9: Mechanical Properties

Glasses are brittle solids. The hardness of a glass is determined by the strength of the bonds forming the network and by the structure of the glass. Fracture of glasses is controlled by the presence of flaws and does not represent the inherent strength of the bonds between atoms. Glasses must be handled with care to maintain their strength, which may degrade by interaction with atmospheric gases. Thermal stresses may be either permanent or temporary and frequently cause fracture of glasses. Annealing of glasses is essential if reproducible products are to be created.