Failure analysis of a locomotive turbocharger main-shaft

A failure investigation has been conducted on a locomotive turbocharger main-shaft. The fracture position is located at a sharp edged groove between two journals with different cross-sectional area. Fractography investigation indicates that the rotating bending fatigue is the dominant failure mechanism of the main-shaft. Detailed metallurgical analysis indicates the root fillet region of the groove had subjected to abnormal high-temperature resulting from the intense friction between the bearing-sleeve and the assisted pushing bearing, which makes the fatigue strength of the root fillet region of the groove decrease. Over-small root fillet radius of the groove by which stress concentration is created facilitates the fatigue cracks to initiate in the root fillet region.