Failure Investigation of an Aircraft Crankshaft Gear Connection
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CASE HISTORY—PEER-REVIEWED
Failure Investigation of an Aircraft Crankshaft Gear Connection Michael Stevenson • David Klepacki Jeff McDougall • Dale Alexander
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Submitted: 4 October 2012 / Published online: 7 November 2012 ASM International 2012
Abstract Improper assembly of an aircraft crankshaft can have serious consequences. If an adequate joint clamping force is not applied to the connection between the crankshaft and crankshaft gear during assembly, relative motion in the system could create flexural loads on connection components, and cause damage such as cyclic fatigue cracking, shear overstress fracture, and plastic deformation. Many factors can contribute to insufficient joint clamping, including poor joint seating, the presence of a foreign object on the faying surface, and failure to apply proper torque during assembly. This paper reviews a case involving a crankshaft gear connection, which separated while the subject aircraft was in flight, causing the engine to fail and the aircraft to crash. To determine the root cause of the failure, a metallurgical analysis was performed. Keywords Crankshaft gear connection Cyclic fatigue cracking Joint clamping
Background A metallurgical failure analysis was conducted on a separated crankshaft gear connection from an aircraft engine involved in a non-fatal crash into a river. At the request of the owner/pilot, the aircraft engine, which was modified for increased horsepower, had been recently disassembled and
inspected. The inspection was prompted by a propeller strike that occurred when the landing gear failed. The aircraft had logged *10 h of flight time since the engine teardown/inspection.
Introduction Components of the subject aircraft available for examination included the subject crankshaft, the crankshaft gear, the lockplate, the crankshaft bolt, and the fractured remnant of the crankshaft dowel. A photograph of the components in the as-received condition is shown in Fig. 1. The investigation was limited to non-destructive analyses, including visual examination and light microscopy, dimensional evaluation (which confirmed critical dimensions), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Visual and Light Microscopic Examination The following observations were made during visual and stereomicroscopic examination of the components: •
• • M. Stevenson (&) D. Klepacki J. McDougall D. Alexander Engineering Systems Inc., 4215 Campus Drive, Aurora, IL 60504, USA e-mail: [email protected]
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The crankshaft bolt showed extensive damage, including plastic deformation of the body, shearing of the apparently engaged threads, and damage to the wrench flats (Figs. 2, 3). The lock plate appeared distorted (Fig. 4) and was fractured in two locations (Figure 5). The end of the crankshaft contained a fractured section at the large end of the dowel (Fig. 6). The large end of the crankshaft dowel was apparently recessed below the crankshaft counterbore surface (Fig. 7).
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J Fail. Anal. and Preven. (2012) 12:617
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