平均应力对50钢超高周疲劳性能的影响

为了进一步拓宽超声疲劳试验的研究范围，对50钢进行了含有平均应力的三点弯曲和非对称拉压疲劳性能试验，得到相应的疲劳，S-N曲线，研究了平均应力对其超高周疲劳性能的影响。结果表明：超声频率加载下平均应力对50钢疲劳性能有显著影响，在应力幅相同的情况下，随着平均应力的增大，疲劳寿命降低；常规疲劳用于描述平均应力影响的Morrow关系仍能描述超声频率加载下高周疲劳（〈10^7周次）范围内拉伸平均应力对50钢疲劳性能的影响，但是不能用来描述超高周范围内拉伸平均应力和弯曲平均应力对疲劳性能的影响；常规疲劳用于描述平均应力影响的Goodman模型仍能很好地描述超声频率加载下一定寿命的应力幅值和平均应力的配合。

Influence of Mean Stress on Fatigue Strength of 50 Steel in Super High Cycle Regime

In order to expand the research range of ultrasonic fatigue, the three-bending and non-symmetric tension-compression fatigue properties of 50 steel were tested and corresponding fatigue S-N curves were obtained. The effect of mean stress was studied. The mean stress shoued remarkable effect on fatigue strength of 50 steel under ultrasonic frequency loading. With increasing of mean stress, fatigue life decreased under the condition with the same stress ampitude. The model of Goodman describing the effect of mean stress in conventional fatigue can still be used to describe perfectly the relation between stress amplitude and mean stress at ultrasonic frequency loading. The model of Morrow that describes the effect of mean stress in conventional fatigue can still be used to describe the effect of mean tensile stress on fatigue behavior in LCF and HCF regime, but it can not describe the effect in ULCF regime at ultrasonic frequency loading.