Showing papers by "Ajit Mal published in 1987"

Calculation of the inplane Green's functions for a layered viscoelastic solid

Abstract: A method is presented for the accurate and efficient calculation of the dynamic Green9s functions for a layered viscoelastic solid under plane strain conditions. The method is based on the classical wavenumber integral representation and a delta matrix formulation of the elastodynamic field. The high efficiency is achieved through the introduction of a new quadrature scheme in which the kernels of the wavenumber integrals are represented by means of polynomials in finite and semi-infinite panels, and the resulting oscillatory integrals are evaluated analytically. The accuracy of the results are controlled through the use of an adaptive procedure whereby the number of panels are increased successively until the desired accuracy is reached, with no previous function evaluations wasted. The computer program currently runs on IBM PCs for all multi-layered structures at all finite frequencies.

A Study of Layer Adhesion by Acoustic Microscopy

Abstract: In this paper we use the metrology mode of a low-frequency acoustic microscope to measure the Rayleigh velocity dispersion over an octave frequency range in layered specimens. Several samples were specially prepared to modify the bond strength at the interface. The measured dispersion, that shows the effects of the modified adhesion dramatically, is compared with computed dispersion curves. We also treat the probablility of exciting the first higher order (Sezawa) mode that may propagate in this regime.

Reflection of Bounded Acoustic Beams from a Layered Solid

Abstract: It is well known that when a bounded beam of acoustic waves is incident on a fluid-solid interface at certain critical angles, the reflected beam is significantly distorted and displaced due to the interference between specularly and nonspecularly reflected waves. Measurement and analysis of the reflected field can be used to estimate certain near surface elastic properties of the solid by means of several alternative nondestructive experimental arrangements [1,2]. In most of these experiments the interface generated leaky waves play a significant role. Thus a good understanding of the interface phenomena is a prerequisite to the design of experiments for their practical applications.