Damage evolution in fibrous composites caused by interfacial debonding

Interfacial debonding between fibers and matrix is one of the dominant damage types in fibrous composites. This paper investigates weakening effect due to the interfacial debonding. For simplification, the fibers are assumed to be rigid since the modulii and strength of fibers are much greater than those of matrix, and the distribution of the radii of fibers is assumed to obey the logarithmic normal distribution. The matrix is assumed to be a viscoelastic material. The boundary of the composite is subjected to transverse loading condition, the direction of which is perpendicular to that of fibers. The interfacial debonding between fibers and matrix is analyzed by the energy criterion, and the evolution formula of nucleated porosity due to the debonding is derived by the statistical approach. A newly defined volume average method is proposed to establish the macroscopic constitutive relation of the composites. The effect of the material parameters of matrix, as well as the size of fibers on the critical stress for the interfacial debonding and damage evolution are discussed in detail. The results obtained in this paper indicate that the macroscopic strain rate, the dispersion degree of the fiber's radii, the adhesive energy at the interface, and loading condition play key roles in the overall mechanical properties of the composites.