An implantable, compatible and networkable nanocomposite piezoresistive sensor for in situ acquisition of dynamic responses of CFRPs

When sensors are embedded in composites for structural integrity monitoring (SIM), the sensors per se, unfortunately, degrade the original integrity of host composites. Envisaging such deficiency and facilitated by advances in nanotechnology, we develop a new type of ultrathin, piezoresistive sensors using spraying coating and nanocomposites formulated with graphene nanoplatelets/polyvinylpyrrolidone. The sensors are deposited on dielectric membranes made of partially pre-cured B-stage epoxy films, electrified using carbon nanotube film (CNT-film)-made wires, and implanted in carbon fibre-reinforced polymer composites (CFRPs), to form a sensor network. Only ~45 μm thick (including wires), the implanted sensors exhibit high compatibility and nonintrusive attributes with CFRPs, enabling composites to perceive broadband signals in situ, ranging from static strain (with a high gauge factor of 34.5) to structure-guided ultrasonic waves up to 450 kHz – the first time that piezoresistive sensors implanted in CFRPs respond to dynamic strains in such a broad frequency band. CFRPs with implanted sensor networks are endowed with capacity of in situ SIM, yet not compromising their original integrity. With remarkably reduced intrusion to composites – as proven in tensile and bending tests, the developed sensors outperform prevailing sensors for SIM of composites such as lead zirconate titanate-based sensors.