Influence of Fillers on the Post-buckling Behavior of the Hat-Stiffened Composite Panels

Post-buckling design is the modern airplane structural design practice of stiffened composite panels subjected to compressive loading, based on what, further weight reduction can be achieved. The stiffener-skin interfacial strength is critical to the load carrying capacity and the usage of fillers can be a solution to increase both the buckling load and the collapse load of the stiffened panels. In this study, the compressive buckling and post-buckling processes of the large stiffened composite panels with five hat-stiffeners and with or without fillers are studied through the compressive loading tests and finite element simulations. It is found that the buckling of the stiffened panel initiates in the skin bays which are the sections of the skin supported by the adjacent stiffeners. The usage of the fillers increases the buckling load, buckling strain and collapse load. Moreover, the stiffness of the stiffeners to support the skin bays is increased and thus, the buckling is postponed and the compressive failure process is changed. The failure initiates from skin-stiffener debonding and finally the stiffeners cripple completely. This work provides research results of the influences of the fillers on the compressive failure process of hat-stiffened composite panels, which can be used as a guide to the design of stiffened composite structures.