In the present research work is demonstrated a cross-scale manufacturing approach for the production of multifunctional glass fiber reinforced polymer (GFRP) composite tubes with a purposely redesigned filament winding process. Up until now, limited studies have been reported towards the multiscale reinforcement direction of continuous fibers for the manufacturing of hierarchical composites at the industrial level. This study involved the development of two different multi-walled carbon nanotube (MWCNT) aqueous-based inks, which were employed for the modification of commercial glass fiber (GF) reinforcing tows via a bath coating unit in a pilot production line. The obtained multifunctional GFRP tubes presented a variety of characteristics in relation to their final mechanical, hydrothermal aging, electrical, thermal and thermoelectric properties. Results revealed that the two individual systems exhibited pronounced differences both in crushing behavior and durability performance. Interestingly, for lateral compression the MWCNT coatings comprising a polymeric dispersant minorly affected the mechanical response of the produced tubes. The crashworthiness indicators of the multifunctional tubes displayed a slight 5% variation to the respective reference values, combined with a more ductile behavior. Moreover, regarding the bulk electrical and thermal conductivity values, as well as the Seebeck coefficient factor, the corresponding tubes displayed a variance of 233% and 19% and an opposite semi-conducting sign denoting a p- and n-type character, respectively.

Rapid development of composite materials in the last decades, as well as their already widespread use in various demanding applications requires reliable methods to monitor their structural integrity. However, nowadays a structural health monitoring (SHM) system should consume as less energy as possible. Smart or multifunctional composites are currently a scientific area of high interest since they have the potential to resolve such issues. A multifunctional composite apart from fulfilling load-bearing purposes, it may simultaneously perform functions such as sensing or energy harvesting. In this study, the thermal energy harvesting capability of an appropriately engineered multifunctional laminate was employed in order to achieve self-powered sensing via directly converting a temperature difference into an electrical current. The generated current was subsequently used to power up externally connected conductive composites. Results showed that the harvested energy can be successfully used to power an on-line monitoring process.