Finite Element Analysis Of Effective Thermo-Mechanical Properties For Nano-Composites With Ceramic Matrix

Ceramic material has extraordinary mechanical properties, but the high brittleness is its fatal defect. It is effective to improve the brittleness by mixing the carbon nanotubes and nano-particles into the ceramic matrix. The purpose of this paper is to investigate the thermo-mechanical coupling properties for ceramic composites reinforced with carbon nanotubes, nano-particles and their hybrids by thermo-mechamics and multi-scale continuum mechanics. The effect of carbon nanotubes, nano-particle and their interactions on the improvement of strength and toughness for ceramic material is discussed.Firstly, an efficient technology for random generation and packing of spherical nano-particles is developed, and it is also extended to the generation and packing of random nanotubes. The two-dimensional and three-dimensional models with random carbon nanotubes, nano-particles and their hybrids are established for different volume fractions. By the thermodynamic theories, the thermal expansion coefficient and thermal residual stress for ceramic composites with the changes of the temperature are calculated, and the results are compared with those from classical theoretical method to verify the reliability of the model.Secondley, by using the constituted models in the above, the mechanical properties for ceramic composites reinforced with carbon nanotubes and nano-particles without damage is investigated by multi-scale homogenization method. Then the impact of the volume fraction and elastic modulus of reinforced phases on the effective mechanical properties of ceramic composites is discussed, and the effectiveness of homogenization method is verified by classical Mori-Tanaka theory. The same approach is applied to analyze the influence of the length of interfacial debonding on the effective mechanical properties for ceramic composites with interfacial debonding.Thirdly, the thermo-mechanicals properties of ceramic composites are further analyzed for the cooling down of the temperature. The radial, tangential and axial thermal residual stress for ceramic composites reinforced with carbon nanotubes are derived by using the elastic mechanics method to the representative volume element, and the results are compared well with those from FEM. The effective coefficient of thermal expansion for ceramic composites is predicted by classical method to verify the reliability of the analyzed model. The influence of some parameters such as coefficient of thermal expansion, elastic modulus, volume fraction, aspect ratio and temperature difference, etc., on the the thermal residual stress and effective coefficient of thermal expansion for ceramic composites is discussed, and the purpose on the study is to provide a basis for the design of ceramic composites.Finally, a cohesive zone model for ceramic composites reinforced with carbon nanotube is established by combining the fracture mechanics with damage theory, and the interfacial damage is discribed by the cohesive element in ANSYS. The relationship between damage evolution and the stress distribution situation is discussed, and the effect of maximum normal contact stress and the maximum crack opening displacement on the development of interfacial damage for ceramic composites is discussed.