Results of a new experimental approach to static fatigue of glass are presented. Using the double‐cantilever cleavage technique, it was possible to observe crack motion and to accurately measure crack velocities in glass. The measured crack velocity is a complicated function of stress and of water vapor concentration in the environment. Experimental results are discussed with reference to current theories of static fatigue.

Stress corrosion cracking of six glasses was studied using fracture mechanics techniques. Crack velocities in water were measured as a function of applied stress intensity factor and temperature, and apparent activation energies for crack motion were obtained. Data were consistent with the universal fatigue curve for static fatigue of glass, which depended on glass composition. Of the glasses tested, silica glass was most resistant to static fatigue, followed by the low‐alkali aluminosilicate and borosilicate glasses. Sodium was detrimental to stress corrosion resistance. The crack velocity data could be explained by the Charles and Hillig theory of stress corrosion. It is probable that stress corrosion of glass is normally caused and controlled by a chemical reaction between the glass and water.

Fracture surface energies of six glasses were measured using the double-cantilever cleavage technique. Values ranged from 3.5 to 5.3 J/m2 depending on the chemical composition of the glass and the temperature of the test. The fracture surface energy increased with decreasing temperature and increasing Young's modulus ; however, exceptions to this behavior were noted. The magnitude of the values obtained is discussed with respect to the theoretical strength of glassand possible irreversible effects at the crack tip such as stress corrosion and plastic deformation are considered.

In this paper, we review the phenomenon of delayed failure, a life‐limiting process for glasses that are subjected to tensile stresses. With the development of crack‐weakening theories (Ingles and Griffith) and the observation that surface damage enhances delayed failure, the scientific community recognized that delayed failure in glass is caused by the growth of cracks that are subjected to tensile stresses. Fracture mechanics techniques were used to quantify crack growth rates in terms of applied stress, temperature, and the chemical environments that cause subcritical crack growth. We review the theories that have been developed to rationalize subcritical crack growth data, including theories based on plastic deformation at the crack tip, chemical adsorption of the reacting species, and direct chemical reaction of the environment with the strained bonds at the crack tip. The latter theory seems to be most consistent with the finding that water reacts directly with the strained Si–O bond because of the ability of water to donate both electrons and protons to the strained bond. Other chemicals having this characteristic also cause subcritical crack growth. Finally, we review the quantum mechanical calculations that have been used to quantify the chemical reactions involved in subcritical crack growth.

No abstract