Дисертації: "Hierarchical composite"

1

Malkin, Robert Edward. "Damage tolerant hierarchical composite structures." Thesis, University of Bristol, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557974.

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The use of fibre reinforced polymers is rapidly increasing in a range of applications, from aviation to sporting goods. While the outstanding material properties offered by modern composites make them widely applicable they often suffer from brittle, catastrophic failure. Their inherent brittleness limits their application for safety critical applications without large safety margins. This thesis sets out to introduce design principles that introduce a degree of 'pseudo- ductile' failure behaviour to advanced fibre composites. Much of the inspiration for the work comes from looking at the failure processes of natural hierarchical materials. Many of these materials are able to sustain large amounts of damage at different length scales without catastrophic failure, with many of them being essentially ceramics. Nacre, a relatively simple discontinuous laminated material, served as a major inspiration. Three main strategies were employed to reduce the effects of brittle fracture. Ply terminations were used to selectively weaken a laminate allowing one large fracture to be replaced with a number of smaller ones. Thereby giving indication of the laminates failure and significantly increasing the strain to failure over a traditional laminate. Ply perforations, where portions of a ply are cut, were used to weaken a laminate allowing the location of the fracture to be controlled. The third method tailored interlaminar fracture toughness allowing for steady crack propagation where traditional laminates would suffer unstable crack growth. The work introduces three distinct and highly expandable methodologies capable of reducing the limitations of modern composites.

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2

Weiland, Michèle. "Modelling hierarchical musical structures with composite probabilistic networks." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/29418.

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Learning and generating musical structures computationally is a challenging task that has taken the interest of a number of research projects since the start of modern computation. This research attempts to demonstrate the approach of using machine learning techniques, namely probabilistic models, to learn and generate large-scale musical structures. Musical works have several defining levels of representation, or musical parameters, such as metre, duration, phrase structure, cadential patterns, pitch. The concept of Hierarchical Input-Output Hidden Markov Models is introduced. These are used in combination with Hierarchical Hidden Markov Models to build composite networks of models that represent musical parameters. The aim is to learn both the local dependencies of the elements that make up the parameters, and the interdependencies between the different parameters. Structured probabilities are extracted from a musical data set, which are then used to generate new pieces of music, providing the models with only a minimum of supervision and expert knowledge. The musical material this study concentrates on is Bach chorales. The composite nature of the networks allows us to experiment with several combinations of models. In order to validate the approach, the generation of two part pieces is used as a preliminary test, later moving on to complete four part works. The musical results, created using a simple “random walk” method, are evaluated with a listening study and analysed using entropy values and music theoretical rules.

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3

McKenzie, Holly S. "Particle encapsulation and modification to afford hierarchical composite materials." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/67281/.

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Within this thesis we explore the synthesis and modification of hierarchical composite particles and responsive microgels. Initially in Chapter 2 we describe the encapsulation of calcium carbonate particles within a polymeric shell, wherein the inorganic core is kinetically trapped within a cross-linked polymer network. Once primed in this shell we illustrate control of polymer shell thickness through a secondary polymerization. We also begin to investigate the possibility of preparing nano-rattles, using the calcium carbonate core as a sacrificial template. In Chapter 3 we expand on the work presented in Chapter 2, by incorporating pendant vinyl groups into the polymer shell of the composite particles from which we use thiol-ene Michael addition to modify their surface. In Chapter 4 perform the encapsulating polymerization from Chapter 2 and 3, but in the absence of the calcium carbonate core. The stable particles formed were found to be pH responsive microgel particles. We illustrate the gelling behaviour of these particles and use as Pickering stabilizers for oil-in-water emulsions which show reversible flocculation on adjustment of the pH. In investigating these microgel particles we also begin to elucidate unanswered questions from Chapters 2 and 3. Finally in Chapter 5 we go back to encapsulation, this time to synthesize multi-layered particles by encapsulation of Laponite armoured soft latexes. We infer how alterations to particle morphology affect the bulk properties of polymer films by mechanical and thermal analysis.

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4

Kelly, Aoife. "Processing of bulk hierarchical metal-metal composites." Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559831.

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Spray forming with eo-injection of a solid particulate phase to form a metal-metal composite has been studied as a new route for manufacture. Two Al-based matrices were investigated: AI-12Si for testing the feasibility of the new manufacturing route and Al-4Cu for providing better mechanical performance. For both composite types, Ti was chosen as the particulate phase and the processing-microstructure-property relationships then studied. At Peak Werkstoff GmbH, Germany 12 wt%Ti particles were eo-injected into an atomised Al alloy droplet spray and eo-deposited to form a rv300 kg billet. The microstructure comprised refined equiaxed a-AI grains (rv5fLm), spherical Si particles (rv5fLm) and uniformly distributed Ti particles (rv80fLm). Sections of the billet were extruded under a range of conditions into long strips 20mm wide and 6mm, 2.5mm and 1mm thickness. At high strains, the Ti particles were deformed into continuous fibres of a few microns in thickness. Accumulative roll bonding was then performed to higher total strains, while maintaining a constant cross-section, reducing the Ti fibres to sub-micron thickness. The fibres were studied by extraction after selective dissolution of the a-AI matrix. There was no interfacial reaction between a-AI and Ti or any measurable oxide formation, thus providing encouragement for the manufacture of metal-metal composites by eo-spray forming. A powder injection pump was successfully integrated and commissioned on the spray forming facility at Oxford University. The pump was calibrated to optimise powder flow rates. Three AI-4Cu+ Ti composite billets were processed with each containing Ti powder with a different processing history. Up to 20vol%Ti was successfully incorporated, however due to the cooling effect from powder injection, porosity was significant. The quenching effect provided a finer AI-4Cu grain structure in the region of Ti injection, and also promoted precipitation of O'-AbCu precipitates. A Ti/ Al-4Cu interfacial reaction was more prominent in the billet spray formed at 850°C than those spray formed at 750°C. Angular Ti processed by a hydride-dehydride route had better deformation characteristics than spherical gas atomised Ti. Deformation processing by extrusion and rolling was investigated for Al-4Cu+20vol%Ti using SEM, EBSD and FIB. After extrusion to a strain of 5, the composite contained elongated reinforcing fibres characteristic of metal-metal composites. The microstructure studied by EBSD revealed equiaxed polygonal Al-4Cu matrix grains. Rolling was not as efficient as extrusion in producing elongated Ti fibres and was attributed to a lower deformation processing temperature. The rolled composites consisted of elongated Al-4Cu grains 1-5J1m in thickness. An UTS of 339MPa at a strain of 3 was attributed to texture strengthening in the Q- AI.

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5

Hajlane, Abdelghani. "Development of hierarchical cellulosic reinforcement for polymer composites." Licentiate thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17655.

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Cellulose is an environmentally friendly material which is obtainable in vast quantities, since it is present in every plant. Cellulosic fibers are commercially found in two forms: natural (flax, hemp, cotton, sisal, wood, etc.) and regenerated cellulose fibers (RCF). The biodegradability, the morphological and mechanical properties make these fibers a good alternative to the synthetic reinforcement (e.g. glass fibers). However, as all other cellulosic fibers these materials also have similar drawbacks, such as sensitivity to moisture and poor adhesion with polymers. The first part of this work concerned a heterogeneous modiﬁcation of cellulose nanocrystals (CNC) by using esteriﬁcation and amidiﬁcation to attach long aliphatic chains. Long-chain aliphatic acid chlorides and amines were used as grafting reagents. Surface grafting with acyl chains was confirmed by Fourier-transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy. It was found that the degree of substitution (DS) of the surface is highly dependent on the method of modification. The contact angle measurement showed that after modification, the surface of CNC was found to be hydrophobic. The second part was devoted to modification of RCF by CNC using Isocyanatopropyl triethoxysilane as coupling agent. Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy and X-ray diffraction analysis were performed to verify the degree of modification. The mechanical properties of the unmodified and modified fibers were analyzed using fiber bundle tensile static and loading–unloading tests. To show the effect of cellulose whiskers grafting on the Cordenka fibers, epoxy based composites were manufactured and tensile tests done on transverse uni-directional specimens. It was found that the mechanical properties were significantly increased by fiber modification and addition of the nano-phase into composite reinforced with micro- sized fibers.
Godkänd; 2014; 20140507 (abdhaj); Namn: Abdelghani Hajlane Ämne: Polymera konstruktionsmaterial/Polymeric Composite Materials Uppsats: Development of Hierarchical Cellulosic Reinforcement for Polymer Composites Examinator: Professor Roberts Joffe, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: PhD, Research Engineer Angelika Bachinger, Swerea SICOMP, Mölndal, Sverige Tid: Torsdag den 12 juni 2014 kl 15.00 Plats: E231, Luleå tekniska universitet

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6

Wicks, Sunny S. "Manufacturing and fracture of hierarchical composite materials enhanced with aligned carbon nanotubes." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90731.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 155-165).
Hierarchical advanced composite structures comprised of both nano- and micro-scale fibers are currently being studied as next-generation materials for multifunctional aerospace applications. Carbon nanotubes (CNTs) are an attractive reinforcing fiber for aerospace composites due to their scale and superior specific stiffness and strength, as well as their potential to enhance multifunctional properties. Nano-scale fibers can address current challenges in composites such as relatively weak through-thickness properties that occur due to matrix-rich regions, including those found at interlaminar ply interfaces, that are prone to delamination and lead to overall reductions in mechanical properties. Existing technologies such as stitching, z-pinning, and braiding provide through-thickness reinforcement; however, these improvements come with simultaneous reductions in in-plane properties. CNTs provide an alternative fiber reinforcement, though currently the literature reveals that laminate mechanical property enhancements are lower than expected. Investigations into how CNTs affect laminate properties have stalled due to difficulties with producing quality laminates and controlling CNT orientation and dispersion. In this work, manufacturing routes of a nano-engineered composite are developed to provide consistent control over laminate quality while placing aligned CNTs (A-CNTs) in the polymer matrix in the interlaminar and intralaminar regions. Manufacturing techniques are developed for growing aligned CNTs on a three-dimensional woven microfiber substrate and infiltrating the fuzzy fiber plies with polymer to realize the Fuzzy Fiber Reinforced Plastics (FFRP) architecture. These FFRP laminates show < 1% void fraction for a viscous marine epoxy system via hand lay-up and effectively void free (<< 1%) laminates for an aerospace epoxy system via infusion. The influence of the A-CNTs on manufacturability is quantified by assessing permeability and compressibility of the fuzzy fiber plies. Less than an order of magnitude decrease in permeability independent of CNT loading is observed (up to 3.6% volume fraction), demonstrating compatibility of the fuzzy fiber plies with both polymer matrices and both manufacturing routes. By contrast, fuzzy fiber ply compressibility increases linearly with CNT loading such that target composite volume fractions of - 50% mnicrofiber volume fraction can only be achieved with added external pressure in ranges typically available in composite production. The mechanisms of Mode I fracture toughness enhancement in FFRP laminates are elucidated experimentally by varying the type of epoxy and length of A-CNTs. Reinforcement effectiveness is found to vary from reduced initiation toughness to 100% increase in steady-state fracture toughness, depending upon the interlaminar fracture mechanisms. Toughness enhancement is less than expected based on idealized fiber pullout models, and is attributed to multiple and competing modes. Fractography reveals toughening mechanisms for both aerospace and marine epoxy laminates at several length scales, from the pull-out of A-CNTs to microfiber tow breakage. The toughening behavior and magnitude of steady-state toughness improvement is found to be highly dependent on the type of epoxy. In the more brittle aerospace epoxy system, modest improvement (~ 33%) in steady-state toughness with long (~ 19 microns) A-CNTs occurs because the cohesive interlaminar matrix failure mode around woven tow features is unchanged and toughening only occurs via increased fracture surface area through CNT pullout and rough epoxy fracture. The tougher marine epoxy allows much larger (up to 100%) steady-state toughness enhancement with A-CNTs by significantly adding instances of microfiber breakage and pullout along with CNT pullout from the epoxy. Varying the CNT length begins to reveal how the geometrical (re)arrangement of microfibers through tow swelling and changes in woven ply nesting affect the crack propagation path and subsequent interlaminar toughness. Fracture of A-CNT polymer nanocomposites isolates CNT-polymer effects from the microfibers and shows no increase in initiation toughness from the A-CNTs, but does confirm the role of CNTs in increasing fracture surface area post crack initiation, i.e., steady-state toughening. This work establishes the dependence of fracture toughness on A-CNT length and polymer type for the FFRP architecture. Future work includes quantifying the contribution of CNT pullout from the matrix on the laminate fracture behavior via modified standard tests for fracture initiation and toughness. Preliminary multifunctional investigations of the FFRP architecture indicate several other promising directions of future work, including damage sensing. Based on new understanding in this work on boh manufacturing and reinforcing mechanisms at work in FFRPs, mechanical and multifunctional enhancement of aerospace composites, particularly carbon fiber FFRP, are enabled.
by Sunny S. Wicks.
Ph. D.

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7

Zikánová, Arlette, Pavel Hrabánek, Milan Kočiřík, Libor Brabec, Klára Juristová, Pavel Čapek, Bohumil Bernauer, Vladimír Hejtmánek, Olga Šolcová, and Petr Uchytil. "Mass transport in the hierarchical porous structure of zeolite-based composite membranes." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196794.

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8

Zikánová, Arlette, Pavel Hrabánek, Milan Kočiřík, Libor Brabec, Klára Juristová, Pavel Čapek, Bohumil Bernauer, Vladimír Hejtmánek, Olga Šolcová, and Petr Uchytil. "Mass transport in the hierarchical porous structure of zeolite-based composite membranes." Diffusion fundamentals 2 (2005) 111, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14450.

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9

Li, Yuan. "Hierarchical Bayesian Model for AK Composite Estimators in the Current Population Survey (CPS)." Thesis, The George Washington University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10748002.

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The Current Population Survey (CPS) is a multistage probability sample survey conducted by the U.S. Census Bureau and the Bureau of Labor Statistics (BLS). The 4-8-4 rotation design is applied to produce overlap in the sample across months. Several weighting steps are used to adjust the ultimate sample in each month to be representative of the population. In order to produce efficient estimates of labor force levels and month-to-month change, the so-called AK composite estimator combines current estimates from eight rotation panels and the previous month’s estimates to estimate current values. Values of coefficients A and K are chosen every decade or so for the nation. The Successive Difference Replicate (SDR) method and Balanced Repeated Replication (BRR) method are currently used by the CPS for estimating the variance of the AK Composite Estimates.

Instead of using constant CPS (A, K) values for AK Composite Estimator over time, one could find the monthly optimal coefficients ( A, K) that minimize the variance for measuring the monthly level of unemployment in the target population. The CPS (A, K) values are stable over time but can produce larger variance in some months, while the monthly optimal (A, K) values have lower variance within a month but high variability across months.

In order to make a compromise between the CPS (A, K) values and monthly optimal (A, K), a Hierarchical Bayesian method is proposed through modeling the obtained monthly optimal ( A, K)’s using a bivariate normal distribution. The parameters, including the mean vector and the variance-covariance matrix, are unknown in this distribution. In such case, a first step towards a more general model is to assume a conjugate prior distribution for the bivariate normal model. Computing the conditional posterior distribution can be approximated through simulation. In particular, it can be achieved by the Gibbs sampling algorithm with its sequential sampling. As the key to the success of this Hierarchical Bayesian method is that approximated distributions are improved as iteration goes on in the simulation, one needs to check the convergence of the simulated sequences. Then, the sample mean after a number of iterations in the simulation will serve as the Hierarchical Bayesian (HB) (A, K). The HB (A, K) estimates in effect produce a shrinkage between the CPS (A, K) values and the monthly optimal (A, K) values. The shrinkage of the estimates of the coefficients ( A, K) occurs by manipulating the certain hyperparameter in the model.

In this dissertation, detailed comparisons are made among the three estimators. The AK Estimator using the CPS (A, K) values, using the monthly optimal (A, K) values, and using the Hierarchical Bayesian (A,K) values are compared in terms of estimates produced, estimated variance, and estimated coefficients of variation. In each month of the data set, separate estimates using the three methods are produced.

In order to assess the performance of the proposed methods, a simulation study is implemented and summarized. In the CPS, eight rotating survey panels contribute to the overall estimate in each month. Each panel is measured in a month at one of its month-in- sample. The month-in- sample range from one to eight. In the simulation, month-in- sample values are generated as if replicate panels were available for estimation. These month-in-sample values are used as the original monthly panel estimates of unemployment to produce CPS-style (A, K) estimates, AK-estimates using monthly optimal ( A, K) values, and AK-estimates using Hierarchical Bayesian ( A, K) values. Performance of each method is evaluated on the simulated data by examining several criteria including bias, variance, and mean squared error.

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10

Robbins, Donald H. "Hierarchical modeling of laminated composite plates using variable kinematic finite elements and mesh superposition." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40117.

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11

Liu, Xinye. "Binary metal organic framework derived hierarchical hollow Ni3S2/Co9S8/N-doped carbon composite with superior sodium storage performance." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1489784678856585.

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12

Strossi, Pedrolo Débora Regina. "Synthesis of metal-zeolite composite materials for bifunctional catalytic reactions." Thesis, Université de Lille (2018-2021), 2021. https://pepite-depot.univ-lille.fr/LIBRE/EDSMRE/2021/2021LILUR065.pdf.

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Les catalyseurs à base de zéolite ont été largement utilisés dans la conversion de la biomasse. Les rendements catalytiques des produits recherchés sont fortement limités en raison de la taille relativement petite des pores dans les zéolithes et la préparation du catalyseur par imprégnation conduit généralement à des nanoparticules métalliques relativement grosses et à un faible contact entre les sites métalliques et acides. Le but de ce travail est la conception de catalyseurs nanocomposites métal-zéolithe contenant des nanoparticules de ruthénium uniformément réparties dans les zéolithes hiérarchiques BEA et ZSM-5. L'utilisation de ruthénium évite la formation de silicates et d'aluminates métalliques inertes difficilement réductibles, tandis que les nanotubes de carbone avec des nanoparticules d'oxyde métallique supportées jouent un rôle de gabarit sacrificiel, ce qui permet de créer une mésoporosité et d'apporter une fonctionnalité métallique à l'intérieur de la matrice zéolithique. Par rapport aux catalyseurs métalliques supportés par des zéolites classiques, les zéolites ruthénium hiérarchiques synthétisées présentaient une activité beaucoup plus élevée et une sélectivité en méthane plus faible dans la synthèse Fischer-Tropsch. La caractérisation des catalyseurs préparés a indiqué l'initiation de la cristallisation des zéolites sur des nanoparticules métalliques. Cet effet a en outre été utilisé pour augmenter la dispersion de nanoparticules métalliques par cristallisation secondaire de Ru supporté sur ZSM-5. Nos résultats montrent une redispersion significative des nanoparticules d'oxyde métallique incorporées et une augmentation de l'activité des réactions modèles. De plus, une stratégie de synthèse a été développée pour la préparation de catalyseurs nanocomposites métalliques et zéolithiques hiérarchiques pour la synthèse directe d'iso-paraffines à partir de gaz de synthèse. Les nanocomposites sont synthétisés en trois étapes. Dans la première étape, la zéolite mère (noyau) est gravée avec une solution de fluorure d'ammonium. La gravure crée de petits mésopores à l'intérieur des cristaux de zéolite. Dans la deuxième étape, les nanoparticules de Ru préparées à l'aide de microémulsion eau-dans-huile sont déposées dans les mésopores de la zéolithe. Dans la troisième étape, une enveloppe de zéolite de zéolites de type MFI (silicalite-1 ou ZSM-5) est cultivée sur les cristaux de zéolite parent recouvrant à la fois la surface gravée et les nanoparticules métalliques. Ainsi, les nanoparticules métalliques deviennent entièrement encapsulées à l'intérieur de la matrice zéolithique. Les paramètres les plus importants tels que la teneur en ruthénium, la mésoporosité de la zéolite, et plus particulièrement, l'acidité de l'enveloppe du catalyseur, qui affectent les performances catalytiques des matériaux nanocomposites synthétisés dans la synthèse Fischer-Tropsch à basse température ont été identifiés dans ce travail. La quantité relative plus élevée d'iso-paraffines a été observée sur les catalyseurs contenant une enveloppe de ZSM-5. La proximité entre les sites métalliques et acides dans l'enveloppe zéolithique des catalyseurs nanocomposites est un paramètre crucial pour la conception de catalyseurs bifonctionnels zéolithiques métalliques efficaces pour la synthèse sélective de carburants de type essence via la synthèse Fischer-Tropsch, tandis que l'acidité du cœur du catalyseur a qu'un impact limité sur les performances catalytiques
Zeolite-based catalysts have been widely used in the conversion of biomass. The catalytic yields of the desired products are strongly limited due to the relatively small size of the pores in zeolites and the catalyst preparation by impregnation usually leads to relatively large metal nanoparticles and low contact between metal and acid sites. The purpose of this work is the design of metal-zeolite nanocomposite catalysts containing ruthenium nanoparticles uniformly distributed in the hierarchical BEA and ZSM-5 zeolites. Use of ruthenium avoids formation of inert hardly reducible inert metal silicates and metal aluminates, while carbon nanotubes with supported metal oxide nanoparticles play a role of sacrificial template, which allows creating mesoporosity and bringing metallic functionality inside the zeolite matrix. Compared to the conventional zeolite supported metal catalysts the synthesized hierarchical ruthenium-zeolites exhibited much higher activity and lower methane selectivity in Fischer-Tropsch synthesis. Characterization of the prepared catalysts has indicated initiation of crystallization of zeolites over metal nanoparticles. This effect has been further used to increase the dispersion of metal nanoparticles by secondary crystallization of Ru supported over ZSM-5. Our results show significant re-dispersion of embedded metal oxide nanoparticles and increase in the activity of model reactions. In addition, a synthetic strategy was developed for the preparation of hierarchical metal and zeolite nanocomposite catalysts for direct synthesis of iso-paraffins from syngas. The nanocomposites are synthesized in three steps. In the first step, the parent (core) zeolite is etched with an ammonium fluoride solution. The etching creates small mesopores inside the zeolite crystals. In the second step, the Ru nanoparticles prepared using water-in-oil microemulsion are deposited in the mesopores of the zeolite. In the third step, a zeolite shell of MFI-type zeolites (silicalite-1 or ZSM-5) is grown on the parent zeolite crystals coating both the etched surface and metallic nanoparticles. Thus, the metal nanoparticles become entirely encapsulated inside the zeolite matrix. Most important parameters such as ruthenium content, zeolite mesoporosity, and more particularly, the acidity of the catalyst shell, which affect the catalytic performance of the synthesized nanocomposite materials in low-temperature Fischer−Tropsch synthesis were identified in this work. The higher relative amount of iso-paraffins was observed on the catalysts containing a shell of ZSM-5. The proximity between metal and acid sites in the zeolite shell of the nanocomposite catalysts is a crucial parameter for the design of efficient metal zeolite bifunctional catalysts for selective synthesis of gasoline-type fuels via Fischer−Tropsch synthesis, while the acidity of the catalyst core has only a limited impact on the catalytic performance

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13

GARCIA, DE MIGUEL ALBERTO. "Hierarchical component-wise models for enhanced stress analysis and health monitoring of composites structures." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729658.

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14

LAVAGNA, LUCA. "Carbon materials and their role as reinforcement in composite materials." Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729657.

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15

Agwubilo, Ikenna. "Manufacture, modelling and characterisation of novel composite tubes." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/manufacture-modelling-and-characterisation-of-novel-composite-tubes(c11f005b-e651-481f-8ef5-4e6784bfbaa7).html.

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This thesis primarily focused on the development of novel composite tubes by braiding. The objective was to use hierarchical scale technique, i.e., micro, meso and macro scales, with the transfer of information from one scale to another to develop novel braided composite tubes. This research was conducted and reported in three journal papers. The aim of the first paper was to predict plane elastic properties for E-glass/epoxy braided composite structures at different braid orientations, by analytical and finite element techniques. The lenticular shape has been used to describe the geometry of the tow. Modified lenticular geometric model was developed to improve an existing geometric model, in terms of tow parameters, thereafter, plane elastic properties from Chamis micromechanical model for E-glass fibre and epoxy matrix without any knockdown effects were used as benchmark to develop predictive models, namely; Lekhnitskii's methodology and braided unit cell meso-scale finite element model to account for the effects of tow geometry, undulations/crimp, cross-over and braid orientations on the plane elastic properties of E-glass/epoxy composite. The results showed agreement in trend between the predictive models, Chamis micromechanical model, and a similar existing model. However, the plane elastic properties were knocked down in predictive models by 30% in the E11 direction and 32% in the E22 direction, when compared with Chamis micro-mechanical model for largest ±65° braid angle, among the braid angles, considered. The aim of the second paper was to manufacture E-glass/epoxy braided tubes at different braid orientations by vacuum bag infusion technique, conduct internal pressure tests, and determine the hoop and axial moduli of the infused tubes. Lekhnitskii's methodology was also used to develop plane elastic moduli by experiment using microscopy results, and by calculation. The experimental elastic moduli of the infused tubes and the experimental elastic moduli from Lekhnitskii's methodology were used to compare the predictive elastic moduli for E-glass/epoxy braided structures by Chamis micro-mechanical model, and the braided unit cell meso-scale finite element model. The two were from another paper. Results showed a perfect agreement in trend between the experimental results and the predictive results. However, the values of the experimental results were close but lower than the predicted results. Optical microscopy was performed on braided tube cross-section to evaluate the level of crimp or undulation. This was done by the determination of tow centreline crimp angle and aspect ratio. Results show that when compared with the predicted crimp, there was an agreement in trend, although the experimental results were lower than the predicted. Also, the knockdown factor was evaluated and used to quantify the reduction in experimental elastic moduli when compared with the predicted. Results showed that the absences of crimp in the Chamis model caused a tremendous difference between it, other predicted models and the experiment results. The elastic moduli of Chamis were by far higher than all others, including other predictive models. The purpose of the third paper was to manufacture E-glass/epoxy braided tube at ±31°, ±45°, ±55°, ±65° braid orientations using vacuum bagging and resin infusion technique, to design and manufacture a rig for tube internal pressures experiment, to determine the hoop and axial stress performances of the tubes by internal pressure experiment, to compare experimental results with laminate analysis predictions to evaluate the effect of crimp on the internal pressure performance of the braided tubes. To use E-glass braided tow meso-scale unit cell finite element model to predict the tow critical stresses, and the optimum braided tube architecture, using tube hoop and axial failure stresses or strains. The tubes were manufactured and subjected to internal pressure test (2:1), to failure. Failure mode was by weeping and bursting. Hoop stress was twice the axial stress. The highest value of hoop stress was at the ±65° braid angle, higher than the hoop stresses at the ±31°, ±45°, and ±55 ° braid angles by 50%, 39%, and 28% respectively. Hoop stress increased with increase in braid angle. The experimental results were validated by laminate analysis predictions by Chamis micro-mechanical model and Lekhnitskii's methodology, and the trend of the laminate analysis prediction matched that of the experimental results. However, the predicted values were higher than the experimental results by 21%, 14%, 11%, 10% for the ±31°, ±45°, ±55°, ±65° braid angles for the Chamis micro-mechanical model and 5%, 7%, 7%, 5% for the ±31°, ±45°, ±55°, ±65 braid angles respectively for the Lekhnitskii's model, showing the severe effect of crimp in the experimental tube, mostly when compared with Chamis micro-mechanical model. Braided tow unit cell finite element model prediction, showed that tow axial stresses increased with increase in braid angle, while the tow transverse stresses decreased with increase in braid angle. The predictions showed that the tow critical stresses and the tube optimum braided architecture lie between the ±65° and 90° braid angles. The tow critical stresses are the stresses at which the tow decreasing transverse stress and the tow increasing axial stress causes the tube to fail.

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Subbaraman, Ramachandran. "A MULTI-SCALE HIERARCHICAL APPROACH FOR UNDERSTANDING THE STRUCTURE OF THE POLYMER ELECTROLYTE MEMBRANE FUEL CELL (PEMFC) ELECTRODES - FROM NANOPARTICLES TO COMPOSITES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1205852564.

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17

Al-Nasri, Salam Khudhair Abdullah. "Treatment of wastewater containing cobalt (Co-59) and strontium (Sr-89) as a model to remove radioactive Co-60 and Sr-90 using hierarchical structures incorporating zeolites." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/treatment-of-wastewater-containing-cobalt-co59-and-strontium-sr89-as-a-model-to-remove-radioactive-co60-and-sr90-using-hierarchical-structures-incorporating-zeolitesa(ff5cff3e-1366-4a35-9b15-0246811d6ad1).html.

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Zeolites were used in this study to remove two types of non-radioactive ions (Cobalt-59 and Strontium-89) from wastewater. This was designed to model the use of ion-exchange technique to remove radioactive Co-60 and Sr-90 from low level wastewater from Al-Tuwaitha site. Al-Tuwaitha site is a nuclear research in Iraq was used for radio-medical and radio-chemical purposes before 1990. In this study, hierarchical microporous/macroporous structures were developed to overcome the diffusivity problem using zeolite. Diatomite and carbon were used to prepare the composite adsorbents by incorporating them with three types of zeolites (A, Y and clinoptilolite). From the XRD, SEM and EDAX measurement it was confirmed that successfully prepared of Iraqi palm tree leafs-Clinoptlolite (IPClinp) and Tamarind stones-Clinoptilolite (TSClinp) composites were obtained in this study as there is no evidence in literature of this being carried out before. The carbons were prepared successfully through the Pyrolysis method for 2h at 900°C in an inert atmosphere from two types of raw waste plant materials of Iraqi Palm Tree leafs (IP) and Tamarind stones (TS). For both types of carbons, the SEM images show organised porosities in different shapes. A third material used as a zeolite scaffold was diatomite (Celatom FW-14) a readily available natural material (dead algae).A hydrothermal treatment was used to build the hierarchical structure of zeolite onto carbon and diatomite materials, the scaffolds were seeded with nano-zeolite crystals prior to the treatment and thereafter mixed with the zeolite gel composition mixture in a stainless steel autoclave. Zeolite seeds were prepared using ball mill method to reduce the particle size of the commercial zeolite to sub-micron range for each type of zeolite. The surface area, morphology, element compositions and structure for each type of zeolite and composite material were characterised using BET method, SEM, EDAX and XRD. The amounts of each type of zeolite on the carbon composites were determined using TGA while that of the diatomite composite was determined by gravimetric analysis. The results show that each type of zeolite was successfully deposited and uniformly organised onto the surface of all support materials. All pure zeolites and composite materials were successfully tested to remove Co2+ and Sr2+ ions from aqueous solutions. It was found that the composite materials had higher ability to remove both ions relative to the pure zeolites. This increase is attributed to the deposition of zeolite (microporous) onto the macroporous structure (carbon and diatomite) which increased the flow accessibility within zeolite in the hierarchical structured composites. Comparison of the removal between the two metal ions indicates that all of the materials had higher uptake for Sr2+ than Co2+ ions. The highest adsorption capacities were realised with Tamarind Stone–ZeoliteA (TSA) in the order 120mg.gz-1and 290mg.gz-1 for Co2+ and Sr2+ ions, respectively. The effect of the experimental variables shows increasing uptake with increasing pH and initial ion concentrations while it decreased with increasing the solution temperature. The Co2+ loaded composites was subjected to vitrification process at 12000C for 2h. The encapsulated composites were leached for 90 and 120 days and no significant Co2+ was recorded in the leached solution. The results show that the composite materials can be used effectively to remove the radioactive ion of Co-60 and Sr-90 ion as they display the same chemical behaviour as Co-59 and Sr-89 studied in this work.

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18

Gregori, Damia. "Revêtements photocatalytiques pour substrats organiques souples." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10060/document.

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Ces dernières années, la photocatalyse hétérogène a connu un essor important comme technique de dépollution de l'eau et de l'air. L'application de ce procédé sur des substrats organiques souples, comme les textiles, présente de nombreux challenges. Les revêtements doivent être photoactifs sans pour autant dégrader les supports. Avec l'utilisation du TiO2 comme photocatalyseur, une bonne fixation des particules est primordiale pour éviter tout relargage dans l'environnement. La structuration des matériaux est également un point important. La porosité des films favorise les interactions polluants/photocatalyseurs mais doit être obtenue à faibles températures pour ne pas décomposer les textiles. Pour se faire, nous avons choisi de synthétiser des revêtements composites en insérant des particules commerciales de TiO2 dans une matrice hybride silicatée, celle-ci servant à la fois de liant au substrat et de couche protectrice. La matrice est préparée par le procédé sol-gel qui permet d'insérer aisément des groupements organiques au réseau silicaté. Ces modifications permettent d'apporter de la flexibilité aux revêtements afin de conserver les propriétés mécaniques des supports. Notre étude s'est consacrée à l'élaboration et à l'optimisation de ces systèmes. Une première partie a été réalisée sur des supports inorganiques afin de définir des comportements modèles, avant de transférer la technologie sur les textiles. L'efficacité des revêtements a été évaluée en phase aqueuse et gazeuse par la dégradation de l'acide formique, du bleu de méthylène et du toluène. La stabilité des supports et des films par rapport aux UV a été suivie par plusieurs techniques analytiques (MEB, XPS, ToF-SIMS, RMN, angle de contact, IR, colorimétrie) en accélérant le photovieillissement des matériaux. Diverses caractérisations mécaniques (abrasion, arrachage, rigidité) sont venues compléter notre étude
Heterogeneous photocatalysis was widely developed these last years for water and air depollution. Applications on organic and flexible substrates, like textiles, induce many challenges. The coating must be photoactive without damaging the media. With the use of TiO2 as photocatalyst, a good fixation of the particles is essential to prevent their release into the environment. The material structuration is also an important point. Film porosity promotes pollutants/photocatalysts interactions but must be obtained at low temperatures to avoid textiles degradation. In this context, we chose to synthesize composite coatings inserting commercial TiO2 particles into a silica matrix used as binder and protective layer. The matrix is prepared by the sol-gel process that allows adding organic groups into the silicate network. Such modification of the structure provides flexibility to maintain the mechanical properties of the supports. Our study is devoted to the development and optimization of these systems. The first part was conducted on inorganic substrates to define models behavior before transferring the technology on textiles. Film efficiency was evaluated in gas and aqueous phase degrading formic acid, methylene blue and toluene. The UV stability of the media and the film was followed by several analytical techniques (SEM, XPS, ToF-SIMS, NMR, contact angle, IR, colorimetry) accelerating the photoaging of the materials. Various mechanical characterizations came to complete our study

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19

Juntaro, Julasak. "Environmentally friendly hierarchical composites." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501202.

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20

Griffiths, Emma. "Micromechanical modelling of advanced hierarchical composites." Doctoral thesis, Faculty of Engineering and the Built Environment, 2020. http://hdl.handle.net/11427/32222.

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Nanoporous metals are uniquely interesting materials. Their high ductility and impressive strength in compression make them a favourable candidate for use in structural applications. However, these materials under-perform when tested in tension. This issue may be addressed by impregnating the nanoporous metal with a polymer. In this work the behaviour of a polymer impregnated nanoporous gold (NPG) composite is explored using the finite element method in three different scenarios: linear elasticity, fracture and electrically stimulated actuation. Using representative volume elements (RVEs), previously unexplored relationships between the macroscopic material response and its microstructure as well as interesting mechanisms and deformation strategies are explored. Firstly the homogenization and micromechanical response under compression of a gold/epoxy nanocomposite is investigated. Investigation into the stress-strain response within the material reveals a complex interaction between the constituents resulting in both compressive and tensile strains. With specific focus on the loading modes of the individual ligaments, significant axial and bending loading as well as an unexpectedly large amount of shear stress is seen. Following this the improved ductility and resistance to fracture of a gold/polymer nanocomposite compared to the pure NPG material is revealed using computational compact-tension tests. It is observed that the polymer stabilizes the gold thus preventing ductile fracture. Several toughening mechanisms are also revealed. Previously unexplored effects of increasing the volume fraction on the ductility and strength of the composite are also explored. The functionality of the gold/polymer nanocomposite as an actuator material is then investigated. A coupled chemo-electro-mechanical material model is adopted to model the electrically stimulated deformation. This is carried out in Abaqus using a novel staggered explicit-implicit solution scheme. Simulation of several RVEs with different gold volume fractions show that while the gold provides strength and support, increasing its volume fraction hinders both the ion transport speed and the total deformation of the nanocomposite. A complex interaction between the stress response and the gold volume fraction is also observed.

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21

Zainol, Abidin Mohd Shukur. "Development of hierarchical composites for structural applications." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/26988.

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The incorporation of carbon nanotubes (CNTs) into the matrix of conventional fibre reinforced composites as fillers offers the potential for mechanical, electrical and thermal multifunctional enhancement without disrupting the pristine in-plane properties. In this research, the CNTs were distributed within a thermosetting matrix system via an extrusion method which alleviated the processing difficulties associated with conventional liquid processing methods. Hierarchical composites (HCs) based on carbon fibres and the manufactured CNT-filled matrix were then produced using a wet powder impregnation technique followed by hot melt consolidation. The use of pure or mixed matrix powder provided either a homogeneous distribution of CNTs or an engineered heterogeneity at the length scale of the powder particle size (at ~11 μm). Mode I fracture toughness and interlaminar shear strength was measured with double cantilever beam (DCB) and short beam shear (SBS) tests respectively. Through-thickness electrical and thermal conductivities were also characterised to ensure the CNTs had imbued multifunctionality to the HCs. Heterogeneous HCs had significantly improved initiation fracture toughness (36%) in comparison to that of the baseline carbon fibre epoxy composite. The fracture toughness was also 29% higher than that of HC manufactured with homogenously distributed CNTs, at similar nanoreinforcement content. The interlaminar shear strength increased with average CNT loading up to 5 wt%E; weight percent to the weight of the epoxy; (1.38 vol%C; volume percent to the volume of the hierarchical composite) but was unaffected by the heterogeneity. The mechanisms for these improvements were investigated through extensive fractography. The through-thickness electrical conductivity exhibited a substantial 357% improvement with the inclusion of 10 wt%E (2.67 vol%C) CNTs. Through-thickness thermal conductivity exhibited 22% improvement regardless of CNTs content. These physical property improvements implied that multifunctionality in mechanical, electrical and thermal characteristics were achieved.

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22

Lamoriniere, Steven. "High performance polyetheretherketone nanocomposites and hierarchical composites." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11798.

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23

Liu, Jingyu. "Development of bioinspired composites with hierarchical structures." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/205618/1/Jingyu_Liu_Thesis.pdf.

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This research presents a novel method for fabrication of bioinspired composites with hierarchical structures, developed via combined 3D print and freeze casting techniques. Mechanical characterization and numerical modelling are conducted at different material length scales to understand the structure-property relationship. Tailored mechanical behaviour and biocompatibility have been achieved, demonstrating great potential for biomedical applications such as personalized implants and scaffolds. This work also provides some new insights on the strengthening and toughening mechanisms in biomaterials.

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Thompson, Benjamin Robert. "Hierarchically structured composites and porous materials." Thesis, University of Hull, 2017. http://hydra.hull.ac.uk/resources/hull:16570.

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This thesis develops a hydrogel bead templating technique for the preparation of hierarchically structured composites and porous materials. This method involves using slurries of hydrogel beads with different size distributions as templates. Mixing hydrogel beads with a scaffolding material and then allowing the scaffold to harden, followed by drying of the composite leaves pores in the place of the hydrogel beads. These pores reflect the size and shape of the templates used and the porosity reflects the volume percentage of hydrogel bead slurry mixed with the scaffolding material. A viscous trapping technique has been developed which utilises the viscosity of methylcellulose to stop sedimentation of the scaffold particles during network formation. Both of these methods are attractive due to being cheap, non-toxic and they use food grade materials which allows their use in a multitude of applications. Porous and hierarchically porous gypsum composites have been prepared using both hydrogel bead templating and viscous trapping techniques, or a combination of the two. The level of control over the final microstructure of the dried composites offered by these techniques allowed for a systematic investigation of their thermal and mechanical properties as a function of the pore size, porosity and hierarchical microstructure. It has been shown that the thermal conductivity decreases linearly with increasing porosity, however it was not dependent on the pore sizes that were investigated here. The mechanical properties, however, were significantly different. The porous composites produced with either small hydrogel beads (100 μm) or methylcellulose solution had approximately twice the compressional strength and Young’s modulus compared to the ones produced with large hydrogel beads (600 μm). The sound insulating properties of porous and hierarchically porous gypsum composites have also been investigated. With increasing porosity, the sound transmission loss decreases, as expected. At constant porosity, it is shown that the composites with large pores perform significantly better than the ones with small pores in the frequency range of 75-2000 Hz. At higher frequencies (>2400 Hz) the composites with smaller pores begin to perform better. The material’s microstructure has been studied in an attempt to explain this effect. The hydrogel templating technique can be used to prepare composite materials if the drying step is not performed. Hydrogel beads have been incorporated into a soap matrix. The dissolution rate of these composites as a function of hydrogel bead size and volume percentage of hydrogel beads incorporated within the soap matrix has been investigated. It has been shown that the dissolution rate can be increased by increasing the volume percentage of hydrogel beads used during composite preparation but it is independent on their size distribution. Finally, three methods of controlling the release rate of encapsulated species from these soap-hydrogel bead composites have been shown. The first method involved varying the size distribution of the hydrogel beads incorporated within the soap matrix. The second involved changing the concentration of the gelling polymer and the final method required co-encapsulation of an oppositely charged polyelectrolyte. A binary hydrogel system has been developed and its rheological and thermal properties have been investigated. It consists of agar and methylcellulose and shows significantly improved rheological properties at high temperatures compared to agar alone. The storage modulus of the two component hydrogel shows a maximum at 55 °C which was explained by a sol-gel phase transition of methylcellulose, evidence of which was seen during differential scanning calorimetry measurements. After exposure of this binary hydrogel to high temperatures above the melting point of agar alone (> 120 °C), it maintains its structure. This suggests it could be used for high temperature templating or structuring of food products. The melt-resistant binary hydrogel was used for the preparation of pancake-hydrogel composites using hydrogel bead templating. Mixing slurry of hydrogel beads of this composition with pancake batter, followed by preparation at high temperatures produced pancakes with hydrogel beads incorporated within. Bomb calorimetry measurements showed that the caloric density could be reduced by a controlled amount by varying the volume percentage of hydrogel beads used during preparation of the composites. This method could be applied to other food products such as biscuits, waffles and breakfast bars. Furthermore, there is scope for development of this method by the encapsulation of flavour enhancing or nutritionally beneficial ingredients within the hydrogel beads.

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Herceg, Tomi. "Nano and hierarchical composites with high CNT loading fractions." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/27246.

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One of the major challenges in the field of nanocomposites has been to distribute and disperse high loading fractions of carbon nanotubes (CNT) in epoxy resins through a route that is scalable to high throughput. Furthermore, CNTs have been employed as an additional constituent in advanced carbon fibre composite materials to improve their poor matrix dominated properties in the drive to manufacture lighter and stronger composite structures. Attempts to produce epoxy based hierarchical composites (HC) with high CNT loadings by introducing nanoreinforcement in the resin have been plagued by processing difficulties related to viscosity and infiltration. Nonetheless, introducing just a few weight percent of CNTs into the matrix of continuous carbon fibre composites has been shown to enhance fracture toughness and compression performance. As such, this thesis tackles an effective way to combine carbon fibre, thermosetting resin and CNTs into hierarchical composites with high loadings of nanoreinforcement. To this end, a readily scalable powder based processing route was developed to produce epoxy based polymer nanocomposites (PNC) with a maximum CNT loading of 18.4 wt% (11.5 vol%). Due to the excellent CNT distribution and dispersion achieved during processing, some practically relevant physical and mechanical properties were enhanced even at the highest CNT loadings: 67 S/m and 0.77 W/ m·K electrical and thermal conductivities, respectively, and 5.5 GPa Young's modulus. Analytical micromechanical models to validate reinforcement due to CNTs were also explored. The nanocomposite powder was also employed as a constituent in a wet powder impregnation process to produce carbon fibre based HC laminates containing as much as 5.5 vol% CNTs (11.5 vol% CNTs in the matrix). The processing parameters were optimised to yield a laminate with 55% fibre volume fraction, making it suitable for structural applications. The through thickness electrical conductivity of the HC containing 5.5 vol% CNTs improved by an order of magnitude; however, the largest enhancement in interlaminar fracture toughness (20%) was observed at an intermediate loading of 2 vol% CNTs. The mechanical underperformance at high CNT loadings was attributed to the heterogeneous microstructure observed to different extents in both PNCs and HCs, and a number of solutions related to material selection and processing design were proposed.

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Nyirabahizi, Epiphanie. "Bayesian and Frequentist Approaches for the Analysis of Multiple Endpoints Data Resulting from Exposure to Multiple Health Stressors." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/136.

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In risk analysis, Benchmark dose (BMD)methodology is used to quantify the risk associated with exposure to stressors such as environmental chemicals. It consists of fitting a mathematical model to the exposure data and the BMD is the dose expected to result in a pre-specified response or benchmark response (BMR). Most available exposure data are from single chemical exposure, but living objects are exposed to multiple sources of hazards. Furthermore, in some studies, researchers may observe multiple endpoints on one subject. Statistical approaches to address multiple endpoints problem can be partitioned into a dimension reduction group and a dimension preservative group. Composite scores using desirability function is used, as a dimension reduction method, to evaluate neurotoxicity effects of a mixture of five organophosphate pesticides (OP) at a fixed mixing ratio ray, and five endpoints were observed. Then, a Bayesian hierarchical model approach, as a single unifying dimension preservative method is introduced to evaluate the risk associated with the exposure to mixtures chemicals. At a pre-specied vector of BMR of interest, the method estimates a tolerable area referred to as benchmark dose tolerable area (BMDTA) in multidimensional Euclidean plan. Endpoints defining the BMDTA are determined and model uncertainty and model selection problems are addressed by using the Bayesian Model Averaging (BMA) method.

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27

Qian, Hui. "Carbon nanotube grafted fibres : a route to advanced hierarchical composites." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5532.

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The feasibility of reinforcing conventional fibre/polymer composites by grafting carbon nanotubes (CNTs) onto the fibre surfaces has been investigated. Different methods were developed for directly growing CNTs on silica and carbon (C320 and IM7) fibres. Pure and N-doped CNTs with controllable length were grown on silica fibres using an injection chemical vapour deposition (ICVD) method. The diameter and crystallinity of both types of CNTs increased during growth, which proceeded via the base-growth mechanism. However, the nature surface of carbon fibres is not favourable for the ICVD method. As an alternative, CNT-grafted carbon fibres were produced using the incipient wetness technique or electrochemical deposition to pre-load catalyst for subsequent CNT growth. The effects of growth parameters on the morphology, density, and alignment of CNTs were explored. The CNT-grafting process maintained or improved the fibre tensile modulus, but resulted in strength degradations, to different extents, depending on the fibre type and growth parameters. The impact of CNT-grafting on the interfacial shear strength (IFSS) was studied using different micromechanical interface tests, based on different fibre/polymer systems. The IFSS was unchanged in push-out tests, likely due to an unusual internal failure of the fibres. In all other cases, the IFSS was significantly increased. Single fibre pull-out tests on C320 carbon fibre/epoxy composites showed a 60% increase, whilst fragmentation tests on poly(methyl methacrylate) composites yielded improvements of 26% and 80-150% for IM7 carbon fibres and silica fibres, respectively. The improvements can be attributed to the increased surface area, excellent fibre wettability by the matrix and mechanical interlocking of CNTs with the matrix. In addition, a new combined in situ AFM/Raman technique proved to be a useful tool to study CNT distribution and orientation within hierarchical composites.

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de, Luca Francois. "Fibre-reinforced composites with nacre-inspired interphase : a route towards high performance toughened hierarchical composites." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/49423.

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Conventional fibre-reinforced polymer composite materials are well known for their high strength, stiffness, low weight and chemical resistance but composites do fail catastrophically, in a brittle manner, with little prior warning. When a fibre breaks in tension, shear stresses transfer load previously carried by the broken fibre to neighbouring fibres through the matrix, leading to local stress concentrations. As tensile loading continues, fibre breaks accumulate in the composite, eventually leading to the formation of a critical cluster, which triggers the failure of the composite. The aim of this research was to develop a novel hierarchical composite architecture consisting of fibres decorated with a nanostructured coating embedded in a matrix. A high performance and tough nanostructured composite interphase, inspired by nacre, should provide additional toughness in tension. A Layer-by-Layer assembly method was used to assemble inorganic nanometre-wide platelets and a polyelectrolyte into a well-organised nanostructure, mimicking the “brick-and-mortar” architecture of nacre, which was developed and characterised. The nanostructure was successfully deposited around conventional reinforcing-fibres, such as carbon and glass fibres, and allowed for absorption of the energy arising from fibre breaks and substantial increase in debonding toughness in single fibre composite models. Impregnated fibre bundle composites were manufactured and tested in tension, which exhibited an increased tensile strength, strain to failure and work of fracture when the nanostructured composite interphase was incorporated. This work was part of the HiPerDuCT programme grant, collaboration between the departments of Aeronautics, Chemical Engineering, Chemistry and Mechanical Engineering of Imperial College London and the University of Bristol.

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Tritschler, Ulrich [Verfasser]. "Hierarchically Structured Composite Materials by Gluing of Anisotropic Nanoparticles / Ulrich Tritschler." Konstanz : Bibliothek der Universität Konstanz, 2015. http://d-nb.info/1113109793/34.

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Hajlane, Abdelghani. "Hierarchical cellulosic reinforcement for composites: enhanced resistance to moisture and compatibility with polymers." Doctoral thesis, Luleå tekniska universitet, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26332.

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Cellulosic fibres (flax, hemp, regenerated cellulose) possess decent mechanical properties and they are gaining interest as an alternative to synthetic reinforcement (e.g. glass fibres) in polymers to reduce the petroleum consumption and pollution. In particular, manmade Regenerated Cellulose Fibres (RCF) have been extensively studied as potential reinforcement in polymer composites. For high performances where stability is highly required, RCF among the cellulosic fibres are well qualified due the advantage of being continuous with regular cross section. However, the hydrophilic character and the sensitivity to moisture reduce the use of fibres based cellulose in composite applications. Indeed, the moisture absorption and the low compatibility leading to weak fibre/matrix interface are major factors behind the less interest of utilizing cellulosic fibres in composite intended for high performances. The short term objective of this thesis was to improve the resistance to moisture and the adhesion of regenerated cellulose fibres (RCF) commercialized under the trade name CORDENKA 700 super 3 to Epoxy matrix through chemical treatments by cellulose nano-crystals via silane coupling agents. In Paper I chemical treatments of cellulose nano-crystals using (CNC) esterification and amidification to attach long aliphatic chains is studied. The treatment was successfully achieved as confirmed by spectroscopic characterisations and led to a decrease of the moisture absorption. Contact angle measurement showed hydrophobic of CNC after treatment. In Paper II, CNC extracted from wastes of date palm tree were grafted on RCF fibres to create hierarchical structure. The effect of grafting CNC on RCF was evaluated by tensile tests both in static and loading-unloading. In fact, treatments were revealed to change slightly the microstructure where the orientation of both crystalline and amorphous phases where re-oriented as X-ray analysis showed. Grafted fibres based unidirectional composite were manufactured and transversally tested. Both mechanical properties and resistance to crack were significantly increased by fibre modification. Another approach for chemical modification of RCF fibres was developed in Paper III. In this paper, the process of modification of RCF by CNC is more environmentally friendly. The γ-methacryloxypropyltrimethoxysilane (MPS) was used as coupling agent to attach the CNC onto the fibres. This treatment involves a mixture of water and ethanol as solvents and was run at relatively low temperature. The impact of the treatment on fibres was scrutinised after each treatment basically by MPS and after grafting CNC. Results showed that the modification by silane decreased the stiffness and strength of fibres while the strain at failure was increased. However, after grafting CNC, stiffness and strain at failure were recovered while the strength remained at the same order of magnitude as for fibres treated only by the coupling agent. The effect of these treatments on moisture absorption and on the adhesion with epoxy matrix was the focus of the Paper IV. In this paper, it was shown that at high relative humidity (RH=64%) the treatment by CNC decreased water uptake by factor of two compare to untreated fibres. Besides, the treatments by CNC at different concentrations lessened the impact of moisture on stiffness and strength of fibres after exposure to the same humidity level (RH=64%). Moreover, the pull-out test performed on fibre bundles showed that the adhesion between fibre and matrix is less affected by moisture (samples conditioned at RH=64%) for CNC grafted fibres compare to untreated fibres. The treatment process by MPS was Scaled-up to Non-Crimp Fabric in Paper V and the interlaminar properties of composites reinforced with RCF were studied. Double cantilevered beam (DCB) test was used to characterize fracture toughness, under static and fatigue loading. Regenerated cellulose fibres exhibit highly nonlinear behaviour and strongly influence the performance of their composites. The obtained fracture toughness values were significantly high compared to those of synthetic fibre reinforced composites. However, due to the high nonlinearity, a concrete conclusion was not easy to make on the effect of fibre treatment on the materials performance. Thus, scanning electron microscopy studies were carried out on fracture surfaces which confirmed the treatment effect, qualitatively, on the improvement of interfacial adhesion.

Godkänd; 2016; 20160508 (abdhaj); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Abdelghani Hajlane Ämne: Polymera konstruktionsmaterial/Polymeric Composite Material Avhandling: Hierarchical Cullulosic Reinforcement for Composites Enhanced Resistance to Moisture and Compatibility with Polymers Opponent: Professor Mikael Skrifvars, Sektionen för textilteknologi, Akademin för textil, teknik och ekonomi, Högskolan i Borås, Borås. Ordförande: Professor Roberts Joffe, Avdelningen för materialvetenskap, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå. Tid: Fredag 10 juni, 2016 kl 10.00 Plats: E231, Luleå tekniska universitet

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Gerlach, Robert. "Characterisation of the strain rate dependent behaviour of 3d composites using a hierarchical approach." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526767.

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Ni, Xinchen. "Nanoengineered hierarchical advanced composites with nanofiber interlaminar reinforcement for enhanced laminate-level mechanical performance." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127728.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2020
Cataloged from PDF of thesis.
Includes bibliographical references (pages 157-177).
At present, there is a need for novel, scalable, and high-performance structural materials that offer unprecedented combinations of stiffness, strength, and toughness at a low density, which can serve in a variety of applications in the aerospace, transportation, defense, and energy industries. To date, composite materials, specifically advanced carbon fiber reinforced plastics (CFRPs), which are comprised of high specific stiffness and strength continuous carbon microfibers and lightweight, relatively compliant polymers, have been among the most attractive materials and are used extensively in the aerospace sector. However, most CFRPs are fabricated by stacking plies in a layer-by-layer fashion, resulting in a weak polymer-rich region, known as the interlaminar region, at each ply interface that leads to poor properties through the laminate thickness.
Although the mechanically superior microfibers are designed to be the primary load carriers, the much weaker polymer matrix causes the laminates to be prone to premature failure with interlaminar delamination, which negatively affects both in-plane and out-of-plane performance. This key shortcoming is known as the Achilles' heel of CFRPs, which hinders their design and wider adoption in critical structural applications. In this dissertation, a novel nanoengineering approach to address the longstanding problem of weak ply interfaces of CFRPs is developed and demonstrated. High densities (>10 billion nanofibers per cm²) of uniformly-distributed vertically aligned carbon nanotubes (A-CNTs) are placed between neighboring plies to bridge the weak polymer-rich interlaminar region in existing prepreg-based laminated composites, creating a hierarchical architecture termed "nanostitch".
The effectiveness of nanostitching is evaluated via various mechanical tests including short-beam shear (SBS), Mode I and II fracture, and double edge-notched tension (DENT), in all of which the nanostitched composites have demonstrated enhanced mechanical performance. Furthermore, the multiscale reinforcement mechanisms resulting from the CNTs are elucidated via a variety of ex situ and in situ damage inspection techniques, including optical microscopy, scanning electron microscopy, lab-based micro-computed tomography, and in situ synchrotron radiation computed tomography (SRCT). Specifically, in SBS, despite no increase in static strength, a 115% average increase in fatigue life across all load levels (60 to 90% of static strength), with a larger increase of 249% in high-cycle (at 60% of static strength) fatigue, is observed.
In Mode I and Mode II fracture, it is revealed that the interlaminar crack bifurcates into the intralaminar region from the interlaminar precrack, and then propagates within the intralaminar region parallel to the nanostitched interlaminar region as an "intralaminar delamination" in steady state. This unique crack bifurcation phenomenon has never been previously observed and is attributed to the A-CNTs adding interlaminar toughness to a level that causes the interlaminar crack to bifurcate into the less tough intralaminar region. In DENT, an 8% increase in ultimate tensile strength (UTS) is observed and is attributed to the A-CNTs suppressing critical interlaminar delaminations very close to final failure (greater than 90% UTS) via in situ SRCT.
In addition to the positive reinforcement results observed for the nanostitched composites, a next-generation higher volume fraction nanostitched composite with additional levels of beneficial hierarchy termed "buckled nanostitch" or "nanostitch 2.0" is created by exploiting the unique buckling behavior displayed by patterned A-CNT forests under compression. This multilevel hierarchical architecture further enhances the composite mechanical performance: SBS strength by 7% and DENT strength by 28%, compared to the baseline composites. The dissertation not only presents a controllable, scalable manufacturing method to produce engineered structural materials that are hierarchically designed down to the nanoscale with enhanced mechanical performance, but it also establishes key new understanding of the complex and coupled strengthening and toughening mechanisms acting at different scales, as well as their effects on macroscopic laminate-level mechanical properties.
A particular focus has been the seminal use of in situ SRCT to study the effects of the hierarchical nanoscale reinforcements, and thus the methods established provide an experimental path forward for future work in this area. Together, these advances open up new opportunities for creating next-generation engineered materials with a suite of programmable properties by controlling their structures and constituents across multiple length scales.
by Xinchen Ni.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Mechanical Engineering

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33

Li, Richard Ph D. Massachusetts Institute of Technology. "Hierarchical carbon fiber composites with radially aligned carbon nanotubes : preservation of in-plane tensile properties." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85806.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 89-94).
Hierarchical carbon-nanotube (CNT)-based composites have significant potential to expand the performance and functionality of aerospace composite structures. Notably, circumferentially aligned CNT arrays have previously been grown on woven alumina filaments to form a "fuzzy fiber" reinforced plastic (FFRP) architecture with demonstrated improvements in inter- and intra-ply mechanical properties as well as multifunctional enhancement via tailorable electrical and thermal conductivities. However, thus far, the development of fuzzy carbon fiber reinforced plastics (fuzzy CFRP) with all-around enhanced mechanical properties has been elusive. In particular, prior work attaining growth of CNTs on carbon fibers (CF) have resulted in drastic reductions in fiber tensile strength (e.g., 55% loss), thereby compromising in-plane tensile properties of the resultant fuzzy CFRP. In this thesis, a novel method for high-yield growth of carbon nanotubes on carbon fiber is refined and implemented in the fabrication of unidirectional fuzzy CFRP plies with preserved tensile properties: Non-covalent functionalization of the CF surface coupled with a low temperature thermal chemical vapor deposition process enable high density catalyst adhesion and CNT growth below critical temperatures that would result in fiber strength loss. Successful scale-up to unidirectional fuzzy CFRP specimens with high (67%) and low (32%) CF volume fractions is presented. Testing results indicate that longitudinal elastic properties are retained for all fuzzy CFRP samples consistent with micromechanical analyses. Unexpectedly, the high fiber volume fraction fuzzy CFRP specimens show a 12% decrease in mean tensile strength that was hypothesized to be due to fiber damage introduced through transverse compression during processing of the fuzzy carbon fiber tows. As such, lower fiber volume fraction fuzzy CFRP specimens were subsequently tested and observed to retain strength. These advances pave the way for scale-up to fuzzy CFRP laminates with integrated multifunctionality and improved interlaminar performance without compromising in-plane mechanical properties critical to aerospace-grade composite materials.
by Richard Li.
S.M.

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34

Abbott, Anthony. "Bacterial cellulose for use in hierarchical composites, macroporous foams, bioinorganic nanohybrids and bacterial-based nanocomposites." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/8976.

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The growing environmental awareness and the not so distant scarcity of fossil feedstocks are promoting nowadays a renewed interest in the use of renewable raw materials derived from biomass, i.e., cellulosic products. Recently, a relatively novel type of cellulose product namely, bacterial cellulose, biosynthesised by cellulose-producing bacteria Gluconobacter xylinus, has appeared as a promising raw material for the development of advanced renewable (nano-) materials owing to its outstanding properties such as inherent nanosize (width: 1 to 25 nm; length: 1 to 9 m), high degree of crystallinity (70% to 90%) and impressive mechanical properties (Young's modulus: 78 to 155 GPa). This thesis describes the preparation of different types of renewable (nano-) materials composed of bacterial cellulose, which includes all-cellulose hierarchical composites, macroporous cryogel microspheres, functional bioinorganic nanohybrids and entirely bacterial-based nanocomposites. Bacterial cellulose was deposited around the surface of sisal fibres by Gluconobacter xylinus, which resulted in a dense bacterial cellulose coating of the surfaces of sisal fibres. Furthermore, the bacterial cellulose coated sisal fibres obtained after surface modification of fibres enhanced the mechanical performance of all-cellulose hierarchical composites owing to an improvement of the quality of the sisal fibres-regenerated cellulose matrix interface. Bacterial cellulose manofibrils were dissolved in DMAc/LiCl cosolvent, then templated into a microsphere shape, regenerated in H2O and freeze-dried to obtain highly porous cryogel microspheres composed exclusively of regenerated bacterial cellulose, which possessed a Brunauer-Emmet-Teller (BET) surface area ranging from 55 m2/g to 123 m2/g. Thioether functionalised bacterial cellulose nanofibrils were synthesised using a "grafting from" approach during the free radical grafting polymerisation of a monomer containing thioether moieties, namely 2-(methylthio)ethyl methacrylate. The thioether moieties grafted from the bacterial cellulose (MTEMA-g-BC) nanofibrils subsequently enabled the preparation of optically functional bioinorganic nanohybrids, where either gold nanoparticles or cadmium telluride quantum dots were chemisorbed onto the thioether moieties functionalised bacterial cellulose nanofibrils. Hydrophobised bacterial cellulose nanofibrils were also synthesised using the same "grafting from" approach using free radical grafting polymerisation of a hydrophobic caprolactone-based macromonomer, caprolactone 2- (methacryloyloxy)ethyl ester. Then, entirely bacterial-based nanocomposites composed of caprolactone grafted bacterial cellulose (PCLMA-g-BC) nanofibrils reinforced poly(3- hydroxy- butyrate) (PHB) matrix were produced by solution casting. The tensile strength and Young's modulus of bacterial-based nanocomposites reinforced with PCLMA- g-BC nanofibrils (i.e., nanofiller content of 10 wt./wt.%) increased by 101% and 170%, respectively, as compared to the neat PHB lm. The findings reported in this thesis highlight the potential and versatility of bacterial cellulose to produce novel and innovative types of renewable advanced (nano-) materials and composites.

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35

Al-Jubouri, Sama. "Synthesis and characterization of hierarchically porous zeolite composites for enhancing mass transfer." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/synthesis-and-characterization-of-hierarchically-porous-zeolite-composites-for-enhancing-mass-transfer(909ecc50-19f6-43b0-816c-e9325ba33816).html.

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The major concern of this work is the development of hierarchically porous structured zeolite composites for ion-exchange applications by deposition of a thin layer of zeolite on inexpensive porous supports which offers better efficiency in separation processes. The merits of utilization of zeolite composites in industrial applications are generally reducing mass transfer resistance and pressure drop. In addition to this they have advantages in the removal of metal ions from wastewater such as increasing the metals uptake and minimizing the volume of waste disposed especially after vitrification. This thesis presents results from a combination of experimental work and simulation study of experimental data to give isotherm and kinetic models. The experimental work shed light on the preparation of zeolite composites using zeolite X (Si/Al ~ 1.35) and clinoptilolite (Si/Al ~ 4.3), studying the performance of these composites on the removal of the Sr2+ and Mn2+ ions and then stabilization of waste materials resulting from the ion-exchange process. Clinoptilolite was hydrothermally synthesized to show the effect of non-framework cations on the removal process. The porous supports were diatomite which is naturally occurring silica and carbon which is obtained from Iraqi date stones by a thermal treatment conducted at 900°C. Coating the support surface with zeolites crystals was conducted in two different ways. The layer by layer approach, which has not previously been used, was used to prepare monolithic carbon clinoptilolite composite using a combination of sucrose/citric acid and zeolite. The other approach was modifying the support surface by ultrasonication in the presence of nanoparticles suspension prepared using ball mill to create nucleation sites and enhance the crystal attachment during hydrothermal treatment. Characterisation was implemented in each case using XRD, SEM, EDAX, TGA and BET method. Ion-exchange experimental results showed higher ion-exchange capacity obtained when the composites were used in comparison to pure zeolites, when a comparison is based on actual weight of zeolite used for removal of Sr2+ and Mn2+ ions. A study of encapsulation of ions showed that it is feasible to solidify the waste materials by vitrification and/or geopolymerization to eliminate leaching of ions to the environment. The simulation studies showed that the ion-exchange kinetic followed the pseudo second order kinetic model. This fitting indicates that the rate of ion-exchange process is controlled by a chemical reaction related to valence forces. The overall ion-exchange process is controlled by a combination of ion-exchange reaction, film diffusion and intra-particle diffusion. Moreover, the thermodynamic studies which were conducted under different temperatures revealed that the ion-exchange of Sr2+ and Mn2+ ions is practicable, spontaneous and endothermic.

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36

Li, Richard Ph D. Massachusetts Institute of Technology. "Catalysis and manufacturing of two-scale hierarchical nano- and microfiber advanced aerospace fiber-reinforced plastic composites." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/120419.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 195-210).
The development of hierarchical nanoengineered "fuzzy fiber" aerospace fiber-reinforced plastic (FRP) composite laminates holds the potential for enabling future generations of lightweight, durable, and multifunctional vehicle structures. By reinforcing the weak matrix-rich regions between individual fibers and plies, the circumferential growth of aligned carbon nanotubes (A-CNTs) on carbon microfibers (CFs) enables new composites with improved strength, toughness, electrical and thermal properties. While these improvements have been empirically demonstrated on alumina fiber FRPs, CNT growth degrades the CFs and sacrifices in-plane FRP properties for the benefits of CNT reinforcement. This thesis presents novel and scalable methods for realizing advanced fuzzy carbon fiber reinforced plastic (fuzzy CFRP) composite laminates with retained CF and interlaminar strength properties. Earth-abundant sodium (Na) is revealed as a new facile catalyst for CNT growth that allows for direct deposition of the catalyst precursor on carbon fabrics without any fiber pretreatments. This new catalyst discovery also enables high-yield CNT growth on a variety of low-temperature substrates. Simultaneously, this finding has led to other novel findings in carbon nanostructure catalysis including a core-shell morphology and the use of other alkali metals (e.g., potassium) for CNT growth. Towards the development of advanced composites, vacuum-assisted resin infusion processes are studied and refined, resulting in high-quality woven and unidirectional fuzzy (via Na-catalysis of CNTs) CFRP laminates. Growth uniformity improvement studies yielded strategies for increasing the quantity of CNT reinforcement within matrix-rich regions. Moreover, a new commercial unidirectional fabric enables the first retention of CF properties concomitant with interlaminar shear strength retention in the fuzzy CFRP architecture. The contributions of this thesis extend beyond CF composites: techniques developed for improving fuzzy CF synthesis were applied towards demonstrating A-CNT growth on SiC woven fabric, desired for creating damage tolerant and multifunctional lightweight vehicle systems. These advances pave the way for improvements in catalysis of nanostructures, electronics interfaces, energy storage devices, and advanced composite materials.
by Richard Li.
Ph. D.

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37

Doineau, Estelle. "Modification de fibres de lin par des nanocristaux de cellulose et du xyloglucane pour le développement de composites biosourcés hiérarchiques Adsorption of xyloglucan and cellulose nanocrystals on natural fibres for the creation of hierarchically structured fibres Hierarchical thermoplastic biocomposites reinforced with flax fibres modified by xyloglucan and cellulose nanocrystals Development of Bio-Inspired Hierarchical Fibres to Tailor the Fibre/Matrix Interphase in (Bio)composites." Thesis, IMT Mines Alès, 2020. http://www.theses.fr/2020EMAL0007.

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Ce travail de thèse vise à développer un traitement de surface de fibres de lin pour l’amélioration des propriétés mécaniques de biocomposites à matrice polymère et renforts en lin. Cette modification de surface s’inspire des structures hiérarchiques présentes dans les systèmes biologiques (os, nacre ou bois), constitués de nano-objets permettant un meilleur transfert de charges dans ces matériaux. Cette présence d’objets de dimensions nanométriques permet notamment d’atteindre des valeurs de contrainte et ténacité élevées et de limiter la propagation de fissures. Dans ces travaux de recherche, des produits dérivés de la biomasse ligno-cellulosique, à savoir les nanocristaux de cellulose (CNC) et le xyloglucane (XG), ont été choisis pour leurs propriétés et leur affinité mutuelle afin de créer des fibres de lin hiérarchiques. Dans un premier temps, l’adsorption de XG et CNC sur les fibres de lin a pu être localisée et quantifiée grâce à des marqueurs fluorescents. De plus, des mesures de force d’adhésion en microscopie à force atomique ont révélé la création d’un réseau extensible XG/CNC sur la surface de la fibre. Par la suite, deux voies ont été proposées avec l’élaboration de biocomposites thermoplastiques (polypropylène/fibres de lin) et thermodurcissables (résine époxy/tissu de lin) utilisant ces fibres nanostructurées. Dans les deux cas, une augmentation du travail à la rupture a été mesurée en micro-tractions et/ou tractions uniaxiales, permettant une plus grande dissipation de l’énergie lors de la rupture. L’ensemble de ces travaux a permis d’évaluer le potentiel de différents renforts en lin hiérarchiques(tissu unidirectionnel ou fibres courtes)pour le développement de biocomposites structuraux avec un focus fait sur la zone d’interphase fibre / matrice
This thesis project aims at developing flax fibres surface treatment for the improvement of the mechanical properties of biocomposites with polymeric matrix and flax reinforcements. This surface modification is inspired by the hierarchical structures present in biological systems (bone, nacre or wood), composed of nano-objects which allow a better transfer of loads in these materials. This presence of nano-sized objects makes it possible to reach impressive strength and toughness values and to limit cracks propagation. In this project, products derived from lingo-cellulosic biomass, namely cellulose nanocrystals (CNC) and xyloglucan (XG), were chosen for their interesting properties and mutual affinity to create hierarchical flax fibres. In a first step, the adsorption of XG and CNC onflax fibres w as localized and quantified using fluorescent markers. In addition, atomic force microscopy measurements of adhesive force revealed the creation of an extensible XG/CNC netw ork on the fibre surface. Subsequently, two paths were proposed with the elaboration of thermoplastic (polypropylene/flax fibres) and thermoset (epoxy resin/flax fabric) biocomposites using these nanostructured fibres. In both cases, an increase of the work of rupture has been measured by micro-and/or uniaxial tensile tests, allowing dissipating more energy upon breakage. All this work has allowed evaluating the potential of different hierarchical natural reinforcements (unidirectional fabric or short flax fibers) for the development of structural biocomposites with a focus on the fiber/matrix interphase zone

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38

Subbaraman, Ramachandran. "A multi-scale hierarchical approach for understanding the structure of the polymer electrolyte membrane fuel cell (PEMFC) electrodes - from nanoparticales to composites." online version, 2008. http://rave.ohiolink.edu/etdc/view.cgi?acc%5Fnum=case1205852564.

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39

Gorka, Joanna. "Polymer-based mesoporous carbons: soft-templating synthesis, adsorption and structural properties." Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1290460109.

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40

Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann, and Stefan Kaskel. "Preparation and application of cellular and nanoporous carbides." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138910.

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A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

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41

Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann, and Stefan Kaskel. "Preparation and application of cellular and nanoporous carbides." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27792.

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A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

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42

Merindol, Rémi. "Layer-by-layer assembly of strong bio-inspired nanocomposites." Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE015/document.

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Les performances exceptionnelles des composites naturels comme la nacre ou le bois émergent de l’arrangement précis d’éléments souples et rigides à l’échelle nanométrique. L’assemblage couche-par-couche permet la fabrication de films avec un contrôle nanométrique de l’organisation et de la composition. Ce travail décrit l’assemblage et les propriétés de nouveaux nano-composites contenant des nano-renforts 1-D (fibrilles de cellulose) et 2-D (plaquettes d’argile). Nous avons combiné les argiles avec une matrice extrêmement souple de poly(diméthylsiloxane) dans une architecture lamellaire imitant celle de la nacre. Nous avons étudié des composites à base de fibrilles de cellulose aléatoirement orientées dans le plan, puis alignées dans une direction pour mieux imiter les parois cellulaires du bois. Les propriétés mécaniques de ces composites bio-inspirés égalent ou surpassent celles de leurs homologues naturels, tout en étant transparents et dans certains cas auto-réparants
Natural materials such as nacre or wood gain their exceptional mechanical performances from the precise organisation of rigid and soft components at the nano-scale. Layer-by-layer assembly allows the preparation of films with a nano-scale control over their organisation and composition. This work describes the assembly and properties of new nano-composites containing 1-D (cellulose nano-fibrils) and 2-D (clay nano-platelets) reinforcing elements. The clay platelets were combined with an extremely soft matrix (poly(dimethylsiloxane)) to mimic the lamellar architecture of nacre. Cellulose based composites with a random in plane orientation of the fibrils were studied first, later we aligned the fibrils in a single direction to mimic further the cell wall of wood. The mechanical properties of these bio-inspired composites match or surpass those of their natural counterparts, while being transparent and in one case self-repairing

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43

Kananovich, Katsiaryna. "Comparaison internationale des systèmes de santé de onze pays : Allemagne, Biélorussie, Canada, Cuba, Danemark, EtatsUnis, France, Norvège, Royaume-Uni, Russie, Suède." Thesis, Paris, HESAM, 2021. http://www.theses.fr/2021HESAC002.

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Cette thèse propose la réflexion sur l’analyse comparative des systèmes de santé et la transmission des connaissances dans le cadre de l’échange des pratiques organisationnelles. La démarche de la thèse s’inscrit dans le cadre de l’analyse des composants des systèmes de santé, l’interaction entre ces différents éléments ainsi que l’environnement externe pour étudier les avantages et les inconvénients de chaque modèle organisationnel. La préparation de thèse engage le travail d'analyse et de synthèse de l'information provenant de 4 langues étrangères
This dissertation proposes a vision on the comparative analysis of health care systems and the transmission of knowledge through the exchange of organisational practices. The dissertation focuses on the analysis of the components of health care systems, the interaction between these different elements and the external environment to study the advantages and disadvantages of each organisational model. The dissertation involves the analysis and synthesis of information from 4 foreign languages

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44

Nigam, Amit K. "Vibration analysis of composite beams using hierarchical finite element method." Thesis, 2002. http://spectrum.library.concordia.ca/2073/1/MQ77981.pdf.

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The conventional finite element formulation has limitations in performing the dynamic analysis of composite beams. The discretization necessary for obtaining solutions with acceptable accuracy in the determination of dynamic response parameters leads to discontinuities in stress and strain distributions. The hierarchical finite element formulation provides us with the advantages of using fewer elements and obtaining better accuracy in the calculation of natural frequencies, displacements and stresses. The hierarchical finite element formulation for uniform and variable-thickness composite beams is developed in the present work. Two sub-formulations of hierarchical finite element method viz. polynomial and trigonometric sub-formulations have been developed. The efficiency and accuracy of the developed formulation are established in comparison with closed-form solutions for uniform composite beams. The static response of uniform composite beams is evaluated using the hierarchical finite element method. The dynamic response of variable-thickness composite beams is calculated based on the developed formulation. A detailed parametric study encompassing the influences of boundary conditions, laminate configuration, taper angle and the type of taper on the dynamic response of the beam is performed. The NCT-301 graphite-epoxy composite material is considered in the analysis and in the parametric study.

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45

McLean, Clayton. "A hierarchical theory for layered beams with piezoelectric actuation." 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=94856&T=F.

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46

Chang, Cheng-Ming, and 張正明. "Biotemplate Hierarchical Polyaniline Composite Films for High Performance Flexible Supercapacitor Devices." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/13773405163797263332.

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博士
中原大學
化學研究所
104
Highly flexible and foldable supercapacitor devices assembled using biotemplated polyaniline composite electrodes are described for the first time in this paper. This electrode architecture provides a facile fabrication route for creating abundant multiscale structures by using a plant species design based on nature resources and facilitates designing a hierarchical ordering morphology that improves the redox exchange and ionic diffusion resistance between the electrodes and electrolyte. The polyaniline composite was prepared using a replica technique and synthetized through in-situ oxidative polymerization by using aniline with conductive carbon materials. The biotemplated electrodes show a high electrochemical specific capacitance of 626 F g−1 in a three-electrode system, an excellent mechanical strength for enduring Z-type folding, and high cycling stability with capacity retention of 87% (545 F g−1). Furthermore, in cyclic voltammetry analysis, the prototype devices exhibit extraordinary elasticity without side reactions in various bending angles. Regarding electrochemical performance, the device responds with a high energy density of 5.06 Wh kg−1 and a high power density of 1685 W kg−1 when based on composite thin film electrodes and maintains 85% cycling retention as well as electrode performance after 1000 cycles. This study clearly reveals that fabricating hierarchical polyaniline composite electrodes through biotemplating yields high electrochemical performance and flexibility, making the electrodes useful for application in energy storage devices for portable electronic products.

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47

Chen, Lin. "Free vibration analysis of tapered composite beams using hierarchical finite element method." Thesis, 2004. http://spectrum.library.concordia.ca/8368/1/MR04415.pdf.

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Compared with the conventional finite element method, hierarchical finite element method has the advantages of using fewer elements and obtaining better accuracy in the calculation of natural frequencies, buckling loads, displacements and stresses. These advantages are also shown in the analysis for uniform or thickness-tapered composite beams. In many of the existing works on the dynamic response, the effect on the mechanical behavior of plies in the tapered composite beam caused by the taper angle is ignored if the angle is small. In the present thesis, this effect is always considered and quantified based on the three-dimensional ply stiffness analysis. The free vibration response of tapered composite beam with different taper angles is studied. Also, based on the ply stiffness analysis, the response of the taper configuration and laminate configuration on the stiffness and vibration response of the tapered beam are studied. (Abstract shortened by UMI.)

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48

CAVICCHIA, CARLO. "Hierarchical latent variable models for dimensionality reduction: an application on composite indicators." Doctoral thesis, 2020. http://hdl.handle.net/11573/1363237.

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This thesis is devoted to the development of new hierarchical latent variable models for Dimensionality Reduction with a specific focus on the construction of Composite Indicators (CIs). Since our society is producing a huge quantity of data, the construction of model-based CIs represents an interesting and still open methodological challenge. This dissertation is motivated by the necessity to provide model-based CIs which are built according to a statistical approach avoiding subjective choices (e.g., normative weights), therefore, the new insights and proposals hope to represent a contribution to the current literature. This thesis provides an introduction to CIs, a brief review of the most used methods in Multidimensional Data Analysis framework, a discussion about measurement models and methodological proposals to model latent concepts. Factor Analysis and its hierarchical extensions have been introduced in order to set the starting point of the analysis. A first proposal represents a new latent factor model that could be used for building CIs, it aims to investigate the hierarchical structure of the data in order to define two levels of CIs. The model, named Hierarchical Disjoint Non-Negative Factor Analysis is composed of two novelties: a model which is the two level hierarchical extension of FA and its disjoint extension with non-negative loadings. The latter model is enriched by considerations about the CIs used for tracking coherent policy conclusions. A set of features, properties and rules useful to build "good" CIs have been presented and explained. The last proposal in the thesis represents a new model for positive data correlation matrices which aims to detect reliable concepts and to build the hierarchy from them to the most general one. The proposed models are illustrated both via simulation studies and real data applications, to analyze their performances and abilities. In particular, the main application in this thesis regards the construction of a hierarchically aggregated index for the multidimensional phenomenon Waste Management in European Union. Waste Management is becoming even more important for its impact on human-being's lives, and many data have been produced about it, therefore the construction of a CI able to reduce its dimensionality and to highlight the main dimensions of it has a extraordinary usefulness in order to provide support to EU countries' action and policies.

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49

Arshad, Wasim. "Static and buckling analyses of curved metallic and composite beams using hierarchical FEM." Thesis, 2005. http://spectrum.library.concordia.ca/8238/1/MR04411.pdf.

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The conventional finite element formulation has limitations in performing the static and buckling analyses of composite curved beams. The hierarchical finite element formulation provides us with the advantages of using fewer elements and obtaining better accuracy in the calculation of displacements, stresses and critical buckling loads. The hierarchical finite element formulation for uniform curved beams made of isotropic and composite materials is developed in the present work. Two sub-formulations of hierarchical finite element method viz. polynomial and trigonometric sub-formulations have been developed. The efficiency and accuracy of the developed formulation are established in comparison with the closed form solutions for uniform isotropic and composite curved beams. The central deflection values of uniform isotropic and composite curved beams are evaluated using the hierarchical finite element method. The critical buckling loads of composite curved beams are calculated based on the developed formulation and the results are validated with the approximate solution by the Ritz method. A detailed parametric study encompassing the influences of boundary conditions, laminate configuration, and the internal degrees of freedom is performed to see their effect on the central deflection and the critical buckling load. The NCT-301 graphite-epoxy composite material is considered in the analysis and in the parametric study.

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50

Nayyar, Karun. "Static and modal analyses of laminated composite plates using hierarchical finite element method." Thesis, 2006. http://spectrum.library.concordia.ca/8835/1/MR16253.pdf.

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Composite materials are widely being used in aircraft, automotive and robotic industries where the components under different loading conditions are subject to motion. There is a need for the accurate prediction of not only their static response but also their dynamic characteristics so that they can be designed against the failure due to various types of possible static and dynamic loads. In the present thesis, static and vibration analyses of laminated plates are conducted using conventional and hierarchical finite element formulations based on First-order Shear Deformation Theory (FSDT). Conventional finite element formulation requires a large number of elements to obtain acceptable results. Besides, the necessity to satisfy internal C 0 or C 1 continuity across the elements' interfaces creates complexity even in simple structures. In order to overcome these limitations, the formulation based on Hierarchical Finite Element Method (HFEM) is developed in the present thesis for static and vibration analyses of laminated composite plates based on first-order shear deformation theory

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Дисертації з теми "Hierarchical composite"

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