Smartflex NiTi Wires for Shape Memory Actuators

Abstract

Shape Memory Alloys (SMAs) are active metallic materials classified nowadays as “smart” or “intelligent” materials. One of the main areas of interest is that of actuators. The use of Shape Memory Alloys in actuators offers the opportunity to develop robust, simple and lightweight elements that can represent an alternative to electro-magnetic actuators commonly used in several fields of industrial applications, such as automotive, appliances, etc. The obvious simplicity of mechanical design and minimum number of moved parts is amazing for an actuator. NiTi SMAs demonstrated to have the best combination of properties. Due to its relatively high recovery stress and strain, actuators providing significant force and stroke can be designed. There are perhaps thousands of applications of NiTi-based actuators mentioned in literature and in patents. Successful applications will build on SMA strengths whilst taking into account its weaknesses. SAES Getters S.p.A., thanks to its vertically integrated process and to the scientific and quality approach, developed a NiTi-based wires family which can represent a very good solution for shape memory actuators. The mechanically stabilized SAES Smartflex NiTi actuators show a very sophisticated profile of properties. In this paper the mechanical, thermal and electrical response of these shape memory wires, at diameters ranging from 25 to 500 mm, under different working conditions, simulating the actual operating condition in real actuators, will be examined in depth and discussed, in order to direct the design of the actuator so that the functional properties of the material can be completely exploited. The thermomechanical properties have been investigated and measured by several methods. The most common and useful tests for these commercially available wires will be also described.