应力比对25Cr2Ni2MoV钢疲劳裂纹扩展门槛值的影响

Effect of stress ratio on fatigue crack propagation threshold value of 25Cr2Ni2MoV steel

对25Cr2Ni2MoV钢进行疲劳裂纹扩展门槛值试验,试样尺寸为紧凑拉伸试样,试验的频率为20 Hz,波形为正弦波,试验环境介质为空气,试验的温度为23℃,试验过程采用连续的降K程序进行测试。试验结果表明,应力比R分别为0.05,0.1,0.3,0.5,0.7和0.8时,有效门槛值?Keff分别为5.30、5.10、3.68、3.34、2.72和2.43 MPa·m,随着应力比的增加,有效门槛值逐渐降低,da/d N曲线向较小的?K方向移动;随着应力比的增加,裂纹闭合效应的影响是逐渐降低的,当应力比R≥0.7时,裂纹闭合效应消失,实际测量的门槛值即为有效门槛值,采用修正后的McEv-ily-Groeger公式,可以得到25Cr2Ni2MoV钢有效门槛值的经验方程。

The fatigue crack propagation threshold test of 25 Cr2 Ni2 MoV steel is carried out. The sample size is the compact tensile specimen. The frequency of the test is 20 Hz,the waveform is the sine wave,the test environment medium is air,and the test temperature is 23 ℃. The process is tested using a continuous decrease K program. The test results show that the effective threshold values ?Keffare 5.30,5.10,3.68,3.34,2.72 and 2.43 MPa· m when the stress ratio R are 0.05,0.1,0.3,0.5,0.7 and 0.8,respectively. As the stress ratio increases,the effective threshold value decreases gradually,and the da/d N curve moves toward the smaller ?K direction. As the stress ratio increases,the crack closure effect is gradually reduced. When the stress ratio R≥0.7,the crack closure effect disappears,and the actual measured threshold value is the effective threshold. Using the modified McEvily-Groeger formula,the empirical equation of the effective threshold value of 25 Cr2 Ni2 MoV steel can be obtained.