アルミニウム合金7075-T6の微小疲労き裂成長挙動の応力比依存性 (主として第I段階き裂成長過程に注目して)

概要

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The growth behaviour of small fatigue cracks was investigated on an luminum alloy 7075-T6 at the stress ratos R of 0, -1 and -2. The effect of stress ratio was discussed on the basis of the detaild observation with special interest in the stage I region of small crack grouth. Cracks initiated at R=-1 and -2, grew to a certain depth by the stage I growth mechanism, and the stage II crack growth followed. The stage I to stage II transition occurred under a constant maximum stress intensity factor which was approximately consistent with the effective threshold stress intensity range, ΔΚ_<eff,th'> for large cracks. At R=0, on the other hand, the stage I crack growth was not observed because of crack initiation at inclusions. At all the stress ratios, small cracks grew more rapidly than large cracks in the same nominal stress intensity range, and grew below the threshold stress intensity range, ΔΚ_<th>, for large cracks. Particularly, the stage I cracks showed much higher growth rate and grew below ΔΚ_<eff,th'> for large cracks. It is suggested that the stage II crack growth rate can be characterized in terms of the effective stress intensity range, while a micromechanics approach is successful to evaluate the stage I crack growth rate.
社団法人日本材料学会の論文
1989-09-15