The Relation between the Delayed Elastic Effect and the Decay of Strength of Silicate Glasses at Room Temperature
JSGT 1947 V31 T036-T049
A relationship is derived between breaking strength and the delayed strain which appears in glass under constant load, namely, 1/PB=kσ+k',in which PBis the breaking strength and σ is the strain. PBand σ were measured at durations of loading varying from 1 minute to 104 minutes in vitreous silica, in “X-S” glass and in sheet glass and the results were in close agreement with the equation. This supports the assumption that stress concentrations arise locally in the elastic matrix of glasses where inclusions of a quasi-viscous component occur, and that these stress concentrations continue to increase as relaxation proceeds in the quasi-viscous component. An explanation is offered of the fact that the inverse of breaking strength plotted against the logarithm of the duration of loading is a straight line. The effect of surface condition on the strength of glass is also discussed, and it is shown that the lack of decay of strength of glass under load after being heated in vacuo is compatible with the “viscous pocket” theory.
J. B. Murgatroyd & R. F. R. Sykes
