结构钢斜对接焊缝连接的统一多轴疲劳寿命预测

Unified multi-axial fatigue life prediction of inclined butt-welded joints of constructional steel

关键词:  斜对接焊缝连接  拉剪循环应力  多轴疲劳  寿命预测  椭球面断裂模型

Key words:  inclined butt-welded joint  tensile-shear cyclic stress  multi-axial fatigue  life prediction  ellipsoidal fracture model

摘要:

为计算处于复杂应力状态下结构钢焊接连接的多轴疲劳寿命,对斜对接焊缝连接的多轴疲劳裂纹失稳扩展应力场进行了基于椭球面断裂模型的理论计算,得到多轴疲劳裂纹萌生与稳定扩展长度和由椭球面断裂模型定义的疲劳破坏面上的最大断裂因子（最大疲劳载荷作用下）及断裂因子幅（疲劳载荷幅作用下）。建立了满足应力边界条件的统一计算疲劳裂纹萌生和稳定扩展寿命的多轴疲劳模型参数和最大断裂因子、断裂因子幅的函数,综合反映了各应力分量对拉剪循环应力作用下全熔透斜焊缝十字接头和斜对接焊缝连接多轴疲劳的影响,推导了拉剪循环应力作用下全熔透斜焊缝十字接头和斜对接焊缝连接的统一多轴疲劳寿命计算式。计算结果表明,推导的统一多轴疲劳寿命计算式对Q345qC钢全熔透斜焊缝十字接头和SAE1050钢斜对接焊缝连接疲劳寿命的计算误差分别为-26.8%~-0.2%和-87.1%~10.2%,现行标准建议的疲劳验算式的计算误差分别为-63.5%~-13.3%和-79.2%~237.33%。提出的多轴疲劳模型可应用于复杂应力状态下结构钢及其连接的多轴疲劳寿命评估。

Abstract:

To calculate the multi-axis fatigue life of structural steel and its welded connections under complex stress conditions, the stress fields on the unstable propagation area of multi-axial fatigue cracks in the inclined butt-welded joint were calculated theoretically based on an ellipsoidal fracture model. The initiation and stable propagation lengths of multi-axial fatigue cracks, as well as the maximum fracture index (under the maximum fatigue load) and the fracture index amplitude (under the fatigue load amplitude) defined by the ellipsoidal fracture model on the fatigue failure area, were calculated. A unified multiaxial fatigue model was established that satisfies the stress boundary conditions and expresses the model parameters, the maximum fracture factor, and the fracture-factor amplitude as functions governing fatigue-crack initiation and steady-state propagation life. The formulation comprehensively accounts for the contributions of individual stress components to multiaxial fatigue of full-penetration oblique cruciform welds and oblique butt weld connections under combined tension-shear cyclic loading. Closed-form unified multiaxial fatigue-life calculation expressions for full-penetration oblique cruciform welds and oblique butt weld connections subjected to tension-shear cyclic stresses are derived. The calculation results show that the calculation errors of the unified multi-axial fatigue life calculation formulas for the multi-axial fatigue life of inclined full-penetration welded cruciform joint of Q345qC steel and butt-welded joint of SAE1050 steel are from -26.8% to -0.2% and -87.1% to 10.2%, respectively. By comparison, the calculation error of the fatigue life formula recommended in the current code are from -63.5% to -13.3% and -79.2% to 237.33%, respectively. The proposed multi-axis fatigue model can be applied to the multi-axis fatigue life assessment of structural steel.