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In this study, the stiffener geometry was optimized using curvilinear 3D printing to enhance the buckling resistance. A bio-inspired skin/stiffener composite that mimicked spider-web structures was generated. A dataset was formulated for the regression analysis, covering buckling stresses under distinct feature values. The regression equations, crafted using a deep neural network trained on the dataset, were evaluated. The derived regression equation was subjected to sequential quadratic programming, a mathematical optimization, to determine the optimal value of the explanatory variable. This was aimed at maximizing the buckling stress-to-stiffener volume ratio, which is the objective variable. The optimized arrangement exhibited significantly improved buckling resistance, with approximately 163% higher buckling stress than conventionally designed structures with straight stiffeners of similar weight. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) laminates are used extensively in aerospace structures. The laminated CFRP composite structures require optimal design of the stacking sequences. Modifications to the stacking sequences change the thermal deformation that results from the CFRP laminate curing process. Even if a stacking sequence provides maximum buckling load, the laminate is unacceptable if it displays large deformations after the curing process. Therefore, this study deals with the constraint of thermal deformation after the curing process. Maximization of the buckling load was targeted as the objective function here. Three types of response surfaces were proposed to estimate the thermal deformation and their fit was investigated. The mode classification method was found to be excellent. Using the mode classification response surface, a stacking sequence optimization to maximize the buckling stress was performed. The new mode classification method was shown to be appropriate for optimization of the curing process constraints. [ABSTRACT FROM AUTHOR]

Abstract: For laminated composite materials, the stacking sequence design is indispensable to make efficient use of the material properties. Laminated composites are usually fabricated from unidirectional plies of given thickness with limited fiber orientations to a small set of angles (e.g. 0°, +45°, 45°, and 90°). An improved version of fractal branch and bound method has been proposed to optimize multiple stacking sequences. The improved method, however, cannot be applied to complicated structures, since it is difficult to determine which is the most effective surface for designing such structures. In the present study, therefore, a new iteration fractal branch and bound method is proposed, which does not require empirical knowledge of the target structure. Here, this method is applied to a hat-stiffened panel to enable the stacking sequences of the two panel laminates and hat-type stiffener to be optimized simultaneously. [Copyright &y& Elsevier]

Stiffened composite panels are often used as structural components in aircraft in order to avoid buckling. It is well known that stacking sequence optimizations are indispensable for laminated composite structures. Stiffened composite panels usually have more than two stacking sequences because they consist of a panel skin laminate and stiffener laminates. This means that the stacking sequences need to be jointly optimized to achieve structural optimization of the stiffened composite panel. The authors have proposed a new stacking sequence optimization method, called the fractal branch and bound method, for optimizing a single laminate. In the present study, the fractal branch and bound method is extended to optimizing multiple stacking sequences. The extended method is applied for obtaining two optimal stacking sequences for the maximization of the buckling load of a hat-stiffened composite panel. The improved method successfully provides two optimal stacking sequences determined in a short period of time. [ABSTRACT FROM AUTHOR]

The fractal branch and bound method was developed by the authors for optimization of stacking sequences to maximize buckling load of composite structures. The method demands an approximation of a design space with a response surface comprising quadratic polynomials for pruning fractal branches of stacking sequences. Approximation of the objective function with quadratic polynomials was confirmed for buckling load maximizations and flutter speed limit maximizations using lamination parameters as predictors. In the present study, flutter speed maximization with a constraint of buckling load is employed as an example of stacking sequence optimization by means of the fractal branch and bound method with a strength constraint. The present paper describes the theoretical background of the fractal branch and bound method. Then approximations are performed using quadratic polynomials with lamination parameters as predictors. After that, effectiveness of this method for supersonic panel flutter of composite laminates was investigated using two cases. Results indicate that the method was applied successfully; a practical optimal stacking sequence was obtained using modified response surfaces. [ABSTRACT FROM AUTHOR]

A new intron method is proposed to optimize stacking sequences and number of plies of composites. The intron method is developed from the recessive-gene-like repair method that is employed for implementation of stacking-sequence constraints without causing decrease of the design reliability of GA. The intron method is attempted for the optimizations of laminated cylinders to maximize the buckling load and minimize the number of plies. As a result, the intron method successfully obtained the real optimal stacking sequences and the number of plies without decrease of design reliabilities. [ABSTRACT FROM AUTHOR]

The present paper proposes a new modified global response surface method using lamination parameters to overcome the problem of how to create zoomed response surfaces. The present study also proposes a new low-cost rule for optimality. The new optimality rule is better for the search-all-branches method for relatively thin laminated composite structures. The new method is applied to a stacking sequence optimization problem of a composite plate with hat-type stiffeners for maximizations of buckling load. FEM analyses are conducted to create a global response surface and the optimal stacking sequence is obtained by using the proposed method. As a result, the new method successfully obtained the true optimal stacking sequence and reduced the computational cost. [ABSTRACT FROM AUTHOR]

Stacking sequence optimizations for composite laminates are combinatorial optimization problems often handled by genetic algorithms (GA). Unfortunately, GAs often require large computational resources for individual evaluation. To overcome this problem, this paper proposes use of lamination parameters in an optimization process approach with GA. The optimization process requires precise approximation of design space using response surfaces to obtain the true optimal result. However, stacking sequence optimizations are discrete optimization problems and it is difficult to judge optimality of an obtained result on the lamination parameter space. For zooming response surfaces, we require an optimality check method. In this study, laminates adjacent to the obtained optimal result are introduced on the lamination parameter space and an optimality-check-test method is proposed. The test method is applied to a buckling load maximization problem of a laminated composite plate; its effectiveness is confirmed by example. [ABSTRACT FROM AUTHOR]