Resumo A soldagem por fricção tem tomado um rumo muito interessante. O presente trabalho teve como objetivo avaliar o efeito do preaquecimento na soldagem por fricção convencional entre a liga de alumínio AA 6351-T6 e o aço SAE 1020. Uma furadeira de coluna foi adaptada para produzir as juntas dissimilares. As soldagens foram realizadas em duas condições: sem preaquecimento e com preaquecimento de 350°C induzido eletromagneticamente. Os parâmetros de soldagem, com exceção do tempo de fricção foram mantidos constantes, pois uma nova variável foi inserida ao processo, a temperatura de preaquecimento. A caracterização microestrutural da solda foi realizada por MO e MEV. A resistência mecânica foi avaliada pelos ensaios de microdureza Vickers e tração. Os resultados mostraram que a utilização do preaquecimento diminui o tempo total de processo pela metade. A análise via MEV-EDX evidenciou que houve interdifusão entre o ferro e o alumínio. Para as duas condições de soldagem, a ruptura ocorreu na interface de ligação. A resistência mecânica das soldas sem preaquecimento foi da ordem de 134 MPa e 113 MPa para as soldas com preaquecimento.

Abstract 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.

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.