Modelling the efficiency of strain transfer across an interphase region in fibre reinforced composites

Although many micromechanical models for the stress transfer between matrix and fibre have been proposed, little work has taken into account the existence of the interphase. The presence of such a region is inevitable due to the nature of composites and their manufacture and, as such, it is vital to establish its effect on the stress transfer between matrix and fibre. This study examines the relationship between strain transfer characteristics and the properties of the interphase region. The relationship was investigated using an axisymmetric finite element model of a short glass fibre composite. For the purposes of the model, the interfaces between both the fibre/interphase and the interphase/matrix were considered to be perfect. The properties of the matrix and interphase materials were incorporated using an elasto-plastic analysis. Five materials, with properties varying from brittle elastic to soft and ductile, allowed differing combinations of matrix and interphase to be examined. Two parameters were defined to describe the behaviour of these model systems; a Stress Transfer Efficiency (STE) and a Stress Transfer Length (STL). The STE was shown to be matrix property sensitive, whilst the STL was sensitive to the properties of the interphase. The plasticity of these constituents was shown to have a large bearing on the level and development of strain transferred to the embedded fibre and the implications of these findings on composite performance are analysed.