Diffraction of Rayleigh waves in a half-space. I. Normal edge crack

Abstract

This paper is concerned with the diffraction of Rayleigh surface waves by an edge-crack normal to the free surface of a half-space. An experimental technique was developed to yield accurate and reproducible measurements of the scattered field on the free surface both in the vicinity of the crack and far away from it. The results show that the nearfield scattered field is very sensitive to the crack length and possesses many characteristic features which are shown to be potentially useful in the area of nondestructive testing and evaluation. The farfield transmission and reflection coefficients AT and AR were measured under both the steady time-harmonic motion and the transient motion of the half-space. In the short-wavelength limit (l/λR≥2), both AR and AT achieve the crack-length-independent values, namely AR=0.41 and AT=0.06; the former agrees with the reflection coefficient of a quarter-space and the latter agrees with the combined transmission coefficient through the leading corner, the tip, and the trailing corner of the crack. For l/λR≤2, AR and AT were found to agree very well with a recent theoretical solution of Achenbach and his co-workers [D. A. Mendelson et al., Wave Motion 2, 277–292 (1980); Y. C. Angel and J. D. Achenbach, J. Acoust. Soc. Am. 75, 313–319 (1984)].