Assessing the Efficacy of Process-Specific Topology Optimization for Direct-Ink Write 3D-Printed Hierarchical Composites and Structures

Abstract Polymers are ubiquitous in modern society. From food packaging to structural components inaerospace applications, plastics can be found. For applications like the latter, there is a requirement for exceptional performance characteristics - whether that be with respect to mechanical stiffness or strength, thermal or electrical conductivity, or other desirable engineering outcomes. As a result, much effort has been exerted in industry and academia toward optimizing the performance of structural components made out of polymers. Performance optimization of structural components, generally speaking, is a multi-layered problem. One layer of this problem is the material design problem – tailoring the properties of the material (by changing/adding to the manufacturing process, leveraging composites, etc.) in the desired component to have certain characteristics. Another layer is the structural design problem – the geometric features of the component (such as shape and topology) that govern its performance in service, such as under mechanical or thermal loading. For polymers, additive manufacturing (AM) is a tool which is very amenable to tailoring, both in terms of material behavior and structural geometry. Its use, in conjunction with structural optimization techniques (e.g. topology optimization, or TO) is the subject of this thesis. First, numerical and experimental benchmarking is presented on minimum mechanical compliance optimization and material extrusion AM techniques (fused filament fabrication, or FFF, and direct-ink writing, or DIW). A major focus of the benchmarking work is the analysis of the impact of mechanical anisotropy and material extrusion orientation on the outcomes of minimum compliance TO designs. Finite element calculations are performed using Matlab scripts and commercial software (ABAQUS) to complement flexural testing of AM specimens made of ABS polymer or epoxy-based polymer matrix composite inks. Next, analysis of multi-material topology optimization (MMTO) and multi-material additive manufacturing (MMAM) is presented. An analysis of choices regarding extrusion of material at the interfaces between materials is presented with corresponding experimental testing (e.g., printing and flexural testing) of specimens with disparate interface designs. Finally, numerical work towards the multi-material thermomechanical optimization of structures with orthotropic material behavior is presented. The main contributions of the thesis work lie in: (i) establishing baseline numerical and experimental evaluations of TO/AM structures using standard TO and AM methods (e.g. SIMP, material-extrusion AM with common infill patterns) (ii) quantifying the impact of process-specific design methodologies for the orientation design of orthotropic composites (iii) presenting a new application of optimization in multiphysics and multi-material TO for isotropic/orthotropic materials that considers elastic compliance and thermal conductance and (iv) initial experimental assessments of printing methodologies for their integrity at material interfaces in multi-material TO structures.