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In the effort to improve oil production riser performance, new materials are being studied. In the present case, a Polymer Matrix Composite (PMC) is being considered as a replacement for carbon steel in flexible risers manufactured by Wellstream Inc., Panama City, Florida. The Materials Response Group (MRG) at Virginia Tech had the primary responsibility to develop the models for long-term behavior, especially remaining strength and life. The MRG is also responsible for the characterization of the material system with a focus on the effects of time, temperature, and environmental exposure. The present work is part of this effort. The motivation to use a composite material in a non-bonded flexible riser for use in the offshore oil industry is put forth. The requirements for such a material are detailed. Strength analysis and modeling methods are presented with experimental data. The effect of matrix crystallinity on composite mechanical properties is shown. A new method for investigating matrix behavior at elevated temperatures developed. A remaining strength life prediction methodology is recalled and applied to the case of combined fatigue and rupture loading. / Master of Science

Τα σύνθετα υλικά αποτελούνται από δυο ή περισσότερα υλικά συνδεδεμένα μακροσκοπικά, έτσι ώστε να προκύπτει ένα πολυφασικό σύστημα με φυσικές ιδιότητες διαφορετικές από αυτές των αρχικών υλικών. Τα επιμέρους υλικά δεν είναι διαλυτά το ένα στο άλλο και μπορούν να αναμιχθούν μεταξύ τους με ελεγχόμενο τρόπο και με καθορισμένες αναλογίες, ενώ είναι και μηχανικά διαχωρίσιμα. Τα σύνθετα υλικά αποτελούνται από δυο φάσεις, τη μητρική και τη φάση ενίσχυσης. Η μήτρα περικλείει τα εγκλείσματα και αποτελεί τη φάση του συστήματος, η οποία δίνει στο σύνθετο την εξωτερική του μορφή. Ο ρόλος της είναι να μεταφέρει τις μηχανικές τάσεις μέσα στο σύνθετο υλικό, να τις κατανέμει ομοιόμορφα ανάμεσα στα εγκλείσματα αλλά και να τα προστατεύει από τις περιβαλλοντικές συνθήκες. Τα διάφορα εγκλείσματα αποτελούν την ενισχυτική φάση του σύνθετου συστήματος και ποικίλουν σε μέγεθος, γεωμετρία και σύσταση. Στην παρούσα εργασία ως ενισχυτική φάση χρησιμοποιήθηκε το ZnO. Το ZnO είναι ένας ημιαγωγός ευρέως χάσματος με μια μη κεντρική συμμετρική δομή κρυστάλλου Βουρτσίτη (Wurtzite) εξαγωνικού πλέγματος Bravais. Ως προπολυμερές για την παρασκευή των δοκιμίων, χρησιμοποιήθηκε εποξειδική ρητίνη. Η συγκεκριμένη ρητίνη είναι ένα τυπικό μονωτικό πολυμερές χαμηλού ιξώδους και η διηλεκτρική της σταθερά καθώς και η αγωγιμότητα της δεν διαφέρουν σημαντικά από τις αντίστοιχες τιμές του ZnO. Στην παρούσα εργασία παρουσιάζεται ο ηλεκτρικός χαρακτηρισμός υλικών καθαρής ρητίνης και σύνθετων συστημάτων ρητίνης-κεραμικού ZnO σε διάφορες συγκεντρώσεις, από 10phr έως 70phr. Για τον ηλεκτρικό χαρακτηρισμό των σύνθετων αυτών, εφαρμόστηκε η τεχνική της διηλεκτρικής φασματοσκοπίας ευρέως φάσματος (BDS-Broadband Dielectric Spectroscopy) στην περιοχή συχνοτήτων από 0.1 Hz έως 1 ΜHz, με χρήση της γέφυρας εναλλασσόμενου Alpha-N της εταιρίας Novocontrol. Η κυψελίδα μετρήσεων που χρησιμοποιήθηκε ήταν η BDS 1200 της ίδιας εταιρίας. Τα δείγματα μελετήθηκαν σε θερμοκρασίες από –100 ºC έως 150 ºC. Τα φαινόμενα διηλεκτρικής χαλάρωσης που καταγράφονται στην παρούσα εργασία περιλαμβάνουν συνεισφορές τόσο από την πολυμερική μήτρα όσο και από την ενισχυτική φάση. Για την παρουσίαση των πειραματικών αποτελεσμάτων διακρίνονται δυο περιοχές θερμοκρασιών. Στην περιοχή των χαμηλών θερμοκρασιών, από –100 ºC έως 20 ºC, καταγράφονται σε όλα τα δείγματα οι διεργασίες β-, γ-χαλάρωσης. Οι διεργασίες αυτές αποδίδονται σε περιορισμένες τοπικές κινήσεις τμημάτων της πολυμερικής αλυσίδας (γ-χαλάρωση) και σε επαναπροσανατολισμό πλευρικών τμημάτων της πολυμερικής αλυσίδας (β-χαλάρωση). Στα σύνθετα δείγματα, σε θερμοκρασία πάνω από τους –30 ºC, εμφανίζεται και η διεργασία χαλάρωσης FDE η οποία αποδίδεται στην ύπαρξη του πληρωτικού μέσου. Στην περιοχή των υψηλών θερμοκρασιών, από +20 ºC έως +150 ºC, εμφανίζεται σε όλα τα δείγματα, στην περιοχή των ενδιάμεσων συχνοτήτων, η α-χαλάρωση. Στην περιοχή των χαμηλών συχνοτήτων, και μόνο στα σύνθετα δείγματα, καταγράφεται το φαινόμενο MWS το οποίο είναι ασθενές λόγω της χαμηλής ηλεκτρικής ετερογένειας μεταξύ των φάσεων του συστήματος. Στην περιοχή των υψηλών συχνοτήτων παρουσιάζεται η διεργασία χαλάρωσης FDE η οποία γίνεται εντονότερη καθώς αυξάνεται η συγκέντρωση του πληρωτικού μέσου. Για όλες τις συγκεντρώσεις, παρατηρείται ότι η εξάρτηση της διεργασίας της α-χαλάρωσης από τη θερμοκρασία περιγράφεται από την εξίσωση Vogel-Fulcher-Tamann (VTF) ενώ η διεργασία χαλάρωσης FDE, παρουσιάζει εξάρτηση από τη θερμοκρασία, η οποία ακολουθεί την εξίσωση Arrhenius. Για τις διεργασίες της α-χαλάρωσης και του FDE στις υψηλές θερμοκρασίες, υπολογίζονται οι ενέργειες ενεργοποίησης. Στην εξάρτηση του πραγματικού μέρους της ηλεκτρικής αγωγιμότητας εναλλασσόμενου , από τη συχνότητα, διακρίνονται τρεις περιοχές. Στην περιοχή των υψηλών συχνοτήτων η ηλεκτρική αγωγιμότητα αυξάνεται σχεδόν γραμμικά συναρτήσει της συχνότητας ακολουθώντας τον νόμο της παγκόσμιας διηλεκτρικής απόκρισης ( ). Στην ενδιάμεση περιοχή συχνοτήτων παρατηρούνται μεταβολές στην τιμή της ηλεκτρικής αγωγιμότητας οι οποίες αποδίδονται στην ύπαρξη διάφορων διεργασιών χαλάρωσης. Στην περιοχή των χαμηλών συχνοτήτων, η ηλεκτρική αγωγιμότητα τείνει προς μια σταθερή τιμή. Αυτή αντιστοιχεί στην αγωγιμότητα συνεχούς ( ) και αυξάνεται συναρτήσει της θερμοκρασίας ακολουθώντας την εξίσωση Vogel-Tamman-Fulcher (VTF). / Polymer matrix – ZnO composites were prepared, in different filler concentrations. Polymer matrix samples were also prepared and investigated as reference. The dielectric response of all samples was studied by means of Broadband Dielectric Spectroscopy (BDS), over a wide temperature range from -100 ºC to 150 ºC and in the frequency range from 10-1 Hz to 1MHz. The results are discussed using the common formalism of ε΄(f), ε΄΄(f) and M΄(f), M΄΄(f). The recorded dielectric processes include contributions from both the polymeric matrix and the presence of the reinforcing phase. The dielectric spectrum exhibits distinct relaxation modes which are attributed (i) to the glass-rubber transition, associated with motions of main chain segments of the polymeric matrix, namely -relaxation, (ii) faster processes related to the local motion of polar side groups, namely -relaxations, (iii) interfacial polarization phenomena known as Maxwell – Wagner – Sillars effect and (iv) possible polarization related to the ferroelectric nature of ZnO. In order to investigate the influence of the reinforcing phase in the dielectric response of the composite materials, all dielectric processes as well as the electrical conductivity are analyzed and discussed as a function of filler concentration.

For polymer-matrix composites (PMCs) that contain insulating matrices and conducting fillers, the electrical properties of the PMCs are especially sensitive to the local concentration of the fillers in the matrix. For PMCs that have phase-segregated microstructures, better prediction of the properties is possible since enhanced control over the distribution of the filler in the matrix can be achieved. In this research, PMMA-ITO nanocomposites were chosen as the composite system in which to explore alternative microstructures, specifically highly phase-segregated microstructures. The microstructures were primarily controlled by varying the ITO particle size and concentration, and the fabrication parameters used to form the nanocomposites. The motivation for this research was to develop correlations between the microstructure and non-destructive measurements in order to improve the predictability of properties in percolating PMCs. As a result of this work, a novel phase-segregated microstructure was discovered, where ITO aggregate-wire structures self-assembled during the composite forming process. Structural analysis of the specimens was conducted primarily using transmission optical microscopy and scanning electron microscopy (SEM). Impedance spectroscopy and optical spectroscopy were the primary NDE characterization tools used for analyzing the variations among the specimens. Ultra-small angle x-ray scattering (USAXS) and stereological techniques were also used to describe the dimensions of the ITO aggregate-wire structures that self-assembled in the PMMA-ITO nanocomposites.

La société CASCADE a été créée pour industrialiser des technologies dites à « cascades lumineuses ». Le principe de ces « cascades lumineuses » consiste à réaliser un ou plusieurs décalages de fréquences lumineuses (ou électromagnétiques) en dopant une matrice polymère transparente par intégration de molécules optiquement actives (MOA), permettant d’adapter le spectre solaire à la photosynthèse et à la fonction chlorophyllienne des plantes. Un intérêt majeur pour les cultures sous serres d’utiliser des films agricoles dopés avec les MOA est de favoriser la précocité des récoltes ou d’accroître la quantité en poids des végétaux récoltés, sans en altérer leur qualité. Les polymères utilisés aujourd’hui dans les films agricoles sont le polyéthylène (PE) et le copolymère poly(éthylène-co-acétate de vinyle) (EVA) dans lesquels les MOA ne sont pas suffisamment stabilisées pour une application industrielle. L’objectif de la thèse vise donc à améliorer la tenue temporelle des MOA dans les matrices polymères PE/EVA par différentes stratégies : (i) l’étude de l’influence de la nature et de la topologie de la matrice polymère, (ii) l’optimisation des formulations existantes par ajout d’additifs ou de compatibilisants et (iii) l’encapsulation des MOA dans des particules de PMMA (non)-réticulées. / The CASCADE company was founded to develop technology said to “light cascades”. These “light cascades” consist of incorporating an appropriate combination of optically active molecules (OAM) into host materials allowing wavelength-shifting effects to optimize the quality and quantity of direct and diffuse sunlight. When such OAM combination is introduced into greenhouse films, an increase of agronomic yields and early crop are observed. Such behavior is due to the fact that OAM allow to adapt the solar spectrum to the photosynthesis and the chlorophyll function of plants. Greenhouse films are based on polyethylene (PE) and/or poly(ethylene-co-vinyl acetate) (EVA) copolymers. When OAM are introduced within such host polymers, their optically efficiency is limited for long term industrial applications. Therefore, the thesis goal is to improve the OAM lightfastness into PE/EVA polymer matrix by different strategies: (i) the study of polymer matrix nature and topology influence, (ii) the optimization of current formulations by additives or compatibilizers adding and (iii) the OAM encapsulation into (un)-crosslinked PMMA particles.

[pt] O objetivo deste trabalho foi sintetizar pós submicrônicos de Y2W3O12 e Al2W3O12 visando estudar o efeito da incorporação destas cargas no coeficiente de expansão térmica (CET) e nas propriedades mecânicas de compósitos de polietileno de alta densidade (PEAD). As partículas de Y2W3O12 foram obtidas pelos métodos de coprecipitação por mistura de reagentes e coprecipitação reversa modificada, com o intuito de avaliar a influência destas rotas no grau de aglomeração dos pós preparados. Ambos os métodos permitiram obter pós submicrônicos de Y2W3O12 0. 0.7 um) com tamanhos de partículas primárias e graus de aglomeração semelhantes, conforme verificado por diversas técnicas de caracterização. As partículas de Al2W3O12 foram sintetizadas pelos métodos de coprecipitação por mistura de reagentes e coprecipitação normal, utilizando duas fontes de tungstênio e os precursores obtidos foram secos no micro-ondas. Os efeitos do pH da síntese (4.2 e 6.0) no estado de aglomeração dos pós sintetizados foram avaliados. Pós submicrônicos de Al2W3O12 0.22 0.87 um) foram produzidos utilizando estas rotas. A coprecipitação pela mistura de reagentes em pH=4.2 permitiram obter pós com aglomerados de menor tamanho (0.22 um). Os compósitos de PEAD foram fabricados por microextrusão-microinjeção, com partículas de Al2W3O12 e Y2W3O12 (0.70 um) em frações volumétricas na faixa de 0.001 0.011. Os compósitos PEAD/Y2W3O12 exibiram reduções no CET de 20 25 porcento quando comparados ao PEAD na faixa de 25 70 °C, enquanto os compósitos PEAD/Al2W3O12 mostraram reduções no CET de 7 8 porcento. O módulo de Young aumentou 11 32 porcento e 21 porcento para os compósitos reforçados com Y2W3O12 e Al2W3O12, respectivamente, enquanto a estabilidade térmica do PEAD foi preservada para todos os compósitos. / [en] The aim of this work was to synthesize Al2W3O12 and Y2W3O12 submicronic powders and study the effect of incorporation of these fillers on thermal expansion coefficient (CTE) and mechanical properties of high density polyethylene (HDPE) composites. Y2W3O12 was synthesized via co-precipitation by mixing reactants and modified reverse strike co-precipitation, to assess the influence of the method on agglomeration degree of powders. Both methods produced Y2W3O12 submicronic powders (0.60 0.70 um), with similar primary particle sizes and agglomeration degrees, as verified by different characterization techniques. Al2W3O12 was synthesized via co-precipitation by mixing reactants and normal strike method, using two distinct tungsten sources and the assynthesized precursors were microwave dryied. The effects of synthesis pH (4.2 and 6.0) on final agglomeration state of the as-synthesized powders were assessed. Al2W3O12 submicronic powders (0.22 0.87 um) were synthesized by these routes. Co-precipitation by mixing reactants at pH=4.2 led to Al2W3O12 powders with smaller agglomerate sizes (0.22 um). HDPE composites were manufactured by micro-compounding, using Al2W3O12 and Y2W3O12 powders with similar particle sizes (0.70 um), at volume fractions in the range of 0.001 0.011. HDPE/Y2W3O12 composites presented CTE reductions of 20 25 porcento compared to neat HDPE, in the temperature range of 25 70 Celsius degrees, while HDPE/Al2W3O12 composites displayed reductions on CTE of 7 8 porcent. Young s moduli of composites were increased 11 32 porcent nd 21 porcent when filled with Y2W3O12 and Al2W3O12, respectively, whilst thermal stability of HDPE was preserved for all composites.

No / The goal of this study was to investigate the fibre orientation distribution (FOD), and subsequent mechanical properties, of an injection moulded plate with two different number averaged fibre lengths, termed in this paper medium (1.35 mm) and long (2.40 mm). Fibre orientation measurements (FOD) were made using the 2D elliptical section method and an in-house developed image analyser. The samples were injected from a pin gate located at the centre and top of the plate. Expansion flow on the divergent flow front from this pin gate resulted in a core region with circumferential alignment, while through thickness shear resulted in the usual realignment of fibres in the flow direction either side of the core, termed the shell layers. Two interesting aspects were discovered from these measurements. First, and most importantly, the FOD was found to be independent of the two fibre lengths in this study, and so predominantly controlled by the mould shape and the interaction with the flow front. Second, the fibres in the core region were found to be much closer packed than those in the shell regions. The interaction between the flow front and the mould shape resulted in a range of FOD across the moulded plate, from equal in-plane orientation at the centre of the plate, to highly aligned at the plate edge. This gave a very useful set of samples from which to test out the well known modified rule of mixtures (MROM). Often the fibre orientation distribution cannot be measured directly, but indirectly using the modified rule of mixtures model in reverse. The samples from this moulding (at two different average fibre lengths) gave an excellent opportunity to validate this often used approach. Both the tensile modulus and strength (measured parallel to the injection direction) were found to show a strong correlation with the measured fibre orientation, with a significant increase in both measures between the centre and the edge of both plates. The increased length of the ‘long’ fibre plate was found to give only a small increase in tensile modulus but a much larger increase in tensile strength. The tensile modulus showed a linear dependence with the measured fourth order orientation tensor average, 〈cos4 θ〉, with respect to the injection direction of the plate, as predicted by the modified rule of mixtures. Excellent agreement was found between the measured modulus and the predictions from the modified rule of mixtures, based only on measured quantities (matrix modulus, fibre fraction and average fibre length) for both plates.

The purpose of this research is to investigate the influence of stitching architectures by using different stitching periodic patterns on the in-plane and out-of-plane mechanical properties. By using the inherent periodic architecture of these composites, their mechanical properties may be tailored for specific applications. Composite structures are extensively used in several industries such as aerospace, automotive, sports, and construction due to their many advantages, which include tailorable mechanical properties, high strength-to-weight ratios, and high specific stiffness. However, due to their low interlaminar tensile strength, composites are prone to delaminations, which can degrade the overall mechanical performance of the structure. Through-thickness stitching provides the third-direction reinforcement to enhance the interlaminar tensile and shear strengths. In this study, quasi-isotropic composite test articles were manufactured and stitched through-thickness using different chain stitch patterns. Full-field surface strain measurements were collected through the non-contact digital image correlation (DIC) technique. A design of experiments (DoE) approach was used to investigate the stitch parameters, such as stitch density (number of stitches per unit area), stitch angle (stitch seam orientation), and linear thread density (thread diameter), and their interactions on the in-plane and out-of-plane mechanical properties. Experimental results are then used to develop a statistically informed response surface model (RSM) to find optimal stitching parameters based on a maximum predicted tensile strength, tensile modulus and flexural strength.

Polymer matrix composites (PMC's) are now being used more and more extensively and over wider ranges of service conditions. Large changes in pressure, chemical environment or temperature influence the mechanical response of such composites. In the present effort, we focus on temperature, a parameter of primary interest in almost all engineering applications. In order to design composite structures without having to perform extensive experiments (virtual design), the necessity of establishing theoretical models that relate the macroscopic response of the structure to the microscopic properties of the constituents arises. In the first part of the present work, a new stiffness versus temperature model is established. The model is validated using data from the literature. The influence of the different polymer's properties (Molecular weight, crystallinity, and filler content) on the model are studied by performing experiments on different grades of four polymers PMMA, PEEK, PPS, and PB. This statistical model is proven to be applicable to very different polymers (elastomers, thermoplastics, crystalline, amorphous, cross-linked, linear, filled, unfilledâ ¦) over wide temperature ranges (from the glassy state to the flow region). The most attractive feature of the proposed model is the capability to enable a description of the polymer's mechanical behavior within and across the property transition regions. In order to validate the feasibility of using the model to predict the mechanical response of polymer matrix composites, the stiffness-temperature model is used in various micromechanical models (rule of mixtures, compression models for the life prediction of unidirectional PMC's in end-loaded bendingâ ¦). The model is also inserted in the MRLife prediction code to predict the remaining strength and life of unidirectional PMC's in fatigue bending. End-loaded fatigue experiments were performed. A good correlation between theoretical and experimental results is observed. Finally, the model is used in the Classical Lamination Theory; some laminates were found to exhibit stress reversals with temperature and behaved like thermally activated mechanical switches. / Ph. D.

Pesquisas e publicações sobre polímeros luminescentes vêm sendo desenvolvidas nos últimos anos devido à inovação acadêmica, porém ainda no âmbito nacional possuem aplicação industrial limitada. Marcadores ópticos processados são pouco explorados devido à dificuldade de processamento dos materiais poliméricos luminescentes com estabilidade de luminescência. Os materiais utilizados para o processamento de polipropileno luminescente foram Poliamida 6 (PA6) dopada com complexo sintetizado de [Eu(tta)3(H2O)2] obtida através do processo de diluição do polímero e técnica de derramamento. As poliolefinas, por serem inertes, não se adequam ao procedimento comum de dopagem, assim no presente trabalho, o polipropileno luminescente foi preparado indiretamente por dopagem com poliamida dopada com complexo de európio em processamento por extrusão. As técnicas de caracterização utilizadas foram a Análise Térmica (TG), Calorimetria Exploratória Diferencial (DSC), Difração de Raios-X (XRD), Espectroscopia de infravermelho (FT-IR) e estudo das propriedades fotoluminescentes. A blenda PP/PA6:Eu(tta)3 processada apresentou propriedades luminescentes observadas nas transições intraconfiguracionais de bandas finas 4f6 - 4f6 relativas aos níveis de excitação de energia 7F0 → 5L6 (394nm), 7F0 → 5D3 (415nm), 7F0 → 5D2 (464nm), 7F0 → 5D1 (525nm) e 7F0 → 5D0 (578nm). Tanto a blenda de PP/PA6:Eu(tta)3 e os filmes de PA6:Eu(tta)3 quando expostos a luz UV (365nm) apresentaram luminescência vermelha. Os resultados de TG mostraram que sob atmosfera de O2 o PP dopado PA6:Eu(tta)3 apresentou maior estabilidade do que o PP puro. Neste trabalho foi possível processar PP/PA6:Eu(tta)3 com propriedades térmicas e fotoestabilidade, que permitem sua utilização com marcador óptico em processamentos. / Research and publications about luminescent polymers have been developed in the last years for the academic innovation; however the industrial application has been very limited in this area. Processed Optical markers are few explored due to the difficult to process luminescent polymeric materials with stable luminescence. The materials used of processing luminescent polypropylene (PP) were polyamide 6 (PA6) doped with europium complex [Eu(tta)3(H2O)2] obtained through the dilution and casting process. Due to their inercy, polyolefins do not fit into the common procedure of doping, in consequence, in this work luminescent polypropylene was indirectly prepared by polyamide 6 doped with europium complex through extrusion process. Product characterization was done using Thermalgravimetry analysis (TG), Differential Scanning Calorimetric (DSC), X-Ray Diffraction (XRD), Infrared spectroscopy (FTIR) and fotoluminescence of emission and excitation. The blend PP/PA6:Eu(tta)3 presented luminescent properties, after semi-industrial process, as observed in the narrow bands of intraconfiguration transitions - 4f6 relatives to energy levels 7F0 → 5L6 (394nm), 7F0 → 5D3 (415nm), 7F0 → 5D2 (464nm), 7F0 → 5D1 (525nm) e 7F0 → 5D0 (578nm) of emission spectrum. Red light of the pellets or film is emitted when excited in UV lamp (365nm). TG results showed under O2 atmosphere that PP doped with PA6:Eu(tta)3 was more stable than pure PP. In this work luminescent PP/PA6:Eu(tta)3 was processed with properties of thermal and photo stability which can be used as optical marker in polymer processing.