FREQUENCY TUNABLE ISOLATOR BASED ON SHAPE MEMORY ALLOY FOR EFFECTIVE SHOCK AND VIBRATION SUPPRESSION

A Shock and vibration isolator is widely used due to its simplicity and effectiveness. It attenuates vibration energy when the external excitation frequency is more than about times its natural frequency, while the vibration around its natural frequency is generally amplified. However, an exciting frequency often varies so that it is difficult to avoid the vibration amplification. In particular, when these amplification phenomena occur in the low frequency domain, induced large vibration displacements degrade the structural integrity. This paper introduces a novel frequency tunable isolator proposed by the present authors. The isolator uses SMA wires as actuator as well as the isolation materials. The isolator material is a compressed mesh washer isolator using the pseudoelasticity of SMA. Frequency tune of the isolator can be easily achieved through a simple electric circuit. Thus, this isolator can be widely applied to various vibration and shock. environments such as in aircrafts and motor vehicles. Particularly, the detail design procedure is presented here for the adaptive shock isolator for launch vehicle in order to achieve both shock attenuation performance and avoidance of the vibration amplification. Launch vehicles experience severe dynamic environment during the flight phase. Specially, pyroshock generated from the several separation events could result in malfunctions of electric components and low frequency vibration below 100 Hz at the maximum dynamic pressure phase could reduce the structural integrity of payload. The resonant frequency of the isolator is selectively controlled in two modes by using an adaptive mechanical system with compressing the isolation materials. The isolator was successfully designed and various test results with frequency tuning are presented, in this paper.