Determination of rayleigh wave critical angle

Abstract

A method of non-destructively evaluating or validating a processed area of an object such as a metallic laser shock peened surface by determining Rayleigh wave angles at various positions on the surface. The Rayleigh wave angle is determined by: (a) directing incident beams of ultrasonic waves onto at least one point of a surface at a plurality of incident angles; (b) simultaneously measuring intensity of a combination of corresponding directly reflected and re-radiated beams at a plurality of corresponding reflected angles equal in magnitude to the incident angles with respect to a line normal to the surface; (c) generating a null angle profile of data indicating intensity versus corresponding incident angles from measured intensities in step (b); (d) determining an intensity curve by applying a polynomial curve fit to a low intensity portion of the null angle profile; and (e) determining the effective critical angle for the corresponding Rayleigh wave by determining a substantially minimum point on the curve. The polynomial curve fit may be a second order polynomial fit and the plurality of incident angles and corresponding reflected angles are predetermined and in close proximity to a predetermined critical angle.