Failure analysis of an aeroengine components

Madan, M and Sujata, M and Raghavendra, K and Bhaumik, SK (2011) Failure analysis of an aeroengine components. Project Report. National Aeronautical Laboratory, Bangalore, India.

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A few components and debris collected from an aeroengine retrieved from the wreckage of a crashed helicopter were sent to this laboratory for analysis. The items received for laboratory tests/investigation are: (a) drive sleeve, (b) coupling sleeve, (c) debris/deposits and (d) non-metallic pieces collected from various parts of the engine, and (e) metal pieces collected from magnetic chip detector (MCD). Debris collected from various parts of the engine was found to be either dust and soil or fragments of non-metallic fabric that was used in some parts of the engine. Compositional analysis confirmed that the metallic particles collected from the MCD were from the shaved off splines of drive and coupling sleeves. The mode of failure in the drive and coupling sleeves was identified to be progressive in nature. There were three fatigue cracks in the coupling sleeve; all of them being initiated at the spline root region. However, it is to be noted that no fracture was associated with these cracks. Hence, fatigue cracks per se were not responsible for the failure of the drive and coupling sleeves. Rather, evidences suggest that the fatigue crack initiation and propagation had occurred subsequent to some other mechanism of failure. It was not possible to unambiguously establish the mode of failure of the splines of the drive and coupling sleeves because of the severe destruction that took place following the failure. But, there were tell-tale marks on the working flank of the available portion of the splines, which were indicative of relative movement between these components in the axial direction. Considering the nature of failure in the present case, this assumes significance. Analysis shows that in the event of such movement, wear on the meshing surfaces of the splines is inevitable. As wear progresses, the clearance between the engaging splines increases. This induces cyclic load of higher magnitude on the splines which increases the vulnerability for fatigue crack initiation at the spline root region. Moreover, the wear on the splines results in loss of material and thereby reduces cross section of the splines. When the cross section reduces to critical limit such that the splines can no longer sustain the application load, they fold or shear off. Although direct evidences to this proposed mechanism is scarce on the component because of the post failure destruction, available signatures, however, point towards such a sequence of failure. This is further supported by metallurgical investigation wherein both drive and coupling sleeves were found conforming to the specifications with respect to (a) chemical composition, (b) microstructure, (c) surface treatment, and (d) hardness profile. The reason(s) for possible axial movement between the drive and coupling sleeves, however, could not be established from the laboratory investigation. In view of the progressive failure in the drive and coupling sleeves, it is justifiable to state that the failure in these components was primarily responsible for the sudden loss of power in the engine. This report provides a detailed account of laboratory investigation with test results and analysis. Also, a few recommendations are suggested for identification of probable cause(s) which could give rise to axial movement between drive and coupling sleeves.

Item Type: Monograph (Project Report)
Uncontrolled Keywords: Aeroengine;Drive and coupling sleeves;Fatigue;Wear
Subjects: CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
Depositing User: Ms. Alphones Mary
Date Deposited: 06 Jul 2011 05:46
Last Modified: 06 Jul 2011 05:46

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