Failure Analysis of a Locomotive Engine Oil Pump Shaft
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TECHNICAL ARTICLE—PEER-REVIEWED
Failure Analysis of a Locomotive Engine Oil Pump Shaft A. R. Mashreghi • S. Saberifar • S. J. Hejazi
Submitted: 7 May 2012 / Published online: 17 May 2013 Ó ASM International 2013
Abstract In this study, the fracture of a locomotive engine oil pump shaft is investigated. According to the reports, all oil pump shafts of this type fail in short periods of time due to the fracture at a location on the shaft which is in contact with a pinion. Stress analysis showed that the shaft bears torsion and cyclic bending stresses in the fracture site. The fracture surface observations revealed that the cracks are generated from the surface, and fatigue fracture occurs due to the cyclic bending stresses. According to the laboratorial analysis, the shaft is a surface-hardened low alloy steel. The lack of suitable pre-heat treatment and surface hardening and the roughness created by the slippage between the shaft and the pinion are concluded to be responsible for the failure of the oil pump shaft.
engine and its turbocharger was chosen for the failure analysis. The driving force is transmitted to the pinion which is mounted on the shaft by a gear. Therefore, the shaft turns the oil pump and hence injects the lubricant into the engine and the turbocharger. The fracture had occurred at the contact surface of the pinion and the shaft. According to the reports, all of the previous shafts had also failed in a short period of time and at the same location. In this paper, a precise fractographic study and a metallurgical investigation of the failed shaft are described and the possible reasons of failure are assessed.
Investigation Methods Keywords Shaft
Failure analysis Fatigue Fracture
Introduction A failed shaft belonging to an oil pump which injects high pressure circulating lubricant into an Alstom locomotive A. R. Mashreghi Department of Mining and Metallurgical Engineering, Yazd University, Safayieh, Daneshgah Blvd. University Main Campus, P.O. Box 89195-741, Yazd, Iran
The chemical composition of the failed shaft material was determined by the spectroscopy chemical analysis method. The microhardness measurements were carried out by a Time-HVS-1000 apparatus under 1.69 N load on the cross section of the material. The surface hardness of various sites was also measured by an Instron hardness tester at a load of 10 Kg. The microstructure at several locations including the fractured surface was observed by an optical microscope and stereo-binoculars.
Results S. Saberifar (&) Research & Development Department, Iran Alloy Steel Company (IASCO), Azadegan Blvd, Martyr Dehghan Manshadi, KM 24 IASCO Private Road, P.O. Box 89195-763, Yazd, Iran e-mail: [email protected] S. J. Hejazi Department of Aircraft Maintenance, Civil Aviation Technology College, Azadi Square, Meraj Street, P.O. Box 13445-418, Tehran, Iran
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Visual and Stereo-Binocular The schematic drawing of the failed oil pump shaft is shown in Fig. 1. The fracture region and the hardness measurement points are also indicated
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