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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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Sander, Tavallaey Shiva. "Wave propagation in sandwich structure." Doctoral thesis, KTH, Vehicle Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3088.
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Tran, Van Luan. "Etude du comportement hygro-thermo-mécanique d'un matériau composite sandwich avec âme balsa utilisé en applications navales." Nantes, 2013. http://www.theses.fr/2013NANT2001.
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Les matériaux composites sandwichs ont été largement adoptés dans le domaine naval car ils présentent des atouts de légèreté et de bonne résistance mécanique. Cependant, leur tenue à l'humidité en environnement marin est encore difficile à prédire et leur résistance au feu constitue l'une des limitations principales à leur utilisation dans un plus grand nombre de cas. Ce travail s'intéresse au comportement d'un composite sandwich à base de peaux en verre-polyester et d'une âme balsa. Le balsa, élément principal du matériau, peut absorber une très grande quantité d'eau ce qui peut alors affecter ses caractéristiques mécaniques. De plus, la présence d'humidité peut influer sur la tenue au feu du matériau. Aussi, afin de mettre en évidence la durabilité du matériau et la physique des phénomènes rencontrés, de nombreuses expériences ont été menées en conditions variées d'humidité, de température et de chargements mécaniques. En complément de résultats classiques obtenus sur le balsa, des essais de tenue au feu ont été associés à des essais de flexion du composite sandwich pour en estimer la résistance en fonction du temps de combustion. Enfin, à partir de résultats expérimentaux associés à la reprise en eau du balsa et du composite sandwich, des modélisations permettant de mieux comprendre et de prédire l'état mécanique de la structure sandwich ont été établisSandwich composite structures have been widely adopted in the naval field because they exhibit both lightness and good mechanical strength. However, their resistance to moisture in the marine environment is difficult to predict, and their fire resistance is one of the main limitations to their use in a greater number of cases. In this work, we focus on the behavior of a composite sandwich composed with glass-polyester skins and balsa core. Balsa, which is the main constituent, can absorb a large amount of water which may affect its mechanical properties. Moreover, the presence of moisture can influence the fire resistance of the material. Thus, in order to highlight the material durability and the physical phenomena encountered, several experiments were performed in miscellaneous conditions of humidity, temperature and mechanical loadings. In addition to classical results obtained on the balsa, testing of fire resistance combined with bending tests on sandwich composite materials were achieved to estimate the residual strength as a function of the combustion time. Finally, from experimental results related to the water uptake of balsa and of sandwich composite, modelling was computed to better understand and predict the mechanical state of the studied sandwich structure
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Hui, Yi. "Development and experimental validation of vibration based damage indicator on a specific twin-wall sandwich structure." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC032.
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La surveillance de santé structurale (SHM) a attiré beaucoup d'attention dans de nombreux domaines tels que l'industrie civile, aéronautique, mécanique, etc., car il est important de surveiller l'état de la structure afin d'éviter des défaillances structurelles imprévues. Le processus d'identification des endommagements à quatre niveaux: existence, localisation, sévérité et prédiction de l'évolution des endommagements peut être partiellement réalisé si un propre indicateur est bien choisi. Il existe différents indicateurs d'endommagements dont la gamme d'application de la fréquence s'étend de la réponse vibratoire à basses fréquences aux régimes ultrasoniques dans la gamme méga hertz.Les structures sandwich sont largement utilisées dans diverses applications d'ingénierie en raison de son rapport rigidité / poids exceptionnellement élevé par rapport aux structures monocoques. Dans ce travail, une structure sandwich a été étudiée et des indicateurs basés sur la réponse vibratoire ont été conçus en utilisant ses caractéristiques de directivité de propagation et d'amortissement relativement élevé de la structure. Des investigations numériques sur différents scénarios d'endommagement (càd, différents types d'endommagement et leurs combinaisons) et une discussion associée sur la plage d'application ont d'abord été effectuées. La configuration expérimentale a été facilement réalisée à l'aide d'un vibromètre laser à balayage Doppler (SLDV). L'endommagement a été détecté avec succès par les indicateurs proposésStructural health monitoring (SHM) has attracted much attention in many engineering fields like civil, aeronautic, mechanical industry, etc. since it is important to monitor the healthy condition of the operational structure in order to avoid unpredicted structural failure which may have severe consequences. The four-level damage identification process: existence, localization, severity and prediction of damage evolution, can be partly realized if a suitable indicator is chosen. It exists different damage indicators whose application range of frequency spans from vibrational response at low frequencies to the ultrasonic regimes in the mega hertz range.The sandwich structures are widely used in various engineering applications due to its exceptionally high flexural stiffness-to-weight ratio compared to monocoque structures. In this thesis a specified twin-wall sandwich structure in polypropylene was studied and vibration-based indicators were designed by taking use of its relative high damping and propagation directivity characteristics. Numerical investigations on different damage scenarios (i.e., different types of defect and their combinations) and an associated discussion on the range of application were first carried out. Experimental configuration was easily realized with the help of a scanning laser doppler vibrometer (SLDV). Defect was successfully detected by the proposed indicators
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Zhang, Shufeng. "Thermomechanical interaction effects in polymer foam cored sandwich structure." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/351349/.
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Polymer foam cored sandwich structures are frequently exposed to elevated temperatures in the range of 50-100°C. Recent theoretical studies showed that elevated temperatures may shift the behaviour of sandwich structures from linear and stable to nonlinear and unstable. Although this prediction has not been experimentally validated, it has aroused concerns on the performance of sandwich structures at elevated temperatures. Thereby, a focused experimental study is required to confirm the thermomechanical interaction effects. The work described in this thesis provides experimental assessments on the thermomechanical interaction effects in polymer foam cored sandwich structures. As a starting point, a novel methodology is proposed to obtain the elastic properties of polymer foam materials at elevated temperatures based on digital image correlation (DIC). The tensile, compressive and shear properties were characterised at temperatures from room temperature to 90°C. It is identified that the thermal degradation of the elastic modulus of polymer foams only depends on the base polymer, regardless of the deformation type or foam density. A master curve is derived which shows the temperature dependence of the Young's and shear moduli of Divinycell H100, H130 and H200 foam. An experimental apparatus is constructed to allow sandwich beam specimens to be subjected to a bending load as well as a well-defined temperature gradient through the beam thickness. The bending deflection, inhomogeneous core shear deformation and the wavy deflection of face sheet at the onset of localised buckling/wrinkling are accurately characterised using DIC. High-speed imaging was also adopted to view the rapid evolution of the wrinkles. It was found that, at elevated temperatures, the core shear strain can be nonuniform through the core thickness and the failure mode can shift to wrinkling instability. Simple analytical models are also developed to predict the behaviour of sandwich beams with transverse temperature gradients and consequently core stiffness gradients. A modification of the classical sandwich beam theory is proposed to predict the stress/strain state, load-defection response and failure mechanism with respect to the core shear yielding and face sheet yielding/fracture. Another analytical model is developed to predict the critical wrinkling stress. Both of the two models agree well with the experiments. The work described in the thesis demonstrates that the stiffness and load carrying capability of polymer foam cored sandwich structures are deteriorated by elevated temperatures. The deterioration can be confidently predicted by the experimentally validated analytical models introduced in the thesis. The study thereby provides a significant step towards an improved understanding of thermomechanical interaction effects in polymer foam cored sandwich structures.
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Besse, Camille. "Development and optimization of a formable sandwich sheet." Phd thesis, Palaiseau, Ecole polytechnique, 2012. https://theses.hal.science/docs/00/69/12/46/PDF/These_Camille_Besse.pdf.
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Le comportement mécanique d'un nouveau type de tôle sandwich métallique apte à la mise en forme est étudié. La couche cœur est composée de deux tôles gaufrées, brasées entre elles. Contrairement aux panneaux sandwichs conventionnels, ce type de tôle sandwich peut être mis en forme par les techniques traditionnelles de travail des métaux. Dans un premier temps, la géométrie de la structure gaufrée est optimisée afin d'obtenir la couche cœur présentant un rapport raideur au cisaillement - densité relative maximal. L'étude se concentre ensuite sur le comportement plastique de la structure sandwich " optimale " à l'aide de simulations par éléments finis d'expériences multiaxiales. On propose un modèle phénoménologique faisant appel à une loi d'écoulement associée et à un modèle d'écrouissage isotrope avec distorsion. Les paramètres du modèle sont identifiés par une approche inverse à partir d'un essai de traction uniaxial et d'un essai de flexion 4 points. Finalement, des simulations de pliage en U sont réalisées, utilisant un modèle détaillé d'une part et un modèle coque d'autre part. Pour différents outils de mise en forme, un bon accord entre les simulations est observé, validant en partie le modèle phénoménologique proposéThis thesis investigates the mechanical behavior of a new type of formable all-metal bi-directionally corrugated sandwich sheet material. Unlike conventional flat sandwich panel materials, this type of sandwich sheet material can be formed into three-dimensional shapes using traditional sheet metal forming techniques. In a first step, the core structure geometry is optimized such as to offer the highest shear stiffness-to-weight ratio. The post yielding behavior of the "optimal" sandwich structure is investigated using finite elements simulations of multi-axial experiments. A phenomenological constitutive model is proposed using an associative flow rule and distortional hardening. An inverse procedure is outlined to describe the sandwich material model parameter identification based on uniaxial tension and four-point bending experiments. In addition, simulations of a draw bending experiment are performed using a detailed finite element model as a well as a computationally-efficient composite shell element model. Good agreement of both simulations is observed for different forming tool geometries which is seen as a partial validation of the proposed constitutive model
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Besse, Camille. "Development and optimization of a formable sandwich sheet." Phd thesis, Ecole Polytechnique X, 2012. http://tel.archives-ouvertes.fr/tel-00691246.
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Le comportement mécanique d'un nouveau type de tôle sandwich métallique apte à la mise en forme est étudié. La couche cœur est composée de deux tôles gaufrées, brasées entre elles. Contrairement aux panneaux sandwichs conventionnels, ce type de tôle sandwich peut être mis en forme par les techniques traditionnelles de travail des métaux. Dans un premier temps, la géométrie de la structure gaufrée est optimisée afin d'obtenir la couche cœur présentant un rapport raideur au cisaillement - densité relative maximal. L'étude se concentre ensuite sur le comportement plastique de la structure sandwich " optimale " à l'aide de simulations par éléments finis d'expériences multiaxiales. On propose un modèle phénoménologique faisant appel à une loi d'écoulement associée et à un modèle d'écrouissage isotrope avec distorsion. Les paramètres du modèle sont identifiés par une approche inverse à partir d'un essai de traction uniaxial et d'un essai de flexion 4 points. Finalement, des simulations de pliage en U sont réalisées, utilisant un modèle détaillé d'une part et un modèle coque d'autre part. Pour différents outils de mise en forme, un bon accord entre les simulations est observé, validant en partie le modèle phénoménologique proposé.
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Barré, Sébastien. "Optimisation d'une structure sandwich dans le cadre d'une utilisation structurelle ferroviaire." Compiègne, 1996. http://www.theses.fr/1996COMPD964.
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Vinhas, Bertolini Peter. "Modélisation des poutres sandwich elasto-piézo-électriques : élément fini raffiné." Paris, ENSAM, 2001. http://www.theses.fr/2001ENAM0001.
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Wilhelm, Arnaud. "Développement d’une méthodologie pour la compréhension du comportement et le dimensionnement d’un bouclier sandwich soumis à l’impact d’un oiseau." Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0005/document.
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Durant le vol d'un aéronef, la collision avec un oiseau est un risque important que les autorités de certification imposent de prendre en compte. Dans le cas du choc sur pointe avant, la protection du fond pressurisé est assurée par un bouclier. La compréhension du comportement d'une telle structure sandwich sous impact est essentielle pour permettre l'amélioration des boucliers existants. Ces travaux ont pour buts de comprendre l'influence des différents paramètres de conception du bouclier sur son comportement et sur la protection de la cible, et de mettre en place une méthodologie pour réaliser une telle étude. Pour cela, un modèle éléments finis générique est créé pour être utilisé dans l'étude paramétrique. Une méthode de mesure de la déformée est proposée pour permettre la comparaison rapide d'un grand nombre de cas et la compréhension du comportement de chaque bouclier. Elle s'appuie sur la décomposition de la déformée en trois modes : Indentation, Flexion et Écrasement. Une étude de criblage est ensuite réalisée pour classer les paramètres de définition par ordre d'influence. L'étude paramétrique est réalisée sur les six paramètres les plus influents. Un plan d'expérience de type carré Latin est choisi et sept grandeurs différentes sont suivies. Le cadre des processus gaussiens est utilisé pour créer des modèles réduits, qui sont utilisés pour étudier l'évolution du comportement du bouclier sur l'ensemble du domaine à l'aide d'analyses de sensibilité. Les effets de chaque paramètre sont identifiés et expliqués. Enfin, une méthode pour l'utilisation de ces modèles réduits dans le cadre d'optimisations est proposéeDuring an aircraft flight, the possible collision with a bird is a major threat, and the certification authorities require to take ît into account. In the case of a nose strike, the pressurized bulkhead is protected by a shield. Understanding the behaviour under impact of such a sandwich structure is essential. This work has two main goals: understanding the design parameters influence on the shield behaviour, and propose a methodology to conduct this study. Firstly, a generic finite element model is created to be used in a parametric study. A tool to measure the shield deformation is proposed to make it possible to easily compare the behaviour of different shields and to help understanding the behaviour of a shield. This tool is based on the projection ofthe shield deformation on a basis comprising three modes: Indentation, Bendîng and Crushing. A screening study is then conducted to rank the design parameters with respect to their influence. A parametric study is then conducted on the six first parameters. A Latin hyper-square is used for the design of experiment and seven different quantifies are studied. The Gaussian processes framework is used to create surrogates models. Global sensitivity analyses are then conducted to study the variation of the shield behaviour in the whole design space. The effects of each parameterare measured and explained. Finally, a method to minimize the shield mass, using the surrogate models to enforce minimal target protection criteria, is presented
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Evteev, Alexander V., Elena V. Levchenko, Irina V. Belova, and Graeme E. Murch. "Formation of a surface–sandwich structure in Pd-Ni nanoparticles by interdiffusion: Formation of a surface–sandwich structure in Pd-Ni nanoparticlesby interdiffusion: atomistic modelling." Diffusion fundamentals 6 (2007) 18, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14192.
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Iu, Vai-pan. "Nonlinear vibration analysis of multilayer sandwich structure by incremental finite elements /." [Hong Kong : University of Hong Kong], 1985. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12322945.
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Riccò, Federico. "Design and engineering of 100% polyurethane sandwich structure for sanitary application." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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This work is based on a team research project developed at DUNA-Corradini SpA. The project consists in design and characterization of innovative composite structure, used principally for the production of shower trays for sanitary application.
Starting from a set of existing PUR materials trademark of DUNA-Corradini SpA, DUNAPOL® T products, we worked to combine them to obtain a new composite sandwich structure for 100% PU based shower trays manufacturing, avoiding the use of glass fibres and styrene-based materials in the final product.
The final prototype must be able to satisfy costumer’s requirements in terms of mechanical properties, weight, and production cost.
A brief literature review is presented, regarding polyurethane chemistry, studied materials and sandwich structures. Mechanical tests were performed to study mechanical behaviour and to classify DUNAPOL® T products for sandwich production.
Impact tests were performed on different sandwich structures to identify best materials for both “skin” and “core”, studying the main parameters that affect impact resistance of polyurethanes. Optimization procedure was applied working on PU formulation, core density and skin thickness principally.
Materials for sandwich structures production able to withstand requirements in terms of impact resistance, were identified. Final sandwich structure obtained is characterized by high weight saving (up to 60%), good dimensional stability and low cost related to raw materials used.
Finally, production of shower tray prototypes with different coatings was performed. Production process suitable for 100% PU-based shower trays was defined, exploiting DUNA-Corradini know-how in PU industry. Production process steps are then validated at DUNA-Corradini laboratories, to obtain shower tray prototypes. Then, a FMEA, failure mode and effect analysis, is applied on the production process considered, based on sandwich and shower tray production carried out in laboratory.
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Iu, Vai-pan, and 姚偉彬. "Nonlinear vibration analysis of multilayer sandwich structure by incremental finite elements." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1985. http://hub.hku.hk/bib/B31230623.
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Lundgren, Eric Charles. "Durable Sandwich Structure Joining Technology for NASA's Ares V Launch Vehicle." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/79693.
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Joining of uniformly-curved composite sandwich panel segments, typical in state of the art aerospace launch vehicles, should be mass-efficient. Adhesively bonded joints can provide increased mass-efficiency over mechanically-fastened joints. But, due to manufacturing sensitivities and certification requirements, conventional bonded joints can be improved upon by introducing structural redundancy. A longitudinal, durable redundant joint (DRJ) architecture featuring multiple adhesive load-paths, via a novel composite preform insert, was proposed to join composite sandwich panel segments of the interstage element for NASA's Ares V launch vehicle. A series of twenty-five static linear-elastic finite element models with plane strain solutions were developed to assess certain characteristics of a joint's structural response when subjected to a simplified circumferential hoop loading convention.
Shear and normal stress distributions at the adherend-adhesive interface along the splice plate bondline of the DRJ are compared with those from a conventional splice joint (CSJ) configuration for a series of linearly increasing bondlines thicknesses and joint overlap lengths. The parameter studies indicate the DRJ configuration's adhesive peak stresses are independent of the joint overlap length at the joint edges. Also, simulated bonding defects, in the form of local adhesive gaps, due to manufacturing processes are investigated to determine the load path redistribution for the DRJ and CSJ configurations. Results for pristine versions of both configurations are included. The defective CSJ joint exhibits severe overloading of certain laminates, while the defective DRJ load redistributions are relatively mild. Between the two primary types of bondline gaps considered for the DRJ configuration, the gap corresponding to the splice plate, a more mature manufacturing operation and also a more easily inspected location than the insert-to-face sheet interface, is noted to be more severe.
A direct joint-to-joint mass-comparison reveals a 164% increase in mass, per unit thickness, between the CSJ and DRJ. To put this in perspective, a second comparison is made using a four-segment sandwich panel barrel. A 3.51% increase in mass is observed between the CSJ and DRJ-based cylinders. Also, for a simplified sizing philosophy, based solely on the peak stresses in the adhesive domain, a CSJ may require a 1.5-inch longer joint overlap than a DRJ. The mass-estimate is recomputed, and the mass percent-increase of the segmented cylinder is reduced to 2.61% over a CSJ configuration.Master of Science
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Bull, Peter H. "Damage tolerance and residual strength of composite sandwich structures." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3757.
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The exploitation of sandwich structures as a means toachieve high specific strength and stiffness is relatively new.Therefore, the knowledge of its damage tolerance is limitedcompared to other structural concepts such as truss bars andmonocoque plate solutions.
Several aspects of the damage tolerance of sandwichstructures are investigated. The influence of impact velocityonresidual strength is investigated. Sandwich panels withfaces of glass fiber reinforced vinylester are impacted bothwith very high velocity and quasi static. The residual strengthafter impact is found to be similar for both cases of impactvelocity.
Curved sandwich beams subjected to opening bending momentare studied. Faceñcore debonds of varying size areintroduced between the compressively loaded face sheet and thecore. Finite element analysis in combination with a pointstress criterion is utilized to predict the residual strengthof the beams. It is shown that it is possible to predict thefailure load of the beams with face-core debond.
Using fractography the governing mode of failure ofcompressively NCF-carbon is characterized. Sandwich panelssubjected to compression after impact are shown to fail byplastic micro buckling.
The residual compressive strength after impact of sandwichpanels is investigated. Sandwich panels with face sheets ofnon-crimp fabric (NCF) carbon are subjected to different typesof impact damages. Predictions of residual strength are madeusing the Budiansky, Soutis, Fleck (BSF) model. The residualstrength is tested, and the results are compared topredictions. Predictions and tests correlate well, and indicatethat the residual strength is dependent on damage size and notthe size of the damaged panel.
A study of the properties of a selection of fiberreinforcements commonly used in sandwich panels is conducted.The reinforcements are combined with two types of core materialand three types of matrix. Also the influence of laminatethickness is tested. Each combination materials is tested inuni-axial compression, compressive strength after impact andenergy absorption during quasi static indentation. Thespecimens which are tested for residual strength are eithersubjected to quasi-static or dynamic impact of comparableenergy level. Prediction of the residual strength is made andcorrelates reasonably whith the test results. The tests showthat if weight is taken into account the preferred choice offiber reinforcement is carbon.
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Berkowitz, Charles Kyle. "Characterization of the debonding of graphite/epoxy-nomex honey comb sandwich structure." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/18188.
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Shipsha, Andrey. "Failure of Sandwich Structures with Sub-Interface Damage." Doctoral thesis, Stockholm, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3184.
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Bail, Justin L. "Non-desctructive investigation & FEA correlation on an aircraft sandwich composite structure." Akron, OH : University of Akron, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1196702586.
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Thesis (M.S.)--University of Akron, Dept. of Civil Engineering, 2007."December, 2007." Title from electronic thesis title page (viewed 02/25/2008) Advisor, Wieslaw Binienda; Faculty readers, Craig Menzemer, Robert Goldbert; Department Chair, Wieslaw Binienda; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
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McCrillis, Ryan D. "Dynamic failure of sandwich beams with fluid-structure interaction under impact loading." Thesis, Monterey, California. Naval Postgraduate School, 2010. http://hdl.handle.net/10945/5101.
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Approved for public release; distribution is unlimitedThe objective of this research is to examine the added mass effect that water has on the dynamic response of a sandwich composite under impact, particularly impact leading to failure. Because sandwich composites are much less dense than water, fluid structure interaction plays a large part in the failure. Composite samples were constructed using vacuum assisted transfer molding, with a 6.35 mm balsa core and symmetrical plain weave 6 oz E-glass skins. The experiment consisted of three phases. First, using threepoint bending, strain rate characteristics were examined both in air and under water. After establishing that the medium had no effect on the beam response under different strain rates, but confirming that previously established relationships between strain rate and ultimate strength for axially loaded glass composites can be applies to sandwich construction in bending, the experiment progressed to impact testing where each specimen, again a one inch wide beam, was subjected to progressively increasing force. The data from this phase showed that submerged samples failed at lower drop heights and lower peak forces with a failure mode dominated by center span skin compression failure. Beams in air were able to withstand higher drop heights and peak forces. Dry sample failure mode was dominated by skin compression failure at the clamped support with occasional evidence of shear failure through the core adjacent to the clamped support. The data from this study will increase understanding of sandwich composite characteristics subjected to underwater impact.
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Evteev, Alexander V., Elena V. Levchenko, Irina V. Belova, and Graeme E. Murch. "Formation of a surface–sandwich structure in Pd-Ni nanoparticles by interdiffusion." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193359.
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HODAR, FRANCOIS. "Caracterisation et modelisation d'une structure sandwich, deformee par une ceramique piezoelectrique pzt." Besançon, 1996. http://www.theses.fr/1996BESA2017.
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La volonte d'assurer la stabilite dimensionnelle de certaines structures spatiales planes a eu pour effet de developper un nouveau concept de materiau-structure appele structure adaptative. Elle est constituee d'une structure inerte sur laquelle sont colles des capteurs, des actionneurs relies par un systeme d'asservissement. L'etude a porte principalement sur la caracterisation et la modelisation d'une structure sandwich deformee par un actionneur. Ce dernier peut etre de natures diverses. Dans le cas present, le choix s'est porte sur les ceramiques piezoelectriques pzt. Avant toute realisation, une caracterisation du pzt a ete entreprise. Elle a revele des comportements originaux que la ceramique soit soumise a un champ electrique ou a une contrainte mecanique ou a un couplage des deux. Les mesures du comportement de la ceramique ont ete principalement realisees dans une gamme de champo electrique et de contrainte qui est celle que rencontre le materiau quand il sert d'actionneur. A la suite de cette caracterisation un modele de comportement deformation/champ electrique de l'actionneur a ete developpe. Enfin, la structure adaptative a ete realisee et caracterisee. Bien que l'ensemble des comportements soit similaire a ceux d'une ceramique piezoelectrique pzt, certaines differences apparaissent. Ces dernieres sont dues d'une part, a l'effet de la contrainte (poutreactionneur) sur le comportement deformation/champ electrique, d'autre part a certaines particularites structurelles. Une modelisation analytique de deformation de poutre par actionneur a ete realisee ; en parallele une methodologie de modelisation par elements finis a ete mise au point pour pouvoir etendre l'etude a la conception de structures adaptatives plus complexes
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Bail, Justin. "Non-Destructive Investigation & FEA Correlation on an Aircraft Sandwich Composite STructure." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1196702586.
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Allaoui, Samir. "Etude et modélisation d'un comportement de structure sandwich de type carton ondulé." Compiègne, 2005. http://www.theses.fr/2005COMP1588.
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La fonction principale de l'emballage est de protéger ce qu'il se vend et vendre ce qu'il protège. L'emballage le plus utilisé est le carton ondulé. Ceci est dû à ses nombreux avantages notamment la protection de l'environnement (complètement recyclable) et son coût réduit. Néanmoins, pour une meilleure optimisation de son utilisation, l'appréhension de son comportement mécanique est nécessaire. Cette étude propose de considérer le sandwich carton ondulé en tant que matériau monolithique. La démarche adoptée est double. Elle aborde le problème d'une part, d'un point de vue expérimental en mettant au point des procédures adaptées à ce type de matériau afin d'identifier les paramètres élastiques homogénéisés et les phénomènes régissant son comportement. Et d'autre part, elle établit un modèle analytique capable de prédire le comportement élastique et non linéaire dans le plan en fonction des paramètres structuraux. Cette approche permet de simplifier les calculs numériquesThe principal function of packing is to protect what it sells and to sell what it protects. One of the more used packing is the corrugated cardboard. This is due to its numerous advantages notably the protection of the environment (completely recyclable) and its reduce coast. Nevertheless, its use in optimum manner requires the apprehension of its mechanical behavior. This study proposes to consider the corrugated cardboard sandwich as a monolithic material. The adopted approach is divided in two parts. First experimental procedures adapted to this material, ared developed in order to identify the homogenized elastic parameters and the phenomena governing its behavior. Then an analytical model is established to predict the elastic and nonlinear behavior in the plane according to the structural parameters. This approach makes it possible to simplify numerical computations
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Styles, Millicent, and milli styles@anu edu au. "Characterisation of the flexural behaviour of Aluminium Foam Sandwich Structures." The Australian National University. Faculty of Engineering and Information Technology, 2008. http://thesis.anu.edu.au./public/adt-ANU20080813.170807.
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Aluminium foam has a range of properties that are desirable in many applications. These properties include good stiffness and strength to weight ratios, impact energy absorption, sound damping, thermal insulation and non combustibility. Many of these characteristics are particularly attractive for core materials within sandwich structures. The combination of aluminium foam cores with thermoplastic composite skins is easily manufactured and has good potential as a multifunctional sandwich structure useful in a range of applications. This thesis has investigated the flexural behaviour of such structures using a combination of experimental and modelling techniques. The development of these structures towards commercial use requires a thorough understanding of the deformation and strain mechanisms of the structure, and this will, in turn, allow predictions of their structural behaviour in a variety of loading conditions.
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The experimental research involved the use of an advanced 3D optical measuring technique that produces realtime, full-field strain evolution during loading. This experimental characterisation of strain evolution in this class of sandwich structure under flexural loading is the first of its kind in the world. The experimental work studied the sandwich structure undergoing four-point bend testing. Initial studies compared the behaviour of the aluminium foam structure with a more traditional polymer foam sandwich structure. The aluminium foam structure was found to have equivalent or improved mechanical properties including more ductile deformation and an enhanced energy absorption. An investigation was conducted on the effect of core and skin thickness on the metal structure and a range of flexural behaviours were observed. Analysis of the strain distribution showed a complex development including localised effects from the non-uniform cellular structure of the material. An understanding of the variation with size is important in establishing design methods for utilising these structures. In particular, it is desirable that finite element simulations can be used to predict behaviour of these structures in a diverse range of loading conditions. This aspect was considered in the second half of this study. An existing constitutive model for aluminium foam, developed for use in compression energy absorption studies, was used to investigate finite element simulations of the flexural behaviour of the sandwich structure. The FE model was able to predict the general deformation behaviour of the thinner skinned structures although the magnitude of the load-displacement response was underestimated. It is suggested this may be related to the size effect on the input parameter characterisation. The strain distribution corresponded well with the experimental strain measurements. It was found a simple increase in the material model input parameters was able to more closely match the magnitude of the load-displacement response while maintaining the appropriate strain distribution. The general deformation shape of the model with the thicker skin corresponded reasonably well with the experimental observations. However, further work is necessary on the element failure criterion to capture the shear cracking observed. The strain distributions of the model predicted this failure with high strain concentrations matching those of the experimental contours. The last part of the thesis describes a parametric study on the effect of the foam material model input parameters on the flexural behaviour of the sandwich structure model. An important conclusion of this work is that this material model for aluminium foam can, with some development, be utilized to provide a viable method for simulating aluminium foam composite sandwich structures in flexural loading situations.
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Wang, Jinghui. "Fabrication, Characterization and Simulation of Sandwich Structure GaN Schottky Diode Ionizing Radiation Detectors." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405497243.
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Tom, Louis-Georges. "Contribution à l'étude numérique de la propagation d'un défaut de collage dans une structure sandwich Nida." Thesis, Le Mans, 2014. http://www.theses.fr/2014LEMA1036/document.
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SAFRAN Aircelle produit des panneaux sandwiches constitués de peaux composites collées sur une âme nid d’abeille (« Nida ») en aluminium pour des applications de nacelle de moteur d’avion. Des décollements locaux peuvent exister à l’interface peau/Nida et réduire significativement la capacité structurale de ces sandwiches. L’objectif de cette thèse entre l’ISMANS et SAFRAN Aircelle réside dans la mise en place d’une approche de type « Virtual testing » pour réduire les coûts de validation et de vérification des sandwiches possédant des décollements.L’originalité de ces travaux vient du choix de la représentation des sandwiches à travers deux familles de modèles : les modèles « âme pleine » (modélisation volumique) prévus pour une utilisation en bureau d’études et les modèles « âme creuse » (modélisation physique des clinquants) permettant d’analyser finement les mécanismes de propagation des décollements peau/Nida. Une technique de sous-structuration a été mise en oeuvre avec succès et a permis de réduire significativement les temps de calcul du modèle « âme creuse ».La mécanique de l’endommagement, avec des éléments à zone cohésive, a été choisie pour déterminer numériquement le seuil de propagation des décollements, après une étude comparative avec la mécanique linéaire élastique de la rupture et une méthode de recalage essais. Pour alimenter les lois d’endommagement disponibles dans les codes industriels, une méthode expérimentale a été proposée. Des essais de type DCB sandwiches ont permis de remonter aux propriétés mécaniques de l’interface en mode d’ouverture et en mode mixte, avec un seul montage. Ces essais ont été recalés avec succès, notamment en mode I purSAFRAN Aircelle manufactures sandwich structures made of composite skins bonded to aluminium honeycomb core for aircraft’s engines nacelles applications. Local disbonds may occur at the skins/core interface and lead to significant strength reduction under in-service loadings. The present work was done with ISMANS and SAFRAN Aircelle and deals with the introduction of a “Virtual Testing” approach in order to reduce substantiation and validation cost of sandwiches structures with embedded disbond.In this study we have two kinds of models at two scales to describe the sandwich behaviour: the “homogeneized” model, which provide an industrial tool for design offices and the “detailed” model, which provide a specific tool for accurate analysis of disbond growth initiation at skin/core interface. Due to the numerical cost of the second type of model, the superelement technique has been successfully used which permits to gain computational costs without altering the result quality.Damage mechanics, with cohesive zone elements, have been chosen to numerically determine the disbond growth threshold after a comparative study with linear fracture mechanics and a full experimental method. Inputs data for industrial code using cohesive zone elements have been studied through an experimental investigation. DCB type tests on reinforced sandwiches were perfomed in order to determine the energy release rate at the skin/core interface. Various mode-mixity and pure opening mode are available using the same testing tool. The latter has been successfully modelled
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Yang, Bing. "Thermoplastic and Thermoset Natural Fiber Composite and Sandwich Performance." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500002/.
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The objective of this thesis is to investigate the effects of adding natural fiber (kenaf fiber, retted kenaf fiber, and sugarcane fiber) into polymer materials. The effects are obtained by considering three main parts. 1. Performance in thermoplastic composites. The effect of fiber retting on polymer composite crystallization and mechanical performance was investigated. PHBV/PBAT in 80/20 blend ratio was modified using 5% by weight kenaf fiber. Dynamic mechanical analysis of the composites was done to investigate the glass transition and the modulus at sub-ambient and ambient temperatures. ESEM was conducted to analyze fiber topography which revealed smoother surfaces on the pectinase retted fibers. 2. Performance in thermoset composites. The effect of the incorporation of natural fibers of kenaf and of sugarcane combined with the polyester resin matrix is investigated. A comparison of mechanical properties of kenaf polyester composite, sugarcane polyester composite and pure polyester in tensile, bending, dynamic mechanical thermal analysis (DMA) and moisture test on performance is measured.. 3. Performance in sandwich composites. The comparison of the performance characteristics and mechanical properties of natural fiber composites panels with soft and rigid foam cores are evaluated. A thorough test of the mechanical behavior of composites sandwich materials in tensile, bending and DCB is presented here.
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Ledi, Koffi Sénanou. "Approche inverse pour l’identification des propriétés viscoélastiques de structures sandwichs amorties." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0250/document.
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Dans ce travail de thèse, une méthode d’identification inverse des propriétés mécaniques du matériau viscoélastique (module de cisaillement et facteur de perte) fonctionnalisé dans une structure sandwich à trois couches symétriques est proposée. L’objectif de ce travail est de pouvoir identifier les propriétés mécaniques in situ. A travers un modèle éléments finis basé sur le modèle Zig-Zag de Rao, notre modèle assure la détermination des paramètres modaux de la poutre sandwich. L'approche inverse consiste en une procédure itérative qui détermine les formes de mode étant donné les paramètres matériaux puis calcule les propriétés viscoélastiques à partir des modes en utilisant un quotient de Rayleigh jusqu'à ce que la convergence sur les propriétés du matériau soit satisfaite. Les paramètres d’entrée du modèle inverse sont les fréquences de résonance et facteurs de perte de la poutre sandwich obtenues expérimentalement. En conséquence, la dépendance en fréquence des propriétés du matériau viscoélastique de la poutre sandwich est déterminée par une démarche automatisée. La méthode a été comparée avec succès aux formules de Ross-Kerwin-Ungar ; à une approche d'optimisation standard et à la littérature. A partir des résultats, nous avons pu déduire les lois de comportement du cœur viscoélastique suivant des modèles rhéologique tels que le modèle de Maxwell généralisé, d’ADF, de GHM et du Zéner fractionnaire. Ce dispositif expérimental couplé à la méthode d’indentification a permis l’investigation des paramètres modaux de la poutre à différentes températures pour étudier l’effet de la température sur les lois rhéologiques. Pour étudier la robustesse de notre méthode, nous avons procédé des essais de reproductibilité, de reproductibilité sur une population d’échantillon. L’efficacité de notre méthode étant été prouvée, une étude de sensibilité a été menée sur les caractéristiques géométriques de notre structure et les paramètres d’entrée. Les résultats obtenus montrent le fort impact de certains paramètres sur l’identificationIn this work, a inverse identification method of the mechanical properties of the viscoelastic material (shear modulus and loss factor) functionalized in a sandwich structure with three symmetrical layers is proposed. The objective of this work is to be able to identify the mechanical properties in situ. Through a finite element model based on Rao's Zig-Zag model, our model ensures the modal parameter determination of the sandwich beam. The inverse approach consists of an iterative procedure that determines the mode shapes given the material parameters and then calculates the viscoelastic properties from the modes using a Rayleigh quotient until convergence on the properties of the material is satisfied. The input parameters of the inverse model are the resonance frequencies and loss factors of the sandwich beam obtained experimentally. As a result, the frequency dependence of the viscoelastic properties of the sandwich beam is determined by an automated way. The method has been successfully compared to Ross-Kerwin-Ungar formulas; a standard optimization approach and the literature. From the results, we have been able to deduce the constitutive laws of the viscoelastic heart according to rheological models such as the generalized Maxwell model, ADF, GHM and fractional Zener. This experimental device coupled to the method of identification allowed the investigation of modal parameters of the beam at different temperatures to study the effect of the temperature on the rheological laws. To study the robustness of our method, we carried out tests repeatability, reproducibility on a sample population. Since the effectiveness of our method has been proven, a sensitivity study has been carried out on the geometrical characteristics of our structure and the input parameters. The results obtained show the strong impact of certain parameters on identification
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Salem, Adel I. "Weight and Cost Multi-Objective Optimization of Hybrid Composite Sandwich Structures." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1478637482819839.
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Ledi, Koffi Sénanou. "Approche inverse pour l’identification des propriétés viscoélastiques de structures sandwichs amorties." Electronic Thesis or Diss., Université de Lorraine, 2018. http://www.theses.fr/2018LORR0250.
Full textAbstract:
Dans ce travail de thèse, une méthode d’identification inverse des propriétés mécaniques du matériau viscoélastique (module de cisaillement et facteur de perte) fonctionnalisé dans une structure sandwich à trois couches symétriques est proposée. L’objectif de ce travail est de pouvoir identifier les propriétés mécaniques in situ. A travers un modèle éléments finis basé sur le modèle Zig-Zag de Rao, notre modèle assure la détermination des paramètres modaux de la poutre sandwich. L'approche inverse consiste en une procédure itérative qui détermine les formes de mode étant donné les paramètres matériaux puis calcule les propriétés viscoélastiques à partir des modes en utilisant un quotient de Rayleigh jusqu'à ce que la convergence sur les propriétés du matériau soit satisfaite. Les paramètres d’entrée du modèle inverse sont les fréquences de résonance et facteurs de perte de la poutre sandwich obtenues expérimentalement. En conséquence, la dépendance en fréquence des propriétés du matériau viscoélastique de la poutre sandwich est déterminée par une démarche automatisée. La méthode a été comparée avec succès aux formules de Ross-Kerwin-Ungar ; à une approche d'optimisation standard et à la littérature. A partir des résultats, nous avons pu déduire les lois de comportement du cœur viscoélastique suivant des modèles rhéologique tels que le modèle de Maxwell généralisé, d’ADF, de GHM et du Zéner fractionnaire. Ce dispositif expérimental couplé à la méthode d’indentification a permis l’investigation des paramètres modaux de la poutre à différentes températures pour étudier l’effet de la température sur les lois rhéologiques. Pour étudier la robustesse de notre méthode, nous avons procédé des essais de reproductibilité, de reproductibilité sur une population d’échantillon. L’efficacité de notre méthode étant été prouvée, une étude de sensibilité a été menée sur les caractéristiques géométriques de notre structure et les paramètres d’entrée. Les résultats obtenus montrent le fort impact de certains paramètres sur l’identificationIn this work, a inverse identification method of the mechanical properties of the viscoelastic material (shear modulus and loss factor) functionalized in a sandwich structure with three symmetrical layers is proposed. The objective of this work is to be able to identify the mechanical properties in situ. Through a finite element model based on Rao's Zig-Zag model, our model ensures the modal parameter determination of the sandwich beam. The inverse approach consists of an iterative procedure that determines the mode shapes given the material parameters and then calculates the viscoelastic properties from the modes using a Rayleigh quotient until convergence on the properties of the material is satisfied. The input parameters of the inverse model are the resonance frequencies and loss factors of the sandwich beam obtained experimentally. As a result, the frequency dependence of the viscoelastic properties of the sandwich beam is determined by an automated way. The method has been successfully compared to Ross-Kerwin-Ungar formulas; a standard optimization approach and the literature. From the results, we have been able to deduce the constitutive laws of the viscoelastic heart according to rheological models such as the generalized Maxwell model, ADF, GHM and fractional Zener. This experimental device coupled to the method of identification allowed the investigation of modal parameters of the beam at different temperatures to study the effect of the temperature on the rheological laws. To study the robustness of our method, we carried out tests repeatability, reproducibility on a sample population. Since the effectiveness of our method has been proven, a sensitivity study has been carried out on the geometrical characteristics of our structure and the input parameters. The results obtained show the strong impact of certain parameters on identification
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Teston, Bénédicte. "Comportement thermique des structures sandwich pour application dans les capots moteurs d'hélicoptères." Paris. ENSAM, 2002. http://www.theses.fr/2002ENAM0010.
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Le travail porte sur l'étude du vieillissement thermique de matériaux sandwich à âme en nid d'abeille et à peau composite, la matrice étant constituée de résines thermostables époxy ou polybismaléimide (BMI) auto-adhésives ou non. Une attention particulière a été portée à la mise au point d'une méthode de caractérisation mécanique permettant d'identifier sans ambigui͏̈té le "point faible" de la structure. Il apparaît que ce dernier est le nid d'abeille dans sa phase initiale (quelques milliers d'heures) de vieillissement. Aux temps plus longs, la rupture se produit préférentiellement à l'interface peau/âme, mais avec les variantes suivantes : dans le cas des sandwichs XE26 à peaux auto-adhésives, la rupture se produit à l'interface nid d'abeille/ménisque de résine et à l'interface fibre/matrice dans les peaux, ce dernier type de défaillance devenant majoritaire aux temps longs. Dans le cas des sandwichs F655, on observe également un mode mixte de défaillance : d'une part une rupture interfaciale ménisque/nid d'abeille par déchaussement, d'autre part, à l'interface trame de verre de l'adhésif/matrice d'adhésif, le second mode tendant à prédominer sur le premier aux temps longs. Pour étudier plus précisément ce second mode, nous avons conçu et réalisé un essai mécanique original de caractérisation de l'interface peau/âme qui constitue un outil efficace pour apprécier l'énergie de rupture et établir sa cinétique d'évolution au cours du vieillissement. L'âme et les peaux, en se dégradant, émettent des produits volatils dont une partie reste piégée dans les cellules du nid d'abeille, générant ainsi une pression qui peut contribuer à l'endommagement du matériau et favoriser le décollement peau/âme.
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Khasawneh, Firas Abdallah. "Characterization of drillability of sandwich structure of carbon fiber reinforced epoxy composite over titanium alloy." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/5871.
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Thesis (M.S.)--University of Missouri-Columbia, 2006.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on September 13, 2007). Vita. Includes bibliographical references.
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Iwai, Kento. "Synthesis and Properties of Zwitterionic Compounds Utilizing an Introducing Unit of a Boranuidyl Group." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263481.
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Léotoing, Lionel. "Modélisation du flambage global, local et interactif dans les structures sandwich en compression." Saint-Etienne, 2001. http://www.theses.fr/2001EMSE0020.
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Une structure sandwich possède une rigidité spécifique élevée en flexion mais, en contre-partie, un comportement mécanique complexe. Ce dernier point est mis en évidence lorsqu'une telle structure est chargée en compression dans son plan, des instabilités géométriques pouvant apparaître à l'échelle globale de la structure ou à l'échelle locale des constituants (âme ou peaux). Le but de cette thèse est de modéliser d'un point de vue analytique et numérique le flambage global et local d'une poutre sandwich mais également les éventuelles interactions entre les instabilités à ces deux echelles d'observation. Un modèle analytique de poutre basé sur une théorie d'ordre supérieur est tout d'abord développé à partir duquel les charges critiques de flambage global et de wrinkling antisymétrique et symétrique des peaux sont isolées. Grâce à ces charges, la construction de diagrammes de conception permet d'identifier rapidement les configurations de poutres sandwich instables localement ou globalement. De plus, ce modèle analytique est utilisé avec succès pour caractériser l'apparition et la stabilité d'une forme de flambage interactif. Ensuite, la construction d'un modèle E. F. "simplifié" permet de retrouver numériquement les résultats analytiques. Les temps de calcul restreints de ce modèle conduisent à caractériser de façon optimale la réponse complète de la poutre sandwich dans un cadre non linéaire géométrique et/ou matériel. La stabilité des différentes formes de flambage est donc discutée ainsi que la grande sensibilité à des défauts géométriques locaux ou globaux. La prise en compte d'une loi de comportement élastoplastique dans l'âme induit un comportement fortement sous-critique, caractérisé par une chute de rigidité globale de la poutre suite à la localisation de déformations plastiquesSandwich structures exhibit a high specific flexural stiffness but also a complex mechanical behaviour. This last point is emphasized when in-plane compression is considered. Indeed, geometrical instabilities can appear at the global scale of the structure or at the local scale of the components (core and skins). The aim of this thesis is to model analytically and numerically the global and local buckling of a sandwich beam, but also the possible interactions between instabilities at these two scales. First, an analytical beam model based on a high order theory is established, which permits to isolate the critical loads associated with global buckling and symmetrical and antisymmetrical wrinkling of skins. Thanks to these loads, design diagrams are built which are useful to quickly identify sandwich beam configurations locally or globally unstable. Moreover, this analytical model is successfully used to characterize the apparition and the stability of an interactive buckling form. Then, a "simplified" FE model is built which permits to find a good correlation between the numerical and the previous analytical results. The low time-consuming calculation of this model leads to an efficient characterization of the complete response of the sandwich beam in a material and/or geometrical nonlinear framework. The stability of the different buckling forms are discussed, as well as the high sensitivity towards global or local geometrical imperfections. The introduction of an elastoplastic constitutive law leads to a very sub-critical response, characterized by a drop in the global stiffness of the beam due to the localization of plastic strains
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Essid, Safa. "Sandwiches à fibres de lin et anas de lin : optimisation structure-imprégnation-propriétés." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMLH05.
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Pour des raisons principalement écologiques, l’allègement des structures sandwiches et la valorisation de la biomasse lignocellulosique sont considérés comme des solutions possibles pour l’innovation durable. Dans ce contexte, les travaux de cette thèse se concentrent sur la fabrication et l’optimisation de structures sandwiches en peaux renforcées de fibres de lin avec des objectifs mécaniques, économiques et environnementaux. Une valorisation d’un sous-produit de la plante de lin que sont les anas de lin est effectuée avec le développement de panneaux agglomérés à base de ces particules. Ces panneaux serviront d’âme aux structures sandwiches. Pour arriver à l’étape d’optimisation, des caractérisations expérimentales des matériaux de matrice et d’âme sont tout d’abord effectuées. Par la suite, un travail sur le couplage entre les procédés d’élaboration et les propriétés recherchées des structures sandwiches est réalisé. L’ensemble des caractéristiques déterminées sont comparées à celles d’un matériau de référence non-biosourcé. Enfin, pour arriver à répondre à la problématique liée à l’optimisation de la conception de structures sandwiches en lin, à rigidité et à résistance à la rupture imposées, trois approches analytique, graphique et numérique sont développées. Cette procédure d’optimisation devra contrôler d’une manière systématique les caractéristiques recherchés des sandwichs en linFor different reasons including ecological ones, the weight reduction of structures and valorization of lignocellulosic biomass are considered as possible solutions towards ustainable innovation. In this context, the work of this thesis focuses on the manufacturing and optimization of sandwich structures with skins reinforced with flax fibers with mechanical, economic and environmental goals. A flax plant by-product called flax shives is valued by the development of agglomerated panels. These panels will serve as a core for the sandwich structures. To reach the optimization stage, experimental characterizations of the matrix and core materials are carried out first. Subsequently, joint work between the production processes and the desired properties of sandwich structures is undertaken. All the characteristics determined are compared with those of a non-bio-sourced reference material. Finally, analytical, graphic and numerical approaches are developed in order to answer the main question related to the optimization of the design of flax based sandwich structures with imposed rigidity and resistance to rupture. This optimization procedure should systematically control the desired characteristics of flax sandwiches
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Ward, Charles. "Modification of a Ground Based Atomic Oxygen Simulation Apparatus to Accommodate Three Dimensional Specimens." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1850.
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The space environment presents various challenges when designing systems and selecting materials for applications beyond Earth’s atmosphere. For mission success, these challenges must be considered. One of the detrimental aspects of the space en- vironment is Atomic Oxygen, AO. Only present in harmful quantities in Lower Earth Orbit, LEO, AO causes significant damage to materials by breaking molecular bonds. California Polytechnic State University’s, Cal Poly’s, space environments laboratory features an apparatus capable of simulating this environment. Very thin or short samples were tested to observe the mass loss due to erosion of the sample material. Recent modifications to the system allow it to expose surfaces of three dimensional objects to AO rather than only those two dimensional objects. Simulating this effect on taller samples makes available the opportunity to test coupons that are then used in additional testing to measure the effect of that erosion on other properties. Challenges in adapting the AO system are explored and addressed, as well as some possible use cases for future work. As a use case, bending moment specimens were exposed to AO prior to testing in four point bending. Multiple regression models were constructed to determine variables contributing to slope changes between specimen pairs’ linear-elastic regions of force-displacement graphs. Results show that AO exposed specimens had significantly gentler slopes in the linear elastic region of the force-displacement curve, meaning that AO exposure reduced structural rigidity of the coupons.
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Brown, Richard A. "The synthesis, structure and characterisation of some iron sandwich complexes and their application to organic synthesis." Thesis, University of Essex, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332412.
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Saifullah, Abu Naser Muhammad. "Fracture properties analysis of rotationally moulded plastics for their application in skin-foam-skin sandwich structure." Thesis, Bournemouth University, 2017. http://eprints.bournemouth.ac.uk/29483/.
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Rotational moulding is a low pressure, high temperature manufacturing method and is considered to be the best for making large hollow shape plastic parts. Due to its long heating cycle, mould rotation during heating and slow cooling rate, it is completely different from injection or other moulding processes. The mechanical properties of rotationally moulded plastics are totally dependent on unique heating or cooling cycles. With the growing demand for rotationally moulded plastics in load bearing and other applications, a better understanding of their fracture properties is essential. In the rotational moulding process, multilayer plastic products such as skin-foam-skin three layered sandwich structures can be manufactured in a single manufacturing step without any joints. It exhibits relatively high stiffness, strength-to-weight ratios and is used increasingly in various applications such as automotive and marine. During the lifetime of the sandwich material, it may face multiple or repeated impact events. Therefore, the aim of this work is to develop a better understanding of the fracture behaviour of rotationally moulded plastics in order to use them in skin-foam-skin sandwich structure and reduce in-service failures due to impact. Here, rotationally moulded two different commercially available Polyethylene (PE) and Polypropylene (PP) plastics are tested. Microstructural details of the plastics are investigated here. Fracture properties, particularly fracture toughness properties are studied using J-integral elastic-plastic fracture mechanics approach to identify the fracture initiation point. Impact properties are also investigated at a wide range of temperatures. PE materials are found to have better fracture properties. It is observed that with the fracture toughness plastic’s microstructure particularly crystal and amorphous region thickness are related. The understanding from these works is followed by the manufacture of rotationally moulded skin-foam–skin sandwich structure and testing of low velocity impact properties of this structure from 20 J to 100 J energy level with a drop weight impact testing machine. PE is used for both in skin and core layer and sandwich samples are manufactured at four different skin-core thickness combinations. Impact force resistance and bending stiffness are found to be increased with an increase of both skin and core layer thickness. Low velocity repeated impact properties of the rotationally moulded sandwich samples are also investigated from 20 J to 50 J energy level at the end of this project to understand the effect of repeated impact on the sandwich structure. The samples are subjected to single impact event repeatedly up-to penetration at each energy level. Impact energy-impact number curve obtained from repeated impact test provides an equation for prediction of the number of repeated impacts for the penetration of the sandwich samples at each energy level.
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Vo, Hoang Nhi. "Development of an Innovative Meta-Panel Sandwich Core for Structure Protection against Blast and Impact Loads." Thesis, Curtin University, 2022. http://hdl.handle.net/20.500.11937/89452.
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This research develops a novel protective structure named “meta-panel” for mitigation of blast/impact loading. The proposed meta-structure consists of local resonators which convert and trap blast/impact energy to kinetic energy through local vibrations of the resonators, hence reducing the loading energy transmission to the protected structures. This design opens a door for a new approach to structural protections from the traditional means of either strengthening and/or energy absorption through large plastic deformations of sacrificial structures.
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Gandy, Helene Tchoutouo Ndjountche. "Adhesiveless honeycomb sandwich structure with carbon graphite prepreg for primary structural application: a comparative study to the use of adhesive film." Thesis, Wichita State University, 2012. http://hdl.handle.net/10057/5388.
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In the past two decades, researchers have been developing prepreg materials with matrix properties that can allow the elimination of the additional adhesive traditionally used between the core and the skins of composite sandwich structures. There have been several publications on self-adhesive prepreg used for sandwich structures; but none with a comparative study for primary structural application, from the same fabrication basis.
This research focused on the properties of adhesiveless honeycomb sandwich structure with carbon graphite prepreg, while assessing the structure with adhesive film at the skin-to-core interface simultaneously. In the study, laminate and honeycomb sandwich panels were fabricated and tested with consistent lay-up, curing, and testing processes, all fully documented. Sandwich panels were made with the CYCOM 977-2 prepreg system from Cytec and the AF191 adhesive film from 3M, while the adhesiveless sandwich panel had the MTM45-1 prepreg systems from Advanced Composites Group (ACG). Laminate panels were also fabricated using the two different prepregs. Specimens from the panels where tested for physical and mechanical properties, as well as moisture absorption performance. The results obtained from the non-destructive testing and the experiments confirmed that the self-adhesive prepreg physical properties met the components and void content recommendations for use in primary structures. In addition to analysis of existing published data, mechanical tests were performed in room, hot and cold temperatures, as well as dry and wet conditions. The results suggested that aramid honeycomb sandwich structure with self-adhesive carbon graphite prepreg systems, alongside similar structure using additional adhesive, demonstrates the ability to be used for primary structure.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering
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Almusawi, Aqil mousa. "Mise en œuvre et optimisation des propriétés d'une structure sandwich en matériaux biosourcés (fibres et bois de chanvre) avec une matrice en polystyrène expansé pour le bâtiment." Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCA009/document.
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La fonctionnalisation croissante des matériaux de constructions ainsi que le besoin de gestion des ressources de l'humanité rend les matériaux traditionnels à base de ciment moins performant.De nouvelles structures de paroi peuvent être envisagées en optimisant le choix de matériaux et leurs agencements. Dans ce travail nous avons choisi d'évaluer une structure pouvant remplir toutes les fonctions d'une paroi type « maison individuelle » ceci en utilisant des matériaux à faible coût et en utilisant des procédés de fabrications classiques. Les matériaux choisis proviennent majoritairement d'une source agricole renouvelable, le chanvre et son sous-produit (la chènevotte) et du recyclage des déchets de polystyrène. Nous avons établi des relations entre différentes propriétés du composites obtenu et les paramètres du procédé en particulier sur la zone des hautes teneurs en renfort et jusqu'à 100%. Nous avons également préparé la phase d'optimisation numérique d'une structure sandwich alvéolaire en modélisant le procédé et les structures ainsi obtenueDue to the rapidly improving functionality of building materials, and increasingly complicated human resource management issues, the traditional cement-based building materials of the past are becoming less and less desirable.These outdated materials are being replaced by new structures of wall that better optimize choices of materials and their layouts. In this study, we propose a multi-function structure to be the unit of a typical wall (individual house), which can be produced via the use of inexpensive materials and classic manufacturing processes. To achieve this, we chose the renewable agricultural source of the hemp plant (hemp yarns and hemp shive particles), along with recycled expanded polystyrene, to manufacture a fully recyclable composite. We established a relationship between the physical-mechanical properties of the resulting composite and the parameters of the manufacturing process, particularly in the zone of high load reinforcement, we successfully manufactured a composite of 100% hemp shive particles. In addition, we have also prepared the numerical optimization phase of an alveolar sandwich structure by modeling the process and the obtained structure
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Bunyawanichakul, Phacharaporn. "Contribution à l'étude du comportement des inserts dans les structures sandwichs composites." Toulouse, ENSAE, 2005. http://www.theses.fr/2005ESAE0012.
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Cette étude analyse le comportement en arrachement des inserts de structure sandwich en âme nid d’abeille et peau carbone. La technologie étudiée est celle d’insert fortement travaillant obtenu par densification de nid d’abeille et utilisé dans l'industrie aéronautique. Des essais d’arrachement ont été effectués et les modes d'endommagements ont été identifiés. Une étude phénoménologique à l’aide d’essais sous chargements progressifs cyclés, d’essais arrêtés et d’essais sur éprouvettes spécifiques ont permis d'identifier le scénario de rupture. Une modélisation éléments finis volumiques qui intègre les lois de dégradation du nid d’abeille en cisaillement transverse, le comportement plastique du potting et les dégradations de la peau composite par poinçonnement ont été développés et permettent une bonne prédiction de la loi d’arrachement ainsi que des charges de dégradation des différents composants et la charge à rupture. Une modélisation du poinçonnement a été développée basée sur un critère quadratique de dégradation initiale suivi par un critère en déformation maximale correspondant à la rupture des fibres par cisaillement transverse. Une étude sensibilité a été effectuée et permet de proposer des solutions optimisées. La modélisation a aussi été appliquée à une technologie d’insert de faible capacité de charge et permet de déterminer les charges limites pour cette technologie. Cette étude montre que le dimensionnement des inserts ne peut être correctement effectué qu'après avoir identifié expérimentalement les divers modes de ruptures propres à chaque technologie et en implémentant les comportements non-linéaires associés.
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Findley, Tara M. "An Experimental Analysis of Auxetic Folded Cores for Sandwich Structures Based on Origami Tessellations." University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1372862614.
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Chatti, Fadhel. "Simulations numériques du comportement mécanique d'un matériau d’âme à base de fibres enchevêtrées destiné aux applications aéronautiques." Thesis, Toulouse, ISAE, 2018. http://www.theses.fr/2018ESAE0040/document.
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Un nouveau matériau d’âme à base de fibres enchevêtrées et réticulées a été précédemment développé dans le but d’améliorer certaines propriétés des structures sandwichs dont l’amortissement vibratoire. Cependant, son comportement mécanique et vibratoire doit être optimisé afin de l’utiliser dans le domaine aérospatial. Plusieurs paramètres morphologiques entrent en jeu lors de sa fabrication. L’objectif de cette thèse est de développer un modèle numérique permettant de mieux comprendre le comportement de ce matériau enchevêtré réticulé. Le comportement d’un volume élémentaire représentatif de fibres de carbone enchevêtrées et non-réticulées est d’abord étudié en compression par éléments finis. La géométrie numérique du réseau de fibres s’appuie sur les données morphologiques du matériau réel. Les simulations numériques permettent de suivre, au cours de la compression confinée, l’évolution des différents paramètres, tels que la distribution des orientations des fibres, la distance entre contacts ou la fraction volumique. Ces résultats constituent une base robuste pour le développement du modèle numérique du matériau enchevêtré et réticulé qui est ensuite utilisé pour modéliser le comportement mécanique en cisaillement, et en particulier pour simuler et expliquer les boucles d’hystérésis observées expérimentalement. A la fin de ce travail, une étude numérique est proposée afin de décrire l’influence des différents paramètres morphologiques sur la rigidité en compression et en cisaillement du matériau enchevêtré réticuléA new core material based on entangled and cross-linked fibers has been previously developed in order to improve certain properties of sandwich structures including vibration damping. However, its behavior must be optimized for use in the aerospace field. Several morphological parameters can be modified during the manufacturing process. The aim of this thesis was to develop a numerical model to better understand the behavior of this entangled cross-linked material. The behavior of a representative volume element of entangled carbon fibers without cross-links is first studied in compression using finite element. The numerical geometry of the fiber network relies on the morphological parameters of a real sample. Numerical simulations make it possible to follow, during the confined compression, the evolution of the different parameters, such as the distribution of fiber orientations, the distance between contacts or the volume fraction. These results provide a robust basis for developing the numerical model of the entangled cross-linked material which is then used to model the mechanical behavior in shear, and in particular to simulate and explain the hysteresis loops observed experimentally. At the end of this work, a numerical study is proposed to study the influence of different morphological parameters on the compressive stiffness and shear stiffness of the entangled cross-linked material
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Strehler, Frank, Marcus Korb, and Heinrich Lang. "Crystal structure of ruthenocenecarbonitrile." Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-166700.
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The molecular structure of ruthenocenecarbonitrile, [Ru([eta]5-C5H4C[triple bond]N)([eta]5-C5H5)], exhibits point group symmetry m, with the mirror plane bisecting the molecule through the C[triple bond]N substituent. The RuII atom is slightly shifted from the [eta]5-C5H4 centroid towards the C[triple bond]N substituent. In the crystal, molecules are arranged in columns parallel to [100]. One-dimensional intermolecular [pi]-[pi] interactions [3.363 (3) Å] between the C[triple bond]N carbon atom and one carbon of the cyclopentadienyl ring of the overlaying molecule are present.
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Del, Broccolo Simone. "Effets de la topologie des cellules d'une structure en nid d'abeille." Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCD001.
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Les panneaux composites sandwich possédant une âme nid d'abeille permettent de disposer à la fois de propriétés statiques hors plan intéressantes (en raison de leur rigidité équivalente élevée) et de caractéristiques de masses faibles. Pour cette raison, ils sont largement utilisés dans les industries aérospatiale, automobile et navale. Les environnements dans lesquels ces matériaux sont utilisés mettent en jeu des efforts dans des gammes de fréquences larges. Si un rapport rigidité / masse élevé est profitable dans le domaine des basses fréquences, il conduit généralement à des comportements vibratoires et acoustiques médiocres lorsque la fréquence d’excitation augmente. La question abordée dans ce travail peut être formulée comme : comment les concepts périodiques peuvent-ils améliorer les signatures vibroacoustiques large bande et les performances de ces structures ? La plupart des solutions vibroacoustiques sont limitées en terme de bande de fréquences d’efficacité, et induisent généralement un ajout de masse. La prise en compte de règles de conception vibroacoustiques à un stade précoce du développement du produit est l'un des principaux objectifs de recherche en vue d’améliorer leurs performances et permettrait de concevoir des structures accordées sans aucune intervention ultérieure ou augmentation de masse. Ce travail se concentre donc sur l'étude des topologies de base de panneaux sandwich existants et a pour objectif de créer de nouvelles structures améliorées. La recherche a été menée en essayant de maintenir les propriétés structurelles souhaitées, ce qui justifie l'utilisation d'une telle solution en premier lieu, mais également en considérant son utilisation potentielle comme plate-forme pour la mise en place d’inserts de matériaux périodiques résonants. Ces noyaux cellulaires ont été fabriqués en utilisant la technique du Kirigami (qui est une variante de l'Origami) : il s’agit d’une ancienne technique japonaise qui consiste à créer des structures 3D en pliant et en découpant une feuille de matériau 2D. Cette technique de fabrication peut être utilisée comme un moyen systématique de produire des configurations générales en nid d'abeilles avec des composites à fibres longues par thermoformage et / ou autoclavage. Le principal indicateur utilisé ici afin d’évaluer les performances vibroacoustiques des topologies innovantes proposées est le nombre et la plage de bandes d'arrêt, également connues sous le nom de bandes interdites, qui décrivent les plages de fréquences dans lesquelles les ondes élastiques ne peuvent pas se propager dans la structure. Ce manuscrit est organisé en cinq chapitres. Le premier consiste en un bref aperçu des structures périodiques dans les différents domaines d'ingénierie. L'accent est mis sur les panneaux sandwich et leurs techniques de fabrication les plus populaires sera également décrit. Le deuxième chapitre présentera au lecteur le concept de propagation des ondes élastiques dans les milieux périodiques. De plus, des phénomènes comme les interférences de Bragg ou les bandes interdites résonantes seront présentés ainsi que la théorie de Floquet-Bloch appliquée aux structures à périodiques typiquement utilisées dans l’aéronautique. Cette dernière dérivation mathématique sera fusionnée avec l'approche d'analyse par éléments finis et mise en œuvre comme base pour les outils de prédiction numérique spécialement développés afin de permettre la réalisation d’investigations paramétriques sur des panneaux sandwich complets ou des cœurs nus. La théorie de Floquet-Bloch permet de récolter des informations cruciales sur le comportement dynamique de l’ensemble de la structure en n’effectuant l’analyse que sur une petite partie de celle-ci (cellule unitaire).[...]Honeycomb sandwich panels are well known to provide interesting static out of plane properties because of their high equivalent stiffness whilst containing mass and for this reason, they are widely used as a ‘building brick’ in the Aerospace, Automotive and Naval industries. The environment in which these materials operate involve external forces which excites them in the mid-low frequency range. However, while a high stiffness/mass ratio is a desirable static property, the vibration frequency domain is usually in the high range and therefore they become poor mechanical and acoustic insulators within the frequency range they are usually subjected to. The question addressed then is simple: how periodic concepts can improve the broadband vibroacoustic signatures and performances of those structures? Most of vibroacoustic solutions are frequency band limited, specific and usually include the addition of mass, which for certain engineering segments is disadvantageous. Including vibroacoustic design rules at early stage of product development is one of the main research targets to improve their performance and would allow to design tuned structures without any later intervention or mass increment. This work focuses on investigating existing sandwich panel core topologies and attempt to create novel improved structures. The research was carried out trying to maintain the desired structural properties which justifies the usage of such solution in the first place but also considering its potential use as a platform for Multiphysics resonating periodic material inserts. Such cellular cores were manufactured using Kirigami, which is a variation of Origami, an ancient Japanese technique that consists in creating 3D structures by folding a 2D sheet of material. This manufacturing technique can be used as a systematic way to produce general honeycomb configurations with off-the-shelf long fibre composites by thermoforming and/or autoclaving. The main indicator on which I will focus to evaluate the vibroacoustic performance of the proposed innovative topologies will be the number and range of stopbands, also known as a bandgaps, which describe the frequency ranges in which elastic waves are not transmitted within the structure, in combination with the constituent material and its damping properties. This manuscript is organised in five chapters. The first one consists of a brief overview on periodic structures in the various engineering domains. Emphasis on Sandwich panels and their most popular manufacturing techniques will also be described. The second chapter will introduce the reader to the concept of elastic wave propagation in periodic media. Also, phenomena like Bragg or resonant bandgaps will be explained as well as the Floquet-Bloch theory applied to macro-scale structures such as aeronautical cellular cores.[...]
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IURLARO, LUIGI. "Development of refined models for multilayered composite and sandwich structures: analytical formulation, FEM implementation and experimental assessment." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2606162.
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Over the last three decades, composite materials have been increasingly used in different engineering field due to their high stiffness-to-weight and strength-to-weight ratios. Nowadays, relatively thick laminated composite and sandwich materials with one hundred or more layers find their applications in primary load-bearing structural components of the modern aircraft. To ensure a reliable design and failure prediction, accurate evaluation of the strain/stress state is mandatory.
A high-fidelity analysis of multilayered composite and sandwich structures can be achieved by adopting detailed 3D finite element models that turn into a cumbersome modeling at high computational cost. Thus, most of the researchers efforts are devoted to the development of approximated models wherein assumptions on the distribution of displacements and/or stresses are made.
In the ‘80s, thanks to the original works by Prof. Di Sciuva, a new modeling strategy of multilayered composite and sandwich structures arose: the so-called Zigzag theories, wherein accuracy comparable with that proper of the Layer-wise models is achieved but saving the computational cost.
For accuracy, computational cost and efficient finite element implementation, the most remarkable Zigzag model, inspired by the Prof. Di Sciuva’s work, is the Refined Zigzag Theory. From its first appearance, the Refined Zigzag Theory has experienced several developments in terms of beam and plate finite element implementations and has been extensively assessed on static problems.
The present research activity supports the great accuracy of the Refined Zigzag Theory and for this reason deals with some overlooked aspects, as the application to the functionally graded materials (Chapter 2), the mixed-field formulation (Chapter 3), the implementation of a beam finite element employing exact static shape functions (Chapter 5) and the correlation with experimental results (Chapter 8). By enriching the Refined Zigzag Theory and using the Reissner Mixed Variational Theorem, a novel higher-order mixed zigzag model is developed (Chapter 4). The higher-order zigzag model constitutes the underlying theory for a beam finite element, suitable for a thermo-mechanical analysis, and a plate element, formulated taking into account only mechanical loads. The results presented (Chapters 6-8), along with those already published in the open literature by other authors, still encourage the use of the Refined Zigzag Theory in the analysis of relatively thick multilayered composite and sandwich structures. Moreover, when the transverse normal stress and the transverse normal deformability effects are not negligible, the novel higher-order mixed zigzag model appears proficient to solve these cases in virtue also of its efficient finite element implementations.
The author’s auspice is that the models belonging to the Refined Zigzag Theory class becomes to attract attention of the companies involved in the design and analysis of multilayered composite and sandwich structures and of the finite element commercial codes that still implemented models not suitable for the analysis of composite and sandwich structures, as extensively demonstrated.
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Njilie, Adamou Franck Éric. "Modélisation et évaluation de l'amortissement de structures sandwichs." Paris 6, 2002. http://www.theses.fr/2002PA066276.
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Gulla-Cazenave, Jean. "Étude de l'influence des paramètres d'élaboration par infusion de résine liquide sur l'endommagement et le comportement à l'impact de matériaux composites à structure sandwich." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30313.
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Lors d'une étude précédente, des prototypes destinés à transporter des matériels militaires lourds (600kg) par hélicoptère ont été produits. Reposant sur l'utilisation de matériaux composites à structure sandwich, ces structures ont convaincu par leur légèreté et leur résistance à la charge, mais ont montré des faiblesses lors de la sollicitation en impact basse énergie / basse vitesse. Lors de cette thèse, nous avons cherché à optimiser la résistance des structures sandwich à ce type d'endommagements en étudiant l'influence des paramètres d'élaboration par un procédé de mise-en-oeuvre industriel. Une étude bibliographique a permis la mise en évidence des paramètres critiques de faisabilité du projet. Le choix du procédé de fabrication a été arrêté à l'infusion de résine liquide, technique couramment utilisée dans l'industrie est facilement utilisable par des petites et moyennes structures. L'état de l'art a également révélé des pistes d'amélioration des structures sandwich via les conditions de fabrication. Un procédé particulier a du être mis en place afin de fabriquer des structures composites sandwich en une seule étape. Avec cette méthode, quatre jeux de paramètres ont été retenus pour l'étude : les températures de fabrication, la nature de la matrice, l'état de surface de l'âme, ainsi que la présence (ou non) d'additifs nano-dimensionnés dans la matrice. Diverses combinaisons de ces paramètres ont été utilisées pour fabriquer des panneaux sandwich ensuite découpés en échantillons afin d'être testés en impact à l'aide d'une tour de chute. Une première série de tests a permis de déterminer les conditions d'impact représentative des cas réellement rencontrés, les techniques permettant l'identification et la caractérisation des endommagements, ainsi que l'observation des comportements pendant l'impact. A partir des observations pendant et après l'impact, nous avons pu constater trois comportements et quatre types d'endommagements, sur l'ensemble des échantillons testés. Ces comportements et endommagements ont pu être reliées aux paramètres d'élaboration sélectionnés. [...]In a previous study, prototypes for heavy military equipment (>600kg) transportation by helicopters were developed. Based on sandwich composite structures, these materials showed promising results in terms of weight reduction and load bearing capabilities, but weaknesses were observed during low velocity/low energy impact solicitations. During this PhD project, we aimed at optimizing sandwich structure's resistance to impacts, by studying elaboration parameter's influences of an industrial production method on impact behaviors. A bibliographic review showed critical parameters for this project's feasibility. We chose to use the Liquid Resin Infusion as the elaboration process; this technique is commonly used in the industry, and is suited for small production structures. State of the art also showed impact resistance improving methods for sandwich structures, in terms of processing conditions. A particular elaboration method was designed, to produce sandwich structures in a one-shot process. In this study, and with this method, four sets of parameters were selected: elaboration temperatures, matrix types, core's surface nature, and whether or not the matrix contained nanoscaled additives. Several combinations of these parameters were used to produce sandwich panels, which were cut in samples, to be impacted on a drop-weight tower. Preliminary testing allowed to determine representative impact conditions, similar to real-life situations, the observation and characterization techniques of damages, and behavior observation methods during impact. Based on that, we were able to identify three behaviors during impact, and four damage types, over all tested samples. These behaviors and damages were linked to the selected elaboration conditions and one set appeared very promising. The analysis of the parameters allowed us to understand the mechanisms occurring during the production of the panel. Residual resistance after impact was characterized by subjecting the samples to consecutive impacts. Four behaviors were observed, directly linked to the damages initially observed. The choice of an optimal structure was confirmed