Measuring device for precise evaluation of torsional creep and recovery data

Abstract

An apparatus has been designed and built up to determine the shear creep compliance and viscosity with high accuracy in a wide range of temperature and time. The characteristic feature of this apparatus is the possibility to measure directly the recoverable compliance and to determine the steady state recoverable compliance Je. Disturbing instrumental forces are minimized by use of a magnetic bearing. The torque is applied inductively by a modified three phase asynchronous motor. The torsional angle is measured with a laser beam reflected from a mirror to an electro-optical measuring device. Sample thermostating is performed by radiation in a heating chamber, which allows observation of the specimen during measurement.First results of creep and creep recovery measurements are reported, which.were carried out on a technical polystyrene above the glass rubbery transition.

Shear creep and recovery of a technical polystyrene

“…Combining the results of this paper with those of [1] the value of the shear creep compliance of the technical polystyrene PS N 7000 is known from the lower part of the glass-rubber transition up to the region of viscous flow. Creep compliance versus creep time is plotted in figure 3 in double-logarithmic scale.…”

“…The reason is the use of the smallest possible sample diameter of 6 mm to get a sufficiently high resolution of signal monitoring under the maximum torque available. Since in this case the sample diameter coincides with the torsional rod diameter, the radiation areas of figure7 in [1] become too small. Additionally, the heat conduction over the torsional rods becomes more disturbing.…”

“…The data described in this paper were obtained on a torsional creep apparatus with a magnetic bearing [1]. The characteristic feature of this apparatus is the possibility to measure directly the recoverable compliance and to determine the steady-state recoverable compliance Je.…”

“…In the flow region the shifting procedure for the creep compliance was performed at a compliance level of 4" 10-3pa-l; in this region the course of the creep curves from 126.7 to 170 °C shows an increase with time with a double-logarithmic slope of one, see figure 8 of [1]. The values of the creep time, where the level of the compliance reaches 4-10-3pa -] are plotted in figure 6 as circles.…”

“…In a previous paper [1] we have reported a measuring device for the evaluation of precise creep and recovery data. With this experimental technique, accurate measurements can be performed with just the same apparatus from the beginning of the glass-rubber 206 transition up to the region of viscous flow.…”