Production of 3D printed nanocomposites with intrinsic Piezoresistive Properties

The need for strain-sensing materials for structural health monitoring remains one of the interesting topics of research activity in many strategic industrial sectors, such as aeronautics and automotive [1]. Although many attempts to produce novel piezoresistive materials are present in the literature, the design of sensoristic material is still a major shortcoming especially when multi-direction strains have to be monitored [2]. 3D printing technology is a valid candidate for manufacturing complex sensors in a fast, agile, and low-cost manner at an industrial scale [3]. In the current work, the effect of 3D printing parameters has been exploited to tune the sensitivity of self-sensing materials and to detect multi-directional strains. Acrylonitrile-butadiene-styrene ABS filled with different weight concentrations of Carbon Nano-Tubes CNTs (ABS-3%CNTs, ABS-5%CNTs, and ABS-8%CNTs) has been printed via Fused Filament Fabrication and electrically and mechanically characterized considering two printing directions, 0° and 90°. Moreover, morphological analyses (e.g. Scanning electron microscopy and Atomic Force Microscopy in TUNA mode) explain the different piezoresistive responses of the 3D printed samples. The evaluation of the gauge factor (G.F.) reveals that the sensitivity increases by lowering the filler concentration for both directions, while G.F. is always higher for the 90° oriented sample than for the 0° printing direction when the same filler content is considered. By combining both printing directions in the same sensor, multi-directional strains can also be detected. The current work proposes the design of a 3D printed strain sensor, eventually embeddable in aeronautical composites, characterized by differentiated sensitivity that is useful to monitor small and large deformations in different directions simultaneously.