Maximizing Buckling Load Factors of Fiber-Placed Composite Cylindrical Shells by Particle Swarm Optimization

Abstract

Automated Fiber Placement (AFP) is a highly automated manufacturing process which has made it possible to manufacture composite parts utilizing curved tow paths resulting in variable stiffness composite structures. Variable stiffness concept can be sought in an optimization framework for favorable structural response. The purpose of this paper is to show how the structural behavior of the composite cylindrical shell can be improved through the use of fiber placement technology in the manufacturing phase of the layers of the cylindrical shell of revolution. For this purpose, a methodology is developed for generating the finite element model of tow-placed variable-stiffness laminated composite cylindrical shells. The developed method allows the calculation of the ply thicknesses including the gaps and overlaps which occur as a result of the manufacturing of the plies of the cylindrical shell using curvilinear fiber paths. For the optimization of the reference fiber path, an optimizer based on Particle Swarm Optimization (PSO) is developed. Both axially variable stiffness and circumferentially variable stiffness cylindrical shell concepts are studied. Buckling load factors of fiber-placed cantilevered composite cylindrical shells are maximized considering the manufacturing constraints and the thickness change due to the occurrence overlaps in the fiber placement process. Buckling loads factors of axially variable stiffness and circumferentially variable stiffness cylindrical shells are determined for different load cases including bending, torsional and axial loading. Optimization results are also compared with results of the baseline constant stiffness cylinders for which ply angle optimizations are also performed. Results show that higher buckling load factors can be obtained for variable stiffness cylinders compared to the constant stiffness laminated cylinders. For the load cases studied, results also show that axially variable stiffness cylinders have higher buckling load factors compared to circumferentially variable stiffness cylinders. It is also shown that by using more parameters in the definition of the reference fiber path around circumferential direction, higher buckling load factor values can be obtained compared to the linear variation of the fiber orientation angle in the circumferential direction.