アルミニウムにおける疲労クラック近くの下部組織観察

抄録

Aluminium polycrystalline specimens of 99.99% purity were fatigued at room temperature by alternating tension and compression. Substructures near the tips of fatigue cracks were observed at various stages of crack propagation using an X-ray microbeam technique. Effects of the crack length and the alternating stress on the characteristics of substructures and the size of plastic zone were examined.
The main results obtained are as follows.
(1) Regardless of the fatigue stress and the crack length, a plastic zone, in which a well-defined substructure is observed, exists around a fatigue crack. The results are in good agreement with the results reported on some fcc metals and alloys fatigued by alternate bending.
(2) The following two factors may be effective in the formation of the well-defined substructure near the tip of a fatigue crack; the stress concentration at the tip of a fatigue crack and a large quantity of vacancies formed during stress cycling.
(3) The characteristics of the plastic zones revealed by the present study by means of structure observations are very similar to those of the plastic zones deduced from the data based on a macroscopic point of view. It seems possible, therefore, that both plastic zones are explained from the same standpoint.