Stiffeners are widely used as building blocks of a wide range of engineering structures because they provide better resistance without significantly increasing the overall weight of the structure. However, stiffened composite structures are subjected to multi-field loading in extremely complex operating environments, which will degrade the strength and may eventually lead to failure of the structure. The presence of a discontinuity in the form of interlayer delamination or interfacial debonds in stiffened composite plates detrimentally affects the structure’s safety and durability. These defects may grow to a critical size, which becomes unstable, causing the entire structure's catastrophic failure. On the other hand, the plates provided with cutouts are extensively used in transport vehicle structures. Cutouts are provided to lighten the structure, for ventilation, and to provide accessibility which degrades the strength of the structures. This will show a completely different behaviour of the structure, so it becomes necessary to study this characteristic.

Buckling characteristics and vibration behaviour of laminated/ delaminated stiffened plate subjected to in-plane edge loading is studied using the Finite Element technique. The 9-noded isoparametric heterosis plate elements have been used to model the panel and the stiffener’s flange, and the 3-noded isoparametric beam element is used to model the web of the stiffener. The debond is introduced at the plate-stiffener interface by creating dummy nodes at the interface, and the fictitious springs are employed to prevent the interpenetration of the nodes. 

Apart from the study related to static stability and vibration problems, a study will be conducted to assess and quantify the damage in the delaminated stiffened plate by using the vibrational approach.