Abstract
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.
Highlights
Takođe je utvrđeno i da je prilikom poslednjeg kompresionog testa, koji se sprovodi na svakih 100 časova rada, izmerena vrednost kompresije prvog cilindra bila znatno niža od vrednosti izmerenih na ostalim cilindrima
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
Summary
Ubrzo nakon poletanja sa matičnog aerodroma, dvočlana posada školskog aviona Utva-75 primetila je problem u radu motora. Motor aviona je bio znatno oštećen sa jasno uočljivom prslinom na glavi prvog cilindra motora. Oštećeni cilindar je demontiran sa motora aviona i poslat u Vojnotehnički institut na forenzičku ekspertizu uzroka otkaza. Uvidom u tehničku dokumentaciju održavanja aviona i motora utvrđeno je da je motor ostvario ukupno 1560 časova rada. Na 1200 časova rada urađen je remont motora i nakon toga motor je ostvario još 360 časova rada do navedenog otkaza. Takođe je utvrđeno i da je prilikom poslednjeg kompresionog testa, koji se sprovodi na svakih 100 časova rada, izmerena vrednost kompresije prvog cilindra bila znatno niža od vrednosti izmerenih na ostalim cilindrima (tabela 2)
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