The capacity to damp mechanical vibrations is one of the most important properties of granite-epoxy composites, even superior to the cast iron one. For this reason, these materials have been adopted for manufacturing of tool machine foundations and precision instruments. This work presents a study concerning the behavior of particulate composite beams, based on granite powder and epoxy, subjected to mechanical vibrations. Composite samples were prepared with different combinations of processing variables, like the weight fraction of epoxy in the mixture and size distributions of granite particles. The damping behavior of the material was investigated adopting the logarithmic decrement method. Samples, in the form of prismatic beams, were excited in the middle point and the output signal was measured in a point located at the extremity. The obtained results showed that composite samples, with weight fractions of about 80% of granite and 20% of epoxy, presented damping properties approximately three times greater than gray cast iron.
RESUMONeste trabalho, foi desenvolvido e caracterizado um compósito híbrido com memória de forma (SMAHC) por meio de uma análise teórico-experimental, no regime elástico, envolvendo a fabricação de vigas laminadas. A viga híbrida foi confeccionada em matriz de epóxi reforçada com fios de SMA e mantas de fibras picadas de vidro-E, com e sem bolsa de vácuo, de cura a frio e quente. A viga possui duas camadas de fios, com e sem roving, afastadas simetricamente o máximo possível do plano médio. Também foram produzidas vigas semelhantes, com e sem fios de aço galvanizado. Os módulos de elasticidade à flexão das vigas foram comparados aos módulos de simulações analíticas. O principal objetivo foi avaliar o aumento controlado da rigidez à flexão quando os fios de Ni-Ti (SMA) foram aquecidos, por efeito Joule, de 25°C a 69°C. As vigas de SMAHC, com fração volumétrica de Ni-Ti até 2%, tiveram um aumento no módulo de elasticidade de até 6,53%, apenas mudando a fase dos fios de martensita (25ºC) para austenita (69ºC). Palavras-chave:Liga Ni-Ti com memória de forma, viga SMAHC, comportamento termoelástico. ABSTRACTIn this paper, a shape memory alloy hybrid composite (SMAHC) was developed and characterized by theoretical and experimental analysis, in the elastic regime, involving the fabrication of laminated beams. The hybrid beam was made of epoxy matrix reinforced with SMA wires and E-glass chopped mat, with and without vacuum bag, as well as cold and hot curing. The two plies incorporating wires reinforced with roving or not, were symmetrically distributed along the thickness direction, as far as possible from the beam´s middle surface. Similar specimens were also produced, substituting the Ni-Ti (SMA) wires by cheaper galvanized steel wires. The flexure elasticity modulus of the beams was compared with those obtained analytically. The main objective was to evaluate the bending stiffness of the beams, when the temperature of the Ni-Ti wires was increased by Joule effect, from 25 ºC and 69 ºC. The SMAHC beams, with volume fraction of Ni-Ti up to 2%, presented an increase in the modulus, up to 6.53 %, by changing the phase of the wires, from the martensite (25 ºC) to the austenite (69 ºC).Keywords: Ni-Ti shape memory alloy, SMAHC beam, thermoelastic behavior. INTRODUÇÃOA crescente demanda da sociedade e uma conjuntura favorável para o desenvolvimento de novos materiais viabilizaram um importante avanço tecnológico na área de estruturas adaptativas [1]. Atualmente, em alguns sistemas estruturais existe uma forte tendência à substituição de atuadores convencionais como motores elétricos; atuadores hidráulicos e pneumáticos que aumentam a complexidade e inviabilizam grandes reduções no peso global, por componentes adaptativos [1]. Neste contexto, JANOCHA [2] destacou o importante papel dos materiais inteligentes na inovação tecnológica, atuando, simultaneamente, como sensores e/ou atuadores, bem como componentes estruturais. Dentre esses materiais, encontram-se os piezoelétricos, magnetorestritivos e ligas com memória de forma...
This investigation is concerned with the mechanical behavior of Shape Memory Alloy Hybrid Composite Beams (SMAHC), that consist of a circular bar of NiTi alloy incorporated in a 500 mm long cylindrical pipe of polypropylene (PP), with external diameter 50 mm and nominal wall thickness 7 mm, wound with a nylon/epoxy layer. The Ni-Ti alloy was characterized using: scanning electron microscopy (SEM); X-ray diffraction (XRD) and Differential thermal analysis (DSC). The nominal chemical composition of the alloy is 50.05 %Ni / 49.95%Ti, and the softer martensite is the predominant phase at room temperature. The approximate martensite (M) to Austenitic (A) phase transformation temperatures were Mstart = 32°C, Mfinal = 46°C, Astart = 38 °C and Afinal = 60°C. For temperature T<Mfinal, Ni-Ti bar presents 100% martensitic phase, whereas for T>Afinal it is fully converted in the Austenitic phase; and its elasticity modulus increases by a factor up to three times. This significant change in stiffness of Ni-Ti, without changing its mass, has motivated the application of such alloy in machine vibration control. The SMAHC beams were subjected to static three-point bending tests, in the elastic regime. Experimental results showed that, in average, at 21°C, the PP pipes effective flexural elastic modulus increased 112%, from 757 MPa to 1609 MPa, when the Ni-Ti bar and the external layer of nylon/epoxy were incorporated to the PP pipe, creating a smart beam. These last results indicate that the SMAHC beam can work as an adaptative structure.
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