Issue 50

N. Boychenko et alii, Frattura ed Integrità Strutturale, 50 (2019) 54-67; DOI: 10.3221/IGF-ESIS.50.07 55 This study aims to explore elastic and nonlinear fracture resistance parameters and analyse constraint parameters taking into account accumulation of damages under various loading conditions within a temperature range. T HE SUBJECT UNDER STUDY AND MATERIAL PROPERTIES n this study, the stress-strain state and the fracture resistance parameters in an aircraft GTE compressor disc (Fig. 1a) were analysed. Slot fillets under the blade are the concentrated stress areas in the compressor disc of the aircraft GTE [3, 5-7]. The ‘dovetail’ type attachment had a broach angle of 26  at the axis of rotation, and partial-through surface cracks occurred in the disc and blade attachment [7, 8-10] (Fig. 1b). The crack propagation usually starts from a quarter elliptical corner surface flows [9, 11]. Crack developed in slot fillet near the disc outer surface. Further, the growing crack intersected the entire thickness of the disc. As a result, the disc rim ruptured (Fig. 1c) [9, 11]. a) b) c) Figure 1 : GTE compressor disc (a) and operation damages of disc and «dovetail type» blade attachment (b, c). Numerical analyses of the stress-strain state under the operating loading conditions were conducted in this study at various temperatures and crack sizes. The first part of numerical calculations focused on the stress-strain state analysis of the compressor disc without cracks. The second part was devoted to the analysis of the compressor disc with operational damage in the slot fillet of the – ‘dovetail’ type disc and its blade attachments. Three types of curvilinear crack geometry were considered. All calculations were performed at room (23°С) and elevated (300°С and 370°С) temperatures with a rotor angular velocity of 925 and 1000 rad/sec. Elastic, plastic and creep conditions were considered. Damage accumulation was analysed in consideration of creep conditions. Thus, numerical investigations were performed for given combinations of the main parameters, such as the angular velocity of the compressor disc, temperature, shape and size of the defect and the elastic, plastic and creep properties of the material. The combinations of the parameters used in the numerical calculations are presented in Tab. 1. Angular velocity, rad/s Temp., °С Disc without crack Disc with surface crack: а=0.34mm, с=0.71mm а=0.76mm, с=1.32mm а=1.5mm, с=2.2mm Elastic Plastic Creep Damage Elastic Plastic Creep Damage 925 23 + + - - + + - - 300 + + + + + + + + 370 + + + + + + + + 1000 23 + + - - + + - - 300 + + + + + + + + 370 + + + + + + + + Table 1: Various parameters employed in the numerical calculations. The compressor disc considered for the numerical calculations was made of titanium alloy VT3-1. The main mechanical properties of the material analysed at three temperatures are summarized in Tab. 2, where, σ 0.2 – yield stress, σ ut – true ultimate tensile stress, Е – Young's modulus, n – strain hardening exponent, α – strain hardening coefficient. I