Research On Effective Thermal Properties Of Woven Carbon/Carbon Composites

Carbon/carbon composite is a composite material composed of carbon fiber reinforcement and carbon matrix.Due to its excellent features,such as lightweight,high modulus,high specific strength,low thermal expansion coefficient,high temperature resistance,carbon/carbon composite has been widely used in aerospace,military,automotive and other fields.As the basic thermal property parameter,the effective thermal conductivity of carbon/carbon composites determines the heat conduction of the overall material.Therefore,how to obtain the effective thermal conductivity conveniently and accurately is essential for further research and application of carbon/carbon composites.In this paper,we will use finite element simulation to study some problems in the calculation process of effective thermal conductivity.Due to the complex internal microstructure of carbon composites and the large span of feature scales,it is necessary to adapt two-scale simulation.Anisotropic pitch-based carbon/carbon composites are one of the high-thermal composite materials,and there are many difficulties in measuring the thermal conductivity of pitch-based matrix.Therefore,an anisotropic pitch-based carbon/carbon composite finite element model is established in this paper.The experimental results can be used to reverse the thermal conductivity of the matrix.This method is of guiding significance for further improving the overall thermal conductivity and optimizing the process flow.As the confusion of the selection of boundary conditions in the literature,this paper has given the details of the temperature boundary conditions,the heat flow boundary conditions and periodic boundary conditions,as well as the calculation method of effective thermal conductivity under each boundary condition.The calculation results under three kinds of boundary conditions in unidirectional carbon/carbon composite and plain weave carbon/carbon composites were compared.The applicable range and relative error of each boundary condition are given.This study provides a basis for the selection of boundary conditions in the finite element simulation of carbon/carbon composites and has very important significance.In the study of heat conduction of carbon/carbon composites,researchers usually adapt two-scale numerical model for finite element simulation.However,because finite element simulation requires a series of complex processes such as modeling,discrete,solving,post-processing,etc.,in practical engineering applications,sometimes a simple and convenient and reliable calculation formula is often favored.Therefore,researchers have developed a variety of analytical models in a variety of ways.But for anisotropic pitch-based carbon/carbon composites,there is currently no formula that can be applied directly.Therefore,this paper first compares several commonly used analytical models,and proves that the Pilling model has a good agreement with finite element simulation results in the calculation of the effective thermal conductivity of isotropic unidirectional carbon/carbon materials.Then,the effective thermal conductivity expression of the anisotropic fiber and the matrix is derived by finite element simulation and introduced to the Pilling model.Analytical model expressions for anisotropic unidirectional carbon/carbon composites are proposed.This model can easily calculate the effective thermal conductivity of an anisotropic unidirectional carbon/carbon composite.