Procena veka i integritet vazduhoplovnih konstrukcija od aluminijumskih legura AA2024 i AA7075 u korozionom okruženju

Abstract

Opšte je poznato da su elementi strukture vazduhoplova, izrađeni od aluminijumskih legura povišene i visoke čvrstoće, u ekspolataciji dominantno izloženi delovanju promenljivog opterećenja, u uslovima delovanja koroziono aktivne radne sredine, a problem se dodatno usložnjava mogućim i realno verovatnim prisustvom grešaka tipa prsline. Na osnovu rezultata ispitivanja, analiziran je uticaj eksploatacionih uslova na stanje osnovnog materijala vazduhoplovne konstrukcije predviđene za rad u uslovima delovanja promenljivog opterećenja, a radi procene integriteta i preostalog veka konstrukcije. Za potrebe istraživanja primenjene su numeričke i eksperimentalne metode, pri čemu je istražen uticaj delovanja promenljivog opterećenja na strukturne elemente vazduhoplova, izrađene od aluminijumskih legura povišene i visoke čvrstoće, 2024-T351 i 7075-T651, sa prisustvom grešaka tipa prsline, a u uslovima delovanja koroziono aktivne radne sredine. Istraživanje uticaja korozije na rast prsline i lom struktura izrađenih od legura aluminijuma 2024-T351 i 7075-T651 provedeno je kroz četiri faze: (1) Ispitivanje uticaja korozije na mehanička svojstva legura aluminijuma 2024-T351 i 7075-T651 – Statička zatezna ispitivanja; (2) Ispitivanje uticaja korozije na parametre mehanike loma legura aluminijuma 2024-T351 i 7075-T651 – Dinamička zatezna ispitivanja; (3) Simulacija rasta zamorne prsline u leguri aluminijuma 2024-T351 – Procena broja ciklusa opterećenja do loma i poređenje sa rezultatima dobijenim eksperimentalnom analizom; (4) Procena broja ciklusa opterećenja do loma okvira trupa aviona, u zavisnosti od dužine inicijalne prsline, opsega napona i vremena izloženosti predmetne strukture dejstvu korozione sredine.

It is generally known that the elements of the aircraft structure, made of aluminum alloys of increased-strength and high-strength, are dominantly exposed to the action of variable load during operation, under the conditions of action of a corrosively active working environment, and the problem is further complicated by the possible and realistically probable presence of cracks. Based on the test results, the impact of operational conditions on the state of the basic material of the aircraft structure intended for operation under variable load conditions was analyzed, in order to assess the integrity and remaining life of the structure. Numerical and experimental methods were applied for the purposes of the research, where the influence of the action of variable load on the structural elements of the aircraft, made of aluminum alloys of elevated and high strength, 2024-T351 and 7075-T651, with the presence of cracks under the conditions of the corrosively active working environment was investigated. The investigation of the effect of corrosion on crack growth and fracture of structures made of aluminum alloys 2024-T351 and 7075-T651 was carried out through four phases: (1) Testing the influence of corrosion on the mechanical properties of aluminum alloys 2024-T351 and 7075-T651 – Static tensile tests: (2) Testing the influence of corrosion on fracture mechanics parameters of aluminum alloys 2024-T351 and 7075-T651 – Dynamic tensile tests: (3) Simulation of fatigue crack growth in aluminium alloy 2024-T351 – Estimation of the number of load cycles to fracture and comparison with the results obtained by experimental analysis: (4) Assessment of the number of load cycles until the breakdown of the aircraft fuselage frame, depending on the length of the initial crack, the stress range and the time of exposure of the structure in question to the effect of the corrosive environment.