C250钢缺口扭转疲劳断裂特征研究

采用体视显微镜和扫描电镜对不同应力比、不同循环寿命下的C250钢缺口扭转疲劳断裂特征进行研究。结果表明:C250钢缺口扭转疲劳断口宏观可分为斜面状、棘轮状、锯齿状和平面状等4类断口形貌。斜面状和棘轮状断口一般出现在R>0、循环周次在105级以上的断口上；锯齿状断口一般出现在应力比R<0、循环周次在105级以上的断口上；平面状断口一般出现在循环周次在104级以下的断口上。在斜面状断口和棘轮状断口上，与轴向呈45°的扩展斜断面上为类解理特征，微观可见典型的疲劳条带特征；与轴向垂直的扩展断面主要为扭转磨损特征；瞬断区为韧窝断裂特征。斜面状断口、棘轮状、锯齿状断口疲劳裂纹的萌生和扩展主要受切应力的作用。而平面状断口裂纹的萌生和扩展主要受平面拉应力作用。

Notch Torsional Fatigue Features of C250 Steel

The characteristics of fatigue fracture of C250 steel with different stress ratio and different cycle life were studied by stereoscopic microscope and scanning electron microscope. The results show that the macroscopic features of C250 steel notch torsion fatigue fracture can be broadly classified into four types of fracture morphology, such as inclined plane,ratchet type,sawtooth type and plane type. Bevel and ratchet fracture usually occur at R>0,the fracture of the loop cycle 105 and above,sawtooth fracture usually occur at R<0、the fracture of the loop cycle 105 and above;and the planar fracture usually occurs on the fracture of the loop cycle at 104 and below. On the slant fracture and ratchet fracture, and on the axis is the expansion of the 45° incline to is a kind of cleavage fracture feature, fatigue stripe is typically seen in the microscopic characteristic. The vertical section of the axial plane is mainly to reverse the wear characteristics. Fracture zone is characterized by dimple fracture. The initiation and extension of the fatigue crack of inclined plane,ratchet type,sawtooth type and plane type are mainly affected by shear stress. The initiation and extension of planar fracture crack is mainly affected by plane tensile stress.