Instrument effects on stress jump measurements

Abstract

Listen

Translate article

Stress jumps occur in fluids that possess a viscous contribution to their total stress. On cessation of shear, such a fluid will show an instantaneous loss of stress, while some of the stress will remain and subsequently decay in some manner, either exponential or otherwise. The results in this paper show that filtering, present in most rheometers, will eliminate the stress jump and not allow its measurement. The torque head inertia for a spring-type torque measuring system is found to greatly influence the measurements and a stress jump is not seen. In fact, the material's true stress relaxation behaviour is far from that measured. The force rebalance torque measuring system is found to accurately measure stress jumps.