NEW METHODS FOR ULTRASONIC NDE OF DIFFICULT MATERIALS

Lead Research Organisation: University of Strathclyde
Department Name: Electronic and Electrical Engineering

Abstract

In many engineering applications, materials that exhibit heterogeneous or otherwise acoustically scattering microstructure are employed, examples include austenitic steels and alloys, concrete and fibre reinforced composites. In ultrasonic non destructive evaluation (NDE) of such highly scattering media, the defect target signal is frequently obscured by clutter echoes, caused by numerous, relatively small (relative to the ultrasonic wavelengths), stationary reflectors, which form part of the internal microstructure of the material. The extent of this clutter can be significant and even defects that are larger than these randomly scattering regions can be difficult to detect. This type of time-invariant clutter noise cannot be reduced by the standard time averaging or correlation techniques that are used to reduce time varying random electrical noise. Accordingly, defect identification invariably involves a compromise between achievable resolution, which is determined partly by wavelength in the material, and the noise arising from scattering in the propagation medium. This project will investigate a range of methods for improved ultrasonic NDE of difficult materials. The approach will involve a combination of ultrasonic beam modelling, novel transducer design and array signal processing methods.

Planned Impact

The major direct beneficiaries of the research are: UK and global industry UK public sector UK society As an RCNDE Targeted project, the primary beneficiaries of a successful outcome will be the sponsoring organisations. The NDE supply chain (e.g. NDE equipment manufacturers, array manufacturers etc) will also benefit, as companies will need to be in a position to supply the new technology to the sponsoring end-user organisations. This project, through its obvious implications for improved safety, will have a direct impact on the wider public. The public sector and society will benefit through safer lifetime operation of for example, aircraft, power installations, oil and gas pipelines, buildings, bridges and other infrastructure. Indirectly, the same three sectors will also benefit from the research outputs via cross fertilisation into other industrial and societal areas such as healthcare, improved underwater technology, food and drug processing, oil and gas extraction etc.

Publications

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Description In many engineering applications, materials that exhibit heterogeneous or otherwise acoustically scattering microstructure are employed, examples include austenitic steels and alloys, concrete and fibre reinforced composites. In ultrasonic Non Destructive Evaluation (NDE) of such highly scattering media, the defect target signal is frequently obscured by clutter echoes, caused by numerous, relatively small (relative to the ultrasonic wavelengths), stationary reflectors, which form part of the internal microstructure of the material. The extent of this clutter can be significant and even defects that are larger than these randomly scattering regions can be difficult to detect. This type of time-invariant clutter noise cannot be reduced by the standard time averaging or correlation techniques that are used to reduce time varying random electrical noise. Accordingly, defect identification invariably involves a compromise between achievable resolution, which is determined partly by wavelength in the material, and the noise arising from scattering in the propagation medium. This project has investigated a range of methods for improved ultrasonic NDE of difficult materials, encompassing analytical modelling, experimental evaluation of industrially relevant samples, novel transducer design and array signal processing methods.

Industrial test samples and standard test blocks were experimentally evaluated in the CUE Facility for Innovation and Research in Structural Testing (FIRST) over a range of array operating frequencies. In addition, some industrial samples were characterised using both Electron Backscatter Diffraction and Spatially Resolved Acoustic Spectroscopy techniques. An efficient methodology was developed to translate the microstructure data from these techniques into finite element models, using the PZFlex platform. Both the experimental and simulation approaches contributed to a database of FMC datasets on which the analytical modelling and signal processing developments were evaluated.

Mathematical modelling methodologies utilised in this work to enhance the interpretation of features from array data acquired in high clutter noise structures included: the Factorisation Method; the Fractional Fourier Transform; and the Born Approximation. The ability of putative inversion algorithms to recover crack properties was demonstrated on experimental data using the Factorisation Method, with the Born Approximation used as the basis for an objective crack sizing algorithm. Importantly, this was developed for use with features within low SNR images and which have been

Array transducer bandwidths in excess of 100% were manufactured within this project using graded matching layer techniques. This enhanced bandwidth at the transducer front-end was shown to enhance target detection through the developed frequency domain signal processing techniques developed.

Both temporal and spectral signal processing techniques have been developed to minimise the contribution of clutter noise, whilst maintaining high quality feature details through array processing of FMC datasets. In the spectral domain, an adaptive frequency compounding methodology has been developed using the Blue Linear Unbiased Estimation approach, which has resulted in 31 and 40dB suppression of speckle noise in experimental datasets recorded from both Inconel and steel samples. In the temporal domain, two new algorithms have been developed: Spatially Averaged Sub-Aperture Correlation Imaging and Correlation for Adaptively Focused Imaging. Both approaches use cross-correlation to suppress incoherent backscatter signal components.

As the project developed it became apparent that the developed algorithms and techniques would require a software framework to enable a more thorough evaluation of their relative performance metrics. Towards this aim, a software platform, cueART, was developed to operate on GP-GPU hardware architectures. Thus, a number of the techniques were converted from Matlab to CUDA to improve their computational efficiency by taking advantage of the parallelization available through the GP-GPU units.
Exploitation Route The body of work encompassing modelling, transduction, advanced signal processing and implementation provides an excellent framework from which to develop ultrasonic array techniques within the NDE and associated fields. Together with the facilities at CUE, the outputs from this project provides the capability for industry to provide (difficult) samples for evaluation using the software and hardware techniques developed.
Sectors Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology

 
Description Extension of array imaging processing platform developed during project to support industrial projects in the aerospace and nuclear fields. Work is ongoing in both areas. In the Aerospace project, we have delivered a new algorithm for trial by GKN and partners to improve inspection throughput and quality for fibre reinforced composite materials. In the nuclear submarine project, as are at an early stage, but looking to replace radiography with an advanced ultrasonic system.
First Year Of Impact 2017
Sector Aerospace, Defence and Marine
Impact Types Economic

 
Description EU
Amount € 1,300,000 (EUR)
Organisation European Commission 
Department Seventh Framework Programme (FP7)
Sector Public
Country European Union (EU)
Start 02/2012 
End 05/2015
 
Description GKN Aerospace
Amount £68,000 (GBP)
Organisation GKN 
Department GKN Aerospace
Sector Private
Country United Kingdom
Start 01/2018 
End 09/2021
 
Description GKN Aerospace
Amount £31,000 (GBP)
Organisation GKN 
Department GKN Aerospace
Sector Private
Country United Kingdom
Start 09/2017 
End 04/2018
 
Description Innovation Centre for Sensor and Imaging Systems CENSIS
Amount £90,000 (GBP)
Organisation Innovation Centre for Sensor and Imaging Systems CENSIS 
Sector Charity/Non Profit
Country United Kingdom
Start 05/2017 
End 01/2018
 
Description University of Strathclyde's Advanced Nuclear Research Centre
Amount £360,000 (GBP)
Organisation Babcock International Group 
Sector Private
Country United Kingdom
Start 02/2018 
End 01/2020
 
Description EngD Project with Doosan Babcock 
Organisation Doosan Babcock Energy Ltd
Country United Kingdom 
Sector Private 
PI Contribution Developed 2D ultrasonic array technology and associated imaging capability, which was transferred to the company by the researcher
Collaborator Contribution Doosan provided industrial pull and system specification for the 2D array transducer approach
Impact Transfer of high efficiency array image processing and 2D ultrasonic array design
Start Year 2011
 
Description Project partnership with Airbus UK 
Organisation Airbus Group
Country France 
Sector Private 
PI Contribution Airbus UK worked with the research team and assisted/contributed to the project outcomes
Collaborator Contribution Industrial steer at project meetings.
Impact A range of signal processing algorithms for ultrasonic inspection of difficult materials.
Start Year 2008
 
Description Project partnership with National Nuclear Laboratory 
Organisation National Nuclear Laboratory
Country United Kingdom 
Sector Public 
PI Contribution National Nuclear Laboratory worked with the research team and assisted/contributed to the project outcomes. Engaged in several projects both research and KE on transduction, inspection and automation.
Collaborator Contribution Industrial steer at project meetings
Impact A range of signal processing algorithms for ultrasonic inspection of difficult materials. Bespoke ultrasonic and electromagnetic inspection approaches.
Start Year 2008
 
Description Project partnership with Shell International Trading and Shipping Company Limited 
Organisation Shell Global Solutions International BV
Department Shell Trading & Shipping Company
Country United Kingdom 
Sector Private 
PI Contribution Shell International Trading and Shipping Company Limited worked with the research team and assisted/contributed to the project outcomes
Collaborator Contribution Industrial steer in project meetings
Impact A range of signal processing algorithms for ultrasonic inspection of difficult materials.
Start Year 2008