A CRITICAL ANALYSIS OF INTERFACE CONSTITUTIVE MODELS FOR THE SIMULATION OF DELAMINATION IN COMPOSITES AND FAILURE OF ADHESIVE BONDS

Delamination in layered composites and debonding in adhesive joints are modeled and analyzed using interfacial mechanics, consisting of interface elements for the kinematical assumption and traction-separation equations for the constitutive model. Material equations are presented for the inelastic behavior of pure and ductile-modified epoxy resins, used for the matrix phase of the composite and in a chemically modified form for the adhesive in bonded structures. Two different modeling approaches are proposed. The first is a brittle fracture model with a stress-based failure criterion and rate-dependent strength parameters together with a mixed-mode energy criterion for the interaction of the three different modes of failure. The second makes use of an elastic-plastic approach with a traction-separation equation for ductile materials and rate-dependent yield stresses. Standard tests for the delamination of layered composites under various modes of failure are simulated by making use of the interface element for bonding/debonding. The model for the inelastic behavior of a thin layer of the structural adhesive is validated up to fracture for various modes of failure due to pure and combined loading in the normal and shear directions. Therefore, the relevant part of the experimental setup for the testing is meshed with finite elements and the results of the simulation are compared to the corresponding test data.