高应力比循环下微动疲劳裂纹萌生位置的预测分析

Prediction of Location of Fretting Fatigue Crack Initiation Subject to High Stress Ratio Cyclic Load

对于微动疲劳问题,循环应力比的大小会影响试件应力状态及分布,从而影响疲劳裂纹的萌生位置。本文通过对一类微动疲劳问题进行有限元法分析,模拟疲劳实验过程,并采用最大应力变化幅Δσθmax作为指标预测了不同应力比下疲劳裂纹的萌生位置。数值分析显示,在应力比不是很大时,试件与微动接触头的边缘存在接触,并在此处产生较大的应力集中,容易萌生裂纹;而在应力比足够高时,微动接触头端部与试件呈恒张开状态,Δσθmax及裂纹萌生发生在距初始接触区边缘一定距离处。疲劳裂纹萌生位置的理论预测结果与相关试验的疲劳裂纹发生位置比较一致。

For fretting fatigue problems, the stress ratio of cyclic load can greatly affect the stress state and distributions as well as the location of fatigue crack initiation. Based on finite element analysis for a kind of fretting fatigue problem, the fretting fatigue test was simulated, and the maximum tangential stress range was used as the criterion value to predict the location of fatigue crack initiation under different stress ratio cyclic load. When the stress ratio is not very high, numerical results show that the specimen get contact with the edge of the pad. Therefore there are severe stress concentrations at that position and fatigue cracks are prone to onset. On the other hand, the edge of the pad keeps separate from the specimen surface when stress ratio is high enough, and the maximum stress range Aa0max as well as fa- tigue crack initiation displace at a distance from the edge of initial contact. The predicted crack initiation locations are in agreement with those from experiments.