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Conical indentation fractures in silicate glass are stable, so that the speed at which they spread can be controlled. The validity of the Griffith fracture condition (energy balance) has been tested for such fractures and confirmed, with qualifications. Measurements on cone fractures are a method for determining accurately the specific fracture energy of brittle materials under physical and chemical conditions that can be chosen at will.
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Frank Roesler (1956) studied this question.
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