Design, Analysis and Experimental Evaluation of 3D Printed Variable Stiffness Structures

Abstract

The rapid progress of additive manufacturing (AM) introduces new opportunities but also new challenges for design and optimization to ensure manufacturability, testability and accurate representation/prediction of the models. The present dissertation builds a bridge between design, optimization, AM, testing and simulation of advanced optimized variable-stiffness structures. The first part offers an insight on the mechanical, viscoelastic and failure characteristics of AM continuous fiber composites. This understanding was used in the second part to investigate the feasibility of different topology and fiber-orientation optimization methods and the manufacturability of the resulting models. The study also assesses the effects of the manufacturing constraints on the stiffness. In the third part, a framework was used to optimize the topology and orientation of lattice structures subjected to stress constraints. This framework uses homogenized stiffness and strength to expedite the optimization, and Hill’s criterion to express the stress constraint. Those properties are implemented in the macrostructure topology optimization to improve the lattice structure stiffness. The optimized design is projected and post-treated to ensure manufacturability. The framework tested for two case studies producing designs with enhanced yield strength. The last part of this research challenges the capabilities of AM to fabricate, for the first time, an optimized flexible wing model with internal structures. The wing was tested in a low-speed wind tunnel to validate a robust computational model which enables the future study of the aeroelastic performance of different optimized wing models. This dissertation demonstrates that the conjoint use of topology and orientation optimization and AM results in advanced lighter structures with enhanced stiffness and/or strength