ホットプレス窒化ケイ素の曲げ強度および破壊じん性に及ぼすヌープ圧こんき裂長さと試験片寸法の影響

概要

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Three-point bending and fracture toughness tests were conducted on two kinds of hot-pressed silicon nitride. To examine the size effect on the bending strength, two kinds of different sized specimens were prepared. The bending strength of the large specimens showed a lower mean value and a larger scatter than that of the small specimens. The Weibull statistics gave insufficient explanation on these differences because the Weibull modulus differed depending on the specimen size. For the fracture toughness tests, a semicircular crack with a radius of 50μm to 1400 μm long was introduced on each specimen surface with the aid of Knoop indentation. The relationship between the fracture stress σ_F and the Knoop-indented crack length 2c was examined. Up to a critical value of 2 c_c, σ_F was incentive to 2c. For 2c> 2c_c, σ_F decreased with increasing 2c. The value of 2c_c differed depending on the materials. The fractographic observation revealed that for 2 c< 2 c_c, the fracture origin was mostly located either at inclusions or defects.
社団法人日本材料学会の論文
1988-08-15