Dissipation of cavitation-induced shock waves energy through phase transformation in NiTi alloys

Abstract

Energy dissipation in aluminum plates coated with a thin layer of Nickel–Titanium (NiTi) alloy subjected to a shock loading is studied. An experimental framework is designed and implemented to apply a shock load on the plates, using a liquid jet generated by collapsing of spark-generated bubbles under water. In this setup, a high-speed camera and a hydrophone are used to characterize the generated bubbles. Moreover, a laser Doppler vibrometer (LDV) and multiple strain gauges are implemented to investigate the vibration and mechanical responses of plates subjected to the water jet induced by cavitation bubbles. Comparing the mechanical response of an Al–NiTi plate with the same system in which the NiTi coating layer is replaced with an Al layer of the same thickness, shows that the propagation of shock waves is activating the forward and reverse phase transformations in NiTi that consequently results in dissipation of the shock wave energy in the material. The results approve the excellent cavitation erosion resistance of NiTi alloys which originates from their superior capability in attenuating stress waves and energy dissipation due to phase transformation, when the shock wave propagates in the material. Finite element simulations are also performed to investigate the energy dissipation capability of aluminum plates coated with a NiTi layer, when the structure vibrates by exerting and removing a concentrated transverse force at the center. When the energy of incident shock waves caused by cavitation bubbles is strong enough, the energy dissipation due to global structural vibrations can complement the energy dissipation due to the phase transformation. The computational results show that the observed energy dissipation in the experiments is exclusively caused by the shock wave propagation, not the transverse vibrations, and also investigate the details of energy dissipation for both NiTi and Al–NiTi composite plates subjected to a cyclic transverse load at the center.