Considerations of the Small-Crack Growth Law Based on COD : Low-Cycle Bending Fatigue Test of an Annealed 0.45%C Steel in the SEM

Abstract

Low-cycle bending fatigue tests were carried out on annealed 0.45% C steel specimens with a blind hole inside a SEM. ΔCOD was measured from SEM photographs. The small-crack growth law was discussed based on the ΔCOD. The main results obtained were as follows : ( 1 ) When strain level is constant, the shapes of the rims of cracks are geometrically similar to each other and the crack opening ratio U is nearly constant. ( 2 ) When the dl/dN's in several specimens are equal, the ΔCOD's near the crack tip are also nearly equal. ( 3 ) The phenomena mentioned above support the small-crack growth law dl/dN∝l.