Resonant Acoustic Determination of Complex Elastic Moduli
Brown, David A.
Garrett, Steven L.
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A 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.
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Tan, Beng Hock (Monterey, California. Naval Postgraduate School, 1991-03);An acoustic resonance based technique using a free-free bar has been extended to investigate the complex (storage and loss) moduli of non-magnetic materials having circular cross section. Using this technique, the bar can ...
Bartlett, David L. (Monterey, California. Naval Postgraduate School, 1994-03);The objective of this research is to investigate the dynamic elastic properties of materials and their temperature and frequency dependence using an acoustic resonance based method. In this technique, the torsional, flexural, ...
Cohen, Steven Robert (Monterey, California. Naval Postgraduate School, 1968-06);The complex shear modulus of both kaolin-water and bentonite-water mixtures has been determined in the laboratory. The method involved measuring the reaction on a torsional elastic wave propagated down a metal rod when the ...