Design assisted fatigue failure of an aircraft's pole piece assembly

摘要

A premature failure of alternator assembly of an aircraft was reported. After stripping of the assembly, one of the pole piece was found fractured. Material of the pole piece was low carbon steel (AISI C1006). Hardness of the pole piece was slightly higher than the standard values. Detailed investigations revealed that the pole piece was fabricated by cold forging, which induced fine surface cracks. Subsequently, during service the fatigue cracks initiated and propagated under high cyclic fatigue loadings from pre-existing fine surface cracks.