Fractografia quantitativa: correlação entre dimensão fractal e tenacidade à fratura em compósitos fibra de carbono/epóxi

The fracture surfaces express the sequence of events of energy release due to crack propagation by linking the relief of the fracture to the loading stresses. This study aims to evaluate the heterogeneity of the critical zone for the advancement of the crack along its entire length in a thermoset composite carbon fiber and epoxy matrix, fractured in DCB testing (Double Cantilever Beam) and ENF (End-Notched Flexure). Investigations were made from image stacks obtained by optical reflection of extended depth from focus reconstruction. The program NIH Image J was used to obtain elevation map and fully focused images of the fracture surface, whose topographies were quantitatively analyzed. The monofractal behavior for DCB samples was assessed as being heterogeneous along the crack front and along the crack for all the conditionings. For the samples fractured in ENF test, there was a strong positive correlation to the natural condition, considering the fibers at 0° for the monofractal dimension and structural dimension (Df and Ds). For fibers at 90° to crack propagation, there was a moderate positive correlation for the textural dimension of natural condition. However, for the samples under ultraviolet condition and those subjected to thermal cycles, there was no correlation between the fractal dimension and fracture toughness in mode II

Desenvolvimento de vasos digestores de amostra para microondas doméstico

The application of microwave radiation on the sample preparation has been expanding increasingly in areas involving decomposition by wet and dry roads, fusion, extraction, acceleration of chemical reactions, for example. Currently, the use of microwave ovens for analytical purposes are recognized for having excellent performance for organic and inorganic samples. In the international market there are several kinds of microwaves oven which adapt the varied purposes, however yet with elevated prices which incapacitate your use as routine equipment in laboratory. Thus, many researchers have been choosing for developing own projects of microwaves oven production or to use domestic oven for the laboratory, with or without adaptations. For the evaluation of the proposed method was used in the Kjeldahl methodology for determining total nitrogen in samples of crude protein, using a domestic microwave oven and a digester pot made up in TeflonTM and distillation by steam. Were made to adapt and characterization of a domestic microwave oven, the confeccion vessel digester and the metal support for the vessel. The accuracy of the proposed method was confirmed by comparison of two methods, the standard method for conventional heating and by the proposed method, with heating by microwave radiation through the calculated values of relative standard deviation analysis

Estudo da eficiência de reforços estruturais em vigas de concreto armado com o uso de chapas de aço coladas com resina epóxi: uma análise qualitativa

In civil engineering, a structure is the whole sustainment of a construction and, thus, it is important that it remains intact throughout its lifetime. An engineering construction must last for decades without losing its functionality. However its purpose may be altered and several times the original structure does not meet the new needs of use. Still, in new buildings, the functionality is altered due to possible flaws in execution and the structure, invariably does not reach the desired solicitation needs. In cases like this, the commonly adopted solutions are, basically, the demolishment followed by the reconstruction of the desired mold or the structural reinforcement. This second option, for long years, has not been put to practice due to certain factors such as the high costs for its implantation, use of inadequate reinforcement execution techniques, and the culture of people involved in the area regarding its use and, in this case, the option would always be the reconstruction. Thoughtout the years, some techniques were developed to allow the execution of structural reinforcements with low costs and in efficient ways. An interesting, fast, efficient and economical technique is the structural reinforcement through metal sheets put together with epoxy resin that can be applied in beams, slabs and pillars. In the present work the different behavior of beams reinforced with this technique. Steel is a very recommended material for these reinforcements due to its characteristics related to traction, compression and the effectiveness of the technique related to its cost. For the attachment the epoxy resin is recommended, since it allows the joining of two materials, in this case, steel and concrete. The efficiency of this union is so considerably high that it rarely produces any flaws in adherence and, normally, when it happens it is due to problems in the execution process, not in the union of materials

Comparação de compósitos obtidos via RTM de resina epóxi e fibra de carbono com e sem descontinuidade nos tecidos

Technology is growing interest in the use of composites, due to the requirement of lighter materials and more resistant, factors essential to meet the project specifications and reduce the operational cost. In the production of high performance structural composites, considering the aerospace criteria, the domestic industry has shown interest in the process of resin transfer molding (RTM) for reproducibility and low cost. This process is suitable for producing components of polymeric composites with relatively simple geometries, consistent thicknesses, high quality finish with no size limitations. The objective of this work was machined carbon steel to make a matched-die tooling for RTM and produce two composite plates of epoxy resin and carbon fiber fabric with and without induced discontinuities, which were compared towards their impregnation with ultrasound, their properties via tensile tests and thermal analysis. In ultrasonic inspection, it was found good impregnation of the preform of both composites. In the thermal analysis it was possible to check the degradation temperature of the composites, the glass transition temperature and it was found that the composites showed no effective cure cycles, but presented good performance in the tensile test when compared with aluminum alloy 7050 T7451 . The results showed that the injection strategy was appropriate since the laminate exhibited a good quality for the proposed application

WiMAX interoperabilidade mundial para acesso de microondas

This paper presents a technique dubbed WiMAX radio link, the IEEE 802.16 was completed in October 2001 and published on April 8, 2002 and is constantly updated, this technology specifies an interface for wireless metropolitan networks (WMAN) and is under control of the WiMAX Forum, which is a group of companies responsible for the dissipation of this technology in the world, the great benefit of this standard is to offer broadband Internet connection in areas where there is no infrastructure such as fiber optics that has a cost higher. The main purpose of this paper is to present the theoretical and technical characteristics of this technology for both the standard for fixed and mobile standard, regulation of frequency bands by the FCC and description of the physical layer, through to basic concepts are used in many other types of radio link and technologies have been adapted and updated for this little-known standard, allowing a greater range and speed, which are specified and differentiate these advancements is one of the contributions of the work done here. After the theoretical conceptualization stage, a real case study has been inserted in this work to demonstrate the effectiveness of this technology deployed. The idea of presenting this case study is linked to a better view of the use of standard in the market, nationwide

Cinética de degradação do sistema resina epóxi/fibra de carbono

With the increasing demand for electricity, the retraining of transmission lines is necessary despite environmental restrictions and crossings in densely populated areas to build new transmission and distribution lines. Solution is reuse the existent cables, replacing the old conductor cables for new cables with higher capacity power transmission, and control of sag installed. The increasing demand for electrical power has increased the electric current on the wires and therefore, it must bear out temperatures of 150°C or more, without the risk of the increasing sag beyond the established limits. In the case of long crossings or densely populated areas, sag is due to high weight of the cable on clearance. The cable type determines the weight, sag, height and the towers dimensions, which are the items that most influence the investment of the transmission line. Hence, to reduce both cost of investment and maintenance of the line, the use of a lighter cable can reduce both number and the height of the towers, with financial return on short and long term. Therefore, in order to increase the amount of transmitted energy and reduce the number of built towers and sag, is recommended in the current work substitute the current core material (steel or aluminium) for alternatives alloys or new materials, in this case a composite, which has low density, elevated stiffness (elasticity module), thus apply the pultruded carbon fiber with epoxy resin as matrix systems and perform the study of the kinetics of degradation by thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC), according to their respective standards

Processamento do compósito de fibra de capim-sapê / epóxi e avaliação da resistência à flexão “t” de Student

In recent years a great worldwide interest has arisen for the development of new technologies that enable the use of products with less environmental impact. The replacement of synthetic fiber plants is a possibility very important because this fiber is renewable, biodegradable and few cost and cause less environmental impact. Given the above, this work proposes to develop polymeric composites of epoxy resin and study the behavior of these materials. Both, the epoxy resin used as matrix in the manufacture of sapegrass fiber composite, as tree composites formed by: epoxy/unidirectional sapegrass long fiber, 75% epoxy/25% short fiber, by volume, and 80% epoxy/20% short fiber, by volume, were characterized by bending, and the composites produced with short fibers random were inspected by Optical Microscopy and Acoustics Inspection (C-Scan). For the analysis of the sapegrass fiber morphology, composites 75% epoxy/25% short fiber (sheet chopped) and 80% epoxy/20% short fiber images were obtained by optical microscope and the adhesion between polymer/fiber was visualized. As results, the flexural strength of composites epoxy/unidirectional long fibers, 75% epoxy/25% short fiber and 80% epoxy/20% short fiber were 70.36 MPa, 21.26 MPa, 25.07 MPa, respectively. Being that composite showed that the best results was made up of long fibers, because it had a value of higher flexural strength than other composites analyzed

Interferência eletromagnética em equipamentos de diatermia por microondas por aparelhos telefonia móvel celular GSM

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Avaliação do efeito ambiental nas propriedades mecânicas e viscoelásticas de compósitos híbridos de titânio/fibra de carbono/resina epóxi

Hybrid composites combining metal plates and laminates with continuous fiber reinforced polymer, called fiber-metal (CHMF), have been particularly attractive for aerospace applications, due mainly to their high mechanical strength and stiffness associated with low density. These laminates (CHMF) consist of a sandwich structure consisting of layers of polymer composites and metal plates, stacked alternately. This setting allows you to combine the best mechanical performance of polymer composites reinforced with long fibers, to the high toughness of metals. Environmental effects should always be considered in the design of structural components, because these materials in applications are submitted to the effects of moisture in the atmosphere, the large cyclical variations of temperature around 82 ° C to -56 ° C, and high effort mechanical. The specimens of fibermetal composite were prepared at EMBRAER with titanium plates and laminates of carbon fiber/epoxy resin. This study aims to evaluate the effect of different environmental conditions (water immersion, hygrothermal chamber and thermal shock) of laminate hybrid titanium/carbon fiber/epoxy resin. The effects of conditioning were evaluated by interlaminar shear tests - ILSS, tensile, and vibration free

Influência do condicionamento ambiental sobre as propriedades viscoelásticas de compósitos aramida/epóxi

The increasing application of structural composites in the aerospace industry is mainly due to its low specific weight coupled with its excellent mechanical properties when in service. As a result of climatic variations that pass the aircraft is of paramount importance to study the influence of weathering on this type of material when subjected to such changes. The purpose of this work is to evaluate the mechanical behavior of specimens of kevlar fiber /epoxy matrix composites, by dynamic mechanical thermal analysis (DMA) and interlaminar shear strength tests (ILSS), after passing through three environmental conditioning: saline fog, hygrothermal and ultraviolet radiation. From the results, we concluded that the laminate was molded supplied homogeneously, not presenting problems such as porosity, delaminations or cracks inside. After a period of 625 hours of exposure to hygrothermal conditioning, we observed a 1,2% maximum of absorption of moisture. Samples subjected to the conditioning by UV irradiation (600 hours) and salt spray showed a reduction of about 24,30% and 32,30%, respectively, on the shear strength (ILSS). In DMA analysis is not observed significant changes on the glass transition temperature. However, when considering the storage modulus of the samples conditioned by UV radiation (1200 hours), salt spray and hygrothermal conditioning there is an increase of 5,34% , 7,19% and 5,57% respectively

Flexão e análise dinâmico-mecânica de compósitos 5HS e NCF com resina epóxi monocomponente produzidos por RTM

In order to study resin distribution and homogeneity of composite laminates manufactured by RTM, it was used CYCOM 890 monolithic toughened epoxy as a matrix with two different configurations of intermediated modulus (IM) carbon fibers: Satin Weave (5HS) and non crimp fabric (NCF). The injection parameters were defined based on Thermo Gravimetric Analysis (TG), Differential Scanning Calorimetry (DSC) and rheological analysis. After processing the material, the resin/fiber impregnation was studied using ultrasonic test, Thermo Gravimetric Analysis, Differential Scanning Calorimetry, Dynamic Mechanical Analysis (DMA) and flexural tests. Therefore, it was able to observe an internal residual stress during the cooling process in both laminates, higher in the composite using NCF fabric due to the lack of symmetry, although a good proportion of fiber/matrix has been verified by the lower values of flexural modulus deviation. The DMA enabled the visualization of glass transition and its association with the inter and intra molecular interaction and movement, in which the NCF composite presented better permeability due to the lowest temperature of glass transition, when compared to the Satin Weave composite

Efeito do tratamento alcalino da fibra na resistência mecânica do compósito epóxi/capim-sapê

Due to growing concerns for reducing environmental damage caused by the use of non-renewable raw materials, there is a growing demand for research related to aggregate technology with environmental preservation. Thus, the use of non-renewable materials and less aggressive materials has been gaining attention. About composite materials, the exchange of synthetic fibers by natural fibers, especially vegetable fiber as reinforcement, has been increasing, due to its physical-chemical properties such as mechanical strength, nontoxic, low cost, low density, processing flexibility, non-abrasive to the process equipment, requiring simple surface treatments, etc. This objective was to process composites reinforced with long fibers of sapegrass in epoxy matrix and characterize the composites through mechanical tests. Three groups of composites were prepared according to the treatment received by the reinforcement: without treatment, alkali treatment at concentration of 5% w/v and alkali treatment at 10% w/v concentration. The materials were analyzed by tensile and flexural, and tests also optical microscopy and scanning electron microscopy (SEM). The results were statistically analyzed. As the main result, the alkali treatment of 5% in the sapegrass fibers increases the tensile and flexural strength, as a consequence of the improve adhesion between matrix and reinforcement

Fadiga em compósitos 5HS carbono/epóxi processados via RTM: relação entre cargas axiais no plano e modos de delaminação

Pós-graduação em Engenharia Mecânica - FEG

Monitoramento de danos estruturais utilizando sensores de nanocompósitos

Pós-graduação em Engenharia Mecânica - FEIS

Preparação e caracterização de nanocompósitos de Fe@SiO2, Fe@Fe3O4 e Fe3O4@PNIPAM

Pós-graduação em Química - IQ