硬質材料のσ_m=ψK_<IC>S_<mf>^<1/2>式によるK_<IC>評価値における停止亀裂起因誤差 [in Japanese] Error Due to Stopped Cracks in K_<IC> Value Estimated by Equation of σ_m=ψK_<IC>S_<mf>^<1/2> for Hard Materials [in Japanese]
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Abstract
In our previous study, we have theoretically derived an equation of σ<SUB>m</SUB>=ψK<SUB>IC</SUB>S<SUB>mf</SUB><SUP>1/2</SUP> based on the fracture theory for general hard materials, where σ<SUB>m</SUB> is the flexural strength of test piece, ψ is a factor, K<SUB>IC</SUB> is the fracture toughness and S<SUB>mf</SUB> is the total macroscopic area of fracture surfaces of all fragments of one test piece, and also experimentally confirmed it's validity on two kinds of hard materials, i.e., WCCo cemented carbides and Si<SUB>3</SUB>N<SUB>4</SUB> base ceramics. In this study, the error due to stopped cracks (cracks which do not cause the formation of fragments, but generate internal fracture surfaces) in the relative value of K<SUB>IC</SUB> estimated by using the above equation was investigated on WC10mass%Co cemented carbide (the size of test piece is 4×3×36mm<SUP>3</SUP> and the span of ii e is 30mm).<BR>The results obtained were as follows; (1)The total macroscopic area of internal fracture surfaces formed by stopped cracks (S<SUB>c</SUB>) increased from 4.7 to 9.3mm<SUP>2</SUP> with increasing σ<SUB>m</SUB>. However, the ratio of S<SUB>c</SUB>/S<SUB>mf</SUB> was almost constant; 0.050.06. (2)A linear correlation was found between σ<SUB>m</SUB> and (S<SUB>m ?? </SUB>+S<SUB>c</SUB>)<SUP>1/2</SUP> in similar manner to σ<SUB>m</SUB>S<SUB>mf</SUB><SUP>1/2</SUP> relation. The slope of the correlation line (ψK<SUP>c</SUP><SUB>IC</SUB>; K<SUP>c</SUP><SUB>IC</SUB> is the fracture toughness estimated by taking into consideration S<SUB>c</SUB>) was nearly the same as that of σmSmf1/2 correlation line (ψK<SUB>IC</SUB>) in accordance with the results that K<SUP>c</SUP><SUB>IC</SUB>/K<SUB>IC</SUB> expressed as {S<SUB>mf</SUB>/(S<SUB>mf</SUB>+S<SUB>c</SUB>)}<SUP>1/2</SUP> was 0.970.98 and the error estimated by equation (K<SUB>IC</SUB>K<SUP>c</SUP><SUB>IC</SUB>)/K<SUP>c</SUP><SUB>IC</SUB> is about 2.5%. Therefore, it was concluded that the error due to stopped cracks or S<SUB>c</SUB> is negligible.
Journal

 J. Jpn. Soc. Powder Powder Metallurgy

J. Jpn. Soc. Powder Powder Metallurgy 43(4), 526530, 19960415
Japan Society of Powder and Powder Metallurgy