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Since the delayed fracture of glass was first reported, a lot of studies have been conducted. In general, it has been understood that the true character of delayed fracture behavior exists in the stress corrosion cracking process in humid environment. The process of delayed fracture in glass, however, has not been made clear sufficiently.One of the reasons for this situation is that delayed fracture characteristics depend extremely upon the defect statistics.On the other hand, when the strength of brittle materials such as glass or ceramics is examined, it is necessary to eliminate the effect of distributed Griffith cracks on strength characteristics. For this purpose, many kinds of testing methods using abraded specimens have been proposed. One of these testing methods utilizes Vickers diamond indented specimens, which may also be employed for the evaluation of delayed fracture characteristics of glass.In this paper, four points bending delayed fracture tests in deionized water were conducted by using the soda-lime-silica glass plate specimens with the initial crack and indentation pit by Vickers diamond indentation.The results show that the lateral crack morphology is a governing factor for the delayed fracture characteristics of the specimens used in this experiment.This fact is brought about by the crack propagation behavior that the initiated crack (radial crack) propagates around the lateral crack.

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Since fatigue is essentially the manifestation of continuous local fracture caused by cyclic stressing, it has been pointed out that fatigue shows the statistical characteristics reflecting the stochastic feature of each fatigue process.Thus, the factors governing this fluctuation can be studied on the basis of both extreme theory and the stochastic process theory.The similar fluctuation also appears in the fatigue crack propagation process, and consequently a number of crack growth curves may be obtained.In this paper, the Monte-Carlo simulation was conducted by assuming the microstructural heterogeneity model as well as the stochastic process model of fatigue crack propagation, and the factors governing the statistical fluctuation in the fatigue crack propagation process were investigated.The results show clearly that such a factor as the difference in resisting power of structure caused by the change in size distribution of structural units like crystal grains, influences considerably the stochastic feature of the fatigue crack propagation process.