蚀坑等效为初始裂纹的疲劳寿命预测方法适用性分析

目的 分析将主导蚀坑等效成初始裂纹进行疲劳寿命预测的适用性。方法 选取LY12CZ航空铝合金试验件为研究对象，进行预腐蚀试验，对试样的腐蚀损伤情况进行观测和对比研究。应用ANSYS软件对不同腐蚀损伤情况的试验件进行有限元分析，分析试验件应力分布的变化。结果 随着腐蚀时间的延长，主导蚀坑附近区域其他点蚀坑的数量和尺寸呈上升趋势。以蚀坑间距离与蚀坑半径之比d/r为指标，d/r<4时，主导蚀坑处的应力分布受到其他蚀坑的影响较大，与试验结果相比，点蚀模型计算得到的疲劳寿命的平均相对误差为19.94%。d/r>4时，主导蚀坑处的应力集中系数基本恢复到单蚀坑时的大小，平均相对误差为3.74%。结论 d/r>4时，可以忽略其他蚀坑对主导蚀坑应力分布的影响，此时将主导蚀坑作为唯一疲劳源进行寿命计算是合理的。d/r<4时，主导蚀坑处的应力分布受到其他蚀坑的影响，此时将主导蚀坑作为唯一疲劳源进行寿命计算时将出现较大误差。

Applicability Analysis of Fatigue Life Assessment Method Equaling Pit as Initial Crack

This paper aims to analyze the applicability of equating the dominant etch pits with initial cracks for fatigue life prediction. The pre-corrosion test of LY12CZ aluminum alloy was carried out, then specimens with different pitting degrees were obtained and compared. The ANSYS software was applied to finite element analysis of test pieces with different corrosion damage conditions to analyze the changes in stress distribution of the test pieces. The results showed that with the continuance of pre-corrosion test, both quantities and sizes of other pits in the zone near the critical pit increased. The ratio of the distance between craters to the radius of the crater, d/r, is used as an indicator, when d/r was less than 4, the other pits had an influence on the stress field of the critical pit, the average relative error of the fatigue life calculated by the pitting model is 19.94% compared with the test results. When d/r was more than 4, the stress concentration coefficient at the dominant erosion crater returns to the size of the single pit, and the average relative error of the fatigue life calculated by the pitting model is 3.74% compared with the test results. When d/r was more than 4, the influence of other pits on the stress distribution of the dominant pit can be ignored, and it is reasonable to use the dominant pit as the only fatigue source for life calculation. When d/r was less than 4, the stress distribution at the dominant pit is influenced by other pits, and a large error will occur when using the dominant pit as the only fatigue source for life calculation.