某马蹄形卸扣为风机塔筒吊座组件，在吊装塔筒过程中发生断裂。采用宏观分析、化学成分分析、力学性能测试、金相检验、硬度测试、扫描电镜分析以及有限元模拟计算等方法，对卸扣断裂原因进行了分析。结果表明：卸扣在制造过程中产生月牙形外力损伤缺口，且卸扣热处理效果不佳，导致材料的韧性较差，在吊装过程中，损伤缺口处成为应力集中点，当裂纹扩展至临界值后发生瞬间断裂。

A horseshoe shackle is the one component of fan tower hoist, which fractured during the process of lifting tower. The macroscopic analysis, chemical composition analysis, mechanical property test, metallographic examination, hardness test, scanning electron microscopy analysis and finite element simulation were used to analyze the reasons of fracture. The results shows that the crescent-shaped external gap formed during the shackle manufacturing process, and poor heat treatment, resulting in lower toughness of the material. And then, the damaged gap became the stress concentration point in the lifting process, and the instantaneous fracture occur when the crack propagate to the critical value.