ACOUSTIC EMISSION FROM A SURFACE-BREAKING CRACK IN A LAYER UNDER CYCLIC LOADING

An isotropic, homogeneous, elastic layer is subjected to a time-harmonic tensile stress of constant ampli-tude parallel to the free surfaces. The cyclic stresses are assumed to generate a surface-breaking crack of length l(t) which propagates normally to the top surface of the layer. The unloading of the crack faces generates acoustic emission, which is composed of Lamb waves. The elastodynamic reciprocity theorem for time-harmonic waves is used to determine the amplitudes of the radiated system of time-harmonic Lamb waves. 1