Detailed design and life prediction methodology of novel SMA actuated repeatable launch locking protective device (RLLPD) for magnetically suspended flywheel (MSFW)

Abstract This paper proposes a detailed design of a novel bias shape memory alloy (SMA) actuated repeatable launch locking protective device (RLLPD) for the magnetically suspended flywheel (MSFW) during the launching state. The proposed SMA actuated RLLPD consists of two bias SMA-spring actuators. One is designed to realize locking/unlocking and the other is intended for triggering. Besides, self-locking blocks are employed to ensure that the MSFW can be safely locked under the vibration of the launching process. Considering the locking method by compressing the flywheel against the mechanical bearing, there are at least three or four locking points to maintain the balance and enhance the locking reliability of the flywheel. Additionally, a force amplifying linkage mechanism is employed using one bias SMA-spring actuator to actuate the movement of two clamps, further reducing the total weight of the RLLPD and amplifying the locking strength. Furthermore, the recovery envelope curve which represents the recovery ability of SMA wire under various spring rate is proposed and computed using thermodynamics constitutive model. Simulation results indicate that the recovery envelope curve coincides with the austenite unloading curve. The thermodynamics constitutive model of SMA considering functional fatigue is utilized to calculate the evolution rate of functional fatigue of SMA wire in the RLLPD. The functional fatigue evolution rate computation algorithm and results are presented. After the design and simulation, a prototype of the locking device is fabricated and tested. According to the performance results, the SMA-actuated locking device can release a preload up to 1000 N. The simulation and experimental results indicate that the life cycle of the locking device is more than 50 times.