Al-Zn-Mg合金の応力腐食割れに関する研究 : 破断寿命に及ぼす試験片形状の影響について

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Al-5.91wt.%Zn-1.96wt.%Mg-0.16wt.%Fe alloy specimens with a thickness of 1mm were prepared five different shapes named H-shape, I-shape,V-shape,0-shape,and U-shape by a fraise-machine, a drill machine, and a hand-saw. They were heated in the condition of aging at 120℃ for 24 hours, after solidification at 450℃ for 30 minute and quenching into water at 0℃. Nineteen test-specimens with the same shape were tested in order to measure failure times of the stress corrosion cracking under three constant applied stresses (80%,60%,40% of 0.2% flow stress, σy,) in 3.5% NaCl + 0.2% H202 water solution of pH 5.2. Nineteen failure times measured were plotted on the Weibull's probability paper which is widely used in the reliability engineering. Cumulative probability distributions of failure time were found to be described as the single Weibull's distribution. The shape parameters (m) of the Weibull's distribution of failure time were found to lie between 3 to 8. The scale parameters (η) of the Weibull's distribution were obtained. The average failure times (μ) were calculated by the values of m and η. The failure probability density function f(t) vs. time (t) curves were plotted in order to compare the effect of the applied stresses in the same shape, and the cumulative failure distribution function F(t) vs. time (t) curves were plotted in order to compare the effect of the five specimen's shapes under the same applied stress. Notch-effects in their shapes to the stress-concentration were calculated by the finite element method and displayed on the computer. The mechanisms of failure which occur with the intergranular cracking and the transgranular cracking were discussed on specimen's shapes and applied stresses by the above mentioned results.
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Al-Zn-Mg合金の応力腐食割れに関する研究 : 破断寿命に及ぼす試験片形状の影響について

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