缺口对TC21合金高周和低周疲劳的影响

Effect of Notch on the High and Low Cycles Fatigue of TC21 Alloy

研究了缺口对TC21合金在不同温度高周和低周疲劳强度的影响。疲劳试样为光滑和V型缺口(Kt=3)2种试样,疲劳载荷为应力控制,循环应力比为0.1,高周疲劳实验温度为315℃,低周疲劳实验温度为室温及400℃。结果表明,在循环应力较低,缺口根部未塑性变形时,缺口使疲劳强度明显降低。循环应力升高使缺口根部产生塑性变形时,缺口对疲劳强度影响降低,当循环应力升高使光滑试样失稳时,缺口试样的疲劳强度高于光滑试样的疲劳强度。断口的SEM分析表明,缺口试样的疲劳裂纹在缺口根部萌生,即使高周疲劳裂纹源也是多个。

The effect of notch on the high cycle and low cycle fatigue strength of TC21 alloy at different temperatures has been investigated in this paper. The fatigue specimens contain two kinds of the stress concentration factors, Kt=1 and Kt=3. The fatigue tests were performed in load-controlled mode and the cyclic stress ratio is 0.1. The high cycle fatigue （HCF） tests were performed at 315 ℃, and the low cycle fatigue （LCF） tests were performed at room temperature and 400 ℃. The results indicated that the notch decreases the fatigue strength when the cyclic stress is lower and the plastic deformation does not take place at the root of the notch. When the cyclic stress is higher so that the plastical deform happens at the root of the notch, the effect of notch on the fatigue strength decreases. When the cyclic stress is high enough to make the unnotched specimens unstable, the fatigue strength of notched specimens is higher than the unnotched specimens. SEM fractography indicates that the fatigue cracks of notched fatigue specimens nucleate at the surface by multiple sources, even in the HCF conditions.