The mechanical properties of steel depend strongly on chemical composition and the parameters used during thermomechanical processing. Understanding how each variable affects such properties is indispensable for obtaining high-quality steel products at a lower cost. However, the large number of variables involved in the manufacturing process makes this a difficult task. It is possible to use statistical tools combined with predictive modelling to identify the most relevant parameters and to create a mathematical function that can adequately describe the mechanical properties of the rebar from the selected input-output pairs. In the present work, information about the chemical composition and the thermomechanical processing variables were collected at steel mills and used to predict the mechanical properties of rebar using linear regression analysis and an artificial neural networks approach. The coefficient of determination between the measured and estimated values was calculated for yield strength (YS), ultimate tensile strength (UTS), UTS/YS ratio, and percent elongation. The estimation performed using the artificial neural network was better than the one calculated by linear regression analysis for all four properties studied. The results showed that an artificial neural network can be useful in evaluating and choosing the most adequate parameters to achieve the desired steel properties.
Over the years the electricity generation based on alternative energy systems applied to remote regions has been increased in Brazil, mainly due to the lack of conventional electric grid structure, specially in places as the Amazon. In this scenario, it is wellknown that the wind power technology attracts great attention because the wind potential available in the country coast is really representative, leading this sort of technology to an important position into the local energy matrix. However, it is necessary to search new technology developments in order to get efficient turbines applied to isolated regions, where usually low wind speeds are found. The small wind systems using diffuser appear as a relevant alternative, which can be adapted to the characteristics of low wind speed conditions. Hence, in this work, an experimental study on diffusers using three different airfoils (SELIG 1223, EPPLER 423 and NACA 4412) was performed. The goal was to evaluate the influence of the diffuser velocity ratio on the classical theory (axial moment theory with diffuser), in order to show the increasing efficiency typically noticed in studies on Diffuser-Augmented Wind Turbines (DAWTs). In this regard, it was concluded that the wind speed increases under diffuser effect even whether the geometric model is composed by two straight parallel airfoils. Consequently, a DAWT might be adapted to low wind speeds usually found in northern Brazil.
Resumo O atendimento das propriedades mecânicas das barras de aço produzidas via o processo de laminação a quente é um ponto indiscutível no quesito qualidade do material, e também uma obrigatoriedade. Para que seja possível esse atendimento das propriedades, existem alguns meios que são utilizados de acordo com o layout do processo ou a composição química do aço, como o Thermex®, que consiste de um resfriamento brusco na área superficial das barras de aço, através do contato com um turbilhão de água por um intervalo curto de tempo. Esse resfriamento superficial brusco faz com que a estrutura cristalina do aço sofra deformações e forme uma estrutura martensítica superficial, bastante resistente e dura. Dessa forma, o presente trabalho utiliza-se de técnicas para caracterização de fases, ensaios mecânicos de tração e microdureza, para identificar e analisar a influência da martensita, formada através do processo Thermex®, nas propriedades mecânicas das barras de aço. Palavras-chave:Laminação a quente; Martensita; Thermex; Barras de aço.
ResumoO presente estudo tem como objetivo avaliar a resistência à corrosão de dois aços alto teor de Manganês com relação à liga 9% Níquel em solução eletrólito 0,001M de NaCl. Para esta pesquisa foram utilizados dois aços com teores de Manganês de 22%, 27% e uma liga 9% Níquel que é amplamente utilizada na indústria petroquímica. Os ensaios realizados para comparação da resistência à corrosão foram o monitoramento do potencial de circuito aberto (OCP) e polarização linear anódica. Foi escolhida a solução de NaCl pela presença da maioria dos tanques de armazenamento e transporte de gás natural se localizarem próximos à região marítima portuária. Foram utilizadas as técnicas de Microscopia Eletrônica de Varredura (MEV), Microscopia óptica e Espectroscopia de Energia Dispersiva de Raios-X (EDS) para a caracterização dos produtos de corrosão. Os resultados obtidos mostraram que os aços alto Manganês apresentaram valores similares de resistência à corrosão, mas ainda inferiores em relação ao aço 9% Níquel. Palavras-chave:Corrosão; Aço Alto Manganês; Aço 9% Níquel, Gás Natural.
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