Section-and-Etch Study of Hertzian Fracture Mechanics

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Abstract
A section-and-etch technique is used to study the mechanics of Hertzian cone-crack growth in glass. With a suitable choice of test environment the cone cracks propagate at a convenient rate through successive phases of stability at constant indenter load. Systematic measurements of the etched-crack lengths as a function of indentation time permit a detailed description of the fracture mechanics. Within a certain range of indenter load, the cone crack is observed to grow as a shallow surface ring to a critical depth prior to full development. This directly confirms a salient feature of the energy balance theory of Hertzian fracture outlined in earlier papers. The current status of the long-standing Auerbach law, which relates the critical fracture load linearly to the indenter radius, is discussed in the light of the present evidence.

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