Resonant Acoustic Determination of Complex Elastic Moduli
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Authors
Brown, David A.
Garrett, Steven L.
Subjects
DYNAMIC MODULUS OF ELASTICITY
Q FACTORS
TORSION
VIBRATION
VISCOELASTICITY
BULK MODULUS
DAMPING
HUMIDITY
ISOTROPY
LOW COST
PHASE LOCKED SYSTEMS
POISSON RATIO
Q FACTORS
TORSION
VIBRATION
VISCOELASTICITY
BULK MODULUS
DAMPING
HUMIDITY
ISOTROPY
LOW COST
PHASE LOCKED SYSTEMS
POISSON RATIO
Advisors
Date of Issue
1991-12
Date
Dec 01, 1991
Publisher
Language
Abstract
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.
Type
Conference Paper
Description
Series/Report No
Department
Organization
Unspecified Center
Identifiers
NPS Report Number
Sponsors
Funding
Format
Citation
NASA, Washington, Technology 2001: The Second National Technology Transfer Conference and Exposition, Volume 2; p. p 32-40
Distribution Statement
Approved for public release; distribution is unlimited.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.