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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.
81

Fonctionnalisation de polymères et applications dans les domaines de l’énergie, de la catalyse, de la cosmétique et de la santé / Functionalization of polymers and applications in the fields of energy, catalysis and health

Morizur, Vincent 03 December 2014 (has links)
Les polymères sont à l’heure actuelle étudiés dans de nombreux domaines comme la chimie, la biochimie, les nanotechnologies, l'électronique, la médecine ou encore les sciences des matériaux et trouvent des applications dans des domaines comme l’industrie automobile, la chimie fine. L’objectif de cette thèse est de réaliser la fonctionnalisation de polymères et de modifier les propriétés de ces matériaux afin d’envisager des nouvelles applications. Nous nous sommes intéressés à des polymères de la famille des poly(aryle éther) et plus particulièrement au poly(éther éther cétone) (PEEK). Ce polymère est connu pour ses propriétés mécaniques, thermiques, électriques ou encore pour sa résistance aux produits chimiques. Dans le premier chapitre, il est question de la fonctionnalisation des différents polymères de départ par des fonctions chlorures de sulfonyle, acides sulfoniques et sulfonamides. Le second chapitre est consacré à la synthèse et à l’étude électrochimique de nouveaux électrolytes polymériques et à de nouvelles membranes pour d’éventuelles applications dans le domaine des batteries au lithium et au sodium, ainsi que dans le domaine des piles à combustible. Dans un troisième chapitre, la préparation de nouveaux catalyseurs métalliques dérivés d’acides sulfoniques polymériques est discutée. Une étude de l’activité catalytique de ces différents catalyseurs a été réalisée sur la réaction d’acylation de Friedel-Crafts. Le quatrième chapitre est consacré à la préparation de nouveaux matériaux ayant des propriétés optiques intéressantes. Enfin dans un cinquième chapitre, la préparation et l’étude de nouveaux matériaux ayant des propriétés antibactériennes sont exposées. / Polymers are now being studied in many fields such as chemistry, biochemistry, nanotechnology, electronics, medicine or material science and have applications in areas such as automotive industry, food industry, fine chemistry. The objective of this thesis is to achieve the functionalization of polymers and modify the properties of these materials in order to consider new applications. We were interested in polymers with the poly(aryl ether) motif, more particularly poly(ether ether ketone) (PEEK). This polymer is known for its mechanical, thermal, electrical properties and for its resistance to chemicals. In the first chapter, we present the functionalization of different polymers by sulfonyl chloride, sulfonic acid and sulfonamide functions. The second chapter is devoted to the synthesis and electrochemical study of novel polymeric electrolytes and new membranes for potential applications in the field of lithium and sodium batteries, as well as in the field of fuel cells. In the third chapter, the preparation of new metal catalysts derived from polymeric sulfonic acids is discussed. A study of the catalytic activity of these different polymeric catalysts was carried out on the Friedel-Crafts acylation reaction. The fourth chapter is devoted to the preparation of new materials with interesting optical properties. Finally, in the fifth chapter, the preparation and the study of new materials with antibacterial properties are reported.
82

Fabrication additive de pièces en polymères thermoplastiques hautes performances et en polyamide 12 par le procédé de frittage sélectif par laser

Dumoulin, Emmanuel 23 January 2014 (has links) (PDF)
Le frittage sélectif par laser (ou Selective Laser Sintering, SLS) des poudres polymères thermoplastiques est maintenant une technique répandue de fabrication additive. Néanmoins, ce procédé n'est industriellement mature que pour une seule famille de polymères, les polyamides. Pour que ce procédé soit employé dans la fabrication de pièces subissant des contraintes thermiques au-delà de 50 °C, il est ainsi nécessaire d'étendre la gamme des matériaux utilisables à des polymères hautes performances tels que les poly(aryl-éther-cétone) ou les poly(aryl-imide). Cette étude décrit la fabrication additive, couche par couche, de pièces aérospatiales complexes en polymères hautes performances. Pour cela, sept poudres en polymère ont été sélectionnées afin d'étudier l'influence de celles-ci sur les différentes phases du procédé et sur la qualité de la matière frittée/fondue. Ainsi, la morphologie de leurs particules, leurs microstructures ou encore leurs densités versées et tapées sont analysées, de même que leurs stabilités thermiques, leurs capacités à absorber l'eau ou à s'écouler. Dans un second temps, une étude paramétrique du procédé a été réalisée dans le but d'aboutir à la fabrication de pièces de bonne qualité matière, tout en portant un intérêt vis-à-vis des évolutions de la poudre cycle après cycle de fabrication. De plus, il est important, dans un souci d'optimisation, d'utiliser toutes les possibilités de forme qu'offre cette fabrication additive et d'en évaluer la résistance mécanique. C'est pourquoi une loi de comportement mécanique d'un polyamide 12 consolidé sélectivement par laser a été déterminée et implémentée dans un code de calcul par éléments finis (ZéBuLoN®). Cette loi de comportement, dans le domaine linéaire et non linéaire, représentative de l'anisotropie du matériau, a ensuite été validée expérimentalement sur des éprouvettes d'essais mécaniques et sur un démonstrateur aérospatial.
83

Elaboration de membranes pour piles à combustible à architecture réseaux (semi-)interpénétrés de polymères / New interpenetrating polymer network membranes as proton exchange membrane fuel cells (PEMFC)

Delhorbe, Virginie 18 July 2011 (has links)
Les membranes polymères utilisées actuellement dans les piles à combustible voient leurs performances diminuer à haute température (T > 90°C) et à faible humidité relative (HR < 50%) [1]. Cette diminution est principalement liée aux pertes des propriétés mécaniques et de conduction dans ces conditions. Afin de remédier à ces inconvénients, des membranes originales présentant une architecture de réseaux (semi-)interpénétrés de polymères [2] ((semi-)RIP) dans lesquelles un réseau hydrophobe est associé à un réseau hydrophile, ont été développées dans le cadre du projet ANR PAN-H « AMEIRICC ».Ces membranes sont constituées d'un réseau fluoré assurant la tenue mécanique et d'un réseau polyélectrolyte sulfoné assurant la conduction protonique du matériau, chacun des réseaux étant issu de différents précurseurs fournis par l'IAM et le LMOPS. Après la réaction de polymérisation/réticulation des deux réseaux, les matériaux sont caractérisés afin de réaliser un retour rapide sur leur synthèse et d'optimiser cette dernière pour parvenir à un matériau présentant les principales propriétés recherchées (conductivité protonique, stabilité thermique et chimique, principalement). Une fois la synthèse optimisée, des premiers matériaux ont été fournis au LMPB, au SPrAM et au LITEN pour la validation des membranes sélectionnées. Les propriétés structurales et les valeurs de conductivité des matériaux ont permis de conclure que les (semi-)RIP présentent une morphologie similaire à celle décrite pour le Nafion dans laquelle la phase fluorée et la phase conductrice ionique sont co-continues. Plusieurs séries de ces membranes ont ensuite été réalisées en modifiant la composition chimique afin d'étudier la variation des propriétés des matériaux obtenus. Enfin, les premiers tests en pile à combustible de ces membranes originales se sont révélés prometteurs.[1] R. Borup, J. Meyers, B. Pivovar, Chem. Rev. 107 (2007) 3904.[2] L. H. Sperling and V. Mishra. The current status of interpenetrating polymer networks. In: Kim SC, Sperling LH, editors. IPNs around the world: science and engineering. New York: Wiley; 1997: p. 1-25. / The polymer membranes currently used in fuel cells are reducing their performance at high temperature (T > 90°C) and low relative humidity (RH < 50%) [1]. This decrease is mainly due to loss of mechanical properties and conduction in these conditions. To overcome these drawbacks, unique membranes having an architecture (semi-) interpenetrating polymer network [2] ((semi-) IPN) in which a hydrophobic network is associated with a hydrophilic network, were developed under PAN-H “AMEIRICC” ANR Project.These membranes consist of fluorinated network ensuring the mechanical and sulfonated polyelectrolyte network ensuring the proton conduction of material, each network being derived from different precursors provided by IAM and LMOPS. After the polymerization/cross linking reaction of the two systems, materials are characterized to carry out a rapid return on their synthesis and optimize it to achieve a material with the main properties (proton conductivity, thermal and chemical stability, primarily). Once the synthesis is optimized, the first materials were provided to LMPB, SPrAM and LITEN for validation of selected membranes.The structural properties and conductivity values of materials led to the conclusion that (semi-) IPN have a similar morphology to that described for the Nafion in which the fluorous phase and the ionic conducting phase are co-continuous.Then several series of these membranes were conducted by changing the chemical composition in order to study the variation of obtained material properties. Finally, the first fuel cell test of original membranes have shown promise.[1] R. Borup, J. Meyers, B. Pivovar, Chem. Rev. 107 (2007) 3904.[2] L. H. Sperling and V. Mishra. The current status of interpenetrating polymer networks. In: Kim SC, Sperling LH, editors. IPNs around the world: science and engineering. New York: Wiley; 1997: p. 1-25.
84

Carbon Nanotube Composites Prepared by Ultrasonically Assisted Twin Screw Extrusion

Lewis, Todd M. 11 September 2014 (has links)
No description available.
85

Friction and lubrication behaviour of metal-on-metal and ZTA ceramic-on-CFR PEEK hip prostheses : friction and lubrication behaviour of metal-on-metal hip resurfacing and ZTA ceramic heads versus CFR PEEK cups with various diameters and clearances using serum-based lubricants with various viscosities

Said, Assma Musbah January 2012 (has links)
The natural hip joint in healthy people has a very low friction with very little (or no) wear. It works as a dynamically loaded bearing and is subjected to about 1-2 million cycles of loading per year. The applied load is the body weight which is tripled when walking and even higher during other activities such as running and jumping. Unfortunately these joints are not always healthy due to various causes such as fractures or disease leading to severe pain which necessitates joint replacement. Currently, the orthopaedic industries are working towards developing an ideal artificial hip joint with low wear, low friction, good lubrication, better fixation/stability and biocompatibility. Many different designs and materials have been investigated with some promising new implants which can be used depending on patients' individual need (large or small joint), activity and age. In this work, two types of artificial hip joints were tested for friction and lubrication studies: Metal-on-Metal (MoM) Biomet hip resurfacing ReCaps with large diameters (>35-60 mm) and different diametral clearances (~ 60-350 µm), and Zirconia Toughened Alumina (ZTA) heads against carbon-fibre-reinforced poly-ether-ether ketone (CFR PEEK) cups with different diameters (>35-60 mm) and diametral clearances (60-1860 µm). Seven serum-based lubricants with different viscosities were used with and without carboxy methyl cellulose (CMC) additions as gelling agent to increase viscosity depending on the CMC content. The maximum load applied was 2000 N for the stance phase with a minimum load of 100 N for the swing phase. A Pro-Sim friction hip simulator was used to investigate the frictional torque generated between the articulating surfaces so as the friction factor can be calculated. Stribeck analysis was then employed to assess the mode of lubrication. For the metal-on-metal hip resurfacing joints, the friction factors were in the range 0.03-0.151 and those for the ZTA ceramic heads versus CFR PEEK cups were in the range 0.006-0.32. Stribeck analyses showed mainly mixed lubrication for both MoM and ZTA ceramic-on-CFR PEEK joints. The experimental results were in agreement with most of the theoretical calculations suggesting mixed lubricating regimes at low viscosities and moving on to fluid film lubrication at higher viscosities. Joints with larger-diameters, lower clearances and lower surface roughness exhibited a higher lambda ratio suggesting improved lubrication. Viscosity flow curves for the serum-based lubricants having viscosity ≤ 0.00524 Pas showed non-linear relationship between viscosity and shear rate indicating non-Newtonian flow with pseudoplastic or shear-thinning characteristic, i.e. viscosity decreased as shear rate increased up to shear rates of ~ 1000 s⁻¹. However, at shear rates greater than 1000 s⁻¹ Newtonian flow became dominant with almost constant viscosity, i.e. a linear relationship between shear stress and shear rate. On the other hand, viscosity flow curves for the lubricants with viscosity ≥ 0.0128 Pas showed non-Newtonian behaviour up to a shear rate of 3000 s⁻¹ with shear-thinning characteristic.
86

Friction and lubrication behaviour of hip resurfacing metal-on-metal and ZTA ceramic on CFR peek implants with various diameters and clearances : friction and lubrication behaviour of hip resurfacing Co-Cr-Mo and zirconia toughened alumina ceramic heads against carbon fibre reinforced poly-ether-ether-ketone cups with various diameters and clearances have been investigated using serum-based lubricants

Ehmaida, Mutyaa M. January 2012 (has links)
Total hip joint prostheses made of CoCrMo heads versus ultra high molecular weight polyethylene (UHMWPE) cups have a limited lifetime, mainly due to the wear of the UHMWPE cups as a result of high friction between the articulating surfaces leading to osteolysis and implant loosening with revision surgery becoming inevitable in more active patients. Tribology plays an important role in developing the design, minimizing wear and reducing friction of hip joint prostheses in order to improve their long-term performance, with good lubricating properties. Metal-on-metal hip resurfacing prostheses have shown significantly lower wear rates compared with conventional metal-on-polyethylene implants and thus osteolysis is potentially reduced leading to increased lifetime of the prosthesis. Nevertheless, excessive wear of metal-on-metal joints leads to metal ion release, causing pseudo-tumours and osteolysis. An alternative approach to such bearings is the use of newly developed carbon fiber-reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cups articulating against ceramic femoral heads due to their better wear resistance compared to UHMWPE. In this study, therefore, friction and lubrication properties of large diameter, as cast, Co-Cr-Mo metal-on-metal hip resurfacing implants with various diameters and clearances have been investigated and compared to those of the newly developed zirconia toughened alumina (ZTA) ceramic femoral heads articulating against carbon fiber reinforced poly-ether-ether-ketone (CFR PEEK) acetabular cups with different diameters and clearances. Friction hip simulator was used to measure frictional torque and then friction factors were calculated along with Sommerfeld numbers leading to Stribeck analysis and hence the lubricating mode was also investigated. This involved using lubricants based on pure bovine serum (BS) and diluted bovine serum (25 vol. %BS+75 vol. %distilled water) with and without carboxymethyl cellulose (CMC) (as gelling agent). Standard Rheometer was used to measure lubricant viscosity ranged from 0.0014 to 0.236 Pas at a shear rate of 3000 . Pure bovine serum, diluted bovine serum without CMC and with CMC (25BS+75DW+0.5gCMC and +1gCMC) showed pseudoplastic flow behaviour up to shear rate of ~139 s⁻¹ above which a Newtonian flow with significant increase in shear stress was observed. The viscosity flow curves for the 25BS+75DW+2gCMC, +3.5gCMC and +5gCMC showed only shear thinning up to a shear rate of 3000 . The shear rate application modified the flow behaviour of bovine serum from a pseudoplastic to a Newtonian flow depending on its purity and CMC content. This will cause a different frictional behaviour depending on joint diameter and clearance, as seen in this work. The experimental data were compared with theoretical iv predictions of the lubricating regimes by calculating theoretical film thickness and lambda ratio. The metal-on-metal Biomet ReCaps showed similar trends of Stribeck curves, i.e. friction factors decreased from ~0.12 to ~0.05 as Sommerfeld numbers increased in the range of viscosities ~0.001-0.04Pas indicating mixed lubrication regimes above which the friction factor increased to ~0.13 at a viscosity of 0.236Pas. The Stribeck analyses suggested mixed lubrication as the dominant mode with the lowest friction factor in the range ~0.09 - ~0.05 at the physiological viscosities of ~0.01 to ~0.04 Pas and that such joints can be used for more active patients as compared to the conventional total hip replacement joints with 28mm diameter. The Stribeck curves for all ZTA ceramic-on-CFR PEEK components illustrated a similar trend with BS fluids showing higher friction factors (in the range 0.22-0.13) than the diluted BS+CMC fluids (in the range 0.24-0.05). The friction tests revealed boundary-mixed lubrication regimes for the ZTA ceramic-on-CFR-PEEK joints. The results, so far, are promising and suggest clearly that the newly developed ZTA ceramic femoral heads articulating against CFR PEEK cups have similar friction and lubrication behaviour at optimum clearances to those of currently used metal-onmetal hip resurfacing implants at the range of viscosities 0.00612 to 0.155Pas. These results clearly suggest that the ZTA ceramic-on-CFR-PEEK joints showed low friction at the physiological viscosities of ~0.01Pas in the range ~0.1-0.05, suggesting that these novel joints may be used as an alternative material choice for the reduction of osteolysis. The result of this investigation has suggested that the optimum clearance for the 52mm diameter MOM Biomet ReCaps could be ~170μm. However, 48 and 54mm joints showed lower friction due to clearances to be >200μm. For the 52mm ZTA ceramic-on-CFR-PEEK joints the optimum clearance seems to be ≥ 630μm radial clearance. These results suggested that increased clearance bearings have the potential to generate low friction and hence no risk of micro- or even macro-motion for the ceramic-on-CFR-PEEK joints. This study found no correlation between theoretical predictions and experimental data for all metal-onmetal and ZTA ceramic-on-CFR PEEK bearings at the physiological viscosity (0.0127Pas). However, at lubricant viscosity of 0.00157Pas, the theoretical prediction of lubrication regime correlated well with the experimental data, both illustrating boundary lubrication. As expected, a decrease in viscosity resulted decrease in the film thickness.
87

Etude de l’influence de la physicochimie et de la texturation de surface sur l’adhérence métal - Poly(Ether Ether Ketone) (PEEK) / Study of the influence of the surface physicochemistry and texturing on the metal-poly(ether ether ketone) (PEEK) adhesion

Gravis, David 15 March 2019 (has links)
La faible densité et les propriétés mécaniques remarquables des composites polymères en font des matériaux de choix pour remplacer les métaux. Cependant, leurs propriétés physicochimiques rendent leurs surfaces peu adhésives pour divers types de revêtements. Pour améliorer l’adhérence de revêtements métalliques sur des substrats de PEEK, et pour mieux comprendre les mécanismes de l’adhésion, les propriétés de surface du matériau ont été modifiées par des procédés physiques en voie sèche.D’une part, cette étude montre que les traitements par plasma oxydants (à basse pression, ou à pression atmosphérique) permettent d’améliorer la mouillabilité de la surface et l’adhérence de revêtements métalliques, par l’augmentation de la polarité de la surface, quantifiée par XPS. D’autre part, cette étude montre que l’ablation laser infrarouge à impulsion femtoseconde permet la gravure d’un motif dense, induisant de meilleures tenues mécaniques de l’assemblage. Enfin, cette étude montre que la modification de la chimie et de la topographie combinées améliore davantage ce potentiel d’adhérence.Le but de cette étude est d’ouvrir une voie vers un modèle décrivant les mécanismes de l’adhésion, influencés par la chimie de surface et la géométrie d’un motif, en s’appuyant sur un modèle mécanique permettant de décrire la dynamique des contraintes se propageant au travers de l’interface, en tenant compte des propriétés mécaniques des matériaux. / Thanks to their low densities and good mechanical properties, polymer composites are good candidates for metal alloys substitutes. However, their physicochemical properties limit their adhesion potential towards several types of coatings. In order to improve metallic thin films adhesion on PEEK substrates, and to better comprehend adhesion mechanisms, dry-phase methods have been used to alter the surface properties of the material.First, this study shows that oxidative plasma treatments (at low or at atmospheric pressure) improve the wettability and the practical adhesion of metallic coatings, by an increase of the polar component of the surface, as measured by XPS. Second, this study shows that dense patterns etched by an infrared femtosecond laser allow good practical adhesion of the metallic thin films on the substrate. Finally, this study shows that the modification of both surface chemistry and the surface topography at the same time further improves the practical adhesion of the metallic thin films.The goal of this study is to propose a route towards a model describing the combined influence of surface texture and chemistry, with the support of a mechanical model describing the dynamics of the stress dissipation through the interface while taking into account the mechanicals properties of the interfacial materials.
88

Computational modeling of materials in polymer electrolyte membrane fuel cells

Brunello, Giuseppe 16 September 2013 (has links)
Fuel cells have the potential to change the energy paradigm by allowing more efficient use of energy. In particular, Polymer Electrolyte Membrane Fuel Cells (PEMFC) are interesting because they are low temperature devices. However, there are still numerous challenges limiting their widespread use including operating temperature, types of permissible fuels and optimal use of expensive catalysts. The first two problems are related mainly to the ionomer electrolyte, which largely determines the operating temperature and fuel type. While new ionomer membranes have been proposed to address some of these issues, there is still a lack of fundamental knowledge to guide ionomer design for PEMFC. This work is a computational study of the effect of temperature and water content on sulfonated poly(ether ether ketone) and the effect of acidity on sulfonated polystyrene to better understand how ionomer material properties differ. In particular we found that increased water content preferentially solvates the sulfonate groups and improves water and hydronium transport. However, we found that increasing an ionomer’s acid strength causes similar effects to increasing the water content. Finally, we used Density Functional Theory (DFT) to study platinum nano-clusters as used in PEMFCs. We developed a model using the atom’s coordination number to quickly compute the energy of a cluster and therefore predict which platinum atoms are most loosely held. Our model correctly predicted the energy of various clusters compared to DFT. Also, we studied the interaction between the various moieties of the electrolyte including the catalyst particle and developed a force field. The coordination model can be used in a molecular dynamics simulation of the three phase region of a PEMFC to generate unbiased initial clusters. The force field developed can be used to describe the interaction between this generated cluster and the electrolyte.
89

Contribution à la compréhension de la fonctionnalisation mécanique de surface des composites à matrice thermoplastique (PEEK) destinés à l'assemblage par collage

Ourahmoune, Reda El Hak 20 December 2012 (has links) (PDF)
L'assemblage des matériaux composites thermoplastiques tel que le PEEK est l'une des problématiques majeure de l'industrie aéronautique. Actuellement, différentes techniques sont développées pour assurer l'assemblage structural de ces matériaux, tels que : le soudage, le rivetage, le boulonnage et le collage. Les enjeux industriels majeurs sont principalement, à l'heure actuelle, la conception des structures simplifiées au maximum afin de réduire les coûts de production et la réduction des consommations énergétiques. A cet effet, l'industrie aéronautique fait fréquemment appel à l'assemblage par collage en raison de nombreux avantages qu'il offre (gain de poids, distribution régulière des contraintes, absence de trous) par rapport aux autres techniques existantes. Le PEEK (PolyEtherEtherKetone), est un matériau polymère semi-cristallin thermoplastique, à hautes performances. Ce matériau est souvent utilise dans l'industrie aéronautique principalement renforce par des fibres de carbone ou de verre. Cependant, du fait du niveau élevé de sa résistance chimique l'assemblage par collage du PEEK et de ses composites nécessitent des traitements de surfaces appropries et optimises. Or, afin d'obtenir un system collé à haute performance, la problématique scientifique et technique doit être concentrée sur la jonction entre les éléments à assembler. En effet, la qualité de cette jonction est de la plus haute importance car elle doit permettre un transfert optimal des contraintes thermomécaniques lorsque l'assemblage est soumis a ses conditions d'usage. Cette étude concerne donc, l'amélioration des propriétés mécaniques (monotones et cycliques) de l'assemblage par collage PEEK/PEEK. Dans cette optique, un traitement de surface simple de mise en œuvre est proposé. Ce traitement est le sablage, qui permet la modification topographique (morphologique) de surface. La compréhension des différents phénomènes d'interaction aux interfaces intervenant dans l'amélioration du comportement mécanique du joint de colle et qui s'inscrit dans la triptyque : " Rhéologie, Physico-chimie et topographie ", est l'enjeu scientifique majeur dans cette thèse. Dans un premier temps, l'influence des paramètres du traitement tels que le temps de projection, la taille des particules, sur la morphologie de surface de différents matériaux à base de PEEK a été analysée, permettant ainsi d'établir la corrélation entre les paramètres morphologiques et les mécanismes de modification topographique de surface intervenant pendant le traitement de surface. L'un des facteurs clefs pour la compréhension des mécanismes d'interaction entre l'adhésif liquide et le substrat solide est la mouillabilité. L'analyse du comportement au mouillage en fonction des différents paramètres du traitement a été réalisée. La mouillabilité des surfaces traitées est fortement affectée par la rugosité de surface créée après ce traitement. La relation entre les paramètres morphologiques et la mouillabilité a été discutée. Enfin, l'influence des paramètres du traitement par sablage sur le comportement mécanique monotone et à long terme (essais de fatigue) sur la résistance du joint colle a été étudié à l'aide d'essais de cisaillement sur éprouvettes à simple recouvrement. Ceci a conduit, à la proposition de paramètres morphologiques surfaciques spécifiques pour l'optimisation du comportement mécanique du joint de colle des matériaux composites à matrice PEEK.
90

Avaliação do efeito ambiental nas propriedades mecânicas do compósito de peek/fibra de carbono processado via moldagem por compressão a quente

Oberdan Martins Silva 06 September 2011 (has links)
A utilização de compósitos com matrizes termoplásticas na indústria aeronáutica aparece com forte tendência de utilização na construção de aeronaves, dado o seu potencial de produção a baixo custo, a sua possibilidade de reciclagem e a facilidade na execução de reparos. Dentre os polímeros termoplásticos utilizados em compósitos, o PEEK (poli(éter-éter-cetona)) tem atraído considerável interesse como um polímero avançado de engenharia, devido ao seu desempenho mecânico, que reforçado com fibras de carbono apresenta características de resistência mecânica desejáveis para serem utilizadas em estruturas de alto desempenho. Entretanto, os compósitos poliméricos podem apresentar mecanismos de degradação quando expostos a ambientes agressivos como a elevada temperatura e umidade e também, a radiação ultravioleta. Neste sentido, o objetivo do presente trabalho é avaliar a influência do condicionamento higrotérmico e da radiação ultravioleta na propriedade mecânica de resistência ao cisalhamento interlaminar (ILSS) e no comportamento viscoelástico (DMTA) do compósito termoplástico de PEEK/fibra de carbono, assim como, avaliar a influência dos parâmetros de processamento na obtenção do compósito via moldagem por compressão a quente. Os resultados mostram que no processamento, a utilização constante de pressão durante a etapa de resfriamento do compósito é fundamental para a sua consolidação, refletindo no ensaio de resistência ao cisalhamento interlaminar (18,4 MPa). As análises viscoelásticas das amostras submetidas aos condicionamentos ambientais (higrotérmico e ultravioleta) mostram que o condicionamento que mais afetou o compósito foi o higrotérmico. As análises demonstraram que a temperatura de transição vítrea das amostras ensaiadas por condicionamento higrotérmico (Tg=115 C) foi muito afetada, comparativamente as amostras não condicionadas (Tg=147 C), indicando o efeito deletério do condicionamento higrotérmico nas amostras. / The use of thermoplastic matrix composites in the aerospace industry comes up with a strong tendency to use in airplane applications, because of potential low cost production, recyclability and making repairs facilities. Among the thermoplastic polymers used in composites, PEEK (poly(ether ether ketone)) has attracted considerable interest as an advanced engineering polymer due to its mechanical performance which reinforced with carbon fibers, provides mechanical strength characteristics desirable for use in high performance structures. However, polymeric composites can present degradation mechanisms when exposed to aggressive atmosphere such as high temperature and moisture, also ultraviolet (UV) radiation. This way, the aim of this study is to evaluate the influence of hygrothermal conditioning and ultraviolet radiation on the interlaminar shear strength (ILSS) mechanical property and the viscoelastic behavior (DMTA) of the PEEK/carbon fiber thermoplastic composite, and also to evaluate the processing parameters influence to make the composite via hot compression molding. The results show in this method that, the use of constant pressure is critical to its consolidation during the composite cooling step, reflecting the shear strength testing (18.4 MPa). The samples viscoelastic analysis subjected to the environmental conditioning (hygrothermal and UV) show that the hygrothermal conditioning the most affected the composite. Analysis showed that the samples glass transition temperature tested by hygrothermal conditioning (Tg=115 C) was very affected compared to non-conditioned samples (Tg=147 C), indicating the hygrothermal conditioning deleterious effect on the samples.

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