焼なまし純アルミニウムの疲労粒界き裂の生成

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The observation has been made on the surface cracks initiated on extremely pure aluminum fatigued by tension and compression. Plate specimens, 0.7 mm thick were completely annealed and then electropolished. The resulting grain sizes were from 0.2 to 1 mm diameters. The tests were made with the strain amplitudes of 0.05% and 0.25%. Their surfaces were observed with an optical microscope and a scanning electron microscope. The slip band patterns observed could be classified in three types: x_1, long and straight one, x_2, wavy one, x_3, meshlike one. Specimen I subjected to the smaller strain amplitude of 1.7×10^6 cycles revealed the many intergranular cracks when the slip bands were removed by a slight electropolishing. By examining the relation between the slip bands and the cracks, the following facts could be clarified: The slip bands of pattern x_1 which lie in direction of from 40°of 55°to the stress axis were in high angles with the cracks along the grain boundaries. On the specimen II fatigued at the larger strain amplitude, the intergranular cracks could also be observed after 2×10^4 cycles. The cracks propagated along the grain boundaries until about a half of fracture life (1.4×10^5 cycles). The relation between the cracks and the slip bands was the same as that which was observed on the specimen I. The following conclusion may be driven: The glides are impeded at the grain boundary and many dislocations pile up there. The grain boundary should be destroyed. Those microcracks join with each other and grow up into an observable crack.
社団法人日本材料学会の論文
1974-08-15

焼なまし純アルミニウムの疲労粒界き裂の生成

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