Fracture reasons of fan blade fastening bolt

During the operation of a wind turbine generator set in a wind farm, several blade fastening bolts broke. The fracture reasons of the bolts were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscope analysis, metallographic examination, mechanical property test and finite element analysis. The results show that there was stress concentration at the thread root of the blade flange and pitch bearing joint surface, and under the action of multi-directional shear stress and tensile stress, the crack source gradually formed. The existence of machining tool marks and inclusions in bolts promoted the formation and propagation of cracks, and finally led to fatigue fracture of bolts.