Failure analysis of components belonging to an aeroengine

Suresh Kumar, M and Madan, M and Venkataswamy, MA and Sujata, M and Bhaumik, SK (2006) Failure analysis of components belonging to an aeroengine. Project Report. National Aerospace Laboratories, Bangalore.

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The aircraft met with an incident on March 23, 2006. On strip examination of the engine, one of the I stage compressor rotor blades was found dislodged and lying in the air intake. It was reported that in addition to this, one more blade had fractured in the airfoil section. The remaining blades of I stage were with the disc and were mechanically damaged to varying extent. The dislodged blade (No.5) and the fractured blade (No.24) were forwarded to the laboratory for analyzing the cause of failure. Two locking pins, one belonging to blade No.5 and the other belonging to blade No.24, were also sent for analysis with the following queries. (a) Whether or not blade No.24 failed by fatigue? (b) Whether or not blade No.5 got dislodged due to failure of blade No.24? If not, what was the reason for dislodgement of blade No.5? (c) In a normal situation, the blade sliding is expected to be in the forward direction. Why in this case, the blade No.5 sliding was in the rearward direction? The investigation was carried out with respect to (a) and (b) and the findings were reported (refer NAL Report No. FA-MT-995-05-2006) with the following conclusions.. (a) Fractographic study confirmed that the blade No. 24 had failed by sudden overload such as impact. There were no evidences of progressive failure like fatigue. (b) The dislodgement of blade No. 5 without any breakage is possible only when the locking mechanism fails. (c) Evidences suggest that the locking pin used for the blade No. 5 is 27.0 mm in length against the specification of 32.0 mm. This is as good as not locking the blade. It is, therefore, believed that this particular blade had dislodged from the disc due to this assembly error leading to subsequent damages in the engine. Subsequent to the above, NAL was requested to carry out investigation on additional components, namely, (a) dovetail portion of slot No.5 from I stage rotor disc and (b) three blades of I stage rotor where half moon cuts were noticed with a view to establish the following. (a) Conformation of the blade sliding in the rearward direction. (b) Nature of damages on the three blades supplied (whether or not due to FOD?) The necessary information, drawing, specification, photographs etc., were provided by the manufacturer for carrying out the investigation on the above components. The dovetail portion of the blade No.5 and dovetail slot No.5 on the rotor disc were examined to look for tell-tale marks, present if any, for conformation of the blade sliding in the rearward direction. The damages on the pin No.5 were also examined in detail in an effort to corroborate the tell-tale marks on the dovetail slot and the blade sliding direction. The dislodged blade i.e., blade No.5 and the other I stage rotor blades were examined to look for damages that would have occurred during blade sliding and its ejection from the rotor disc. In the event of blade sliding in the rearward direction, firstly, the blade is expected to have severe damages due to obstruction caused by the stator blades. In such a case, the blade would get fractured into pieces by the impact forces acted upon the blade by the stator blades. Secondly, once the blade moves out of the dovetail slot in the rearward direction, it cannot come out into the air intake without damaging most of the I stage rotor blades. None of these were found to have occurred in the present case and hence, the evidences do not support the theory of blade sliding in the rearward direction. The signatures left on the blade retaining pin and the dovetail slot No.5 of the rotor disc were analyzed. These signatures also did not conform to the findings of the DI committee wherein it was established that the blade sliding was in the rearward direction. On the contrary, there were adequate evidences to suggest that the blade No. 5 sliding was in the forward direction. A detailed account of the findings is submitted in this report.

Item Type: Monograph (Project Report)
Uncontrolled Keywords: Aeroengine; compressor rotor blade; locking pin; assembly error
Subjects: AERONAUTICS > Aeronautics (General)
CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
Depositing User: Raghavendra R chandu
Date Deposited: 25 Jul 2011 05:42
Last Modified: 25 Jul 2011 05:42

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