Anisotropic Mechanical Model For Ceramic Matrix Mini-Composite And Failure Simulation Of Woven Structure

Ceramic matrix composites(CMCs)have a broad application prospect in high-performance aero-engine because of its excellent high-temperature comprehensive mechanical properties and economic efficiency.CMCs is the critical technology to break through the performance bottleneck of aero-engine.With the help of computer simulation technology,the designability advantages of CMCs can be brought into full play,and the comprehensive mechanical properties of CMCs structure can be improved.Besides,the product design cycle will be shortened,and the research and development costs will reduce.As a result,the application of CMCs structure in aero-engine can be accelerated.However,a complete theoretical system of CMCs structure design has not been formed at this stage.The main reason is that the lack of anisotropic mechanical models of ceramic matrix mini-composites,and the failure simulation method of CMCs structure is not perfect.Under this background,testing methods of anisotropic mechanical behavior for ceramic matrix mini-composites were proposed in this dissertation.Two kinds of test samples with cylindrical and sheet structures were designed.The clamping and loading device,deformation measurement,and data acquisition device were also developed.The mechanical tests of ceramic matrix mini-composites under axial tension,transverse tension,and in-plane shear load were carried out,and the critical mechanical data such as nonlinear response,elastic modulus,and failure load under the corresponding load were obtained.The breakthrough of the testing methods of anisotropic mechanical behavior for ceramic matrix mini-composites is helpful for the research of damage mechanisms.It lays a foundation for the construction and verification of mechanical model.The in-situ test method based on submicron X-ray computed tomography(XCT)and optical microscope were proposed.The anisotropic damage characteristics of ceramic matrix mini-composites were studied comprehensively by using in-situ test,digital image correlation,acoustic emission and failure fracture observation technology.The damage process under axial tension,transverse tension,and in-plane shear load were restored.The damage evolution law under corresponding load was obtained,and the anisotropic damage mechanism of ceramic matrix mini-composites was revealed.The directionality of the load-bearing characteristics of the fiber and the matrix was verified.The quantitative relationship between the matrix crack density and the cumulative energy of acoustic emission was clarified.A measurement method of matrix crack density based on acoustic technology was proposed.Based on the advanced synchrotron radiation light source and micro CT 3D reconstruction technology,the difficulty of high fidelity 3D microstructure modeling of ceramic matrix mini-composites is overcome.The pore type and distribution characteristics in the microstructure of the material were analyzed.The numerical analysis method of the effect of porosity on the elastic modulus was proposed.The influence of pore type,pore content,pore distribution,and component volume content on the elastic properties of the ceramic matrix mini-composite was revealed.A high-precision model of the anisotropic elastic properties for the ceramic matrix mini-composite was built.The average prediction error of the model is 7.36% for axial tension,3.87% for transverse tension,4.21% for longitudinal shear,and 1.39% for transverse shear.A set of scalar damage variables was used to describe the anisotropic damage evolution process of ceramic matrix mini-composite.By taking the initiation and propagation of matrix cracks as the driving force of damage,a unified damage evolution model with clear physical significance was established.Based on the experimental observation and analysis,the anisotropic evolution model of matrix crack density was established.The damage mechanics method was used to model and calculate the anisotropic nonlinear response of ceramic matrix mini-composites.The nonlinear response error of the model is less than 3.91% for axial tension,7.84% for transverse tension,and 7.51% for shear.Based on the XCT three-dimensional reconstruction technology,a high fidelity modeling method of woven CMCs microstructure was developed.The finite element model of a real woven structure was established by the interactive component identification and the mesh reconstruction method with multiple iteration steps.The mesh number of the model is 6.04% of the traditional voxel type model.Taking the progressive damage analysis method as the framework and considering the anisotropy of mechanical behavior of ceramic matrix mini-composites,the multi-scale model was established.Then the macro stress-strain response,the distribution and evolution of the micro strain field,the distribution and evolution of matrix cracks,and the failure process of the microstructure of woven CMCs under shear load were simulated.Combined with the test results,the validity of the failure simulation method of woven CMCs structure was verified.