The Diamond Pyramid Hardness of Glass in Relation to the Strength and Structure of Glass. Part II. Silicate Glass

JSGT 1954 V38 T501-T535

It has been shown in the previous paper* that the diamond pyramid hardness (DPH) number is independent of load-at any rate for loads smaller than those which would cause fractures to occur in the glass, and that it is capable of measurement to an accuracy better than 5 parts in 500. It has also been shown that the DPH number varies from 710 kg/sq. mm for fused-silica glass down to 495 kg/sq. mm for a full-lead crystal glass and that it provides a measurement of the" yield-point" or elastic limit of glass. Furthermore, since the measurements are made on extremely minute areas of the glass surface, the values obtained are independent of the Griffith flaws necessary to explain large-scale strength phenomena and provide a measurement of a strength property of glass in the solid state which can be made with considerable accuracy and which is sensitive to composition changes. To determine how this strength property is affected by different oxides in silicate glasses, several series of experimental glasses have been melted and the DPH numbers of the glasses determined. The results are set out later in this paper, and are discussed in relation to the generally accepted views on glass structure considered briefly below.

L. Ainsworth