Micromechanical Behavior of FRP Composites with Higro-Thermal Damage

Abstract

The stress field in a representative volume element (RVE) of a composite material formed by e-glass fibers and polymer matrix is investigated. The assumed RVE is a regular domain in plane strain, including 25 fibers and under a shear load field. Damage in the form of interface debonding is included in the model, in order to represent damage due to higro-thermal action (not produced by mechanical loads). The specific form of damage follows micrographs obtained in experiments, from which debonding may be approximated as a shallow ellipse. The redistributions of stresses is investigated using a finite element representation of the RVE using the general purpose finite element code ABAQUS. Both elastic and elasto-plastic models are studied in order to identify likely propagation patterns of the assumed initial damage. Parametric studies are reported by varying the extent of damage (length of the ellipse), the fiber volume fraction, and the number of fibers affected by damage. The results for elastic models show that damage at one interface affects the eight fibers in the neighborhood (a Moore neighborhood), four of which increase their stress levels and the other four (in diagonal with respect to the fiber affected) decrease their values. Results from elasto-plastic models indicate that the number of voids decreases the load at failure only if the voids are aligned.