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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Manufacture, modelling and characterisation of novel composite tubes

Agwubilo, Ikenna January 2016 (has links)
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.
22

‘In-Yer-Head’ Theatre : Staging the Mind in Contemporary British Drama. Towards a Quantum Psychopoetics of the Stage / Le théâtre « in-yer-head » : écritures de l’espace mental sur la scène britannique contemporaine. Vers une psychopoétique quantique du drame

Ayache, Solange 20 January 2017 (has links)
Cette étude s’intéresse à l’espace mental comme nouveau terrain d’exploration du drame britannique contemporain, et examine les manifestations d’un mouvement qui « met en pièces » les régions inexplorées des pensées inconscientes et les contrées impénétrables du traumatisme. Puisant dans les découvertes de la psychanalyse et des sciences cognitives, inspiré par le changement de paradigme de la mécanique quantique et ses interrogations sur le rôle et la nature de la conscience, ce théâtre non plus tant « in-yer-face » que « in-yer-head » s’éloigne de la sensibilité des années 1990. Les pièces de Crimp, Kane, Churchill, Cooper, Frayn, Stephens, Payne, Haddon, Ravenhill, Neilson et d’autres déconstruisent et reconstruisent le personnage comme la somme virtuelle de tous ses possibles. Le mode d’existence spéculatif, diffracté et pluriel du sujet renouvelle les définitions du réalisme psychologique et du réalisme théâtral. Ce travail étudie les modalités de cette « psychopoétique quantique » autour de concepts clés comme la probabilité ou l’incertitude, et montre comment des métaphores issues de la théorie quantique comme la dualité onde-particule ou les mondes multiples servent à illustrer l’indétermination de la psyché en évoquant les mécanismes de défense et autres symptômes qui constituent la réalité subjective d’esprits affectés par le traumatisme, la psychose, le stress ou la maladie neurologique. Nous montrons qu’en explorant la nature de la conscience, du soi et de la réalité ainsi que la condition des femmes, ces pièces posent des questions philosophiques sur le libre arbitre et la possibilité de choix dans un monde devenu plus incertain et imprévisible que jamais. / This study asserts that the human mind has become the new frontier in contemporary British drama, and interrogates and assesses manifestations of this movement which stages uncharted regions of thought and the dark territories of traumatic mindscapes. Drawing on theories from psychoanalysis and cognitive science, and inspired by the paradigm shifts of quantum mechanics and its interrogations on the role and nature of consciousness, this new theatre moves from “in-yer-face” to “in-yer-head” and away from the sensibility of the “nasty nineties.” Plays by Crimp, Kane, Churchill, Cooper, Frayn, Stephens, Payne, Haddon and others deconstruct and reconstruct the character as thevirtual sum of all her possibilities. In these mental spaces, the subject’s speculative, diffracted and plural mode of existence redefines psychological realism and stage realism. Examining the modalities of a quantum “psychopoetics” around key concepts such as probability and uncertainty, I show how metaphors borrowed from quantum theory based on the double slit-experiment, the wave-particle duality, the wavefunction collapse, the observer effect, quantum decoherence, quantum entanglement, and the many-worlds interpretation are used to emphasise the intrinsic indeterminacy of our minds. They evoke a number of psychological defense mechanisms and other symptoms that constitute the subjective reality of disturbed minds affected by trauma, psychosis, stress or neurological disease. By exploring the nature of mind, the self, and reality, and the condition of women, these plays address philosophical questions about free will and choice in a world that has become more uncertain and unpredictable than ever.
23

Algometrická analýza vlivu zavřeného úchopu na měkké tkáně v oblasti ruky a předloktí. / Algometric analysis of influence of crimp grip on soft tissues of hand and forearm.

Vávrová, Hana January 2013 (has links)
Title: Algometric analysis of influence of crimp grip on soft tissues of hand and forearm. Objectives: The main aim of this thesis is comparison and evaluation of changes of nociceptors sensitivity treshold in chosen points of upper extremities area before and after defined strain using pressure algometer. Methods: Data for the experiment was obtained using pressure algometr. Pain threshold was measured in defined 42 points in the order given at each subject firstly before strain and again immediately after defined strain of upper extremities (one minute hangig by the both hands in crimp grip on a campus board in this way: 10 sec strain plus 10 sec break, all six times). Then were measured values statisticaly analysed. Sources for processing of theoretical part of this work were obtained from expert articles and literature which follow up the given task. Results: Statisticaly important results show, that decreasing of pain threshold (on average by 100 - 160 kPa) comes about in tissues of upper extremity immediately after its loading in crimp grip, which means increasing of nociceptors sensitivity. At the same time it has been proved that nociceptors sensitivity in the area of tendon pulleys correlates with frequency of their injury quoted in a literature (that is the highest sensitivity in the...
24

C-Ply (Trademark) NCF Carbone extra fin : Etude du procédé de fabrication et optimisation du renfort / C-Ply (Trademark) Ultra light CarbonNCF : Study of the manufacturing process and textile reinforcement optimization

Singery, Vicky 03 February 2016 (has links)
L’industrie aéronautique travaille sur l’amélioration des systèmes propulsifs parl’introduction de composites dans la fabrication des aubes de soufflante afin d’alléger lastructure et ainsi de réduire la consommation en carburant des avions. Ces pièces réaliséesen tissage 3D présentent généralement des irrégularités de surface. Une manière d’optimisercet aspect est d’ajouter un pli additionnel de surface : nos travaux de thèse portent sur ledéveloppement de ce pli sous la forme d’un renfort « Non Crimp Fabric » (NCF) biaxial extrafinen fibre de carbone de module intermédiaire (IM), inférieur à 100 g/m², régulier et ayant unebonne déformabilité. Lors de nos travaux de thèse, nous avons utilisé la méthode des plans d’expériencepour améliorer la technologie d’étalement afin de répondre aux exigences demandées. Nousavons pu définir la configuration optimale d’étalement permettant d’atteindre la cible d’un pliinférieur à 50 g/m² en fibre de carbone IM. Pour réaliser un NCF extra-fin, après étalement,les plis sont assemblés par couture afin d’assurer la tenue du renfort. La combinaison decouture choisie (armure, tension, longueur, jauge …) conditionne l’aspect du NCF et sacapacité à être manipulée et déformée. Nous avons donc optimisé les paramètres de coutureafin d’obtenir les propriétés souhaitées. Après avoir optimisé l’étalement des fibres et l’assemblage des plis, nous avons réalisé et caractérisé les renforts NCF extra-fins pour valider leurs propriétés. Nous sommesfinalement parvenus à mettre au point un renfort NCF en fibre de carbone IM, inférieur à50 g/m² par pli ayant un taux de couverture supérieur à 98 % et une bonne capacité à sedéformer. / Aircraft manufacturers are working on the improvement of their engines bymanufacturing fan blades with advanced composite materials to reduce fuel consumption.However, fan blades are made from 3D woven fabrics which often have surface irregularities.It can be minimized by an additional thin layer on the surface : our thesis work is focused onthe development of a new textile structure based on ultra-thin biaxial “Non Crimp Fabric” (NCF)technology. This spread NCF made from intermediate modulus (IM) carbon fibers must belighter than 100 gsm, regular and deformable.During our thesis work, we used Design of Experiments (DOE) methodology to improvethe spreading technology used by Chomarat to make ultra-light NCF materials and meet theestablished requirements. We were able to reach the ultra-thin ply target of less than 50 gsmper ply. After optimizing the spreading process these thin ply tapes are stitched together tocreate NCF. Stability, visual aspect, handling and deformability are dependent on the stitchingsettings (stitching pattern, tension, length, gauge, etc.). Therefore we optimized the stitchingparameters to get the desired properties.After the spreading and stitching process had been optimized, the NCF weremanufactured and tested to validate the desired properties had been achieved. The testingconfirmed that we were able to develop a new carbon fiber NCF that was less than 50 gsm perply, had a coverage rate of higher than 98 % and had good deformability characteristics.
25

Tow level hybridisation for damage tolerant composites

Selver, Erdem January 2014 (has links)
Fibre reinforced composites have higher specific strength and stiffness in comparison to metals. However, composites are susceptible to impact damage resulting in degradation of mechanical properties especially compression strength. Numerous studies have been conducted to improve the impact damage tolerance of composite laminates using modified resin systems, thermoplastic matrices, 3-D fibre architectures and through thickness reinforcement. This work is primarily focussed on incorporating non dissolvable polypropylene fibres (PP) in a thermoset matrix for improving the damage tolerance. Commingling and wrapping techniques have been investigated. PP fibres have been incorporated at the preform stage and hence do not adversely affect the viscosity of the resin during infusion. The healing effect of PP fibres on impact damaged composite laminates when heating is introduced has also been studied. High velocity impact test results showed that using commingled glass/PP fibres increased the total energy absorption of composite laminates by 20% due to the extensive plastic deformation of the PP fibres and through the use of toughening mechanisms in the form of resin cracking and delamination. It has been found that PP fibres provide protection to the glass fibres during low velocity impact loading, so fewer fibre breakages occur which lead to improved residual properties compared with pristine glass laminates. Compression after impact (CAI) tests showed that the residual strength as a percentage of non-impacted strength increased with percentage of PP fibres used. For impact of 20-50J, glass/epoxy laminates retained 32 45% of their compressive strength while laminates with 7%, 13% and 18% PP fibres retained 37 50%, 42-52% and 43-60% of their compressive strength, respectively. It was also observed that glass/PP woven laminates had better compressive strength retention (62 83%) than the glass/PP non-crimp laminates (37-50%). Composite laminates with high-modulus PP fibres (Innegra) exhibited higher residual compression strengths in comparison to laminates with lower modulus PP fibres. For 15-50J impact, glass/Innegra laminates showed residual compression strength of 50 63% in comparison to 39-60%; laminates without thermoplastic fibres exhibited 33 43% residual compression strength. Modulus of thermoplastic fibres appears to be important at higher energy levels. Healing of damaged commingled laminates produced a significant reduction in the damage area and a corresponding increase in CAI strength after heating at 200ºC; CAI strength of healed laminates is about 85% of undamaged samples in comparison to 60% for non-healed samples. A novel micro-wrapping technique, developed in this work, demonstrated significant reduction in damage area (46%) in comparison to the commingling method. Core wrapped laminates had higher residual strength (43-60%) than glass laminates (33-43%). Better PP distribution in core-wrapped composites helped to decrease the PP rich areas and the impact damage did not propagate easily in comparison to commingled composites. However due to the reduction in damage area, impact energy absorption in core wrapped laminates was lower than for commingled.
26

Hodnocení kvality připojení vodičů nízkonapěťových ovládacích obvodů / Quality evaluation of the connection of low-voltage control circuit cables

Chabiniok, Pavel January 2018 (has links)
This master’s thesis deals with evaluation of quality of the connection of low-voltage control circuit cables, with the emphasis on quality assurance of crimps. An analysis of possible quality control methods, including a map of the crimping process, was created. Further, the thesis includes proposals for improvement of the original system. Furthermore, a proposal of non-destructive inspection system was produced. The conclusion summarizes the knowledge gained in quality control of crimping, including practical recommendations.
27

Evaluation of adhesive binders for the development of yarn bonding for new stitch-free non-crimp fabrics

Al-Monsur, Md. Abdullah, Bardl, Georg, Cherif, Chokri 18 September 2019 (has links)
Non-crimp fabrics (NCFs), especially multi-axial warp-knitted fabrics, are used as reinforcement materials for fiberreinforced composites. The manufacturing of multi-axial warp-knitted fabrics by a conventional stitch bonding process to produce NCF has several disadvantages, such as filament damage, low production speed, yarn disorientation, etc. In order to overcome the existing limitations, the idea of using an adhesive binder to attach the fabric layers is a promising approach, so that the use of stitching yarns can be eliminated. The fundamental investigations presented in this paper show that the selection of the binder material has a major influence on the parameters of the textile products. Whereas the tested hotmelt adhesives offer a short curing time and a small but nevertheless sufficient bonding strength between bonded yarns, the tested reactive adhesives show a bonding strength up to 10 times higher, but at a considerably longer curing time. The reason for the different bonding strength is identified in the different penetration into the yarns. The experiments also show a significant influence of the fiber type and sizing, which needs to be taken into account when selecting fabric binders.
28

Textile reinforcement structures for concrete construction applications––a review

Friese, Danny, Scheurer, Martin, Hahn, Lars, Gries, Thomas, Cherif, Chokri 19 June 2023 (has links)
The use of non-metallic, textile reinforcement structures in place of steel reinforcement is a key component in making concrete constructions more sustainable and durable than they currently are. The reason for this is the corrosion resistance of textile reinforcements, which makes it possible to reduce the thickness of the concrete cover and at the same time extend the service life of concrete structures. This reduces the amount of cement required and thus also the emission of the greenhouse gas carbon dioxide. By means of textile manufacturing technologies, customized, load-adapted reinforcement topologies can be adjusted to the requirements of highly stressed and well-designed concrete components. The objective of this paper is to give an overview of recent research literature dedicated to textile reinforcement structures that are already used for concrete applications in the construction industry as well as those currently under development. Therefore, textile reinforcement structures, which are divided into one-, two- and three-dimensional topologies, as well as common materials used for textile-reinforced concrete are reviewed. Most research has so far been devoted to two-dimensional textile reinforcement structures. Furthermore, novel approaches to the fabrication of textile reinforcement structures for concrete applications based on robotic yarn deposition technologies are addressed.:1.) Introduction 2.) Materials for textile reinforcement structures for construction applications 3.) Textile reinforcement structures for construction applications 4.) New developments in robot-supported manufacturing technologies for construction applications 5.) Conclusion
29

Adhesion problematics and curing kinetics in a thermosetting matrix for stitch-free non-crimp fabric

Kruppke, Iris, Hund, Rolf-Dieter, Cherif, Chokri 18 September 2019 (has links)
Non-crimp fabrics (NCF) have become established in the fields of the automotive, aircraft, and wind power industries, which has led to an increasing demand of fiber plastic composites. In order to utilize the known excellent load-bearing properties of NCF and also to reduce the related disadvantages such as fiber undulation caused by stitching yarn, inclusions of resin and filament breakage by the stitch-bonding process have to be addressed. Hence, an alternative manufacturing technology is presented. This technology is defined by the punctiform application of a polyester hot melt adhesive to enable different geometries of NCF and ensure the position of the high-performance fiber in the load direction. The new manufacturing process, on the one hand, demands new testing methods to investigate the adhesion between the used adhesive and highperformance fibers, while, on the other, the surface of the adherend (carbon fiber) needs to be improved. Oxyfluorination is used here for the surface modification. Different tests such as peel test, shear test and transverse tensile test were developed and evaluated with different adhesives and high-performance yarns based on glass and carbon. The influence of the used copolyester hot melt on the curing kinetics of an epoxy matrix was investigated by differential scanning calorimetry using quasi-isothermal and non-isothermal measurements. In addition, the interface between the thermoplastic epoxy resin and the copolyester hot melt was analyzed by scanning electron microscopy.
30

Experimental comparison of a macroscopic draping simulation for dry non-crimp fabric preforming on a complex geometry by means of optical measurement

Mallach, Annegret, Härtel, Frank, Heieck, Frieder, Fuhr, Jan-Philipp, Middendorf, Peter, Gude, Maik 29 October 2019 (has links)
Scope of the presented work is a detailed comparison of a macroscopic draping model with real fibre architecture on a complex non-crimp-fabric preform using a new robot-based optical measurement system. By means of a preliminary analytical process design approach, a preforming test centre is set up to manufacture dry non-crimp-fabric preforms. A variable blank holder setup is used to investigate the effect of different process parameters on the fibre architecture.The real fibre architecture of those preforms is captured by the optical measurement system, which generates a threedimensional model containing information about the fibre orientation along the entire surface of the preform. The measured and calculated fiber orientations are then compared with the simulation results in a three-dimensional overlay file. The results show that the analytical approach is able to predict local hot spots with high shear angles on the preform. Macroscopic simulations show a higher sensitivity towards changes in blank holder pressure than reality and limit the approach to precisely predict fibre architecture parameters on complex geometries.

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