Dissertations / Theses on the topic 'Composite Structures'
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Plessas, Spyridon D. "Fluid-structure interaction in composite structures." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/41432.
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Approved for public release; distribution is unlimited.In this research, dynamic characteristics of polymer composite beam and plate structures were studied when the structures were in contact with water. The effect of fluid-structure interaction (FSI) on natural frequencies, mode shapes, and dynamic responses was examined for polymer composite structures using multiphysics-based computational techniques. Composite structures were modeled using the finite element method. The fluid was modeled as an acoustic medium using the cellular automata technique. Both techniques were coupled so that both fluid and structure could interact bi-directionally. In order to make the coupling easier, the beam and plate finite elements have only displacement degrees of freedom but no rotational degrees of freedom. The fast Fourier transform (FFT) technique was applied to the transient responses of the composite structures with and without FSI, respectively, so that the effect of FSI can be examined by comparing the two results. The study showed that the effect of FSI is significant on dynamic properties of polymer composite structures. Some previous experimental observations were confirmed using the results from the computer simulations, which also enhanced understanding the effect of FSI on dynamic responses of composite structures.
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BABAEI, IMAN. "Structural Testing of Composite Crash Structures." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2910072.
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Denli, Huseyin. "Structural-acoustic optimization of composite sandwich structures." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 168 p, 2007. http://proquest.umi.com/pqdlink?did=1251904511&Fmt=7&clientId=79356&RQT=309&VName=PQD.
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Violette, Michael A. "Fluid structure interaction effect on sandwich composite structures." Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5533.
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Approved for public release; distribution is unlimited.The objective of this research is to examine the fluid structure interaction (FSI) effect on composite sandwich structures under a low velocity impact. The primary sandwich composite used in this study was a 6.35-mm balsa core and a multi-ply symmetrical plain weave 6 oz E-glass skin. The specific geometry of the composite was a 305 by 305 mm square with clamped boundary conditions. Using a uniquely designed vertical drop-weight testing machine, there were three fluid conditions in which these experiments focused. The first of these conditions was completely dry (or air) surrounded testing. The second condition was completely water submerged. The final condition was a wet top/air-backed surrounded test. The tests were conducted progressively from a low to high drop height to best conclude the onset and spread of damage to the sandwich composite when impacted with the test machine. The measured output of these tests was force levels and multi-axis strain performance. The collection and analysis of this data will help to increase the understanding of the study of sandwich composites, particularly in a marine environment.
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Daynes, Stephen. "Intelligent Responsive Composite Structures." Thesis, University of Bristol, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520593.
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Oehlers, Deric John. "Mechanisms in composite structures /." Title page, abstract and table of contents only, 2004. http://web4.library.adelaide.edu.au/theses/09END/09endo285.pdf.
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Swanson, Gary D. "Structural efficiency study of composite wing rib structures." Thesis, This resource online, 1987. http://scholar.lib.vt.edu/theses/available/etd-04292010-020010/.
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Yang, Nana. "Structural strength and reliability analysis of composite structures." Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=13242.
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Ullah, Israr. "Vibration-based structural health monitoring of composite structures." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/vibrationbased-structural-health-monitoring-of-composite-structures(f21abb03-5b46-4640-9447-0552d5e0c7d6).html.
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Composite materials are in use in several applications, for example, aircraft structural components, because of their light weight and high strength. However the delamination which is one of the serious defects often develops and propagates due to vibration during the service of the structure. The presence of this defect warrants the design life of the structure and the safety. Hence the presence of such defect has to be detected in time to plan the remedial action well in advance. There are a number of methods in the literature for damage detection. They are either 'baseline free/reference free method' or using the data from the healthy structure for damage detection. However very limited vibration-based methods are available in the literature for delamination detection in composite structures. Many of these methods are just simulated studies without experimental validation. Grossly 2 kinds of the approaches have been suggested in the literature, one related to low frequency methods and other high frequency methods. In low frequency approaches, the change in the modal parameters, curvatures, etc. is compared with the healthy structure as the reference, however in the high frequency approaches, excitation of structures at higher modes of the order of few kHz or more needed with distributed sensors to map the deflection for identification of delamination. Use of high frequency methods imposes the limitations on the use of the conventional electromagnetic shaker and vibration sensors, whereas the low frequency methods may not be feasible for practical purpose because it often requires data from the healthy state which may not be available for old structures. Hence the objective of this research is to develop a novel reference-free method which can just use the vibration responses at a few lower modes using a conventional shaker and vibration sensors (accelerometers/laser vibrometers). It is believed that the delaminated layers will interact nonlinearly when excited externally. Hence this mechanism has been utilised in the numerical simulations and the experiments on the healthy and delaminated composite plates. Two methods have been developed here - first method can quickly identify the presence of the delamination when excited at just few lower modes and other method identify the location once the presence of the delamination is confirmed. In the first approach an averaged normalised RMS has been suggested and experimentally validated for this purpose. Latter the vibration data have then been analysed further to identify the location of delamination and its size. Initially, the measured acceleration responses from the composite plates have been differentiated twice to amplify the nonlinear interaction clearly in case of delaminated plate and then kurtosis was calculated at each measured location to identify the delamination location. The method has further been simplified by just using the harmonics in the measured responses to identify the location. The thesis presents the process of the development of the novel methods, details of analysis, observations and results.
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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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Le, Riche Rodolphe. "Optimization of composite structures by genetic algorithms." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164513/.
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Brown, Jessica H. "A machine system for the rapid production of composite structures." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/19452.
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Lannamann, Daniel L. "Structural health monitoring : numerical damage predictor for composite structures." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA390997.
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Davies, Andrew. "Crashworthiness of composite sandwich structures." Thesis, Imperial College London, 2002. http://hdl.handle.net/10044/1/8402.
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Almaskari, Fahad. "Modelling Damage in Composite Structures." Thesis, University of Manchester, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525981.
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Lombetti, D. M. "Tufting of complex composite structures." Thesis, Cranfield University, 2015. http://dspace.lib.cranfield.ac.uk/handle/1826/11076.
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This study focuses on the effect of tufting on the mechanical and electrical properties of carbon composites using a variety of tuft materials, such as aramid, steel and copper. Several configurations were investigated based on a case study, involving the reinforcement of stiffener-to-skin interfaces of a tail cone. The effect of tuft and base composite material, tufting depth and inclination on the delamination resistance in mode I was evaluated, the associated bridging laws were determined and the failure mechanisms were identified. A simplified superposition model of the delamination response of tufted composites was developed. The electrical performance of tufted composites was determined in simulated lightning strike tests and set against the through-the-thickness electrical conductivity of the materials. The results of mechanical testing showed that the delamination performance depends strongly on the material response of the tufts, with both the bridging behaviour and final toughness levels influenced directly by the strength, ductility and ultimate strain of the tufts. Interactions between the tufts and the surrounding composite, such as interfacial shear and bridging induced by tuft pull-out, play a significant role in the overall behaviour generating a deviation from a simple superposition of the base material and tuft response. The balance between interfacial shear and tuft elongation results in a decreasing trend of delamination toughness with increasing tufting depth for low ductility materials, whilst the trend is reversed for the high ductility copper tufts. This balance is also affected by the properties of the base material, with tougher matrices leading to dominance of shear effects and a weaker enhancement introduced by tufting. Inclination of tufts leads to an increase in crack energy release rate due to the activation of a ploughing mechanism. Metallic and carbon tufts have a positive effect on lightning strike response, with copper tufting offering strike protection at an improved level compared to standard copper mesh solutions.
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Hou, An. "Strength of composite lattice structures." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12475.
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Lei, Sheng-Yuan. "Deformation micromechanics in composite structures." Thesis, University of Manchester, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488306.
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Millhouse, Scott C. "Hydrodynamic forces on composite structures." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/42686.
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Approved for public release; distribution is unlimitedUsing a tow tank environment an experiment was set up to measure for response of composite samples of varying stiffness to a geometrically comparable more rigid aluminum sample which was tested at increasing speeds. Also, a square composite shape was tested in a frame providing clamped boundary conditions. Testing of this sample over varying speeds was also performed at varying position angles and was analyzed for force, strain and flow visualization. Results show complex behaviors in fluid flow and structural deformation because of the effects of the free surface and fluid-structure interaction. The comparable mass density between composite plates and water results in pronounced fluid structure interaction. Proximity to the free surface highly influences the test data along with the position angle. Negative position angles in combination with high speeds result in an air pocket open to the atmosphere which translates to a sharp decrease in strain on the sample. Positive position angles yields different free surface effects including vortices and the onset of cavitation.
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Monroy, Aceves Carlos. "Design optimisation of composite structures." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611672.
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Yee, Jeffrey Cheze Hui. "Thin CFRP composite deployable structures." Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614308.
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Cui, Yuefeng. "Adaptive multistable flexible composite structures." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/25513.
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A composite laminate with unsymmetric layup may exhibit two distinct stable configurations at room temperature due to the residual thermal stresses imparted during curing. This bistability leads unsymmetric composite laminates to be good candidates for adaptive flexible structures in particular for the fields of aerospace and aircraft. To extend the application potential of bistable composite laminates, the multistable behaviour of continuous compound composite surfaces are investigated. Two connection approaches are presented in this research. By tailoring the asymmetric bistability of indi- vidual composite elements, continuous surfaces composed of series-connected bistable composite shells demonstrate a high degree of multistability. This model can be developed to design longer composite surfaces possessing more stable shapes. In addition, a high degree of multistability is achieved by connecting square composite elements in a tessellated feature. By reducing the interactions between adjacent elements, a tessellated surface composed of n bistable elements shows a theoretical maximum 2n stable shapes. Finally, potential applications of highly multistable composite surfaces are introduced. The proposed multistable designs improve the flexible functionality of the adaptive structures.
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Malkin, Robert Edward. "Damage tolerant hierarchical composite structures." Thesis, University of Bristol, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557974.
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The use of fibre reinforced polymers is rapidly increasing in a range of applications, from aviation to sporting goods. While the outstanding material properties offered by modern composites make them widely applicable they often suffer from brittle, catastrophic failure. Their inherent brittleness limits their application for safety critical applications without large safety margins. This thesis sets out to introduce design principles that introduce a degree of 'pseudo- ductile' failure behaviour to advanced fibre composites. Much of the inspiration for the work comes from looking at the failure processes of natural hierarchical materials. Many of these materials are able to sustain large amounts of damage at different length scales without catastrophic failure, with many of them being essentially ceramics. Nacre, a relatively simple discontinuous laminated material, served as a major inspiration. Three main strategies were employed to reduce the effects of brittle fracture. Ply terminations were used to selectively weaken a laminate allowing one large fracture to be replaced with a number of smaller ones. Thereby giving indication of the laminates failure and significantly increasing the strain to failure over a traditional laminate. Ply perforations, where portions of a ply are cut, were used to weaken a laminate allowing the location of the fracture to be controlled. The third method tailored interlaminar fracture toughness allowing for steady crack propagation where traditional laminates would suffer unstable crack growth. The work introduces three distinct and highly expandable methodologies capable of reducing the limitations of modern composites.
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Harper, Paul. "Fatigue of composite truss structures." Thesis, University of Bristol, 2009. http://hdl.handle.net/1983/817d2f6f-1364-465c-baaa-a5d8ca405658.
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Truss assemblies offer a high stiffness, light-weight option for the construction of aerospace and civil structures. Their more widespread use is currently limited by significant design challenges associated with the nodal joints between struts, particularly in relation to fatigue. The initial focus of this research degree was the multi-partner, DTI funded `Nodal Optimisation of Truss Structures (NOTS)' project, which explored the potential of replacing a conventional metallic panel aircraft rib with a composite truss structure. The role of the author's work within NOTS was to aid the design of the adhesively bonded nodal joint through the implementation of a fatigue test programme. The NOTS project highlighted the need for improved analysis techniques in relation to both bond-line failure and delamination. To address this requirement, a numerical fatigue crack propagation law was developed within the explicit finite element code 'LS-Dyna. ' The law can be used to evaluate whether the crack tip strain energy release rate is sufficient for crack growth to occur and if so, to simulate the rate and direction of growth. The novelty of this work lies in the detailed analysis of the numerical cohesive zone which forms ahead of the crack tip and is critical to the accurate implementation of the fatigue degradation law. The extraction of strain energy release rate from the cohesive zone enables a direct link with the Paris Law for crack growth and experimental parameters obtained from standard fracture toughness specimens. The analysis technique has been validated using models of standard mode I, mode II and mixed mode specimens. It has then been applied to analyse fatigue crack propagation in both an adhesively bonded single-lap joint and the nodal joint developed within the NOTS project. Recommendations have been provided to guide further development of the analysis technique and to enable its integration within the design process
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Winkworth-Smith, Charles G. "Cellulose composite structures – by design." Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/28823/.
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The aim of the work presented in this thesis was to investigate different mechanical and chemical pre-treatments which can dramatically change the properties of native cellulose and add alternative routes to structure formation. Ball milled cellulose, which had a reduced crystallinity, degree of polymerisation and degradation temperature, was rehydrated in excess water resulting in recrystallisation. Fully amorphous samples recrystallised to the more thermodynamically stable type II polymorphic crystal structure. Flash differential scanning calorimetry (DSC), which allows thermal transitions to be scanned at much higher rates than conventional DSC, was able to register a glass transition temperature for amorphous cellulose. The next stage of the study focussed on the production of freeze dried galactomannan foams. Cellulose fibres provided reinforcement to the foams. The level of reinforcement was related to fibre content, size, crystallinity and surface roughness. Microfibrillated cellulose (MFC) provided the greatest reinforcement due to its much higher surface area and fibrillated structure. Extrusion was found to be a useful alternative to homogenisation for the production of MFC and to create foams using alternative processing to the freeze drying routes. A novel molten salt hydrate, LiCl/urea/water, was found to swell native cellulose and reduce its crystallinity. A weak gel-like structure was formed at ambient temperature. Micro DSC results showed that this structure was melted out at 60oC but the process was reversible indicating hydrophilic to hydrophobic conformational changes on the surface of the cellulose fibres, although these were likely to be dependent on the celluloses having a low degree of polymerisation. In these solvent conditions starch granules were eroded from the outside rather than being swollen as has been found for some ionic liquids and underwent total dissolution in LiCl/urea/water. Fenugreek and xyloglucan, which are both highly branched, were found to increase in viscosity in LiCl/urea/water relative to water, possibly due to the breakage of all intramolecular associations whereas the viscosity of konjac which is predominantly unbranched did not change. Locust bean gum (LBG) had a lower viscosity in LiCl/urea/water compared to water due to the disruption of aggregates. Confocal microscopy showed that fenugreek and LBG are able to bind to cellulose in water, however, the conformational change of fenugreek in these solvent conditions inhibited it from binding to cellulose in LiCl/urea/water whereas conformational change allowed xyloglucan to bind to cellulose in LiCl/urea/water whilst it was unable to bind in water. Konjac did not bind to cellulose in either solvent system. The pre-treatments shown in this work will enable the creation of novel cellulose composites.
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Lee, Hao. "Damage modelling for composite structures." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/damage-modelling-for-composite-structures(ee416524-935c-487d-bcd5-282875e6027a).html.
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Modelling damage in composite materials has played an important role in designing composite structures. Although numerical models for the progressive damage in laminated composites (e.g. transverse cracking, delamination and fibre breakage) have been developed in the literature, there is still a need for further improvement. This thesis aimed at developing damage models suitable for predicting intra-laminar and inter-laminar damage behaviour in fibre-reinforced composite materials. Several approaches such as fracture mechanics and continuum damage mechanics have been adopted for constructing the damage model. Meso-macro-mechanics analysis was performed to gain an insight into the entire damage process up to the final failure of the composite laminate under various conditions. Cohesive elements were placed in the finite element model to simulate the initiation and propagation of matrix crack and delamination in cross-ply laminates. This helped to understand the direct interactions between damage modes, i.e. whether one damage mode would initiate the other damage mode. The formation of a single matrix crack and its propagation across the layer thickness was also revealed. A new cohesive zone/interface element model was developed to consider the effect of through-thickness compressive stress on mode II fracture resistance by introducing friction into the constitutive law of the conventional cohesive zone model. Application of the model to practical problem in composite laminates shows that this model can simulate delamination failure more accurately than the cohesive element in ABAQUS.Damage models based on continuum damage mechanics were proposed for predicting intra-laminar damage and interlaminar damage. Five intra-laminar failure modes, fibre tension, fibre compression, matrix tension, matrix compression and shear failure, were modelled. Damage initiation was predicted based on stress/strain failure criteria and damage evolution law was based on fracture energy dissipation. The nonlinear shear behaviour of the material was considered as well. These models have been implemented into ABAQUS via a user-defined material subroutine and validated against experimental/numerical results available in the literature. The issue related to numerical implementation, e.g. convergence in the softening regime, was also addressed. Numerical simulation of the indentation test on filament-wound pipe was finally conducted and damages generated in the pipe were predicted using the above developed damage models. The predictions show an excellent agreement with experimental observations including load/indentation responses and multiple delaminations shape and size. Attempt was made to detect damage-induced leakage path in the pipe after indentation.
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Gupta, Priyank, and Srikanth Ananthasubramanian. "Early assessment of composite structures." Thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-241268.
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To meet the need of lightweight chassis in the near future, a technological step of introducing anisotropic materials like Carbon Fibre Reinforced Plastics (CFRP) in structural parts of cars is a possible way ahead. Though there are commercially available tools to find suitability of Fibre Reinforced Plastics (FRPs) and their orientations, they depend on numerical optimization and complexity increases with the size of the model. Nevertheless, the user has a very limited control of intermediate steps. To understand the type of material system that can be used in different regions for a lightweight chassis, especially during the initial concept phase, a more simplified, yet reliable tool is desirable. The thesis aims to provide a framework for determining fibre orientations according to the most-ideal loading path to achieve maximum advantage from FRP-materials. This has been achieved by developing algorithms to find best-fit material orientations analytically, which uses principal stresses and their orientations in a finite element originating from multiple load cases. This thesis takes inspiration from the Durst criteria (2008) which upon implementation provides information on how individual elements must be modelled in a component subjected to multiple load cases. This analysis pre-evaluates the potential of FRP-suitable parts. Few modifications have been made to the existing formulations by the authors which have been explained in relevant sections. The study has been extended to develop additional MATLAB subroutines which finds the type of laminate design (uni-directional, bi-axial or quasi-isotropic) that is suitable for individual elements. Several test cases have been run to check the validity of the developed algorithm. Finally, the algorithm has been implemented on a Body-In-White subjected to two load cases. The thesis gives an idea of how to divide the structure into sub-components along with the local fibre directions based on the fibre orientations and an appropriate laminate design based on classical laminate theory.
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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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Flor, Felipe Rendeiro. "Damage monitoring in composite structures via vibration based method: metal-composite bonded joints and sandwich structures." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-04042016-161659/.
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The present document covers the studies over Structural Health Monitoring systems via vibration based methods. The topic is organized in two parallel studies. The first one analyzes the integrity of metal-composite single lap bonded joints. The second one approaches similar analyses for sandwich structures. The monitoring was made by investigating the dynamic response both computationally and experimentally to verify the reliability of applying vibration based SHM procedures, specifically with the objective of identifying the presence of debonding damage. The dynamic responses were obtained via accelerometers and piezoelectric sensors placed on top of the investigated structures (on the outward surface). The purpose for the accelerometers is to provide reference data for the analyses involving the piezoelectric sensors. Different metrics of damage identification were investigated, all working over a determined frequency range. They quantify the damage by analyzing either the magnitudes or phase angles of the dynamic responses among the undamaged and damage structures. This present work proposed modifications to some methodologies of damage quantification found in the literature and compared the results. The new metrics offered more reliable values for the damage quantification on several of the analyses. It was verified that the metrics are valid for the scenarios observed in the present study. The experimental analyses showed also the influence on the dynamic response due to the position of small elastomeric elements. In regards to the finite element analyses, the computational models showed similar results to the experimental data, the more accurate ones being the models for the bonded joints. For the computational models, improvements can be applied into the piezoelectric sensor (e.g. by using new finite element formulations), as well as the region of debonding (e.g. by using contact algorithms). It is important to highlight that the elastic properties of the skins for the sandwich structure were obtained by the literature, so the model can be improved in the future by applying properties obtained experimentally.Esta dissertação aborda os estudos realizados no campo de Sistemas de Monitoramento da Integridade Estrutural por meio de métodos baseados em vibrações. O tópico abordado é organizado em dois estudos paralelos. O primeiro é relativo ao monitoramento da integridade de juntas coladas metal-compósito. O segundo versa sobre análises semelhantes em estruturas sanduíche. O monitoramento foi executado através das análises das assinaturas dinâmicas das estruturas, tanto computacionalmente quanto experimentalmente, visando avaliar a capacidade de metodologias vibracionais de SHM em detectar dano de descolamento. As respostas dinâmicas foram obtidas por meio de acelerômetros e sensores piezelétricos dispostos sobre a superfície das estruturas avaliadas. Os acelerômetros fornecem dados de referência para as análises realizadas com base nas respostas do sensor piezelétrico. Diferentes métricas de identificação de dano são abordadas, sendo que todas estão baseadas em análise no domínio da frequência, utilizando parâmetros de magnitude ou ângulo de fase das estruturas danificadas e intactas. O presente trabalho propôs alterações em algumas das metodologias encontradas na literatura e comparou os resultados das métricas originais com as modificadas. As métricas modificadas apresentaram resultados mais consistentes em vários cenários de análise. Constatou-se também que as métricas abordadas mostram-se válidas para os casos observados no presente estudo. As análises experimentais também evidenciaram a influência na assinatura dinâmica da estrutura sanduíche causada pelo posicionamento de pequenos elementos elastoméricos. Com relação às análises via elementos finitos, os modelos computacionais apresentaram resultados similares aos obtidos experimentalmente, sendo os da junta colada os mais precisos. Tais modelos computacionais podem ser melhorados no futuro por meio de uma modelagem mais detalhada dos elementos piezelétricos (por exemplo: por meio de novas formulações), como também da região de descolamento (por exemplo: por meio da implementação de algoritmos de contato). Deve-se ressaltar também que as propriedades elásticas das lâminas externas da estrutura sanduíche foram obtidas da literatura, assim sendo, o modelo poderá ser melhorado em estudos futuros por meio do emprego de propriedades obtidas experimentalmente.
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Khoo, Stephen W. "Low velocity impact of composite structures." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/7388.
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Soleiman, Fallah Arash. "Behaviour of blast resistant composite structures." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/11919.
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Chang, Min-Yung. "Active vibration control of composite structures." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-09162005-115021/.
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Mills-Brown, Joseph. "High temperature composite materials and structures." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.617589.
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The recent resurgence and growing interest in high temperature structures to maximise design space and performance in motorsport applications, led to the need for greater understanding of high temperature composite materials. This study aimed to investigate suitable materials for high temperature structures with application to the motorsport environment. Composite materials were quickly identified as the most appropriate materials given the needs of motorsport, with polysialate composites championed after a thorough review of available materials. A commercially available composite reinforced with silicon carbide fibres was selected to meet the study requirements. This led to the need for thermal and mechanical characterisation in order to provide temperature dependant data suitable for accurate design of high temperature structures. The result of .this was a full engineering dataset for the most widely used polysialate composites, filling In significant gaps in the literature, whilst simultaneously producing a novel and unique high temperature tensile testing rig for this composite laminates. In turn, this new data was exploited with application to a polysialate composite case study structure; an exhaust liner used on current Formula One vehicles. This required full understanding of the thermal and mechanical load cases experienced by the liner, in order to accurately simulate the liner and environment using finite element analysis. Not only did this provide an application of the newly acquired temperature dependant material properties, but it also highlighted the need for temperature dependant properties in the design of high temperature structures. The study, its aims and approach, were validated through comparison of simulation failure predictions against component failed in service.
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Russell, Jacob E. "Dynamic response of composite structures underwater." Thesis, Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/37704.
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Approved for public release; distribution is unlimitedThis paper presents a comparison of the dynamic response of composite structures that are subjected to low velocity impacts while being suspended both in air, and submerged in water. As the U.S. Navy continues to use larger composite components in the construction of their ships, an understanding of the effect of submergence in water (i.e., fluid-structure interaction) on various locations of the structures can be instrumental in the design process of ship components. To better understand the responses at varying locations due to fluid-structure interaction, a composite plate was made with several strain gages affixed in one quadrant. The plate was then subjected to increasing impact forces while suspended in air, as well as being submerged in water. Additionally, a beam sample was also tested under the same conditions, with strain gages being affixed in-line with the impact rod. By comparing the strain gage responses between the open air and submerged samples, a better understanding of the magnitude of the fluid structure interaction is achieved, identifying critical locations in the samples that are most likely to fail.
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Padhi, Gouri S. "Numerical failure modeling of composite structures." Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312862.
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Kontis, Nikolaos. "Damage tolerance of composite stiffened structures." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488883.
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Composite stiffened panels have been extensively used in primary aerospace applications, due to their efficient stiffness/weight ratio and the ability to tailor properties. Despite their apparent superiority to metals, the susceptibility of composites to damage has proved to be a critical factor. A common example in practice is the barely visible impact damage caused by a low velocity impact event. Such events can generate inter-laminar defects (delaminations), which under compressive loading can reduce the strength and stability of the structure. There is a need to establish the influence of such damage on composite stiffened structures. Current practice allows for delamination induced strength reduction by applying strain limits to the material that ensure delamination does not produce failure before uhimate levels of loading. However, these limits are established via coupon tests, which focus on the scale of the delamination only and do not account for the interaction at the structural scale.
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Dizy, Suarez Julian. "Homogenisation of slender periodic composite structures." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24732.
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The increasing efficiency and performance requirements on current aircraft requires the use of novel configurations and analysis methodologies which capture their behaviour both accurately and efficiently. In spite of the great improvements in computational power, simulating the full 3D structure is too costly and unviable for conceptual design stages. Hence, reduced order models that accurately describe the behaviour of these engineering structures are demanded. This work focuses on those that have a dominant dimension and, because the characteristic length of the sought response so allows it, can be assimilated into a 1-D beam model. A homogenisation technique is introduced to obtain the full 6x6, i.e. including transverse shear effects, equivalent 1-D stiffness properties of complex slender composite structures. The classical 4x4 stiffness matrix is obtained for periodic structures, that is, without the usual assumption of constant cross sections. The problem is posed on a unit cell with periodic boundary conditions such that the small-scale strain state averages to the large-scale one and the deformation energy is conserved between scales. The method is devised such that its implementation can be carried out using a standard finite-element package whose advantages can be exploited. This technique is readily applicable to engineering models. It provides a new level of modelling flexibility by employing tie constraints between different parts so that parametric analyses or optimisation can be performed without re-meshing. The proposed methodology allows local stress recovery and local (periodic) buckling strength predictions; nonlinear effects such as skin wrinkling can therefore be propagated to the large scale. Numerical examples are used to obtain the homogenised properties for several isotropic and composite beams, with and without transverse reinforcements, taper or thickness variation, and for both linear and geometrically-nonlinear deformations. The periodicity in the local post-buckling response disappears in the presence of localisation in the solution and this is also illustrated by a numerical example. Finally, the code originated from this work, SHARP.cells, is coupled with a nonlinear beam solver.
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Spendley, Paul R. "Design allowables for composite aerospace structures." Thesis, University of Surrey, 2012. http://epubs.surrey.ac.uk/810072/.
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Recent developments in aircraft design have seen the Airbus A380 and the Boeing Dreamliner employ significant amounts of advanced composite materials. There is some thought however, und the motivation for this current work, that these materials continue to suffer a weight penalty. In this work tests required to generate design allowables which accommodate environmental effects and holes arc performed on Carbon/epoxy quasi-isotropic laminatcs. The test data is treated statistically to provide B-basis allowables for each specimen type and condition. It was seen that the notched specimens (coupons containing a centrally placed through hole) displayed significantly less scatter in strength than unnotched specimens. This is significant when considering the widespread use of deterministic knock-down factors as an alternative route to obtain design allowables which accommodate environmental effects and/or holes. This results in an over-conservative design allowable being employed in subsequent structural design calculations. The possibility for using notched coupons to determine design allowables was explored using the COG (Critical Damage Growth) model. This showed that. given two of the three parameters. the unnotched and notched strength, and fracture toughness the variation in strengths could be reasonable predicted. This leads to a more representative design allowable by maintaining the statistical nature of the B-basis allowable. During the statistical treatment of the test data it was also seen that although current aerospace guidelines recommend a particular distribution model (i.e. the Wcibull distribution) this can also leads to an artificially reduced design allowable. These findings suggest that the use of notched specimens can lead to a reduced development test programme and reduced structural weight.
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Saillant, Jean-Francois. "Study of multilayer piezoelectric composite structures." Thesis, University of the West of Scotland, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.742766.
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Steeves, Craig A. "Mechanics of failure in composite structures." Thesis, University of Cambridge, 2001. https://www.repository.cam.ac.uk/handle/1810/272005.
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Vovk, S. Ya, and O. Yu Pazen. "Fire resistance of composite concrete structures." Thesis, КТИ КЧС МВД РК, 2017. http://hdl.handle.net/123456789/4038.
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Vovk, S. Ya, and O. Yu Pazen. "Fire resistance of composite concrete structures." Thesis, КТИ КЧС МВД РК, 2017. http://hdl.handle.net/123456789/4037.
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Jaswal, Priya. "Health Monitoring of Large Composite Structures." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1562842764406158.
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Zhang, Chao. "Mechanical behavior of tubular composite structures." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1627489300935781.
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Faggiani, Andrea. "Optimisation of postbuckling stiffened composite structures." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/8001.
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The thesis starts off with an introductory chapter on composite materials. This includes a definition of composites, a brief history of composite materials, their use in aerostructures (primarily as stiffened structures), and also optimization of composite structures. A literature review is then presented on postbuckling stiffened structures. This includes both experimental investigations on stiffened composite panels and investigations into secondary instabilities and mode jumping as well as their numerical modelling. Next, the Finite Element (FE) modelling of posthuckling stiffened structures is discussed, relating how ABAQUS models are set up in order to trace stiffened composite panels' buckling and postbuckling responses. An experimental programme conducted on an I-stiffened panel is described, where the panel was tested in compression until collapse. The buckling and postbuckling characteristics of the panel are presented, and then an FE model is described together with its predicted numerical behaviour of the panel's buckling and postbuckling characteristics. Focus then shifts to the modelling of failure in composites, in particular delamination failure. A literature review is conducted, looking at the use of both the Virtual Crack Closure Technique (VCCT) and interface elements in delamination modelling. Two stiffener runout models, representing two specimens previously tested experimentally, are then developed to illustrate how interface elements may be used to model mixed mode delamination. The previously discussed panel is revisited, and a global-local modelling approach used to model the skin-stiffener interface. FE models of a stiffened cylindrical shell are also considered, and again the postbuckling characteristics of the shell are compared with experimental results. . The thesis then moves on to optimization of composite structures. This starts off with a literature review of existing optimization methodologies. A Genetic Algorithm (GA) is devised to increase the damage resistance of the I-stiffened panel. The global-local ABAQUS model discussed earlier is used in conjunction with the GA in order to find a revised stacking sequence of both the panel flanges and skin so as to minimize skin-stiffener debonding subject to a variety of design constraints. A second optimization is then presented, this time linked to the FE model of the stiffened cylindrical shell. The objective is to increase the collapse load of the shell, again subject to specific design constraints. The thesis concludes by summarising the importance of the work conducted. FE models were created and validated against experimental work in order to model a variety of composite stiffened structures in their buckling and postbuckling regimes. These models were able to capture the failure characteristics of these structures relating to delamination at the skin-stiffener interface, a phenomenon widely observed experimentally. Various optimizations, able to account for failure mechanisms which may occur prior to overall structural collapse, were then conducted on the analysed structures in order to obtain more damage resistant designs.
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Cullinan, Jack Francis. "In-situ repair of composite structures." Thesis, University of Bristol, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.738199.
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GARG, RAVIN. "Design of Crashworthy Automotive Composite Structures." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2910074.
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Kabche, Jean Paul. "Structural Testing and Analysis of Hybrrid Composite/Metal Joints for High-Speed Marine Structures." Fogler Library, University of Maine, 2006. http://www.library.umaine.edu/theses/pdf/kabchejp2006.pdf.
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Na, Gwang-Seok. "Load-displacement behavior of frame structures composed of fiber reinforced polymeric composite materials." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26699.
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Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2009.Committee Chair: Dr. Leroy Z. Emkin; Committee Co-Chair: Dr. Abdul-Hamid Zureick; Committee Member: Dr. Dewey H. Hodges; Committee Member: Dr. Kenneth M. Will; Committee Member: Dr. Rami M. Haj-ali. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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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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