Nonlinear Inspection Using Phased Arrays

Lead Research Organisation: University of Bristol
Department Name: Mechanical Engineering


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.

Planned Impact

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.


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Villaverde EL (2021) Optimal Extraction of Ultrasonic Scattering Features in Coarse Grained Materials. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Potter J (2018) Characterization of Nonlinear Ultrasonic Diffuse Energy Imaging. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Velichko A (2018) Strategies for data acquisition using ultrasonic phased arrays. in Proceedings. Mathematical, physical, and engineering sciences

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Velichko A (2021) Local scattering ultrasound imaging. in Scientific reports

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Potter J (2016) Ultrasonic array imaging of contact-acoustic nonlinearity in The Journal of the Acoustical Society of America

Description We have discovered how standard ultrasonic equipment can be used in a new way to measure extremely small and hard to detect defects inside engineering materials. Further to that we have developed a series of protocols and a level of understanding that has enabled us to produce a methodology to enable the developed approaches to be reliably deployed by industry. In addition developments resulting from the research have determined how these techniques may be taken further to begin to characterise the state of components. A software tool is in the process of being released to enable industrial partners to try these techniques out for themselves.
Exploitation Route Our findings may be used as a complement to existing NDE approaches in order to improve the sensitivity of existing approaches. The work we have done here helps to demonstrate where these approaches may be useful to ensure that the most appropriate tool is selected for inspections in all cases.
Sectors Aerospace, Defence and Marine,Energy,Transport

Description The development of the approaches in this work have begun to be trialled industrially. We have done several small scoping exercises with Industrial partners who see significant potential in the approach and aim to employ it practically. Specifically taking advantage of the ability to image small fatigue cracks at an early stage using normal equipment. Although at an early stage it is hoped these trials will lead to broader industrial deployment and specific use outside of academia. We have developed software tools to enable partners to trial these techniques with a lower level of initial knowledge and are hopeful this will lead to more widespread use of the approaches developed.
First Year Of Impact 2018
Sector Energy
Impact Types Economic

Description Collaboration with RMIT Australia researchers 
Organisation RMIT University
Department School of Engineering
Country Australia 
Sector Academic/University 
PI Contribution We have highly advanced experimental techniques to measure material nonlinearity at multiple points in a specimen. This is an approach that is not used everywhere and so in this collaboration we are offering experimental approaches that will allow the models to be validated.
Collaborator Contribution Researchers at RMIT in Melbourne have developed numerical simulations directly relevant to the research being carried out in this grant. These models will allow us to better understand the systems that we measure experimentally.
Impact No research outputs have arisen yet
Start Year 2017
Description Collaboration with researchers at University of Twente 
Organisation University of Twente
Country Netherlands 
Sector Academic/University 
PI Contribution I was contacted by researchers at the University of Twente about applications of my fellowship research to a problem they have. This has led to a research visit (Feb. 20) to use the developed techniques at the University of Bristol.
Collaborator Contribution Our partners have brought samples and knowledge of an industry sector that I am my team have limited knowledge of, specifically the Dutch water Industry.
Impact None yet
Start Year 2019
Description Working with EPRI researchers in the US to determine the applicability of the developed approaches for power station inspection 
Organisation Electric Power Research Institute (EPRI)
Country United States 
Sector Charity/Non Profit 
PI Contribution We have been applying the techniques that we have developed as a result of the fellowship work to the problems of power station inspection through this body.
Collaborator Contribution The partner has provided funding to attend their institution and access to real world power station components.
Impact At this point there are no outcomes but a paper is in preparation.
Start Year 2018