Nonlinear analysis of microscopic instabilities in fiber-reinforced composite materials

Abstract Failure induced by fiber microbuckling is a frequent failure mode in continuous fiber-reinforced composite materials subjected to compression along the fibers direction. This failure mechanism may lead to a notable decrease of the compressive strength of composite materials since may also induce the initiation and propagation of cracks at the micro-structural level. A detailed microscopic continuum analysis with an appropriate representation of different sources of nonlinearities is usually required to capture the effects of different microscopic failure modes (instability, fracture damage, for instance), at the expense of a very large computational effort. In order to avoid a direct modeling of all microstructural details of the composite solid, micromechanically based multiscale techniques can be adopted in coupling with first order homogenization schemes. To this end a semiconcurrent two-scale approach is proposed in which the macroscopic constitutive law is evaluated resolving a micromechanical BVP in each macroelement of the homogenized domain; the microscopic model adopts a full finite deformation continuum formulation to study the interaction between local fiber buckling and matrix or fiber/matrix interface microcracks in presence of unilateral self-contact between crack surfaces. Numerical results are obtained to provide accurate predictions of the critical load level associated to microscopic instabilities in 2D fiber-reinforced composite solids