一种改进的疲劳裂纹扩展表达式

A modified constitutive relation for fatigue crack growth

疲劳裂纹扩展率表达式是采用疲劳裂纹扩展理论预报疲劳寿命的核心。迄今为止,已有上百种不同的疲劳裂纹扩展率公式被提出。近年来,作者们致力于对新近提出的裂纹扩展率公式进行比较研究。通过初步研究发现,McEvily公式能解释比较多的异常疲劳现象,因此,它有比较强的预报能力,值得作深入研究。本文针对它采用固定斜率不能与很多实验结果有很好拟合的缺点,提出采用变斜率的改进形式。通过采用不同材料(钛合金D16Cz、铝合金D16Cz、ARMCO-iron)、不同应力条件(R≥0、R<0、R=-∞)下的疲劳裂纹扩展数据进行分析验证,发现不管是疲劳短裂纹扩展还是疲劳长裂纹扩展,改进后的McEvily关系均具有良好的疲劳性能预测能力。

The fatigue crack growth rate is the core for predicting fatigue life by use of fatigue crack propagation （FCP） theory. Up to now, there are more than one hundred expressions proposed. In recent years, the authors carried out comparative studies on the newly-presented fatigue crack growth rate formula.On the basis of a previous pilot study,it is shown that the McEvily relation is worth for further study due to its better prediction ability and its ability of explaining more abnormal fatigue phenomena.In order to further improve the fitness for many test results using McEvily relation,the authors put forward a modified relation by using the variable slope instead of the constant.Fatigue crack growth data for different materials （Aluminum, Titanium, ARMCO-iron） in wide stress ratio range （R≥0, R〈0, R=-∞） were cited for the analysis and validation of the modified McEvily relation,and all the comparative results, both short-crack and long-crack growth, are shown that the modified relation has a better fitness than the original.