In situ sensing of multiple parameters for multi-functional adhesives

Hlatky, Maximilian (2025). In situ sensing of multiple parameters for multi-functional adhesives. University of Birmingham. Ph.D.

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Abstract

Optical fibre sensors (OFS) have been widely recognised for their effectiveness in monitoring processes associated with epoxy-based polymers. Building on this foundation, this research expands the application of OFS to adhesive joints, facilitating in situ monitoring during manufacturing. This approach provides a robust and comprehensive means of ensuring bond quality and performance.

The study centres on fabricating single-lap joints (SLJs) using aluminium-to-aluminium, composite-to-composite, and aluminium-to-composite configurations. These joints were produced under varying surface preparation conditions, including different grit-blasting durations and silane concentrations, to assess their effects on bond strength and joint performance. Additionally, the integration of advanced sensor technologies, such as Fourier transform infrared spectroscopy (FTIR), fibre Bragg gratings (FBGs), Fresnel reflection sensors (FRS), and Fabry-Perot (FP) cavities, enabled the monitoring of critical parameters, including refractive index evolution, functional group changes, temperature, and shrinkage.

A comparative analysis of cure kinetics measured by FTIR and FRS demonstrated that FRS offers a cost-effective alternative to FTIR for monitoring the cure kinetics. The quantitative correlation of data between these methods reinforces the reliability of FRS for real-time monitoring applications. Furthermore, embedding multiple sensor types within SLJs provided valuable insights into the curing dynamics and performance of adhesive joints across diverse conditions. Additionally, a relation between FRS noise and viscosity could be established by comparing parallel rheology results with the noise thresholds of the FRS traces.

Key findings reveal that higher concentrations of silane treatments significantly reduce the ultimate tensile strength (UTS) of grit-blasted CFRP joints while not significantly improving aluminium joints. Additionally, surface roughness was found to correlate with the formation of microvoids in adhesive layers; increased roughness led to a higher density of voids, potentially compromising bond integrity. These results emphasise the critical role of precise surface preparation in achieving durable adhesive bonds.

This research demonstrates the capability of OFS to enable in situ monitoring of key parameters, such as refractive index, temperature, shrinkage, and chemical changes in functional groups. Furthermore, the successful integration of these sensors highlights their potential for both real-time process monitoring and post-process evaluations, advancing the development of smarter adhesive joint technologies for a wide range of engineering applications.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):