日本機械学会論文集
Online ISSN : 2187-9761
ISSN-L : 2187-9761
材料力学,機械材料,材料加工
高湿度中における高強度Al合金7075-T6押出材の疲労き裂伝ぱ機構
皮籠石 紀雄仮屋 孝二陳 強中村 祐三永野 茂憲王 清遠
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2015 年 81 巻 825 号 p. 14-00694

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Effect of humidity on the growth mechanism of a fatigue crack in an age-hardened Al alloy was investigated in relative humidity environments of 25% and 85% at loading frequencies of 50Hz and 6Hz. Macroscopic growth mode of a crack in low humidity was a tensile one irrespective of loading frequency. By contrast, the mode in high humidity was changed from the shear one to the tensile one with increase in fatigue life at 50 Hz, while it was the tensile mode only in the wide range of fatigue life at 6 Hz. In low humidity, the crack propagated by forming striations which are general in fatigue of many metals. On the other hand, in high humidity, most of fracture surface was occupied by many slip planes in the shear mode crack and by granular facets in addition to striations in the tensile mode one. The crack growth rate in high humidity was higher in the shear mode crack than in the tensile mode one. The differences in growth mechanism and growth rate of a crack were explained by the content of diffused hydrogen generated by reaction of water vapor and aluminum in addition to the microstructure with sub-grain and texture and the cyclic softening behavior of the alloy.

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