Effect of Air on the Mode II Fatigue Crack Growth Mechanism and Threshold

摘要

In order to make clear the effect of air on the Mode n fatigue crack growth mechanism and threshold, the Mode II fatigue crack growth test was carried out in a vacuum. The Mode n fatigue fracture surface of the specimen tested in a vacuum was clearer than that tested in air. The Mode II fatigue crack of the specimen tested in a vacuum was more indistinct than that tested in air. This is because that the influence of oxidation in a vacuum was smaller than that in air. The layer with the microstructural change was observed in the vicinity of the Mode II fatigue crack. The Vickers hardness of the layer of the specimen tested in a vacuum was 770. The value was much higher than that of the original matrix (HV=190). The layer consisted of very line grains (approx 130nm). The Mode II threshold stress intensity factor range. DELTA K_(11th), in a vacuum was tentatively estimated to be larger than that in air based on the assumption of the same frictional coefficient.