Wen Zhixun

Study on Fatigue Properties of Turbine Disk Groove Modeling Specimens of GH4720 Alloy

Abstract Based on the structural features and the work status of the aero-engine turbine disk groove, the experimental and theoretical analysis of the fatigue failure mechanism and the crack growth life of the groove modeling specimen of GH4720 alloy were carried out. The fatigue failure of the groove modeling specimen of GH4720 alloy can be divided into three stages: (i) due to the high stress concentration, slip systems are activated and then cracks initiate; (ii) with the increase of loading cycles, adjacent intergranular dislocations and slip systems are activated, cracks transfer between grains; (iii) with the increase of the stress intensity factor range and the cooperation of shear stress and principal stress, the dislocations motion in different slip systems and the crack propagation are accelerated. A fatigue crack growth life model of GH4720 alloy has been established. The crack growth lives obtained from the finite element analysis and the life model have a good agreement with the results of the experiment. It is demonstrated that the life model can be used in engineering to predict the remaining life of turbine disk.

Numerical Simulation on the Creep Damage Evolution of Nickel-Based Single Crystal Specimens with Slant-Angled Film Cooling Holes

Abstract Numerical calculations have been performed to study the creep damage evolution of nickel-based single crystal specimens with slant-angled film cooling holes. The emphasis is the effect of different slant angles on creep properties. The slant angles are 0°, 15°, 30° and 45°. The results show that the distributions of the resolved shear stress around film holes are different under different slant angles. The directions of crack propagation are θ =±54° when α =0°, 15°, 30°; however when α =45° the crack propagation directions are along θ =±46°. The specimen with α =30° has the longest failure life. In the higher stress region near the cooling hole, the phenomenon of stress relaxation will appear, such as resolved shear stress, Mises equivalent stress and stress σ 11 . And with the time increasing, they reach stable values. Different specimens have different damage distributions. The maximum damage points appear at locations 0°, 0°, 13° and 26° from horizontal direction when the slant angles are 0°, 15°, 30° and 45°, respectively. And thickness has influence on the distribution of resolved shear stress along the holes.

Effects of Strain Rate and Temperature on Mechanical Property of Nickel-based Superalloy GH3230

Abstract High temperature tensile tests of nickel-based superalloy GH3230 were carried out at various strain rates from 10−3 s−1 to 10−1 s−1 over temperature range from 1144 K to 1273 K. The emphasis has been put on the effect of strain rate and temperature on the plastic flow stress. The results show that flow stress increases and the hardening exponent n decreases with the strain rate increasing or temperature decreasing. The strain rate sensitivity exponent m is a constant independent of temperature according to the interdependencies of flow stress, strain rate and temperature. The thermal deformation activation energy of GH3230 was calculated as 441 kJ/mol. The full recrystallization will occur when the temperature is about 1273 K and the microstructures with uniform and fine grains can be obtained. The SEM result shows that the fracture mode of all specimens is micro-porous aggregation ductile fracture caused by damage, the variation of temperature has not much effect on fracture morphology at various temperatures, but fracture dimple becomes deeper and larger while the strain rate decreasing.