屈服点的不稳定性对超高周疲劳的影响研究

摘要

核电站的蒸汽发生器管道采用碳锰钢制成,设计寿命40年,长期受循环温度载荷和高频振动载荷作用后,在管道连接处出现裂纹。实际工作中,循环温度载荷作用后的材料产生循环塑性变形,屈服点这一重要力学性能发生变化。材料在单向拉伸载荷作用下超过Lüders带后,出现硬化效应,屈服强度提高。研究屈服应力点的变化对材料的超高周疲劳性能的影响。试验采用压电陶瓷超声疲劳试验机,考察并比较单向拉伸、低周疲劳载荷作用后,材料超高周疲劳性能的变化。实验结果表明：单向拉伸（5%）提高了材料的屈服点,同时也提高了超高周疲劳强度;而低周疲劳载荷作用后,随着屈服应力点的降低,超高周疲劳性能下降。%Pipes of steam generator in nuclear power station are made of C-Mn steel and their design service lifetime is over 40 years.During service,the crack may appear in the joints under cyclic temperature loading and high frequency vibration.In reality,with the temperature changing,components have cyclic plastic deformation and the yield stress of the steel changes too.The monotonic deformation which is beyond Lüders strain makes the steel harden and the yield stress increases.The influences of yield stress changing on the performance of the steel′s very high cycle fatigue（VHCF） after 2 kinds of preloading are investigated in this paper.Experiments are carried out in an ultrasonic fatigue test machine to investigate effect of preload of monotonic tension or low cycle fatigue（LCF） on VHCF.The test results show that monotonic tension（5% deformation） heightens the steel′s yield stress and improves the VHCF strength.However,the preload of LCF leads to the yield stress decrease and weakens the performance of VHCF.