Factors Influencing Design of SMA Actuators

Abstract

Given the complex nonlinear nature of SMA responses, understanding their coupled thermomechanical responses of different components has been of significant interest for both researchers and application developers [1]. SMA component responses in different applications can be significantly affected by several factors like material compositions, component geometries, operating temperature, loading conditions, loading rates, thermomechanical history, processing conditions etc. and mostly combination of several of these parameters in many cases. Since these materials demonstrate complex non-linear responses due to phase transformations resulting in microstructural changes, it is imperative to understand their influence on the overall mechanical response of SMA components. The factors listed below and their affect on the mechanical response is taken up in this chapter.

Design and experimental analysis of a smart bearing using shape memory alloy springs

“…The best combination of geometrical parameters achieved was as follows: spring with an effective diameter of 10 mm built with a 1.5 mm diameter wire and assembled with three active coils. The springs are previously manufactured by shape setting (Lecce and Concilio, 2015; Rao et al, 2015). It is important to keep disk position and equivalent stiffness in order to ensure no changes in shaft height.…”

“…For thermal treatment ( 450 ° C for 25 min) (Figure 7(b)), the springs are covered with a thin sheet metal to prevent unwinding. After thermal treatment, helical springs as shown in Figure 7(c) are obtained (Rao et al, 2015).…”

“…SMA springs are able to change equivalent stiffness of rotor bearings. The limitation is phase transformation speed, which depends on heat transfer rate (Lagoudas, 2008; Rao et al, 2015).…”

“…Assuming springs to behave like a thermal mechanical closed system, and not taking into account radiation and mechanical works energy, energy balance can be estimated, which results in the model presented as equation (4) (Bergman et al, 2011; Rao et al, 2015)…”

“…where R is electrical resistance, I electrical current, h convection coefficient, c p is specific heat of material, ρ specific mass, V is volume, T is temperature, and T ∞ is the environmental temperature. Ideal values of current ( I ) and temperature ( T , T ∞ ) are provided by previous experiment (Oliveira et al, 2017), while material parameters ( R , c p , ρ ) are generic and provided from the literature for NiTi (Rao et al, 2015).…”