Investigations On Buckling And Postbuckling Behavior For Advanced Composite Grid Stiffened Structure With A Delamination

A finite element method has been developed to investigate the nonlinear buckling and postbuckling behavior of advanced composite stiffened structure (AGS) with delamination under compressive load, and delamination growth in the skin during the postbuckling process was also considered. The research work of this paper is the main sub-part of the project of the National Natural Science Foundation in China "The mechanism of advanced grid structure (AGS) with damage", Grant No. 10302004, and National Basic Research Program of China "New theory of optimum design for extra-light porous materials and their structures", Grant No. 2006CB601205.On the basis of the Mindlin first order shear effect theory and the Von-Karman non-linear deformation assumption, a composite laminates element and a beam element are adopted to model the skin and the stiffener, respectively. By coordinate transformation and the geometry continuum condition of the skin and the stiffener, the element tangent stiffness matrices for the AGS are deduced. A finite element numerical method has been developed to study the nonlinear buckling, postbuckling and delamination growth of composite grid stiffened structures with embedded delamination in the skin. A progressive failure criterion is applied to describe the failure of the skin and the ribs including the damage of matrix, fiber break and fiber-matrix shear failure during the loading process. The total energy release rate is used as the criteria of delamination growth, and a virtual crack closure technique (VCCT) combined with a self-adaptive grid moving technology is adopted. A nonlinear contact element is employed to avoid the overlap of the upper and the lower sub-laminates. According to the numerical investigation of some typical examples, the effects of configuration, size, and location of the delamination, stiffness degradation caused by progressive damage failure and the stiffness ratio of ribs to skin on the buckling, postbuckling and delamination growth of composite grid stiffened structure with embedded delamination subjected to a compressive load are discussed.Linear and nonlinear buckling, postbuckling, delamination growth and failure evolvement during postbuckling are investigated for composite grid stiffened plates and shells of different stiffened forms and delamination locations, and some meaningful conclusions are obtained.