微小き裂の下限界応力拡大係数幅ΔK_<th> に及ぼす硬さとき裂形状の影響

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The dependence of ΔK_<th> on crack size and material properties under stress ratio R=-1 was studied on various materials and microstructures. The values of ΔK_<th> for all materials investigated were standardized with one geometrical and one material parameter. The geometrical parameter, √< area>, is the square root of the area which is occupied by projecting defects or cracks onto the plane normal to the maximum tensile stress. The relationship between ΔK_<th> and √< area> is expressed as follows : K_<th>∝ (√< area>) ^<1/3> (a) The most relevant material parameter to standardize the data was the Vickers hardness,and the following relationship was obtained: K_<th>∝ (H_V+C) (b) The constant C in Eq. (b) reflects the difference of nonpropagation behavior of small cracks in soft and hard metals. By combining Eqs.(a) and (b),the following equations were derived for predicting ΔK_<th> and the fatigue limit σ_w of cracked members. ΔK_<th>=3.3×10^-3(H_V+120)(√< area>) ^<1/3> (c) σ_w=1.43(H_V+120)(√< area>) ^<1/6> (d) where the units are ΔK_<th>: MPa・m^<1/2>, √< area>μm and H_V:(kgf/mm^2). Equations (c) and (d) are applicable to crack having √< area> approximately less than 1000μm.
社団法人日本材料学会の論文
1986-08-15