中文摘要：

以断裂的飞机主轮毂连接螺栓为研究对象，详细地分析了连接螺栓断口的形貌、化学成分、硬度和金相组织。研究结果表明，由于外来的Al合金和砂粒进入了螺纹，在飞机滑跑和降落时，螺栓振动受力，在螺纹根部形成划伤痕，致使螺纹根部发生多个疲劳区，众多疲劳区扩展汇成2条主裂纹相对扩展，直到在中间相遇形成一个台阶，2条主裂纹的快速扩展区发现正断的韧窝，表明是过载断裂。该分析结果将有助于飞行事故的调查并得出正确的失效分析结论。

英文摘要：

The fractograph, chemical composition, degree of hardness and microstructure of the failed screw of wheel hub of civil aviation aircraft are analyzed by SEM and energy spectrum. The results show that the fracture of the screw is caused by the aluminum alloy and sand grain from the external environment. The screw is stricken to mark the root segment of it with a scar because of vibration while the aircraft flies off and lands. Therefore many fatigue zones appeare on the root segment of the screw. Two main cracks formed by the confluence of many fatigue zones spread oppositely, and a step appears when the two main cracks meet at last. The overload fracture occurrs due to fatigue cracking according to the dimple. The results are very helpful for the aircraft accident investigation to find out the right failure analysis results.