Affiliation:
1. University of Toyama
2. Southwest Jiaotong University
Abstract
Fatigue fracture of some high-strength steels occurs at small defect in the subsurface
zone of a material at low stress amplitude level and in a high-cycle region of more than 106 cycles
(gigacycle fatigue life), whereas surface fatigue crack initiation occurs at high-stress amplitude and
low cycles. There is a definite stress range where the crack initiation site changes from a surface to
a subsurface defect, giving a step-wise S-N curve or a duplex S-N curve. From the experimental
results, fatigue fracture mode was classified into three types, such as, surface inclusion induced
fracture mode, subsurface inclusion induced fracture mode without granular bright facet (GBF) area
and that with the GBF, depending on stress amplitude level and stress ratio. The GBF area was
observed in the vicinity of a non-metallic inclusion at the fracture origin inside the fish-eye in
gigacycle fatigue regime. It was made clear from the discussion with fracture mechanics that the
transition of fracture mode was affected by compressive residual stresses on the specimen surface.
Fracture-mode transition diagram was proposed through the experimental and theoretical
investigation. Also, from the evaluation of the fatigue life based on the estimated subsurface crack
growth rate from the S-N data, effect of inclusion size on the dispersion of fatigue life was
explained, and S-N curve for subsurface inclusion-induced fracture depended on the inclusion size
was provided.
Publisher
Trans Tech Publications, Ltd.
Cited by
22 articles.
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