Abstract A model for analyzing mixed-mode delamination problems in laminated composite plates under general loading conditions is studied. The first-order shear deformable laminated plate theory and the interface methodology, which in turn is based on fracture mechanics, are adopted. The laminate is modeled as an assembly of laminated plate and interface layers in the thickness direction. When the limit case of interface stiffness coefficients approaching infinity is considered, a perfect adhesion between plate models is simulated. On the other hand, delamination between sublaminates is taken into account by assuming zero values for interface stiffnesses. Lagrange and penalty methods are adopted to simulate connections between plate elements. By using a variational approach and the virtual crack closure concept, expressions for total energy release rate and its mode components along the delamination front are obtained, in terms of both interface variables and plate stress resultant discontinuities. These ...