σ_m=ΨK_<IC>S_<mf>^<1/2>式と到達可能強度推定法のMnZnフェライトへの適用の可否 [in Japanese] Applicabilities of Equation of σ_m=ΨK_<IC>S_<mf>^<1/2> and Estimation Method of Attainable Strength to MnZn Ferrite [in Japanese]
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Abstract
In order to clarify whether our theoretically derived equation of σm=ΨKicSmf<SUP>1/2</SUP>(σm; threepoints bending fracture strength, Ψ shape factor, K<SUB>IC</SUB>; fracture toughness, S<SUB>mf</SUB>; total macroscopic area of fracture surface) can be applied to brittle materials having considerably lower K<SUB>IC</SUB> and σm than those of WC10mass%Co cemented carbide, etc., the relation among σm, K<SUB>IC</SUB> and S<SUB>mf</SUB> was investigated for MnZn ferrite (K<SUB>IC</SUB>; 1.3MPa.m<SUP>1/2</SUP>, the mean value of σm; 0.18GPa) as an example. In addition, the applicability of equation of σo=σd{1+2(a/ρ)<SUP>1/2</SUP>} or σ0<SUP>1</SUP>=σ0<SUP>1</SUP>+2σ0<SUP>1</SUP>ρ<SUP>1/2</SUP> a<SUP>1/2</SUP>, i.e., the applicability of the estimation method of attainable strength (σ<SUB>a</SUB>; σ<SUB>d</SUB> or σ<SUB>m</SUB> at 2a=mean grain size) to MnZn ferrite was also investigated {σo; ideal bending fracture strength, i.e., the strength which is assumed to be obtained when the length (2a) of longer axis of fracture source becomes imaginarily zero, although the actual attainable minimum value of 2a is the mean grain size of the materials, σ<SUB>d</SUB>; external stress which operated on the fracture source at the moment of fracture, ρ; effective curvatureradius of the edge of fracture source}.<BR>The results obtained were as follows: (1) The linear correlation was found between σm and Smf<SUP>1/2</SUP>, in a similar way to the cemented carbide, etc., which indicates that the equation of σm=ΨK<SUB>IC</SUB>S<SUB>mf</SUB><SUP>1/2</SUP>is also applicable to the ferrite or brittle materials with considerably low K<SUB>IC</SUB> and σ<SUB>m</SUB>. The ratio of the slopes of two regression lines of the ferrite and the cemented carbide coincided well with the ratio of the measured K<SUB>IC</SUB> values of both materials. This indicates that the Vvalue in equation ofσ<SUB>m</SUB>=ΨK<SUB>IC</SUB>S<SUB>mf</SUB><SUP>1/2</SUP> of this ferrite was nearly equal to that of the cemented carbide; the ψ values of both materials were about 15×10<SUP>3</SUP>m<SUP>3/2</SUP>. (2)The equation of σ<SUB>d</SUB><SUP>1</SUP>=σ<SUB>0</SUB><SUP>1</SUP>+2σ<SUB>0</SUB><SUP>1</SUP>+2σ<SUB>0</SUB><SUP>1</SUP>ρ<SUP>1/2</SUP>a<SUP>1/2</SUP> also held for the ferrite. The σ<SUB>a</SUB> of this material was estimated to be about 0.26GPa, which was about 44% higher than the measured mean value of σm (0.18GPa).
Journal

 J. Jpn. Soc. Powder Powder Metallurgy

J. Jpn. Soc. Powder Powder Metallurgy 45(6), 529534, 19980615
Japan Society of Powder and Powder Metallurgy