Strength criteria for fiber reinforced composite materials

The ultimate behaviour of fiber reinforced composites is frequently described by phenomenological failure criteria, whose origin is fundamentally empirical. A theoretical tool for defining in a rigourous way a strength criterion for this class of materials ìs provided by the homogenization theory, applied to the limit analysis. Such a criterion is called 'macroscopic', since it describes the overall strength of the composite material, starting from the knowledge of the strength properties of its constituents (matrix and fibers) and of their geo- metrical arrangement. Furthermore, the possibility of failure at the fiber-matrix interface can easily be taken into account. By means of this model, the ultimate behaviour of several composites subjected to uniaxial and biaxial stress was described; the theoretical results obtained are in good agreement with available experimental data. This approach provides a particularly suitable method for designing new composite materials according to strength requirements.