缺口高应变区疲劳裂纹形成寿命的尺寸效应

本文给出了两种考虑缺口尺寸效应的疲劳裂纹形成寿命的预测方法。一种是用高应变区体积考虑尺寸效应,通过缺口的△W-N;数据建立起经验公式。另一种是用疲劳缺口系数K_f代替理论应力集中系数K_8以考虑尺寸效应,通过用K_1修正后的△代替△J得到寿命预测公式。两种方法前者精度较高,后者更为简便。 文章还给出了一种用断裂力学确定疲劳缺口系数K_1值的方法。并指出用缺口循环J积分预测疲劳裂纹形成寿命比用Neuber公式计算缺口最大形变功密度范围来预测疲劳裂纹形成寿命更接近实验结果。

SIZE EFFECTS ON FATIQUE CRACK INITIATION LIFE IN HIGH STRAIN AREAS NEAR NOTCHES

Two approches predicting fatigue crack initiation life that the notch size into account are presented in this paper. The first approach considers size effect in terms of high strain area volume near notches and establishes an empirical fomula using W versus Ni data. In the second approach fatique notch factor Kf is substituted for theoritical stress concentration factor Kt to take the size effect into account and J modified with Kt is used to replace J to obtain life pre dieting formula. The accuracy of the first approach is found higher, but the second approach is simpler.An approach to determine fatique notch factor Kf using fracture mechanics method is also given in this paper. Finally it is pointed out that the prediction of fatique crack initiation life by notch cyclic J integral is closer to the test results than that by notch tip's maximum deformation work range derived from Neuber formula.