This thesis is concentrated on the long-term fracture of thick unidirectional glass and carbon fibre composites subjected to transverse stress. The objective was to develop a methodology for predicting the long term lifetime of a composite rotor used as part of a flywheel based energy storage system. The flywheel design is based on accommodating high hoop stresses induced during the high speed rotation. However, the different Poisson's ratios of the constituent materials in the rotor result in a complex stress distribution with significant stresses introduced in a direction transverse to the fibres. The possibility has been raised that the lifetime of the rotor will be limited by crack growth in this transverse direction, originating from defects (pores, cracks etc) that can be introduced into the rotor during its manufacture. The approach explored in this work has been to adopt a fracture mechanics based methodology whereby the rate of crack growth in a thick composite is measured as a function of an applied stress intensity. The basic fracture parameters for the material were measured such that the time taken for a crack to grow to a size sufficient to cause failure under an operating stress could be calculated. The materials were also examined to characterise the nature, size and extent of inherent defects. The stress distribution in the rotor under operating conditions was modelled using finite element analysis. The combination of information on inherent defects, stress directions and crack growth rates enable predictions to be made concerning the likely lifetime of the composites. Proof stress diagrams were also constructed in order to demonstrate an approach to product quality assurance testing. The end point of the work was to identify critical manufacturing defect sizes that could be tolerated under the specified operating conditions. The methodology developed for lifetime predictions was critically assessed and considered to be generally acceptable. The work did however raise some concerns regarding the applicability of a conventional fracture mechanics approach applied to heterogeneous composite systems where the size of the cracks are very small. It is recommended that future work should concentrate on studying this area with an emphasis on crack nucleation studies rather than on further crack propagation work.

Made available in DSpace on 2015-05-14T13:21:17Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3853620 bytes, checksum: 97de931d5237e1217f3d658829e243a8 (MD5) Previous issue date: 2012-03-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Ricin (RCA 60) is an inhibitor of ribosomes protein toxic, of class II, extracted from castor bean endosperm of the seed, consisting of two peptide chains (RCA-A 30 and RCA-B 30) linked by a disulfide bridge covalently formed by the combination of 17 amino acid residues. Its toxicity has been observed in animals, insects and humans, being by inhalation, ingestion or injection, and, therefore, has been used in the production of chemical weapons, paradoxically, with medical applications. The main analytical methods for the detection and determination of RCA 60 employing chromatographic separations, biosensors and immunochemical assays. In another hand, there are no reports in the literature employing voltammetry for determining RCA 60. In this work the electrochemical oxidation of the RCA 60 was studied using a glassy carbon electrode (GC). Moreover, it has been developed a voltammetric method by square wave voltammetry (SWV) with pre-concentration over a boron-doped diamond electrode (BDD) for determination of ricin. Two main peaks of quasi-reversible electrochemical oxidation of the RCA 60 were observed on GC by SWV and cyclic voltammetry. The study of the pH by differential pulse voltammetry showed wide dependency (2.0 ≤ pH ≤10.0) at the peak potentials, so that the reaction mechanism involves transferring of 2H+/2e- and 1H+/1e-, to the P1 and P2, respectively, with appearance of an oxidation product at pH  7.0 due to peak P2. Both peaks showed maximum current intensity at pH 7.0. Although similar electrochemical behavior was observed for samples of RCA 60 different cultivars in this electrode, the strong evidence of poisoning of the electrode surface was decisive for the choice of BDD for the development of a voltammetric method. Tests with an analytical standard RCA 60 chain A (RCA-A 30) on GC, confirm the peaks P1 and P2. P2 is more sensitive for analytical purposes. An irreversible behavior for P2 was observed for the RCA-A 30 in sulfuric acid (0.1 mol L-1, pH 1.0), facilitated by pre-concentration by adsorption on BDD. The excellent voltammetric response of the pre-concentrate material, allowed the development of a sensitive and reliable method, with a linearity range from 3.3 to 94 nmol L-1 with a limit of detection and quantification of 19.0 and 62.0 g L-1, respectively. Recovery of 90.9% was verified for 3.3 x 10-8 mol L-1 of RCA-A 30 spiked in a RCA 60 extracted from the castor bean cultivar BRS Paraguaçu sample, which are within the limits suggested by the AOAC. New applications of the method for other real samples are in progress. / A Ricina (RCA 60) é uma proteína tóxica inibidora dos ribossomos, de classe II, extraída do endosperma da semente da mamona, constituída por duas cadeias peptídicas (RCA-A 30 e RCA-B 30) ligadas covalentemente por uma ponte dissulfeto, formada pela combinação dos resíduos de 17 aminoácidos essenciais. Sua toxicidade tem sido observada em animais, insetos e humanos, seja por inalação, ingestão ou injeção, tendo, por conseguinte, sido utilizada na produção de armas químicas, paradoxalmente, com aplicações medicinais. Os principais métodos analíticos para a detecção e determinação de RCA 60 empregam separações cromatográficas, biossensores e ensaios imunoquímicos. Por outro lado, não existem trabalhos na literatura que empregam voltametria para determinação de RCA 60. Assim, neste trabalho a oxidação eletroquímica da RCA 60 foi estudada usando um eletrodo de carbono vítreo (CV). Além disso, foi desenvolvido um método voltamétrico por voltametria de onda quadrada (VOQ) para a determinação da RCA-A 30 com pré-concentração, empregando um eletrodo de diamante dopado com boro (DDB). Dois principais picos de oxidação eletroquímica quase-reversíveis da RCA 60 foram verificados sobre CV por VOQ e voltametria cíclica. O estudo do pH por voltametria de pulso diferencial revelou ampla dependência (2,0 ≤ pH ≤ 10,0) com os potenciais de pico de modo que o mecanismo de reação envolve a transferência de 2H+/2e- e 1H+/1e-, para os P1 e P2, respectivamente, com surgimento de um produto de oxidação em pH  7,0, decorrente do pico P2. Ambos os picos apresentaram intensidade de corrente máxima em pH 7,0. Embora tenha sido observado comportamento eletroquímico similar para amostras de RCA 60 de cultivares diferentes nesse eletrodo, a forte evidência de envenenamento superficial do eletrodo foi determinante para a escolha do DDB para desenvolvimento do método voltamétrico. Testes com o padrão analítico da cadeia A da RCA 60 (RCA-A 30), confirmam os picos P1 e P2, sendo P2 mais sensível para fins analíticos. Um comportamento irreversível para P2 foi diagnosticado para RCA-A 30 em ácido sulfúrico (0,1 mol L-1, pH 1,0), facilitado pela pré-concentração por adsorção sobre DDB. A excelente resposta voltamétrica do material pré-concentrado, permitiu o desenvolvimento de um método sensível e confiável, com uma faixa de linearidade de 3,3 a 94 nmol L-1 com um limite de detecção e quantificação de 19 e 62 g L-1, respectivamente. Recuperação de 90,9% foi verificado para 3,3 x 10-8 mol L-1 de RCA-A 30 em um extrato deslipidado de RCA 60, extraído da cultivar de mamoneira BRS Paraguaçu, respectivamente, o que está dentro dos limites sugeridos pela AOAC. Novas aplicações do método para outras amostras de cultivares de mamoneira estão em curso.

Made available in DSpace on 2016-08-19T12:56:31Z (GMT). No. of bitstreams: 1 Glene Henrique Rodrigues Cavacalte.pdf: 1209542 bytes, checksum: 36cc863cc05d8037efc2752ed3e32121 (MD5) Previous issue date: 2008-02-22 / FUNDAÇÃO SOUSÂNDRADE DE APOIO AO DESENVOLVIMENTO DA UFMA / This work reports the optimization and validation of an eletro-analytical method for to determine eugenol in essential oil, it obtained of the green leaves of Cinnamomum zeylamicum (cinnamon), with application tested in other essential oils of scientific interest, such as the Origanum (oregano) and Dioic Pepper L (dioic pepper). The vegetable species was collected in Maioba, Paço do Lumiar district, and it submitted to Botanical identification in the Herbarium of the Federal University of Maranhão. The essential oils were extracted for hydrodistillation process and it submitted to the eletro-analytical analyses. Voltammetric of Differential Pulse was the technique chosen, that it use the glass carbon as work electrode, and the buffer Britton Robisson with 55% of Ethanol as electrolyte. They were used an tested in the otmization the following parameters: oxidation potential (+524mV), deposition time (100 s), scan speed (40m V/s), pulse amplitude (100 mV) and pH (3,3). The analytical curve was used as tool for determination of the eugenol percentage in the sample, the procedure was validated, it obtaining LDM = 3,12 x 10-7 mol.L-1 and LQM = 1,12 x 10-6 mol.L-1. The employed method provaided 64,31 % of eugenol in the cinnamon species, 20,2 and 78,31 % in the oregano and dioic pepper essential oils, respectively. The use of the methodology present evidences the potentiality of the application of the differential pulse technique with glass carbon electrode supplying an answer voltammetric precise and exact for the analysis of the eugenol in essential oils. / Este trabalho relata a otimização e validação de um método eletro-analítico para determinação de eugenol em óleo essencial, obtido das folhas verdes de Cinnamomum zeylamicum (canela), com aplicação testada em outros óleos essenciais de interesse científico, como o Origanum (orégano) e Pimenta dioica L (pimenta dióica). A espécie vegetal foi coletada na Maioba, município de Paço do Lumiar, e submetida à identificação Botânica no Herbário da Universidade Federal do Maranhão. Os óleos essenciais foram extraídos por processo de hidrodestilação e submetidos às análises eletro-analíticas. A técnica escolhida foi a Voltametria de Pulso Diferencial, usando como eletrodo de trabalho carbono vítreo, e eletrólito o tampão Britton Robisson com 55% de Etanol. Os parâmetros testados e revelados na otmização foram os seguintes: potencial de oxidação (+524mV), tempo de deposição (100 s), velocidade de varredura (40m V/s), amplitude de pulso (100 mV) e pH (3,3). A curva analítica foi usada como ferramenta para determinação do percentual de eugenol na amostra, o procedimento foi validado, apresentando LDM = 3,12 x10-7 molL-1 e LQM = 1,12 x 10- 6molL-1. O método empregado forneceu um percentual de 64,31 % de eugenol na espécie de canela, 20,2 e 78,31 % nos óleos essenciais de orégano e pimenta dióica respectivamente. O emprego da presente metodologia evidencia a potencialidade da utilização da técnica de pulso diferencial com eletrodo de carbono vítreo, fornecendo uma resposta voltamétrica precisa e exata para a análise do eugenol em óleos essenciais.

Die Einhaltung von Brandschutzanforderungen ist ein wichtiger Aspekt für sichere Baukonstruktionen. Beim innovativen Werkstoff textilbewehrter Beton, der einen Verbundwerkstoff aus einer Feinbetonmatrix und textiler Bewehrung darstellt, ist das Brandverhalten bisher nur unzureichend erforscht worden. Insbesondere das Tragverhalten der einzelnen Komponenten unter hohen Temperaturen stellt noch eine Wissenslücke in der heutigen Forschung dar. Dieser Artikel befasst sich mit den experimentellen Untersuchungen an einer Feinbetonmatrix, die ein Größtkorndurchmesser von 0,6 mm aufweist, sowie an AR-Glas- und Carbongarnen. Basierend auf instationären Versuchen werden das Spannungs- und Dehnungsverhalten unter hohen Temperaturen abgeleitet und Ansätze zur rechnerischen Beschreibung des Hochtemperaturverhaltens vorgeschlagen. / The design of structural members under fire attack is an important aspect for safe constructions. For the innovative material textile reinforced concrete (TRC), which is a composite material made of fine-grained concrete and textile reinforcement, the fire behavior has not been investigated insufficiently yet. Especially the load-bearing behavior under high-temperatures of the single components marks a gap in the state-of-the-art of science and technology today. This article deals with experimental investigations on a fine-grained concrete matrix, which has maximum grain size of only 0.6 mm, as well as yarns made of AR-glass and carbon. On the basis of transient tests the stress and strain behavior under high temperatures is derived. Finally, a calculative approach for the hightemperature behavior is presented.

Das Trag- und Verbundverhalten textiler Bewehrungen wurde in den vergangen Jahren umfassend experimentell untersucht. Die dabei gewonnenen Erkenntnisse stützen sich jedoch fast ausschließlich auf einaxiale Beanspruchungszustände. Grundsätzlich können aus dem Vergleich von Versuchen an Rovings und an textilen Bewehrungsstrukturen Rückschlüsse auf den Einfluss der Quer- und Stützfäden und der verschiedenen Bindungstechniken auf das einaxiale Tragverhalten von Textilbeton getroffen werden. Offen bleibt jedoch, inwieweit sich die gefundenen Gesetzmäßigkeiten auf mehraxiale Beanspruchungssituationen übertragen lassen. Dadurch werden Fragen bezüglich des Tragverhaltens textiler Bewehrungen unter mehraxialen Zugbeanspruchungen aufgeworfen, welche die Motivation für die vorliegende Arbeit liefern. Die hierzu durchgeführten experimentellen Untersuchungen umfassen 84 Einzelversuche und wurden in einem speziell für zweiaxiale Zugbeanspruchungen entwickelten Versuchsaufbau durchgeführt. Als textile Bewehrungen kamen zwei verschiedene Gelegearten aus AR-Glas und Carbon zum Einsatz. Die Ergebnisse konnten die bisher ausschließlich an einaxialen Dehnkörpern gewonnenen Erkenntnisse über das Tragverhalten textiler Bewehrungen grundsätzlich bestätigen. Für den Übergang von Zustand I zum Zustand II konnte eine Abhängigkeit der Erstrissspannung vom Spannungsverhältnis nachgewiesen werden. Die Merkmale der Zustände IIa und IIb zeigen hingegen keine signifikante Abhängigkeit vom Verhältnis aus Längs- und Querzugspannung. Darüber hinaus haben offenbar durch Querzug induzierte bewehrungsparallele Risse keine maßgeblichen Auswirkungen auf das Verbundverhalten der Rovings in Längsrichtung. Eine wesentliche Erkenntnis aus den biaxialen Zugversuchen mit Carbon betrifft den Einfluss der Welligkeit. Es wurde deutlich, dass der Abbau der Welligkeit in beschichteten textilen Bewehrungen hochgradig lastabhängig ist. In zahlreichen Versuchen mit Carbon kam es innerhalb des Zustands IIb zu Delamination, einem bisher in diesem Umfang nicht beobachteten Effekt. Die Erkenntnisse hinsichtlich des Abbaus der Welligkeit wurden im Anschluss auf das Tragverhalten von AR-Glas übertragen und führten zu einer Neubewertung des bei AR-Glas beobachteten Steifigkeitsdefizits im Zustand IIb. Weiterhin wurde der Einfluss der Orientierung der Bewehrung unter einaxialer Beanspruchung an scheibenartigen Probekörpern untersucht. Es zeigte sich, dass die untersuchten Bewehrungen aus AR-Glas hinsichtlich der Tragfähigkeit bei schiefwinkliger Beanspruchung deutlich unempfindlicher reagieren als Bewehrungen aus Carbon. Für die Reduktion der effektiven Faserbruchspannungen wurde ein mathematisches Modell vorgestellt, welches eine getrennte Beschreibung der geometrischen Einflüsse sowie alle sonstigen, die Faserbruchspannung reduzierenden Effekte erlaubt. / The load bearing and bond behaviour of textile reinforcements has been comprehensively studied experimental in recent years. The findings are based almost exclusively on uniaxial loading. Generally, from the comparison of tests on rovings and fabrics conclusions can be drawn about the influence of transverse and supporting threads and different binding patterns on the uniaxial load-bearing behaviour. However, it remains open, to what extend the found principles are applicable to multi-axial loading situations. This raises questions about the load bearing behaviour under multi-axial tension loading, which provide motivation for this work. For the experimental studies on 84 specimens a specially developed test setup for biaxial tensile loading was used. Two different types of textile reinforcements made from AR-glass and carbon fibres were examined. The results generally approve the findings on the structural behaviour of textile reinforcements exclusively derived from uniaxial tests. A relationship between first cracking stress level and biaxial stress ratio has been found. The characteristics of the cracking phases and during stabilized cracking, however, show no significant dependencies on the ratio of longitudinal and transverse tensile stresses. Furthermore, parallel cracks induced by transverse tensile stresses have no significant impact on the bond behaviour of longitudinal rovings. An essential result from biaxial tensile tests with carbon is the strong influence of waviness. It became clear that the reduction of waviness in coated textile reinforcement is highly load-dependent. In numerous experiments with carbon reinforcement delamination occurred during stabilized cracking – an effect, that has been observed in this large scale for the first time. The findings regarding the reduction of the waviness were subsequently applied to AR-glass and led to a revaluation of the known stiffness deficit in the phase IIb. Furthermore, the influence of reinforcement orientation has been studied on discoidal specimens under uni-axial loading. It was found that the load bearing capacity of carbon reinforcement is much more sensible to load orientation than AR-glass. A mathematical model was presented, which allows the separate description of geometric factors and as well as all other effects that reduce the fibre tensile strength.

Textilbewehrter Beton ist ein Verbundwerkstoff aus einer Feinbetonmatrix und einer kraftgerichteten textilen Bewehrung aus ARGlasfaser- oder Carbongelegen. Die heterogene Materialstruktur der textilen Bewehrung im Verbundbaustoff Textilbeton führt zu einem komplexen Tragverhalten mit einer Vielzahl sich zum Teil gegenseitig in ihrer Wirkung beeinflussender Effekte. Aufgrund der abweichenden Material- und Verbundeigenschaften können für die Bemessung von textilbewehrten Betonbauteilen die aus dem Stahlbetonbau bekannten Modelle nicht pauschal übertragen werden. In diesem Beitrag werden die wesentlichen Erkenntnisse experimenteller Untersuchungen von textilbewehrten Elementen unter Biege- und Querkraftbeanspruchung dargestellt, die Mechanismen des Tragverhaltens beschrieben und empirisch abgeleitete Berechnungsmodelle vorgestellt.

Textile high-performance filament yarn subjected to extremely high thermal loads can be found in various technical application fields. Besides the mechanical loads, textile fiber materials have to also satisfy high safety requirements in these applications with respect to thermal loads. Some of the main fields of application in the field of mechanical engineering are turbines, drive devices, rocket components and fire protection coatings. Textile grid-like structures are also being increasingly used in civil engineering as reinforcements (textile concretes). The design and development of textile structures for these applications demands studying and acquiring the material behavior under high thermal loads. Neither sufficient data nor standardized testing methods have been extensively achieved for evaluating the tensile characteristics of filament yarns under thermal influences. Hence, studying the thermal behavior of these yarns, which are used as input material for the reinforcing structures, is essential. The impact of the standard atmospheric condition on the oxidation behavior of the yarns, as in the case of carbon filament yarns and their influence on the physicochemical and tensile mechanical properties, have to be studied as well. This paper aims to address this issue and provides an insight into the current research about the development and realization of a novel test stand and the subsequent study of tensile mechanical behavior for textile high-performance fiber material under extreme thermal loads together with their physicochemical behavior.