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Resonant Acoustic Determination of Complex Elastic ModuliA simple, inexpensive, yet accurate method for measuring the dynamic complex modulus of elasticity is described. Using a 'free-free' bar selectively excited in three independent vibrational modes, the shear modulus is obtained by measuring the frequency of the torsional resonant mode and the Young's modulus is determined from measurement of either the longitudinal or flexural mode. The damping properties are obtained by measuring the quality factor (Q) for each mode. The Q is inversely proportional to the loss tangent. The viscoelastic behavior of the sample can be obtained by tracking a particular resonant mode (and thus a particular modulus) using a phase locked loop (PLL) and by changing the temperature of the sample. The change in the damping properties is obtained by measuring the in-phase amplitude of the PLL which is proportional to the Q of the material. The real and imaginary parts or the complex modulus can be obtained continuously as a function of parameters such as temperature, pressure, or humidity. For homogeneous and isotropic samples only two independent moduli are needed in order to characterize the complete set of elastic constants, thus, values can be obtained for the dynamic Poisson's ratio, bulk modulus, Lame constants, etc.
Document ID
Document Type
Conference Paper
Brown, David A. (Naval Postgraduate School Monterey, CA, United States)
Garrett, Steven L. (Naval Postgraduate School Monterey, CA, United States)
Date Acquired
September 6, 2013
Publication Date
December 1, 1991
Publication Information
Publication: NASA, Washington, Technology 2001: The Second National Technology Transfer Conference and Exposition, Volume 2
Subject Category
Distribution Limits
Work of the US Gov. Public Use Permitted.

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