@techreport{oai:jaxa.repo.nii.ac.jp:00044660,
 author = {下河, 利行 and 浜口, 泰正 and SHIMOKAWA, Toshiyuki and HAMAGUCHI, Yasumasa},
 month = {May},
 note = {When a new factor serving as an error of applied stress is added to an identical condition under which an S-N curve has been obtained, it causes a deviation from the expected fatigue life, and the amount of the deviation is related to the slope of the S-N curve. In the present paper, the accumulated effect of all factors causing the fatigue life scatter is regarded as an error in applied stress. The equivalent stress is defined as the sum of the applied stress and the error in applied stress. This concept is applied to the results of a series of fatigue tests on 2024-T4 aircraft structural aluminium alloy speciments with a sharp notch(Kt=8.25) at a constant temperature and humidity. The interrelation between the scatter of the equivalent stress, the S-N curve, where N is the median fatigue life, and the scattering of fatigue life is discussed. The main results of this study are: (1)When an applied stress is higher than or equal to 8 kg/mm2, a fatigue crack grows throughout most of the whole life of a specimen. When an applied stress is not higher than 7 kg/mm2, the fatigue life is covered by the two periods of fatigue crack nucleation and propagation. Nevertheless, there is no significant difference in the distribution shape and the scatter of fatigue life between the two stress ranges. (2)The scatter of fatigue life obtained in the experiment is much smaller than many other fatigue test results. (3)The equivalent stress distribution is found to be an almost normal distribution. The standard deviation of the equivalent stress is nearly constant(0.256 to 0.375 kg/mm2) regardless of the stress level, and its coefficient of variation ranges from 0.0148 to 0.0494. (4)The proposed equivalent stress distribution model, which has a normal distribution with the constant standard deviation regardless of the stress level, gives a good explanation of the experimental results within the interpolate region of the S-N curve drawn from the experimental results. (5)The following facts have been verified experimentally and theoretically: In the range where the S-N curve on a semi-logarithmic scale is nearly straight, the fatigue life distribustion is considered to be a log-normal distribution. Wnen the applied stress is lower and the slope of the S-N curve is gentler, the fatigue life distribution departs from a log-normal distribution, and its skew is more pronounced. However, because the standard deviation of the equivaient stress obtained in this study is comparatively small, the shape of the fatigue life distribution has a tendency to from the log-normal type. (6)The coefficient of variation of fatigue life is about four to six times as large as that of the equivalent stress., 資料番号: NALTR0412000, レポート番号: NAL TR-412},
 title = {航空機用アルミニウム合金2024-T4切欠き材(Kt=8.25)における疲れ寿命のばらつきとS-N曲線との関係（温度および湿度を一定にした実験室内における実験）},
 year = {1975}
}