Appropriate utilization of the unit cell method in thermal calculation of composites

The unit cell method is widely used in thermal calculations of composite. The formulation of a unit cell involves construction of geometric configuration and derivation of boundary conditions. The process is closely related to the structure symmetries of composites and the macro heat flux. In this work, two issues are studied to further appropriate utilization of such method. First, unit cells that formulated based on different paths with different structure symmetries could have the same configuration while different boundary conditions, and leads to some confusions; second, the uniform temperature boundary condition is frequently used without rigorous mathematical derivation and physical consideration, and leaves some uncertainty of its reliability. In this work, three typical composites, unidirectional fiber reinforced, plain woven and three-dimensional four-directional braided composites are studied. For each composite, one unit cell is formulated and two types of boundary conditions are derived. The influence of formulation path on unit cell formulation and the application scope of uniform temperature boundary conditions are then clarified based on corresponding calculations and analysis.