下限界応力拡大係数ΔK_<th>に及ぼすき裂寸法と材質の影響

概要

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The dependence of ΔK_<th> on crack size and geometry, and Vickers hardness H_v under stress ratio R=-1 was studied. The effects of crack size and geometry are unified with a geometrical parameter √(area) which is the square root of the area occupied by projecting defects or cracks onto the plane normal to the maximum tensile stress. The dependence of ΔK_<th> on √(area) is expressed by ΔK_<th> ∝ (√(area))^<1/3> and that of ΔK_<th> on H_v is expressed by ΔK_<th>∝(H_v+C). For small cracks and defects with √(area)≦1000 μm, the following equation for predicting ΔK_<th> and the fatigue limit σ_ω are available : ΔK_<th>=3.3×10^<-3>(H_v+120)(√(area))^<1/3> σ_ω=1.43(H_v+120)/(√(area))^<1/6> where the units in these equations are ΔK_<th> : MPa・m^<1/2> , σ_ω : MPa, √(area) : μm. For cracks and defects with √(area) >1000 μm, the dependence of ΔK_<th> on crack size gradually changes from (√(area))^<1/3> to (√(area))^0 and this causes the difference in the exponent n in the equation of the type σ_ω^nl=C which was first obtained by N.E. Frost, and was confirmed later by other researchers. Although the tendency of many data indicates that there may be a linear correlation between ΔK_<th> for a large crack and H_v, more systematic studies are necessary to establish the exact relationship between ΔK_<th> and H_v.
一般社団法人日本機械学会の論文
1986-06-25