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The failure mechanism of delamination fracture in composites is investigated. A model based on the fracture mechanics principles is applied to describe the in situ delamination failure process. The crack tip plastic zone developed in the thin resin layer between fibers is considered as the major energy dissipation mechanism. The model expresses delamination fracture toughness GIc (laminate), Mode I critical strain energy release rate, as a function of several resin properties. The delamination behavior of several epoxy/fiberglass systems was characterized using the width-tapered double cantilever beam method. The GIc (laminate) results are correlated with the resin properties based on the in situ failure model. Resin modulus E and yield stress σy are found to dictate the translation from GIc (resin) to GIc (laminate. Residual stresses in the laminates can also significantly weaken the delamination resistance. A comprehensive comparison between laminate and resin fracture toughness reported in the literature is analyzed from the viewpoint of the mechanism modelled.
delamination, failure mechanism, fracture mechanics, fracture toughness, crack propagation, composite materials, resin properties, residual stress, crack tip plastic zone
Senior staff scientist, Composite Materials Department, Ciba-Geigy Corporation, Anaheim, CA