Change in Surface States and Incipient Fatigue Cracks in Electro-Polished Low Carbon Steel (Plain and Notched Specimens) under Rotating Bending Stress

抄録

Using electro-polished low carbon steel specimens, the change in surface states and the incipient fatigue cracks of plain and notched specimens subjected to rotating bending stress were investigated. The main results obtained are as follows. (1) When the limit stress for macro-crack initiation σ_w1 is repeated, the amount of slip bands appearing at the root of notch is nearly equal, not only after 10⁷ cycles but also at every cycle ratio, even if the maximum stress ασ_w1 at the bottom of notch is different in various radii of the notches. (2) In the specimens with various radii of the notches, the limit stress for slip bands initiation σ_ws is almost proportional to the stress σ_w1, that is, σ_ws≌(0.85∼0.9)σ_w1. (3) The incipient fatigue cracks, which appear on plain specimens after 10⁷ cycles of the stress σ_w1, can hardly sustain the tensile stress statically and dynamically.