3D Printed Smart Materials of Continuous Wire Polymer Composites for Sensing Applications

Smart material with sensing capability is an exciting new technology that will impact many applications, including structural health monitoring, biomedical implants, wearable sensors, and actuators. Internal damage in polymer composites is usually hard to predict, and they need to be continuously monitored for any sign of internal damage for safety issues and to increase the life cycle. In this study, continuous wire polymer composites (CWPCs) were 3D-printed using the fused filament fabrication (FFF) technique to produce functional smart materials with different sensing capabilities like strain and thermal sensing. Here, the integrated wire within the conductive polymer composite structure acts as a sensing element. For strain sensing characterization, different design parameters such as matrix type, wire type, and loading condition were investigated to study the effect of these parameters on the efficacy of the CWPC sensor. The different matrices used have different mechanical properties representing rigid (polylactic acid) and flexible (thermoplastic polyurethane) structures to widen the range of applications of CWPCs as strain sensors. The change of the electrical resistance of the integrated wire within the CWPCs was measured under tensile loading and plotted against the applied strain. The results of this electromechanical testing demonstrate the ability of CWPCs to be used as strain sensor for either rigid or flexible structures. To check the reliability and reversibility of CWPCs structure as strain sensor, the electromechanical behaviour was investigated under fatigue/cyclic loading. The results of this work demonstrate the reverse piezoresistance behaviour of the CWPC sensor. From thermal sensing standpoint, different design parameters like wire type, matrix type, and sensor thickness were studied to investigate the application of CWPCs as temperature and heat flux sensors which can be readily designed and adapted to suit unique and bespoke thermal applications. The change of the electrical resistance of the integrated wires was correlated to the applied temperature to measure the heat conducted through a surface. A prototype of a real-world application was designed for the heat flux measurements using CWPC sensor. Generally, this study demonstrates the applicability of FFF technique to print sensors with continuous integrated wire with tuneable properties for different sensing applications.