Critical Frontal Process Zone Size and Fracture Toughness

概要

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Our previously proposed technique for estimating critical sizes of the frontal process zone (FPZ) in ceramics is improved using exact solutions of stress distributions around a crack and elliptical hole tips in an infinite plate for calculating critical local stress. In the present work, a three-point flexure test is carried out with V-notched ceramic specimens (Single-edge V-notched beam method), and the relation between the strength and notch depth is successfully established. The critical local stress at the crack propagation is calculated at a characteristic distance from the notch tip based on a local fracture criterion. Exact solutions for a crack or elliptical hole in an infinite plate are used to estimate the critical local stress. In this study, attempts were made to estimate the critical size of the FPZ, fracture toughness, and flexural strength of several ceramic materials. A comparative study between mechanical properties and the critical size of the FPZ indicates that the fracture toughness and product of strength and square root of the critical FPZ size holds a linear relation. This result suggests that both the strength and critical size of the FPZ must be increased to enhance the fracture toughness of ceramics.
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