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Thermal barrier coating systems (TBCs) are widely used in turbines. However, premature failures have impaired the use of TBCs and cut down their lifetime. The thermally grown oxide layer (TGO) thickening and the material thermal expansion misfit under thermal cyclic loading significantly affect the interfacial stress field and stability of TBCs. In this study, the stability evaluation method of TBCs under thermal cyclic loading based on energy is established using the visco-elastoplastic and shakedown theorem. The semicircular shape interface is used to simplify the complicated interfacial undulations in FEA model. And actual TGO thickness obtained from experiment is used to simulate the bond coat oxidation. Then the effect of TGO thickening on the stability and stress field of TBCs under thermal cyclic loading is analyzed through the numerical simulation. It is concluded that estimating from the stress-strain evolution behavior, the local stability of the TBCs decreases with the TGO thickening, and assessing from energy, TBCs shows instable with TGO thickening.

Pre-bulging effect on the sheet hydroforming process of irregular box with unequal height and flat bottom was investigated by means of numerical simulation and experiment. The influences of pre-bulging height and pre-bulging pressure on the forming were discussed respectively. The pressure loading path was optimized. The results show that pre-bulging has important influences on the forming results. Too high pre-bulging height causes the crack and obvious crease at the punch nose near the lowest corner. Too low pre-bulging height causes fracture at the punch nose of the highest corner. Pre-bulging pressure has a smaller effect on the fracture at the punch nose of the highest corner when the pre-bulging height is reasonable. But over high pre-bulging pressure causes crack and obvious crease at the punch nose near the lowest corner. Failure can be avoided by using reasonable pre-bulging height and pre-bulging pressure.

An finite element model of orthogonal dry cutting with separate line is established according to the constitutive relation of large thermo-elastic-plastic displacement and the principle of virtual work in metal plastic deformation process,. The influence of cutting depth on residual stress was simulated for materials GH4169 with high speed. The residual stresses are analyzed on the machined surface and subsurface. The result shows that tensile residual stress of the machined surface is minimum value when the cutting depth is 0.2mm. the deeper is the depth of cut, the large the augmentation of compressive stress on the subsurface, which proves foundation for cutting process of dry-machined difficult-to-machine material with high speed and make it more efficiently to control the integrity of the machined surface.

The wear resistance of coated tool can be predicted widely by experiments and theoretical analysis. In the paper, an unique method is adopted to analyze influence of high speed on key stresses of the coated tool .First, through the cutting process simulation with different high cutting speeds, contact stress, shear stress and temperature distribution of the surface of the coated tool can be obtained when the cutting process is steady. Then the stresses and temperature are applied to the coated tool to analyze the key stresses in the tool. The result shows the potential failure of coated tool can be predicted by Finite element analysis correctly. Crack between coating and substrate may occur at the same position with different cutting speeds.

Grinding induces residual stresses, which can play an important role on the fatigue of the component. In general, residual stresses in a ground surface are primarily generated due to three effects: thermal expansion and contraction during grinding, plastic deformation caused by the abrasive grains of the wheel and phase transformations due to high grinding temperature. It was found that thermal expansion and plastic deformation in the grinding process were the major causes of residual stresses. In this paper, an analysis model for the calculation of residual stresses induced by a surface grinding process on an ultrahigh-strength steel (Aermet100) workpiece is presented. Firstly, the stress distribution induces by thermal expansion was obtained base on the transient heat conduction equation and the thermal properties of Aermet100. All the calculations were based on the moving heat source solution which was modeled as a uniformly distributed, 2D heat source moving across the surface of a half-space, found in Carslaw and Jaeger. The results show that the near surface residual stress is predominantly tensile and that the magnitude of this stress increases with increasing heat flux values. Secondly, the plastic deformation caused by the abrasive grains of the wheel was simulated base on the grain-workpiece interaction. The chip formation process and the material removal mechanisms can be examined using the micro-scale approach. The results show that the residual stress induced by the grinding force itself is generally compressive which is smaller than the residual tensile stress induced by thermal stress. Therefore, the residual stress brought about by grinding operation is generally a tensile stress. This paper offers an insight into the mechanism understanding of thermal and mechanical residual stresses induced by surface grinding. Key words: grinding, residual stress, grain

An analytical model based on multilayer structure with thermal expansion mismatch caused by temperature gradients was established to predict the residual stress in the system. The solution obtained from the model is independent of the number of layers. Three simplified models: bi-layer structure, coating system and film system with great compatibility are developed considering different engineering application. And the bilayer structure is verified by Stoney’s equation under the same conditions. Tri-layer coating system ZrO2/ Al2O3/1Cr18Ni9Ti is established in order to research the effect of temperature variations on the residual stress between different layers. The results suggested the stress has obvious mutation in coating interface with different temperature variation. And the residual stress with different temperature variation in different layers is larger than that with identical temperature variation. Key words: multilayer structures; residual stress; analytical model; thermal expansion mismatch; temperature variation

The most commonly used Micro tubular solid oxide fuel cell (MT-SOFC) anode material is a two phase nickel and yttria stabilized zirconia (Ni/YSZ) cermet. And the mechanical stability of anode support layer, in anode-supported electrolyte designs, is very important for large scale applications. During the assembly of stack and normal operation, MT-SOFC is easy to crack under the residual stress induced by manufacture and thermal stress due to multi-physics coupling. In this work, MT-SOFC model was founded on the background of MT-SOFC stack of electric vehicle and was analyzed by finite element method, based on theories of multi-physical field coupling. In order to find out which is the main reason for cracking, the residual stress due to manufacture and work were investigated separately. Thermal stress based on residual stresses of operating are studied for further research of life of MT-SOFC. It concluded that the failure of the MT-SOFC occurs mainly because of the residual stress due to the mismatch between the coefficients of thermal expansion of the materials of the electrode assembly, thermal stress will increase the mismatch in some partial areas. The results are important for studying the life and final spallation of MT-SOFC of electric vehicle.

The most commonly used Micro tubular solid oxide fuel cell (MT-SOFC) anode material is a two phase nickel and yttria stabilized zirconia (Ni/YSZ) cermet. And the mechanical stability of anode support layer, in anode-supported electrolyte designs, is very important for large scale applications. During the assembly of stack and normal operation, MT-SOFC is easy to crack under the fuel pressure and thermal loading due to various mechanical properties. In this study, MT-SOFC model was founded on the background of MT-SOFC stack of electric vehicle and was analyzed by finite element method, based on theories of elasto-plasticity, thermo-mechanical coupling. The effect of thermal load was investigated. It concluded that the failure of the micro-tubular cell occurs mainly because of the residual stress due to the mismatch between the coefficients of thermal expansion of the materials of the electrode assembly. The results are important for studying the life and final spallation of MT-SOFC of electric vehicle.

Mechanical property of coating under the micro-contact load such as impact and sliding wear significantly influence the reliability of surface coating. In order to research the influence, a contact model between the rigid multi-asperity surface and coating was found based on the G-W model in the background of Thermal Barrier Coatings(TBCs) used in aircraft engine blade. The distribution of stress in subsurface of the micro-contact process was analyzed based on the theories of contact mechanics and tribology with the elasto-plastic finite element method. The effect of coating thickness, elastic modulus, yield strength on the distribution of residual stress for TBCs was investigated. It conclude that primary reason of coating failure are cumulation of plastic deformation and excessive interfacial stress. The results are significant for studying the life and final spallation of TBC system and other coating.

Transition curve is very important to bending strength and life of gear. In order to improve the bending strength of gear, the shape of three kinds of transition curve (ordinary fillet cutter tip, single circle arc cutter tip and double circle arc cutter tip) was analyzed respectively, the relationship of double circle arc cutter tip parameters was established, the relation model of sensitive part of gear and stress concentration factor ( J and γ) was determined, the effect of different transition curves of gear on bending strength ( ) was explored. The results of analysis show that the bending strength of gear cut by double circle arc cutter tip increases by 10% comparing with that of gear cut by ordinary fillet cutter tip. It provides theories foundation for the design of high bending strength gear.

Grinding induces tensile residual stresses, which can play an adverse role on the fatigue and wear resistance of the component. In this paper, a calculation model of residual stresses induced by a surface grinding process on a ultrahigh-strength steel workpiece (Aermet100) is presented, which includes the transient heat conduction equation、a thermal elastic-plastic constitutive equation and the Von Mises yield condition. The model giving the energy conducted as heat in the workpiece as a function of the grinding wheel speed, the workpiece speed, and the cutting depth is proposed. It is shown that, for such grinding conditions, the simulation leads to tensile residual stresses which increase with the wheel speed and cutting depths increase. The paper offers an insight into the mechanism understanding of thermal residual stresses induced by surface grinding.

Mathematical models of basic parameters, force and thermal parameters of cutting were obtained by applying the thermo-elastic-plastic theory and the heat-balance theory, according to the principle of residual stress generation in cutting process. Based on the 2D finite element model of chip molding with separation surface, the direct way was applied in thermo-mechanical coupling, and residual stress of cutting GH4169 were simulated and analyzed by finite element. The results showed that the residual stresses are changed from tensile to compressive with the development of depth away from the workpiece surface. Also its values are changed according to a certain rule as varying the cutting speed. These provide a foundation for the control of cutting quality of workpiece.