Spiral Dislocations on Glass Fracture Surfaces

Abstract

Within a certain range of composition spiral defects were observed on etched soda-lime-silica glasses. The patterns described spirals of Archimedes and appeared to originate from interstitial defects in the glass. Mutual stress influence effects were observed. The hypothesis of an existing torque field around the interstitial defects was useful in explaining the spiral mechanism. Application of mechanical torque stresses produced the spiral effect. In some cases it appeared feasible to apply stress energy relationships developed from dislocation theories to these minute flaw patterns. A dynamic spherical indenter technique was developed to study structural variations in these glasses. The lengths of flaws produced by a rolling indenter were found to be sensitive to changes in the silica content of the glasses and less affected by variations in the soda-lime ratio. The effects of heating and crystallization were also studied.