Stiffened composite panels and shells are often used in different aircraft structural design. The deformations associated with post-buckling response can produce severe bending and shear loads at the skin-stringer interface. It can cause stiffener separation from the skin. Therefore, accurate computational methods are required to analyze and predict skin-stiffener debonding failures [1-3]. To analyze the skin-stringer debonding the fracture mechanics approach has been used based on 3D solid or shell finite element analysis results. A combined shell/3D modelling technique was developed in [4]. The 3D solid finite element model is used only in vicinity of the delamination front and the remainder of the structure is modelled using plate or shell elements. Such shell/3D technique can combine the computational efficiency of the shell finite element model with the accuracy of the full three-dimensional solution in the area of delamination.