Fracture analysis of impeller blade of a locomotive draught-fan

This paper presents the failure analysis of the impeller blade of a locomotive draught-fan. Visual examination indicates that blade was fractured at the 15–33 mm distance from the blade root and the failure mode is instantaneous fracture. Metallurgical observation reveals that the fractured blade had been repair-weld on the upper surface (the convex side) and the lower surface (the concave side) of blade before fracture. Many casting defects produced by welding are presented at the interface between the repair-welding region and the substrate as well as within the repair-welding region. The crack was originated from three large shrinkage cavities at the interface between the repair-welding region and the substrate due to the stress concentration at the pores, and propagated from the concave side toward the convex side of blade. Finite element method (FEM) was utilized to determine the static stress of the blade under operation conditions and dynamic characteristic of blade. FEM results indicate that failure did not occur at the maximum stress area due to static forces and the mechanical resonance of blades did not contribute to blade failure.