Characterisation and Exploitation of Ultrasonic Guided Wave Modes for Structural Health Monitoring of Glass-Fibre-Reinforced-Polymer Structures

Abstract

Recently, great interest has arisen on the application of guided waves on composite materials, owing to the successful results achieved in metallic structures. Due to its more complex nature, guided wave technology for composites is still unmatured, requiring further research to be deployed in commercial structures. The work presented in this thesis focuses on overcoming some of the obstacles for its deployment, and better understanding uncertainties about its propagation and detection capabilities. Calculation of dispersion curves in composites hinders the use of guided waves, since material properties are not commonly available so existing techniques are unable to calculate them. In this thesis, a new experimental technique is presented for the creation of dispersion curves without requiring any prior knowledge of material properties and being able to be deployed on site. Firstly, the proposed technique is applied to an aluminium plate to validate its performance, where the formulation of its theoretical basis is explained in detail. Validation is achieved using synthesized signals, signals from finite element simulations and experimental signals from an aluminium plate, where accuracies to within 1% are reached. Subsequently, the proposed technique is applied to a biaxial GFRP plate to validate its applicability in composite structures. A finite element model is carefully created to obtain the full velocity profile and experimental tests are carried out for calculating the velocities at every direction. Results achieve high agreement with theoretical values and also with results from a well-known experimental technique (2D FFT). Then, a wave propagation analysis using three different lay-ups is carried out to study the complex propagation pattern and excitability of the shear horizontal mode. Finally, a study of delamination detection sensitivity is performed, where the three fundamental wave modes are evaluated individually under the same conditions. Results from FE analysis and experimental tests are presented along with best practices recommendations for future studies.

Date of Award	19 Jun 2019
Original language	English
Awarding Institution	University of Bath
Sponsors	European Commission & TWI Ltd
Supervisor	Richard Butler (Supervisor) & Charles Courtney (Supervisor)