Nonlinear Inspection Using Phased Arrays

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Ageing infrastructure and the move towards more advanced materials raises new, currently unsolved, inspection challenges. Fatigue and creep damage are two of the most common modes of failure in engineering structures, yet both are extremely difficult to detect in early stages of development. Similarly, there is a growing need to inspect bonded joints, be it adhesively bonded composites for major engineering components, or diffusion bonded metal components such as super-plastically deformed fan blades. This lack of inspection technique is artificially limiting the lifetimes and use of engineering components and was recently highlighted as a key requirement on the 5-10 year horizon by a group of industrial end-users of Non-Destructive Evaluation (NDE). They specifically highlighted the need for ``techniques identified for crack precursors, difficult and new engineering materials''.This fellowship will enable the applicant to develop practical and deployable nonlinear ultrasonic inspection techniques for monitoring of each of these damage scenarios, making use of recent developments in ultrasonic equipment, specifically highly flexible phased array systems and novel experimental techniques. The use of phased arrays, which are specifically tailored for NDE, is key. They allow multiple measurements without sensor repositioning, eliminating the high coupling and alignment variability that can readily mask the extremely small nonlinear signals. Even more importantly, the approach in this fellowship will enable localisation of nonlinearity within a specimen. This is currently not possible with any degree of reliability and represents a key barrier to wider adoption of this exciting inspection approach.