予き裂導入試片を用いた構造用セラミックスの破壊靭性評価(第4報) : 粒径の異なるα-アルミナ焼結体の破壊特性

概要

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Fracture toughness (K_<IC>) and crack extension resistance (R-curve characteristic) were evaluated for α-alumina polycrystals with different grain sizes. The K_<IC> values were measured by the SEPB and IF methods (JIS R 1607). The K_<IC> for a polycrystal with a large grain size measured by the SEPB was about 1.5 time as large as that measured by the IF method. The deviation of the K_<IC> decreased when the pop-in crack in the specimen used for the SEPB test was cut off by saw notch leaving only its front portion. Therefore, the large value of the K_<IC> obtained by the SEPB method for a polycrystal with a large grain size was due to the fracture surface traction behind the front portion of the pop-in precrack. The SEPB and SEVNB specimens of alumina with a large grain size were also provided for a stable fracture test in bending, and their R-curve characteristics were obtained from load-deflection curves during fracture. As unstable fracture often occurred during the bend test, a pair of elastic rectangular specimens without notch or precrack were placed on both sides of and parallel to the test specimen to improve the stability of the fracture process. The K_<I0> at the initiation of the crack was determined from the point where the compliance change of the specimen and AE occurred during the bend test. The result suggested the K_<IC> values were overestimated when the SEPB method was applied to R-curve materials.
1992-03-01