Ultrasonic inspection of the surface crack for the main shaft of a wind turbine from the end face

Abstract

The integrity of the main shaft plays a significant role in the safety of wind turbine. Stress concentration often occurs where the main shaft and the bearing are assembled in the wind turbine. The surface breaking of transverse crack on the outer circumference thus becomes a major dangerous source. In this research, a finite element (FE) model is developed to analysis the echoes on the end face, which are often confused in the identification of the crack signals. The propagation of ultrasonic waves and its reflection on the shaft boundary will be investigated in details. The relationship between the amplitude of the crack echo and the radial position of the piezoelectric transducer is explored optimized comprehensively. Then, an ultrasonic measurement methodology are established for the examination of the main shaft from the end face. A circular scanning experiment for the shaft testing on surface cracks have been implemented. The results show that the crack depth less than 5 mm can be examined, although the total size of the shaft is Φ600 mm × 1285 mm. All artificial cracks in the high-stress zone have been detected with the aid of a B-scan imaging, which reveals the position of defects. This research will provide an effective regular inspection technique for the wind turbine shaft examination.