Determination of Complex Modulus From Measured End-Point Accelerations of an Impacted Rod Specimen

Abstract

A method is presented for determination of the complex modulus of a linearly viscoelastic material from measured end-point accelerations of an impact-loaded rod specimen. An iterative numerical scheme was used. An approximate analytical solution was also established for the case of small accelerometer mass relative to the specimen mass. Tests were carried out at room temperature for polypropylene, with relatively high losses, and polyamide 6, with relatively low losses. Tests were also performed at temperatures between 20 and 140°C for the former material. Valid results were obtained in the approximate frequency range of 400 Hz to 200 kHz with specimen diameters between 11 and 21 mm, and specimen lengths between 200 and 800 mm. For polypropylene these results are in good agreement with those obtained by using a different method developed by Blanc. For polyamide 6, however, there was some disagreement for the imaginary part of the complex modulus. The method was convenient to use at elevated temperatures as well as at room temperature. It should be suitable for fast routine testing of materials provided that the losses are not too low.