• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

SECTION LISTING

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Nov 1989

Volume 86, Issue S1, pp. S1-S125

Return to All Sections
back to top
RSS Feeds
back to top Session T. Structural Acoustics and Vibration II: Characterization of Viscoelastic Polymers
Invited Papers
FREE

Measurement of polymer complex modulus properties using several techniques (A)

Thomas M. Lewis and Dominique Legros

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S50-S50 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
Various techniques for measurement of the dynamic mechanical properties of polymers are discussed. Special emphasis is given to the vibrating beam, SDOF resonance, SDOF impedance, creep, relaxation, forced oscillation (Metravib viscoanalyzer), and forced torsional oscillation (Metravib micromechanalyzer) techniques. Material property data, generated over wide ranges of temperature and frequency (using the above techniques), are presented in terms of reduced frequency upon application of an Arrhenius temperature‐frequency shift function. Comparison of these properties in the reduced frequency format indicates good correlation between techniques. Specific examples are included consisting of data generated from commercially available materials in both shear and tension‐compression states of stress from which estimates of Poisson's ratio may be determined.
FREE

The ASTM E‐756 Damping Standard—The good, the dangerous, and the pitfalls (A)

Michael L. Drake

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S50-S50 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
The resonant cantilever beam test procedure is a reliable test method from which complex modulus data can be determined. The ASTM E‐756‐83 Standard was developed around this test procedure. This test method has been used since Oberst started work in the early 1950s. Ross, Kerwin, and Ungar expanded the usefulness of the test through the development of sandwich equations. Although the test procedure is reliable, it was developed when the fundamental interest in complex modulus data was focused on the transition region. As a result, when users begin to stretch the viscoelastic properties testing further into the rubbery and glassy regions problems developed. This paper will detail the idiosyncrasies of this test method and the analytical equations used to calculate the complex modulus data from the raw test data. It will be demonstrated that apparently good, self‐consistent data can be very inaccurate. The effects of test specimen configuration and the modulus of the viscoelastic material on the accuracy of the complex modulus data and the utility of the various test specimens will be discussed. The commonality of the problems in the best test with other popular test methods will also be discussed and suggested test parameters will be given to enhance complex modulus data accuracy.
FREE

Frequency‐temperature superposition in polymer damping behavior (A)

David I. G. Jones

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S51-S51 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
The problem of determining optimum shift factors for frequency‐temperature dependence of polymeric material complex modulus properties has not been fully resolved even half a century after the pioneering work of Williams, Landel, and Ferry. The question of what form, such as the WLF (Williams, Landel, Ferry) equation or the Arrhenius equation, best depends on both the material and th&quality of the test data. In most cases, the data scatter is sufficient to prevent a definitive choice. These issues will be discussed with reference to available test data for several polymeric materials, obtained by various measurement techniques. It will be shown that the least ambiguous shift factor estimates are obtained when data scatter is as low as possible, and the frequency range of data at each temperature is as wide as possible, as would be expected. It will also be shown that differences arising from the use of different shift factor equations are not sufficient for most engineering applications.
FREE

Presentation and modeling of complex modulus (A)

Lynn Rogers

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S51-S51 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
One of the historical challenges in the field of passive vibration damping technology is the modeling of experimental complex modulus data as a function of temperature and frequency. Several models exist for the temperature shift function (TSF); i.e., Arrhenius, WLF, exponential, etc. Several models of complex modulus as a function of reduced frequency also exist. All existing TSF and CM models fail to represent at least some sets of data with desired accuracy and efficiency. Consider a linear, constant coefficient, stable system, and its frequency response function. It is well known that if the real component of the complex‐valued frequency response function is given over the infinite frequency range, then the imaginary component may be obtained. The complex modulus of vibration damping materials is such a system. Extensive work with fractional calculus based models for complex modulus has established their viability and potential attractiveness. A ratio of factored polynomials of one‐half order is proposed to model the complex modulus. This CM model is attractive from a number of viewpoints: The proper interrelationship of the real and imaginary components is guaranteed; an adequately large number of terms may be used in order to accurately model the complex modulus; an expression may be developed for the real component that lends itself to fitting data by collocating through a number of points; closed‐form expressions may be developed for compliance, relaxation modulus, and creep compliance which also lend themselves to collection fitting of experimental data, etc. With modern computational power, this model becomes both accurate and efficient. Previous work has established the slope of the TSF as the characteristic which causes complex modulus data to be properly shifted; therefore, a new approach to modeling the TSF is proposed. The new model is based on determining values of slopes at equally spaced temperatures, fitting a cubic spline through these points (i.e., knots), storing the coefficients, and integrating the cubic spline analytically. The concept of reduced temperature is introduced, used as a convenience for the present effort and proposed as an additional method of presenting data in a form useful to the damping industry. The core of the revolutionary concept is using the simultaneous modeling of both real and imaginary components as the criteria to enable the set of data to establish its TSF. Previous techniques have used real modulus, imaginary modulus, and loss factor as a function or reduced frequency, sometimes in a least‐squares sense, and sometimes visually, as the criteria. The above CM and TSF models are essential to the iteration strategy required to determine parameter values for both models. The iteration scheme is conceptually straight‐forward. Approximations to the CM and to the TSF are obtained. For each TSF knot, the reduced temperature is used to determine the associated reduced frequency, the current loss factor curve is compared to the corresponding experimental value and the value of the slope adjusted accordingly, the real component collocated for the updated TSF, etc. Examples are given and discussed.
FREE

Design of polymers for viscoelastic damping applications (A)

R. E. Wetton and J. L. Duncan

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S51-S51 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
The large frequency dependence of the dynamic moduli of polymers allows the design of materials with special damping and engineering applications. The temperature dependence of these properties is, however, a drawback in many cases. The present paper reviews the changes of Youngs, shear, and bulk moduli with frequency and temperature. Their accurate measurement and predictions via time/temperature superposition methods are discussed, as are the relationships between these parameters with changing temperature. The design of elastomers with high damping and minimized temperature variation is discussed with some examples.
FREE

Internal friction in polymer systems (A)

Jozef Bicerano and James K. Rieke

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S51-S52 (1989); (2 pages)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
Internal friction is an effective mechanism for dissipating energy in polymer systems. Of particular interest is the ability to dampen and absorb unwanted acoustic and mechanical vibrations. The use of internal friction will become more effective when detailed geometric, thermodynamic, and kinetic models are developed for the physical phenomena producing the vibration damping. A model that relates the viscoelastic properties of polymeric systems to their molecular level structures has been developed. This model considers the nature of the temperature and frequency dependences of the storage and loss components of the complex moduli of polymers. It provides correct and internally consistent correlations. Therefore, it constitutes a first step in an attempt to bridge the gap between the results of application of an external stress (such as acoustic or mechanical vibration) and the molecular level properties of the polymers.
FREE

Characterizing viscoelastic materials using the free volume microprobe (A)

Bret A. Mayo, James P. Pfau, and Duryodhan Mangaraj

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S52-S52 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

Show Abstract
A great deal of effort has been directed toward the development of new polymer blends and interpenetrating polymer networks in recent years. This approach has emerged as an important means of developing new polymeric materials and improving properties such as sound damping. The thermodynamic models that best describe polymer‐polymer interactions have an important free volume contribution. Until recently, however, there was no technique that could make a direct, nondestructive measurement of the molecular free volume. Using the free volume microprobe (FVM), it is now possible to characterize both the average free volume site size and the relative number of free volume sites. Thus it is possible to make some assessment of the total free volume as well as the free volume distribution. The basic theory of the FVM technique will be presented as well as some supporting data from a series of miscible, immiscible, and partially miscible polymer blends.
Return to All Sections
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close