抄録
The comprehension of the statistical fatigue property of structural steels is increasingly considered to be important as the basic data in designing with high reliability.
The authors had formerly reported the results of statistical fatigue tests performed on several structural alloys. The distribution characteristics in fatigue strength of the material were discussed by examining the distribution of the deviations in stress of individual test data from the median S-N curve. The present paper deals with heat-to-heat change of the statistical fatigue property analysed by the same method as before, for each 3 heats of 0.45%C carbon steel and 1%Cr-0.2% Mo-0.35%C low alloy steel. The effects of heat treatments and sharp notch were studied for 12 test conditions in total, each comprising more than 120 test specimens.
It was revealed that the Vickers hardness of heat treated materials coming from one heat obeyed the normal distribution law, and the fatigue strength of smooth specimens could be predicted by the same distribution law; while the fatigue strength of notched specimens showed an asymmetric distribution having a larger scatter in the weaker side and being approximated by Weibull's function. The variation coefficient of fatigue strength increases under the effect of notch, in varying degree depending upon heat treatment condition, probably reflecting microstructural differences at the fatigue crack tips. The heat-to-heat change in variation coefficient of fatigue strength for smooth specimens was explained by the variation of material's homogeneity, e. g. chemical composition, and by the substantial fatigue variation which increases with increasing fatigue strength of the material.
