Effect of Composition on the Mechanical Properties of Aluminosilicate and Borosilicate Glasses

Elastic moduli and fracture toughness were determined for several glasses in the systems soda‐alumina‐silica, calcia‐alumina‐silica, and soda‐boric oxide‐silica. Results for the aluminosilicates are analyzed in terms of Al 3+ :Na + ratios. The mechanical properties do not show maxima or minima at the Al 3+ :Na + ratio of 1, in contrast to conductivity, helium permeability, and refractive index. The moduli and toughness increase with Al 3+ :Na + ratio, which is consistent with increased coherency of the glass network. Glasses which contain B 2 O 3 instead of Al 2 O 3 have slightly higher moduli but are considerably tougher. The moduli of calcium aluminosilicate glasses are ∼25% greater than sodium aluminosilicates, whereas the fracture toughnesses are similar.