Experimental investigations on the damping behaviour of superelastic NiTi

Abstract
A set of experimental investigations on the micro- and macromechanical transformation behaviour of superelastic NiTi as well as on elementary structures with integrated NiTi components has been undertaken with respect to damping. At low frequencies the transformation process during tensile tests has been observed and documented using in-situ optical microscopy [1]. For an estimation of the attainable damping capacity, experiments on a pre-strained string were performed. Pre-strained to approximately 25% martensite the damping capacity of NiTi for low amplitudes is in the range of steel. Increasing amplitudes lead to much higher damping values for NiTi. In the completely transformed stage NiTi exhibits an amplitude independent damping behaviour with values that are smaller than those observed in experiments with steel [2]. Further experiments have been performed with coil springs made from NiTi. These springs were used to increase the damping capability in a vibrating system compared to the same system with steel springs. Again increasing pre-stress as well as increasing vibration amplitudes lead to a stronger damping of the NiTi springs and the vibrating system. The calculated damping values result from a linear analysis.