Sound velocity and young's modulus in polyethylene

Abstract

Abstract The sound velocity was measured in bars for a number of low‐ and high‐density polyethylene samples. The longitudinal oscillations in the bar were generated electrodynamically. It was observed that the sound velocity decreased somewhat with length. Therefore all sound velocity measurements were made in bars with the same length and diameter. After each measurement the density was determined also. It was observed that a linear relationship exists between sound velocity and density. The degree of polymerization has no direct influence on the sound velocity. Young's modulus obtained from sound velocity measurements was represented as a function of density also. Young's modulus obtained from sound velocity measurments proved to be about three times larger than values obtained from bending and tensile tests. The very small deformations involved in sound velocity measurements and the elimination of time‐dependent viscoelastic effects because of the oscillations are mentioned as the most likely reasons for this.