Some experimental studies of fatigue slip bands and persistent slip bands during fatigue process of low-carbon steel

Abstract

Initiation and propagation behaviours of fatigue slip bands and persistent slip bands in lowcarbon steel have been investigated: fatigue slip bands were expressed quantitatively as a volume fraction which was products of the slip bands area ( Σ A s A 0 ), the depth ( h s h 0 ) and the number of slipped grains ( G s G 0 ). It was shown that distributions of fatigue slip bands and persistent slip bands showed the maximum at the angle division of 0° ~ 10° (at and near the normal to the stress axis) and decreased gradually with increasing of the angle. And the normalized volume fraction of fatigue slip bands increased linearly in proportion to the number of cycles independently of the stress amplitude σ a and the angle θ. The increment in volume fraction of fatigue slip bands meant the increment in fatigue damage and the fatigue life decreased in proportion to the increment in volume fraction of fatigue slip bands until its value reached a certain content. Then, the initiation rates of fatigue slip bands, persistent slip bands and stage I microcracks showed the increasing tendency with increasing of stress amplitude σ a , and the propagating rates from fatigue slip bands to persistent slip bands and from fatigue slip bands to stage I micro-cracks were also similar increasing tendency with stress amplitude.