On the basis ofa 2D 4-node Mindlin shell element method, a novel self-adapting delamination finite element method is presented, which is developed to model the delamination damage of composite laminates. In the method, the sublaminate elements are generated automatically when the delamination damage occurs or extends. Thus, the complex process and state of delamination damage can be simulated practically with high efficiency for both analysis and modeling. Based on the self-adapting delamination method, linear dynamic finite element damage analysis is performed to simulate the low-velocity impact damage process of three types of mixed woven composite laminates. Taking the frictional force among sublaminations during delaminating and the transverse normal stress into account, the analytical results are consistent with those of the experimental data.
The reliability based optimization （RBO） issue of composite laminates trader fundamental frequency constraint is studied. Considering the tmcertainties of material properties, the frequency constraint reliability of the structure is evaluated by the combination of response surface method （RSM） and finite element method. An optimization algorithm is developed based on the mechanism of laminate frequency characteristics, to optimize the laminate in terms of the ply amount and orientation angles. Numerical examples of composite laminates and cylindrical shell illustrate the advantages of the present optimization algorithm on the efficiency and applicability respects. The optimal solutions of RBO are obviously different from the deterministic optimization results, and the necessity of considering material property uncertainties in the composite structural frequency constraint optimization is revealed.
An adaptive approximation-based optimization （AABO） procedure is developed for the optimum design of a composite advanced grid-stiffened （AGS） cylinder subject to post-buckling. The design taking account of post-buckling under ultimate load will be able to promote the structural efficiency compared to the conventional design in which only the linear buckling is allowed. The beam-shell offsets technique is utilized for modeling the stiffener-skin connection, and the Newton-Raphson method is employed for the post-buckling analysis. A few structural analysis efforts are carried out for establishing the Kriging model of the collapse load of the AGS cylinder for optimization to significantly increase the optimization efficiency. The multi-island genetic algorithm （MIGA） is utilized for global optimum search. An adaptive approximation framework is proposed to resolve the computational burden caused by the large domain of design variables, and it is demonstrated that much less computational expense than that of the traditional approximation-based optimization method can be achieved. The utility of making use of commercial optimization package iSIGHT in conjunction with the finite element （FE） code MSC.MARC to develop the preliminary design tool of the composite AGS cylinder is evaluated as well.
