Measuring the dynamic moduli of glassy polymers: analysis of the Rheovibron

Abstract

A mechanical model for the Rheovibron DDV‐II, an instrument for measuring the dynamic tensile moduli of polymers, has been proposed and analyzed to derive expressions for the moduli which take into account system compliance, sample yielding within the tensile grips, and system inertia. These effects require a correction to the raw data of 20–30% for glassy polymer samples in the tensile geometry, and the correction factor varies substantially with temperature, frequency, sample width and thickness, and among different polymers. In addition to the standard tensile grips, a new sample holder was introduced which adapts the Rheovibron to the flexural geometry. Experiments were carried out on samples of poly(methyl methacrylate) (PMMA) in tension and in flexure, on rigid aluminum samples, on a PMMA tensile sample with variable system inertia, and on a tensile specimen of bisphenol‐A polycarbonate at various temperatures, the model describing the behavior of the system quantitatively. It is concluded that for accurate determination of the dynamic moduli in tension, the temperature, frequency, and sample dependence of the correction factors must be taken into account.