Theoretical analysis of acoustic waves propagating in materials with continuous variations of near-surface elastic constants

摘要

The near-surface elastic properties (NSEPs) of materials take on continuous distribution after surface modification such as surface polishing. In this paper, the influence of the continuous variations of NSEPs on the ultrasonic waves propagating in finite-thick and semi-infinite-thick plates is investigated. An orthogonal polynomial extended method is presented to study the acoustic waves propagating in metals with continuous distribution of NSEPs. By this method, the near-surface layer of the materials does not need to be discrete sublayers, which can avoid the presence of pseudoacoustic waves. The velocities of different ultrasonic wave modes in finite-thick and semi-infinite-thick plates with continuous distributions of NSEPs are obtained. In addition, the influence of the near-surface layer's thickness and the distribution of the NSEPs on the relative velocity dispersion of Lamb waves and surface acoustic waves are discussed, providing further theoretical foundation for the inversion of near-surface properties.