せん断モードの疲労き裂進展とは？

抄録

Mode I and Mode II are defined as terms of fracture mechanics which express the deformation mode of a crack under some loading. However, the terminology which expresses the fatigue crack propagation mode under a mode or mixed-mode loading is not clearly defined until now. For example, it is not clear what is called the mode of fatigue crack propagation in which the initial crack under the Mode II loading propagates along the maximum shear plane in macro-scale and propagates along the maximum principal stress plane in micro-scale; that is zig-zag shape fatigue crack. It is considered that the unclear classification such as “Tensile mode” and “Shear mode” prevents the development of this field. In this paper, we pointed out the definition problem of shear mode fatigue crack propagation to predict the propagation behavior of fatigue crack. Focusing on the phenomenon, not the loading, we propose the terms “Plastic deformation mode” and “Damage accumulation mode” fatigue crack propagation. The revealed fatigue crack propagation phenomenon under cyclic pure Mode II loading is the achievement of the author’s previous study. Furthermore, we propose a method for predicting fatigue crack propagation behavior in each mode and a method for classifying existing fatigue cracks.