques de remaillage anisotrope. La pertinence des simulations numériques dans les régimes de concentration dilués à semi-dilués a été jaugée par une comparaison expériences-simulations avancée.De là, dans le régime de concentration dilué, nous montrons que le confinement de l’écoulement et le comportement rhéofluidifiant du fluide suspensif ont une influence mineure sur la cinématique des fibres, si ces dernières sont suffisamment éloignées des plateaux de compression. Si ce prérequis n’est pas respecté, l’effet du confinement devient important. Des modifications au modèle heuristique d’haltère de la littérature ont été proposées pour corriger la cinématique de fibres. Dans le régime semi-dilué, des déviations de la cinématique de fibres sont également observées au cœur des suspensions. Ces déviations sont principalement liées aux interactions hydrodynamiques entre fibres suffisamment voisines. La cinématique des fibres prédite par le modèle de Jeffery et les approximations de champ affine sont mises en défaut. Dans le régime concentré, si l’évolution de l’orientation globale de la suspension est étonnamment bien décrite par l’équation de Jeffery, de très importantes fluctuations des champs de translation et de rotation des fibres sont observées à l’échelle des fibres. Celles-ci sont induites par les nombreux contacts entre fibres qui peuvent par ailleurs être correctement prédits par le modèle de tubeThis study focuses on the processing of short fibre-reinforced polymer composites. The physical and mechanical properties of these materials are mainly affected by the position and orientation distribution of fibres induced during their forming. Thus, we analysed the flow-induced micro-mechanisms that arose at the fibre scale during the forming stage of these complex systems which behave as non-Newtonian fibre suspensions. For that purpose, an original approach was developed by combining 3D imaging technique and direct numerical simulation, both performed at the fibre scale. Hence, several model fibre suspensions with a non-Newtonian suspending fluid and with a concentration regime that ranged from dilute to concentrated were prepared . They were subjected to confined lubricated compression loadings using a rheometer mounted on a synchrotron X-ray microtomograph. Thanks to very short scanning times, 3D images of the evolving fibrous microstructures at high spatial resolution were recorded in real-time. These experiments were also simulated using a dedicated Finite Element library enabling an accurate description of fibre kinematics in complex suspending fluids thanks to high performance computation, level sets and adaptive anisotropic meshing. The efficiency of the numerical simulation from the dilute to semi-dilute concentration regimes was assessed through experimental and numerical comparisons.Then, we showed that the confinement effect and the non-Newtonian rheology of the suspending fluid had a weak effect on the fibre kinematics, if the fibres were sufficiently far from the compression platens, typically the fibre-platen distance should be larger than twice the fibre diameter. Otherwise, confinement effects occurred. Some extensions of the dumbbell model were proposed to correct the fibre kinematics in this flow conditions. In semi-dilute concentration, deviations of the fibre kinematics compared to the Jeffery’s predictions were also observed and related to hydrodynamic interactions between fibres. In this case, the predictions of Jeffery’s model and the related assumption of affine fibre motions are less relevant. In the concentrated regime, even if the overall orientation of fibre suspension could be astonishingly well described by using the Jeffery’s model, strong fluctuations on each fibre motion and rotation were observed. These deviations were induced by the numerous fibre-fibre contacts, which could be correctly predicted by the tube model
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Hofmann, John. "Extension of the Method of Ellipses to Determining the Orientation of Long, Semi-flexible Fibers in Model 2- and 3-dimensional Geometries". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23921.
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The use of fiber-reinforced polymer composites formed via injection molding is of increasing interest due to their superior mechanical properties as compared to those of the polymer matrix alone. These mechanical properties, however, are strongly dependent on the fiber length and orientation distributions within a molded part. As such, there is a need to understand and model the orientation evolution of chopped fibers in flow in order to accurately simulate the final fiber orientation distribution within injection molded parts. As a result of this, accurate and reliable experimental measurement of fiber orientation is needed.
Within this research, the application and validity of the Method of Ellipses for determining the orientation of long, semi-flexible glass fibers within injection molded composites has been investigated. A fiber suspension with an average length of approximately 3.9 mm was the focus of this study and assumed to be representative of commercial distributions. A novel method to quantify fiber curvature was developed and utilized to show that flexibility in center-gated disc and the end-gated plaque samples was minimal on average for the selected fiber length distribution. Thus, it was determined that the Method of Ellipses was applicable when utilized to obtain reliable orientation data for the selected long glass fiber suspension and within the chosen geometries that exhibit 1-, 2-, and 3-dimensional velocity fields. However, a modified image analysis width was found to be necessary in regions of highly aligned fibers, due to the increase in ellipse size and the need to reduce the number of partial objects and thus minimize error. This allowed for a direct comparison of the experimental orientation behavior of short and long glass fibers within the center-gated disc and the end-gated plaque, as well as the effect of the orientation distributions on the global modulus of the part.Ph. D.
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Shipton, Paul David. "The compounding of short fibre reinforced thermoplastic composites". Thesis, Brunel University, 1988. http://bura.brunel.ac.uk/handle/2438/5788.
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It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique.
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Diao, Hele. "Carbon fibre reinforced polymer composites with enhanced ductility". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44273.
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Carbon fibre reinforced polymers (CFRPs) have high strength and stiffness, low density, long fatigue life in the fibre direction and good corrosion resistance. Nowadays, CFRPs are been used in aeronautics, wind turbine blades, sports goods and civil industry. However, one fundamental limitation of CFRPs is their brittleness (low ductility): CFRPs fail catastrophically at a relatively low strain (1.5% to 1.8%) under the tension with little warning or residual load-carrying capacity. To overcome this weakness, there is considerable interest to enhance the ductility of CFRPs exhibiting increased failure strains under tension and more progressive, graceful failure modes. In this work, three different methods were developed to improve the ductility of unidirectional (UD) CFRPs. The first method was to introduce fibre waviness into UD composites. The fibre alignment angles of the resulting composites and control composites were assessed and it was found that fibre waviness in UD composite did result in a stepwise tensile failure mode and an enhanced strain to failure. The second method was using an air-assisted fibre tow spreading and commingling technology to manufacture continuous intermingled carbon fibre/glass fibre hybrid tows. After defining and quantifying the degree of hybridisation (at the filament level) of two carbon fibre/glass fibre hybrid tows, the one with the higher degree of hybridisation was selected to manufacture intermingled UD hybrid composites. It was found that hybridising of continuous glass and carbon fibres resulted in the composites with an increased failure strain. Moreover, these hybrid composites failed more gradually. The final method investigated for introducing ductility was the introduction of ply cuts into PEEK interleaved UD carbon fibre/PEEK composites, which were manufactured by compression moulding. The resulting cut-ply interleaved carbon fibre/PEEK composite possessed a non-linear tensile stress-strain curve and ductility strain of 0.4%, which is due to shearing of the PEEK interleaves in the overlap regions between the cut carbon fibre plies.
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Hill, Paul Spencer. "The environmental degradation of fibre reinforced pultruded polymer composites". Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240930.
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Haji, Kamis Haji Elmi Bin. "Three dimensional analysis of fibre reinforced polymer laminated composites". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/three-dimensional-analysis-of-fibre-reinforced-polymer-laminated-composites(0ba2ceae-129c-4d09-bdbd-de110e7b3617).html.
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The thesis presents the structural behaviour of fibre reinforced polymer (FRP) laminated composites based on 3D elasticity formulation and finite element modeling using Abaqus. This investigation into the performance of the laminate included subjecting it to various parameters i.e. different boundary conditions, material properties and loading conditions to examine the structural responses of deformation and stress. Both analytical and numerical investigations were performed to determine the stress and displacement distributions at any point of the laminates. Other investigative work undertaken in this study includes the numerical analysis of the effect of flexural deformation of the FRP strengthened RC slab. The formulation of 3D elasticity and enforced boundary conditions were applied to establish the state equation of the laminated composites. Transfer matrix and recursive solutions were then used to produce analytical solutions which satisfied all the boundary conditions throughout all the layers of the composites. These analytical solutions were then compared with numerical analysis through one of the commercial finite element analysis programs, Abaqus. Out of wide variety of element types available in the Abaqus element library, shells and solids elements are chosen to model the composites. From these FEM results, comparison can be made to the solution obtained from the analytical. The novel work and results presented in this thesis are the analysis of fully clamped laminated composite plates. The breakthrough results of fully clamped laminated composite plate can be used as a benchmark for further investigation. These analytical solutions were verified with FEM solutions which showed that only the solid element (C3D20) exhibited close results to the exact solutions. However, FEM gave poor results on the transverse shear stresses particularly at the boundary edges. As an application of the work above, it is noticed that the FEM results for the FRP strengthened RC slab, agreed well with the experimental work conducted in the laboratory. The flexural capacity of the RC slab showed significant increase, both at service and ultimate limit states, after FRP sheets were applied at the bottom surface of the slab. Given the established and developed programming codes, exact solutions of deflection and stresses can be determined for any reduced material properties, boundary and loading conditions, using Mathematica.
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Stanford-Beale, Christopher Andrew. "High temperature deformation of short fibre reinforced aluminium based composites". Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315905.
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Pearce, Neil Robert Lewarne. "Process-property-fabric architecture relationships in fibre-reinforced composites". Thesis, University of Plymouth, 2001. http://hdl.handle.net/10026.1/2596.
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The use of fibre-reinforced polymer matrix composite materials is growing at a faster rate than GDP in many countries. An improved understanding of their processing and mechanical behaviour would extend the potential applications of these materials. For unidirectional composites, it is predicted that localised absence of fibres is related to longitudinal compression failure. The use of woven reinforcements permits more effective manufacture than for unidirectional fibres. It has been demonstrated experimentally that compression strengths of woven composites are reduced when fibres are clustered. Summerscales predicted that clustering of fibres would increase the permeability of the reinforcement and hence expedite the processing of these materials. Commercial fabrics are available which employ this concept using flow-enhancing bound tows. The net effect of clustering fibres is to enhance processability whilst reducing the mechanical properties. The effects reported above were qualitative correlations. Gross differences in the appearance of laminate sections are apparent for different weave styles. For the quantification of subtle changes in fabric architecture, the use of automated image analysis is essential. Griffm used Voronoi tessellation to measure the microstructures of composites made using flow-enhancing tows. The data was presented as histograms with no single parameter to quantify microstructure. This thesis describes the use of automated image analysis for the measurement of the microstructures of woven fibre-reinforced composites, and pioneers the use of fractal dimensions as a single parameter for their quantification. It further considers the process-property- structure relationships for commercial and experimental fabric reinforcements in an attempt to resolve the processing versus properties dilemma. A new flow-enhancement concept has been developed which has a reduced impact on laminate mechanical properties.
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Russell-Floyd, Richard S. "Acoustic emission and acousto-ultrasonics on aromatic polymer composites". Thesis, University of Bath, 1991. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293342.
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Scott, David William. "Short- and long-term behavior of axially compressed slender doubly symmetric fiber-reinforced polymeric composite members". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19276.
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Okoli, Okenwa Obinna Ifeanyichukwu-Izejiora. "Experimental determination of transient dynamic response of fibre reinforced polymer composites". Thesis, University of Warwick, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273471.
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Tann, David Bohua. "Retrofitting of mechanically degraded concrete structures using fibre reinforced polymer composites". Thesis, University of South Wales, 2001. https://pure.southwales.ac.uk/en/studentthesis/retrofitting-of-mechanically-degraded-concrete-structures-using-fibre-reinforced-polymer-composites(efce1110-34e1-457d-8ec5-3ef5da026018).html.
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This research involves the study of the short term loaded behaviour of mechanically degraded reinforced concrete (RC) flexural elements, which are strengthened with fibre reinforced polymer (FRP) composites. The two main objectives have been: (a) to conduct a series of realistic tests, the results of which would be used to establish the design criteria, and (b) to carry out analytical modelling and hence develop a set of suitable design equations. It is expected that this work will contribute towards the establishment of definitive design guidelines for the strengthening of reinforced concrete structures using advanced fibre composites. The experimental study concentrated on the laboratory testing of 30 simply supported, and 4 two-span continuous full size RC beams, which were strengthened by either FRP plates or fabric sheets. The failure modes of these beams, at ultimate limit state, were examined and the influencing factors were identified. A premature and extremely brittle collapse mechanism was found to be the predominant type of failure for beams strengthened with a large area of FRP composites. A modified semi-empirical approach was presented for predicting the failure load of such over strengthened beams. Despite the lack of ductility in fibre composites, it was found that the FRP strengthened members would exhibit acceptable ductile characteristics, if they were designed to be under strengthened. A new design-based methodology for quantifying the deformability of FRP strengthened elements was proposed, and its difference to the conventional concept of ductility was discussed. The available techniques for ductility evaluation of FRP strengthened concrete members were reviewed and a suitable method was recommended for determining ductility level of FRP strengthened members. A non-linear material based analytical model was developed to simulate the flexural behaviour of the strengthened and control beams, the results were seen to match very well. The parametric study provided an insight into the effects of various factors including the mechanical properties and cross sectional area of FRP composites, on the failure modes and ductility characteristics of the strengthened beams. Based on the findings of the experimental and analytical studies, design equations in the BS 8110 format were developed, and design case studies have been carried out. It was concluded that fibre composites could effectively and safely strengthen mechanically degraded reinforced concrete structures if appropriately designed. The modes of failure and the degree of performance enhancement of FRP strengthened beams depend largely on the composite material properties as well as the original strength and stiffness of the RC structure. If the FRP strengthened elements were designed to be under-strengthened, then the premature and brittle failure mode could be prevented and ductile failure mode could be achieved. It was also found that existing steel reinforcement would always yield before the FRP composite reached the ultimate strength. Furthermore, a critical reinforcement ratio, above which FRP strengthening should not be carried out, was defined. It was concluded that FRP strengthening is most suitable for reinforced concrete floor slabs, bridge decks, flanged beams and other relatively lightly reinforced elements. The study also revealed that to avoid a brittle concrete failure, existing doubly reinforced members should not be strengthened by FRP composites.
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Garekani, Amir Hossein Afrasiabi. "Numerical modeling of orthogonal cutting of carbon fibre reinforced polymer composites". Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58401.
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The focus of this study is on the orthogonal cutting of fibre reinforced composites. A thorough review of the literature is presented in both experimental and numerical work that has thus far been conducted. It is found that in orthogonal cutting of composites, cutting forces, chip formation mechanism and the extent of damage below the cutting plane are highly dependent on the fibre orientation. With fibre orientation increasing from 0° to 90°, cutting forces tend to increase and chips become more dust-like.
Two modeling approaches are most commonly adopted for the prediction of force and chip formation, namely the micro-mechanical and the macro-mechanical approach; in the former, the fibre and the matrix are modeled as separate phases and their interface is defined by a traction-separation law. In the latter, the composite is represented by an anisotropic equivalent homogeneous material. It is shown that the numerical predictions are in good agreement with experimental results. With ABAQUS being the most commonly used tool for modeling of composite orthogonal cutting, a two-dimensional macro-mechanical model for cutting of CFRP was created in ABAQUS using Hashin’s damage model. The cutting forces were predicted for fibre orientations of 0°, 30°, 45°, 60°, 90° and 135°. Good prediction of cutting forces with the available experimental data in the literature was obtained. The model however fails to predict the complete chip formation mechanism due to limitations in the material model. A similar model was developed in LS-Dyna using MAT_054 for composites. The cutting forces were found to be sensitive to the damage input parameters, mainly the strain-to-failure of the elements. However, the complete chip formation and chip release was captured in this model which correlated well with the experimental observations.
It is suggested that for improved modeling capability, better understanding of the damage behaviour of FRP, especially at the micro-scale is needed. Also, the existing work is found to be limited to orthogonal cutting and drilling separately; it is however worth looking into both items in one study and linking the two processes through a geometric transformation which is the established framework in metal machining.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Wong, Rita Sheung Ying. "Towards modelling of reinforced concrete members with externally-bonded fibre reinforced polymer, FRP, composites". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62958.pdf.
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Lau, Shuk-lei. "Rehabilitation of reinforced concrete beam-column joints using glass fibre reinforced polymer sheets". Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B32001630.
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Wilkinson, Simon B. "Residual stress and through depth modulus properties of short fibre reinforced composites". Thesis, University of Newcastle Upon Tyne, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308979.
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Lau, Shuk-lei, e 劉淑妮. "Rehabilitation of reinforced concrete beam-column joints using glass fibre reinforced polymer sheets". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B32001630.
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Hughes, John Mark. "On the mechanical properties of bast fibre reinforced thermosetting polymer matrix composites". Thesis, Bangor University, 2000. https://research.bangor.ac.uk/portal/en/theses/on-the-mechanical-properties-of-bast-fibre-reinforced-thermosetting-polymer-matrix-composites(0fdca4e4-8d50-4a16-afd0-37d78cfb8a64).html.
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Bast fibre reinforced, unsaturated polyester matrix composites were fabricated using non-woven mats of hemp or jute fibre as reinforcement. Composites were also prepared using chopped strand mat glass fibre as reinforcement. The short-term mechanical properties of the laminates were assessed. It was observed that at equivalent fibre volume fractions the stiffness of the glass fibre reinforced material only marginally exceeded that of the two, unmodified bast fibre, reinforced materials. At equivalent fibre volume fractions, however, the strength of the glass fibre reinforced composite was found to be significantly greater than that of the bast fibre reinforced materials. It was noted that in the bast fibre reinforced composites, the onset of non-linear behaviour occurred at relatively low applied stresses. Work of fracture in static three-point flexure and Charpy impact strength tests, indicated that the toughness of the plant fibre reinforced material was as much as an order of magnitude less than that of the glass fibre reinforced material. Fracture mechanics techniques were used to further quantify toughness and confirmed this to be so. Furthermore, these tests indicated that the microstructure of the bast fibre reinforced material should be examined more closely. Microscopy conducted on the fibres revealed that these were often subject to extensive micro-compressive damage. It was postulated that uneven fibre straining characteristics could lead to compromised interfacial properties, which might in turn detrimentally affect the macroscopic behaviour of the composite. A technique known as half fringe photoelasticity was used to investigate the stress-field in the matrix surrounding the fibre defects. It was observed that not only did concentrations of stress occur in the vicinity of these, but also that the shear stress distribution along the length of the fibre was interrupted by the presence of the defects. The implications of fibre defects upon composite properties are discussed.
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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.
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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).
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Scudder, Lawrence Philip. "Characteristics and testing of carbon fibre reinforced polymer composites using laser generated ultrasound". Thesis, University of Warwick, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283488.
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Prickett, Andrew C. "Intralaminar cracking of fibre reinforced composites : a fracture mechanics and ToF-SIMS study". Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/798035/.
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Bolimowski, Patryk Adam. "Microcapsule-based self-healing in carbon fibre reinforced polymer composites : towards design and application". Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.705473.
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Curnick, Paul. "An investigation on the machining of multidirectional glass and carbon fibre reinforced polymer composites". Thesis, University of Wales Trinity Saint David, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683075.
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Lee, Tuan Kuan 1976. "Shear strength of reinforced concrete T-beams strengthened using carbon fibre reinforced polymer (CFRP) laminates". Monash University, Dept. of Civil Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/6647.
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Alisawi, Mazin Yaseen. "Effect of indenter size on damage of carbon fibre-reinforced polymer composites under impact loads". Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/40675.
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The applications of composite materials have been increasing significantly in recent decades. The major effect limiting the use composite materials is the lack of understanding of their response and their structural integrity under dynamic loads. Delamination under dynamic load is particularly recognised as the most critical damage process in laminated composites. The objective of this thesis is to experimentally and numerically investigate the fundamental phenomena associated with delamination. This is important develop a further knowledge of the response and damage mechanisms of composite materials under low-velocity impact and static load. Various parameters that affect the delamination of composite material have been studied in this work, including the diameter of the hemi-spherical indenter and the type of load at the same energy level. The difference between the shape and size of delamination area between different plies has been examined using x-ray commutated tomography. Cohesive elements have been used in the ABAQUS finite element modelling to determine failure criteria that correspond with the experimental work. It is found that the main delamination area occurs on the tension side of laminates subjected to bending, and that it also depends on the difference in angle between adjacent plies. The effect of the indenter radius to thickness of plate ratio on the relation between force and damage evolution have been studied numerically for different thickness of plate. This analytical study was repeated for both isotropic and anisotropic materials to show the effect of material type on the previous relation. It is found that the initiation of the delamination can be assessed from the existence of a delamination threshold load in a force-displacement curve under quasi-static load or in a displacement-time curve under dynamic load.
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Emeanuwa, P. C. "Structure and properties of internal weld lines in injection moulded thermoplastics and short fibre reinforced composites". Thesis, University of East Anglia, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376356.
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Chandrasekaran, Swetha [Verfasser], e Karl [Akademischer Betreuer] Schulte. "Development of nano-particle modified polymer matrices for improved fibre reinforced composites / Swetha Chandrasekaran. Betreuer: Karl Schulte". Hamburg-Harburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2014. http://d-nb.info/1059804107/34.
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Ellis, Keith. "The use of an interphase to improve the transverse properties of unidirectional glass fibre reinforced polymer composites". Thesis, University of Bath, 1990. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760611.
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Vasiukov, Dmytro. "Damage modeling of fibre reinforced polymer composite materials under cyclic loadings by a simplified approach". Thesis, Lille 1, 2013. http://www.theses.fr/2013LIL10043.
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Ce travail de thèse présente le développement de modèles numériques pour la modélisation de l’endommagement des matériaux composites à fibres continues et matrice polymère. L’objectif est de fournir des outils numériques efficaces pour prédire l’endommagement sous chargement monotone et cyclique. Deux modèles ont été développés, un basé sur une approche multi-échelle d’homogénéisation et l’autre défini dans le cadre de la mécanique de l’endommagement. Ce dernier est utilisé dans une nouvelle approche pour prédire la durée de vie des matériaux composites. La première approche est une méthode multi-échelle afin d’étudier l’influence de l’endommagement à l’échelle microscopique sur le comportement macroscopique du composite. Le comportement macroscopique est déterminé par homogénéisation d’une cellule unitaire. L’approche est appliquée au cas d’un composite unidirectionnel afin d’étudier l’influence de l’endommagement de la matrice. Pour contourner les difficultés d’une approche multi-échelle, un modèle mésoscopique basé sur le couplage entre la plasticité et l’endommagement est proposé. Le modèle est validé et confronté à d’autres modèles ainsi qu’à des résultats expérimentaux. La dernière contribution est le développement d’une nouvelle approche pour la prédiction de la durée de vie des matériaux composites s’appuyant sur l’hypothèse que le matériau atteint un état stabilisé d’endommagement. Cette hypothèse permet d’utiliser l’analyse simplifiée pour prédire les états stabilisés. Le modèle de fatigue proposé est une loi puissance entre le nombre de cycles et les forces thermodynamiques associées à l’endommagement. L’approche est validée à partir de résultats expérimentauxA numerical framework for the modeling of the damage in fibre reinforced polymer composite materials has been developped. The objectives were to provide efficient numerical tools to predict the damage under static and cyclic loading. Two different models were proposed, one based on a fully computational multi-scale homogenization technique and a second one under the hypothesis of the meso-mechanics associated with a coupled damage-plastic constitutive model. The latter has been used in a new approach developped to predict the life of composite structures. As a first approach, a multi-scale application has been developed to better understand the influence of the damages occuring at lower scales on the macroscopic response. The macroscopic is defined by homogenization of a unit cell. The scheme is used to analyze the effect of the matrix damage on the material response in the case of unidirectional composites. To overcome the difficulties of the multi-scale approach, a meso-scale phenomenological model based on the coupled plasticity with continuous damage mechanics is proposed. All comparisons of the simulation with experiments and other models have shown good agreements. The third contribution is the development of a new approach to predict the life of composite materials based on the assumption that the material reaches a damage stabilized state during his life. This assumption makes it possible to use the simplified analysis. The life of the material is considered depending on the level of the thermodynamical forces associated with damage at the stabilized state by the use of a power law. Good agreements are obtained with experimental results
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Nguyen, Phi Long. "Experimental and numerical study on thermo-mechanical behaviour of carbon fibre reinforced polymer and structures reinforced with CFRP". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1130/document.
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Le polymère renforcé de fibres de carbone (CFRP) est l'une des solutions courantes pour réparer/renforcer/ fortifier/ rétrofiter les structures en génie civil en raison de ses avantages dans les propriétésmécaniques, la durabilité et la maniabilité. Cependant, des problèmes d'incendie récents ont soulevédes inquiétudes quant à la performance au feu du CFRP et des structures renforcées par CFRP. Dansla littérature, il existe plusieurs études sur l'évolution de la performance mécanique de CFRP et desstructures renforcées par CFRP pendant ou après l'exposition à différents niveaux de température quisont proches des températures obtenus durant un feu. Cependant, les résultats sont dispersés en raisonde la diversité des matériaux utilisés, de la différence dans les protocoles d'essai et de la limitation del'installation d'essai pour une utilisation à température élevée. Des études analytiques et numériquessont également menées avec une étude paramétrique pour observer, améliorer et proposer desrecommandations pour les directives de conception. Cependant, le manque de données expérimentalesa une influence significative sur applicabilité des résultats disponibles.Cette recherche caractérise les comportements des CFRP et de la structure renforcée avec du matériauCFRP dans trois conditions distinctes concernant la température élevée et la charge mécanique quisont proches des différents cas d'application au feu. Les méthodes expérimentales et numériques sontutilisées pour mener cette recherche afin d'étudier plus en détail l'état de chaque matériau au cours desétudes de cas. En particulier, l'essai résiduel est utilisé pour étudier la performance mécanique desspécimens refroidis après exposition à température élevée en respectant l'évaluation du comportementrésiduel des structures renforcées en CFRP en situation post-incendie à des fins de réparation /renforcement. Deux essais thermomécaniques sont utilisés pour étudier la performance mécanique deséchantillons à différentes températures élevées et leur performance thermique à différents étatsmécaniques en respectant la situation d'incendie pour la prédiction et la conception. Les deux dernierscas portent sur l'influence de l'ordre de chargement sur les résultats pour confirmer la validité desdonnées mécaniques expérimentales obtenues à différentes températures lors de l'évaluation de laperformance au feu de la structure renforcée par CFRP où les effets mécaniques et puis les effetsthermiques sont combinés.Dans la première partie expérimentale, 86 essais sur deux types de CFRP (un préfabriqué en usine etun fabriqué manuellement en laboratoire) ont été étudiés dans la plage de température de 20°C à712°C. La performance du matériau CFRP est généralement réduite lorsque la température augmente.Les résistances thermomécaniques et résiduelles du P-CFRP diminuent graduellement de 20°C à700°C, tandis que le module de Young varie de moins de 10% de 20°C à 400°C et ensuite diminuesignificativement à 600°C. La performance thermomécanique identifiée de CFRP a été inférieure quesa performance résiduelle, en particulier à une température supérieure à 400°C. En outre, latempérature élevée et la charge mécanique sont expérimentalement pertinentes et l'ordre dechargement a donc un faible effet sur les performances du matériau dans des conditionsthermomécaniques. Un nouveau modèle analytique, proposé pour l'évolution de la résistance ultimethermomécanique en fonction de la température, a montré sa capacité à s'adapter à deux CFRP étudiéset à ceux testés dans des conditions thermomécaniques similaires dans la littérature [etc...]Carbon fibre reinforced polymer (CFRP) is one of common solutions in repairing / reinforcing/strengthening/ retrofitting structures in civil engineering due to its advantages in mechanicalproperties, durability and workability. However, recent issues have raised concerns for fireperformance of CFRP and CFRP reinforced structures. Throughout the literature, there are severalinvestigations on the evolution of mechanical performance of CFRP and CFRP reinforced structuresduring or after exposing to different levels of temperature which are close to temperatures obtainedduring a fire. However, the results are scatter due to the diversity of materials used, the difference intest protocols, and limitation in test facility for elevated temperature use. Analytical and numericalstudies are also conducted with parametric investigation to observe, improve, and proposerecommendations for design guideline. Additionally, missing gap in experimental data has asignificant influence on the applicability of the available results.This research characterizes the behaviours of CFRPs and of concrete structure reinforced with CFRPmaterial under three separated conditions concerning elevated temperature and mechanical loadingthat are close to different cases of fire application. The experimental and numerical methods used inthis research are to further investigate the status of each material during the case studies. Particularly,residual test is used to study the mechanical performance of specimens cooled after exposing toelevated temperature respecting the evaluation of the remained behaviour of CFRP reinforcedstructures at post-fire situation for repairing/ retrofitting purpose. Two thermo-mechanical tests areused to study the mechanical performance of specimens at different elevated temperatures and theirthermal performance at different mechanical statuses respecting the fire situation for predicting anddesigning purpose. The two final cases focus on the influence of loading order on the results toconfirm the validity of experimental mechanical data obtained at different temperatures whenapplying for evaluating the fire performance of CFRP reinforced structure where mechanical effectsand then temperature effects are combined.In the first experimental part, 86 tests on two types of CFRP (one pre-fabricated in factory and onemanually fabricated in laboratory) were studied in the temperature range from 20°C to 712°C. Theperformance of CFRP material is generally reduced as the temperature increases. The thermomechanicaland residual ultimate strengths of P-CFRP gradually decrease from 20°C to 700°C, whileits Young’s modulus varies less than 10% from 20°C to 400°C and then significantly decreases at600°C. The identified thermo-mechanical performance of CFRP was lower than its residualperformance, especially at temperature beyond 400°C. Furthermore, the elevated temperature andmechanical load are experimentally shown to be relevant and thus the loading order has a small effecton the material performance under thermo-mechanical conditions. A new analytical model, proposedfor the evolution of thermo-mechanical ultimate strength in function of temperature, has shown theability to fit with two studied CFRPs and with those tested under similar thermo-mechanical conditionin the literature [etc...]
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Bettelli, Mercedes Amelia. "Effect of Induction-Heat Post-Curing on Residual Stresses in Fast-Curing Carbon Fibre Reinforced Composites". Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80527.
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Manufacturing induced shape distortions is a common problem for composite materials. Due to the non-isotropic nature of carbon fibre reinforced polymers (CFRP) unavoidable deformations occur during part production. During fabrication of polymer composites, the material obtains its final shape at elevated temperatures. The curing process involves a transition from the liquid state to the solid, glassy state, allowing bonding between fibres and matrix. As the material cools the mismatch in thermal expansion coefficients and cure shrinkage obtained during the matrix polymerization leads to residual stresses on the mechanical level within composite part. There is a great interest from the aircraft and automotive industries, to increase the ability to understand development of shape distortions and residual stresses during the cure, since these deformations often lead to dissatisfaction of tolerances and it is essential to predict the deformations beforehand in order to compensate time and cost. In this context, a study of residual stresses during the curing process of thermosetting resin composites is presented. A methodology is proposed for predicting the formation and development of manufacturing- induced residual stresses. The present project reports on a comprehensive experimental study on the dependency of different short curing cycles on the build-up of residual stresses in a carbon fibre/fast-curing epoxy system and evaluate of post-curing methods through induction heating and oven post-curing with unidirectional [904] and unsymmetrical [9020] laminates. It includes characterization in thermo-elastic properties and degree-of-cure of the material by Thermal bending test, thermal expansion test, mechanical tensile test and Differential Scanning Calorimetry (DSC) in non-post-cured and post-cured laminates. The results showed slight variation in the thermal properties and not effect in the mechanical properties at different cure and post-curing conditions. Analytical data by Laminate Analysis program validated the experimental thermo-elastic data with analytical simulations. In addition, it is shown improvements in the temperature distributions in the post-curing by induction heating with different experimental set-ups, however, oven post-curing showed a more systematic system, higher heat efficient a low cure temperature, with more consistent mechanisms of shape distortions and residual stresses compared to induction heating. These findings are relevant for the future development of prediction methods for process induced deformations of Fast Curing Epoxy Resins (FCER).
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Angelidis, Nikolaos. "Damage sensing in CFRP composites using electrical potential techniques". Thesis, Cranfield University, 2004. http://dspace.lib.cranfield.ac.uk/handle/1826/127.
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This Thesis investigates the damage sensing capabilities of the electrical potential measurement technique in carbon fibre reinforced polymer composites. Impact damage was introduced in multidirectional laminates and its effect on potential distribution studied. It was found that delaminations and fibre breakages within the laminate can be detected and located by measuring potential changes on the external composite surface. The extent and size of potential changes were significantly affected by the position of the current electrodes in relation to the potential measurement probes. A numerical model was developed investigating the effect of different size delaminations, located in various positions within the lamina, on electrical potential distributions on the external ply, and a quantitative analysis of the numerical results is presented. The numerical simulations demonstrated that the measured potential changes on the external ply were in proportion to the delamination size. The numerical and experimental results were compared and the optimum configuration of current electrodes and potential probes for damage detection selected. The response of electrical potential to mechanical strain, in unidirectional and multidirectional samples was also investigated. It was found that the conductive medium, used for introducing the current, defines the piezo-resistance performance of the composite. A finite element model was developed able to predict the effect of inhomogeneous current introduction in unidirectional specimens on electrical potential and piezo-resistance. The effects of temperature and water absorption on potential measurements were also presented.
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Dennis, Grant. "Development of injection moulded self-lubricating short-fibre reinforced composites for use as plain bearing liner materials in aerospace applications". Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/97497/.
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This thesis is concerned with the development of short fibre and particle reinforced polymer composites for plain bearing liners for aerospace applications. Detailed experimental investigations of the tribological and mechanical characteristics of these materials has been completed. The thesis culminates with the identification of two possible materials that have the potential for direct injection moulding of a bearing liner. 1. Developing an Injection moulding process A thorough understanding of the capability of injection moulding PEEK composites was achieved through experimental investigation. Knowledge of the impact of varying injection moulding parameters on the final material was identified. 2. Friction and wear testing A bespoke test rig, in line with aerospace standards, was developed to allow the investigation of composite materials. Testing was conducted at room and high temperatures. A full analysis of the impact of the selected bulk material, short fibres and fillers was completed. Key parameters such as coefficient of friction, wear and fatigue life were identified. Further testing using optical microscopy was completed to enhance the understanding of the wear process and to support the findings of the detailed friction and wear testing program. 3. Mechanical testing The mechanical performance of PEEK materials was investigated through experimental analysis and available data. Again the impact of differing ratios of fillers and short fibres was determined. In addition static testing was used to investigate instantaneous strain and creep of selected materials. 4. Development of PEEK blends A final testing programme of two identified blends was completed that aimed to optimise for wear, friction and mechanical performance. The materials selected ware successful in matching aspects of the established design criteria but further work on the blends needs to be completed. However one of the selected materials is being proposed for an in service aerospace application.
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Zhang, Zhong Yi. "Visualisation and quantification of the defects in glass-fibre reinforced polymer composite materials using electronic speckle pattern interferometry". Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/22078.
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Non-destructive testing (NDT) of glass-fibre reinforced polyester (GRP) composite materials has been becoming increasingly important due to their wide applications in engineering components and structures. Electronic Speckle Pattern Interferometry (ESPI) has promising potential in this context because it is a non-contact, whole-field and real-time measurement system. This potential has never been fully exploited and there is only limited knowledge and understanding available in this area. This reality constrains the wide popularity and acceptance of ESPI as a novel NDT technique. Therefore it is of considerable importance to develop an understanding of the capability of ESPI with respect to damage evaluation in GRP composite materials. The research described in this thesis is concerned with an investigation into the applicability of ESPI in the NDT of GRP composite materials. Firstly, a study was carried out to determine excitation techniques in terms of practicality and effectiveness in the ESPI system. Three categories of defects were artificially introduced in GRP composite materials, namely holes, cracks and delaminations each with different geometrical features. ESPI was then employed to evaluate the three kinds of defects individually. It has been found that cracks and holes on back surfaces can be defined when the technique is used in conjunction with thermal excitation. Internal Temperature Differential (ITD) induced fringe patterns were more efficient than External Thermal Source (ETS) induced fringe patterns with regard to detecting the presence of holes and cracks. In the case of delamination, ESPI was found to be capable of detecting the damage when used in combination with mechanical excitation originating from a force transducer hammer. The geometrical features and magnitudes of delaminations were also established as being quantifiable. The validation of ESPI as an NDT technique was carried out in an attempt to establish a better understanding of its suitability and have more confidence in its applications. Four damaged specimens were Subjected to ESPI examination in conjunction with visual inspection, ultrasonic C-scan and sectioning techniques. The geometrical features and magnitudes of damage evaluated using ESPI showed a good correlation with those evaluated by conventional techniques. Poor visibility and readability is an inherent problem associated with ESP! due to an overlapping between the noise and signal frequencies. An improvement of image quality is expected in an attempt to achieve a wide acceptance of ESPI as a novel NDT technique. It has also been demonstrated that this problem can be tackled using optical phase stepping techniques in which optical phase data can be extracted from the intensity fringes. A three-frame optical phase stepping technique was employed to produce the "wrapped" and "unwrapped" phase maps which are capable of indicating internal damage with high visibility and clarity. Finally ESPI was practically employed to evaluate damage in GRP composites introduced by quasi-static and dynamic mechanical loading. It was found that ESP! was capable of monitoring the progressive damage development of specimens subjected to incremental flexural loading. The initial elastic response, damage initiation, propagation and ultimate failure of specimens were clearly characterised by the abnormal fringe pattern variations. In a similar manner, ESPI was employed to evaluate the low velocity falling weight impact induced damage. A correlation was established between the magnitude of damage and the impact event parameters as well as the residual flexural properties.
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Gibson, Millan-John. "Fibre Length Distribution and Dispersion during the Injection Moulding Process: An experimental study evaluating fibre length attrition and dispersion during processing of long glass fibre reinforced polymer composites in injection moulding including an evaluation of long glass fibre measurement techniques". Thesis, University of Bradford, 2018. http://hdl.handle.net/10454/17360.
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This project evaluates fibre length dispersion and distribution within the injection moulding process of long glass fibre reinforced polypropylene, sponsored by Autodesk Simulation.
The primary material used in this investigation was a 15 mm long glass fibre reinforced polypropylene consisting of two fibre content levels, 20 wt. % and 40 wt. %.
A review of previous research was compiled in this study to evaluate various glass fibre measurement methods and fibre breakage studies to establish where along the injection moulding process fibre breakage predominantly occurs and which process parameters have the greatest influence on fibre length distribution along the screw.
Based on literature findings, a manual fibre length measurement method was developed and applied in this study and benchmarked against existing commercially available automated software programs and found to be more accurate in obtaining a reliable fibre length distribution within a glass fibre reinforced sample.
Fibre length measurements from the nozzle confirmed that the majority of fibre breakage had already occurred in the screw. Measurements taken along the screw showed a drastic decrease in weighted average glass fibre length from initial pellet form to the end of the metering zone with sudden transitions to lower weighted average values seen at the beginning of the feeding zone and along the compression zone.
Fibre dispersion results from the nozzle and along the screw through the use of a μ-CT scanner showed a complex fibre flow and orientation of fibres with the preservation of fibre clusters being seen all along the injection moulding process but chiefly in the feeding and compression zones of the screw.
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Nciri, Mariem. "Modélisation du comportement des composites à fibres courtes non-alignées en dynamique". Thesis, Valenciennes, 2017. http://www.theses.fr/2017VALE0016/document.
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L’utilisation de composites à matrice thermoplastique renforcée par fibres courtes (TRFC) connait une forte croissance pour une large gamme d’applications industrielles pour des conditions de chargement extrêmes (e.g. pare-chocs d’automobiles). Il est donc indispensable de développer des modèles de comportement des TRFC tenant compte des spécificités du matériau pour une large gamme de vitesse de déformation. Toutefois, le comportement de ces composites est complexe. Cette complexité est due, en premier lieu, au comportement viscoélastique (VE)-viscoplastique (VP) de la matrice avec une sensibilité à la pression. A cela s’ajoute les caractéristiques complexes du renfort en termes de distributions d’orientation des fibres courtes. De plus, le comportement de ces composites est affecté par des phénomènes d’endommagement coexistants (e.g. endommagement de la matrice et décohésion l’interface fibre/matrice). Dans ce travail, un modèle permettant la prise en compte de l’ensemble de ces phénomènes est proposé. Sa formulation est basée sur la décomposition du matériau en un milieu matriciel et plusieurs milieux de fibres, sur la base d’une décomposition additive du potentiel thermodynamique. Cette approche permet une implémentation simplifiée avec une résolution successive (mais non indépendante) du comportement de chaque milieu. Un avantage immédiat est la possibilité de prendre en compte tout type de comportement matriciel et tout type d’orientation. L’interface fibre/matrice, siège de la transmission de l’effort est modélisée par un transfert par cisaillement, avec sur une hypothèse locale d’iso-déformation dans la direction de la fibre. L’endommagement ductile de la matrice est pris en compte par un modèle d’endommagement anisotrope. La dégradation de l’interface fibre/matrice est décrite par un modèle de décohésion initiée en pointe de fibres. Un critère de rupture se basant sur le taux maximal de vide crée par décohésion est enfin introduit. La caractérisation du modèle est basée sur des campagnes d’essais quasi-statiques et dynamiques pour le cas de polypropylène pur et renforcé par fibres courtes de verre, à différents angles de chargement par rapport à la direction d’injection. Ces essais sont complétés par des observations au microtomographe permettant la caractérisation des distributions d’orientation locale des fibres. Des observations au MEB ont enfin permis de constater une éventuelle influence de la vitesse de sollicitation sur les mécanismes d’endommagementShort fibre-reinforced composites are commonly used in a variety of engineering applications, including automotive and aerospace industry. Today, their use is progressively extended to parts possibly subjected to severe loading conditions (e.g. crash...), characterised by high strain rates. Therefore, an efficient modelling that takes into account material’s specificities at a large strain rate range is needed. A constitutive model of viscous behaviour of short-fibre reinforced composites (SFRC) where complex distributions of fibre orientations are taken into account is proposed in this work. The approach considered for the computation of composite macroscopic behavior is based on an additive decomposition of the state potential. The SFRC is assimilated to an assembly of several fibre media embedded in a polymeric matrix medium. One of the main assets of this approach is the possibility to model reinforcement with complex distributions of fibre orientations. Moreover, this decomposition allows the implementation of complex behaviour laws coupled with damage models. The polymeric matrix behaviour is typically strain-rate sensitive, i.e. viscoelastic-viscoplastic. This property has to be taken into account when the modelling of the composite behaviour over a large range of strain rate is intended. Therefore, a viscoelastic constitutive model, based on generalised Maxwell model, and a viscoplastic correction scheme, based on an overstress approach, are implemented for matrix material. The developed constitutive model is then coupled to two damage laws. The first one is introduced in the framework of Continuum Damage Mechanics in order to model the anisotropic ductile damage behaviour of the matrix material. The second one deals with fibre/matrix interfacial degradation through an interfacial debonding law. In order to identify the parameters involved in the present model, experimental tests are performed (case of polypropylene reinforced with short glass fibres). Microcomputed tomography is used for the characterisation of the fibres distribution of orientation. The efficiency of the proposed model is demonstrated by comparisons between numerical and experimental responses in different loading conditions, including dynamic loadings
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Beguinel, Johanna. "Interfacial adhesion in continuous fiber reinforced thermoplastic composites : from micro-scale to macro-scale". Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI051.
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L’intérêt croissant de l’industrie pour les matériaux composites thermoplastiques est motivé par leurs propriétés de thermoformabilité, de recyclabilité ainsi que leurs capacités de cadences de production élevées. Le développement de matériaux pré-imprégnés thermoplastiques, apparus dès les années 1980, s’est imposé comme un moyen efficace de contourner les fortes viscosités des polymères utilisés en réduisant la distance d’écoulement des polymères à l’état « fondu ». Cette étude s’est plus particulièrement intéressée au développement de composites à base de tissus de verre et de carbone pré-imprégnés par un latex acrylique, le TPREG I. En outre, les propriétés mécaniques élevées des matrices acryliques, alliées à un coût relativement faible, en font un matériau intéressant, de nature à permettre un saut technologique dans la conception et la fabrication de composites structuraux à matrice organique. Notre étude s’est concentrée sur la mesure de l’adhésion à l’interface fibre/matrice acrylique car cette région est au cœur du transfert de charge de la matrice vers les fibres et conditionne donc les propriétés mécaniques du composite. Nous avons choisi d’évaluer l’adhésion interfaciale en combinant des analyses de mouilllage avec des tests mécaniques aux échelles microscopique et macroscopique. Le test micromécanique de la microgoutte permet de mettre en évidence le rôle central de l’ensimage des fibres sur la contrainte de cisaillement interfaciale. L’adhésion thermodynamique, déterminé par des mesures d’énergie de surface, est en accord avec la contrainte de cisaillement et souligne l’influence de la polarité de l’ensimage. A l’échelle macroscopique, les essais de traction hors-axe sur composites unidirectionnels permettant de solliciter l’interface en cisaillement quasi-plan ont mis en exergue une corrélation entre les échelles micro et macro. L’étude a également permis de dégager une forte augmentation de l’adhésion grâce à une modification de la matrice acrylique, ainsi qu’une dégradation des propriétés interfaciales à l’échelle micro par vieillissement hydrolytique. Cette étude constitue une première base de données concernant les propriétés interfaciales de composites thermoplastiques acryliques et démontre l’importance d’une étude multi-échelles dans la conception de nouveaux compositesThe present study was initiated by the development of a new processing route, i.e. latex-dip impregnation, for thermoplastic (TP) acrylic semi-finished materials. The composites resulting from thermocompression of TPREG I plies were studied by focusing of interfacial adhesion. Indeed the fiber/matrix interface governs the stress transfer from matrix to fibers. Thus, a multi-scale analysis of acrylic matrix/fiber interfaces was conducted by considering microcomposites, as models for fiber-based composites, and unidirectional (UD)macro-composites. The study displayed various types of sized glass and carbon fibers. On one hand, the correlation between thermodynamic adhesion and practical adhesion, resulting from micromechanical testing, is discussed by highlighting the role of the physico-chemistry of the created interphase. Wetting and thermodynamical adhesion are driven by the polarity of the film former of the sizing. On the other hand, in-plane shear modulus values from off-axis tensile test results on UD composites are consistent with the quantitative analyses of the interfacial shear strength obtained from microcomposites. More specifically, both tests have enabled a differentiation of interface properties based on the fiber sizing nature for glass and carbon fiber-reinforced (micro-)composites. The study of overall mechanical and interface properties of glass and carbon fiber/acrylic composites revealed the need for tailoring interfacial adhesion. Modifications of the matrix led to successful increases of interfacial adhesion in glass fiber/acrylic composites. An additional hygrothermal ageing study evidenced a significant loss of interfacial shear strength at micro-scale which was not observed for UD composites. The results of this study are a first step towards a database of relevant interface properties of structural TP composites. Finally, the analyses of interfaces/phases at different scales demonstrate the importance of a multi-scale approach to tailor the final properties of composite parts
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Qazi, Samiullah. "Comportement mécanique sous sollicitations alternées de voiles béton armé renforcés par matériaux composites". Phd thesis, INSA de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-00961220.
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Les enquêtes récentes sur les séismes ont fait ressortir l'importance des murs en béton armé en tant que partie intégrante des structures. L'évolution des règlements prend en compte ces considérations, par contre le bâti existant doit subir des renforcements dans l'objectif de leur mise en conformité. Dans cette thèse une étude expérimentale faite sur douze murs (six élancés et six courts) renforcés par un collage externe en composite a été conduite. Les murs ont été conçus en étant sous-renforcés à la flexion et cisaillement. Quatre de ces six échantillons ont été renforcés par des bandes de PRFC collées. Deux spécimens, un témoin et un renforcé, ont été soumis à un test de chargement statique et quatre échantillons, l'un témoin et trois rénovés, ont été soumis à des essais de charge cyclique. La discussion et l'analyse des tests incluent la description de la fissuration, l'analyse de la rigidité, de la capacité de charge ultime, de la ductilité.
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VERDEAU, TRUFFIER CAROLINE. "Influence des conditions d'elaboration sur la zone interfaciale de materiaux composites hautes performances a matrice thermoplastique". Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0117.
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Microstructure et proprietesmecaniques de composites unidirectionnelles polyetherethercetone/ fibres carbone, sulfure de polyphenylene/fibres de carbone et polyetherimide/fibre de carbone. Influence de temps rapide, refroidissement lent etc. Essais mecaniques. Cohesion interne. Mise en evidence d'une phase "transcristalline". Modelisation du comportement viscolastique
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Guetta, Brigitte. "Vieillissement hygrothermique de composites a matrice psp : etude cinetique, mecanique et spectroscopique". Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0057.
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Avena-Barthelemy, Anne. "Comportement a long terme de materiaux composites immerges a grande profondeur". Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0049.
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Etude du vieillissement de polymeres renforces ou non de fibres de verre ou de mousses syntactiques immerges dans l'eau sous des pressions de 0 a 300 bars. Adsorption d'eau, proprietes mecaniques, eclatement des microspheres dans les mesures syntactiques
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Blanc, Rémy. "Etude de l'injection des composites polyesters thermodurcissables : relations entre la phase de remplissage des moules et l'orientation du renfort". Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0140.
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Apres presentation du procede zmc, etude de l'orientation des fibres de verre sur 3 geometries de pieces. Etude experimentale du remplissage des moules et de la rheologie du materiau. Modelisation de l'influence de la reticulation et de la pseudoplasticite par une loi rendant compte du comportement non newtonien hereditaire; integration de cette loi dans un modele thermomecanique de remplissage. Calcul de l'orientation des fibres par la theorie de jeffery; resultats montrant l'influence des parametres experimentaux (longueur des fibres, reactivite. . . )
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Trejo, O'Reilly José Antonio. "Synthèse d'agents de couplage, réactions de greffage en surface de fibres cellulosiques et propriétés d'interface fibres-matrices dans des matériaux composites à base de polystyrène". Grenoble INPG, 1997. http://www.theses.fr/1997INPG0019.
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L’objectif principal de ce travail est la modification chimique des fibres cellulosiques, afin d'améliorer leurs propriétés interfaciales lors de leur utilisation comme renforts dans des matériaux composites à matrice polymère organique (polystyrène). La synthèse d'un nouvel agent de couplage pour le système cellulose-polystyrène a été entreprise par la voie de copolymérisation cationique. Une caractérisation complète de cet agent de couplage a été faite par ftir, analyse élémentaire, #1h-nmr, calorimétrie différentielle (dsc) et chromatographie par exclusion stérique (ces). La réactivité de ce copolymère a été vérifiée vis-a-vis des oh et des amines primaires par ftir. Les caractéristiques essentielles pour pouvoir l'utiliser comme agent de couplage sont : une bonne miscibilité avec le polystyrène (matrice), de longues chaînes (mn 20000) et la présence des groupements réactifs (isocyanates) sur la chaîne polymère. A titre comparatif, d'autres agents de couplage ayant des structures et des masses différentes ont été utilisés. Deux d'entre eux portent des anhydrides comme fonctions réactives vis-à-vis de la cellulose. La modification chimique des charges cellulosiques a été vérifiée par ftir, analyse élémentaire, microscopie a balayage (meb). De plus, l'énergie de surface des diverses dérives cellulosiques a été mesurée par goniométrie (angle de contact) et chromatographie inverse (igc). L’imperméabilisation des surfaces cellulosiques vis-à-vis des liquides polaires a été vérifiée. L’adhésion (cisaillement interfacial) entre la cellulose et le polystyrène a été mesurée par des techniques micromécaniques sur composites monofilamentaires. Les techniques utilisées ont été la multifragmentation et le déchaussement ('pull-out'). POUR LES COMPOSITES A BASE DE FIBRES CELLULOSIQUES COURTES, L'EFFET DU RENFORCEMENT A ETE VERIFIE A L'AIDE DE LA SPECTROSCOPIE DYNAMIQUE (DMA). LES PARAMETRES SUIVANTS ONT ETE ETUDIES : TAUX DE RENFORT ET FACTEUR DE FORME (LONGUEUR/DIAMETRE). LE MODELE D'HALPIN-KARDOS REPRESENTE CORRECTEMENT LE COMPORTEMENT DE NOS MATERIAUX.