Investigation of mechanical failure cause of an aircraft piston engine cylinder head

The piston engine of the training aircraft Utva-75 malfunctioned during the flight mission due to the cracking of its cylinder head. After successful forced landing, the damaged cylinder assembly was removed from the engine and sent to the lab for forensic expertise. Fractographic examination of the mating fracture surfaces revealed that the fatigue was the main cause of the cylinder head failure. The metallography examination has shown that the fatigue was promoted from pre-existing material defect due to an elevated presence of porosity forms at the crack initiation zone. The finite element method, utilized to determine the stress state of the cylinder assembly, confirmed that the crack origin was located at the most stress area.