Micromechanical analysis of interfacial debonding in unidirectional fiber-reinforced composites

In this paper the behaviour of unidirectional fiber-reinforced composites with imperfect interfacial bonding is investigated by using the finite element method. The matrix and the fibers are considered homogeneous, isotropic and linearly elastic; an interfacial failure model is implemented by connecting the fibers and the matrix at the finite element nodes by normal and tangential brittle-elastic springs. Numerical analyses are carried out on a unit cell extracted from a composite model characterized by a periodic microstructure. The micromechanical simulations provide the first failure loci (FFL), i.e. the envelopes of the composite average strains corresponding to the initiation of the debonding, and the instantaneous overall moduli of the damaged composite corresponding to several interface damage configurations. The results show that the intersections of the FFL with prescribed planes are defined by curves associated with different interface failure modes. Besides, damage induced by fiber–matrix debonding is strongly anisotropic and dependent on the load history.