Study On Anisotropic Thermal Conductivity Of Quartz Fiber Felt/fabric 3D Needle-punched Prefor

Radome,which located at the head of space vehicle,is a key component integrating heat protection,wave transmission and force bearing.With the continuous development of space vehicles to hypersonic and ultra long endurance,the severe service environment puts forward higher requirements for the high temperature resistance of radome materials,that is,they should have excellent high temperature ablation resistance and low thermal conductivity,so as to protect the safety of devices inside the radome.Quartz fiber needle-punched preforms have become an ideal material for the development of a new generation of radome because of its excellent interlayer performance,light weight,high strength,high temperature resistance and wave transmission performance.It has been rapidly developed and widely used in recent years.For the analysis of anisotropic heat conduction of needle-punched preforms with complex structure,a cross scale integrated transformation method of heat conduction of finite element of the quartz fiber felt/fabrics needle-punched preform(QFF/FNP)was established in this study.Anisotropic heat conduction behavior of finite element simulation of textile materials with different structures under multi-level is carried out,temperature distribution characteristic and heat transferring path of textile materials with different structures were ontained,anisotropic thermal conductivities of textile materials under multi-level were predicted.Heat conduction mechanism of textile materials at different structures was illustrated from different levels.Numerical and experimental results of thermal conductivity of the corresponding level showed good agreements.Direct reference for finite element study of multi-layer composites can be applied based on this study.The major research contents and conclusions of this paper are summarized as follows:Firstly,via needling the cross laminations of quartz fiber felts and fabrics layer by layer,QFF/FNPs at different needle-punched densities were made,and its interlayer peeling tests at different needle-punched densities were conducted.3D image observation of fiber bundles in Z direction of QFF/FNPs was conducted by 3D profilometer modeled VR5200,then length range of fiber bundles in Z directions of QFF/FNP at different needle-punched densities was mastered.Hot-Disk thermal constant analyzer was used to measure the specific heat,anisotropic thermal conductivity and thermal diffusion coefficient.Change rules of anisotropic thermal properties vs.needle-punched densities were illustrated.Furthermore,at the micro(yarn)scale,geometry parameters of 3D model of twist yarns were determined by Micro-CT technology and electron microscope observation,based on the modeling method of virtual fibers,then the finite element model of thermal conduction of the yarn with the axial twist and randomly fiber distribution in its section was established.Heat conduction behavior of twist yarns was simulated,temperature distribution and transferring path of the heat flux among fibers were mastered clearly,anisotropic thermal conductivity of the twist yarns was predicted.Thirdly,at the meso(fabric)scale,twill fabrics were as the typical structure,3D image of the fabric was obtained by Micro-CT technology,geometry parameters of the fabrics were determined.Considering fabrics’ measurement method of heat conduction,the finite element model of heat conduction of laminated fabric was created.Anisotropic heat conduction behaviors of finite element simulation of laminated twill fabrics were conducted.Detailed tempareture distribution and heat transferring characteristic were obtained,anisotropic thermal conductivities were predicted,it is found that the thermal conductivity in the warp direction is bigger than that in weft and thickness directions,and the thickness one is the smallest.Fourthly,at the meso(fiber felt)scale,reconstruction of 3D solid element model of quartz fiber felt was realized by second-development of Python-Abaqus,experimental measurement and mathematical statistics.Anisotropic thermal transferring behaviors of fiber felt(including temperature distribution and heat flux transferring)were simulated by finite element method,and anisotropic thermal conductivity was predicted.Finally,at the macro(needle-punched preforms)scale,detailed 3D and 2D morphology of the inner geometry structure of QFF/FNP at different needle-punched densities by Micro-CT technology.The size and fiber volume content(FVC)of fiber bundles in Z direction of QFF/FNP at different needle-punched densities were obtained by Image-J software.Furthermore,based on the layered homogenization method,from the research on the thermal conductivity of each component element of needle-punched preform,finite element model of QFF/FNP at different needle-punched densities containing randomly distributed fiber bundles in Z directions were established by random distribution algorithm.Heat conduction behaviors of finite element of QFF/FNP at different needle-punched densities were carried out,detailed temperature and heat flux distribution were obtained,moreover,anisotropic thermal conductivity of QFF/FNPs were predicted.Numerical and experimental results indicated that: thermal conductivity in plane directions of the QFF/FNP decreased with the increment of the needle-punched density,and that in thickness direction of the QFF/FNP increased with the increment of the needle-punched density.