Tesis sobre el tema "Hierarchical composite"
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Malkin, Robert Edward. "Damage tolerant hierarchical composite structures". Thesis, University of Bristol, 2011. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557974.
Texto completoWeiland, Michèle. "Modelling hierarchical musical structures with composite probabilistic networks". Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/29418.
Texto completoMcKenzie, Holly S. "Particle encapsulation and modification to afford hierarchical composite materials". Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/67281/.
Texto completoKelly, Aoife. "Processing of bulk hierarchical metal-metal composites". Thesis, University of Oxford, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559831.
Texto completoHajlane, 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.
Texto completoGodkänd; 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
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.
Texto completoCataloged 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.
Zikánová, Arlette, Pavel Hrabánek, Milan Kočiřík, Libor Brabec, Klára Juristová, Pavel Čapek, Bohumil Bernauer, Vladimír Hejtmánek, Olga Šolcová y 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.
Texto completoZikánová, Arlette, Pavel Hrabánek, Milan Kočiřík, Libor Brabec, Klára Juristová, Pavel Čapek, Bohumil Bernauer, Vladimír Hejtmánek, Olga Šolcová y 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.
Texto completoLi, 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.
Texto completoThe 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.
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.
Texto completoLiu, 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.
Texto completoStrossi, 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.
Texto completoZeolite-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
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.
Texto completoLAVAGNA, LUCA. "Carbon materials and their role as reinforcement in composite materials". Doctoral thesis, Politecnico di Torino, 2019. http://hdl.handle.net/11583/2729657.
Texto completoAgwubilo, 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.
Texto completoSubbaraman, 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.
Texto completoAl-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.
Texto completoGregori, Damia. "Revêtements photocatalytiques pour substrats organiques souples". Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10060/document.
Texto completoHeterogeneous 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
Juntaro, Julasak. "Environmentally friendly hierarchical composites". Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501202.
Texto completoGriffiths, Emma. "Micromechanical modelling of advanced hierarchical composites". Doctoral thesis, Faculty of Engineering and the Built Environment, 2020. http://hdl.handle.net/11427/32222.
Texto completoZainol, Abidin Mohd Shukur. "Development of hierarchical composites for structural applications". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/26988.
Texto completoLamoriniere, Steven. "High performance polyetheretherketone nanocomposites and hierarchical composites". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/11798.
Texto completoLiu, 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.
Texto completoThompson, Benjamin Robert. "Hierarchically structured composites and porous materials". Thesis, University of Hull, 2017. http://hydra.hull.ac.uk/resources/hull:16570.
Texto completoHerceg, Tomi. "Nano and hierarchical composites with high CNT loading fractions". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/27246.
Texto completoNyirabahizi, 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.
Texto completoQian, Hui. "Carbon nanotube grafted fibres : a route to advanced hierarchical composites". Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/5532.
Texto completode, 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.
Texto completoTritschler, 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.
Texto completoHajlane, 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.
Texto completoGodkänd; 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
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.
Texto completoNi, 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.
Texto completoCataloged 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
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.
Texto completoCataloged 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.
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.
Texto completoAl-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.
Texto completoLi, 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.
Texto completoCataloged 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.
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.
Texto completoThis 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
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.
Texto completoGorka, 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.
Texto completoBorchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann y 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.
Texto completoDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann y Stefan Kaskel. "Preparation and application of cellular and nanoporous carbides". Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27792.
Texto completoDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
Merindol, Rémi. "Layer-by-layer assembly of strong bio-inspired nanocomposites". Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAE015/document.
Texto completoNatural 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
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.
Texto completoThis 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
Nigam, Amit K. "Vibration analysis of composite beams using hierarchical finite element method". Thesis, 2002. http://spectrum.library.concordia.ca/2073/1/MQ77981.pdf.
Texto completoMcLean, Clayton. "A hierarchical theory for layered beams with piezoelectric actuation". 2004. http://link.library.utoronto.ca/eir/EIRdetail.cfm?Resources__ID=94856&T=F.
Texto completoChang, Cheng-Ming y 張正明. "Biotemplate Hierarchical Polyaniline Composite Films for High Performance Flexible Supercapacitor Devices". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/13773405163797263332.
Texto completo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.
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.
Texto completoCAVICCHIA, CARLO. "Hierarchical latent variable models for dimensionality reduction: an application on composite indicators". Doctoral thesis, 2020. http://hdl.handle.net/11573/1363237.
Texto completoArshad, 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.
Texto completoNayyar, 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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