Characteristics of pressure pulses propagating through water-filled cracks

Abstract

A series of experiments was conducted at Queen's University Belfast with a specially designed experimental apparatus in order to investigate the characteristics of, and the effect of crack geometry on, impact-induced pressure pulses propagating through water-filled cracks. The pressure pulses propagated with speeds of ranging from 50 to 300 m/s, whereby the speed increased with increasing crack width. It was found that changes in crack geometry such as right angle corners do not affect the propagation of the pressure pulse. The slow speed of propagation was attributed to the aeration of the water, which changes the water into a two-phase medium with dramatically increased compressibility. The pressure pulses also attenuated; the slowest most quickly with higher frequencies being damped out preferentially, whereby the rate of attenuation appeared to be mainly a function of time. A previously proposed theoretical model, which was based on the assumption of a two-phase medium, was improved and shown to model the experimental results satisfactorily. The experimental and numerical results suggested that, within the very short time scale of the pulse propagation, the water inside of a crack constitutes an elastic medium with viscoelastic damping.