Geometry projection for additively manufacture variable stiffness continuous fiber-reinforced polymer structures—A unified topology optimization approach for multi-layered composite laminates

Continuous fiber fused filament fabrication (CF4) is a layer-by-layer technique used to print carbon fiber-reinforced polymers (CFRPs) with a spatial in-plane variation of the fiber orientation, thus offering great flexibility in fabricating variable-stiffness CFRP laminates (VS-CFRP-Ls). However, not only is the design of VS-CFRP-Ls unintuitive, but the material directionality also introduces a nonconvex design space further amplified by the various VS-CFRP-Ls' design parameters. Designing multi-layered VS-CFRP-Ls, therefore, requires advanced computational design tools---such as topology optimization based on the geometry projection method---to take full advantage of the design freedom compatible with CF4. This thesis addresses these challenges by developing computational tools for optimizing multilayered VS-CFRP-Ls. Unlike constant stiffness composites, VS-CFRP-Ls lack analytical formulations, necessitating discretization techniques like finite element analysis. The research develops and investigates several topology optimization formulations to streamline the design process, considering CF4's manufacturing constraints and material distribution strategies. The method reduces design variables by employing geometry projection within TO while ensuring manufacturability. Extensions of this approach cater to additive manufacturing requirements, yielding multilayered VS-CFRP-L designs with enhanced mechanical properties. Numerical examples demonstrate the efficacy of the proposed methodology in achieving stiffness-driven VS-CFRP-Ls designs, which can be manufactured using conventional and additive manufacturing processes.