A Computational Approach Together With Its Numerical Implementation For Simulating The Damage Evolution Of Continuous Fiber-reinforced Ceramic Matrix Composites Based On The Phase Field Method

There are various failure forms of engineering materials,the most severe one is fracture failure,which often results in huge economic losses and casualties.In the past,experimental and theoretical methods were used to study the damage and fracture characteristics of materials.With the development of computer science,the improvement of hardware performance,the rapid development of numerical algorithms and software technology,and the combination between structural/material damage fracture mechanics and numerical simulation methods,simulation of material fracture failure behavior and mechanism are effectively performed,saving a lot of time and cost.Fiber-reinforced ceramic matrix composites are widely used in extreme service conditions in aerospace,nuclear power and other fields due to their excellent properties such as oxidation resistance,high temperature resistance,high specific strength,high specific modulus,chemical corrosion resistance,and high wear resistance.The preparation process of such composite materials is extremely complicated,involving multifield coupling effects such as fluids,mechanics,heat,and chemistry.Natural defects,such as pores and micro-cracks inside,are inevitable.In order to accurately predict its service performance and ensure the reliability of components in extreme environments,it is urgent to develop a fiber-reinforced ceramic matrix composite microstructure internal damage evolution simulation algorithm,and therefore explore the influence mechanism of different natural defects on material damage and service performance.Currently,studies regarding component/material damage and failure based on the phase field method mostly focus on isotropic homogeneous materials.However,fiber-reinforced ceramic matrix composites are typical anisotropic materials,the damage evolution mostly occurs on the location of fibermatrix interface and natural defects,with effects such as crack deflection,bridging,and fiber pulling out.Therefore,in this work,based on the phase field method and the intelligent modeling method of the continuous fiber-reinforced ceramic matrix composite(CFRCMC)microstructure,considering the anisotropic properties of the fiber filament/bundle material,a CFRCMC damage evolution simulation method is established to investigate the effects of natural defects and its intrinsic mechanism.In this dissertation,the following work has been conducted:(1)Theoretical derivation and algorithm development of the phase field method: Based on the principle of crack dispersion,the CFRCMC damage field finite element control equation and the displacement field control equation are derived.A new strain tensor operator is proposed in combination with eigenvalue decomposition technique in the literature.The numerical code was written by MATLAB and its correctness was verified(2)Intelligent parametric modeling of CFRCMC microstructure: Combining the characteristics of the CFRCMC model and the intelligent local mesh refinement method,a parametric modeling strategy for the microscopic composition of the two-dimensional woven fabric-reinforced ceramic matrix composite is established.Combined with ceramic matrix composite macro,the anisotropic properties of the tough fiber bundles and the phase-field simulation method,the effective simulation of the damage evolution process in the CFRCMC microstructure was implemented,and the performance evolution results of the material failure process were obtained.(3)The distribution and size characteristics of defects such as natural pores and microcracks in CFRCMC were summarized,and the influence of defects on material damage evolution was explored from the perspectives of pore shape and location,and microcrack shape.In addition,the influence of random multi-pores on the damage and crack propagation path of ceramic matrix composites was further analyzed.(4)The simplified two-dimensional CFRCMC microstructure model was extended to the three-dimensional CFRCMC model,and the phase field simulation code was implemented using MATLAB.The results is verified by a simplified example model.Considering the CFRCMC material characteristics and internal defect statistical information,the internal damage evolution law of the CFRCMC three-dimensional material was analyzed.