The Crack Propagation by the Stress Amplitude below the Fatigue Limit

Abstract

The greater part of the service load is occupied by the stress amplitudes below the fatigue limit. And the effect of this kind of stress amplitudes on the fatigue life is a quite important factor in estimating fatigue strength under service load. A fatigue test with a normalized 0.35% carbon steel under programmed rotating bending load was carried out. Cracks were initiated by the stress amplitudes above the fatigue limit, them they were propagated by the stress amplitudes below the fatigue limit, and the rate of crack propagation was measured. The test results show that the condition of crack propagation under the stress ampltudes below the fatigue limit is decided by the magnitudes of them and the crack length which was initiated by the stress amplitudes above the fatigue limit. And the behavior of crack propagation in cracked specimens is similar to that in sharply notched specimens.