Piezoresistive and Mechanical Performance of Multifunctional Architected Nanocomposites Processed via DLP Additive Manufacturing Technique

Abstract

Architected materials are synthetic materials that exhibit unusual mechanical properties which originate from the design of their cellular or porous architecture. The physical realization of these architected materials has been enabled by advancements in manufacturing technologies, especially in the area of additive manufacturing (AM), which has opened new pathways for the design of new material architectures with unprecedented mechanical and functional properties. This project is concerned with the design, fabrication, and testing of multifunctional architected materials with the ability to self-monitor the degree of deformation or damage induced in a structure. The Digital Light Processing (DLP) technique was employed to additively manufacture cellular materials with complex architectures and tunable mechanical and functional properties. The strain sensing functionality of the 3D printed materials was achieved by adding a small weight fraction of CNTs to the liquid feedstock resin, which resulted in a percolating network with high piezoresistive sensitivity. By optimizing the resin composition and synthesis route, electrical percolation in the 3D printed nanocomposites was achieved at an ultra-low MWCNT loading of 0.01 phr (parts per hundred resin), providing a conductivity of 3.5 × 10−5 Sm−1 , which is significantly higher than the values reported in the extant works for similar nanocomposites. The thermal, structural, and morphological properties of the 3D printed nanocomposites were evaluated using various material characterization techniques (DSC, TGA, DMA, SEM, etc.), and their mechanical and piezoresistive responses were evaluated in uniaxial tension and compression tests. Three different classes of metamaterials were considered, namely (i) 2D lattices with chiral, hexagonal, re-entrant, and triangular unit cell geometries and (ii) geometrically graded 3D lattice structures (Octet and Kelvin structures) with varying unit cell size in a single direction, and (iii) 2.5D lattices (also known as honeycombs) with a bio-inspired sea-sponge-like architecture. The piezoresistive responses of these lattice structures were distinctly different in the elastic and inelastic phase of deformation and were found to strongly depend on the topology and relative density of the lattices. Moreover, significant differences between the strain-sensing characteristics of bend- and stretch-dominated lattice structures were identified and discussed. These results suggest that DLP 3D printing is a promising technique for creating multifunctional materials with complex cellular architectures and ultra-low nanofiller loading, which could unlock new applications in wearable strain sensors and self-sensing structural systems.

Date of Award	Apr 2023
Original language	American English
Supervisor	Andreas Schiffer (Supervisor)