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To reduce the volume, axial length and cost, a radial three-pole five-degree-of-freedom (5-DOF) integrated hybrid magnetic bearing (HMB) is studied, which the rotor can be levitated stably in one unit. Firstly, the configuration and suspension principle are introduced. The mathematical models of suspension forces are deduced by the magnetic circuit analysis. Then, according to radial and axial bearing capacity, the design method of main parameters is given. Finally, the magnetic circuit, suspension mechanism, air gap flux density, force-current relationships are calculated and analyzed by three-dimensional finite element method. The research results have shown that the structure of the 5-DOF integrated HMB is reasonable, and the suspension mechanism, mathematical model and design method are correct. [ABSTRACT FROM AUTHOR]

Magnetoelectric (ME) behavior for PZT/Ni composites with PZT embedded in Ni is investigated. The embedded composites show a four-state phenomenon of ME coupling. Upon applied magnetic fields, polarization reversal occurs when the applied static magnetic field exceeds a certain value. Based on the experimental data, a geometric factor k is proposed which captures the size effect on the ME behavior. To quantify the ME behavior of the embedded composites, finite element analysis is performed, which fits well with the experimental data. The calculation enables us to deduce that the four-state ME coupling is related to the change of the compressive force on the contact surfaces between PZT and Ni upon the applied magnetic field. The results are of importance for both the basic understanding of the ME coupling in the embedded PZT/Ni composites and the potential device applications, such as four-state memory devices, magnetic field switches, etc. [ABSTRACT FROM AUTHOR]

Flexible conductive textiles have attracted an increasing amount of attention due to being flexible and stretchable with multi-functions, in addition to the strain sensing function. In this paper, an integrated numerical method is established to predict the strain sensing behavior of PPy-coated flexible conductive fibers. Based on our previous investigation on the strain sensing behavior of the PPy-coated elastic conductive fibers, it has been known that the main strain sensing mechanisms of the conductive fibers are micro-cracks opening under stretching and closing under unloading. Therefore, in the numerical approach, extended finite element method is used to simulate the multi-crack initiation and propagation. Then, by establishing a representative element model including a single crack, the resistance variation with the increase in crack width/depth can be obtained using the electric–thermal package in ABAQUS software. Combining the relationship between crack width and strain, the relationship between fractional increment in resistance ( Δ R / R 0 ) and the strain can be obtained. The prediction of the fractional increment in resistance ( Δ R / R 0 ) versus strain is consistent with the experimental results of PPy-coated Lycra fibers. The new integrated method is further verified by experimental results of PPy-coated XLA fibers, showing that the integrated numerical approach can capture the complicated strain sensing mechanisms of PPy-coated elastic fibers and predict the strain sensing behavior of flexible conductive fibers. This approach will make it possible to shorten the period, and reduce the cost in R&D of the PPy-coated electrically conductive fibers, comparing with the corresponding experimental work. [ABSTRACT FROM AUTHOR]

Experimental observations display that there exist two types of cracks induced by thermally grown oxide (TGO) in electron beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs), which will lead to the coating spallation. Up to now, the failure mechanism induced by TGO is not clear. In this work, a finite element model with real thermally grown oxide morphology for crack propagation in TBCs is established by taking the advantage of commercial finite element package (ABAQUS) and image processing technique (Coreldraw). The coating failure mechanism under thermal mismatch stress is investigated. Present analysis and discussions show that the horizontal crack tends to propagate through the top coat layer toward the interface during the cooling stage, while the interface crack initiates at the points located in the middle region and then propagates in two side directions simultaneously, and mode II fracture plays a dominant role in the whole crack propagation process. Finally, two failure mechanisms of the TC/TGO interface are proposed in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a modeling and experimental study using a multi-frequency electromagnetic (EM) sensor system, for non-destructive evaluation of rail decarburisation. The EM sensor is configured with a H-shaped ferrite core, which was excited with a multi-frequency waveform over the range of approximately 1–100 kHz. Finite-element (FE) simulation was carried out to establish the link between the EM sensor output and the level of decarburization. Rail samples with different levels of decarburisation, due to different bloom reheat times prior to rolling were tested in the laboratory. It was found that the zero-crossing frequency of the EM sensor response is linearly proportional to the decarburisation level by FE simulation, theoretic analysis and experiment. This finding is helpful in understanding the response of the EM sensor to rail decarburisation and could lead to a non-contact, non destructive method for use during rail manufacturing. In addition, on-site measurement (tests carried out in the Rail & Section Mill at Tata Steel) was taken on a 110 m long rail product, with the results indicating that the EM sensor response correctly follows the expected decarburisation profile along the rail length. [ABSTRACT FROM AUTHOR]

Time-dependent creep behavior of rocks is crucial not only for assessing geophysical hazards, such as earthquake rupture and volcanic eruption, but also for analyzing the long-term stability of rock engineering structures, such as underground mines and underground excavations. In the present paper, multiple stress-stepping creep tests on green sandstone under uniaxial stress conditions were performed. Results from stress-stepping creep experiments show that creep strain rates are highly dependent on the level of applied stress. Then, a time-dependent creep model based on damage constitutive law at a mesoscale was proposed to model the time-dependent behavior of heterogeneous brittle rocks. In the proposed model, the rock heterogeneity is considered by assuming the rock parameters following a statistical Weibull distribution, and both the maximum tensile strain criterion and the Mohr-Coulomb criterion are used as two damage thresholds to control the rock damage. The damage-based creep model is implemented by programming on the basis of finite-element software. Then the model was validated by comparing the numerical simulations with the experimental results. The model accurately captures the time-dependent creep behavior observed in the laboratory. It was then used to simulate the time-dependent evolution of damaged zone around an opening under different lateral pressure coefficients. The distribution of damage around the opening is realistically reproduced, and the simulations indicated that the spatial distribution of damage zones, as well as time to failure, is closely related to the lateral pressure coefficient. [ABSTRACT FROM AUTHOR]

Brake disc with textured surface was introduced for fade resistance during braking process. The microdimple arrays of disc surface were fabricated by laser peening process, which can not only increase surface roughness but also accelerate heat dissipation, in turn, to raise friction coefficient of brake system and resist heat fade phenomenon through reducing the interface temperature of brake disc. Analysis of brake disc temperature distribution during single braking process under non-axisymmetric load was conducted by using finite element method (FEM) and the coupled heat conduction and elastic equations were solved with contact problems. The computational results showed that the value of temperature in radial direction of dimpled disc proved to be lower than smooth disc obviously. Heat fade and premature wear could be effectively relieved because the laser textured surfaces exerted an essential influence on the disc surface temperature distribution and the maximal contact temperature. [ABSTRACT FROM AUTHOR]

The effects of warm laser peening at different treating temperatures on damping capacity of Ti-6Al-4V titanium alloy were investigated based on the experimental study, the mechanism of damping capacity improvement on Ti-6Al-4V alloy treated by warm laser peening was discussed; moreover, the compressive residual stress (CRS) and its relaxation under vibration condition were simulated by finite element method (FEM), the stability of residual stress in Ti-6Al-4V titanium alloy subjected to warm laser peening processing was revealed based on the creep theory. It is shown that high dislocation density obtained by warm laser peening under the temperature of dynamic strain aging (DSA) is a critical factor for damping capacity improvement. Owing to higher damping capacity introduced by warm laser peening, the vibration stress is reduced and thus causes a lower creep rate and a slower residual stress relaxation speed than laser peening at room temperature. [ABSTRACT FROM AUTHOR]

To study the effect of morphology of thermally grown oxide on the stress distribution and evolution under cyclic thermal loading, a three-dimensional finite element model of a turbine blade with thermal barrier coatings is developed, in which the coating deposition process, high temperature creep and elastic–plastic behavior are taken into account. Based on the simulation results, dangerous regions in thermal barrier coatings can be predicted. It is shown that, during the cooling stage, tensile stress occurs at the peak of thermally grown oxide/bond coating interface, and compressive stress lies in the valley. With the increase of thickness and amplitude of thermally grown oxide, both the maximum tensile and compressive stresses increase, and the stress distribution is more sensitive to its amplitude than thickness. [ABSTRACT FROM AUTHOR]

Aiming to improve the quality of part surfaces in cold roll-beating, the movement of the roller during the process was analysed. The relationships between the relative positions of the roller and the workpiece were determined. A finite element model was established for cold roll-beating simulation, which was based on the thermal effects under different roller speeds. Based on the simulation results, the change in equivalent stress resulting from the thermal-mechanical mechanism was analysed, and its influence on work hardening was determined. The theoretical basis for the control of the influence of coupled thermal-mechanical mechanism on work hardening was derived to ensure high-quality part surfaces during cold roll-beating. [ABSTRACT FROM AUTHOR]

Determination of interfacial adhesion energies of thermal barrier coatings is important for understanding failure mechanisms and predicting their lifetime. Combined compression test with a cohesive zone finite element model, it is shown that the interfacial adhesion energy is in the range of 100–130 J/m 2 . Based on the nonlinear delamination theory, the critical interfacial adhesion energy of delamination is 120 J/m 2 and the corresponding loading phase angle is −56°. With the increase of the half-length of the crack, the crack propagation tends to be steady with a steady-state interface energy release rate of 150 J/m 2 , and delamination experiences almost pure mode II. These results obtained from finite element simulations and theoretical analyses are in good agreement with the available values determined by other testing methods reported in the literatures, which confirms the validity of this method. [ABSTRACT FROM AUTHOR]

The interaction of surface cracking and interfacial delamination in thermal barrier coatings under tension is investigated by using a cohesive zone finite element model. It is found that the surface crack density has a significant effect on the initiation and propagation of interfacial delamination. The interfacial delamination length decreases with increase of the surface crack density. The influence of ceramic coating thickness and interfacial adhesion parameters on surface cracking and interfacial delamination is discussed. It is shown that the saturated crack densities decrease with increase of the ceramic coating thickness and interfacial delamination length, and the critical surface crack density without interfacial delamination decreases as the interfacial adhesion energy increases. The results imply that the larger the surface crack density and interfacial adhesion energy are, the less the probability of interfacial delamination. [ABSTRACT FROM AUTHOR]

Loosening of bolted connections in a structure can significantly reduce its load-bearing capacity. Detecting loosening of bolted connections at an early stage can prevent failure of the structure. Due to the complex geometry of a bolted connection and material discontinuity between clamped components, it is difficult to detect loosening of a bolted connection using conventional nondestruc-tive test methods. A vibration-based method that uses changes in natural frequencies of a structure to detect locations and extent of damage can be used to detect loosening of bolted connections since the method focuses on detecting a stiffness reduction, which can result from loosening of bolted connections. Experimental and numerical damage detection was conducted to detect loosen-ing of bolted connections in a full-size steel pipeline with bolted flanges using the vibration-based method. With the recent devel-opment of a modeling technique for bolted connections in thin-walled structures, an accurate physics-based finite element model of the pipeline that is required by the vibration-based damage detection method is developed. A trust-region search strategy is employed to improve the damage detection method so that global convergence of the damage detection algorithm can be ensured for underdetermined systems, and robustness of the algorithm can be enhanced when relatively large modeling error and measure-ment noise are present. The location and extent of loosened bolted connections were successfully detected in experimental damage detection using changes in natural frequencies of the first several elastic modes of the pipeline; the exact location and extent of the loosened bolted connections can be detected in numerical simula-tion where there are no modeling error and measurement noise. [ABSTRACT FROM AUTHOR]

A nonlinear, planar model of a slack cable with bending stiffness and arbitrarily moving ends is developed. The model uses the slope angle of the centroid line of the cable to describe the motion of the cable, and the resulting integropartial differential equation with constraints is derived using Hamilton's principle. A new method is developed to obtain the spatially discretized equations, and the Baumgarte stabilization procedure is used to solve the resulting differential-algebraic equations. The model can be used to calculate the equilibria and corresponding free vibration characteristics of the cable, as well as the dynamic response of the cable under arbitrarily moving ends. The results for an equilibrium and free vibration characteristics around the equilibrium are experimentally validated on a laboratory steel band. The methodology is applied to elevator traveling and compensation cables. It is found that a vertical motion of the car can introduce a horizontal vibration of a traveling or compensation cable. The results presented are verified by a commercial finite element software. The current method is shown to be more efficient than the finite element method as it uses a much smaller number of elements to reach the same accuracy. Some other interesting features include the condition for a traveling or compensation cable equilibrium to be closest to a natural loop and a direct proof that the catenary solution is unique. [ABSTRACT FROM AUTHOR]

In this work, tensile creep tests for Sn-1.0Ag-0.5Cu-0.02Ni solder have been conducted at various temperatures and stress levels to determine its creep properties. The effects of stress level and temperature on creep strain rate were investigated. Creep constitutive models (such as the simple power-law model, hyperbolic sine model, double power-law model, and exponential model) have been reviewed, and the material constants of each model have been determined based on experimental results. The stress exponent and creep activation energy have been studied and compared with other researchers' results. These four creep constitutive models established in this paper were then implemented into a user-defined subroutine in the ANSYS™ finite-element analysis software to investigate the creep behavior of Sn-1.0Ag-0.5Cu-0.02Ni solder joints of thin fine-pitch ball grid array (TFBGA) packages for the purpose of model comparison and application. Similar simulation results of creep strain and creep strain energy density were achieved when using the different creep constitutive models, indicating that the creep models are consistent and accurate. [ABSTRACT FROM AUTHOR]

Due to bending-torsion coupled vibrations of the L-shaped beams and numerous uncertainties associated with the bolted joints, modeling structures with L-shaped beams and bolted joints is a challenging task. With the recent development of the modeling techniques for L-shaped beams by the authors (He and Zhu, 2009, "Modeling of Fillets in Thin-Walled Beams Using Shell/Plate and Beam Finite Elements," ASME J. Vibr Acoust., 131(5), p. 051002), this work focuses on developing new finite element (FE) models for bolted joints in these structures. While the complicated behavior of a single bolted connection can be analyzed using commercial FE software, it is computationally expensive and inefficient to directly simulate the global dynamic response of an assembled structure with bolted joints, and it is necessary to develop relatively simple and accurate models for bolted joints. Three new approaches, two model updating approaches and a predictive modeling approach, are developed in this work to capture the stiffness and mass effects of bolted joints on the global dynamic response of assembled structures. The unknown parameters of the models in the model updating approaches are determined by comparing the calculated and measured natural frequencies. In the predictive modeling approach, the effective area of a bolted connection is determined using contact FE models and an analytical beam model; its associated stiffnesses can also be determined. The models developed for the bolted joints have relatively small sizes and can be easily embedded into a FE model of an assembled structure. For the structures studied, including a three-bay space frame structure with L-shaped beams and bolted joints, and some of its components, the errors between the calculated and measured natural frequencies are within 2% for at least the first 13 elastic modes, and the associated modal assurance criterion values are all over 94%. [ABSTRACT FROM AUTHOR]

large number of statistics indicate that water inrush has a direct relationship with geological structures such as fault and karst collapse columns. Understanding the mechanism of water inrushes controlled by geologic structures is of vital importance for adopting effective measures to prevent their occurrence. The work begins with formulization of a damage-based hydromechanical model based on elastic damage theory. Next, the model is numerically implemented with finite element method by employing a finite element package called COMSOL Multiphysics, and is also validated against some existing experimental observations. Finally, the model is used to simulate the mining-induced groundwater inrushes when the effect of faults and karst collapse columns is considered in the numerical simulation, and some suggestive conclusions for preventing water inrushes and optimizing underground mining operations are drawn. [ABSTRACT FROM AUTHOR]

Fillets are commonly found in thin-walled beams. Ignoring the presence of a fillet in a finite element (FE) model of a thin-walled beam can significantly change the natural frequencies and mode shapes of the structure. A large number of solid elements are required to accurately represent the shape and the stiffness of a fillet in a FE model, which makes the size of the FE model unnecessarily large for global dynamic and static analyses. In this work the equivalent stiffness effects of a fillet in a thin-walled beam are decomposed into in-plane and out-of-plane effects. The in-plane effects of a fillet are analyzed using the wide-beam and curved-beam theories, and the out-of-plane effects of the fillet are analyzed by modeling the whole fillet section as a slender bar with an irregular cross section. A simple shell/plate and beam element model is developed to capture the in-plane and out-of-plane effects of a fillet on a thin-walled beam. The natural frequencies and mode shapes of a thin-walled L-shaped beam specimen calculated using the new methodology are compared with its experimental results for 28 modes. The maximum error between the calculated and measured natural frequencies for all the modes is less than 2%, and the associated modal assurance criterion values are all over 95%. The methodology is also applied to other thin-walled beams, and excellent agreement is achieved between the natural frequencies from the shell/plate and beam element models and those from the solid element models. While the shell/plate and beam element models provide the same level of accuracy as the intensive solid element models, the degrees of freedom of the shell/plate and beam element models of the thin-walled beams are only about 10% or less of those of the solid element models. [ABSTRACT FROM AUTHOR]

A coupled thermomechanical finite element model has been developed to simulate the temperature, stress and shape development during the solidification process of squeeze casting. In the model, the effect of latent heat and volume shrinkage due to solidification, and the mutual dependence of interfacial heat transfer and casting deformation were taken into account. A thermo-elasto-viscoplastic constitutive model was adopted for simulating the response of the solidified shell to the squeeze pressure, and an iterative approach was employed to calculate the displacement of the punch in each time step. The model can be used to investigate the evolution of temperature and stress distribution in the casting during the solidification process. [ABSTRACT FROM AUTHOR]

With torsional friction being introduced into the calculation of heat generation and deformation, a 3D rigid viscoplastic FE (finite element) model was established to describe the continuous drive friction welding process. In this model, the workpiece was treated as a deformable body with rigid viscoplastic incompressible material. The friction stress was calculated using Coulomb friction law and shear friction law at different stages of friction welding process respectively. The model simulated two continuous drive friction welding cases by performing coupled thermal and mechanical analyses. Simulations successfully predict the thermal history of the joint as well as deformation rate and final geometries. Meanwhile, the possibility of defect occurrence is also obtained. Experiments on continuous drive friction welding of GH4169 superalloy rod were carried out. The temperature history and the final geometry of the welded joint were measured and compared with the calculated results, which show a good agreement between them. [ABSTRACT FROM AUTHOR]

A comprehensive finite element method employing a subroutine to link up submodules of commercial code ANSYS is proposed to perform analysis of projection welding in quantitative detail. In order to solve the complexity due to dynamic changes in heat and electrical current flow paths, as well as temperature-dependent material properties, information about contact interfaces and the geometry of the projection areas have been taken into account. By updating parameter information among these submodules in an incremental manner, a truly thermal-electrical-mechanical coupled numerical analysis is realized for projection welding simulation. A case study of an automotive door assembly welding process is carried out and a series of experiments is conducted to confirm the validity of the newly developed method. The agreement between the experimental and numerical results is satisfactory, indicating that the incrementally coupled finite element method may be suitable for projection welding research. Finally, future work to extend this method in optimizing projection welding process design is also presented. [ABSTRACT FROM AUTHOR]

A damage mechanics-based numerical model for simulating the fracture process of concrete is presented. The model is based on knowledge of heterogeneity of concrete at the meso-level, in which the concrete is assumed to be a three-phase composite made up of the cement matrix phase, the aggregate phase and the matrix-aggregate interface phase. The constitutive law of each phase is defined on the basis of elastic damage mechanics, the finite element method is employed as the basic stress analysis tool, and the maximum tensile strain criterion and the Mohr-Coulomb criterion are adopted as damage thresholds. A simple method analogous to the smeared crack method is used for tracing the crack propagation process and for capturing the interaction of multiple cracks. Based on this model, a numerical simulation program, named Concrete Fracture Process Analysis (CFPA), was developed. The influences of various parameters of the model on its performance, including the Weibull distribution parameters, constitutive parameters and the number of elements are discussed in detail. Issues in the realistic simulation of concrete behaviour are also examined. Results from numerical simulations of concrete specimens under a variety of loading conditions using CFPA are presented in the companion paper. [ABSTRACT FROM AUTHOR]

Abstract: We consider fully discrete finite element approximations of the forced Fisher equation that models the dynamics of gene selection/migration for a diploid population with two available alleles in a multidimensional habitat and in the presence of an artificially introduced genotype. Finite element methods are used to effect spatial discretization and a nonstandard backward Euler method is used for the time discretization. Error estimates for the fully discrete approximations are derived by applying the Brezzi–Rappaz–Raviart theory for the approximation of a class of nonlinear problems. The approximation schemes and error estimates are applicable under weaker regularity hypotheses than those that are typically assumed in the literature. The algorithms and analyses, although presented in the concrete setting of the forced Fisher equation, also apply to a wide class of semilinear parabolic partial differential equations. [Copyright &y& Elsevier]

• A damage phase field based FEM model considering thermal cycling and growth stresses is developed. • The interaction between the thermal cycling and growth stresses accelerates TBCs damage. • The delamination mechanisms of TBCs under different interface roughness are obtained. The growth of thermally grown oxide (TGO) is often regarded as a key factor causing failures of thermal barrier coatings (TBCs) because it leads to thermal cycling and growth stresses. However, the delamination mechanism of TBCs induced by the growth process of TGO is still unclear. Here, a finite element method (FEM) considering both thermal cycling and growth stresses is developed. The accumulation of damage and crack nucleation, propagation, and coalescence are obtained using a phase field damage model. The results indicate that there is a critical TGO thickness of 8–10 μm, which may result in delamination of the TBCs. Both thermal cycling and growth stresses induce the premature failure of TBCs. The delamination mechanism induced by thermal cycling and growth stresses is obtained. When the interface roughness is A / L ≥ 1/4, the cracks pass through the TGO/TC interface and propagate in the TC layer. When the interface roughness is A / L ≤ 1/8, the cracks propagate along the vicinity of the TGO and will not pass through the TC/TGO interface. When the interface roughness is 1/8 < A / L less than 1/4, the cracks bifurcate at the vicinity of TGO interface, and one branch propagates in the TC and the other propagates along the vicinity of the TGO. [ABSTRACT FROM AUTHOR]

Abstract Despite being the most used ceramic biomaterial in hip joint prosthesis, Zirconia Toughened Alumina (ZTA) is liable to undergo several degradation mechanisms in vivo , which might drastically affect its structural performance over time. Our standing point in this investigation was that neither in vitro tests nor finite elements simulations are yet capable to fully reproduce the complexity of the in vivo conditions. Through accurate analyses of retrievals, we attempt to add more pieces to the puzzle of in vivo loading history and to obtain better insight into the ZTA degradation mechanisms. For doing so, we applied a previously established automated scanning protocol to investigate the coupling between a ZTA femoral head and its metal stem counterpart in a short-term (20 months) retrieved hip implant. Metal contamination on the ZTA surface was severe and polymorphic transformation widespread on the whole surface of the taper, though reaching different values depending on the specific zone of the taper. Clear signs of third body abrasive wear and fatigue crack initiation could be found by means of laser and electron microscopies, and X-ray spectroscopy. Highly resolved mapping by Raman micro-spectroscopy revealed very high monoclinic fractions and pronounced residual stress magnitudes despite the relatively short in - vivo lifetime. Graphical abstract Unlabelled Image Highlights • We studied the degradation phenomena at the ceramic-taper/metallic-stem interface in a 20 months retrieved ZTA femoral head; • Several micro-cracks were spread all over the ceramic taper surface with lengths varying from few μm to 1 mm; • Metal staining was present as evenly distributed stripes on the crests of the mechanically machined pristine surface; • Significant phase instability was found, with monoclinic volume fraction values reaching up to 50%; • Early monoclinic transformation caused grain pullout, leading to extensive third body wear phenomena on the taper surface. [ABSTRACT FROM AUTHOR]

The erosion behavior of EB-PVD thermal barrier coatings (TBCs) with real morphology was investigated based on finite element (FE) simulation. Firstly, an FE modeling method was developed to establish a geometric numerical model using a scanning electron microscope. Secondly, an empirical correlation between the depth of penetration and some characteristic parameters of the erodent particle (i.e. diameter, impact velocity and angle) was obtained by means of simulation. There is almost no difference in the depth of non-dimensional penetration between the real morphology and the simplified model; however, there are obvious differences in the dynamic kink band process in these two models. Due to the non-uniform size of the columnar structure of the EB-PVD TBCs, kink bands are irregular in the real morphology model, which redisplays this experimental phenomenon perfectly. Based on the plastic instability model, the relationship between particle impacting energy and kink band structure evolution in TBCs was set up. Lastly, the crack driving force to produce a surface crack was analyzed. The tensile stress along the column direction is small for TBCs under erosion conditions, with the critical dimensionless impact energy to start a crack being below 0.16 and about 0.195 for the real micro-structure and the simplified model, respectively. These results indicate that the real morphology would be more susceptible to erosion failure compared to the results of previous theoretical or numerical estimations. [ABSTRACT FROM AUTHOR]

Thermally grown oxide (TGO), besides bringing extra mismatch between layers in thermal barrier coatings (TBCs), induces volumetric expansion and local large deformation in constrained interface, which results in huge growth stress and then causes the spallation of coatings. Therefore, characterization on the dynamic growth of oxide and stress evolution during oxidation is desirable, but still intractable, especially considering local finite deformation. In the present research, the effects of growth stress evolution in the thermally grown oxide(TGO) on failure mechanism of TBCs are investigated through developing both finite deformation mechanics-oxidation growth model and corresponding finite element method (FEM). Results demonstrate that the TGO growth rate decreases as oxidation time increases and is uneven in different positions, which is consistent with the experimental observations. The maximum tensile stress and compressive stress are situated at the peak and valley regions of bond coating layer, respectively. However, the stress distribution in top coating is opposite to that of bond coating. It implies that the thermal stress in the TGO layer dominates the failure of the TBCs. Compared with small deformation analysis, the maximum stress value in finite deformation description is closer to the experimental result, and it is more suitable to evaluate the growth stress induced by the growth of TGO layer. [ABSTRACT FROM AUTHOR]