疲労寿命のばらつき特性とフェライト粒径の関係

抄録

It is important to evaluate the scatter in fatigue life. In the present study, rotating bending fatigue tests of 0.21% C steel having three ferrite grain sizes were carried out respectively. The initiation and growth behavior of cracks which led to the fracture of the specimens were examined. The fatigue data were statistically analyzed, and the following results were obtained. The scatter in the crack propagation behavior at the stress close to fatigue limit is especially large. Such a large scatter depends on the behavior of microcracks whose length is about 8 times smaller than the grain size. However, the scatter in propagation behavior of cracks 8 times larger than the grain size is relatively small. Distributions relating to all phases of lifetime can be expressed by the two-or three-parameter Weibull distribution. The coefficient of variance CV vs σ_a/σ_w relation for these distributions can be individually expressed as a narrow band independent of ferrite grain size.