Simulate Study Of Effective Mechanics Properties For Nonwoven Carbon/Carbon Composites Based On Homogenization Theory

Carbon/carbon(C/C) composites offer unique mechanical properties for high temperature applications where high strength, wear resistance, and lightweight components are desirable. For these reasons C/C composites have been extensively investigated and applied. Some factors, such as carbon fiber types, carbon fiber directions, knitting styles and carbon matrix microstructure, will influence the mechanical properties of C/C composites. However, it is too difficult to determine the mechanical properties of C/C composites by testing them with various knitting styles, because of the complicated manufacture processing, long times and high product cost, to optimize knitting structures. It is a good way to choose good knitting structures by theory predicting, then to research the optimization of material manufacturing process. The research in this paper intends to combine homogenization method with finite element method (FEM), and to predict effective parameters and micromechanics of nonwoven C/C composites in microcosms. Some useful results acquired will afford instructions for optimal design of these composites.First, the brief theory of homogenization method has been given. Then, the finite element method is combined with homogenization theory (HFEM) to predict the effective properties of nonwoven C/C composites and realize the effective combination of macro and microcosmic. Then, this method (HFEM) is applied to predict and analysis the effective properties of 1D, 2D and 2.5D C/C composites. For these, the base cell of 1D and 2D C/C composites are constructed. By equivalent treatment, the periodical boundary condition of unit-cell can be satisfied in element, which is called fixed displacement conditions. Based on these, HFEM is used to predict the effective properties 1D, 2D and 2.5D C/C composites. By comparing the results of present method with those of other methods and experimental, it is considered that more accurate results of effective elastic modulus can be obtained by means of HFEM. Further, the influence of material parameter to the effective properties of 1D C/C composites is analyzed with two cell models. It is found that the effective elastic modulus will increase and poiss ratio will decrease with the increasing of carbon fiber contains. Moreover, the effective properties of 2D and 2.5D C/C composites based on 1D results are calculatet and the influence and coupling of parameter, such as carbon fiber contains, carbon fiber direction angle and carbon matrix performance, to the effective properties of 2D plain woven cloth and twill woven cloth C/C composites are analyzed and some useful results are obtained. It is proposed that the microscopic structure parameters should be selected reasonably to acquire expected C/C composites. The influence of defects in the base-cell models to the effective properties is studied. The research is the foundation of C/C composites optimal design.Finally, the micro structure stress of 1D and 2D C/C composites in the base-cell models are simulated and dicussed, the influence of varying micro structure parameters and structure changing to microstructure stress field are analyzed and the influence of defects in the base-cell models to microstructure stress field are studied. The results showed that the different stations and shapes of defects will affect the microstructure stress field.