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.