Visual Vibrometry and its application to NDT through the use of various video and signal processing techniques

The project focuses on the field of visual vibrometry and its application to ultrasonic non-destructive testing (UNDT) through the use of various video and signal processing techniques. The concept of visual vibrometry as a method of NDE is explored by utilising regular consumer cameras to recover signals from standard frame-rate videos. Visual vibrometry has significant potential to be a major method for rapid large area monitoring within NDE. As visual vibrometry works on the basis that in-service damage alters vibrational modes in a way that is imperceptible to the human eye, but visible through image processing. A common form of NDT involves the use of ultrasonic sound waves to extract underlying material and dynamic properties of a system. One aim of the project is to combine the ability of ultrasonic guided waves, in order to penetrate a part at depth, with the ability of visual systems. In particular, to explore how large area visual monitoring approaches may be employed to monitor the state of structures. For the video data collected, forced excitation is utilised as opposed to simply recording the passive response of the structure

One goal is to successfully image structural vibrations at frequencies significantly greater than the advertised frame-rate of the camera and extend the use of the camera beyond its hardware specification. This may be achieved by exploiting short exposure times and periodic excitation common in UNDT, even when the excitation frequency exceeds the Nyquist sampling limit. This will involve using stroboscopic effects and exploiting camera exposure times in order to achieve this and essentially 'cheat' the camera system in to sampling at a significantly higher frame-rate than normally possibly. These cases are intended to be analysed by taking into account stroboscopic effects produced, where natural frequencies and input excitations are either calculable or known, respectively. The final challenge will be whether these developments may be pushed far enough to allow the measurement of displacement from useful ultrasonic frequency. In order to provide the basis for visual vibrometry as a method to monitor and detect damage in parts.

To achieve these goals a simulation and post processing tool has been developed as a means to validate experimental testing and to predict the behaviour of experimental testing. Where, the simulated video was designed to imitate real data and used a noise model defined on results from experimental testing performed to investigate the relationship between noise and intensity levels as shown in figure 1.

The simulated test video provides a means to test experimental set ups prior to physical testing and may be used to explore the effects of key camera parameters on the results. As the dynamics of the camera are highly influential on the performance of the testing, each of the camera testing parameters will be investigated and quantified. A relationship between image quality, frame-rate and exposure time is required and will likely be quantified by using a signal to noise ratio relationship as well as the accuracy of the identified output displacement amplitude and phase. By exploring the effect of each camera and test parameter using the simulation, the limitations of the testing may be explored. Such as, identifying the smallest possible pixel displacement that may be reliably and accurately extracted from video data.

The proposed CDT in NDE will deliver impact (Industrial, Individual and Societal) by progressing research, delivering commercial benefit and training highly employable doctoral-level recruits able to work across industry sectors.

Industry will benefit from this CDT resulting in competitive advantage to the industrial partners where our graduates will be placed and ultimately employed. The global NDE market itself has a value of USD15 billion p.a. [Markets and Markets NDE report January 2017] and is growing at 8% per year. Our partners include 49 companies, such as Airbus, Rolls-Royce, EDF, BAE Systems, SKF and Shell, whose ability to compete relies on NDE research. They will benefit through a doctoral-level workforce that can drive forward industrial challenges such as increased efficiency, safer operation, fewer interruptions to production, reduced wastage, and the ability to support new engineering developments. Our 35 supply chain partners who, for example, manufacture instrumentation or provide testing services and are keen to support the proposed CDT will benefit through graduates with skills that enable them to develop innovative new sensing and imaging techniques and instrumentation. To achieve this impact, all CDT research projects will be co-created with industry with an impact plan built-in to the project. Our EngD students will spend a significant amount of their time working in industry and our PhDs will be encouraged to take up shorter secondments. This exposure of our students to industry will lead to more rapid understanding, for both parties, of the barriers involved in making impact so that plans can be formulated to overcome these.

Individual impact will be significant for the cohorts of students. They will be trained in an extremely relevant knowledge-based field which has a significant demand for new highly skilled doctoral employees. These graduates will rejuvenate an ageing workforce as well as filling the doctoral skills and capability gaps identified by industry during the creation of this CDT. Our industrial partners will be involved in training delivery, e.g. entrepreneurial training to equip our graduates with the skills needed to translate new research into marketed products. Many of the partners are existing collaborators, who have been engaged regularly through the UK Research Centre in NDE (RCNDE), an industry-university collaboration. This has enabled the development of a 5,10 & 20 year vision for research needs across a range of market sectors and the CDT training will focus on these new priorities. Over the duration of the CDT we will actively discuss these priorities with our industry partners to ensure that they are still relevant. This impact will be achieved by a combination co-creation and collaboration on research projects, substantive industrial placements and as well as communication and engagement activities between academic partners and industry. Events aimed at fostering collaboration include an Annual CDT conference, technology transfer workshops, networking events as well as university visits by industrialists and vice versa, forming a close bond between research training and industrial impact. This approach will create lasting impact and ensure that the benefits to students, industry and society are maximised.

Society will benefit from this CDT through the research performed by our CDT graduates that will underpin safety and reliability across a wide range of industries, e.g. aerospace, energy, nuclear, automotive, defence and renewables. As NDE is an underpinning technology it feeds into many of the UK Government's Industrial Strategy Challenge Fund Grand Challenges, for example in energy, robotics, manufacturing and space. It is aligned to the EPSRC prosperity outcomes, e.g. the Productive Nation outcome requires NDE during manufacture to ensure quality and the Resilient Nation requires NDE to ensure reliable infrastructure and energy supplies.