Linear viscoelastic properties of epoxy resin polymers in dilatation and shear in the glass transition region: 2. Measurement of the glass transition temperature

Abstract

Measurements of the 20 second creep compliances in dilatation and shear, over a range of temperature spanning the glass transition region, have been made for six epoxy resin polymers. The linear thermal expansion behaviour has been determined in the same temperature range. Shear and dilatational compliances, and the linear thermal expansion properties may all be measured on the same specimen. Values of the glass transition temperature derived from 20 sec shear and bulk compliance data agree well with values obtained from thermal expansion data. When T g was derived from creep data obtained at longer creep times (in part 1 of this paper), it was found that T g in dilatation exceeds T g in shear. It was shown that this is consistent with the difference in activation energies in dilatation and shear obtained in part 1 of this paper. An example is given of how systematic errors of the order of 1°C in temperature measurement may lead to maxima or minima when Poisson's ratio is calculated from measured values of shear and tensile compliances.