The strength of annealed and heat-treated glass

Abstract

This report develops statistical methods of choosing allowable design stresses for annealed and heat-treated glass. The results are easy to apply but additional fundamental knowledge of some properties of glass is needed before they can be used to the best advantage. The report draws attention to these gaps in existing knowledge and makes recommendations for further research. The report discusses the influence of the known causes of strength variations between nominally identical specimens in relation to two types of glass typical of those used by the aircraft industry, and shows that improved control of heat-treatment processes offers the best hope of a big increase in the useful strength of glass. Chemical protection of the glass surfaces, or changes of composition which increase the intrinsic strength and chemical stability of the glass, would increase the useful strength of both annealed and heat-treated glasses. The potential benefits for heat-treated glass are small compared with those obtainable by improved control of the heat-treatment processes but are nevertheless important.