Strength and Static Fatigue of Abraded Glass Under Controlled Ambient Conditions: III, Aging of Fresh Abrasions

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Abstract
The effect of aging under various conditions on the strength and static fatigue of freshly abraded specimens has been studied. For both grit‐blast and emery cloth abrasions the liquid nitrogen (fatigueless) strength increased with storage time after formation of the abrasions for specimens stored in liquid water or in an atmosphere containing water vapor. After 1 day of storage in water the strength increase was about 60% of the freshly abraded value for emery cloth abrasions and about 30% for grit‐blast abrasions. The aging depended strongly on the medium in which the specimens were stored and on the relative humidity when they were stored in air. In very dry air or vacuum the aging effect appeared to be eliminated. Static fatigue curves (strength vs. load duration) in water were measured for specimens containing fresh abrasions and aged abrasions. Ordinary aging did not change the static fatigue behavior of fresh abrasions. The liquid nitrogen strength and static fatigue also were studied for specimens which had been baked at 470°C. in high vacuum after being abraded. This treatment increased the fatigueless strength by approximately the same amount as aging in water. The rate of static fatigue, however, which was unaffected by ordinary aging, was reduced by a factor of approximately 25 for vacuum‐baked as compared with fresh abrasions. Possible mechanisms for aging are discussed in some detail. It is proposed that the observed aging effects on the fatigueless strength can be accounted for by an increase of the radii of the tips of the abrasion cracks in the surfaces of the specimens. The suppression of fatigue for the vacuum‐baked specimens is believed to be related to the non‐wettability of their surfaces which was observed in the course of the experiments.

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