An integrated micromechanical and macromechanical approach to fracture behavior of fiber-reinforced composites

Abstract

An integrated micromechanical and macromechanical fracture criterion (IMMFC) has been developed for the fracture characterization of fiber-reinforced composites. The Griffith's energy balance equation has been modified to include the energy absorption due to physical failure processes, characteristic of the heterogeneous and anisotropic nature of these materials. A local elastic energy release rate in the presence of plasticity has been defined and used as a criterion for the onset and growth of cracks in both micromechanics and macromechanies analyses. A crack growth simulation technique based on the virtual crack extension method has been developed for a three-dimensional (3-D) finite element analysis. A 3-D finite element micromechanical model is used to study the effects of broken fibers, cracked matrix and fiber-matrix debond on the fracture toughness of the unidirectional composite. The crack growth resistance curves ( R-curves) concept has been used to bridge the micromechanics and macromechanics approaches. The energy release rates at the onset of the unstable crack growth in the micromechanics analysis are used as critical energy release rates in the macromechanics analysis. The approach has been shown to be very effective in predicting the onset and growth of cracks in general multilayered composite laminates by applying the criterion to predict the initiation and growth of cracks and associated damages in a single-edged notched [ ± 45 0 ] s graphite/epoxy laminate subjected to inplane tension normal to the notch.