网架结构螺栓球节点中M39高强度螺栓变幅疲劳性能试验

螺栓球网架结构在悬挂吊车循环荷载作用下，节点处高强度螺栓易发生疲劳破坏。本文利用MTS疲劳试验机完成了7组M39高强度螺栓在轴向拉伸应力循环下的变幅疲劳试验，通过对疲劳断口的形貌分析，揭示了变幅疲劳的破坏特征，基于miner线性累计损伤法则对试验数据进行折算，得到对应的等效常幅应力，经拟合绘制了变幅疲劳破坏的S-N曲线并给出表达式，最后将此次变幅疲劳数据和已有的M39高强度螺栓常幅疲劳对比，证明了变幅疲劳破坏寿命可以等效成常幅疲劳问题来分析计算。本次变幅疲劳试验结果所得的应力循环次数达200万次时对应的容许应力幅为现行规范中的1.45倍。

Experimental Study on Variable Amplitude Fatigue Behavior of M39 High Strength Bolts in Bolted Spherical Joints of Grid Structures

Under the cyclic load of suspension crane, the high strength bolts at the bolt ball joints of grid structure are prone to fatigue failure. In this paper, seven groups of M39 high strength bolts were tested by MTS fatigue testing machine under axial tensile stress cycle. The failure characteristics of variable amplitude fatigue were revealed through the analysis of fatigue fracture morphology. Based on miner''s linear damage rule, the equivalent constant amplitude stress is obtained by converting the test data. The S-N curve of variable amplitude fatigue failure is drawn and the expression is given. Finally, the comparison between the variable amplitude fatigue data and the existing M39 high strength bolt constant amplitude fatigue proves that the variable amplitude fatigue failure life can be equivalent to the constant amplitude fatigue problem. When the number of stress cycles is 2 million, the allowable stress amplitude is 1.45 times of the current code.