Control of vibrations in TiNi by periodic martensitic transformations

Principles of vibration control based on the use of shape memory alloys (SMAs) are discussed. Control feasibilty is due to high damping properties of these alloys and their ability to produce deformation at heating in the course of the reverse martensitic transformation (shape memory effect). Control is based on the choice of a temperature variation law of the SMA active part introduced into a vibrating system. As an experiment, vibration of a torsional pendulum at a constant temperature and under periodic heat inpulses is studied. In the course of each impulse the active part material made of TiNi is transformed into austenite and then back to martensite after heating stops. Depending on the impulse time position in reference to the vibration phase, three types of control are obtained: high damping, amplification and support of sustained vibrations. Theoretical simulation of these phenomena is based on a microstructural model of the SMAs mechanical behaviour. Temperature regimes resulting in the best vibration damping are determined for a pendulum with a large elastic and small SMA rods.