Ispitivanje uzroka mehaničkog otkaza glave cilindra avionskog klipnog motora

Abstract

Tokom leta školskog aviona Utva-75 došlo je do otkaza motora usled pucanja glave cilindra. Nakon uspešno izvršenog prinudnog sletanja oštećeni sklop cilindra je demontiran sa motora aviona i poslat na forenzičku ekspertizu. Fraktografskim ispitivanjem prelomne površine utvrđeno je da je uzrok otkaza zamor materijala glave cilindra. Metalografska ispitivanja pokazala su da je uzrok nastanka zamorne prsline postojanje značajne poroznosti materijala upravo u zoni nastanka loma. Numerička simulacija naponskog stanja sklopa cilindra, izvršena metodom konačnih elemenata, potvrdila je pretpostavku da je lom iniciran u zoni najveće koncentracije napona.

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.