微小欠陥材の ΔK_<th> に及ぼすき裂の幾何学的パラメータと平均応力の影響

概要

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Push-pull fatigue tests under different mean stresses (σ_m=-98, 0, +98 MPa) were carried out on annealed low carbon steel containing an artificial drilled hole (the diameter of the hole : d=50, 100, 200 μm). The experimental results were compared with those of rotating-bending tests. The geometrical parameter controlling ΔK_<th> was proposed on the basis of the analytical result on surface cracks with various shapes. The conclusions are summarized as follows: (1) The effect of defects increased with increasing mean stress from compressive to tensile stress. This is because the propagation of cracks emanated from defects is dependent on the magnitude of mean stress. (2) The true stress at the surface of rotating-bending fatigue specimens was calculated on the basis of cyclic stress-strain curve and the true stress of fatigue limit under bending was found to be nearly equal to that of push-pull fatigue under zero mean stress. (3) ΔK_<th> of the specimens containing small surface cracks with arbitrary shape can be evaluated uniquency using the geometrical parameter√<area>, where area is the area of a defect projected in the direction of the maximum principal stress. The effect of mean stress on the relationship between ΔK_<th> and √<area> was also shown.
社団法人日本材料学会の論文
1985-10-15