Simultaneous Measurements in Shape Memory Alloy Springs to Enable Structural Health Monitoring by Self-Sensing Actuation

Abstract

The vital sensing parameter on self-sensing actuation in the spring form of shape memory alloy (SMA) is determined through experimental analysis. A unique measurement technique is adopted that interlinks the electro–thermo–mechano features during the shape memory effect in NiTi, NiTiCu, and NiTiFe springs. The influence of the spring index, the number of active turns, material composition, and transition temperature is assessed. SMA spring’s effective functional behavior to be used as an actuator and or a sensor is ensured via the measurement of electrical parameters—the resistance, inductance, and impedance variations revealed during the solid–solid phase change, i.e., displacement. However, the spring form of SMA would exhibit variation in inductance and a variation in electrical resistance, which in turn is considered a variation in the electrical impedance, which may also be appropriate sensing information. The thermo-mechanical and thermo-electrical measurements are synchronized using an impedance analyzer and data acquisition module with a specific programming technique. The active spring is equivalently a series resistance–inductance circuit, since the collective effect of a decrease in resistance and increase in inductance with an increase in temperature offers increased $\frac{L}{R}$ and vice versa to support structural health monitoring.