Compositional effects on the fracture behaviour of alkali-silicate glasses

The two-point bend strength and the fracture toughness of a series of soda-potassia-silicate and soda-potassia-calcia-silicate glass fibres have been measured. There is a clear variation of mean strength with composition for the soda-potassia-silicate glasses, however, there is much less variation of mean strength with composition for the soda-potassia-calcia-silicate glasses. There is also a greater variation of fracture toughness with composition for the soda-potassia-silicate glasses than for the soda-potassia-calcia-silicate glasses. The mean strength, fracture toughness and inferred flaw sizes for the soda-potassia-calcia-silicate glasses are all less than the equivalent values for the soda-potassia-silicate glasses. These results are related to the structural models and durability of the glasses tested.