Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve Zhiwei Yu • Xiaolei Xu • Xiaoyan Guo
Submitted: 14 March 2010 / in revised form: 19 November 2010 / Published online: 14 December 2010 Ó ASM International 2010
Abstract 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. Keywords Main shaft Bearing sleeve Low-cycle and rotation-bending fatigue Wear friction Failure analysis
Background A locomotive turbocharger main shaft and a bearing sleeve assembled with the main shaft were received to failure analysis (Fig. 1). It was reported that the locomotive turbocharger main shaft had been in service for 105,000 km
of operation before fracture. The failed main shaft was made of 42CrMo steel. The hardness of core material is specified as HRC25-30 and some journals of main shaft are to be induction-quenched (journals A, C, D, and E, marked in Figs. 1, 2) to obtain the surface hardness of HRC56-62. The failed sleeve was made of 38CrMoAl steel. The internal and external surfaces were to have been nitrided to a depth of at least. Investigation Methods The chemical composition of the failed main shaft and bearing sleeve materials was determined by spectroscopy chemical analysis. The microstructure in various regions was observed by SEM. The fracture and damage surfaces were analyzed by visual and SEM observation to study the failure mechanism. Microhardness profiles were made on an MH-6 Vikers meter using a load of 300 g to determine the depth of nitrided layer on the sleeve. According to the Chinese standard (GB1542-89) [1], when the hardness value of the position measured is equal to the interior hardness value ? HV50 (in present work, HV0.3331), the depth from the position to the surface is defined as the nitrided layer depth. Observation Results Fracture and Surface Damage Morphology Main Shaft
Z. Yu X. Xu (&) X. Guo Electromechanics and Material Engineering College, Dalian Maritime University, Dalian, China e-mail: [email protected]
The fractured main shaft is shown in Fig. 2. It can be seen that the fra
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