Thermal oxidation description methodology of thermal barrier coatings on gas turbine blades considering service characteristics

Predicting the thickness of Thermally Grown Oxide(TGO)and the residual stresses induced by TGO growth in the Thermal Barrier Coatings(TBCs)is significant work in analyzing the failure of TBCs.In practical applications,the operating temperature,oxygen partial pressure,aluminium content in TBCs,and porosity of the topcoat affect the oxidation rate.Therefore,a novel oxidation rate model is proposed to describe the effect of such factors.The parameters in the proposed model were fitted with isothermal degradation test data from prior literature.Then,a method for calculating the residual stress in a disk-shaped specimen was developed based on the oxidized growth strain model and the oxidized model.Finally,a variable-temperature oxidation experiment was performed to validate the new oxidation model.The average error between the predicted and experimental thicknesses is approximately 10%,and the average error between the residual stresses is 30%.Under the variable-temperature condition,the error between the predicted thickness and the average experimental thickness is 3.9%.

A discussion of fatigue properties of notched specimens subjected to prestressing treatment machined from FGH4097

Experimental and numerical investigations were performed to reveal the effect of prestress on the fatigue properties of FGH4097 so as to quantitatively evaluate the overspeed benefit of the disc of aeroengine. A corresponding experiment was performed to examine the effect of prestress on the fatigue life of FGH97. A complete model describing the fatigue properties of the prestressed notch specimen was proposed. After the modification of mean stress, stress gradient and prestressing treatment, the model is finally verified by fatigue test of presstressed notch specimens machined from FGH4097 with satisfactory accuracy and good engineering applicability. The new model highlights that for the variable fatigue loads, the introduction of appropriate prestress is expected to benefit to the notch specimens and certainly to the disc of aeroengine regards of their fatigue properties. Both the calculation method of fatigue life parameters and the prestress correction model are proved to have good prediction accuracy.

Lock-in phenomenon of tip clearance flow and its influence on aerodynamic damping under specified vibration on an axial transonic compressor rotor

In this study,the lock-in phenomenon of Tip Clearance Flow(TCF)instabilities and their relationship to blade vibration are investigated numerically on an axial transonic rotor with a large tip clearance.The capabilities of simulating instability flow and lock-in phenomenon are verified on a transonic rotor and a NACA0012 airfoil by comparing with the test data,respectively.The lock-in phenomenon is first numerically confirmed that may occur to TCF instabilities when its frequency is close to the blade vibration frequency.The lock-in region becomes wider with the vibration amplitude increasing,and it is also affected by modal shapes.For the rotor at the simulation conditions in this study,the bending mode results in a wider lock-in region than the torsional mode.In the lock-in region,the phase difference between the Tip Clearance Vortex(TCV)and the blade vibration changes with the flow condition and the frequency ratio of the blade vibration and the TCV instabilities.The frequency of the TCV instabilities reduces with the mass flow decreasing.Therefore,reducing mass flow and increasing frequency ratio have similar effects on the TCV phase,which causes a significant variation on the unsteady pressure amplitude in the blade tip area.Thus,the aerodynamic damping changes significantly with the TCV phase.The aerodynamic damping displays a nonlinear relationship with the vibration amplitude,and it changes from negative to positive with the vibration amplitude increasing at the same frequency ratio.The negative damping is mainly provided by the tip area of the blade.For unlocked conditions,the period of the TCF instabilities fluctuates over time,and it cannot be directly separated by their frequency features.Inter Blade Phase Angle(IBPA)also has an important influence on the feature of the TCV instabilities.The occurrence of frequency lock-in also requires“appropriate”IBPA.For the examined working conditions,the frequency lock-in occurs under 0 ND(Nodal Diameter),but not under 8 ND.However,no matter 0 ND or 8 ND,the phase of TCV always locks onto the IBPA at the examined conditions.

A new fatigue life prediction model considering the creep-fatigue interaction effect based on the Walker total strain equation

The performance of high-temperature components of aero-engines under the CreepFatigue Interaction(CFI)behavior gets more attention recently.In this research,the creepfatigue tests of two superalloys of Powder Metallurgy(PM)FGH96 and direct aging GH4169 were performed at 650°C with different types of dwell,and the fracture morphology of FGH96 specimens was observed by Scanning Electron Microscopy(SEM)to analyze the creep-fatigue fracture feature and crack initiation.Additionally,according to phenomenology,the effect of dwell was introduced to develop a new uniaxial fatigue life prediction model based on the total strain equation,which has capability to take dwell time and load ratio into account together.The equations were utilized to model the test data of PM FGH96 and GH4169,together with data of another superalloy PM FGH95 conducted previously.A prominent prediction ability of the model in creep-fatigue life prediction of different superalloys has been manifested.Most data points of test data and estimated data are located within two times scatter band,which is ideal in engineering.