時効硬化Al合金押出し材のせん断形疲労き裂の伝ぱ機構

Translated title of the contribution: Growth Mechanism of Shear Mode Fatigue Crack of Age-Hardened Al Alloy

皮籠石 紀雄, 仮屋 孝二, 陳 強, 後藤 真宏, 中村 祐三

Research output: Contribution to journalArticle

Abstract

In order to investigate the growth mechanism of a shear mode fatigue crack in an extruded bar of an age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out using plain specimens of the alloy in environments of controlled relative humidity of 25%, 50%, 75% and 85%, distilled water and nitrogen gas. Fatigue strength was decreased by high humidity. The growth mechanism of a fatigue crack was different depending on environment and stress level. Although most of fractures occurred by the growth of a tensile mode crack, a crack propagated in a shear mode accompanying with slip planes and voids at high stress levels in high humidity and at all stress levels tested in nitrogen gas. The shear mode crack was related to the marked texture of the alloy. Growth rates of the shear mode crack were higher in high humidity than in nitrogen gas. Growth mechanisms of the shear mode crack were different between environments in nitrogen gas and in high humidity. That is, the reason for the growth of a shear mode crack in nitrogen gas was the suppression to growth of a tensile mode crack by reversible slip due to absence of oxide film. On the other hand, in high humidity, the growth of a shear mode crack was promoted by the formation and coalescence of voids, suggesting that the acceleration of the growth rate of a crack may be assisted by hydrogen accumulated around precipitated particles on glide planes.
Original languageJapanese
Pages (from-to)890-897
Number of pages8
JournalZairyo/Journal of the Society of Materials Science, Japan
Volume60
Issue number10
DOIs
Publication statusPublished - 2011

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