停留きれつに関するFrost, Dugdale, Phillipsの実験について

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When a specimen with a sharp notch is subjected to a alternating load of moderate magnitude, there are occasions when the developed crack does not propagate itself 'further unless the load on the specimen is increased, although the fatigue crack has developed at the root of the notch. Such a crack is called non-propagating fatigue crack. Frost et al. carried out the direct stress fatigue test on mild steel flat plate specimens with edge notches and closely observed the circumstances to get non-propagating cracks. According to their experiments the maximum tensile stress to develop non-propagating crack is independent of the notch root radius. They showed further that the non-propagating fatigue crack does not develop in specimens under a pulsating load of which the mean part is larger than the half amplitude. In this paper, explanations of their results are given by a theory developed by the author, concerning the existence of branch point for zero mean load. The theory is based mainly on the following two facts that : (i) the mode of strain-(or stress-) repetitions at the tip of a fatigue crack is nearly of pulsating type, irrespective of the mode of the loading on the specimens, and (ii) in specimens of which non-propagating cracks can be observed, the crack initiating stress at the root of the notch, is larger than or equal to the yield point of the material, and lastly, (iii) a small yielded zone, appeared at the tip of the crack during load repetitions, makes the strength of the material ahead of the tip of crack not to differ so much from that of the root of the notch where yielding occurs before the initial crack develops there.
社団法人日本材料学会の論文
1958-07-15

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石橋正
九州大学工学部

停留きれつに関するFrost, Dugdale, Phillipsの実験について

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