Study the Effect of Carbon Fiber Volume Fraction and their Orientations on the Thermal Conductivity of the Polymer Composite Materials

The effect of fiber volume fraction of the carbon fiber on the thermal conductivity of the polymer composite material was studied. Different percentages of carbon fibers were used (5%, 10%, 15%, 20%, and 25%). Specimens were made in two groups for unsaturated polyester as a matrix and carbon fibers, first group has parallel arrangement of fibers and the second group has perpendicular arrangement of fibers on the thermal flow, Lee's disk method was used for testing the specimens. This study showed that the values of the of thermal conductivity of the specimens when the fibers arranged in parallel direction was higher than that when the fibers arranged in the perpendicular direction The results indicated that the thermal conductivity increases with the increasing the fiber volume fraction. Minimum value was (0.64 W/m.C) for parallel arrangement and (0.1715 W/m.C) for perpendicular arrangement at (Vf = 5%) . Maximum value for parallel and perpendicular were (2.65 W/m. C) and (0.215 W/m.C) at (Vf = 25%) respectively. Keyword: Carbon Fiber, Thermal Conductivity, Polymer, Composite Materials. Introduction Thermal conductivity is defined as the transfer of heat from area of high temperature to that of low temperature. The thermal conductivity of solids materials is greater than that of liquids and gases materials. The thermal conductivity of solid material is four times than that of gases material. This is due to the difference between the voids for two materials. The transfer of the thermal power is depending upon the component of materials. The free electrons are responsible for the transferring the thermal power through the conduct materials, while for the insulating materials such as polymers, the photons is responsible for this phenomena [1]. The fiber volume fraction and their orientation have greater effect on the thermal analysis of the composite specimens. The ability of the composite material to resist or conduct the heating depends on the quantities and qualities of the constituents. The typical applications of epoxy-based fiber-reinforced composite materials are as insulators, mechanical supports and composite tubes in combination with metal tubes as thermal standoffs in large size superconducting underground energy storing magnets to take up compressive loads with minimum thermal loss [2]. Oronizo Manca et. al. [1] studied the thermal response of the composite materials by evaluating the thermal response of the specimens to different heating conditions. M.W. Gaglord [3] said that the composite materials have anisotropic properties; therefore it has high thermal conductivity along the fiber direction and low thermal conductivity in a direction perpendicular to the fiber direction. Charles A. Sorrell [4] tried to develop new high – performance materials for use in industrial heating application, including glass melting, steel production, . etc., and the major focus of this project was on optimizing a Mohammed Sellab Al-khwarizmi Engineering Journal, Vol.4 , No. 1 PP 80-89 (2008) 81 specific aerogel composite material to the precise thermal mechanical and chemical requirements of a given industrial process. B.W. James and P. Harrison [5] used the finite difference method in the calculation of temperature distribution and heat flow in composite materials made from anisotropic materials by taking in to account the local reorientation of the grid and the temperature distribution. Heat flow was derived for a composite material made from two materials with anisotropic thermal conductivities. Zhan-Sheng Guo et. al. [6] studied the experimental and numerical temperature distribution of thick polymeric matrix laminates during an autoclaves vacuum bag process. The finite element formulation of transient heat transfer problem was carried out for polymeric matrix composite materials from the heat transfer differential equations. F.Rondeaux et.al. [7] developed a specific thermal conductivity measurement facility for solid materials at low temperature where the thermal conductivity measurements on preimpregnated fibers glass epoxy composite are presented in the temperature of 4.2 K to 14 K for different thicknesses in order to extract the thermal boundary resistance. Lamees A. Khalaf [8] studied the mechanical and physical properties for unsaturated polyester reinforced by fiber glass and nylon fiber composites and found that the thermal conductivity decreases with the increase the volume fraction, it also decrease with increase of nylon fiber layers for the samples of laminar reinforced system. Saad M. Elie [9] studied the mechanical properties and thermal conductivity for polymer composite material reinforced by aluminum and aluminum oxide particles and found that the thermal conductivity increased with the increase of the weight fraction of metallic and ceramic particles and reach a maximum value of (0.319 W/m.  C) for the composite material with (Al2O3) reinforced at a weight fraction of (20 %) and reached to (0.407 W/m.  C) for the composite material with (Al) reinforcement at the same weight fraction. The aim of this research is to study the effect of fiber volume fraction and their orientation (parallel and perpendicular to heat flow) of the reinforcement material (carbon fibers) on the thermal conductivity. The specimens were made from polyester reinforced with five different volume fraction of carbon fiber which is equal to (5%, 10%, 15%, 20% and 25 Vol. %). The reinforcement material (carbon fiber) was arranged in two groups. The first group the carbon fibers was aligned in the parallel direction to the thermal flow while the second group the carbon fibers was aligned perpendicular to the thermal flow . Theoretical analysis There are two ways for transfer of the thermal energy, 1The vibrating waves of the lattice. 2The movement of the free electrons. The thermal conductivity is defined by the following formula: q= -k dT/dx (1) The equation (1) used only for study state of thermal flow and when the thermal flux does not change with time. The minus sign means that the transfer of heat is starting from hot part to the cold part. The theoretical thermal conductivity is calculated by the following equation [2]:                       