Modeling inelastic matrix crack tip deformation in a double cantilever beam specimen

A finite element model is created to investigate the contribution of inelastic matrix deformation at the crack tip to the composite toughness in a double cantilever beam specimen. The constituent properties are explicitly incorporated into the analysis using a global-local model and discrete fiber and matrix layers in the local model. The results indicate that there is little difference between the global and local J-integrals for matrices that do not exhibit pressure-dependent plastic deformation. Plastic deformation occurs in matrix layers away from the crack tip, but the majority of the deformation in terms of strain intensity occurs in the resin-rich region at the crack tip. This localized intensity causes the crack tip strains and plastic energy dissipation levels to be much higher in crack tips that are highly constrained by the layer of fibers, even though plastic volumes are lower. The results shed new light on previous explanations for the difference between ductile matrix and composite toughness and the thickness effect observed in adhesive bonds using ductile adhesives.