Failure of a crankshaft of an aeroengine: A contribution for an accident investigation

The objective of this work is to determine the main cause of failure of a crankshaft from an ULM airplane aeroengine. The core of this paper is focused in the analysis of the damage mechanisms which were in the base of a catastrophic failure of the crankpin journal. Based on a preliminary observation of the fracture surface, there are clear evidences of a fatigue process as both beach and striation marks have been identified. The judicious characterization of the failing mechanism, including the identification of the crack initiation site and the assessment of the crack propagation rate, is of paramount importance to support the investigation of this aircraft accident. In this context, an exhaustive observation of the fracture surface by means of optical and electronic microscopic techniques, in parallel with microstructural examinations, were carried out as determinant information for the correct assessment of the contributive causes to this accident.

► An aeroengine crankshaft failure was analyzed to determine the damage mechanisms.
► The fracture surface shows striation marks consistent with a fatigue process.
► Ratcheting was identified in the crack initiation site.
► The crack front geometry indicates a predominant cyclic bending condition.
► Root failure is the combined effect of several stress concentration features.