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Abstract This study investigates the development of thermoplastic polyurethane (TPU) filaments incorporating multi‐walled carbon nanotubes (MWCNT) to enhance strain‐sensing capabilities. Various MWCNT reinforcement ratios are used to produce customized feedstock for fused filament fabrication (FFF) 3D printing. Mechanical properties and the piezoresistive response of samples printed with these multifunctional filaments are concurrently evaluated. Surface morphology and microstructural observations reveal that higher MWCNT weight percentages increase filament surface roughness and rigidity. The microstructural modifications directly influence the tensile strength and strain energy of the printed samples. The study identifies an apparent percolation threshold within the 10–12 wt.% MWCNT range, indicating the formation of a conductive network. At this threshold, higher gauge factors are achieved at lower strains. A newly introduced Electro‐Mechanical Sensitivity Ratio (ESR) parameter enables the classification of composite behaviors into two distinct zones, offering the ability to tailor self‐sensing structures with on‐demand properties. Finally, flexible structures with proven application in soft robotics and shape morphing are fabricated and tested at different loading conditions to demonstrate the potential applicability of the custom filaments produced. The results highlight a pronounced piezoresistive response and superior load‐bearing performance in the examined structures.
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This content will become publicly available on January 1, 2026
Topology-Engineered Piezoresistive Lattices with Programmable Strain Sensing, Auxeticity, and Failure Modes
This study investigates the programmable strain sensing capability, auxetic behaviour, and failure modes of 3D-printed, self-monitoring auxetic lattices fabricated from in-house engineered polyetheretherketone (PEEK) reinforced with multi-walled carbon nanotubes (MWCNTs). A skeletally-parametrized geometric modelling framework, combining Voronoi tessellation with 2D wallpaper symmetries, is used to systematically explore a vast range of non-predetermined topologies beyond traditional lattice designs. A representative set of these architectures is realized via fused filament fabrication, and multiscale characterization—including macroscale tensile testing and microstructural analysis—demonstrates tuneable multifunctional performance as a function of MWCNT content and unit cell topology. Real-time resistance measurements track deformation, damage initiation, and progression, with the sensitivity factor increasing from below 1 in the elastic regime (strain sensitivity) to as high as 80 for PEEK/MWCNT at 6 wt.% under inelastic deformation (damage sensitivity). Implicit architecture-topology tailoring further allows fine-tuning of mechanical properties, achieving stiffness values ranging from 9 MPa to 63 MPa and negative Poisson’s ratios between –0.63 and –0.17 using ~3 wt.% MWCNT at a relative density of 25%. Furthermore, a novel piezoresistive finite element model, implemented in Abaqus via a user-defined subroutine, accurately captures the electromechanical response up to the onset of ligament failure, offering predictive capability. These results demonstrate how architecture-topology tuning can be leveraged to customise strain sensitivity and failure modes, enabling the development of multifunctional piezoresistive lattice composites for applications such as smart orthopaedic implants, aerospace skins, and impact-tolerant systems.
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- Award ID(s):
- 2048182
- PAR ID:
- 10610461
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Materials Horizons
- ISSN:
- 2051-6347
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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