Laser-induced graphene for structural health monitoring of composite materials

Abstract

Fibre-reinforced polymeric composites (FRPs) have been widely used in aerospace, marine and renewable energy applications for decades due to their light weight, high specific strength, and exceptional corrosion resistance. Structural health monitoring (SHM) enables the detection of undesirable structural changes and damage that improve composites' reliability. Utilisation of laser-induced graphene (LIG) as flexible sensors has recently attracted a lot of interest due to its ease of synthesis and scalable production. However, the integration of LIG as sensors with structural components is challenging due to its fragile microstructure. This PhD thesis overcomes the challenge by demonstrating novel ways of LIG synthesis on composite structures and investigating its sensing performance.
The first part of the thesis presented a novel cork-derived LIG sandwich composite structure for impact damage sensing. A LIG mesh was embedded as the core material of the composite which enables detection of impact damage and its severity. A machine learning (K-Nearest Neighbours) model was proposed to improve the accuracy of damage classification.
The second part investigated the same cork-derived LIG as an embedded sensor for strain sensing under cyclic and monotonic tensile loading. The LIG sensors of different widths showed width-dependent piezoresistivity, with a maximum gauge factor of 133 at 0.08% strain, indicating high sensitivity. LIG piezoresistive behaviour can be described using a mathematical model based on percolation theory.
The third part demonstrated the use of paper-derived LIG directly engraved on glass fiber composites to function as a cost-effective surface strain sensor. The results show that the LIG gives a more stable response to tensile strain compared to compressive strain. A crack-bridge model was developed to describe the piezoresistivity of the LIG sensors. It is also demonstrated that the paper-derived LIG is capable of detecting moisture uptake in the composite structures and solvent leaks, enabling environmental sensing.
Overall, this PhD bridges the gap between low-cost LIG synthesis and its SHM application in self-sensing composite structures. The findings enhance the understanding of LIG's piezoresistive behaviour and lay a foundational framework for the design of LIG sensors for SHM applications.

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Identifiers

ORCID for Suan Pu: orcid.org/0000-0002-3335-8880

ORCID for Andrew Hamilton: orcid.org/0000-0003-4627-849X

ORCID for Meisam Jalalvand: orcid.org/0000-0003-4691-6252

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