The Delayed Elastic Effect in Silicate Glasses at Room Temperature

JSGT 1947 V31 T017-T035

Using a torsion balance of high sensitivity with an optical lever for the measurement of strain, the delayed elastic effect has been measured at 12° in vitreous silica, in a borosilicate glass and in a sheet glass. Strain measurements were made at intervals from 1 minute after loading up to a time when the apparatus could detect little further increase in a convenient time period (about 20,000 to 40,000 minutes). Expressing the delayed strain between 1 minute and 10 minutes after loading as a percentage of the total strain, the following values were found: for vitreous silica 0·12%, for Wembley X-8 0·55%, and for sheet glass 1·2%. The empirical equation, strain=a+blogt (a and b being constant for a particular glass), was shown to hold to a close approximation for the three glasses, although it does not express the results when very close to the limiting strain. It was demonstrated that the delayed elastic effect is reversible and regularly reproducible, and in all respects conforms with the assumption that glass consists of a truly elastic matrix containing inclusions of viscous components possessing a wide range of viscosities.

J. B. Murgatroyd & R. F. R. Sykes