Analysis And Optimization Design For Thin Wall Stiffened Composite Panels

Thin wall stiffened composite panels, with efficient weight loss and good design property, were widely used in aircraft and aerospace structures under compression loads. In this paper, system structure research for thin wall stiffened composite panels based on stiffened composite element method was carried out, in which the initial imperfection was introduced in the process of analysis, and the damage cumulative of stiffness degradation is also considered, moreover, the cohesive cohesion bond unit for simulation the debonding failure of the skin and stiffener was developed. On the basis of the structure analysis, optimization design of thin wall stiffened composite element panel containing cohesive cohesion bonding unit was proposed in this paper. There are two steps in the optimization process, the first step is layout size update sequence optimization design based on agent model, and the second step is layer order optimization design based on Multi-Island genetic algorithm (MIGA).The main work of this paper includes the following two parts:(1) Structure analysis method of thin wall stiffened composite panels was investigated. Firstly, eigenvalue instability buckling analysis was done for thin wall stiffened composite element panel, and top five order buckling instability mode and corresponding buckling factor of the structure can be obtained. Then nonlinear buckling analysis was carried out, while the first order eigenvalue buckling mode was regarded as initial imperfection in structure analysis. By comparing the results with that of neglecting initial imperfection has verified the necessity of initial imperfection in analysis for such structure. After that the principle of damage cumulative with stiffness degradation was introduced in the structure analysis and the results meet well with composite material damage process step by step. Finally, the debonding of skin and stiffener was modeled by cohesive cohesion bond unit, and this made the simulation more realistic for the structure analysis under compression load. At last, the results obtained in this article were compared with the experimental results in the COCOMAT, which confirmed the effectiveness of the above method for composite stiffened panel structure analysis.(2) Optimization design of thin wall stiffened composite element panel considering cohesive cohesion bond unit is put forward. The optimization process includes two steps, and the main ideal of the optimization is as follows:firstly, the design of experiments (DOE) of Optimal Latin hypercube design in Isight was introduced to collect sample points in the first level optimization, and then to calculate the response value of the sample points in ABAQUS; after that, the mass and buckling factor kriging agent model was set up with the sample points and the corresponding response value; follow on, structure layout size optimization design was carried out with the minimum update sequence quadratic programming method (NLPQL). The second level optimization is layer order optimization of the skin and stiffener based on the previous step optimization results by Multi-Island genetic algorithm (MIGA). Finally, the optimization design scheme of thin wall stiffener composite element panel with cohesive cohesion bond unit was established and by comparing to the initial design results indicated that the optimization effect is very significant, meanwhile, the optimization results is checked in ABAQUS, and the results shows that the accuracy of the optimization model is high.The research of this paper is supported by the Fundamental Research Funds for the Central Universities "The failure theory and optimization design of integration of light weight thin wall composite panels (DUT12LK02)." of Dalian University of Technology and the National Basic Research Program of China (No.2014CB046506).