繰返し変形に伴ってき裂先端近傍に生じるひずみの測定とそれに基づく疲労き裂成長過程の検討

概要

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The strain in the vicinity of a crack tip was examined under cyclic loading by means of the grid method, where special attention was given to the strain behavior during one load cycle. Both the longitudinal and shear strains, ε_y and γ_<rθ>, were intensely developed in the directions of θ≒±60°ahead of the crack tip, where θ is the angle inclined with respect to the general direction of crack extension. The variation in the two strains during half a cycle was also extremely great in these directions. Such a strain variation was quite small in a V-shaped region situated between the two directions of θ≒50°〜60°and θ≒-50°〜-60°. One of the cracks which branched into these two directions finally grew. Then an "ear" was left at the position where the tip of another crack was located. The crack extension process in the midthickness region of the specimen seems to be different from the one observed on the specimen surface. Some analogy, however, was realized between the midthickness and surface regions through the SEM observations ; a quite deep groove was left on the fracture surface among typical striations in the former, corresponding to an "ear" formed in the latter. Therefore, it was suggested that consideration of the crack extension process through surface observations might provide some useful general information on the fatigue crack growth process.
一般社団法人日本機械学会の論文
1993-03-25