對稱 二重 表面缺陷의 疲勞龜裂成長擧動에 對한 硏究 = A Study of the Fatigue Crack Growth Behavior of Twin Surface Cracks

다국어 초록 (Multilingual Abstract)

This paper is concerned with the fatigue crack growth behavior for twin surface cracks.
PMMA was selected for the specimen material because PMMA is transparent and the crack length of thickness direction can be measured exactly. Tension specimens having twin circular arc-shaped notch were used in the testing process.
The results obtained from a series of experiments are summarized as follows:
1. The fatigue crack propagation of shallow-type surfacs cracks such as the case of crack aspect ratrio c/a = 0.151 initiated at the deepest point of the crack. Therefore, stress intensity factor at this point is estimated to be maximum value.
2. The fatigue crack growth race of the width direction was larger than that of the thickness direction.
3. The interaction behavior between two surface cracks was obseved in the fatigue crack growth rates toward the thickness direction as well as in those in the width direction, particularly, in the latter was greater than in the former.
The more surface crack-tips approache closely, the greater the fatigue crack growth rate increases rapidly by the crack-tip interaction effect.
4. During the stable fatigue cracks are propagating, two surface cracks keep the feature approximately semi-elliptical cracks having major axis to minor axis length ratio of 3/2.