采用成组法和升降法开展了室温某17-4PH末级长叶片叶根纵、横方向光滑与缺口试样的疲劳试验,获得了两个方向上材料的S-N曲线,并对典型疲劳断裂试样进行了断口宏微观形貌观察.结果表明:叶片叶根纵、横方向的疲劳强度基本一致,在长寿命区,纵向疲劳强度略高于横向;光滑试样的疲劳断裂主要呈现单裂纹源特征,而缺口试样呈现多裂纹源汇聚的断裂形貌.结合试样缺口根部的弹塑性应变分析,进一步讨论了叶片叶根纵、横方向的疲劳缺口效应.
High cycle fatigue tests of both smooth and notch specimens in longitudinal and transverse directions of the blade root of 17-4PH stainless steel were carried out under R=-1 by using the group method and the staircase method and their S-N curves were experimentally obtained.The fracture morphologies of both smooth and notch specimens were also examined.The results show that the fatigue strengths of longitudinal and transverse directions are almost the same,although the fatigue strength in the longitudinal direction is slightly higher than that in the transverse direction especially within the long life ranges.SEM observations of fracture surfaces indicate that single crack initiation becomes dominant for the smooth specimens,while multifatigue crack initiation growth and their gathering becomes the main characteristic features for the notch specimens.Fatigue notch effect of the 17-4PH stainless steel was also discussed according to the elastic-plastic strain analysis of the notch root.
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