8.8级螺栓用ML40Cr钢的疲劳性能和裂纹扩展行为

Fatigue Properties and Crack Growth Behavior of ML40Cr Steel for 8.8-grade Bolts

针对紧固螺栓在不同预紧力下的疲劳可靠性问题,对ML40Cr钢母材进行拉-拉疲劳和对称三点弯曲实验,研究输电铁塔用8.8级紧固螺栓用钢的疲劳性能和裂纹扩展行为。拉-拉疲劳实验的结果表明,在不同应变幅的疲劳加载条件下,以材料抗拉强度的50%作为平均应力时ML40Cr光滑试样的疲劳极限为263 MPa,缺口试样的疲劳极限为95 MPa。用有效应力(σ)参数法处理平均应力对ML40Cr疲劳曲线的影响,得到8.8级螺栓用钢ML40Cr的疲劳缺口敏感度为0.31。依据对称三点弯曲实验的疲劳实验结果,得到8.8级螺栓用钢ML40Cr的裂纹扩展速率关系式为da/d N=10-10(?K)2.2。探讨ML40Cr用钢的缺口疲劳强度和疲劳裂纹扩展机制。

ML40 Cr steel for 8.8-grade bolts of power transmission towers was selected as research object in this paper. Considering the fatigue reliability of the bolts fastened under different pre-stresses,tension-tension fatigue and symmetric three-point bending experiments were conducted to investigate the fatigue properties and fatigue crack propagation behavior of ML40 Cr steel samples, respectively. The experimental results show that the fatigue limits for smooth samples and notched samples of the ML40 Cr steel are 263 MPa and 95 MPa, respectively when the 50% of tensile strength was adopted as the mean stress with different stress amplitudes. The effect of the mean stress on the stress-fatigue life(S-N) curve of the ML40 Cr steel samples was investigated by the effective stress method and the corresponding fatigue notch sensitivity 0.31 was obtained. According to the results of symmetrical three-point bending tests the Paris formula of ML40 Cr steel for 8.8 bolts is fitted as da/d N = 10-10(△K)2.2. Mechanisms of notch fatigue strength and crack growth of the ML40 Cr steel for the bolts were also discussed.