Intrinsic Self-Sensing in Advanced Composites Enabled by Carbon Nanostructures

QC 20260409

Abstract

Lightweight composite structures have become essential in modern aerospace engineering, where increasing demands for fuel efficiency, reduced emissions, and improved operational reliability place new requirements on both materials and manufacturing. As composite components grow more advanced, featuring co-cured components, complex geometries, and thinner design margins, the need for improved insight into their internal behaviour becomes critical. Existing sensing technologies struggle to provide local, in-situ information from the composite’s interior during manufacturing or throughout its service life, without compromising structural integrity. This creates a gap between the capability of current sensing approaches and the monitoring demands required by the complexity of next-generation composites.

This thesis addresses this gap by investigating the feasibility of embedding nanomaterial-based sensing structures, primarily vertically aligned carbon nanotube (VACNT) forests, into fibre-reinforced polymer composites. The overarching aim is to explore how such sensors can be integrated with minimal structural intrusion, from where their sensing behaviour originates, and how they can provide reliable, multifunctional monitoring both during manufacturing and in the cured state. The work spans the development of embedding and contacting strategies, bottom-up characterisation to investigate sensing mechanisms, and the exploration of both direct current (DC) and alternating current (AC) measurement approaches. Collectively, the research seeks to expand the understanding of how nanomaterial sensors interact with composite materials and how they can support the design of future multifunctional aerospace structures.

The findings demonstrate that VACNT forests can be embedded into composite laminates without compromising the composite’s mechanical structure, while providing robust and reproducible sensing capabilities. A bottom-up analysis helps determine that the embedded VACNT forests’ thermoresistive behaviour is governed by fluctuation-assisted tunnelling, and their linear piezoresistive response originates in the intrinsic piezoresistivity of individual CNTs. The VACNT forests enable local in-situ cure monitoring of prepreg laminate, detecting key process transitions. Strategies for sensing in conductive carbon fibre environments are established, as well as comparisons with alternative nanomaterial-based sensors such as graphene coatings. Finally, by transitioning from DC resistance to AC impedance measurements, the work shows that embedded CNT structures can detect high transverse pressures and exhibit frequency-dependent sensing sensitivity.

Together, these results establish VACNT forests as a promising, multifunctional, and structurally compatible sensing concept for advanced composite structures, offering new pathways for embedded process monitoring, structural health monitoring, and the development of next-generation multifunctional aerospace components.

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