Laminated Composite Shell Structure Parameters To Optimize The Design And Stability Analysis

Composites have stronger specific strength, higher specific stiffness, lower density, and better fatigue threshold behavior than metals, which has been widely applied for astronautical and aeronautical structures.The design optimization of composite laminates can improve the cost effective, combat and flight abilities of aircraft with a lighter structure weight meeting structural stiffness and strength design requirements. Shell structure may cause large deformation when suffering to more serious applied force, which would lead to nonlinear geometrical problem and structural load-carrying instability. In this view, structural geometrical nonlinearity and post buckling stability under some loading forms should be analyzed.The thesis briefly outlines the algorithmic theories and iterative methods of parametric optimization, and designs the optimal algorithm procedure and flow chart for composite laminated structures. Taking ply depths of composite laminated skin as design variables, the static analysis and optimization design of composite vertical wing structure of a helicopter is performed, with ANSYS software system, for its light weight objective under given structural stiffness and strength, in which, APDL-command facilities is applied to achieve structural geometrical model, static analysis and structural design optimization.The thesis discusses the application of finite element numerical analysis in composite shell structure stability, which covers the following contents: (1) nonlinear strain relation and displacement interpolation principle; (2) second-order functional variation and eigenvalue equation of strain energy for shell structure; (3) a set of numerical algorithmic procedure for solving large-scale algebraic equations. The thesis briefly introduces arc-length methods for geometrical nonlinear solution, including linear arc-length, spherical arc-length methods and explicit iterative format of spherical arc-length constraint. As guidelines of the foregoing theoretical work, the nonlinear analysis of composite veritical structure of a helicopter and a laminated composite wing of some unpiloted plane are computed and analyzed with MSC. Marc software system, in which PCL-command facilities were applied to obtain structural geometrical model, static analysis and nonlinear analysis.