Piezoelectric actuators for dynamic applications must be pre-stressed to avoid tensile stress and to improve their reliability. The actuating behavior of piezoelectric actuators depends strongly on the load characteristics: If the load increases with extension of the piezoelectric ceramic, e.g. when using a classical spring, the actuator cannot reach its nominal displacement; when the load remains constant, e.g. when acting against a mass load, full nominal displacement can be obtained at a maximum operating voltage. A general objective for the design of pre-stressing elements is to realize a small stiffness and sufficient load capacity. For standard materials this requires a good compromise in dimensioning. The nonlinear, hysteretic stress-strain diagram of superelastic shape memory alloys (SMA) is characterized by two stress plateaus during loading and unloading. In this strain range of up to 8%, the stress is nearly constant. Uniaxial tensile loaded spring bars made of superelastic SMA exhibit a theoretical stiffness of 0 N/m in the superelastic range of deformation. Therefore, the constant stress plateaus can provide both, low stiffness and sufficient load capacity. The concept of pre-stressing piezoelectric actuators with superelastic SMA will be analytically designed. In particular, the stress-strain behavior of NiTi-based superelastic SMA will be investigated by measuring major and minor hysteretic loops.

This content is only available via PDF.
You do not currently have access to this content.