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Metal coating and embedding fibre optical sensors for industrial applications

González, T. (2023). Metal coating and embedding fibre optical sensors for industrial applications. (Unpublished Doctoral thesis, City, University of London)


This thesis documents the development of two monitoring systems based on metal-coated Fibre Bragg Grating sensors, which are to be validated in two distinct industrial applications within harsh environments. One is intended for the naval sector as part of the NEXT-BEARINGS project, while the other is designed for the energy sector within the framework of the NEWSOL project.

The objective of the first application, within the NEXT-BEARINGS (Development of a new generation of naval components for the ship shaft line) project, was to monitor the degradation of antifriction materials in bearings for the naval sector using embedded FBGs with metal coating to measure strain and temperature. The second application, within the framework of the NEWSOL (New StOrage Latent and sensible concept for highly efficient CSP Plants) project, aimed to monitor the performance and operation of novel concrete energy storage components using metallically coated FBGs for Concentrated Solar Power (CSP) plants, which operate at temperatures of up to 550°C. Despite their differences in industrial settings, both applications share similar harsh environments and high temperatures. Therefore, the FOS monitoring solutions developed in this work are all based on metal-coated FBGs as strain and temperature sensors.

In this thesis, a metallic coating procedure based on a combination of sputtering and electroplating deposition techniques was developed to apply metallic coatings of Ni and Cu to the FBGs and optical fibres. This procedure allows for the coating of longer lengths of fibre (hundreds of meters) and various thicknesses ranging from a few microns to hundreds of microns. Furthermore, after coating the sensors, a procedure was developed to embed these coated sensors into the antifriction bearing material, which is a tin alloy base, using various techniques such as laser cladding and TIG welding.

To verify the research, the metallic coated and embedded FBGs were validated under operational conditions for each use-case. In the case of the NEXT-BEARINGS project, validation was carried out using two distinct test benches adapted to fulfill different technical objectives. On one hand, the response of the embedded FOS within the antifriction material was analysed using a dedicated fatigue machine developed for this purpose. On the other hand, to validate the embedded FOS response for bearing condition monitoring, a test bench designed for testing antifriction bearings in a real vessel was used. During these validations, the metallic-coated embedded FBGs were subjected to pressures up to 250 bar, rotary speeds up to 667 rpm, and temperatures up to 65°C for more than 5500 hours, providing a stable response throughout the tests.

In the case of the NEWSOL project, three different validations at laboratory scale, mid-scale, and real scale were conducted. The metallic-coated FBGs were embedded in various thermal storage components made using novel high thermal resistant concretes, and they were tested at temperatures up to 550°C. The embedded FBGs were capable of monitoring the concrete curing process, the operation of the storage components, and the degradation of the concrete.

The research concludes by considering future directions for the work in these and other industry sectors.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
[thumbnail of Gonzalez Thesis 2023 PDF-A.pdf]
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