Evaluation of Fracture Toughness for Ceramic Materials
Toshimitsu Fujii, Tetsuro Nose
pp. 717-725
Abstract
Toughening mechanisms hitherto proposed, such as microcracking, crack-path-deflection, crack-bowing, and transformation-induced-plasticity, are briefly introduced. The increase in crack resistance (rising R-curve) due to the process zone wake is discussed in relation to test methods and precracking techniques. Stable crack extension is apt to be accompanied by the increase in crack resistance due to the wake of transformation or frictional interlocking, whereas pop-in crack extension seems to be little attended by these phenomena. The loading rate dependence of KIC value is also discussed. The KIC value can be affected by the time dependent phenomena such as stress corrosion cracking even at room temperature and crack tip blunting, stable crack extension, etc., at elevated termperatures.
Various test methods tentatively used to evaluate the critical stress intensity factor, KIC for ceramic materials are explained, and their advantages and disadvantages are discussed, partly referring to the results of the round robin tests organized by the Japan Fine Ceramics Association (J.F.C.A.). The bridge-indentation method, a new precracking technique, is also briefly explained.
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