Development and implementation of an alternative method for complete characterization of surface-breaking cracks using ultrasonic Rayleigh waves

Abstract

This thesis focuses on developing a new method for characterizing surface cracks using Rayleigh waves, providing an alternative to current nondestructive testing (NDT) approaches. Surface cracks are common in many industries, and traditional methods like eddy current testing (ECT) for crack sizing have drawbacks, requiring a complex calibration and highly trained inspectors. ECT also faces challenges in large-area inspections, demanding additional scanning arrangements and having limited penetration depth, affecting detection range. Recent research interest has grown in the wedge technique-based Rayleigh wave crack sizing method due to its unidirectional excitability and capacity to scan large areas with few probe locations. However, challenges arise as Rayleigh wave features generated at crack tips are often weak and masked by noise and they mostly attenuate before reaching the receiving probe due to the couplant at the wedge-test specimen interface. Consequently, sizing the crack depth is difficult using a pulse-echo setup. Moreover, the flexibility to generate Rayleigh waves on different waveguides using the same wedge is limited, as the wedge angle depends on the Rayleigh wave wavelength. This thesis addresses these issues by introducing an alternative Rayleigh wave excitation method using a conventional phased array transducer, offering capabilities similar to the wedge technique but overcoming its limitations. This new method is then extended to innovate a surface crack sizing approach based on a specific mode-converted Rayleigh wave originating from the crack tip, relying solely on time-of-flight (TOF) information. Moreover, a novel method is introduced for acquiring Rayleigh wave full matrix capture (FMC), which is then utilized with the total focusing method (TFM) imaging algorithm to generate images of surface cracks. This comprehensive approach allows for the complete characterization of surface cracks, including length and depth estimation in a single measurement—a capability lacking in existing NDT methods. The performance of the proposed methods is demonstrated through finite element simulations and experiments. The findings of this thesis demonstrate accurate sizing of the crack length and depth within a 5% error margin. In conclusion, the study suggests that the presented surface crack characterization method has the potential to be a suitable alternative to current NDT methods.

Date	8 Apr 2024
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Pierre Bélanger (Supervisor)