Investigation of Aircraft Piston Engine Head Failures

What effect does a deformed (mushroomed) thread have on stresses in the thread root? This model of an air-cooled aircraft engine cylinder head and barrel was developed and analyzed using elastic-plastic materials with temperature dependency and complicated contact at the thread interface, including shrink-fit between barrel and head, to find the answer to this question. The finding was that localized yielding (bottom and middle figures) at the deformed edge and the penetration of the deformed edge into the adjacent thread locked the barrel and head together and reduced alternating stress levels at the thread root. The positive findings were used as part of a National Transportation Safety Board investigation into incident with favorable finding for the client.

Year: 2003 Client: confidential
Fields: nonlinear analysis, FEA, plasticity, failure analysis

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