The in-plane shear modulus of fibre reinforced composites as defined by the concept of interphase

In this paper we describe a model to find the approximate equations for determining the in-plane shear modulus of a unidirectional fibre reinforced composite from the constituent material properties. Classical elasticity theory has been applied to the simplified model of a composite unit cell in which the concept of an interphase between fibre and matrix is taken into account. Thus the model considers that the composite material consists of three phases, that is the fibre, the matrix, and the interphase which is the part of the polymer matrix lying close to the fibre surface which possesses different physico-chemical properties from those of the main constituents. Thermal analysis was used for the determination of the thickness and volume fraction of the interphase. The theoretical results are compared with other theoretical expressions and with experimental data. The model introduced in this paper seems to be an improvement for the shear modulus.