Propagation of Low-Frequency Elastic Disturbances in a Composite Material

[+] Author and Article Information
W. Kohn

Department of Physics, Revelle College, University of California-San Diego, La Jolla, Calif.

J. Appl. Mech 41(1), 97-100 (Mar 01, 1974) (4 pages) doi:10.1115/1.3423283 History: Received October 01, 1972; Revised April 01, 1973; Online July 12, 2010


In the limit of low frequencies the displacement u(x, t) in a one-dimensional composite can be written in the form of an operator acting on a slowly varying envelope function, U(x, t): u(x, t) = [1 + v1 (x)∂/∂x + [[ellipsis]]] U(x, t). U(x, t) itself describes the overall long wavelength displacement field. It satisfies a wave equation with constant, i.e., x-independent, coefficients, obtainable from the dispersion relation ω = ω(k) of the lowest band of eigenmodes: (∂2 /∂t2 − c̄2 ∂2 /∂x2 − β∂4 /∂x4 + [[ellipsis]]) U(x, t) = 0. Information about the local strain, on the microscale of the composite laminae, is contained in the function v1 (x), explicitly expressible in terms of the periodic stiffness function, η(x), of the composite. Appropriate Green’s functions are constructed in terms of Airy functions. Among applications of this method is the structure of the so-called head of a propagating pulse.

Copyright © 1974 by ASME
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