During the past few years, in comparison to traditional riveted structures, integral metallic skin stringer structures have played more and more important roles in aircraft design due to the fact they are economical and also have the ability to reduce weight. Their wide application in aircraft, especially large integral structures is limited because of the fact that they have shortcomings in damage tolerance performance. Hence, calculating the crack growth lives and improving the damage tolerance performance of integral structures by selecting appropriate materials or choosing rational structures is a critical work. Therefore the purpose of this thesis is to find effective analysis methods of integral metallic skin-stringer panels for the use in engineering. Cont/d.

The use of composite materials brought a tremendous breakthrough in the scientific world of aerospace engineering. The lack of understanding of the failure of composite materials can be disastrous. Composite laminated structures need to be thoroughly studied and investigated in the design stage. In this thesis, formed-hat skin stringer made of composite laminates is investigated. Delamination is the most common failure of laminated composites, which has two stages delamination onset and delamination propagation. In the preliminary design phase, firstly the structures need to be investigated for low-velocity impact to check the formation of damage onset due to the impact that may arise during manufacturing. In the detailed design phase, the structure is investigated to study the evolution of delamination growth under loading conditions. The structure is modeled using 3 D elements because of the presence of Interlaminar stresses in the width and thickness direction and anisotropic nature. In this thesis, more emphasis is given on the interface between the skin and the stringer. The debonding effect of the interface is studied using cohesive zone model(CZM).