Caracterização termomecânica de um fio atuador de liga com memória de forma de NI-TI

• Autor(a) principal: Lima, Walber Medeiros
• Data de Publicação: 2017
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/123456789/11573
• topic: Ligas com memória de forma; Ciclagem térmica; Estabilidade funcional; Shape memory alloy; Thermal cycles; Functional stability; CNPQ::ENGENHARIAS::ENGENHARIA MECANICA

Ni-Ti shape memory alloys (SMA) have been the target of several studies because of their excellent physical and mechanical properties. For this reason, the alloys are used in various applications such as sensor and/or actuator. The amount of recoverable deformation and the functional stability of the shape memory effect are two of the most important characteristics in the development of applications with SMA. The functional stability of a LMF actuator has been studied through thermal cycles between the temperature range at which deformation and shape recovery occur, having an indispensable purpose when it comes to the use of memory materials in practical applications. In this sense, the study of the thermomechanical characterization of a Ni-Ti SMA actuator wire subjected to a thermomechanical cycle (training and cycling) by Joule effect, applying an alternating electric current of the square type, which will result in an important scientific contribution and technological, because for practical use is expected the functional stabilization of the material, otherwise, probably in a few work cycles the application would fail due to residual deformation (elongation) of the material. In the study, a mechanical apparatus was used together with an electronic instrumentation and a graphical interface to obtain the experimental results and then a microstructural analysis by scanning electron microscopy in order to analyze the longitudinal section of the samples. Experimental results of the characterization showed that samples with better stability both in elongation and in reversible deformation (0.39% or 0.5%) are observed in the samples submitted to a thermomechanical training of 100 MPa and then to a cycling with a load of 100 or 150 MPa and with temperature below the final temperature of the austenite (Af), respectively, because they presented a lower nucleation of cracks in the surface and center regions.