Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve

A failure investigation was conducted on a locomotive turbocharger main shaft and a bearing sleeve which had been assembled with the main shaft. The fracture of the main shaft took place at a sharp edged groove between two journals with different cross-sectional areas. The dominant failure mechanism of the main shaft was low-cycle and rotation-bending fatigue. Wear failure occurred on the bearing sleeve through a mixed mode of abrasive and adhesive wear. Detailed metallurgical analysis indicated that the bearing sleeve and the journal surface assembled with the sleeve had been subjected to abnormally high temperatures which led to increased friction between the bearing sleeve and the bearing bush, the sleeve, and the journal surface. In addition, the abnormally high temperature softened the induction-hardening case on the journal surface and decreased the fatigue strength. Fatigue crack initiation occurred at the root fillet of the groove because of the stress concentration in that area.