Topology-engineered piezoresistive lattices with programmable strain sensing, auxeticity, and failure modes

Abstract

This study investigates the programmable strain sensing capability, auxetic behaviour, and failure modes of 3D-printed, self-monitoring lattices made 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-traditional, non-predetermined topologies. 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 electrical 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). 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 at ∼3 wt% MWCNT and 25% relative density. Furthermore, a novel piezoresistive finite element model, implemented in Abaqus via a user-defined subroutine, accurately captures stress-induced intrinsic piezoresistivity, geometry-driven deformation, and damage evolution up to the onset of ligament failure. Together, the experimental results and predictive modelling enable “design for strain-sensitivity” and “design for failure”, demonstrating how architecture–topology tuning can be leveraged to tailor strain sensitivity, auxeticity, and failure modes—ultimately guiding the development of multifunctional piezoresistive architected composites for applications such as smart orthopaedic implants, aerospace skins, and impact-tolerant systems.