Diffraction of elastic waves by cracks: application to time-of-flight inspection

We obtain expressions for the angular variation of diffracted signal amplitude when infinite plane P or SV waves are incident on a semi-infinite crack. The importance of these calculations to non-destructive testing by the time-of-flight technique is discussed. We obtain the optimum angles to use for the case of a defect symmetrically placed with respect to transmitter and receiver. These angles are those for which the ratio of emitted signal amplitude to incident wave amplitude is a maximum.

We compare two methods of obtaining the exact solution for the diffraction of elastic waves at a semi-infinite crack. Both methods involve the solution of a set of integral equations, the equations being different in the two methods. In the far-field approximation the results from these methods are shown to be equivalent.