Abstract

Shape Memory Alloys (SMA) are smart metallic materials that have being increasingly studied due to their functional properties of recovering original shape by heating after pseudo plastic deformation and super elasticity. In this context, SMA helical springs can be used as actuators or sensors in several areas. This work aims to perform thermal and mechanical characterization of Ni-Ti SMA helical springs produced by investment casting process consisting of induction melting followed by centrifugal casting (ICC). Thermal characterization of the springs was performed by Electrical Resistance as a function of Temperature (ERT), while the mechanical characterizations in static and dynamic regimes were performed in an Instron Model E10000 machine. Results of thermal analysis by ERT showed that the helical Ni-Ti springs have phase transformation corresponding to the super elastic effect (SE) at room temperature (~23.5±0.5 °C). Reversible deformations under uniaxial tensile were of the order of 80% and dynamic tests showed that mechanical behavior vary according to the frequency and deformation amplitude. At last, it was verified that Ni-Ti SMA helical springs produced by ICC process present functional characteristics, which are suitable for super elastic applications such as springs manufactured by conventional processes.

Keywords: Helical springs; Shape memory alloys; Ni-Ti alloys; Investment casting