塔式起重机起重臂疲劳裂纹扩展的机理分析

Forming Mechanism of Fatigue Crack of Cargo Boom in Tower Crane

塔式起重机起重臂下弦杆疲劳裂纹影响因素多,裂纹形成过程复杂。从塔式起重机起重臂的工作载荷和焊接残余应力特征出发,应用断裂力学理论分析了起重臂疲劳裂纹萌生点和疲劳裂纹的扩展过程。针对塔式起重机承受随机载荷的特点,应用时间循环法估算塔式起重机起重臂的疲劳裂纹扩展寿命。研究结果表明:疲劳裂纹在下弦杆与腹杆焊接处萌生;疲劳裂纹扩展的主要原因是交变应力与变幅小车循环次数的累积作用,并为现役塔机的安全评定提供了理论分析依据。

The forming process of the fatigue crack of the cargo boom in the tower crane is complicated.According to the service load and the welding residual stress characteristics of the cargo boom,the fracture mechanics theory was used to analyze the fatigue crack of the lower chord initiation point and the fatigue crack development process.By using the equations for the stable propagation period of constant amplitude loading fatigue cracks,the fatigue life of the cargo boom of tower cranes is estimated.Results show that the crack initiation site is the lower chord and web member welded joint;the main propagation factor of the fatigue crack is the alternation of stress and cycle-index accumulated by the trolley,These analyzed conclusions provide theoretical reference for the active security assess of using tower crane.