Modelling of Ultrasonic Response from Rough Defects

This proposal seeks funding for a three year research programme into the back-scattering of ultrasound from rough surfaces, with specific application to the Non-Destructive Evaluation (NDE) of rough cracks. This addresses an important industrial goal: to be able to predict with confidence the reflection of ultrasound from a rough defect, at any chosen angle and frequency, which could then be used to make the case for a desired plan for inspection. The research will extend knowledge in two complementary areas: the creation of an envelope approach to predict the minimum back-scatter to be expected with confidence from a statistical description of the roughness, and the development of Finite Element modelling procedures to guarantee accurate, but efficient, modelling of the scattering from detailed representations of specific rough defects. The work will be undertaken jointly by a mathematical and an engineering team, both at Imperial College. The proposal is being submitted within the UK Research Centre in NDE (RCNDE) to the targeted research programme, the funding for which is earmarked by EPSRC for industrially driven research.

Modelling of the reflection of ultrasound from complex defects is a topic of very great current interest in both academia and industry. In academia the availability of faster cheaper computing power is enabling rapid development of numerical modelling capability, now making possible for the first time the accurate simulation of ultrasound scattering from realistic defects. In industry, the possibility of doing this is providing a strong pull to get these new capabilities into use. The present generation of modelling software in use in industry, based on ray models, is well developed for the planning of inspection setups and for training inspectors, but it is conspicuous that there is a serious weakness in the ability of these tools to make reliable predictions of the reflection of the ultrasound from realistic defects. As a result, modelling is not yet achieving its potential to be used as a predictive tool to demonstrate the safety of specific inspection plans. If this could be achieved then huge cost savings would be enabled by replacing experimental technical justifications by modelling ones. Furthermore, the improved capability would reduce conservatism in the assessment of inspection results, so saving further large sums. The particular modelling topic of this proposal, reflections from rough cracks, has been identified to be of great value to the companies which have to make technical justifications for inspections of safety-critical nuclear power plant, hence the two particular companies, British Energy and Rolls-Royce, which are collaborating in the work. An indication of the importance of this particular topic is that it has been identified as a specific research goal in the UK HSE Nuclear Research Index. However, the capability will also be of value to other sectors where safety-critical cases have to be made, significantly including fossil fuel power plant for which the next generation of designs will use the high performance high temperature materials currently associated with nuclear plant. The primary route to communication of the results of the project to industry will be to the two collaborating companies. Both of these companies have backgrounds in developing modelling and experimental methods for the qualification of inspections for nuclear plant components. They are thus well set up to bring the findings into use. They will be engaged in the project programme throughout, including provision of information and participating in the review meetings, and so will take on the understanding during the project as well as the formal deliverables at the end. Additionally, the other industrial members of the UK Research Centre in NDE (RCNDE) will be informed of the principal steps of progress, via the RCNDE annual review, and so will be able to take early advantage of the new capabilities. The NDE group at Imperial College has an outstanding record in technology transfer, via licensing, close working with partner industrial companies, and spinning out new companies, and are strongly focused on delivering the benefits of research to industry. They are thus well positioned to judge the appropriate transfer routes and maximise the the transfer of useful findings to industry.