循环压缩载荷下缺口残余拉应力场的X射线分析

用细束 x 射线研究了循环压缩载荷下缺口残余拉应力的分布及变化。试验表明,循环压缩加载后形成的残余拉应力大于一次压缩加载后的数值,压缩应力幅对残余拉应力分布的影响大于压缩平均应力的影响,其原因除了加载-降载过程中形成的残余应力直接与应力幅有关外,尚与应力幅加剧材料循环软化程度有关。形成疲劳裂纹后,在完全卸载的裂纹面上,残余拉应力基本松弛,但垂直于裂纹面稍远处的残余拉应力仍保持有相当大的数值,这部分残余应力是否对裂纹扩展起作用,在计算残余应力的应力强度因子时如何予以考虑值得注意。

Tensile Residual Stress Field Around Notch Root Under Cyclic Compression

Tensile residual stress field around notch root under cyclic compression was investigated experimentally with X-ray diffraction technique for 40Cr steel.The results indicate that the magnitude of tensile residual stress under cyclic compression is greater than that under monotonic compression, and the development of tensile residual stress appears more sensitive to compressive stress amplitude than to compressive mean stress.This may be due to the strong effect of stress amplitude on cyclic softening of tested material,as well as the un-loading range during test. The tensile residual stresses in the place close to cracked surface were relaxed to a large amount during crack propagation from the notch root, but those away from the cracked surface still kept greater values. These stable stresses should have an influence on the growth behavior of fatigue crack,and should be taken into consideration in the calculation of residual stress intesity factor.