Verônica Scarpini Cândido

Fabrication of Artificial Stone from Marble Residue by Resin Transfer Molding

Artificial stones have recently been worldwide commercialized but are still not produced in Brazil. This has motivated efforts for the local fabrication of a similar stone. Thus, an artificial ornamental stone (AOS) was fabricated by means of a resin transfer molding (RTM) process. Marble residues were placed inside a hermetic mold under vacuum. A still fluid polyester resin, already mixed with a catalyst and a thinner, was injected into the mold. After curing, the density and water absorption of the AOS were evaluated. The material was also subjected to both compression and bend mechanical tests. The AOS microstructure was analyzed by scanning electron microscopy, which was then related to the obtained physical and mechanical properties.

Characterization of Epoxy Matrix Composites Incorporated with Sugarcane Bagasse Fibers

Sugarcane bagasse is a typical waste generated in the production of sugarcane and ethanol. This agro-industrial waste is commonly used as fuel in the industry boiler for the steam and energy generation. However, part of the bagasse waste is disposed and may pollute the environment. The fibers extracted from the sugarcane bagasse have been considered as addition to polymeric composites. In the present work epoxy composites incorporated with 30% in volume of continuous sugarcane bagasse fibers were evaluated in terms of their mechanical properties. As compared to the neat epoxy, the bagasse fiber displayed an increase in elastic modulus but a decrease in strength and ductility. The analysis of the composite microstructure by scanning electron microscopy revealed flaws and pores that could justify these preliminary obtained results.

Formulation and Characterization of Polypropylene Composites Alkali Treated Bagasse Fiber

Polymer composites reinforced with natural fiber that were obtained as industrial wastes, are of particular interest due to both the environmental benefits and economical advantages. In the present work sugarcane bagasse fibers, obtained as a waste from sugar and ethanol production, were incorporated in an amount of 25wt% into a polypropylene matrix. These fibers were previously alkali treated with NaOH to improve their adherence to the composite matrix. Thermal analyses were conducted in both types of composites, with untreated fibers and with alkali treated fiber. The result indicated that the alkali treatment improves the compatibility between the bagasse fiber and the polypropylene matrix, which then provides more thermal resistance.

Dynamic-Mechanical Performance of Sponge Gourd Fiber Reinforced Polyester Composites

The engineering applications of natural materials to replace synthetic ones has marked increased in past decades owing to environmental, societal and economical issues. Among these natural materials, the lignocellulosic fibers obtained from plants are successfully being used as polymer composites reinforcement is substitution of the traditional glass fiber. One relatively unknown lignocellulosic fiber with potential for composite reinforcement is that extracted from the sponge gourd. In the present work, the dynamic-mechanical performance of unsaturated orthophtalic polyester matrix composites was evaluated for different volume fractions of continuous and aligned sponge gourd fiber reinforcement. The results revealed that an increasing incorporation of sponge gourd fiber improved the composite viscoelastic stiffness, while decreasing its glass transition temperature.

Addition of Ornamental Stone Waste to Improve Distinct Formulations of Clayey Ceramics

Clayey ceramics are being traditionally fabricated in the municipal area of Campos dos Goytacazes, Rio de Janeiro, Brazil, by a mixture of different clays to attend the technical specifications. In several cases, the simple mixture of clays is not able to grantee the required properties for a given fired ceramic product. In the present work, distinct formulation using two types of clays, with or without the addition of ornamental stone waste, were investigated for the effect on the technical properties of ceramics fired at 950°C. The results indicated that at this firing temperature the ornamental stone waste was not able to act as a fluxing agent and only the linear shrinkage was effectively improved.

CARACTERIZAÇÃO MECÂNICA E MICROESTRUTURAL DE CONCRETO GEO POLIMÉRICO SUBMETIDO À FADIGA

Verônica Scarpini Cândido Alisson Clay Rios da Silva Fernanda Santos da Luz Sergio Neves Monteiro Resumo Cimentos provindos de reações álcali-ativadas abrem novas oportunidades para o futuro, como a utilização de polímeros inorgânicos, conhecidos como geopolímeros. Estes materiais são considerados ecologicamente corretos, pois seu processo de fabricação não envolve a emissão de CO2 e é possível utilizar resíduos industriais como matéria prima. Neste trabalho, foi desenvolvido um concreto de cimento geopolimérico (CCG) e sua resistência à fadiga foi comparada com outro concreto correspondente de cimento Portland (CCP). Foram utilizados alguns parâmetros fixos na dosagem de ambos os concretos, como consumo de aglomerantes, relação água/aglomerante e teor de argamassa. O estudo foi realizado por meio de ensaios dinâmicos, avaliando os efeitos de diferentes níveis de tensões, máximas e mínimas, e frequência aplicada. Os resultados de fadiga nas diversas variações realizadas mostraram um melhor desempenho ao comportamento em fadiga do CCG em relação ao CCP. Na análise microestrutural foi observada uma melhor aderência matriz/agregado no CCG quando comparado com o CCP, o que pode explicar sua maior resistência perante a fadiga. Palavras-chave: Geopolímero; Concreto geopolimérico; Fadiga.

The Effect of Phase Transformation on the Tensile Fracture of Austenitic Stainless Steel

The tensile fracture of two austenitic stainless steels with different degrees of stability for low temperature strain induced martensitic transformation was investigated. A stable AISI type 310 stainless steel displayed typical tensile stress-strain curves with decreasing work hardening rate at temperatures in the interval of 25 to-196°C, in which no martensitic transformation occurred. By contrast, a metastable type 302 stainless steel with martensitic transformation from 25 to-196°C showed a range of plastic deformation with increasing work hardening rate. The fracture of the stable 310 steel presented the characteristic cup and cone ductile aspect with micro dimples and sparse evidence of intergranular cracks. On the contrary, the martensitic transformation in the metastable 302 steel causes a neckless fracture with generally brittle appearance, despite the relatively high strain attained at fracture. At-80 and-196°C, associated with higher amount of transformed martensite, the fracture surface was covered with micro-craters formed around inclusions enveloped by thin strain induced martensite lamellae.

Influence of Martensitic Transformation on the Fatigue of Low Temperature Metastable Stainless Steel

The influence of martensitic transformation on the fatigue of AISI 316 type stainless steel, which presents a low temperature metastable behavior, was investigated at-196 and 25°C. Fatigue tests were conducted on both annealed and cold worked conditions. The results from stress versus number of cycles curves showed that the fatigue resistance is not affected by the “dynamically” induced martensite in annealed specimens at both temperatures. On the contrary, the previously induced “static” martensite in work hardened specimens contributes to decrease the fatigue resistance limit. The contribution of the martensite stability is discussed.

Special Effects in Deformation Mechanism Maps for Austenitic Stainless Steels

The domains of the existence of deformation mechanisms in a map associated with phase transformation and mechanical effects related to aging processes were investigated in austenitic stainless steels. It was also discussed the participation of grain boundary sliding, both as an additional deformation mechanism and a damage accumulation process. A prediction analysis for two typical high temperature engineering systems was attempted based on the map information. This prediction indicates the possibility of grain boundary sliding and creep strain jumps to interfere with the expected operational life of components in these systems operating at high temperatures.

Tensile Behavior of Epoxy Composites Reinforced with Thinner Fibers of Sugarcane Bagasse

Surgarcane bagasse is an industrial waste partially used as fuel for sugar and ethanol processing boilers. A considerably amount of bagasse, however, is disposed into the environment without a practical use. Research works are investigating the possible application of the fibers of these bagasse waste as reinforcement of polymer composites. Thus, the aim of the present work was to evaluate the mechanical behavior of epoxy composites reinforced with different volume fractions, up to 30 %, of thinner sugarcane bagasse fibers. Specimens with aligned fibers were tensile tested at room temperature and the ultimate strength, elastic modulus and total deformation results indicated a superior performance as compared to composites reinforcement with average thicker bagasse fibers