Estimation of Crack Propagating Property by the Rotating Bending Fatigue Tests of Specimens with a Small Hole

Abstract

The rotating bending tests of specimens with a small hole were made on five materials. The main results obtained are as follows: (1) The life for crack propagation under the stress of (1+ζ) times the fatigue limit of plain specimens is greatly different for different materials (ζ: a positive constant). (2) When the crack length l is small, the rate of crack propagation dl/dN is nearly proportional to 6ⁿl (n: material constant). The values of n are 3∼8. The difference in the value of n is based on the difference in the crack closure behavior. (3) The relation between the crack length l and the relative number of cycles normalized by the life for crack propagation is independent of stress levels and materials. (4) When the crack lendth l is equal, the form of crack surface is also equal, irrespective of stress levels and materials. (5) The rotating bending fatigue test of specimens with a small hole is suitable for the estimation of crack propagating property of a material.