螺栓连接件微动疲劳特性分析

Analysis of Fretting Fatigue Characteristics of Bolt Connections

工程中钢结构构件经常采用螺栓连接,被连接部位多处于复杂受力状态,单轴疲劳理论已无法满足该形式下构件的寿命评估需求.针对现有理论不足,本文建立了螺栓连接件有限元模型,研究了不同工况下被连接件微动疲劳裂纹萌生位置,并基于临界平面的多轴疲劳理论,比较了四种常用模型的适用性以及预测了连接件的疲劳寿命.结果表明:(1)裂纹萌生位置位于受拉端螺栓孔附近的滑移粘着区,在相同螺栓预紧力下,该位置与施加的疲劳载荷大小无关;(2)基于临界平面方法的四种模型均可以较好判断裂纹萌生位置,其中SWT(Smith-Watson-Topper)模型对不同载荷水平下的螺栓连接件微动疲劳寿命预测效果较好,大部分预测结果位于±2倍分散带之内,预测结果优于其他三种模型;(3)在规范规定的螺栓预紧力范围内,被连接件裂纹萌生区域距孔边的距离与预紧力大小无关,可能是由于预紧力变化范围内的粘着滑移区未发生明显变化所致,并且随着预紧力减小,被连接件的寿命预测值反而增大.

In engineering, steel structures are often connected by bolts, and the connected parts are mostly in a complex state of force.The uniaxial fatigue theory can no longer meet the requirements of the life evaluation of the components under this condition. In view of this shortcoming, a finite element model of bolted joints is established, and the fretting fatigue crack initiation positions of the connected parts under different working conditions are studied. Based on the multi-axial fatigue theory of the critical plane, the applicability of the four commonly used models is compared and the fatigue life of connector is predicted. The results show that:(1) The crack initiation position is located in the slip adhesion zone near the bolt hole at the tension end. Under the same bolt preload, this position has nothing to do with the fatigue load;(2) The four models based on the critical plane method can well judge the location of crack initiation. Among the four models, the SWT(Smith-Watson-Topper) model has the best prediction accuracy on the fretting fatigue life of bolted connections under different load levels. Most of the predicted results are within ±2 times of dispersion zone, and the prediction accuracy is better than that of the other three models;(3) Within the bolt pre-tightening force range specified in the standard, the distance between the crack initiation area of the connected part and the edge of the hole has no correlation with the pre-tightening force, which may be due to the fact that the adhesion slip area has not changed within the range of the pre-tightening force. As the pre-tightening force decreases, the predicted life of the connected part is instead increased.