The Flow Of Glass At High Stress Levels. I. Non-Newtonian Behaviour Of Homogenous 0.09 Rb 0.92 Sio2 Glasses

A homogeneous 0.08 Rb 0.092 SiO glass has been tested at temperatures between 480 and 555C (low-stress viscosities between (formula) and at stress levels up to (formula) or more. At low stress levels, Newtonian behaviour was observed; at stress levels above some critical stress, the viscosity was observed to decrease with increasing stress. This critical stress for non-Newtonian flow was found to be about (formula) approximately independent of temperature. The variation of viscosity with stress in the high-stress region can be described by absolute rate theory only by assuming a flow volume which increases with increasing stress.