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Rotary bending fatigue tests were carried out by using smooth specimens of medium car-bon steel with two ferrite grain sizes.In order to clarify the physical background of the scatter in fa-tigue behavior,the statistical characteristics of the initiation and growth of short fatigue crack were in-vestigated.Results show that the short crack initiation and growth life distribution can be expressed bytwo-or three-parameter Weibull distribution.The Weibull distribution of the mixed type is weU fittedto the crack length distribution for both steels.The knee values of Weibull plots are related to the grainsize.The crack length distribution before the knee point can be expressed by a two-parameter Weibulldistribution,and that after the knee point can be represented by two-or three-parameter Weibull distri-bution.It was found that the initiation life,growth life and crack length distribution were affected bythe grain size.
Rotary bending fatigue tests were carried out by using smooth specimens of medium car-bon steel with two ferrite grain sizes. In order to clarify the physical background of the scatter in fa-tigue behavior, the statistical characteristics of the initiation and growth of short fatigue Results were shown that the short crack initiation and growth life distribution can be expressed bytwo-or three-parameter Weibull distribution. The Weibull distribution of the mixed type is weU fittedto the crack length distribution for both steels.The knee values of Weibull plots are related to the grainsize. The crack length distribution before the knee point can be expressed by a two-parameter Weibulldistribution, and that after after the knee point can be represented by two- or three-parameter Weibull distri-ution. It was found that the initiation life, growth life and crack length distribution were affected bythe grain size.