随机谱中小幅载荷对裂纹扩展寿命的影响

采用7050-T7451铝合金标准中心裂纹拉伸试样进行随机谱载荷下的疲劳裂纹扩展试验，研究在不同低载截除水平、不同裂纹参考长度下，裂纹扩展寿命及其分散性的变化。采用F检验法，对不同载荷谱下的裂纹扩展寿命的方差及相同载荷谱，不同裂纹长度的寿命的方差进行检验。分析表明，第一级和第二级截除水平下的裂纹扩展寿命的分散性没有显著差别，当载荷截除水平提高到最大幅值载荷的21％时，寿命分散性显著变大；相同载荷谱下，不同裂纹长度对应的扩展寿命的分散性没有显著差别。试验结果也表明，本文所考察的3个水平的小幅值载荷对裂纹扩展寿命的均值有显著影响；因此，在损伤容限和可靠性分析中，这些小幅值载荷是不可忽略的。

The Influence of Low Amplitude Cycles in Random Spectra on Crack Growth Life

Crack propagation experiments with CC(T) specimens under three omission levels of low amplitude cycles of random spectra were conducted to investigate the influence of low amplitude cycles on crack growth life in 7050-T7451 aluminum alloy.The deviations of crack growth life under different spectra and under the same spectra with three crack lengths were studied via Fisher test.The results indicate that the dispersivity of crack growth life under the first two omission levels shows no remarkable differences,however,the dispersivity increases significantly when the omission level is enhanced to 21% of the maximum stress amplitude.The dispersivity related to different crack lengths under the same spectrum loading can be considered to be same.It can also be seen from the experimental results that the three omission levels of low amplitude cycles investigated in this paper has significant influence on the mean value of crack growth life.Therefore,these low amplitude cycles can not be neglected in damage tolerance and reliable assessment.