Efeitos do envelhecimento ambiental acelerado em compósitos poliméricos

The advantages of the use of vegetable fibers on the synthetic fibers, such as glass fibers, in the reinforcements in composites are: low cost, low density, good tenacity, good thermal properties and reduced use of instruments for their treatment or processing. However, problems related to poor performance of some mechanical natural fibers, have hindered its direct use in structural elements. In this sense, the emergence of alternative materials such as hybrids composites, involving natural and synthetic fibers, has been encouraged by seeking to improve the performance of structural composites based only on natural fibers. The differences between the physical, chemical and mechanical properties of these fibers, especially facing the adverse environmental conditions such as the presence of moisture and ultraviolet radiation, is also becoming a concern in the final response of these composites. This piece of research presents a comparative study of the strength and stiffness between two composite, both of ortoftalic polyester matrix, one reinforced with fibers of glass-E (CV) and other hybrid reinforced with natural fibers of curauá and fiberglass-E (CH). All the comparative study is based on the influence of exposure to UV rays and steam heated water in composites, simulating the aging environment. The conditions for the tests are accelerated through the use of the aging chamber. The composites will be evaluated through tests of uniaxial static mechanical traction and bending on three points. The composite of glass fiber and hybrid manufacturing industry are using the rolling manual (hand lay-up) and have been developed in the form of composites. All were designed to meet possible structural applications such as tanks and pipes. The reinforcements used in composites were in the forms of short fiber glass-E quilts (450g/m2 - 5cm) of continuous wires and fuses (whose title was of 0.9 dtex) for the curauá fibers. The results clearly show the influence of aging on the environmental mechanical performance of the composite CV and CH. The issues concerning the final characteristics of the fracture for all types of cargoes studied were also analyzed

Efeitos da radiação uv, temperatura e vapor aquecido nos compósitos poliméricos: monitoramento, instabilidade estrutural e fratura

The application of composite materials and in particular the fiber-reinforced plastics (FRP) has gradually conquered space from the so called conventional materials. However, challenges have arisen when their application occurs in equipment and mechanical structures which will be exposed to harsh environmental conditions, especially when there is the influence of environmental degradation due to temperature, UV radiation and moisture in the mechanical performance of these structures, causing irreversible structural damage such as loss of dimensional stability, interfacial degradation, loss of mass, loss of structural properties and changes in the damage mechanism. In this context, the objective of this thesis is the development of a process for monitoring and modeling structural degradation, and the study of the physical and mechanical properties in FRP when in the presence of adverse environmental conditions (ageing). The mechanism of ageing is characterized by controlled environmental conditions of heated steam and ultraviolet radiation. For the research, it was necessary to develop three polymer composites. The first was a lamina of polyester resin reinforced with a short glass-E fiber mat (representing the layer exposed to ageing), and the other two were laminates, both of seven layers of reinforcement, one being made up only of short fibers of glass-E, and the other a hybrid type reinforced with fibers of glass-E/ fibers of curaua. It should be noted that the two laminates have the lamina of short glass-E fibers as a layer of the ageing process incidence. The specimens were removed from the composites mentioned and submitted to environmental ageing accelerated by an ageing chamber. To study the monitoring and modeling of degradation, the ageing cycles to which the lamina was exposed were: alternating cycles of UV radiation and heated steam, a cycle only of UV radiation and a cycle only of heated steam, for a period defined by norm. The laminates have already undergone only the alternating cycle of UV and heated steam. At the end of the exposure period the specimens were subjected to a structural stability assessment by means of the developed measurement of thickness variation technique (MTVT) and the measurement of mass variation technique (MMVT). Then they were subjected to the mechanical tests of uniaxial tension for the lamina and all the laminates, besides the bending test on three points for the laminates. This study was followed by characterization of the fracture and the surface degradation. Finally, a model was developed for the composites called Ageing Zone Diagram (AZD) for monitoring and predicting the tensile strength after the ageing processes. From the results it was observed that the process of degradation occurs Abstract Raimundo Nonato Barbosa Felipe xiv differently for each composite studied, although all were affected in certain way and that the most aggressive ageing process was that of UV radiation, and that the hybrid laminated fibers of glass-E/curaua composite was most affected in its mechanical properties

Laminados compósitos de PRFV: efeitos da descontinuidade geométrica e do envelhecimento ambiental acelerado

The growing demand in the use of composite materials necessitates a better understanding of its behavior related to many conditions of loading and service, as well as under several ways of connections involved in mechanisms of structural projects. Within these project conditions are highlighted the presence of geometrical discontinuities in the area of cross and longitudinal sections of structural elements and environmental conditions of work like UV radiation, moisture, heat, leading to a decrease in final mechanical response of the material. In this sense, this thesis aims to develop studies detailed (experimental and semi-empirical models) the effects caused by the presence of geometric discontinuity, more specifically, a central hole in the longitudinal section (with reduced cross section) and the influence of accelerated environmental aging on the mechanical properties and fracture mechanism of FGRP composite laminates under the action of uniaxial tensile loads. Studies on morphological behavior and structural degradation of composite laminates are performed by macroscopic and microscopic analysis of affected surfaces, in addition to evaluation by the Measurement technique for mass variation (TMVM). The accelerated environmental aging conditions are simulated by aging chamber. To study the simultaneous influence of aging/geometric discontinuity in the mechanical properties of composite laminates, a semiempirical model is proposed and called IE/FCPM Model. For the stress concentration due to the central hole, an analisys by failures criteria were performed by Average-Stress Criterion (ASC) and Point-Stress Criterion (PSC). Two polymeric composite laminates, manufactured industrially were studied: the first is only reinforced by short mats of fiberglass-E (LM) and the second where the reinforced by glass fiber/E comes in the form of bidirectional fabric (LT). In the conception configurations of laminates the anisotropy is crucial to the final mechanical response of the same. Finally, a comparative study of all parameters was performed for a better understanding of the results. How conclusive study, the characteristics of the final fracture of the laminate under all conditions that they were subjected, were analyzed. These analyzes were made at the macroscopic level (scanner) microscope (optical and scanning electron). At the end of the analyzes, it was observed that the degradation process occurs similarly for each composite researched, however, the LM composite compared to composite LT (configurations LT 0/90º and LT ±45º) proved to be more susceptible to loss of mechanical properties in both regarding with the central hole as well to accelerated environmental aging

Descontinuidade na seção transversal em laminados compósitos poliméricos: efeitos e propriedades

The growing demand in the use of composite materials necessitates a better understanding its behavior to many conditions of loading and service, as well as under several ways of connections involved in mechanisms of structural projects. It is know that most of the structural elements are designed with presence of geometric discontinuities (holes, notches, etc) in their longitudinal sections and / or transversals, and that these discontinuities affect the mechanical response of these elements. This work has aims to analyze a study of the mechanical response, when in the presence geometric discontinuity, of polymer matrix composite laminates (orthophthalic polyester) to the uniaxial tensile test. The geometric discontinuity is characterized by the presence of a center hole in the transversal section of the composite. In this study, different kinds of stacking sequences are tested, with and without the presence of the hole, so as to provide better understanding of the mechanical properties. This sense, two laminates were studied: the first is only reinforced by with seven layers short mats of fiberglass-E (CM) and the second where the reinforcement of fiberglass-E comes in the form of bidirectional fabric (CT), with only four layers. The laminate CT has the presence of anisotropy (sense of continuous fibers with respect to the applied load) as the main parameter influencing its mechanical behavior, behavior this, not observed for the CM. In addition to the mechanical properties was also studied the fracture characteristics developed in each composite laminated. The results also showed that the presence of the hole in the transversal section decreased the ultimate strength of laminates and changed the final characteristic of fracture in all kinds of composite laminated studied

Obtenção de novos derivados de ß-naftol e cardanol hidrogenado e avaliação dos seus efeitos antioxidativos em gasolina automotiva

The chemical nature of the hidrocarbons found in gasoline directly affects the formation of oxidation complexes known as gums. Such complexes are slightly soluble in gasoline and their formation is delayed with the use of inhibitors, known as antioxidants. In this study, a synthetic compound (βnaphtol) and a natural subproduct (hydrogenated cardanol, derived from cashewnut shell liquid CNSL) have been used in order to generate novel antioxidant substances. These compounds were submitted to chemical reactions including alkylation, nitration and reduction, with the purpose of forming the following derivatives: 6(Nethyl,Nethylamino)βnaphtol (AO1); 6(Nethyl,Ndiethylamino)βnaphtol (AO2); aminoβnaphtol (AO3); 2(Nethyl,Nethylamino)pentadecylphenol (AOC1), 2(Nethyl,Ndiethylamino)pentadecylphenol (AOC2) and aminopentadecylphenol (AOC3). The derivatives were subjected to accelerated oxidative stability assays (Potential Gum and Induction Period) and to storage assays (Washed Gum and ASTM Color) during six months, with naphtha provided by the petroleum refinery RPBC (Refinaria Presidente Bernardes de Cubatão, in Brazil). The results for the derivatives were compared to those for commercial additives [DBPC (2,6ditbutyl4methylpcresol) and PDA (N,N disecbutylpphenylenediamine)], which were also added to the naphtha produced at RPBC at the moment of sampling. From all tested antioxidants, the novel antioxidant AOC1 (derived from hydrogenated cardanol) yielded a better global performance. During the period of time in which the naphtha was stored, an examination of this material was carried out in parallel, using the mass spectrometry technique. This study allowed to monitor the formation of a triolefinic compound, as well as the observation of subsequent formation and rupture of the olefinic constituents. As an eventual result from these experimental investigations, a reaction route leading to gum formation has been suggested

Efeitos de sentido das não coincidências do dizer na escrita acadêmica

Universidade Federal do Rio Grande do Norte

Didática do plurilinguismo: efeitos da intercompreensão de línguas românicas na compreensão de textos escritos em português

This exploratory study aims to present some readings as Doyé (2003), Carrasco Perea (2003), Melo Araújo e Sá (2004), Chavagne (2009) and Alas-Martins (2010; 2011) which helped to confirm some ways for showing that a plurilingual environment can enable a trend in improving the understanding of written texts in the mother tongue, and can collaborate on a better perception of the world around a person with all their different nuances. The study describes the methodology and some results of our doctoral research that resulted in the insertion of the experimental discipline called Intercomprehension of Romanic Languages (ILR) in the curriculum in the city of Natal / RN / Brazil, and it was justified because of high functional illiteracy degree among young people up to 15 years old according to the educational data from IBGE research on 2010. The results were verified through an experimental action-research which was characterized by Lewin (1946); Nunan (1992); Thiollent (1994) and Trip (2005) in two schools: Professoara Terezinha Paulino de Lima (municipal school) and Professora Ana Julia de Carvalho Mousinho (State of Rio Grande do Norte), with 95 students from the final years of primary education. The corpus of this research was subjected to a series of condensed techniques like the nonparametric test from Kruskal and Wallis (1952) and the parametric test ANOVA as an effort to provide statistical significance to the analysis of the results indicated in the book of ILR activities. The research presented some skill views about reading comprehension of written texts according to perspective of Ringbow (1987), Giacobbe (1990), Alarcão (1991; 2009a and 2009b), Corder (1992), Castellotti (2001) and Degache (2003), and the possibilities of transfer these skills for learning Portuguese as pointed out by Meissner, Klein and Stegmann (2004); it indicates a positive trend towards the understanding of LM according to analyzing the scores of written tests and texts by participants in solving tasks

Entre o sagrado e o profano: os efeitos de sentido revelados nos testemunhos de um blog evangélico

The testimonial is a way of statement that demonstrates or admit the existence of a reality with which the enunciator has contacted. This is, thus, pushed to say what he saw, heard or touched. In this paper, we verified the effects of senses produced in the blog of Bishop Macedo, founder of the Universal Church of the Kingdom of God (UCKG), from a corpus which consists of nine testimonies of presumed believersselected among 64 statements distributed during the year, 2012. Instead of instantaneous testimonials, on a live presentation, these media narratives are underpinned by attributes such as hyperlinks, visuals, language translators, besides mechanisms of interaction and sharing in other spheres from mediatic slant. The problem of this analysis was born from the observation of regular points in the discursive architecture of these testimonials, when was identified the existing relation force between the sacred and the profane, everyday practices. During six months, analysis of the empirical material, we found some effects of the senses on the testimonials, as the dialectic structure and the need for denuding a precarious past, an engagement to shield the figure of Macedo and the UCKG towards society; a update of a crusade against other religions; and the presence of certain sensuality in self-deprecation of the deponents, and an unequal relation of forces (sacred and profane) in the construction of truth. In order of succeeding in this investigation, we used the theoretical and methodological assumptions of Analysis of French Discourse (AD), denouncing the qualitative nature of the research. As a methodological principle, we still use transdisciplinarity, which validated some of our dialogues, especially with philosophy. The conception of discourse modeled by a media support and transpassed by the subject(s) and story (ies) characterized the perspective of the research

Efeitos da previdência rural na agricultura familiar da microrregião Serra de São Miguel - RN

The objective of the present work is to verify the effects of Rural Social welfare in the family agriculture of the microrregião Serra de São Miguel-RN. The study based on available bibliography on the theme, in secondary data and in a rising amostral accomplished in three municipal districts (Encanto, São Miguel and Riacho de Santana) of the microrregião. The universe of the study was the establishments of the family agriculture appeared in the Agricultural Census of 2006, in those municipal districts. The unit of considered analysis was the rural family, with the interviews being applied close to the farmers' families with and without retired rural. The sample was of 94 present families in the family establishments. The results demonstrate that the Rural Precaution reaches a significant covering degree in the rural area of the researched municipal districts, with an average of 1,57 beneficiaries for home in the families with retired. The data of the research attest that the family agriculture in the microrregião Serra de São Miguel-RN it has few favorable conditions for his/her development, once, besides the shortage of lands and of the climatic factor of the area, the returned public politics the family farmers' totality - like PRONAF and PAA -, it has been unable to give effective answers for the improvement of the life conditions in the rural way, have seen the minimum amount of families reached by those politics, be in function of the drawing or of the atmosphere where they are done. In this context, he/she stands out the importance of the Rural Precaution that, in function of the application of the constitutional devices that you/they guaranteed his/her universalization, it has been the only relevant public politics that, in fact, it has been reaching her/it all their beneficiary potentials. Given the general situation of the family agriculture of the microrregião and of the specific characteristics of the researched family establishments, the hypothesis was corroborated that the rural retirement doesn't contribute directly to the increase / making possible of the family agriculture. In spite of 57,4% of the families with retired have declared to use resources of the retirement in the costing of the rural activity carried out by the family, the annual medium value of the expense just located around 7,02% of the annual value of the retirements gained by the families in the year of 2010. Data the low levels in that the social reproduction of the great majority of the family establishments of the microrregião, the maintenance of the families is operated represents the main destiny of the resources precautions. It was also confirmed the hypothesis that the Rural Precaution constitutes the main monetary contribution of the families with retired. For more than 93% of the families with retired, the retirements doing 50% or more of the total of the family monetary income, and in the composition of the rural income of the families with retired and pensioners, the originating from income the rural retirements are equal to 65,24% of the total of the annual income obtained by the families. It is ended, because, that the rural precaution, given to the adversities for the development of the family agriculture, of the operational inefficacy of the public politics and of the few opportunities of generation of existent income in the local savings, it is the main responsible for the reduction of the poverty and, consequently, for the improvements of the conditions of life of the families of and with seniors in the rural way of the microrregião Serra de São Miguel-RN

Efeitos de interface em bicamadas magnéticas acopladas

We have developed a theoretical study of magnetic bilayers composed by a ferromagnetic film grown in direct contact on an antiferromagnetic one. We have investigated the interface effects in this systems due to the interfilms coupling. We describe the interface effects by a Heisenberg like coupling with an additional unidirectional anisotropy. In the first approach we assume that the magnetic layers are thick enough to be described by the bulk parameters and they are coupled through the interaction between the magnetic moments located at the interface. We use this approach to calculate the modified dynamical response of each material. We use the magnetic permeability of the layers (with corrections introduced by interface interactions) to obtain a correlation between the interface characteristics and the physical behavior of the magnetic excitations propagating in the system. In the second model, we calculated an effective susceptibility of the system considering a nearly microscopical approach. The dynamic response obtained by this approach was used to study the modifications in the spectrum of the polaritons and its consequences on the attenuated total reflection (ATR). In addition, we have calculated the oblique reflectivity. We compare our result with those obtained for the dispersion relation of the magnetostatic modes in these systems

Propriedades ópticas de nanocristais de SiGe: efeitos de dopagem e desordem

We have used ab initio calculations to investigate the electronic structure of SiGe based nanocrystals (NC s). This work is divided in three parts. In the first one, we focus the excitonic properties of Si(core)/Ge(shell) and Ge(core)/Si(shell) nanocrystals. We also estimate the changes induced by the effect of strain the electronic structure. We show that Ge/Si (Si/Ge) NC s exhibits type II confinement in the conduction (valence) band. The estimated potential barriers for electrons and holes are 0.16 eV (0.34 eV) and 0.64 eV (0.62 eV) for Si/Ge (Ge/Si) NC s. In contradiction to the expected long recombination lifetimes in type II systems, we found that the recombination lifetime of Ge/Si NC s (τR = 13.39μs) is more than one order of magnitude faster than in Si/Ge NC s (τR = 191.84μs). In the second part, we investigate alloyed Si1−xGex NC s in which Ge atoms are randomly positioned. We show that the optical gaps and electron-hole binding energies decrease linearly with x, while the exciton exchange energy increases with x due to the increase of the spatial extent of the electron and hole wave functions. This also increases the electron-hole wave functions overlap, leading to recombination lifetimes that are very sensitive to the Ge content. Finally, we investigate the radiative transitions in Pand B-doped Si nanocrystals. Our NC sizes range between 1.4 and 1.8 nm of diameters. Using a three-levels model, we show that the radiative lifetimes and oscillator strengths of the transitions between the conduction and the impurity bands, as well as the transitions between the impurity and the valence bands are strongly affected by the impurity position. On the other hand, the direct conduction-to-valence band decay is practically unchanged due to the presence of the impurity

Efeitos de campos aleatórios e de anisotropias em vidros de spins

Ising and m-vector spin-glass models are studied, in the limit of infinite-range in-teractions, through the replica method. First, the m-vector spin glass, in the presence of an external uniform magnetic field, as well as of uniaxial anisotropy fields, is consi-dered. The effects of the anisotropics on the phase diagrams, and in particular, on the Gabay-Toulouse line, which signals the transverse spin-glass ordering, are investigated. The changes in the Gabay-Toulouse line, due to the presence of anisotropy fields which favor spin orientations along the Cartesian axes (m = 2: planar anisotropy; m = 3: cubic anisotropy), are also studied. The antiferromagnetic Ising spin glass, in the presence of uniform and Gaussian random magnetic fields, is investigated through a two-sublattice generalization of the Sherrington-Kirpaktrick model. The effects of the magnetic-field randomness on the phase diagrams of the model are analysed. Some confrontations of the present results with experimental observations available in the literature are discussed

Teoria cinética não extensiva: efeitos físicos em gases e plasmas

The standard kinetic theory for a nonrelativistic diluted gas is generalized in the spirit of the nonextensive statistic distribution introduced by Tsallis. The new formalism depends on an arbitrary q parameter measuring the degree of nonextensivity. In the limit q = 1, the extensive Maxwell-Boltzmann theory is recovered. Starting from a purely kinetic deduction of the velocity q-distribution function, the Boltzmann H-teorem is generalized for including the possibility of nonextensive out of equilibrium effects. Based on this investigation, it is proved that Tsallis' distribution is the necessary and sufficient condition defining a thermodynamic equilibrium state in the nonextensive context. This result follows naturally from the generalized transport equation and also from the extended H-theorem. Two physical applications of the nonextensive effects have been considered. Closed analytic expressions were obtained for the Doppler broadening of spectral lines from an excited gas, as well as, for the dispersion relations describing the eletrostatic oscillations in a diluted electronic plasma. In the later case, a comparison with the experimental results strongly suggests a Tsallis distribution with the q parameter smaller than unity. A complementary study is related to the thermodynamic behavior of a relativistic imperfect simple fluid. Using nonequilibrium thermodynamics, we show how the basic primary variables, namely: the energy momentum tensor, the particle and entropy fluxes depend on the several dissipative processes present in the fluid. The temperature variation law for this moving imperfect fluid is also obtained, and the Eckart and Landau-Lifshitz formulations are recovered as particular cases

Efeitos de acoplamentos biquadráticos e campos aleatórios em vidros de spins

In this work we have studied the effects of random biquadratic and random fields in spin-glass models using the replica method. The effect of a random biquadratic coupling was studied in two spin-1 spin-glass models: in one case the interactions occur between pairs of spins, whereas in the second one the interactions occur between p spins and the limit p > oo is considered. Both couplings (spin glass and biquadratic) have zero-mean Gaussian probability distributions. In the first model, the replica-symmetric assumption reveals that the system presents two pha¬ses, namely, paramagnetic and spin-glass, separated by a continuous transition line. The stability analysis of the replica-symmetric solution yields, besides the usual instability associated with the spin-glass ordering, a new phase due to the random biquadratic cou¬plings between the spins. For the case p oo, the replica-symmetric assumption yields again only two phases, namely, paramagnetic and quadrupolar. In both these phases the spin-glass parameter is zero. Besides, it is shown that they are stable under the Almeida-Thouless stability analysis. One of them presents negative entropy at low temperatures. We developed one step of replica simmetry breaking and noticed that a new phase, the biquadratic glass phase, emerge. In this way we have obtained the correct phase diagram, with.three first-order transition lines. These lines merges in a common triple point. The effects of random fields were studied in the Sherrington-Kirkpatrick model consi¬dered in the presence of an external random magnetic field following a trimodal distribu¬tion {P{hi) = p+S(hi - h0) +Po${hi) +pS(hi + h0))- It is shown that the border of the ferromagnetic phase may present, for conveniently chosen values of p0 and hQ, first-order phase transitions, as well as tricritical points at finite temperatures. It is verified that the first-order phase transitions are directly related to the dilution in the fields: the extensions of these transitions are reduced for increasing values of po- In fact, the threshold value pg, above which all phase transitions are continuous, is calculated analytically. The stability analysis of the replica-symmetric solution is performed and the regions of validity of such a solution are identified

Efeitos interfaciais em heteroestruturas quânticas nô-abruptas: GaAs/ALxGa1-xAs

Um minuncioso estudo das propriedades de confinamento em heterostructuras bidimensionais(poços quânticos) GaAs/AlxGa1_xAs, com interfaces graduais é realizado. Um modelo teórico que represente bem a variação da fração molar do alumínio nas interfaces, resultante do aparecimento de micro-rugosidades e ilhas durante os processos de crescimento e recozimento pós-crescimento da amostra, é elaborado. Vários perfis desta fração molar de alumínio nas interfaces são considerados. Soluções analíticas da equação de Schrodinger, na aproximação da massa efetiva constatne nas interfaces, resultando em equações transcendentais, que possibilitam a obtenção dos níveis de energia dos portadores, decorrentes do seu confinamento quântico, são apresentadas. Energias de ligação e de confinamento de excitons 2D, utilizando-se um método analítico e numerérico e a aproximação do potencial efetivo, são também calculadas. Resultados numéricos para os níveis de energia dos portadores e para as energias de ligação e de confinamento dos excitons 2D, em poços quânticos GaAs/Al0.35Ga0.65As não-abruptos, sem e com a presença de campo elétrico aplicado para vários perfis interfaciais da fração de molar, são mostrados. Para a obtenção desses resultados, faz-se uso do método dos degraus múltiplos e da técnica da matriz de transferência, e adota-se, como operador de energia cinética, o de Ben-Daniel e Duque para uma massa efetiva dependente da posição. Conclui-se que um modelo que leva em conta a existência de interfaces não-abruptas e seus diversos perfis é indispensável para uma melhor descrição das propriedades opto-eletrônicas de poços quânticos GaAs/AlxGa1-xAs, enquanto que a aproximação das interfaces abruptas apresenta-se bastante limitada