High-strength strain-sensing composite material based on freestanding carbon nanotube films for real-time structural health monitoring

This study presents, for the first time, a composite material that integrates exceptional mechanical strength with sensitive strain-sensing capabilities, uniquely engineered for real-time structural health monitoring. In a novel approach, we employ freestanding carbon nanotube (CNT) films with aligned CNTs embedded in an epoxy matrix through vacuum bagging. The aligned CNT film was synthesized by floating catalyst chemical vapor deposition (FC-CVD). The parameters responsible for CNT alignment were determined and subsequently optimized, including winding rate, carrier gas flow, and precursor input, resulting in enhanced tensile strength and gauge factor (GF). This novel methodology yields an unprecedented tensile strength of 1.21 ± 0.06 GPa and a GF of 23, the highest GF for CNT composites with GPa-level strength. The remarkably elevated GF facilitates intrinsic strain detection through piezoresistivity, obviating the need for external sensors. This capability represents a significant advancement over traditional CNT powder-based composites that face challenges of agglomeration and low GF. The microstructural analysis identifies CNT bundle fracture as the primary failure mechanism, underscoring robust interfacial bonding. The study highlights the potential of CNT film-based composites in advanced structural applications, offering superior mechanical properties and integrated health monitoring capabilities through intrinsic strain sensing.