The development of fibre-optic acoustic emission sensors for structural health monitoring

Willberry, James Owen (2022). The development of fibre-optic acoustic emission sensors for structural health monitoring. University of Birmingham. Ph.D.

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Acoustic emission (AE) is widely used for condition monitoring of critical components and structures. Conventional AE monitoring techniques use piezo-electric AE sensors to detect elastic stress waves emitted from a source, such as a propagating crack. These sensors are often surface mounted and secured in place using magnetic hold-downs or adhesive tape to monitor structural components. Coupling sensor and structural
components is achieved with the use of an appropriate ultrasonic couplant due to the high frequency signals emanating from an AE event (up to 1 MHz). The couplant is crucial to permit an efficient transfer of elastic waves between damage source and sensor. Piezo-electric sensors tend to be relatively bulky, so cannot be embedded into composite materials. The embedding process protects sensors against environmental
stresses, prolonging operational lifetime and enhancing device sensitivity. In addition, piezo-electric AE sensors are affected by electromagnetic interference meaning that when required in challenging conditions such as in flammable or explosive environments, AE sensors need to be manufactured as intrinsically safe. Fibre-optic acoustic emission sensors (FOAES) offer several advantages over conventional piezoelectric AE sensors. FOAES can be both surface-mounted to various materials or embedded into composites owing to their small size and acrylate coating relieving the stress concentration around the sensor. The immunity of FOAES to electromagnetic interference makes these sensors attractive for condition monitoring across a wide range of operational environments. This is because the FOAES employs light at the sensing region to interrogate elastic stress waves instead of electrical components used in piezo-electric AE sensors. This study discusses the approach employed for manufacturing sensitive and reproducible FOAES in addition to methods used to characterise them. Towards the end of the investigation, a comparison between AE signals captured using both conventional piezo-electric sensors and FOAES is also provided.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Metallurgy and Materials
Funders: Other
Other Funders: School of Metallurgy and Materials
Subjects: T Technology > T Technology (General)


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