数値シミュレーションによる欠陥を有するセラミックスの破壊強度評価 : 第1報,基礎理論とアルミナセラミックスへの応用

概要

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It is well known that the fracture strength of ceramics with small defects is lower than the strength estimated by linear fracture mechanics, based on the strength of a large defect. This phenomenon can be explained by the increase in the crack resistance with crack propagation. This R-curve behavior is caused mainly by grain bridging in the wake of the crack. Recently the grain-bridging stresses for alumina and silicon nitride have been measured experimentally. In this study, the fracture strength is estimated by numerical simulation, based on grain-bridging stresses. In the simulation, the effective stress intensity factor at the crack tip, K_<tip>, and the effective fracture toughness at the crack tip, (K_<tip>)_c, are used for the conditions of stable and unstable crack propagation. It is found that the fracture toughness for long cracks, K_<Ic>, depends on specimen geometries, and the maximum values of K_c approach (K_<tip>)_c as the initial crack length approaches the width of the specimen. Furthermore a convenient method to evaluate (K_<tip>)_c experimentally is discussed.
社団法人日本機械学会の論文
1994-04-25