Endoscopic cheap optical transducers (CHOTs) for on-wing ultrasonic inspection

Ageeva, Victoria (2016) Endoscopic cheap optical transducers (CHOTs) for on-wing ultrasonic inspection. PhD thesis, University of Nottingham.

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The instrumentation and the developments presented in this thesis aim to address the challenges associated with in-service non-destructive testing of aeroengine components, imposed by severe restrictions on component accessibility.

In-service non-destructive testing (NDT) is essential to ensure early detection of service-induced damage and prevent catastrophic failures of such safety-critical aeroengine components as turbine/compressor blades and disks, increasing the safety of operations and dramatically reducing the cost of engine changes.The main concern during their inspection is detection of fatigue cracking, typically initiated on the surface of the part. The application of inspection techniques used during overhaul to on-wing testing is restricted both by the complex, spatially-confined access to the components and the inaccessibility of the high-stress concentration surfaces in the full engine assembly. Two routinely-used techniques providing a solution to these challenges are the use of endoscopes for access and surface acoustic waves to inspect parts of the assembly.

CHOTs are optically-activated ultrasonic transducers located on the surface of a sample, that use laser illumination to remotely generate and detect ultrasound, providing a non-contact wireless alternative to conventional piezoelectric transducers (PZTs). The benefits of optical activation are paired with fibre-optic light delivery in an endoscopic pulser -- a simple portable ultrasonic inspection system with flexible instrumentation, beneficial for testing hard-to-reach components in locations with limited access or hazardous environments.

This thesis presents the instrumentation of the endoscopic pulser and the development of the self-adhesive portable CHOTs (SA CHOTs) to complement its potential field application by enabling transducer delivery to components in-service and application to large and curved parts, previously limited by laboratory-based direct on-sample CHOT fabrication. The developed transducers overcome frequent barriers for industrial adaptation of fully-optical inspection systems presented by the sample surface conditions such as reflectivity and roughness. The NDT capabilities of the CHOTs endoscopic pulser are demonstrated by performing detection of machined slots on controlled aluminium samples and representative industrial parts using 4--5 MHz surface acoustic waves. System capabilities for active structural health monitoring (SHM) as well as inspection of samples in motion are demonstrated.

Although in its present configuration the size of the endoscope exceeds practical access requirements, the potential of the system for further development and miniaturisation is discussed.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Clark, Matthew
Stratoudaki, Theodosia
Smith, Richard J.
Somekh, Michael G.
Keywords: laser ultrasonics, optical transducers, CHOTs, endoscopic inspection, ultrasonic inspection, aerospace, non-destructive testing, in-situ inspection, non-contact inspection
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800 Electronics
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 38682
Depositing User: Ageeva, Victoriya
Date Deposited: 06 Feb 2017 14:36
Last Modified: 13 Oct 2017 20:42
URI: https://eprints.nottingham.ac.uk/id/eprint/38682

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