The Stability Analysis And Optimization Research Of Doubly-curved Composite Shells

Doubly curved composite shells and stiffened doubly curved shells are the typical structures in aircraft design. Its typical failure modes are buckling and a variety of damages caused by buckling. It is very important to study the stability and the post-buckling carrying capacity of doubly curved composite shells and stiffened doubly curved shells. The influence of various parameters on the stability of doubly curved composite shell and the carrying capacity are analyzed by the author; the influence of initial delamination imperfection on stability and carrying capacity is examined; meanwhile, using multi-objective optimization algorithm, doubly curved composite shell structures are optimized.The main contents are:Based on an improved arc length method (Riks) provided by Abaqus which is one of the finite element software, the influence of key parameters on doubly curved composite shell is analyzed.According to test results provided by literature, the accuracy of the analysis is verified; on this basis, the influence of ply mode, ply angles, and the number of layers on buckling and post-buckling stability of the doubly curved composite shell is discussed; the influence of curvature radius on post-buckling stability and carrying capacity of quadrilateral doubly curved shell or spherical shell is systematically analyzed. All of the above analysis leads to a conclusion that the larger the curvature radius of the structure is, the better post-buckling carrying capacity it has; the smaller the curvature radius is, the better the pre-buckling carrying capacity the structure has.Based on the calculation method of release rate of the node separation using the virtual crack closure technique (VCCT), the influence of the initial delamination and delamination growth on post-buckling stability and carrying capacity of composite plate or doubly curved composite shell is discussed. The influence of delamination depth, delamination area, delamination distribution, delamination form, radius of curvature, and other key parameters on delamination growth and the post-buckling stability is mainly discussed. It shows that the buckling center is close to the delamination center, and the thinner the thinnest sub-layer is, the higher the possibility of local buckling is and the easier delamination growth can be; the larger the stratified area is, the higher the possibility of local buckling is and the easier delamination growth can be; the larger the radius of curvature is, the clearer the sign of global buckling becomes; delamination form can also affect in-plane carrying capacity significantly.This article uses ABAQUS MATLAB, and iSIGHT to achieve single-objective and multi-objective optimization design of the structure of composite, discusses the Advantages and disadvantages of using multi-island genetic algorithm (MIGA) to achieve single-objective and multi-objective optimization design of the structure of composite; according to result of comparison, the idea of achieving multi-objective optimization of the structure of composite using non-dominated sorting genetic algorithm with elitist strategy (NSGA-Ⅱ) is proposed. Gives a example of multi-objective optimization of the stiffened cylindrical shell of composite using NSGA-Ⅱ to prove the feasibility.