  Delamination is a critical mode of failure that occurs between plies in a
composite laminate. The cohesive element, developed based on the cohesive zone
model, is widely used for modeling delamination. However, standard cohesive
elements suffer from a well-known limit on the mesh density-the element size
must be much smaller than the cohesive zone size. This work develops a new set
of elements for modelling composite plies and their interfaces in 3D. A
triangular Kirchhoff-Love shell element is developed for orthotropic materials
to model the plies. A structural cohesive element, conforming to the shell
elements of the plies, is developed to model the interface delamination. The
proposed method is verified and validated on the classical benchmark problems
of Mode I, Mode II, and mixed-mode delamination of unidirectional laminates, as
well as on the single-leg bending problem of a multi-directional laminate. All
the results show that the element size in the proposed models can be ten times
larger than that in the standard cohesive element models, with more than 90%
reduction in CPU time, while retaining prediction accuracy. This would then
allow more effective and efficient modeling of delamination in composites
without worrying about the cohesive zone limit on the mesh density.
