On the Viscoelastic Spectrometer

Abstract

Extensive studies of viscoelastic properties of high-polymeric materials have necessitated the development of an apparatus which can measure full-automatically the viscoelastic functions of the materials, such as complexdynamic modulus, relaxation modulus, and creep compliance, over the range of frequency (time) and temperature as wide as possible.In this paper, the apparatus which has been designed and constructed by the authors for such multiple purposes as above under tensile deformation will be discussed. The apparatus can also be used for simpleshear deformation of the testspecimen by a slight modification of the specimen jaws.The apparatus has servo-mechanism which can control the static strain or stress of the testspe cimen constant during the forced vibration for dynamic measurements. This servo-mechanism of keeping the static condition of the specimen constant is very important for successful measurement of dynamic properties automatically and is also helpful for making the apparatus multi-versatile in uses as follows:a. Dynamic experiment under constant static tension.b. Dynamic experiment under constant static deformation.c. Stress relaxation experiment.d. Strain creep experiment.e. Constant rate deformation and cyclic deformation.The essential point for measuring full-automatically the viscoelastic functions, such as dynamic modulus as functions of frequency and temperature, is to obtain the stress and strain amplitudes and their phase difference as directreading quantities. By means of this apparatus these purposes have been satisfactorily attained within the range of frequency from 1 to 100 cps and of temperature from -60 to 200°C.The limitation of frequency range coverable depends mainly upon the technique for detecting the error of the phase difference so fine as less than 0.1 degree: i.e., its lowest limit is to be determined by the capacity for the directreading of the three quantities, of such electrical analogue technique as adopted here, and its highest limit by the relation of measuring frequency with resonance frequency of the apparatus, especially of the stress detector (4000 cps), and with the geometrical dimension of the specimen for longitudinal wave propagation. The lowest limit of measurable frequency can be expanded in some extent as low as 0.01 cps by analyzing manually the stress and strain waves recorded, however electrical-digital technique may be recommendable and will be discussed in the following paper.The limitation of temperature range coverable, especially of lowest limit, depends on the technique of cooling the testspecimen and will be easily improved by changing the technique of circulating dryice-methanol mixture to that of blowing dry air cooled by liquid nitrogen.Illustrations are given of the experimental results on the frequency dependence of complex dynamic tensile modulus (C.D.T.M.) for three kinds of epoxy resin at 25°C., the temperature dependence of C.D.T.M. for atactic polyvinyl alcohol at 1, 10 and 100 cps, and the frequency dependence of C.D.S.M. of a polyvinyl chloride foam, which was obtained full-automatically at various temperatures.