This paper explored the effect of adding organic fibers from either bamboo or sugarcane on the mechanical properties of concrete. Cylindrical and prismatic specimens were made containing 2% and 5% v/w (volume to weight) of vegetable fibers to concrete. Following 28 days of curing period, the samples were evaluated for compressive strength, tensile strength using diametric compression, tensile strength during bending and static modulus. It was discovered that all concretes produced met the minimum strength of 20 MPa recommended by NBR 6118 for structural purposes, and it was observed an increase of the compressive strength on the specimens with addition of organic fibers. Moreover, an increase in the compressive strength was observed in the specimens with fiber addition, although no significant variation of water absorption was noticed when compared with the standard concrete. In conclusion, the concrete containing 2% v/w of bamboo fibers showed better mechanical strength and static modulus of elasticity when compared to both concrete with sugar cane fibers addition and the concrete without any additional fibers.
Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Friction Butt Welding between 6351-T6 Aluminum Alloy and SAE 1020 Steel Assisted by Electromagnetic InductionAbstract: Friction welding has become interesting in terms of its application. In this context, this paper aimed to evaluate the effect of preheating the conventional friction butt welding between the aluminum alloy AA 6351-T6 and low-carbon steel SAE 1020. An adapted and instrumented drill was applied to make dissimilar joints. Welding was done under two conditions: without preheating and with electromagnetically induced preheating to about 350°C. The welding parameters, with the exception of friction time, were kept constant for both conditions because a new variable was introduced to the process, the preheating temperature. The welding characterisation was analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). Vickers microhardness and traction testing were used to evaluate the welding mechanical strength. The results obtained shown that preheating application decreases by half the total time of the process. The SEM-EDX analysis showed that there was interdiffusion between iron and aluminum. For both welding conditions, the rupture occurred on the bonding interface of the specimens. The mechanical strength of the welds without preheating was of the order of 134 MPa and 113 MPa for welds with preheating.Key-words: Friction welding; Dissimilar materials; Electromagnetic induction. IntroduçãoA soldagem de materiais dissimilares como o alumínio e o aço desperta grande interesse na indústria do transporte. A busca por materiais mais leves com intuito de reduzir o peso nas estruturas veiculares é alvo de frequente pesquisa, em especial na indústria automobilística [1]. No entanto, a união desses materiais é um grande desafio, pois eles possuem propriedades mecânicas e térmicas muito distintas, e quando soldados pelos processos de fusão formam quantidade apreciável de compostos intermetálicos frágeis (CIM), os quais reduzem a resistência da solda [2,3].Nesse cenário, uma alternativa para soldagem de materiais dissimilares são os métodos de união no estado sólido. Esses processos são caracterizados por ocorrerem em temperaturas mais baixas, sem que haja fusão dos metais de base, logo, a formação de fases intermetálicas é reduzida [4]. Dentre os processos no estado sólido, os métodos de soldagem por fricção são os que têm sido mais utilizados na união de dissimilares [5], como a união de alumínio e aço.
ResumoEste trabalho objetiva o estudo da influência da adição de fibras vegetais de bambu e cana-deaçúcar nas propriedades mecânicas do concreto. Para este trabalho foram confeccionados corpos-de-prova cilíndricos e prismáticos nos quais foram adicionados 2% e 5% em volume das fibras à massa do concreto. Após a cura, conforme NBR 5738 (2003) [1], os mesmos foram testados via ensaios de resistência à compressão conforme NBR 5739 (2007) [2], resistência à tração por compressão diametral, conforme NBR 7222 (2011) [3], resistência à tração na flexão conforme NBR 12142 (2010) [4] e módulo de elasticidade estático, conforme NBR 8522 (2008) [5]. Verificou-se após os testes que todos os concretos produzidos atenderam a resistência mínima a compressão de 20 MPa, recomendado pela NBR 6118 (2003) [6] para fins estruturais. Foi observado um aumento da resistência à compressão em relação à mistura padrão. O concreto com adição de fibras de bambu apresentou melhor resistência mecânica em relação ao concreto com adição das fibras de cana-de-açúcar e ao concreto sem adição. Abstract This work aimed to study the influence of the addition of vegetable fibers from bamboo and sugar cane on the mechanical properties of concrete. Implementing the same body-of-proof cylindrical and prismatic, which were added 2% to 5% per volume of fibers to the mass of concrete were made. After healing according to NBR 5738 (2003) [1], they were tested by testing of compressive resistance, according to NBR 5739 (2007) [2], tensile strength by diametric compression according to NBR 7222(2011) [3], tensile strength in bending according to NBR 12142 (2010) [4] and static modulus, according to NBR 8522(2008) [5]. It was found after testing all concretes produced met the minimum strength of 20 MPa recommended by NBR 6118 (2003) [6] for structural purposes. An increased compression resistance compared to the standard mixture was observed. The concrete with added bamboo fibers showed better mechanical strength compared to concrete with the addition of sugar cane sugar and plain concrete fibers.
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