Compression Research Of 3D Woven Composites Stiffened Panels

Stiffened panels are widely used in aerospace structures,such as fuselages and wings,mainly because of their high efficiency in terms of stiffness to weight and strength to weight ratios,as well as improving the production efficiency and economic efficiency.Distincting from traditional laminates,3D woven composites,reinforced with three dimensional textile preforms and fully integrated by continuous fiber with multi-axial in-plane and out-of-plane fiber orientations,exhibit various remarkable advantages.The out-of-plane fibers provide additional stiffness and strength in the thickness direction to restrain the delamination,as well as to improve the property of the connection zone.Therefore,it is of great practical value to study the mechanical properties of 3D woven composite stiffened panels.The panel is 2.5D interlock woven composites(2.5DIWC),while the straight-stiffeners are 3D woven orthogonal composites(3DWOC).They are coupled together with the Z-fibers from the stiffener passing straight thought the thickness of the panel.The nature of woven composites is not uniform at the micro scale,but it can be idealized as homogeneous medium with equivalent anisotropic properties.In this paper,four different micro-models are established to analyze their mechanical properties by using the finite element method.Then,the whole reinforcement structure is reconstructed with a set of cells,and the mechanical properties of 3D woven composites stiffened panels are finally predicted.Based on Ha-shin failure criterion,a progressive damage model is carried out to simulate the compressive behavior of the stiffened panel.The 3D woven composite stiffened panels are manufactured using RTM process and then tested.A good agreement between experimental results and numerical predicted values for the compressive failure load is obtained.From initial damage to final collapse,the panel and stiffeners do not separate each other in the connection region.The main failure mode of 3D woven composite stiffened panels is compressive failure of fiber near the loading end corner.The thesis was completed in the State Key Laboratory of Mechanics and Control of Mechanical Structures.