An efficient approach to the design of damage tolerant CFRP stiffened panels

Due to the high stiffness-to-weight and strength-to-weight ratios, Carbon Fiber Reinforced Polymer (CFRP) based composite materials are gaining increasing attention and growingly applied in modern aircraft structures. As one of the load-carrying members, the stiffened panels are widely used in the aircraft structures, such as: fuselage, wing and tail. These thin walled panels will buckle under the compressive or shear loading, which is a major consideration in the design process. However, in order to fully exploit the large post buckling reserves of CFRP stiffened panels, their damage behaviour and failure modes must be well understood. Being the anisotropic nature of strength/stiffness properties of CFRP structures and highly nonlinear nature of post buckling analysis brings unique challenges for the design and analysis. In this research, a parametric model based on the Global Local Analysis has been developed to determine damage tolerance of the CFRP panels. A Progressive Damage Model and Bilinear Cohesive Zone Model (CZM) with linear softening characterization have been used for the intralaminar and interlaminar damage (skin/stiffener de-bond) analysis respectively. The model has been validated by analysing Hat and T stringer stiffened Single Stringer Compression Specimens (SSCS) and a fair comparison has been found with literature available numerical and experimental data. Meanwhile, a simplified model has been proposed for Hat stringer stiffened SSCS panel, which make the parametric model computationally efficient. For the parametric design of the panels like the de-bond size/location, mesh sensitivity study, stiffener size etc. the simplified model increases the computational efficiency with satisfactory accuracy.