A model for static and fatigue behavior of fibre-reinforced composites

The necessity to describe the overall mechanical behaviour of composite materials is a crucial task since composites are widely used in many practical applications. Several mechanical models for such materials have been developed by using various approaches such as micromechanical (physically based), homogenization models (mathematically based), etc. . In the present paper the behaviour of Fibre-Reinforced Composites is examined through the formulation of a non-linear constitutive law, based on homogenization concepts and by taking into account the debonding phenomena. The elasto-plastic macro constitutive equations for such materials, is firstly obtained considering an elasto-plastic matrix and an imperfect bond between the matrix and the fibres; by considering the actual shear stress distribution along a single fibre and by energetic considerations, the fibre-matrix sliding is determined. By an averaging process the overall non-linear constitutive law of the composite is finally obtained. In the case of cyclic loading, the degradation of the mechanical properties must be considered to simulate fatigue damaging. Damage parameters are assumed to obey a S-N-type relationship (Wöhler curves). The proposed constitutive law with degradation has been implemented in a F.E. code. In order to assess its reliability, some numerical simulation have been performed both in static and cyclic loading situations and compared with available results.