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为了对钢桥焊接细节进行疲劳寿命评估,分别采用标准圆棒试件和沙漏型光滑试件进行静力拉伸试验和成组轴向拉伸疲劳试验,引入存活率和置信度得到了具有概率水平保证的安全疲劳寿命曲线,并针对焊接接头疲劳寿命离散性较大的现象,进行微观层面的硬度测试和疲劳断口电镜扫描试验,研究焊缝试件过早萌生疲劳裂纹的微观机理。试验结果表明:Q345qD对接焊缝的疲劳性能较好,随应力水平下降疲劳寿命显著提高,并给出了寿命随应力水平变化的拟合式;本批次Q345qD对接焊缝疲劳强度远远超过相同构造的规范取值,持久疲劳极限在S_(max)=260 MPa附近;焊接热输入对焊缝组织有较大影响,热影响区硬度波动明显,组织不均匀和焊接缺陷是导致低应力水平过早疲劳断裂的主要原因。
In order to evaluate the fatigue life of steel bridge welding details, the static tensile test and the group of axial tensile fatigue test were conducted using standard round bar specimens and hourglass smooth specimens, respectively. The survival rate and confidence were introduced to obtain the probability of fatigue life. Level safety fatigue life curve of the weld joint. The micro-scale hardness test and the fatigue fracture-scanning electron microscopy (SEM) test were carried out to study the microscopic mechanism of premature sprout fatigue crack in the weld joint. The test results show that the fatigue performance of Q345qD butt weld is better, and the fatigue life is obviously improved with the decrease of stress level, and the fitting formula of life span with stress level is given. The fatigue strength of Q345qD butt weld far exceeds the same The fatigue limit of the structure is around S max = 260 MPa. Welding heat input has a significant influence on the microstructure of the weld. The hardness of the HAZ fluctuates obviously. The microstructure and weld defects lead to the low stress level The main reason for early fatigue fracture.