Surface Motion Excited by Acoustic Emission From a Buried Crack

The surface motions excited by acoustic emissions produced by fracture processes at the edge of a buried, penny-shaped crack are investigated. Firstly, wave-front approximations to the emissions generated by the sudden growth of a tensile crack in an unbounded elastic solid are reviewed. Then these approximations are Fourier transformed to give the high-frequency portion of their spectra. Secondly, time and frequency-domain approximations to the surface motions excited by this growing crack, when it is buried in a half-space, are calculated. These results are then scrutinized to elucidate what parts of the signals measured at the surface carry information about the crack’s size, its orientation, and the fracture processes near the crack tip.