The interface between a fibre and its matrix represents an important element in the characterization and exploitation of composite materials.

A large volume of results for a wide range of composite systems exists, but rather little comparison and potential consistency have been reached for fibres and/or for matrices. Recently a materials mechanics approach has been presented to describe the interface by three parameters, the inter-facial energy [J/m2], the inter-facial frictional shear stress [MPa] and the mismatch strain [-] between fibre and matrix.

The model has been used for the different modes of fibre pull-out and fibre fragmentation.

In fibrous composite materials the fibres and matrix interact to produce the resulting properties of the composites. This interaction takes several forms. The fibres and matrix separately contribute with their “own” properties (often in a fraction-weighted way), and these properties of the constituents are both the stiffness, the stress and the strain (elongation). The fibres and the matrix also interact with each other through the interface between them and contribute additional behavior and properties.

Normally composite materials are composed of (one type of) fibres of cylindrical geometry with one long dimension and two small transverse dimensions, which normally form a roughly equiaxed cross section, that is often represented by a circular cross section. The representative model for the composite is thus a straight circular fibre in a block of matrix.