Failure analysis of an isometric polygonal shaft fracture

•Both experimental methods and theoretical calculation are used in this paper.•The large eccentricity between the shaft and hub hole is the root cause of the fracture.•The fracture of the isometric polygonal shaft belongs to fatigue fracture and is multi-source fatigue.•The fracture of the shaft is caused by both bending and torsion.

Failure analysis of an isometric polygonal shaft used in a coal mine reducer has been carried out. Chemical analysis, micro-structural characterization, metallographic test, hardness measurements, theoretical calculation and finite element simulation were used for the analysis to determine the fracture reasons. The analysis results show that the feature of the isometric polygonal shaft belongs to fatigue fracture and is multi-source fatigue. Fatigue sources have occurred on the surface of the shaft and the fracture of the shaft is caused by both bending and torsion. The eccentricity between the shaft and hub hole can lead to large bending deformation which can generate high stress concentration. The large eccentricity can be the root cause of the fracture.