某型号旋翼直升机飞行过程中发生异常震动，检查发现尾梁站位BS 135.00附近的尾传动轴整流罩固定支架铆钉处有沿尾梁周向扩展的裂纹。对裂纹断口进行了宏观和微观观察、化学成分分析、金相组织检查和硬度检测，并利用有限元分析方法对尾梁结构进行模态分析，计算出尾梁结构的固有频率与振型。最后，结合模态分析结果和维护手册上的要求，对蒙皮产生裂纹的原因进行综合分析。结果表明: 蒙皮裂纹的失效模式为疲劳断裂; 尾桨振动超标，使其与尾梁产生共振，是裂纹产生的主要原因。

Abnormal vibration was found when a certain type of helicopter in the process of flight. It was found after inspection that there was a crack along circumferential propagation at the rivet of fixed bracket on the tail drive shaft fairing button near BS 135.00 stations of tail boom. Macroscopic and microscopic observation, chemical composition analysis, metallographic examination and hardness testing were carried out for the fracture of the crack, and modal analysis was used to calculate the natural frequency and vibration mode of the tail beam structure by finite element analysis method. Finally, the causes of cracking of the skin were analyzed by combining the results of modal analysis and the requirements of the maintenance manual. The results show that the failure mode of skin was fatigue. The main reason for the cracking was that the tail rotor whose vibration exceeded the standard resonated with the tail beam.