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

Abstract

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 σw1 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 ασw1 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 σws is almost proportional to the stress σw1, that is, σwsb(0.85∼0.9)σw1. (3) The incipient fatigue cracks, which appear on plain specimens after 107 cycles of the stress σw1, can hardly sustain the tensile stress statically and dynamically.