Session: 13-13-01: Functional Origami and Kirigami-inspired Structures and Materials

Paper Number: 172596

Mechanical Response of Origami-Based Architected Materials: Effects of Geometry and Material Properties 

Origami-based mechanical metamaterials have emerged as promising candidates for lightweight, deployable, and tunable structures due to their inherent foldability, auxetic behavior, and large deformation recoverability. Among these, the Miura-Ori pattern is particularly notable for its single degree-of-freedom (DOF) kinematics and geometric programmability. By joining mirrored Miura-Ori strips into tubular assemblies, the structures maintain their flat-foldable nature while enabling more versatile configurations. When arranged in aligned or rotated (zippered) fashion, these tubes enable architected materials with direction-dependent stiffness. In this work, we define the X-direction along the length of the Miura-tubes, with Y- and Z- at the tubes' cross-section. The tubes are aligned along the Z-direction and zipper-coupled along the Y-direction.  With a single-DOF kinematics, the assembly allows bidirectional folding (X- and Y-directions) and reversible auxetic behavior characterized by a switch in the sign of Poisson’s ratio.

Prior research has developed analytical models to describe the kinematics and Poisson's ratio of zipper-coupled metamaterials and employed numerical simulations to investigate how folding angle influences stiffness. However, experimental studies have remained limited in scope, focusing primarily on manufacturing aspects. No experimental work to date has systematically examined the effects of folding angle and material properties on tunability and scalability (via geometric magnification) of mechanical behavior  (e.g., stiffness). 

This study presents a systematic characterization of zipper-coupled metamaterials fabricated via 3D printing using three common polymers with distinct mechanical properties: Polylactic Acid (PLA), Polyethylene Terephthalate Glycol (PETG), and Thermoplastic Polyurethane (TPU). Samples with initial folding angles of $\psi = 35^\circ$, $40^\circ$ and $55^\circ$, and panel thicknesses of $0.5\,\text{mm}$ and $1\,\text{mm}$ were tested under quasi-static compression in the principal X-, Y-, and Z-directions. 
Key mechanical metrics, including absorbed energy, peak force, and stiffness, were obtained to assess the influence of geometry and material on mechanical performance and anisotropy.

The resulting zipper-coupled origami metamaterials demonstrated pronounced tunability governed by extrinsic geometric parameters determined by the initial folding angle ($\psi$). Panel thickness had a substantial effect on overall stiffness, while its influence on the degree of anisotropy was more subtle.  Specifically, at lower initial angles, stiffness in the Y-direction was most significantly affected by panel thickness. Conversely, for other directions, a general trend of decreasing anisotropy between X- and Z-direction stiffness was observed with higher extension (i.e., lower initial angle). 

The non-foldable Z-direction generally exhibited the highest stiffness, particularly in samples with thicker panels. This direction also showed a range of responses to folding angle, varying with each material's intrinsic properties (e.g., brittleness). The observed behavior in the Z-direction captured out-of-plane effects not accounted for in existing analytical models. The stiffness in the foldable X- and Y-directions was influenced almost oppositely by the initial folding angle: X-direction's stiffness decreased with increasing folding angle (lower extension), while Y-direction stiffness generally increased. These trends align with numerical predictions. The Y-direction consistently exhibited the lowest stiffness, never exceeding half of the stiffness measured in the X-direction. Notably, the magnitude of these anisotropic effects was also geometry- and material-dependent, with higher $\psi$ generally increasing relative stiffness changes between directions, specifically in more flexible materials.

In flexible materials such as TPU, the X-direction absorbed significantly more energy at lower angles, though both peak value and anisotropy decreased with increasing angle, becoming nearly isotropic at $\psi = 55^\circ$. Conversely, for more brittle materials (e.g., PLA), the non-foldable Z-direction often exhibited the highest energy absorption at higher folding angles and panel thickness.
To assess scalability, we fabricated samples with all geometric dimensions doubled and evaluated whether stiffness scaled proportionally. Results indicate that this relationship is material-dependent; stiffness scales more consistently with geometry in flexible materials.  Our findings highlight the programmable mechanical behavior of zipper-coupled origami metamaterials under compression, supporting their potential use as load-bearing, directional energy absorbers in aerospace and protective systems.

Presenting Author: Melika Alavi Rice University

Presenting Author Biography: Melika Alavi is a Ph.D. student in Civil Engineering at Rice University, specializing in advanced structural mechanics and mechanical metamaterials. Her current research focuses on origami-based structures for applications such as tunable and energy-absorbing devices. She holds a B.Sc. and M.Sc. in Mechanical Engineering, with prior research on lattice-based sandwich structures.

Authors:

Melika Alavi Rice University
Larissa Novelino Rice University