Failure Analysis of a Jet Engine Gearbox Drive Gearshaft Ball Bearing
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FEATURE
Failure Analysis of a Jet Engine Gearbox Drive Gearshaft Ball Bearing Rodolfo Villa • Scot Roswurm
Submitted: 18 October 2012 / in revised form: 23 February 2013 / Published online: 22 March 2013 ASM International 2013
Abstract The case study presented in this article details the failure investigation of an M50 alloy steel bearing used in a jet engine gearbox drive assembly. It discusses the investigative steps and analytic tools used to determine the root cause, highlighting the importance of continuous, thorough questioning by the investigating activity. The combined analyses demonstrated that the bearing failed by a single event overload as evidenced by bulk deformation and traces of foreign material on the rolling elements. The anomalous transferred metal found on the rolling elements subsequently led to the discovery of overlooked debris in an engine chip detector, and thus resulted in a review of several maintenance practices.
concentrations in the engine chip detector were found following the failure of the engine core module. Subsequent tear down of the engine revealed that the source of metallic debris was the Gearbox Drive gearshaft assembly. Specifically, the failure was found to have originated at the thrust bearing attached to a bevel gearshaft that is rotated by the engine low pressure turbine shaft. The bearing and key neighboring components were submitted to the Metallurgical Analysis Section at Tinker AFB for failure analysis.
M50 Bearing Overload Foreign material
The Gearbox components were received disassembled and separated in bags. The parts were photographed in the asreceived condition for documentation purposes. The components of interest to this investigation are shown in Fig. 1. The outer race (OR), inner race (IR), and rolling elements (bearing balls) were also received separated. No cage or remnant cage fragments were recovered. Each component was examined visually to identify key features of interest. For brevity, only the most relevant pieces of evidence will be discussed.
Keywords
Introduction and Background Bearing failures in turbine engine applications usually result in significant damage, leaving very little to evaluate. Occasionally, a bearing is found with sufficient evidence to reach a definitive conclusion. Regarding the subject bearing, it was reported that abnormally high metallic This article is an invited paper selected from presentations at the Microscopy & Microanalysis 2012 Annual Meeting, held July 29August 2, 2012 in Phoenix, Arizona, and has been expanded from the original presentation. R. Villa (&) S. Roswurm Metallurgical Analysis Section, Tinker AFB, 3001 Staff Dr. Tinker AFB, Oklahoma City, OK 73145, USA e-mail: [email protected] S. Roswurm e-mail: [email protected]
Laboratory Analysis
Beveled Gear and Sleeve The most notable features on the beveled gear and gearshaft sleeve were the apparent heavy localized gouging on one side of each component (Fig. 2). The gouging on the gear was isolated to the larger diameter porti
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