Mechanics of 3D Printed Multi-material Metamaterials with Cooperative Components

Abstract

Conventional mechanical metamaterials often exhibit unique mechanical properties arising from their geometric arrangement. Metamaterials with cooperative components are deliberately designed with a focus on the interaction between individual elements, where the properties of these elements are engineered to work together synergistically to achieve targeted behaviors and properties. This dissertation aims to design and explore the mechanics of mechanical metamaterials with cooperative components. These components are designed to have specific shapes, sizes, and material properties to enable unusual mechanical properties including negative Poisson's ratio, programmable deformation, and significantly enhanced toughness. In Chapter 2, the fundamental mechanics of two-phase laminae fabricated via multi-material polymer jetting is investigated. The influences of printing direction, layer thickness, and material mixing at dissimilar material interfaces on the overall mechanical properties of 3D-printed laminae are systematically analyzed. In Chapter 3, bio-inspired two-phase auxetic chevron composites are designed. By cooperatively tuning two levels of laminae with different principal directions, the effective Poisson’s ratio is shown to be tunable across a wide range, from positive to negative. Unlike cellular auxetic materials, these new designs eliminate voids and pores, achieving auxetic behavior without sacrificing stiffness. Furthermore, the designs demonstrate significant potential for resisting impact, enhancing mechanical stability, and efficiently reducing thermal stresses. In Chapter 4, the static and dynamic mechanical responses of 3D auxetic laminates are investigated. Using Classical Laminate Theory (CLT) and finite element simulations, the interplay of fiber orientations, phase stiffness, and impact dynamics is explored. Experiments validate the auxetic laminates’ ability to dissipate energy efficiently and reduce damage under impact. In Chapter 5, a novel class of three-dimensional (3D) auxetic chevron-patterned composites is introduced, designed to exhibit negative Poisson’s ratios in two orthogonal planes under uniaxial compression. Comparative mechanical testing demonstrates that the auxetic designs significantly outperform non-auxetic and unidirectional counterparts in energy absorption, achieving a 4–6-fold improvement due to effective load redistribution and bending-dominated deformation mechanisms. In Chapter 6, the role of fiber waviness in enhancing the toughness of polymer composites is investigated through sacrificial bonding and hidden length mechanisms inspired by biological materials. Utilizing multi-material 3D printing, composites with varying waviness levels are fabricated and tested, demonstrating improved energy absorption, strain hardening, and resilience to strain-rate effects while preserving stiffness.