Surface cracks in metals and their characteristics using Rayleigh waves

The development of broadband pulsed ultrasonic Rayleigh wave methods in non-destructive testing has been greatly hindered by the lack of an analytical description of the propagation and scattering of the waves. The present study presents a review of the previous work on Rayleigh waves in all the fields where they are of interest, in geophysics, seismology, civil engineering, non-destructive testing end high frequency electronics. A series of mathematical models, which use finite difference approximations, are then presented and used to provide both visual and quantative numerical descriptions of the propagation, interaction and scattering of Rayleigh waves with a range of single-medium configuration, the half, quarter and three-quarter spaces, up and down steps, ruled open slots, and the two-media configurations of welded quarter spaces and the filled slot. The techniques of finite difference modelling have not previously been applied to Rayleigh wave non-destructive testing problems and in addition to this new application of the basic technique, extensions to the range of nodal formulations are made, including the "presentation of a new second order approximation for the free surface/interface node for welded quarter spaces. The results obtained with the numerical models are tested by a series of practical experiments on aluminium and steel test blocks. The model results were found to be in agreement with those given by the practical experiments and with those of previous workers who have used numerical, analytical, experimental and visualisation techniques, where they exist. Following from the ana1ysis of the results of the numerical and experimental work in this study, the author proposes a development in experimental methods for the characterisation of surface features using the advantages of new transductions. Suggestions are made for extending and improving the basic finite difference methods and for the range of configurations which could be studied