STRESS RELEASE IN GLASS A PHENOMENON INVOLVING VISCOSITY AS A VARIABLE WITH TIME*

Abstract

ABSTRACT This paper contains a discussion of the well‐known Adams and Williamson annealing law which makes the rate of release of stress in glass proportional to the second power of the stress and points out certain fundamental objections to such a law. A new expression free from these objections and taking into consideration the change of viscosity with time at constant temperature is given as ‐df/dt = Mfφ, where M is a modulus and φ the instantaneous fluidity. Experiments made with an ordinary lime glass show that this law holds for the release of mechanical stresses imposed on strain‐free glass as well as for the release of thermal stresses in chilled samples. The value of M found for these two types of stress at two different temperatures is 5.9 (±0.5) × 10 10 dynes/cm. 2 .