As the notch root radius in the notch-tension specimen is reduced, a limit is reached beyond which sharper machined notches are not feasible. Sharper notches, potentially, can be formed by fatigue action. The fatigue notches have a flank angle of effectively zero, while the notch root radius is from two to three orders of magnitude less than that for the machined notches. It is important to know the effect of a fatigue notch on the notch strength of a steel, which in the present work was a 4340 steel heat-treated to characteristic strength levels.
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