Damage Propagation And Failure Analysis Of Damaged Composite Sandwich & Stiffened Plates

The dissertation is focus attention on a numerical simulation for the damage propagation and failure characteristic of damaged composite sandwich and stiffened plates during compressive loading process, which is a sub-part of the project of National Science Foundation in China "Damage Propagation, Failure and Load Capability" (No.59975014). The analytical models, methods and techniques established in the research work are useful for the analyzers and designers of composite engineering structures, and the conclusions given by some parametric discussions are essential to get a better understanding of mechanism for the damage tolerance design.The research in the dissertation consists of two major parts, which main contents for each of the chapters are briefly introduced as follows:Part I: Damage and Failure Analysis of damaged Composite Sandwich PlatesIn chapter 1, a state of arts for study on low-velocity impact and residual compressive strength of the composite sandwich structures is systematically summarized, and then the research orientation and contents for the dissertation are put forward.In chapter 2, a finite element model for the composite sandwich plates is developed, based on the Zig-Zag deformation assumption and the first order shear deformation theory, and the finite element buckling analysis governing equations for the plates under mechanical, thermal and/or thermal-mechanical mixed loads are deduced respectively. By Von -Karman nonlinear deformation relations and Total Lagrange formulation, an incremental governing equation for postbuckling analysis is established and a corresponding effective computational scheme is presented..In chapter 3, some essential models of the buckling and postbuckling analysis for the damaged composite sandwich plates are constructed, which are delamination model, bridging model, multi-scalar damage model and contact model; respectively. A flow chart of the computational program is described. The buckling critical loads and corresponding modes for the damaged plates under the mechanical, thermal and/or thermal-mechanical mixed loading cases are investigated, respectively. By some typical numerical examples and discussions, it can be seen that, the effects of the sizes of matrix micro-cracking and interfacial crack between the face and core, and the bridging stiffness upon the buckling critical loads and modes are significant.In chapter 4, an effective postbuckling numerical analysis method is developed, which is based on the Global-Local variational principle. The influences of contact effect, sizes and shapes of the matrix micro-cracking and face/core interfacial crack, ply angles of the laminated faces and boundary conditions of the plates etc. upon the postbuckling behavior of the damaged composite sandwich plates are also discussed.In chapter 5, a brief introduction of some calculating methods for energy release rate (ERR) of the crack bodies is presented. The values of the total strain energy release rate alongthe front contour of the face/core interfacial crack are predicted by using virtual crack closure technique (VCCT). An effective mesh scheme is given. From some typical numerical examples, the effects of geometrical nonlinearity, interfacial crack sizes and shapes upon the distribution of ERR along the front contour of the face/core interfacial crack are studied. In chapter 6, the main contributions of part I are given.Part II: Damage Propagation and Failure Analysis of damaged stiffened PlatesIn chapter 1, a current achievement for study on the buckling, postbuckling behavior and delamination growth of laminated beams, plates and stiffened plates with/without delaminations is surveyed, and a brief research description of the dissertation is presented.In chapter 2, a tangent stiffness matrix formula of four-node C?element for the laminated plate is deduced, which is based on the first order shear deformation theory and the Von -Karman nonlinear deformation assumption. The advantages of the element are superior precision and wit...