Showing papers by "Ajit Mal published in 1985"
TL;DR: In this paper, a modified version of the wave number integral approach is applied to the calculation of the motion produced in a multilayered solid by dynamic sources, and a new method of pole removal is introduced to facilitate separation of the continuous and the discrete spectral responses of the medium.
107 citations
TL;DR: In this paper, the surface response of an infinite, homogeneous elastic plate to an internal dislocation across an infinitestimal area is investigated by means of a classical integral transform in the frequency domain and the spectral response of the plate is expressed in terms of the modal contributions due to the real, imaginary and complex roots of the Rayleigh-Lamb equation.
Abstract: The surface response of an infinite, homogeneous elastic plate to an internal dislocation across an infinitestimal area is investigated. As a companion problem, the normal displacement of the plate surface due to a time-dependent surface load is also calculated. The first problem is relevant for the detection of crack initiation in structural materials through the analysis of high-frequency elastic waves generated by the event. The solution to the second problem is needed for the calibration of test equipment used in the detection of the waves. The problems are formulated by means of a classical integral transform in the frequency domain and the spectral response of the plate is expressed in terms of the modal contributions due to the real, imaginary, and complex roots of the Rayleigh-Lamb equation. Time histories of the response are obtained through the inversion of the spectra by a Fast Fourier Transform (FFT) routine.
104 citations
TL;DR: In this paper, a modified version of the Clenshaw-Curtis quadrature scheme is applied to evaluate wavenumber integrals of the form ∫ a b F(x) cos (rx) d x and ∫ b F (x)J n(rx)d x, shown to be much more efficient than other commonly used methods for the numerical evaluation of this type of integral.
57 citations
TL;DR: In this article, a theory for the calculation of the acoustic material signature of a multilayered elastic half-space overlain by a fluid is presented, where the solid layers are composed of homogeneous isotropic linearly elastic materials and are firmly bonded at the interfaces.
Abstract: A theory is presented for the calculation of the acoustic material signature of a multilayered elastic half‐space overlain by a fluid The solid layers are composed of homogeneous isotropic linearly elastic materials and are firmly bonded at the interfaces The calculation procedure is valid at an arbitrarily high frequency of excitation Results are presented for a uniform, a single layered and a four layered model of the half‐space at two frequencies of excitation; one moderate (35 MHz) and the other relatively high (370 MHz) Several new features of the material signatures and their possible use in the material characterization of layered specimen are indicated
42 citations
01 Jan 1985
TL;DR: In this article, the acoustic material signature (AMS) has been refined to yield increasingly quantitative information of acoustic velocities in homogeneous and layered structures, but the imaging mode, though it led to the visualization of subsurface structures and associated defects, has to date been used largely as a qualitative tool in nondestructive evaluation.
Abstract: Since the first disclosure of the acoustic material signature1, the acoustic microscope has been explored to perform both imaging and metrology functions2 on a variety of specimens in industry and in the scientific laboratory. The acoustic material signature (AMS) has been refined3 to yield increasingly quantitative information of acoustic velocities in homogeneous and layered structures. However, the imaging mode, though it led to the visualization of subsurface structures5 and associated defects6, has to date been used largely as a qualitative tool in nondestructive evaluation.
3 citations
01 Jan 1985
TL;DR: In this paper, the spectral response of an elastic plate to sources of acoustic emission is computed by summing the residues at the roots of the Rayleigh-Lamb spectrum, and an FFT inversion gives the transient response of the plate.
Abstract: The response of an elastic plate to sources of acoustic emission is a problem of current interest in the development of nondestructive inspection methods. So far the two main approaches that have been used to calculate the response are the ray theory and the normal mode technique. In this paper we present another method based on a classical integral transform technique. Working in the frequency domain, the spectral response is computed by summing the residues at the roots of the Rayleigh-Lamb spectrum. An FFT inversion gives the transient response of the plate.
1 citations