Multiscale Modeling Of Thermal Properities Of Silcon Carbide And Epoxy Resin Composites

With the economic development and technological progress,people put forward higher requirements on the application of thermal polymer materials.Due to the limitation of the existing theoretical and experimental conditions,more and more researchers begin to use the simulation method to explore the thermal mechanism of polymer materials.In this paper,epoxy resin(EP)and silicon carbide(SiC)were used as the research object.First,the effects of the particle size of SiC on the thermal conductivity of EP/SiC composites and the crosslinking degree on the interface thermal conductance of EP/SiC composites were investigated by the non-equilibrium molecular dynamics(NEMD)simulation at the microscopic level;second,taking into account the limitation of the microscopic simulation,the volume fraction of SiC and the random distribution of SiC on the EP/SiC composites were investigated by the finite element(FEM)simulation at the macroscopic level with the microscopic simulation results as input parameters.The mechanism of thermal conductivity of polymer materials was explored by micro-macro combination method,which provided some theoretical prediction and guidance for improving the thermal conductivity of polymer composites.Main research contents:(1)The effect of particle size of SiC on the thermal conductivity of EP/SiC composites was investigated.The result showed that the thermal conductivity of the composites increased with the increasement of the particle size of SiC.The Vibration Power Spectra(VPS)of composites was analyzed,the result showed that the overlapping area of VPS of EP and SiC decreased gradually with the increase ment of the particle size of SiC,indicating that the phonon collision between these two parts was weakened;The peak of VPS of EP decreased with the increasement of the particle size of SiC and began to move to the low frequency,indicating that the increase ment of the particle size of SiC had a positive effect on the phonon propagation of EP;the VPS of SiC from the perpendicular to the heat flow direction and along in the heat flow direction were both occured at the range of 0-30 THz,indicating that these two kinds of VPS had an enhancement to the thermal conductivity of the composite materials and the peak value of VPS from the the perpendicular to the heat flow direction decreased with the increasement of the particle size of SiC,indicating that the promoting effect of the perpendicular to the heat flow direction's is greater than the along in the heat flow direction's.(2)The effect of the crosslinking degree on the interface thermal conductance of EP/SiC composites was investigated.The result showed that the interface thermal conductance of the composites decreased first and then increased with the increasement of the crosslinking degree of EP.The VPS of composites was analyzed,the result showed that the overlapping area of VPS of EP and SiC increased first and then decreased with the increasement of the crosslinking degree,indicating that the phone collision between these two parts enhanced first and then weakened and the interface thermal conductance decreased first and then increased,the out-of-plane and in-plane of the VPS of SiC were both increased first and then decreased with the increasement of the crosslinking degree,indicating that the interface thermal conductance decreased first and then increased;the VPS of the-CH2 atoms and the-NHatoms on EP were both major occured at the range of 0-50 THz,the VPS of the-OH atoms on EP major occurred at the range of 0-20 THz and the VPS of these three major atoms vibrated in a wide range of frequencies,indicating that the thermal conductivity of EP was mainly carried out by the phonon diffusion scattering,thus lead the thermal conductivity was not high.(3)the effect of the volume fraction and the random distribution of SiC on the thermal conductivity of EP/SiC composites were investigated.The result showed that the increasement of the volume fraction of SiC was beneficial to improve the thermal conductivity of the composites.The random distribution of SiC was more favorable to the thermal conductivity of the composites and the larger the volume fraction of SiC,the greater the effect of the random distribution,which made the thermal network in the composites system form easier;The number of the mesh seeds and the external load of the heat flux had little effect on the thermal conductivity of the composites system.