Depth profiling of residual stress in steel by laser ultrasonics

Abstract

Depth profiling of residual stress in steel is of great interest in many practical applications. Conventional techniques are either destructive (x-ray diffraction and hole drilling) or with obvious restriction (Barkhausen noise). This paper presents a noncontact and nondestructive laser ultrasonics method for determining the depth profile of the residual stress layer in steel samples. It is known that surface acoustic waves penetrate into solids to a depth proportional to the wavelength. They are expected to be dispersive in the presence of gradients in physical properties such as residual stress. Based on the dispersion theory, the depth dependence of an effective velocity v(z), which is related to the stress profile S(z), can be fitted from the frequency dependence of the phase velocity v(w). Due to the advantage of wide bandwidth, laser-generated and -detected surface acoustic waves (SAW) offer a promising nondestructive stress depth profiling method. The profiles obtained by SAW are compared with the stress data obtained by other techniques. a)Also at Service de Métallurgie Physique, Université Libre de Bruxelles, Belgique.