某发动机空中停车事件的失效分析

对一台发生空中停车的发动机进行了现场分解调查和实验室分析工作。分解发现肇事件是1组低压涡轮4级(LPT4)静子叶片,该叶片组因固定沟槽断裂而向后翘起打断所有LPT4转子叶片,并将低压涡轮部分5级(LPT5)和全部6级(LPT6)叶片打断。宏观和微观观察表明断裂的LPT4静子叶片均属于高周疲劳断裂,疲劳断裂的主要原因是固定沟槽内倒角过小。有限元法分析结果表明叶片倒角过小降低了叶片抵抗振动应力的能力;影像法测量结果表明内倒角不符合厂家的技术要求;金相分析表明内倒角不符合技术要求的原因是该处曾进行过焊修和再加工,属修理不当造成的。

Failure Analysis on In-flight Shutdown of an Aero Engine

An in-flight shutdown engine is disassembled and key components are taken to a lab for investigation.It is found by disassembling investigation that a cluster of low pressure turbine stage 4(LPT4)vanes causes the trouble.The cluster of vanes fracture at the hook and cock baekwards so as to break all LPT4 blades and part of LPT5 and almost all LPT6 vanes and blades.Macro and micro observation results show that all vanes fracture because of high cycle fatigue caused mainly by small transition radii of the hook.Calculation by means of the finite element method indicates that the small transition radii significantly decrease the ability of the blades to resist vibration stress.In addition,the size of the transition radii is below the technical requirements of the manufacturer.Metallurgical observation reveals that the vanes have been welded and reprocessed for repair,which results in the small transition radii condition.