疲劳荷载特性对8.8级M24高强度螺栓疲劳裂纹扩展机理影响探析

An Analysis on the Influence of Fatigue Loading to the Fatigue Crack Propagation Mechanism of 8.8 Grade M24 High-Strength Bolts

为研究常幅疲劳荷载特性对高强度螺栓疲劳裂纹扩展的影响,针对钢结构端板连接用8.8级M24高强度螺栓在不同应力比/应力幅作用下常幅疲劳试验所得到的24个试件断口形貌进行定量分析,并采用ABAQUS软件数值模拟高强度螺栓应力集中情况,探讨含初始裂纹高强度螺栓裂纹尖端应力强度因子与荷载特性、预制裂纹形状之间的关系。结果表明:在轴向受拉疲劳荷载作用下,螺母与螺栓啮合第1圈螺纹处为疲劳断裂最不利位置;试件断口稳定扩展区面积与应力比/应力幅呈负相关,快速扩展区面积与应力比/应力幅呈正相关;裂纹尖端应力强度因子随应力比/应力幅的增大而增大;预制半椭圆形裂纹短/长轴之比(a/c)越大,应力强度因子扩展有限元(XFEM)解与解析解误差越大。

In order to study the influence of fatigue loading to the crack propagation of high-strength bolts,the fracture morphology of 24 specimens is quantitatively analyzed based on the constant-amplitude fatigue tests for grade 8.8 highstrength bolts of the end-plate connection under different stress ratios or stress amplitudes.The stress concentration of high-strength bolt is simulated by using ABAQUS software,and the relation between the stress intensity factor(SIF)at the initial crack tip of high-strength bolt,loading characteristics,and crack shape is further simulated and discussed.The results show that the most critical position of fatigue fracture under cyclic axial tensile loading is the first thread of the bolt engaged in the nut.The area of stable fracture expansion zone is negatively correlated with stress ratio and stress amplitude,while the area of rapid fracture expansion zone is positively correlated with stress ratio and stress amplitude.The stress intensity factor of crack tip increases with the increase of stress ratio and stress amplitude.Additionally,a larger ratio of short axis to long axis(a/c)of the semi-elliptic crack will create a larger error between the XFEM solution and analytical solution of stress intensity factor.