THERMAL-EXPANSION COEFFICIENTS OF FIBER COMPOSITES DEFINED BY THE CONCEPT OF THE INTERPHASE

The thermal expansion behavior of unidirectional composites has been studied. In this analysis a model which introduces the concept of the boundary interphase has been used. The expansion coefficients of the composite were calculated by using this concept to determine the influence of the interphase which depends on the quality of adhesion between fiber and matrix. In the present paper it has been assumed that the interphase material was inhomogeneous with properties varying from the fiber surface to the matrix. Three laws of variation have been taken into consideration in order to derive expressions for the thermal expansion coefficients in which appears the role of this interphase layer possessing physico-chemical properties different from those of the constituent phases. A thermal analysis method was used in order to find the extent of the interphase layer. The results are assessed by comparing them with those given by other theories.