Optimization of the Effective Thermal Conductivity of a Composite

Composite materials by definition are a combination of two or more materials. Although the idea of combining two or more components to produce materials with controlled properties has been known and used from time immemorial, modern composites were developed only several decades ago and have found by now intensive application in different fields of engineering (Vasiliev&Morozov, 2001). These materials are used in various design to improve the characteristic of various construction and reduce their weight. The properties of these materials and the problems of obtaining structural elements based upon them have been studied by researchers and engineers all over the world. The fields of composite applications are diversified (Freger et al., 2004). They include structural elements of flying vehicles, their casinos, wings, fuselages, tails and nose cones, jet engine stators, panels form various purposes, main rotors of helicopters, heat – proofing components, construction elements such as panels, racks, shields, banking elements, etc. Any property of a composite which is made of two (or more) materials has the value which is the resultant of a few factors. Obviously, the most important are the values of a certain property of each constituent material. However, one of the factor that also influences the resultant value of a property of a composite as a whole is its geometrical structure. Such resultant properties are commonly called effective properties of a composite. Temperature is the most important of all environmental factors affecting the behaviour of composite materials, mainly because composites are rather sensitive to temperature and have relatively low effective thermal conductivity. For instance, advanced composites for engineering applications are characterized with low density providing high specific strength and stiffness, low thermal conductivity resulting in high heat insulation, and negative thermal expansion coefficient allowing us to construct hybrid composite elements that do not change their dimensions under heating (Vasiliev & Morozov, 2001). Because experimental evaluation of effective properties (e.g. thermal conductivity) of composites is expensive and time consuming, computational methods have been found to provide efficient alternatives for predicting the best parameters of composites, especially those having complex geometries. To achieve a reliable prediction, one needs to work on two aspects: a good description of the structural details of fibrous materials, and an efficient numerical method for the solution of energy equations through the fibrous structures (Wang et al. 2009). The need to determine the thermal conductivity of fibres for design purposes has been the motivation of work (Al-Sulaiman et al., 2006). Authors developed four