Physics & Astronomy ETDs

Publication Date

5-27-1968

Abstract

The acoustic velocities in polymethylmethacrylate have been measured with an ultrasonic pulse echo technique as functions of frequency, temperature and pressure. At atmospheric pressure, data on the velocities and attenuation coefficients were obtained over the range of temperature from 22°c to 75°c and for the frequency range of 6 to 30 MHz. At the temperatures of 25, 40, 55 and 75°c, the pressure dependence of the longitudinal and shear velocity was obtained to 150,000 psi at a frequency of 6 MHz. From the frequency measurements of the velocities, the complex elastic moduli in polyrnethylmethacrylate were calculated at room temperature. The pressure dependence of the velocities allowed the determination of the elastic constants as a function of pressure. It was found that the measured velocities for increasing pressure were generally lower than those for decreasing pressure by about 0.5% for the longitudinal measurements and about 0.8% for the shear· measurements. However, the acoustic measurements of the velocities at atmospheric pressure after the specimens had been exposed to 150,000 psi were usually within 0.1% of the initial values. After exposure to pressure the lengths of the specimens also reproduced the initial measurements to within 0.05%. A discussion is presented which illustrates some of the applications of the data reported here with respect to equation of state determinations in polymeric materials at elevated pressures.

Degree Name

Physics

Level of Degree

Masters

Department Name

Physics & Astronomy

First Committee Member (Chair)

John Root Green

Second Committee Member

Seymour Samuel Alpert

Third Committee Member

Christopher Dean

Fourth Committee Member

Alice Hunter

Language

English

Document Type

Thesis

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