Ultrasonic Echo Characteristics and On-machine Detection Method of Small Tooth Cracks in Generator Rotors

doi:10.3901/JME.2024.08.011

Abstract

Abstract: The small teeth of the generator rotor have extremely high prestress under the restraint of the retaining ring. However, because of its frequent start and stop, the centrifugal stress of the retaining ring changes with the rotation speed, which causes the alternating concentrated stress of the tooth root of the small tooth. Therefore, the fatigue crack of the small tooth root is an important concern of the regular inspection of the generator. Shooting at the problems including the unknown reflection echo characteristics, serious signal attenuation and low detection accuracy of the small tooth crack under the l retaining-ring double-layer structure, the ultrasonic echo characteristics of cracks with different geometrical characteristics are explored through the finite element acoustic simulation model, the generation mechanism and evolution law of ultrasonic signal are confirmed and the coda index characterizing the existence of cracks is constructed. Correspondingly, the scanning strategy and the judging criteria for the ultrasonic-based crack detection are figured out. Eventually, the effectiveness of the method for the qualitative and localization detection of simulated cracks is verified by a small tooth-retaining ring simulation bench. This method provides a new way for the in-situ rapid detection of cracks in small teeth of generator rotors.

Key words: fatigue crack, non-destructive testing, ultrasound, crack state

CLC Number:

TH17

LIANG Peng, ZHAO Wenzhuo, WU Tonghai, RAN Yi. Ultrasonic Echo Characteristics and On-machine Detection Method of Small Tooth Cracks in Generator Rotors[J]. Journal of Mechanical Engineering, 2024, 60(8): 11-21.

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