Some observations on the propagation of fatigue cracks

Abstract

The current researches on crack propagation in Materials Division of MERL mainly arose from two short fatigue determinations which formed a very small Dart of a Darjer [1] by the author and a colleague. It was shown that mild steel bars of about 2 inches diameter, containing a circumferential V-notch 0.2 inch deep, had the same fatigue strength under reversed direct stress whether the root radius of the notch was 0.002 inch or 0.025 inch. Further considerations of this matter were described in another paper [2] in which it was shown that cracks occurred at the bottom of the sharp notches at a very early stage of the fatigue test.