Failure analysis of a bridge crane shaft

Failure analysis of a shaft used in a bridge crane has been carried out. The shaft fractured in the keyway with evidence of fatigue. Chemical analysis, micro-structural characterization, fractography, hardness measurements, and finite element simulation were used for the analysis. The microstructure was predominantly tempered martensite; large amounts of oxides, micropores, and manganese sulfide inclusions were found. The geometry of the keyway also promoted the initiation crack because the width and height were erroneously designed. It was concluded that all these factors produced fatigue failure. It is recommended to first guarantee the chemical composition and microstructure of the material. Secondly, use magnesium or calcium additions in the steel casting process to obtain better shape control of inclusions and, finally, accomplish the geometric parameters recommended by the standard to avoid high stress concentration factors.