Environmental effects on viscoelastic behavior of carbon fiber/PEKK thermoplastic composites

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Determinação da temperatura de referência T0 da curva mestre na região de transição dúctil-frágil de aços ARBL

Materiais estruturais utilizados no projeto de equipamentos e instalações industriais podem apresentar mudança de seu comportamento à fratura quando se varia a temperatura. Este tipo de comportamento caracteriza-se pela existência de uma curva de transição, onde 3 regiões ficam bem definidas: os patamares inferior e superior e a região de transição. Na região de transição, os resultados experimentais apresentam alto espalhamento e são bastante dependentes da geometria ensaiada. Para solucionar este problema, foi desenvolvido um modelo analítico experimental, que resultou na edição da norma ASTM E1921-97. O trabalho inclui um estudo da influência de diversas rotas de tratamentos térmicos aplicadas em um aço 4130 utilizado pela indústria aeronáutica, um aço de qualidade API utilizado pela indústria petrolífera e um aço da classe A516 atualmente utilizado pela indústria nacional de vasos de pressão, na microestrutura, propriedades mecânicas de tração e tenacidade à fratura. Os resultados mostraram que o aço 4130 A450, apresentou a melhor correlação entre resistência e tenacidade entre as microestruturas pesquisadas. Este comportamento deve estar associado a rota de tratamento térmico aplicada a esta condição. O tratamento de austêmpera possibilita a formação de bainita que, tradicionalmente é conhecida por apresentar elevados valores de tenacidade. O método proposto pela ASTM pode ser considerado viável para as diversas microestruturas pesquisadas ampliando a aplicação da metodologia que recomenda o ensaio apenas para aços ferríticos. No entanto, a metodologia da Curva Mestra em materiais tratados termicamente deve ser conduzida de forma a se estabelecer parâmetros que considerem as modificações microestruturais sofridas pelo material.

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

Estudo da propagação de trinca por fadiga sob carregamento de amplitude variável

For engineering projects that require high reliability levels, is often not enough know only physical and chemical material properties. It’s necessary understand the failure mode of these materials in operation to ensure security level in the project and establish more stringent criteria in the analysis of structural integrity. Due to this need, aircraft industry has been using aluminum alloys in their designs and projects. “Currently more than 70% of aircraft structures are built of high strength aluminum alloys among which stand out 7075-T6 and 2024-T3 alloys, which are considered basics for being used in the new alloys development.” (PASTOUKHOV & VOORWALD, 1995). Some years ago ALCOA develops Al 2524 alloy that has emerged as refinement of Al 2024 (Al, Cu. Mg) alloy, with purpose of improve fracture toughness and fatigue resistance on structural components. The present research addresses testing of fatigue crack propagation under variable amplitude loading for Al 2024 alloy, observing the interaction effects from application of overhead blocks and plastic zone at the crack tip and makes an analysis of fracture surface images

Avaliação da tenacidade à fratura em juntas soldadas circunferenciais de tubulações de processo

This work aims to analyze the toughness of a welded joint in the presence of a crack through the analysis of maximum tension the material can withstand the presence of this type of defect, since a discontinuity is likely to occur in this type of joint and its detection and its design is simple, using non-destructive testing techniques. The study will be conducted through the CTOD test - Crack-Tip Opening Displacement, with type specimens SE (B) - Single Edge Bend taken from a weld in the L-C position in relation to the length (longitudinal axis) of a test tube. The main idea is to simulate the welding conditions for the manufacture of industrial pipes, made in boiler shops (pipe-shop) within petrochemical plants. These pipes are often subject to operation with flammable and toxic subjected to high pressures and temperatures, where one can break the line can cause irreparable damage to the plant, the environment and the health of surrounding communities. With this study we evaluate whether the weld metal has the same properties as fracture toughness of the base material. This study shows the importance of using a qualified welding procedure for performing quality welds while maintaining the properties of the fracture toughness of the base metal. It was found from the results of tests using a welding procedure described for carrying out welding ensures mechanical properties very close to the base metal, which in terms of design is great, since one can ensure that the weld will the same characteristics of the base metal specified for the assembly of the pipe

Comportamento fractal de superfície da zona de estiramento em aço 300M temperado

Fracture surfaces are the fracture process marks, taht it is characterized by energy release guieded by failure mode. The fracture toughness express this energy em stress and strain terms in pre-cracked samples. The strectch zone is the characteristic region forms by the transition of fatigue fracture and final fracture and it width demonstrate the relation with failure energy release.The quantitative fractography is a broadly tool uses in failure surfaces characterization that it can point to a material’s aspect or a fracture process. The image processing works like an investigation tool, guinding a lot of studies in this area. In order to evaluate the characterization effectivity and it respectivity studies, it used 300M steel that it was thermal treated by an aeronautical process known and it characterized by tensile test and energy dispersive spectroscopy (EDS). The tensile test of this material, made by ASTM E8, allowed the head treatment effectivity confirmation, beyond of mechanics porperties determination. The EDS confirmed the material composition, beyond of base the discussion about fracture mechanism presence. The fracture toughness test has also made, that it works to obtain the fracture surfeaces studies below self-similarity and self-affinity approaches. In front of all the exposed it was possible to conclude that the fractal dimension works like a study parameter of fracture process, allowinf the relation of their values with changes in thickness, which interferes directly in material’s behaviour in fracture toughness approach

Fractografia quantitativa e o conceito de tenacidade à fratura para a análise do efeitodo choque térmicos em TiO2

The present study evaluated the use of semicircular bending test (SCB) as an alternative to conventional bending test to examine the effect of thermal shock. Still, studies the behavior of fracture surfaces generated by monofractal behavior analysis, which allows us to evaluate the contributions of the microstructure and the mechanical context in forming reliefs during the crack propagation. The fractal analysis is made from elevation maps obtained by reconstruction method by extension of the focus stacks of digital images acquired in microscope. The specimens used were samples semicircular pressed TiO2 (rutile) with and without heat shock, prepared for testing mode I loading. Were also produced, specimens in the form of bars for Weibull statistical analysis. From the three-point bending test, we found the variation of fracture toughness between the samples after the heat shock and natural condition. The SCB test was feasible for the analysis of thermal shock resistance. The results showed that the value of the fracture toughness decreases as the heat shock treatment

Caracterização de cerâmicas a base de nitreto de silício para aplicações estruturais

The need for development of new materials is a natural process in the companies’ technological point of view, seeking improvements in materials and processes. Specifically, among the materials, ceramic exhibit valuable properties, especially the covalent ceramics which have excellent properties for applications which requires the abrasion resistance, hardness, high temperatures, resistence, etc. being a material that has applications in several areas. Most studies are related to improvement of properties, specially fracture toughness that allows the expansion of its application. Among the most promising ceramic materials are silicon nitride (Si3N4) which has excellent properties. The goal of this work was the development and caracterization of Si3N4-based ceramics, doped with yttrium oxide (Y2O3), rar earth concentrate (CTR2O3) and cerium oxide (CeO2) in the same proportion for the evaluation of properties. The powders' mixtures were homogenized, dried and compressed under pressure uniaxial and isostatic. Sintering was carried out in 1850 ⁰C under pressure of 0,1MPa N2 for 1 h with a heating rate of 25 ⁰C / min and cooling in the furnace inertia. The characterizations were performed using Archimedes principle to relative density, weight loss by measuring before and after sintering, phase analysis by X-ray diffraction, microstructure by scanning electron microscope (SEM), hardness and fracture toughness by the method Vickers indentation. The results obtained showed relative density of 97-98%, Vickers hardness 17 to 19 GPa, fracture toughness 5.6 to 6.8 MPa.m1/2, with phases varying from α-SiAlON and β-Si3N4 depending the types of additives used. The results are promising for tribological applications and can be defined according to the types of additives to be used

Obtenção de rochas sintéticas a partir de resíduos de vidro comercial e pó de granito

Pós-graduação em Engenharia Mecânica - FEG

Efeito de protocolos de cimentação na carga de fratura para uma cerâmica de dissilicato de lítio

Pós-graduação em Odontologia Restauradora - ICT

Caracterização do fator de intensidade de tensão em corpos trincados através do método dos elementos finitos

The industry generally has sought materials with high mechanical resistance, low density, thermal stability and corrosion resistance. In the aerospace industry, for example, the use of aluminum alloys, such as Al 2024-T351 and Al 7075-T7351, have become essential. However, the use of these materials often do not resulted in a satisfactory performance of the component, since the presence of cracks can cause total rupture of the component, even with a tension below the yield stress of the material, unexpectedly. In this work, these aluminum alloys were analyzed and samples were modeled by the finite element method. Moreover, in the models were applied two different types of cracks, central and edge crack, a vertical force was applied to result in a tension 70% of the yield stress of the material analyzed. Through stress asymptotic distribution in the region near the crack tip were calculated the values of the stress intensity factors for each crack length, after the stress intensity factors characterized were compared graphically with the values of fracture toughness found in the available literature

Caracterização microestrutural e crescimento subcrítico de trincas em cerâmicas odontológicas

Pós-graduação em Odontologia Restauradora - ICT

Avaliação da resistência à fratura de próteses fixas temporárias reforçadas por uma malha experimental

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Influência da adição do nióbio no comportamento mecânico e microestrutural do aço SAE 6150

Pós-graduação em Engenharia Mecânica - FEG

Influência da espessura da infraestrutura em Zircônia (3Y-TZP)na resistência mecânica da porcelana de cobertura

Pós-graduação em Reabilitação Oral - FOAR