Analysis and research on fracture cause of connecting bolt of wind turbine spindle

Abstract

On a certain day in 2018, the main shaft connecting bolt of a wind turbine in a wind farm broke and failed during operation. In order to find out the cause of fracture, the fractured spindle connecting bolt was comprehensively detected and analyzed by means of appearance state analysis, chemical element composition analysis, mechanical property detection analysis, microstructure detection and fracture micro area analysis. The results show that the main reason for the fracture of the main shaft connecting bolt is that the hydrogen penetrates into the bolt surface due to improper process control during the production process, resulting in hydrogen embrittlement in the local area of the thread root. Thus, during the operation of the fan, under the combined action of bending, shear and tensile stress, the connecting bolt of the main shaft cracks at the bottom of the first thread on the side of the self rigid rod with the most concentrated stress, and expands in the form of “herringbone” brittle fracture until the overall fracture failure. It is recommended to check the bolts in the same batch to prevent hydrogen embrittlement in the whole batch.