LOW-FREQUENCY ULTRASONIC NDE OF AN INTERPHASE LAYER

Vikram K. Kinra, Changyi Zhu, Paul Jaminet, and Vasu lyer Department of Aerospace Engineering Center for Mechanics of Composites Texas A&M University College Station, Texas

ABSTRACT

An ultrasonic technique for a sitnultaneous measurement of the acoustical properties of a three-layered medium (adherend/interphase layer/adherend) has been developed. normally incident longitudinal waves are considered. It is assumed that the wavelength may be large compared to all three thicknesses; this shows the use of low-frequency transducers. The inverse problem has been solved for the following two cases: (1) Simultaneous determination of thickness (h) and wavespeed (c) of any one of the three layers, given h and c for the remaining two; and (2) Simultaneous measurement of the three thicknesses, given the three wavespeeds.

INTRODUCTION

When two materials are joined to form a composite, there frequently develops a new phase at the interface. It is well known that the mechanical properties of this interphase have a significant influence on the effective properties of the composite. Consequently, in recent years there has been a great deal of activity in the area of ultrasonic nondestructive evaluation of the interphase properties. Similarly, ultrasonic measurement of the mechanical properties of an adhesive layer in an adhesively-bonded joint is also a problem of current technological interest. There are many other situations (e.g. in geophysics) where one is interested in measuring the acoustic properties of a layered medium.
Ultrasonics has been used extensively for NDE of the acoustical properties of an elastic layer. A classical method is the so-called pulse echo method (Papadakis, 1976). A key assumption here is that the successive echoes from the two specimen faces should be clearly separable in the time domain. Currently, only relatively thick specimens can be tested: h > 3X where h is the thickness and X is the wavelength. Additional restrictions are that the material should be non-dispersive and non-attenuative. If the material is dispersive one can go over to the frequency domain via the use of Fourier transforms and measure frequency-dependent phase velocity and/or attenuation using ultrasonic spectroscopy.

Ultrasonic Characterization and Mechanics of Interfaces ASME 1993 (AMD-Vol. 177) (Book Contents)
ISBN No. 0-7918-1043-7
Library of Congress Catalog Number 93-73596
Copyright 1993 by
THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS All Rights Reserved Printed in U.S.A.

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