Study On The Effect Of Lay-up On The Thermal Conductivities Of Carbon Fiber/Epoxy Resin Composites

Carbon fiber reinforced plastic (CFRP) has a wide application prospect in the fieldof multifunctional structures (e.g. microelectronic devices and satellites) due to itsadvantages, such as low density, low thermal-expansion coefficient, high thermalconductivity, adaptability to large-size, light-weight, high-strength structures,large-scaled production and commercialization. Considering its anisotropy of thermalconductivity, cross stacking is a common lay-up way in the practical CFRP structures.The effect of ply angle on the thermal conductivity of M40J/E648, T700/E648andmesophase pitch based carbon fiber composites (MPCFRP) is systematically studied inthis paper. Based on analytical method, finite element method (FEM) and numericalfitting method, the predicted models are established to predict and investigate thethermal conductivities of the CFRP composites. Then the predicted results are comparedwith the experimental data. The main work includes:The mechanical and thermal properties of unidirectional CFRP, which prepared byautoclave process, are experimentally investigated. Compared M40J/E648andT700/E648, the modulus of M40J/E648composite is relative higher than that ofT700/E648, which tensile and flexural modulus is161.7GPa and181.0GPa,respectively. On the contrary, the strength of T700/E648is higher than that ofM40J/E648, which tensile and flexural strength is1486MPa and1687MPa,respectively. There is an evident difference between longitudinal linear-expansioncoefficient and transverse linear-expansion coefficient for the unidirectional composite.The former is nearly zero-expansion or negitative expansion, while the latter is slightlylower than that of epoxy resin. The heat capacity of the composites increases with theincreasing angle between the fiber direction and the testing direction, furthermore, thatincreases linearly with the increasing temperature. On the contrary, the thermaldiffusion of the composites reduces with the increasing angle and temperature, whichdeclines within20%ranging from room temperature to423K.Thermal conductivity of the unidirectional CFRP is experimentally investigated inthis paper. The results show that the thermal conductivity of M40J/E648and T700/E648in the fiber direction is23.20W/mK and10.22W/mK, while that in the thicknessdirection is1.81W/mK and1.96W/mK, respectively. And the corresponding fibervolume fraction of the two composites is60.3%and64.2%, respectively. The thermalconductivities of the composites increase as the test temperature increasing. The thermalconductivity of M40J/E648, T700/E648and T700/E23A composites is up to33.97,15.19, and15.13W/mK at the test temperature423K, respectively.The finite elementmodel is established to analyze the thermal conductivity of the unidirectional CFRP.Good agreement is observed between the calculated results and the experimental data. Considering anisotropy, the thermal conductive properties of the CFRP with typicallay-ups are studied through analytical and finite element methods. In-plane thermalconductivities of M40J/E648composites with orthogonal stacking is12.13,10.35and12.02W/mK in the direction of0°,45°and60°, respectively. And that of M40J/E648composites with [0/45/-45/0] stacking is16.13,11.49and10.71W/mK in the directionof0°,45°and60°, respectively. The thermal conductivity variation rule of othercarbon-fiber composite is similar with that of M40J/E648composites.High thermal conductivity mesophase-pitch based carbon fiber is used asreinforcement to prepare unidirectional CFRP. And thermal conductivity property ofunidirectional MPCFRP is investigated by experiments and theoretical analysis. Theresults show that the experimental thermal conductivity of unidirectional MPCFRP is upto59.39W/mK in the fiber direction, while the theoretical data can be up to282.45W/mK. Based on the theoretical analysis, the thermal conductivity ofunidirectional MPCFRP (60%fiber volume fraction) in fiber direction can be up to169W/mK at room temperature. And that of MPCFRP with orthogonal stacking in planeprincipal-direction is more than66W/mK. There is a great prospect of application inmultifunctional structures for MPCFRP due to its excellent thermal conductivityproperties.