Studies On The Precise Algorithm Of Coated Structures Based On Green’s Functions And The Design Of Dedicated Simulation Platform

Coated structure, which consists of coating and substrate,is widely used in machinery, electronics, aerospace, biological engineering and other fields, for its wearability, corrosion resistance, heat insulation and other excellent performances. Coated structures have the following five properties:(1) The coatings get thinner and thinner, the thickness of which is often in micron level. (2) During working, a mass of mechanical energy and thermal energy are sealed in the coating, and the gradient of mechanical and thermal fields change dramatically in the extremely thin layer. (3) The whole structure is heterogeneous and this will result in complex stress distribution on the interface between coating and substrate. (4) More and more anisotropic coated structures are used in recent years. (5) Devices with coated structure often work in a multi-fields coupling environment. All above features make it difficult for us to obtain the solution of the fields in coated structures, no matter based on analytical method or numerical method. An efficient and accurate computing method and the dedicated simulation platform are urgently needed for the design and simulation of advanced coated structures.Firstly, for the orthotropic and transverse isotropic coated structures, the two-dimensional and three-dimensional Green’s functions under the normal and tangential point forces are presented systematically based on the corresponding general solutions which are expressed by harmonic functions. Based on the obtained Green’s functions, the relationship between the anisotropic properties and the elastic fields are revealed, and the failure mechanisms of this kind of coated structures are also investigated. Firstly, the form of general solutions, the type of loadings, the feature of the structure field and the effect of the interface are taken into consideration, and the harmonic functions with undetermined constants are constructed by trial-and-error method. Then substituting these harmonic functions into the general solutions above, and considering the boundary conditions on the surface and the compatibility conditions on the interface, the undetermined constants can be determined and the corresponding Green’s functions for the coated structures are obtained. At last, the relationship between the anisotropic properties and the elastic fields are revealed, and the failure mechanisms of this kind of coated structures are investigated.Sencondly, based on the three-dimensional governing equations of isotropic thermoelastic materials, the corresponding general solutions are derived by virtue of operator theory, Almansi theory and other transform methods. For the thermal barrier coated structures, the three-dimensional Green’s functions of thermoelastic field of coated structures under a point heat source are given based on the obtained general solutions. The relationship between the thermoelastic properties and the thermoelastic fields of coated structures are revealed, and the failure mechanisms of this kind of coated structures are investigated. General solutions play an important role in solving partial differential equations, and their forms will exert directly influence on the solving method and the difficulties. For the thermoelastic coupling effect, more factors should be taken into consideration when the harmonic functions are constructed. Meanwhile, the boundary condition and interface continuous condition with thermoelastic coupling effect also increase the complexity of the issues. The harmonic functions are constructed with all above factors considered, and the corresponding Green’s functions are obtained.Finally, based on the obtained Green’s functions and the superposition principle, a highly precision algorithm for coated structures under the arbitrary loading is proposed, namely BGM (Method Based on Green’s Function). The dedicated simulation platform is designed based on BGM and Matlab GUI, which will provide a powerful tool to precise analysis and design of coated structures. BGM keeps the advantages of precise calculation of Green’s functions, and this makes it possible to get the mechanical and thermal fields, which change dramatically in the coated structures and distribute complexly on the interface. The computational accuracy is under control of Scarborough criterion, and the calculation program is optimized by eliminating redundancy calculate and only considering direct contribution of Green’s functions to the solutions. Typical contact problems and thermoelastic coupling problems are simulated and discussed by BGM, and this shows that the BGM is accurate, efficient and steady. By virtue of Matlab GUI technique, the platform is built with a user-friendly interface, and easy to master. And it is convenient to engineering applications.