钢结构端板连接用M24高强度螺栓疲劳裂纹扩展数值分析

Numerical analysis of fatigue crack propagation of M24 high-strength bolts for end plate connection of steel structure

为探究高强度螺栓疲劳裂纹扩展机理,基于30个M24高强度螺栓常幅疲劳试验数据,对典型螺栓断口进行宏、微观分析,采用ABAQUS有限元软件对含预制裂纹的高强度螺栓进行数值模拟,重点探讨了螺栓在不同长度预制裂纹下的应力分布情况及预制裂纹的几何特征对应力强度因子(stress intensity factor,SIF)、裂纹扩展方向的影响。结果表明:在相同应力比下,疲劳扩展区径向长度随着平均特征应力幅的增加而降低,降低幅度为21.8%和5.7%,且瞬断区韧窝深度随着疲劳辉纹间隙的增大而加深;预制裂纹几何特征对螺栓应力分布影响明显,试件疲劳断裂SIF与裂纹预制长度、裂纹径向/环向之比呈正相关关系,但与预制裂纹初始角度无明显关系。此外,还建立了基于试件应力变化率判断疲劳裂纹长度变化率的预测公式,指出了高强度螺栓疲劳断裂过程的位移变化率在n/N>0.75时有明显改变。

In order to explore the fatigue crack propagation mechanism of high-strength bolts,based on the constant amplitude fatigue test data of 30 M24 high-strength bolts,the macro and micro analysis of typical bolt fractures were carried out.The ABAQUS finite element software was used to simulate the high-strength bolts with prefabricated cracks.The stress distribution of bolts under different lengths of prefabricated cracks and the influence of geometric characteristics of prefabricated cracks on stress intensity factor(SIF)and crack propagation direction were discussed.The results show that under the same stress ratio,the radial length of the fatigue propagation zone decreases by 21.8%and 5.7%with the increase of the average characteristic stress amplitude,and the dimple depth of the instantaneous fracture zone increases with the increase of the fatigue striation gap.The geometric characteristics of the prefabricated cracks have obvious influence on the stress distribution of bolts.The fatigue fracture SIF of specimens is positively correlated with the prefabricated length of cracks and the ratio of radial/circumferential direction of cracks,but has no obvious dependence on the initial angle of prefabricated cracks.In addition,a prediction formula for judging the change rate of fatigue crack length is established based on the stress change rate of the specimen,which indicates that the displacement change rate of the high-strength bolt fatigue fracture process changes significantly when n/N>0.75.