Teses / dissertações: "Composite materials Al"

1

Freitas, Ricardo Luiz Barros de [UNESP]. "Fabricação, caracterização e aplicações do compósito PZT/PVDF". Universidade Estadual Paulista (UNESP), 2012. http://hdl.handle.net/11449/100281.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Um material compósito é constituído pela combinação de dois ou mais materiais, onde se procura sintetizar um novo material multifásico, e que abrigue as melhores características individuais de cada um de seus constituintes. Compósitos de polímeros (matriz) e ferroelétricos (inclusões) podem manifestar piezoeletricidade, ou seja, a produção de uma resposta elétrica devido a uma excitação mecânica, e vice-versa. Nesta tese o material polimérico usado para preparar os filmes ou lâminas de nanocompósitos é o PVDF, e, o material cerâmico é formado por nanopartículas de PZT. Ambos os materiais são dielétricos, porém, com características muito distintas (por exemplo, o PVDF tem aproximadamente 1/4 da densidade e 1/250 da constante dielétrica do PZT). O PZT é muito utilizado em transdutores, principalmente devido aos seus elevados coeficientes piezoelétricos, contudo, é quebradiço e sofre desgaste quando empregado na forma de filmes ou lâminas. Por outro lado, o PVDF é um polímero piezoelétrico que apresenta grande flexibilidade e excelentes resistências mecânica e química, porém, seus coeficientes piezoelétricos são apenas moderados. A fim de se aumentar a flexibilidade do PZT, mistura-se o pó cerâmico, na forma de nanopartículas, com o PVDF, também pulverizado. Na tese, evidencia-se que o compósito constituído por esta combinação cerâmica-polímero proporciona uma nova classe de materiais funcionais com grande potencial de aplicação, por terem combinadas a resistência e rigidez das cerâmicas, e, a elasticidade, flexibilidade, baixa densidade e elevada resistência a ruptura mecânica dos polímeros. O novo material tem grande resistência a choques mecânicos, flexibilidade, maleabilidade, e, principalmente, coeficientes piezoelétricos relativamente elevados. Amostras do compósito...
A composite material is constituted by the combination of two or more materials, which synthesizes a new multiphase material, and has the best individual characteristics of each of its constituents. Polymer composites (matrix) and ferroelectric (inclusions) can express piezoelectricity, i.e. the production of an electrical response due to a mechanical excitation, and vice versa. In this thesis the polymeric material used to prepare the films or slides of nanocomposites is the PVDF, and, ceramic material is formed by PZT nanoparticles. Both materials are dielectrics, however, with very different characteristics (for example, the PVDF is approximately 1/4 density and 1/250 relative permittivity from PZT). The PZT is widely used in transducers, mainly due to their high piezoelectric coefficients, however, is brittle and suffers wear and tear when employed in the form of films or slides. On the other hand, the PVDF is a piezoelectric polymer that offers great flexibility and excellent mechanical and chemical resistances, however, its piezoelectric coefficients are only moderate. In order to increase the flexibility of PZT, ceramic powder is mix, in the form of nanoparticles, with PVDF, also sprayed. In theory, it becomes evident that composite consisting of this ceramic- polymer combination delivers a new class of functional materials with great potential for application, because they combine the strength and rigidity of ceramics, and elasticity, flexibility, low density and high resistance to mechanical disruption of polymers. The new material has great resistance to mechanical shock, flexibility, suppleness, and, primarily, relatively high piezoelectric coefficients. PZT/PVDF composite samples were fabricated and characterized aiming to applications such as: piezoelectric actuators, acoustic emission detectors, and energy... (Complete abstract click electronic access below)

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2

Palmer, Nathan Reed. "Smart Composites evaluation of embedded sensors in composite materials /". Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/palmer/PalmerN0809.pdf.

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As an emerging form of renewable energy, horizontal wind turbines have experienced advancements in improving efficiency and reliability. These advances have pushed the limits of current technology used in wind turbines. Smart blades have been proposed as a method of addressing these limitations. Sensor integration within blade construction is the first step in development of smart blades. Thus, several low cost sensors were chosen, 1 axis strain gages, polyvinylidene fluoride films (PVDF), and single mode fiber optics either coated in acrylate or polyimide. To ensure successful bonding between sensor and composite two surface treatment techniques were developed. The first, dipping of the sensor into a bath of 20% by weight solution of nitric acid and the second was submersion of the sensor in the nitric acid for ten seconds prior to removal. These treatments were compared against sensors not surface treated prior to embedding. These sensors were embedded within samples created of fiberglass and epoxy or vinyl ester resin. Two different material tests were conducted. Tensile testing allowed for evaluation of sensor sensitivity, sensor failure point, material tensile modulus, and material tensile strength. Mode I fracture toughness evaluation, indicated the level of successful bonding which occurred during resin curing. Field Emission Scanning Electron Microscopy (FESEM) was conducted to further confirm the level of bonding between resin and sensor, post fracture. Results for embedded strain gages showed an adverse effect for vinyl ester samples. Epoxy samples fared better, thus concluding manufacturing success for epoxy samples, submersion being preferred, and alternative methods needed for vinyl ester samples. PVDF films had good qualitative FESEM images combined with increasing trends. It was concluded that integration for both resin groups with sensors submerged in nitric acid was successful. Fiber optics coated in acrylate also showed good bonding under FESEM imaging as well as testing. It was thus concluded that submersion was the preferred treatment. Lastly, fiber optics coated in polyimide embedded in vinyl ester composites showed significant drawbacks and it was concluded that alternative methods need exploration. Those embedded in epoxy were successfully integrated and submersion in nitric acid showed the most potential.

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3

Karlsson, Johan. "Composite material in car hood : Investigation of possible sandwich materials". Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-45633.

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4

Podnos, Eugene Grigorievich. "Application of fictitious domain method to analysis of composite materials /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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5

Yan, Chang (Karen). "On homogenization and de-homogenization of composite materials /". Philadelphia, Pa. : Drexel University, 2003. http://dspace.library.drexel.edu/handle/1860/246.

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6

Symington, Mark C. "Cellulose based composite materials". Thesis, University of Strathclyde, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501684.

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Natural fibre composites are a fast growing research area, with many observable research branches. In this thesis, studies into natural fibre composites are undertaken. This includes work into the base fibre mechanical properties, pre-processing techniques and the influence of alkalisation and silanation, both common fibre processing methods used to improve interfacial properties. The effects of these pre-processing techniques were also evaluated using Fourier transform infrared spectroscopy (FT-IR). It was observed that the processing had shown definite signs of altering the surface functional groups. For the studies into the base fibre strengths, it was found that natural fibres are highly variable. with the testing complicated by difficulties in measuring cross sectional areas. It was also found that natural fibres are sensitive to moisture, which affects their mechanical properties somewhat, although no conclusive trends were derived.

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7

Dyer, K. P. "Fatigue of composite materials". Thesis, Swansea University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636755.

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A study has been undertaken of fatigue in glass fibre reinforced composites. Two matrix resins were tested; an isophthalic polyester and a polyurethane-vinyl-ester, which was designed to have superior properties, including toughness and resistance to hydrolytic attack. Three different types of glass fibre fabrics were used for reinforcement, a conventional woven roving and two novel stitch-bonded cloths. The resins and cloths were combined into eight lay-ups in order to consider the effects of matrix, cloth and lay-up on fatigue strength and lifetime. The fatigue study was extended to evaluate the micromechanisms that occur in these composites during fatigue and how damage accumulated throughout the sample lifetime. This involved measuring stiffness changes during fatigue cycling combined with microscopic study of the samples. The damage mechanisms that occurred were similar to those seen by previous authors on different materials and from this, it was concluded that the same mechanisms occur independent of material and lay-up but these parameters affect the point in the specimen lifetime at which the damage occurs. After the data had been obtained, two experimental models were compared against data obtained in the S-N and damage accumulation studies to evaluate whether existing models would predict the behaviour of these composites. It was found that modelling of the linear portion of the S-N curve was fairly accurate but the damage accumulation model was not suitable. The composites were also fatigue tested in various environments and compared against the results obtained in air. Distilled water, sea water and dilute HCl were chosen as being the most likely encountered in the service of these materials. It was found that distilled water and sea water have minimal effect on fatigue in these composites during the short lifetimes used in this study, but it is suggested that the effect would increase with lifetime. The dilute HCl acid also had a smaller than expected effect. This study was backed with various tests which studied methods of water transport into these materials and the effects of the environments on matrix and fibre properties. Finally, initial studies have been made into methods of fabricating these materials into composite tubes with the aim of studying their properties in torsion and possibly tension-torsion.

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8

Yang, Heechun. "Modeling the processing science of thermoplastic composite tow prepreg materials". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/17217.

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9

Gambone, Livio R. "The effect of R-ratio on the mode II fatigue delamination growth of unidirectional carbon/epoxy composites". Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/29968.

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An investigation of the effect of R-ratio on the mode II fatigue delamination of AS4/3501-6 carbon/epoxy composites has been undertaken. Experiments have been performed on end notched cantilever beam specimens over a wide range of R-ratios (-l ≤R ≤0.50). The measured delamination growth rate data have been correlated with the mode II values of strain energy release rate range ∆G[formula omitted]), maximum strain energy release rate (G[formula omitted]) and stress intensity factor range (∆K[formula omitted]). The growth rate is dependent on the R-ratio over the range tested. For a constant level of ∆G[formula omitted], the crack growth rate decreases with increasing R-ratio. A similar trend is observed when the data is plotted as a function of G[formula omitted]. The effect of plotting the growth rate as a function of ∆K[formula omitted] is to produce an R-ratio dependence opposite to that obtained by either the ∆G[formula omitted] or G[formula omitted] approach. For a constant level of ∆K[formula omitted], the crack growth rate increases with increasing R-ratio. Master equations which completely characterize the fatigue behaviour as a function of ∆G[formula omitted] and ∆K[formula omitted] have been derived, based on the observation that the growth rate law exponent, n and constant, A are unique functions of R-ratio. Values for n are surprisingly large and increase with increasing R-ratio whereas values for A decrease with increasing R-ratio. The effect of time-at-load has been considered in an attempt to explain the existence of the R-ratio dependence of the growth rate. The correct trend can be established for the exponent, n but not for the constant, A. Friction between the crack faces, particularly at higher R-ratios, is proposed as a possible explanation for the observed anomaly. Further evidence of a frictional mechanism operating at higher R-ratios has been discovered through a postmortem fracture surface examination. Additional fractographic observations are presented over the entire range of R-ratios tested. In regions subjected to negative R-ratio cycling, there is no evidence of the characteristic mode II hackle features. Instead, loose rounded particles of matrix material are found. An extensive amount of hackling is observed in regions subjected to low positive R-ratio cycles. The extent of hackle damage visibly decreases in areas where higher levels of R-ratio are imposed. A correlation between the general fracture surface morphology and the fatigue data provides support for the hypothesis that energy for delamination is always available in sufficient quantity, and that growth is dependent on the stresses ahead of the crack tip being sufficiently high.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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10

Counts, William Arthur. "Mechanical behavior of bolted composite joints at elevated temperature". Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17315.

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11

Wood, Geoffrey Michael. "Treatment of polyethylene fibre for improved fibre to resin adhesion in composite applications". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28528.

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Tensile properties of polyethylene fibres are shown to be very good in comparison to properties of other advanced composite reinforcing fibres. Nevertheless, the use of polyethylene fibres in polymeric matrix composites suffers due to a poor fibre to resin adhesion. However, its ballistic properties are excellent because of the poor adhesion and also fibre ductility. Applications involving structural use of polyethylene fibres are limited by, among others, the low compressive and shear strengths. These are affected strongly by the degree of adhesion. Improvements in bonding are expected to result in greater commercial appeal for the fibres as the property limitations are reduced. Ultra Violet radiation has been shown previously, in laboratory scale batch studies, to induce graft co-polymerization of monomers to polyethylene films. Improvements in wettability and adhesion result when the grafted polymer is compatible to the bonding medium. In this study the technique was adapted to bench scale, continuous fibre treatment, whereby the monomer was surface grafted to the polyethylene substrate. Acrylic acid monomer was used for this due to its relative safety, small molecular size, and high reactivity. Reaction initiation was provided by use of a benzophenone photosensitizer due to the stability of polyethylene to UV radiation. The reaction was performed by pre-coating the fibres with reactants, then exposure to UV radiation. Results of the continuous process for fibre treatment indicate that the monomer concentration and temperature of the preliminary soakings are key variables. Adhesion improvement was measured by single fibre pullout tests and interlaminar shear strength (ILSS) tests. Of these, the ILSS appeared to be more sensitive for judging small improvements. Tensile tests were used to judge property deterioration due to treatment, and flexural property tests gave a preliminary indication of material behavior. The ILSS showed marked improvement from 1.5 ksi for untreated material to over 5.2 ksi for the better treatments. A competing treatment, plasma, shows ILSS values around 3 ksi. The flexural test indicated that failure of UV-grafted polyethylene was in tension, whereas failure of plasma and untreated material was in compression. The study has proven successful in improving the adhesion of polyethylene fibres to an epoxy resin matrix. Commercial viability is currently being developed through decreased process residence times and irradiation exposures.
Applied Science, Faculty of
Materials Engineering, Department of
Graduate

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12

Teh, Kuen Tat. "Impact damage resistance and tolerance of advanced composite material systems". Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06062008-170512/.

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13

Zhang, Fangzhou. "Multiscale modeling of laminated composites under extreme environmental conditions". Thesis, Cachan, Ecole normale supérieure, 2014. http://www.theses.fr/2014DENS0027/document.

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À haute température, l'oxygène réagit avec la matrice organique du matériau composite, ce qui change les propriétés du matériau et réduit la résistance à la rupture globale. Mais la compréhension de la dégradation du composite stratifié oxydé, en particulier son comportement à l'échelle du pli, est aujourd'hui limitée et phénoménologique. Les travaux dans cette thèse ont été réalisés pour donner notre contribution sur les aspects méthodologiques de ce sujet. Des essais sont réalisés pour caractériser expérimentalement le comportement d'éprouvette oxydée : en particulier, un nouveau essai, l'essai 'oxy-délaminage', a été développé pour identifier la ténacité du matériau composite vieilli. Une stratégie a été proposée d'étudier le problème à partir des propriétés de la matrice oxydée à l'échelle fibre/matrice et jusqu'à la reproduction et la prédiction du comportement de fissuration transversale des échantillons oxydés à échelle méso via un procédé d'homogénéisation
At high temperature, the oxygen reacts with the organic matrix of composite material, which changes the material properties and reduces the resistance to global failure. But understanding on the degradation of the oxidized composite laminate, particularly its damage behavior, is now limited and phenomenological. Work in this thesis has been made to give our contribution to the methodological aspects of this topic. Tests are performed to characterize experimentally the behaviors of the oxidized specimens: in particular, a new test test oxy-delamination ', was developed to identify the tenacity of composite material aged. A strategy has been proposed to study the problem from the properties the oxidized matrix at the fiber/matrix scale up to the reproduction and predicting the behavior of transverse cracking of the sample at the scale of a ply via a homogenization process

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14

Biggerstaff, Janet M. "Vibrational Damping of Composite Materials". Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3204578.

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Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed April 3, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 218-224).

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15

Liu, Liu. "Durability of Polymer Composite Materials". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14002.

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The purpose of this research is to examine structural durability of advanced composite materials under critical loading conditions, e.g., combined thermal and mechanical loading and shear fatigue loading. A thermal buckling model of a burnt column, either axially restrained or under an axial applied force was developed. It was predicted that for a column exposed to the high heat flux under simultaneous constant compressive load, the response of the column is the same as that of an imperfection column; the instability of the burnt column happens. Based on the simplified theoretical prediction, the post-fire compressive behavior of fiberglass reinforced vinyl-ester composite columns, which have been exposed to high heat flux for a certain time was investigated experimentally, the post-fire compressive strength, modulus and failure mode were determined. The integrity of the same column under constant compressive mechanical loading combined with heat flux exposure was examined using a specially designed mechanical loading fixture that mounted directly below a cone calorimeter. All specimens in the experiments exhibited compressive instability. The experimental results show a thermal bending moment exists and has a significant influence on the structural behavior, which verified the thermal buckling model. The trend of response between the deflection of the column and exposure time is similar to that predicted by the model. A new apparatus was developed to study the monotonic shear and cyclic-shear behavior of sandwich structures. Proof-of-concept experiments were performed using PVC foam core polymeric sandwich materials. Shear failure occurred by the extension of cracks parallel to the face-sheet/core interface, the shear modulus degraded with the growth of fatigue damage. Finite element analysis was conducted to determine stress distribution in the proposed specimen geometry used in the new technique. Details for a novel apparatus used for the fatigue testing of thin films and face sheets are also provided.

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16

Matemilola, Saka Adelola. "Impact damage to composite materials". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319939.

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17

Murphy, Craig E. "Pyroelectric thin film composite materials". Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260162.

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18

Delfa, G. L. a. "Aerospace composite materials in fire". Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519566.

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19

Alur, Kashyap. "Nonlinear mechanics of composite materials". Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53600.

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Composite materials have been an area of active research in recent years due to the possibility of obtaining multifunctional structures. Viscoelastic layered composites with parallel plane layers consisting of a stiff constituent and a soft viscoelastic constituent are of particular interest as they have been shown to exhibit simultaneous high stiffness and high damping. Such materials would be useful in structural applications and in high vibration environments such as in a vehicle or machinery. They would provide the rigidity required while simultaneously dissipating mechanical energy. The finite deformation mechanics of parallel plane viscoelastic layered composites has not been extensively studied. Under compressive loads they are very susceptible to instabilities. Buckling, for example is an elastic instability seen in load bearing materials. Since viscoelastic materials are rate and time dependent, the buckling modes for these composites not only depend on these factors, but also on the volume fraction of the stiff constituent. Three different cases are identified in the buckling and post-buckling response of these composites: non-dilute (high volume fraction), transition (intermediate volume fraction) and dilute (small volume fraction) cases. Due to buckling from the application of prestrain, the stiffness and damping of these composites can be tuned by orders of magnitude. Adaptive and multifunctional materials can be designed taking advantage of this idea and the rate dependence of the modes of deformation.

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20

Zhu, Fuyou. "Advanced materials for composite armour". Thesis, Queen Mary, University of London, 2009. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1775.

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Composite integral armour plays an important role in future combat system. Despite numerous experimental studies there are still disadvantages such as complex manufacturing process, relatively big damage area, difficult to repair and limit shape etc. Composite integral armour without all these problems is essential for the success of future main battle tank which has a total weight of only 20 tons. 3D fabrics are seen as potential solution to poor impact damage tolerance of textile composites. Binder yarns in through-thickness direction can bridge cracks and stop crack tip growth resulting very good impact damage tolerance. The major purple of this work is to incorporate new materials and new configuration into composite integral armour. The underlying premise is that ballistic performance of new armour is judged mainly by single hit ballistic limit followed by damage resistance which in turn followed by energy absorption in high energy low velocity impact. Computer simulation of 3D textile composites and damage mechanism study were used through-out the study for analysing and explaining experimental results. Judged by these properties, conclusions regarding to ballistic performance of eight 3D texile composties were made. The benefit of the work will be a new explanation of composite armour research. This will help the success of future combat system.

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21

Buck, Lyndon. "Furniture design with composite materials". Thesis, Bucks New University, 1997. http://bucks.collections.crest.ac.uk/9977/.

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This thesis examined the feasibility of fibre composite reinforcement in the furniture industry. The development of post war furniture design was reviewed, with particular emphasis on the main design movements and the use of new materials and technologies. The use of fibre composite materials in contemporary furniture was discussed in terms of technical development, environmental effects and psychological acceptance. Fibre reinforcements and adhesives were compared, as were fabrication techniques applicable to the existing British furniture industry. Particular emphasis has been placed on the fibre reinforcement of laminated timber sections as a method of overcoming many of the manufacturing problems of composites. Methods of analysing the behaviour under load of fibre reinforced laminated wood were reviewed. Resistance among the furniture buying public to modem, non-traditional furniture design was discussed, along with ways of making composite materials more aesthetically acceptable. Experimentation to determine the mechanical properties of fibre composite reinforced wood against wood control samples was undertaken, along with methods used to analyse the results for flat and curved samples. Modulus of elasticity, modulus of rupture and impact strength were measured, as was the level of distortion of the samples before and after testing. A full size chair form was produced to demonstrate the behaviour of the material on a larger scale. The development of the design was discussed in terms of ergonomic requirements, aesthetics, practicality and environmental concerns. The problem of predicting the behaviour of complex shapes was discussed and a finite element analysis of the form is carried out to gain an accurate picture of the composite's performance. Production of fibre reinforced materials was discussed, along with the furniture industry's reluctance to invest in new materials and technologies. The feasibility of adapting traditional furniture making skills and equipment to the production of fibre composite reinforced wood has been assessed.

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Beglinger, Jarrod (Jarrod Thomas) 1976. "Forming of advanced composite materials". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/31077.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998.
Includes bibliographical references (p. 45).
Two significant aspects of advanced composite material forming are examined. First, the fiber deformation of aligned fiber composites formed to double curvature parts is analyzed. Aligned fiber composite lay-ups were formed over hemispherical tools and the fiber deformation was mapped. The data were intended to support the model which predicts trellising of composite fibers in double curvature. The data are, in general, too ambiguous to clearly support this model. Second, springback of woven fiber material-single curvature parts is investigated. A 90° bend was formed for varying laminate lay-ups at varying temperatures via a double diaphragm process. Principal objectives were to qualify the effects of varying lay-ups and temperatures on the net amount of springback observed. The data show that 0/90 woven lay-ups experience more springback than either +45 degree or quasi-isotropic woven lay-ups, and that heating the laminates marginally decreases the springback experienced.
by Jarrod Beglinger.
S.B.

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23

Venkatasubramanian, Rajiv. "Composite Nanoparticle Materials for Electromagnetics". University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352993374.

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Baker, Christopher R. "Assessing Damage in Composite Materials". University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1390315001.

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Whiteside, M. B. "Stochastic analysis of composite materials". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9986.

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This thesis describes the development of stochastic analysis frameworks for use in engineering design and optimisation. The research focuses on fibre-reinforced composites, with the stochastic analyses of an existing analytical failure model for unidirectional composites and of a unit cell numerical model of a 2D 5-Harness satin weave. Stochastic failure envelopes are generated through parallelised Monte Carlo Simulation of deterministic, analytical, physically based failure criteria for unidirectional carbon fibre/epoxy matrix composite plies. Monte Carlo integration of global variance-based Sobol sensitivity indices is performed and utilised to decompose observed variance within stochastic failure envelopes into contributions from physical input parameters. It is observed how the interaction effect can be used to identify domains of bi-modal failure, within which the predicted failure probability is governed by multiple failure modes. A reduced unit cell (rUC) model of a 5-Harness satin weave is constructed and analysed deterministically in uniaxial and biaxial loading conditions. An algorithm is developed and implemented to fully automate the rUC construction such that stochastic variations of the crimp angle can be evaluated. Monte Carlo Simulation is employed to propagate the effect of the crimp angle through the deterministic model and the probabilistic response compared with data obtained experimentally. It is observed how simulated variability compares well in uni-axial compression, but under-predicts observed experimental variability in uni-axial tension. The influence of vertical stacking sequence of plies is also demonstrated through the study of in-phase and out-of-phase periodic boundary conditions. The research highlights various, potential advantages that stochastic methodologies offer over the traditional deterministic approach, making a case for their application in engineering design and providing a springboard for further research come the day when greater computational power is available.

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26

Vukicevic, Uros. "TiO2 nanorod polymer composite materials". Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/7669.

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The remarkable characteristics of Ti02 are widely used, from everyday life applications (pigments, food/cosmetics additives) to more specialised systems, including photovoltaics and structural composites. Use in polymers is substantial (25% of all Ti02 produced), but most applications and research focus on commercial powders. A new generation of Ti02 nanoparticles has emerged, based on very small, single-crystals, with well-defined morphology and phase. A limited number of papers report the use of this new nanoscale Ti02 in polymer nanocomposites, and indicate improved properties. Although the synthesis of anisotropic nanoparticles (e. g. nanorods) has been well-reported, use in polymer nanocomposites remains largely unreported. This thesis broadly covers three topics: (1) synthesis of Ti02 nanorods using different sol-gel routes in presence of structure directing agents, (2) modification of the nanorod surface chemistry in order to control dispersion and surface properties and (3) fabrication of titania nanorod-polymer composites. Singlecrystal anatase nanorods were produced with variable aspect ratio (3-12), depending on the specific structure directing agent (SDA) used during synthesis. Due to organic functionalisation at the nanorod surface, nanorods could be well dispersed in chloroform. A new procedure, based on the self-cleaning ability of Ti02 under UV, was developed for removal of organics from the nanorod surface, without compromising the nanorod morphology, crystallinity or dispersibility. This powerful tool can be used to change the surface character of the nanorods to generate aqueous TNR dispersions. Stable dispersions were achieved using quaternary ammonium hydroxides to modify the surface electrostatically and sterically. Once dispersed individually, the surface can be further modified by sol-gel chemistry. Composite work involved blending both organic and water-soluble polymers with nanorod dispersions in chloroform and water, respectively, to produce composite films of exceptional optical transparency, even for nanorod loadings up to 30 wt%. The films possess very strong, wavelength-tuneable UV absorbance, which could be used in UV filters and optical limiting. The presence of SDAs or dispersants at the nanorodpolymer interface hinders strong adhesion, as evidenced by marginally lower tensile strength and thermal stability of the nanocomposites. The photo-stability of the nanorod composites is comparable to that of the pure polymer and better than that of composites with commercial equiaxed TiO2 nanoparticles.

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Pospíšil, Tomáš. "STOCHASTIC MODELING OF COMPOSITE MATERIALS". Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-233889.

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Práce je věnována generování náhodných struktur dvousložkových vláknových kompozitních materiálů a statistickým metodám analýzy náhodnosti těchto struktur. Byly vyvinuty čtyři algoritmy a vygenerované struktury byly statisticky porovnány s reálnými daty.

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Somanath, Nagendra. "A finite element cure model and cure cycle optimization for composite structures". Thesis, This resource online, 1987. http://scholar.lib.vt.edu/theses/available/etd-04272010-020304/.

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Call, Russell Kent. "Parameter establishment and verification of a fabrication stress model and a thermo-kinetic cure model for filament wound structures". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-08142009-040256/.

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Wright, Richard J. "Bolt bearing creep behavior of highly loaded polymer matrix composites at elevated temperatures". Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17362.

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Bulsara, Vatsal N. "Effects of fiber spatial distribution and interphase on transverse damage in fiber-reinforced ceramic matrix composites". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/21429.

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Gopalan, Sriram. "Quasi-static and dynamic mechanical characterization of reinforced polyurethane foam /". free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p1418024.

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Chang, Sheau-Miin. "Critical evaluation of strong organic fibers vis-a-vis mechanical performance in flexible structures". Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/8479.

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Kokan, David R. "Development and use of an improved filament-winding process model". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12261.

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Ward, William F. "A theoretical investigation into the inelastic behavior of metal-matrix composites". Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17244.

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Veazie, David R. "Modeling of fiber reinforced composites incorporating distinct interface properties". Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/17385.

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Kothidar, Arjun. "Use of finite element method to evaluate the strength response of notched composite laminates under tension". Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/A_Kothidar_120508.pdf.

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Thesis (M.S. in mechanical engineering)--Washington State University, December 2008.
Title from PDF title page (viewed on July 6, 2009). "Department of Mechanical and Materials Engineering." Includes bibliographical references (p. 115-118).

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Enemuoh, Emmanuel Ugochukwu. "Smart drilling of advanced fiber reinforced composite materials /". free to MU campus, to others for purchase, 2000. http://wwwlib.umi.com/cr/mo/fullcit?p9998482.

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James, Aaron. "Development of composites materials from waste paper and plastic". Australian Digital Thesis Program, 2006. http://adt.lib.swin.edu.au/public/adt-VSWT20070130.165426/index.html.

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Thesis (PhD) - Swinburne University of Technology, Industrial Research Institute Swinburne - 2006.
A thesis submitted for the degree of Doctor of Philosophy, Industrial Research Institute Swinburne, Swinburne University of Technology - 2006. Typescript. "August 2006". Includes bibliographical references (p. 361-389).

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Klug, Jeremy Hager. "High-performance adhesive systems for polymer composite bonding applications /". Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9883.

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Lee, Jaehong. "Vibration, buckling and postbuckling of laminated composites with delaminations". Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-170322/.

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Lorandi, Natália Pagnoncelli. "Estudo das propriedades dinâmico-mecânicas e fluência de compósitos epóxi/tecido não-dobrável de carbono produzidos por VARTM e RFI". reponame:Repositório Institucional da UCS, 2016. https://repositorio.ucs.br/handle/11338/1844.

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A excelente relação custo-peso-desempenho de compósitos poliméricos em relação aos materiais tradicionais tornou-se motivo para o desenvolvimento de materiais avançados para aplicação estrutural, como compósitos epóxi/fibra de carbono, e com isso, novos métodos de processamento, diferentes resinas (matriz) e tecidos de fibras (reforço). Polímeros e seus compósitos apresentam comportamento viscoelástico, e fatores como estabilidade dimensional e resistência mecânica a longo prazo devem ser considerados quando utilizados na indústria aeronáutica. A análise dinâmico-mecânica (DMA) permite a avaliação das propriedades viscoelásticas do material, e ensaios de fluência possibilitam o estudo da deformação do material em função do tempo, sob tensão e temperatura constantes. Neste trabalho, compósitos epóxi/tecido não-dobrável (NCF) de carbono foram produzidos utilizando-se duas técnicas de fabricação: moldagem por transferência de resina com vácuo assistido (VARTM) e infusão de resina em filme (RFI), e uma análise comparativa entre os dois compósitos foi realizada. O módulo de armazenamento, E’, do compósito RFI foi aproximadamente 10 GPa maior ao longo da região vítrea e a Tonset aproximadamente 60°C mais alta em relação ao VARTM. O compósito RFI também apresentou uma região de transição vítrea mais larga (a partir da curva de tan δ). Esses resultados foram associados às relaxações moleculares e maior cooperatividade das cadeias, assim como maior rigidez do compósito RFI. Os ensaios de fluência foram realizados em três diferentes tensões e temperaturas, e o compósito VARTM apresentou maior deformação em função do tempo, indicando uma interface fibra/matriz mais fraca e um compósito menos rígido, e corroborando com os resultados de resistência ao cisalhamento interlaminar, a qual foi maior para o compósito RFI. Os modelos de Findley e de Burger foram aplicados e ambos ajustaram-se bem às curvas experimentais de fluência. Os parâmetros de cada modelo foram associados ao comportamento viscoelástico dos compósitos e relacionados com os demais resultados.
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The excellent cost-weigh-performance relationship of polymeric composites compared to traditional materials became a reason to development of advanced materials for structural application such as carbon/epoxy composites, and with that, new processing methods, different resins (matrix) and fabrics (reinforcement) producing. Polymers and their composites present viscoelastic behavior, and so issues such as dimensional stability and long-term resistance must be taken into account when used by aeronautic industry. Dynamic-mechanical analysis (DMA) allows the evaluation of viscoelastic properties, and with creep tests, it is possible to study materials strain as function of time, under constant stress and temperature. In this study, epoxy/carbon NCF composites were manufactured by two techniques: vacuum assisted resin transfer molding (VARTM) and resin film infusion (RFI), and a comparative analysis between both composites was made. Storage modulus, E’, for RFI composite was approximately 10 GPa higher along the glassy region and Tonset approximately 60°C higher than VARTM composite. RFI composite also presented a wider glass transition region (form tan δ curve). These results were associated to the molecular relaxation and higher chain cooperative motion, and to the higher stiffness of RFI composite. Creep strain tests were performed in three different stress levels and temperatures, and VARTM composite presented larger creep strain with time, indicating a weaker interface fiber/matrix and a lower stiffness composite, and corroborating with short-beam shear resistance. Findley and Burger’s model were applied and both agreed well with experimental creep curves. Parameters of each model were associated to composites viscoelastic behavior and they were related to the other results.

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Smith, Jay David. "Internal damage characterization for composite materials under biaxial loading configuration". Thesis, Montana State University, 2007. http://etd.lib.montana.edu/etd/2007/smith/SmithJ0507.pdf.

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Wu, Xiang. "Thermoforming continuous fiber reinforced thermoplastic composites". Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/9383.

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Hsu, Sheng-yuan. "On the prediction of compressive strength and propagation stress of aligned fiber-matrix composites /". Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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Zaghi, Stefano. "Multiscale multiphysics simulation in composite materials". Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/665129.

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The improvements in terms of computational power provides the capability to analyze with more detail the materials behavior. On one hand, going deeper in the materials to study an increasingly smaller dimension and capture micro- or nano- changes. On the other hand, the increasing computational memory allows to perform finite elements analysis with billions of nodes, that permits to obtain more accurate results. In this sense, the focus of this work is the numerical modeling of the microscale behavior of inhomogeneous materials, with special attention to composite materials under thermo-mechanical loading conditions. This work also proposes and implements optimization tools, at a constitutive law level, as well as the level of both, macro- and micro-structural algorithms. The thesis is proposed as compendium of articles written during the last years and all published in Q1 international journals. In the first publication, a novel damage-mechanics micro-model is presented, able to represent the mechanical behaviors of masonry constituents. The proposed micro-model is based on a tension-compression continuum damage model. The adoption of appropriate failure criteria enables controlling the dilatant behavior of the material, even though this aspect is not generally associated to continuum damage models as it is for plasticity models. The study proposes a simple solution to this issue, consisting in the appropriate definition of the failure surfaces under shear stress states, together with the formulation of proper evolution laws for damage variables. The model keeps the simple and efficient format of classical damage models, where the explicit evaluation of the internal variables avoids nested iterative procedures, thus increasing computational performance and robustness. Another purpose of this research is to carry out a critical comparison of the proposed continuous micro-model with other two well-known discrete micro-modeling strategies. The second publication presents a full thermo-mechanical multiscale methodology, covering the nano-, micro-, and macroscopic scales. In such methodology, direcly deriving from the Classical First-Order Multiscale Method, fundamental material properties are determined by means of molecular dynamics simulations. Afterwards, the material properties obtained are used at the microstructural level by means of finite element analyses. Finally, the macroscale problem is solved while considering the effect of the microstructure using a thermo-mechanical homogenization on a representative volume element (RVE). The publication that close this thesis presents two computationally efficient multiscale procedures able to predict the mechanical non-linear response of composite materials. This is achieved, using an RVE Data Base (DB) calculated a-priori. Through the definitions of an equivalent damage parameter ($d_{eq}$), function of the global stress at the microscale, a series of strain controlled virtual tests of the RVE are performed storing in the DB the homogenized stress and strain state reached at certain levels of d_eq. Afterwards, the solution of the macroscale structure can be solved using the interpolation of the stored data. The first proposed procedure, named Discrete Multiscale Threshold Surface definition (DMTS), stores in the database the tenso-deformational state in which damage starts. Once reaching this state, a non-linear analysis will require the construction of the RVE to analyze the material damage evolution. On the other hand, the second method proposed, named Discrete Multiscale Constitutive Model (DMCM), is completely based on offline data and uses only the stress information stored in the DB to obtain the failure threshold and the non-linear material performance. In the article, special attention has been paid on the construction and validation of the Data Base, as well as on the study of a complete composite structure comparing the speedup obtained with both methods.
En las últimas décadas, el avance en términos de poder computacional ofrece la capacidad de analizar más detalladamente el comportamiento de los materiales. Por un lado, profundizar los materiales para estudiar una dimensión cada vez más pequeña y capturar micro o nanocambios. Por otro lado, la capacidad de memoria computacional permite realizar análisis de elementos finitos con miles de millones de nodos, lo que permite obtener resultados lo más exacto posible. El objetivo de este trabajo es la modelización numérica del comportamiento microescala de materiales no homogéneos, con especial atención a los materiales compuestos, en condiciones de carga termo-mecánica, y la aplicación de herramientas de optimización de las leyes constitutivas, así como en a nivel macro y micro estructural. La tesis se propone como un compendio de artículos publicados en revistas internacionales. En la primera publicación, se presenta un micro-modelo basado en el daño mecánico, capaz de representar los comportamientos mecánicos de las estructura de mampostería. El micro-modelo propuesto se basa en un modelo de daño continuo por tensión-compresión. La adopción de criterios de daño apropiados permite al analista controlar la dilatancia del material, aunque este aspecto no está generalmente asociado a los modelos de daño continuo como lo es para los modelos de plasticidad. El estudio propone una solución simple a este problema, que consiste en la definición apropiada de las superficies de daño bajo estados de tensión de cortante junto con la formulación de leyes de evolución apropiadas para las variables de daño. El modelo mantiene el formato simple y eficiente de los modelos de daños clásicos, donde la evaluación explícita de las variables internas evita los procedimientos iterativos anidados, aumentando así el rendimiento computacional. Otro objetivo de esta investigación es realizar una comparación crítica del micro-modelo continuo propuesto con otras dos estrategias bien conocidas de micro-modelado discreto. Posteriormente, se presenta una metodología termomecánica multiescala completa, que cubre las escalas nano, micro y macroscópica. En dicha metodología, derivada directamente del Método Multiescala de Primer Orden, las propiedades fundamentales del material se determinan mediante simulaciones de dinámica molecular que se implementan en consecuencia a nivel microestructural por medio de análisis de elementos finitos. Por otro lado, el problema de macroescala se resuelve considerando el efecto de la microestructura mediante homogeneización termo-mecánica en un elemento de volumen representativo (RVE). Finalmente, se proponen dos procedimientos multiescala computacionalmente eficientes capaces de predecir la respuesta mecánica no lineal de materiales compuestos. Esto se logrará utilizando una base de datos (DB) calculada a priori. A través de las definiciones de un parámetro de daño equivalente (d_eq), funciónes de la tensión global de la microescala, se actuarán una serie de pruebas virtuales de la microescala con deformación controlada para almacenar en el DB el estrés y la tensión homogeneizadas alcanzado en ciertos niveles de d_eq. Posteriormente, la solución de la estructura de macroescala mediante el método multiescala de primer orden se reemplazará por la interpolación de los datos almacenados en el DB. El primer método propuesto, llamado Discrete Multiscale Threshold Surface (DMTS), proporcionará la generación de la RVE en la parte no lineal de la estructura, mientras que el segundo, llamado Discrete Multiscale Constitutive Model (DMCM), es completamente independiente del micromodelo porque solo se utiliza la información de estrés almacenada en el DB. En el articulo se ha prestado especial atención a la creación y validación de la base de datos y al estudio de una estructura compuesta completa comparando la aceleración en terminos de tiempo computationál obtenido

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Mutnuri, Bhyrav. "Thermal conductivity characterization of composite materials". Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4468.

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Thesis (M.S.)--West Virginia University, 2006.
Title from document title page. Document formatted into pages; contains vii, 62 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 61-62).

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Mårtensson, Eva. "Modelling electrical properties of composite materials". Doctoral thesis, KTH, Electrical Systems, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3594.

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Composite field grading materials are used to avoid stressconcentrations in high voltage applications such as cableaccessories and generator or motor end windings. The compositematerials consist of an insulating matrix filled with suitableconducting or semi-conducting particles. Silicon carbide (SiC)powder is one such filler that is being employed. The compositematerials display complex electrical characteristics that aredependent on filler properties, particle concentration,frequency and electric field. Optimization of the stressgrading properties would be facilitated if the characteristicof a specified material mixture could be calculatedapproximately.

In this thesis a microscopic model for the local behavior atthe SiC grain contacts as well as a macroscopic model for theglobal performance of the composite material are presented. Thedc and ac characteristics of different SiC powders and variouscomposite materials have been studied by experiments andsimulations. The electrical properties of ethylenepropylene-diene monomer (EPDM) rubber filled with the SiC grains havebeen characterized by several time and frequency domainmeasurement techniques.

It is shown that the SiC grain contacts can be modeled bySchottky-like barriers. The SiC powders are heavily doped andthe dominating conduction mechanismin the major part of thefield range is tunneling by field emission, amplified bypre-avalanche multiplication. The frequency dependentproperties are governed both by the interfacial barrier regionsand by the surrounding dielectric.

A three-dimensional electrical network model for describingthe frequency dependent electrical properties of the compositematerials has been developed. Accounting for different types ofcontacts between the filler grains is fundamental for theresulting characteristics. The distribution of the conductingparticles in the matrix also affects the electrical propertiesand a well dispersed, and not only random, arrangement is morerealistic. Non-linearity is incorporated in an amended version,which treats the timedependent case.

The model has been implemented in a MATLAB® program andthe calculations have been compared to measurements on EPDMrubber filled with SiC grains. It is demonstrated that thenetwork simulations reproduce the general characteristics ofrelevant concentration, frequency and field dependentexperimental results.

Keywords:field grading; composite materials; SiC;rubber; electrical properties; nonlinear; time-dependent;model; network; conduction mechanisms; Schottky-barrier;

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Bonnaud, Etienne. "On mechanical modeling of composite materials". Doctoral thesis, KTH, Hållfasthetslära (Avd.), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24644.

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Russell, Benjamin Peter. "The micromechanics of composite lattice materials". Thesis, University of Cambridge, 2010. https://www.repository.cam.ac.uk/handle/1810/252176.

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