  In this study a phenomenological three-dimensional coupled (3DC) mixed-mode
cohesive zone model (CZM) is proposed. This is done by extending an improved
version of the well established exponential CZM of Xu and Needleman (XN) to 3D
contact problems. Coupled traction-separation relationships are individually
presented for normal and transverse directions. The proposed model preserves
all the essential features of the XN model and yet correctly describes
mixed-mode separation and in particular mixed-mode closure conditions.
Moreover, it provides the possibility to explicitly account for all three
components of the gap function, i.e. separations in different directions. The
3DC model has some independent parameters, i.e. interface properties, similar
to the XN model. All the cohesive zone parameters can be determined using
mode-I and mode-II experiments.
