Onsager’s Reciprocal Relation and Effective Coefficients of Transverse Coupled Hygrothermal Diffusion in Fiber Reinforced Composites

Abstract

A method for the determination of the effective constant coefficients of the transverse coupled hygrothermal diffusion is presented. Onsager’s reciprocal relation [2] is utilized to reduce the number of the diffusivity coefficients of constitutive materials from four to two. The so called cross coupling diffusivities are expressed in terms of the thermal conductivity and the coefficient of diffusion. The representative volume element of the composite is analyzed by applying a twodimensional finite element model. It is assumed that the composite is undamaged, and there is no resistance in diffusion and heat conduction at the interface of the fiber and the matrix. The method is tested numerically with a set of different cases. The coupling affects most clearly to the heat flux in the tests. The average coupled heat flux is significantly greater than the uncoupled heat flux.