Effect Of Characteristics For Carbon Nanotube On Mechanical Properties Of Ceramic Matrix Composites

Owing to their special structure and excellent performance,carbon nanotubes have been developed a new nanomaterial which is used as the reinforcing phase of the composites.Composite materials is reinforced with carbon nanotubes,which has made many achievements in metal and polymer matrix composites.The ceramic material whose excellent performance is high temperature resistance,abrasion resistance and light weight,and it is widely used in aerospace,military and industrial production,but the brittleness of ceramic materials has been restricting its further development and application.the ceramic matrix composite is composed by special structure and excellent properties of carbon nanotubes,which can effectively improve the fracture toughness of ceramic materials,But at present,there are some problems in this field,such as dispersion,interface and aggregation.Based on existing research in the present thesis,the effective mechanical properties of ceramic composites with nano-tube,the influence of the lined,cosined and winded nano tube on the mechanical properties for nano composites is analyzed by using the continuum mechanics theory,homogenization theory,shear lag theory,cohesive theory and the methods of finite element analysis,and the influence of the geometrical characteristics of carbon nanotubes on the strengthening and toughening mechanism of composites is confirmed.Firstly,four classical theories and methods for predicting the effective elastic properties of carbon nanotube composites are introduced.Based on carbon nanotube composites,compared with the predicted results of the mixing rule(VR limit theory),Mori-Tanaka method,generalized self consistent method and finite element method,the reliability of result that are calculated by the finite element method(ANSYS)is proved.Secondly,the research object is ceramic matrix composites reinforced by the lined and waved nano tube with solid and tubular shapes,the finite element software ANSYS and the double scale asymptotic homogenization theory is used to analyze the influence of the diameter,length,bending properties and anisotropy of nano tube on the mechanical properties for nano composites.Thirdly,besed on the elastic mechanics,the axial stress distribution of carbon nanotubes and matrix for ceramic composites reinforced with carbon nanotubes are derived by usingthe modified shear lag theory.Three dimensional representative volume element models for ceramic matrix composites reinforced by the tubular shapes of carbon nanotubes are constituted on the ANSYS platform,under axial loading,the influence of aspect ratio,volume fraction,anisotropy and interface debonding of carbon nanotube on the axial stress distribution for carbon nanotubes and matrix is analyzed,and the results are compared with the theoretical methods to verify the consistency of the two methods.Fourthly,In order to further study the influence of the geometrical shape of carbon nanotubes on the mechanical properties for nano composites,The effective stiffness for ceramic composites reinforced with waved and cosined carbon nanotubes are calculated by using the finite element software ANSYS and the double scale asymptotic homogenization theory.Simulation of ceramic matrix composites reinforced by the waved and cosined carbon nanotubes is used to analyze the influence of the diameter,length and anisotropy of nano tube on the mechanical properties and local stress for nano composites.Finally,using the damage mechanics and the cohesion model theory,under transverse load the interface damage evolution for ceramic matrix composites reinforced by the tubular shapes of carbon nanotubes is analyzed by the cohesive zone model in ANSYS.The influence of the maximum normal contact stress,the maximum crack opening displacement and the wall thickness of tubular carbon nanotubes on the interface damage evolution is the main research content.