Piezoresistive behavior of MWCNT/PA12 honeycomb composites processed via selective laser sintering

Abstract

This study examines the piezoresistive and mechanical behaviors of multiwalled carbon nanotube (MWCNT)/polyamide (PA12) lattice composites processed via selective laser sintering (SLS). Firstly, neat PA12 powder was ballmilled with either 0.3, 0.5, or 1.0 wt% MWCNT loading to obtain nanoengineered powder feedstocks. The feedstocks were used to realize electrically conductive MWCNT/PA12 bulk and honeycomb lattice structures via SLS. The piezoresistive and mechanical characteristics of bulk samples were assessed under tensile, compressive, and flexure loadings while those of honeycombs were investigated under in-plane and out-of-plane compression. The morphological and thermal characterizations were carried out to gain insight into the processing-structure-property relations. The microstructural observations, including in situ μ-CT imaging, revealed that the porosity of the sintered parts significantly increased (≈150%) with increasing MWCNT loading, resulting in reduced elastic stiffness and strength of the sintered composites, despite their slightly higher crystallinity (+6% for 0.5 wt% MWCNT loading). The bulk nanocomposites exhibited excellent piezoresistive characteristics, showing a maximum gauge factor of 31 (in compression), which is significantly higher than the sensitivity factors of extant piezoresistive self-sensing composites. The honeycomb structures showed a maximum specific energy absorption of 3 and 24 J g−1 at 40% relative density under in-plane and out-of-plane compression loading, respectively. It was also demonstrated, that the MWCNT/PA12 honeycombs possess excellent strain sensing characteristics due to their pronounced piezoresistivity, reporting gauge factors up to 25 and 17 for in-plane and out-of-plane loading, respectively.