Micromechanics for a long fibre reinforced composite model with a functionally graded interphase

A unit cell model based on the interaction between the fibre and a matrix at the micromechanics scale for a long fibre reinforced composite is developed. An interphase zone is defined to describe the load transfer between the fibre and matrix. The interphase zone has functionally graded properties, and occupies a region including the physical boundary between the fibre and matrix. Material paring constants k and l are introduced to define the size of the interphase zone, independent of the volume fraction of reinforcement for a given set of materials. This model allows the prediction of the average stress in the composite as well as the constituents.