STUDY ON FATIGUE DAMAGE BELOW THE FATIGUE LIMIT AND THE COAXING EFFECTS

Rotary bending fatigue tests were carried out for smooth specimens of a mediumcarbon steel with two different grain sizes near the fatigue limit. The process of fatigue damagewas observed by replication method, and the effects of grain size,stress level and microstructure on surface damage were studied. The effect of following cycle stress level on the coaxing effects was also discussed. The fatigue limit is the maximum stress at which the short fatigue crack initiates and becomes a non-propagating crack.. The length of non-propagating crack is related to grain sizes and stress level. The coaxing effects disappear when the following stress level is greater than the critical value.