FRACTURE-BEHAVIOR OF INTERLEAVED FIBER RESIN COMPOSITES

Interleaving, the technique of inserting a tough material into the composite laminate as extra interlaminar layers, has been used successfully to enhance the damage tolerance of brittle composites. Both carboxyl-terminated butadiene acrylonitrile (CTBN) and polyurethane (PU) were used to modify various epoxy resins. These modified epoxy resins were then chosen as interleaf materials for toughening graphite/epoxy composites. The effects of adding a thin interleaf phase on the microstructure and the fracture resistance of the resulting laminates were investigated. The results obtained from double cantilever beam (DCB) tests and end notched flexure (ENF) tests demonstrate that the tensile opening mode (Mode I) and the shear mode (Mode II) critical strain energy release rates of a graphite/epoxy laminate can be improved considerably by the technique of interleaving. The damage tolerance of interleaved composites, as assessed by the impact fatigue tests, is much greater than that of the control sample. The critical stress intensity factor, K1c, of interleaved materials was also measured by use of compact tension specimens and was correlated with the mechanical properties of the corresponding interleaved composites.