Design and implementation of tunable multi-degree-of-freedom vibration absorber made of hybrid shape memory helical springs

This study used hybrid smart materials, shape memory alloy wire enclosed by shape memory polymer sleeves, to design a tunable vibration absorber for vibration reduction over a frequency range. The superelastic wire was trained into helical spring and sleeved with several layers of shape memory polymer to form the structural part of the absorber. Different electric currents could be employed to control the heating and temperature of the shape memory materials in order to tune the dynamic characteristics of the absorber. A theoretical formulation for the configuration design of this absorber based on the principle of minimum total potential energy was derived. In addition, the experimental results showed that with a control current of 1.6A the heated vibration absorber could demonstrate a 61.6% change in its first modal frequency. After assembling the absorber onto the main structure, the tunable capacity of the absorber under different control currents was measured. Accordingly, the optimal control current spectrum over the interested frequency span for minimizing the frequency response spectrum under base excitation was determined. With this proposed tunable vibration absorber, the vibration reduction of a structure under sinusoidal base excitation at different frequencies was effectively demonstrated.