Stiffness degradation of composite skin fields due to strength and buckling onset

Abstract

Suitable and fast calculation methods with sufficient accuracy are required to optimise large composite structures. The present paper introduces a progressive stiffness degradation analysis (PSDA), which computes skin buckling onset and strength failure initiation of skin fields separated by stiffeners, as well as the subsequent damage propagation using closed form solutions. This constitutes a simplified, but much faster approach compared to state of the art progressive failure analyses, which incorporate finite element simulations. Therefore, the computational effort can be reduced. This paper illustrates the process of the PSDA and then verifies this simplified approach by means of one example.

Metaheuristic Optimization of Laminated Composite Plates with Cut-Outs

“…The design variables in the optimization process are ply thickness and fiber angle orientation. Primarily, the laminates consist of nine layers, as per Führer [42]. Concerning the choice of optimization technique, Cakiroglu et al [23] have shown that the harmony search (HS) optimization technique was capable of obtaining dispersed stacking sequences that perform better than conventional sequences, such as the [45, −45, 0, 90, 0, 90, 0, −45, 45] fiber angle sequence used by Führer [42].…”

“…Primarily, the laminates consist of nine layers, as per Führer [42]. Concerning the choice of optimization technique, Cakiroglu et al [23] have shown that the harmony search (HS) optimization technique was capable of obtaining dispersed stacking sequences that perform better than conventional sequences, such as the [45, −45, 0, 90, 0, 90, 0, −45, 45] fiber angle sequence used by Führer [42]. The present study adopted the optimum stacking sequence from the analyses done by Cakiroglu et al [23] as a starting configuration and further improved this stacking sequence in the presence of cut-outs.…”

“…As the starting configuration for the stacking sequence, the best-performing layup is taken from the previous study by the authors for all three aspect ratios [23]. These layup configurations are further optimized, and the results are compared to the performance of plates with cut-outs having the regular stacking sequence from Führer [42].…”

“…Due to constraints related to manufacturing techniques, the layer thicknesses were kept above 0.1 mm in all design vectors. Another design constraint was the total laminate thickness which was not allowed to exceed 2.25 mm to keep the results comparable to the study of Führer [42]. The initial population of candidate solution vectors is updated throughout the harmony search optimization.…”

“…The buckling loads of rectangular composite laminates with circular, rectangular, and triangular cut-outs under uniaxial compression are maximized using the harmony search process. Layer thicknesses and fiber orientation angles of the nine layers [42] constitute design vectors with eighteen design parameters. The population of design vectors consists of ten vectors of eighteen variables.…”