Correlation between the Fatigue Limit of a Material with Defects and Its Non-Propagating Crack : Some Considerations Based on the Bending or Torsional Fatigue of a Specimen with a Diametrical Hole

抄録

From our experiments carried out about the bending and torsional fatigue of S35C specimens with a diametrical hole (each specimen has a round hole or its connected holes), the following results were obtained. 1) In the case of a specimen with a diametrical hole, the root radius of the notch at the branch point is constant (ρ₀&cong;0.5 mm in our material), as in the case of the bending fatigue test of the circumferential notched specimen. This means that the fatigue limit of the material with defects is mainly determined by the limit stress for propagation of its non-propagating crack. 2) when the fatigue limit of a specimen with a diametrical hole is determined by the crack strength (whenρ<ρ₀), the fatigue limit is mainly dominated by the diametrical hole in the perpendicular direction of the maximum tensile stress. This means that the fatigue limit of a material with defects is more influenced by the size of defect than by the sharpness of defect. 3) It is case of a plain specimen, τ_w/σ_w&cong;0.6; but in the case of the specimen with a diametrical hole, τ_w/σ_w=0.750.9. This shows that the effect of defect in the bending fatigue is greater than in the torsional fatigue.