1993 年 59 巻 566 号 p. 2248-2252
Recently, it has been reported that the fracture stress σf and the fracture toughness Kc of engineering ceramics, measured by use of short precracks, have values lower than, σf = KIC/(πc)1/2 and KC = KIC, which might be expected from the conventional fracture mechanics. In the present study, assuming that these phenomena are due to the effect of a microdefect formed ahead of a main crack under applied stress, we propose a main crack-microdefect interaction model and formulate it using the theory of continuous distribution of dislocation in order to explain the above experimental results. As a result, we obtain the stress intensity factor K at the tip of the microdefect in a closed form. Supposing that macroscopic fracture would be caused when the stress intensity factor K reaches the plane-strain fracture toughness KIC, we can obtain the analytical expressions of the fracture stress σf and the fracture toughness Kc and explain the above phenomena theoretically.