Numerical Simulation For Failure Process Of Thermal Barrier Coating System Based On Crack Open Displacement(COD) Method

Thermal Barrier Coating system(TBCs)is an advanced material which is widely applied on the metal surface.Because of its excellent good thermal stability,antioxidant activity and anti-corrosion property,TBCs is used in gas turbine or aircraft engine components for thermal protection.TBC usually consists of four layers: the top ceramic layer(TC),the thermally grown oxide(TGO),bond coat(BC)and the metal substrate.TGO formation process at the high temperature oxidation phase directly affected TGO deformation,bond coat yield failure,creep and other mechanical properties.Simultaneously,the huge TGO growth stress was generated in TGO formation,which had an important influence on the TBCs failure.In this work,TBCs displacement stability and TGO crack situation were firstly explored by experimental study whereas the relationship between TGO growth thickness and time was obtained.The increased thickness of TGO in every thermal cycle was additionally achieved and TGO internal crack was observed.Furthermore,the stress-strain relationship of metal substrate and TGO were in-house measured,and some material property parameters were accessed,as well as the influence of content of yttrium was discussed.It builds for a good preparation for the subsequent numerical simulation in which the necessary material properties for TGO and metal substrate are needed from the experimental measurement.Then,a new numerical simulation program for simulating TGO displacement stability at the dwell time of high temperature in each thermal cycle was developed based on UMAT together with other subroutines in ABAQUS.Numerical simulation results were obtained by finite element analysis for thin TGO(less than 1μm).For the case of small TGO thickness(less than 1μm),the review for the previous works finds that Karlsson’s study was considered as a classic method for modeling TGO deformation at the periphery of the surface groove.To validate the accuracy of the present method in this work,a comparative study between simulation results from these two methods is performed showing the good agreement for the first few thermal cycles at which TGO thickness just attains 1μm.Furthermore,the present method in this work can work better for the subsequent thermal cycles while Karlsson’s method stops running due to the problem of numerical convergence.Last,a series of numerical simulations for TGO crack propagation are also performed based on Crack Open Displacement(COD)method for investigating failure process of TBCs in which TGO formation was dynamically simulated cycle by cycle.By comparing experimental deformation results and FEM results,the accuracy of finite element analysis was verified again.This work provides a basis for TBCs optimization design and prediction of TGO failure.