PSI - Issue 13

R.R. Yarullin et al. / Procedia Structural Integrity 13 (2018) 902–907 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

903

2

damage due to creep, erosion and wear, impact damage or a combination of above failure mechanisms. The present trend in today’s high performance gas turbine engines requires an increase in the thrust to weight ratios, higher turbine inlet temperatures and higher operating pressure ratios. Such hard operating conditions lead to increasing of stress level. In some cases, these stresses may exceed the yield strength of the material and critical zones of the compressor disk will be subject to plastic stain. Shlyannikov et al. (2001) showed that in general, common failure locations for turbine disks under operation conditions are often at critical zones, such as central and bolt holes, disk/blade attachment area, and key slots. Under these conditions, a key point of the aircraft GTE component life analysis is knowledge of the nonlinear fracture mechanics parameters for corner cracks with regard to the three dimensional geometry under complex stress loadings. This paper provides a full-size 3D analysis of cracked aircraft GTE compressor disk in order to determine elastic and elastic-plastic constraint parameters for various crack sizes and different service temperatures. The subject of this study is high pressure compressor disk of D-36 aircraft GTE (Fig. 1a). As was shown by Shaniavski (2003), the cracks initiation in this type of compressor disks are occurred in a disk and blade «dovetail type» attachment (Fig. 1b). The fatigue failure of compressor disks was detected for a service lifetime equal to 3800 h/cycle. In all of these failures, crack propagation started from part-trough quarter elliptical corner surface flows. They developed in slot fillets under the blades near the disk outer surface. Further, the growing crack intersects the full thickness of the compressor disk and rupture of disk rim is occurred (Fig. 1c). 2. Subject for study and material properties

a) c) Fig. 1. High pressure compressor disk of D-36 GTE (a) and operation damages of disk and blade «dovetail type» attachment (b, c). GTE compressor disk is heavily loaded due to centrifugal and thermal loads. Under nominal operating conditions high pressure compressor section is operated at 300 ⁰ C and 925 rad/s. The material of a compressor disk is two-phase titanium alloy VT3-1. Tensile properties of titanium alloy VT3-1 at room and high temperature were determined according to ASTM standard E8 and E21, respectively, and are listed in Table 1. Where E is Young’s modulus, σ s is nominal ultimate tensile strength, σ 0 is monotonic tensile yield strength, σ u is true ultimate tensile strength, δ is elongation, ψ is reduction of area, n is strain hardening exponent, and α is strain hardening coefficient. The results indicate that the VT3-1 alloy is very sensitive to temperature changes, an increase in test temperature results in degradation in mechanical properties. b)

Table 1. Main mechanical properties of two-phase titanium alloy under different temperatures.

σ 0 , MPa 1005

σ S , MPa 1073

σ u , MPa 1214

Temperature, °C

α

δ, %

ψ, %

Material

n

E, GPa

+23

1.115 0.990

12.880

100.1

21 13

46 55

VT3-1

+300

753

889

956

8.915

96.1