Upscaling architected metamaterials for applications in civil infrastructure: auxetic lattices for confining concrete

Abstract

The current understanding of auxetic metamaterials in structural engineering applications is limited. Auxetic materials exhibit lateral contraction under compressive loads, possessing a negative Poisson's ratio. The research addresses this gap, focusing on the use of auxetics for steel reinforcement in structural concrete elements to enhance sustainability by reducing material usage without compromising safety.

The research goals include:

Describing the state of the art in auxetic materials for concrete structural elements.
Investigating auxetic behavior under different loading conditions (compression, tension, shear, and bending).
Developing a geometrical design for auxetic steel reinforcement, considering practical aspects like manufacturability and mortar flow.
Performing numerical analyses on proposed beams under various loading conditions, comparing Young's modulus and Poisson's ratio.
Exploring upscaling solutions for architected metamaterials.

The research follows a systematic approach:

Literature Study:
Examines the use of auxetics in concrete structural elements.
Selects a bow-tie architecture for its adaptability and manufacturability using Laser Powder Bed Fusion (LPBF).

Geometrical Study:
Focuses on a cantilever beam subjected to rotation, ensuring pure bending with a linear geometry.
Chooses a range of unit cell angles for desired structural behavior.
Designs unit cells and beams, considering compatibility, continuous lattice, and manufacturability.

Numerical Study:
Utilizes FEM software (ABAQUS) to analyze effective Young's modulus and Poisson's ratio.
Validates models against literature using Euler-Bernoulli beam theory.
Studies the influence of boundary conditions on results.

Upscaling Technologies:
Explores technologies for upscaling auxetic lattices beyond current LBPF methods.
Proposes multi-robotic fabrication for automated assembly using conventional rebar.

Findings and conclusions include:

Selected Architecture:
Chooses bow-tie architecture for its modifiability and manufacturability.
Proposes "single cells" and "three angle" units for different loading conditions.

Design Expansion:
Develops a stacking sequence for a 3D lattice, considering dimensions and relative density.
Creates beams with auxetic, cubic, non-auxetic, combined, and gradual behaviors.

Numerical Model Conclusions:
Affirms constant moment and zero shear in designed beams.
Emphasizes the dominance of effective modulus in lattice geometry.
Validates Poisson's ratio behavior in different beams under pure bending.

Upscaling Proposal:
Recommends multi-robotic fabrication for full-scale lattice construction.
Uses software like Rhinoceros 7 and COMPAS FAB for design and control.

In summary, the research contributes to understanding auxetics in structural applications, providing insights into their behavior under various loads, proposing practical designs, and exploring upscaling possibilities. The proposed approach and findings aim to advance the use of auxetics in steel reinforcement for sustainable and safe construction practices.