Repurposing Grain Boundaries for Graphene Origami Auxetic Metamaterials with Enhanced Fatigue Resistance.

Abstract

Graphene represents the pinnacle of intrinsic material strength, yet it remains functionally limited by a lack of plasticity and severe degradation in mechanical performance associated with porosity-driven upscaling. Although graphene origami (GOri) offers a deterministic alternative to porous networks, its realization has been restricted to chemically functionalized, metastable frameworks. Here, we demonstrate a computational design strategy that repurposes grain boundaries (GBs) observed in large-scale chemical vapor deposited (CVD) graphene as topological precursors for stable GOri structures. Using molecular dynamics (MD) simulations, we show that periodic pentagon-heptagon (5-7) ring arrays within the tilted GBs can facilitate out-of-plane corrugations of the graphene domains, mimicking macroscopic folding creases without chemical modification. Our study also shows that the mechanical response of the proposed structure is highly tunable via linear grain size (µ) and dimensionless aspect ratio (α), enabling a wide range of control over tensile strength, elastic modulus, and negative Poisson's ratio (NPR), reaching -3.77. Furthermore, the developed GB-GOri architecture achieves a 20% enhancement in fatigue strength and a fatigue life exceeding 150% of that of functionalized counterparts through pseudo-plastic deformation. Effectively, this GB-assisted defect engineering promotes stable crack growth and provides proof-of-concept for the future experimental fabrication of graphene-based auxetic metamaterials.

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