Effect of Wave Process of Plastic Deformation at Forging on the Fatigue Fracture Mechanism of Titanium Compressor Disks of Gas Turbine Engine

Abstract

The low-cycle fatigue behavior of the VT3-1 titanium alloy (Ti–6Al–3Mo–2Cr alloy) under loading with a triangular and trapezoidal shape of cycle waveform was studied on round specimens prepared from forged compressor disks of a gas turbine engine. The filament type structure after forging has alternating filaments with the ductile and quasi-brittle state of the metal as a result of the wave process of plastic deformation during the metal forging process. The crack propagation, regardless of the cyclic waveform shape, occurs by the crack meso-tunneling mechanism: initially, the cracks propagate along the filaments by a quasi-brittle mechanism with the formation of a facetted pattern relief on the fracture surface reflecting the two-phase structure of the titanium alloy, and then, the bridge between the meso-tunnels is fractured with the formation of fatigue striations. The part of the crack growth duration Np/Nf in the durability Nf is determined on the basis of measuring the fatigue striation spacing, and it depends on the crack path with respect to the material filaments. The growth of a fatigue crack in the case of in-service failure of a compressor disk of a gas turbine engine is considered, taking into account the crack meso-tunneling effect, and the fatigue crack growth duration in the disk is determined on the basis of quantitative fractography.

The in‐service fatigue fracture mechanisms for the I‐stage low‐pressure compressor disk of the aircraft engine D30KU‐154

“…The microstructure at these locations shows a clear texture reflecting the stamping technological process. Such structure is also common for the titanium alloy components for aircraft 2 …”

“…Similar scenario of crack initiation and early crack growth had been observed earlier for other types of aircraft engines. The VHCF type of fracture surface was reported for titanium disks installed at different stages of compressor 1,2 . The observed morphology of the fracture surface shows a high sensitivity of the two‐phase titanium alloy to dwell time and superimposed high frequency loading on low frequency high amplitude loads.…”

“…Because of the complex multiaxial loadings of aircraft structures and wide amplitude and frequency spectrum of the loads, different aircraft structures can experience all known fatigue regimes from low cycle fatigue (LCF) to very high cycle fatigue (VHCF). Thus, for different elements the corresponding inspection and maintenance periods should be set according to the loading conditions 2 . Short inspection and maintenance intervals would give a high probability of early crack detection and therefore operational safety of the structure.…”

“…Thus, for different elements the corresponding inspection and maintenance periods should be set according to the loading conditions. 2 Short inspection and maintenance intervals would give a high probability of early crack detection and therefore operational safety of the structure. However, too short inspection and maintenance intervals would decrease the inspection accuracy due to the "human factor" and increase the cost of operational aircraft maintenance.…”

Wave Process of Plastic Deformation of Titanium Alloys, Determining the Mechanisms of Destruction of Compressor Discs at Different Scale Levels

“…DOI 10.25205/978-5-4437-1353-3-144 ВОЛНОВОЙ ПРОЦЕСС ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ ТИТАНОВЫХ СПЛАВОВ, ОПРЕДЕЛЯЮЩИЙ МЕХАНИЗМЫ РАЗРУШЕНИЯ ДИСКОВ КОМПРЕССОРОВ НА РАЗНЫХ МАСШТАБНЫХ УРОВНЯХ 1,2 Шанявский А.А., 2 Никитин А.Д., 1 Солдатенков А.П. 1 Авиационный регистр Российской Федерации, Московская область, Химки 2 Институт автоматизации проектирования РАН, Москва В процессе эксплуатации авиационных двигателей имеют место разрушения дисков компрессоров ГТД, которые изготавливают из титановых сплавов ВТ3-1 и ВТ8 [1,2]. Диски испытывают нагружение в полётном цикле, которое связано с высокой их напряжённостью, и могут достигать предельного состояния по разным критериям в зависимости от места зоны зарождения и роста трещины.…”