The Mechanism of Brittle Rupture in Glass
JSGT 1944 V28 T406-T431
Griffith's “crack theory” and the weak molecular bond theory of the strength of glass are tested by strength phenomena recorded by different investigators, and it is concluded that modifications are necessary to these theories to account for the facts. The suggestion is made that Griffith “flaws” consist of pockets of quasi-viscous material surrounded by larger three-dimensional aggregates, and that when the pocket material has yielded to an applied stress the fact that it then carries no load makes the pocket the equivalent of a “hole” in the glass. Such a “hole” would act as a stress concentrator. In this way the time elapsing before breakage occurs is explained as being due to the time required for the stress in the quasi-viscous material to relax. By means of a model representing the stress concentration at a pocket an equation is derived relating the breaking strength, PB,with time. Values of the breaking strength calculated from this equation, PB−a=b/tk, are in good agreement with published experimental results.
J. B. Murgatroyd
