Thermal conductivity of rubber composite materials with a hybrid AlN/carbon fiber filler

Abstract

Composite materials with high thermal conductivity have the advantages of corrosion resistance, fatigue resistance, easy processing, and electrical insulation and hence are widely used in industries concerned with high heat dissipation, such as aviation, aerospace, and electronics. Adding with high thermal conductivity, such as carbon black, metal particles, carbon fiber, and carbon nanotubes, to rubber matrix materials is recognized as an efficient method to improve the thermal conductivity of the resulting composite materials. However, when single filler is used, the content of the often must be improved to obtain high thermal conductivity, which entails a complicated process and high production cost. In this study, a hybrid filler of spherical aluminum nitride (AlN) and carbon fiber is added to rubber matrix materials. These hybrid filler particles greatly influence the thermal conductivity of the composite materials. To explore the effects of the hybrid on the thermal conductivity of the composite materials, a three-dimensional random representative volume element (RVE) model filled with both spherical AlN and carbon fiber was developed using a random sequential addition method and homogenization theory. The size of the RVE model was 40 μm×40 μm×40 μm. To prevent the formation of larger fillers by the aggregation of small fillers, a lower volume fraction of filler was investigated in this study. ANSYS software was used to simulate the influence of the space distribution, volume ratio, and filling fraction of the two on the thermal conductivity of the composite material with hybrid fillers. A steady-state heat conduction model was adopted, and a temperature gradient from 20 to 40°C was applied in the X , Y , and Z directions. The results showed that the thermal conductivity was different in the three directions due to the difference in the orientation of the carbon fibers. It can be seen from the temperature distribution clouds that there are many thermal network paths in the direction of higher thermal conductivity. The average thermal conductivity in all directions could macroscopically characterize the thermal conductivity of the composite materials. Carbon fiber plays a dominant role in the thermal conductivity of the composite material, and the thermal conductivity increases linearly with the ratio of the fillers. When the volume fraction of the carbon fibers is constant, the thermal conductivity of the composite material increases slowly with the increase in the AlN fraction. In comparison, when the volume fraction of AlN is constant, the thermal conductivity of the composite material increases rapidly with the increase of in the carbon fiber fraction. Because of enhanced synergistic effects between the in the matrix, a lower filling fraction of carbon fibers could be used to obtain higher thermal conductivity when designing the structure of composite materials. The results of this study provide a theoretical basis for the preparation of composite materials with high thermal conductivity.