某型直升机主桨叶大梁断裂故障分析

Fracture fault analysis of main blades girder on a helicopter

针对某型直升机桨叶疲劳断裂、压力传感器未报警故障,通过故障树分析法开展桨叶失效分析、压力信号器故障模式分析,在此基础上探明故障机理。宏、微观断口分析表明:剥落坑从大梁表面的非金属镶嵌物处起始,断口从疲劳剥落坑底部起源,具有明显高周疲劳断裂特征。能谱分析发现,大梁表面存在富Si、O镶嵌物。普查发现压力信号器存在手检功能正常、基准腔压力低的故障模式。综合分析认为,喷丸工艺参数不合理,大梁局部表面存在初始缺陷,在载荷作用下疲劳裂纹在缺陷部位萌生并扩展,大梁裂纹扩展贯穿至内腔时,大梁漏气压力下降,但压力信号器密封失效导致基准腔压力泄漏,告警功能丧失,桨叶监控安全机制失效,穿透裂纹沿大梁两侧方向扩展,23个起落后桨叶断裂。

In view of the fatigue fracture fault of the main blade girder of a helicopter and the failure of fault warning from the pressure sensor,a fault tree was applied to analyze the reason of the faults.Blade failure and main fault mode of the pressure sensor were analyzed,based on which the mechanism of the accident was discussed.The results of macro and micro fractographic analysis showed that spalling holes appeared from multiple non-metallic tesseras on the surface of the girder and the fracture appeared from the bottom of the fatigue spalling holes on the external surface of the lower main girder,which demonstrated clear characteristics of fracture caused by high-cycle fatigue.Energy spectrum analysis to the source area of the fracture showed the existence of Si and O-rich tesseras on the surface and sub-surface of the main girder.General investigation carried after the accident showed that the pressure sensor had the fault mode of proper manual inspection function but without warning when the pressure level of the base chamber was low.Comprehensive analysis indicated improper shot-peening parameters.There were initial defects on part of the surface of the main girder,which led to the initiation and extension of fatigue crack from the part of defect because of the fatigue load.Pressure level of the main girder dropped out of air leakage when the fatigue crack extended throughout the inner chamber.Meanwhile,the sealing component of the pressure sensor failed,leading to pressure loss of the base chamber.In this way,the warning function and blade monitoring safety mechanism failed and the crack running through the main girder extended along both directions of the girder,leading to the fracture of the blade after 23 ups and downs.