Nonlinear Inspection Using Phased Arrays

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.

The techniques that will be developed in this fellowship will provide a means to determine the remaining service life available in engineering components, the key impact. This is a major requirement as infrastructure approaches the end of its design life and we wish to continue using it. These approaches will help to support the development of advanced materials by providing NDE techniques to support their use. The potential impact here is huge.
The Ultrasonics and Non-Destructive Testing research group is the only centre globally with expertise in both nonlinear and phased array based techniques. My position within the group, leading the nonlinear activities, leaves me uniquely placed to accomplish this ambitious body of work. One outcome of the proposed work will be to ensure that the UNDT group at Bristol is the world centre for practical nonlinear phased array work, with direct industrial application, to the benefit of UK plc.
The industrial support for the project from four partners covering a very wide range of application cases makes the potential impact of the work clear. To ensure a rapid transition from state-of-the-art research to practical deployment, industrial secondments are planned for the applicant at the beginning and end of the project and are supported by the partners. This will have significant impact in forging closer links with industry leading to support for postgraduate researchers and help to establish Bristol as a global centre of excellence in nonlinear NDE. In addition it will result in a series of companies using these new technologies and acting as evangelists to the wider community.
The key outcomes from the fellowship will be the developed approaches for material characterisation, with software tools to support their industrial application and web resources to communicate their potential to a wider non-academic audience.