NDT 2007 Abstracts: 3A-4A
Wednesday 19 September
Session 3A – Aerospace/Composites
Benchmarking shearographic NDT for composites
J Gryzagoridis, D Findeis
Mechanical Engineering, University of Cape Town, Cape Town, South Africa. T: +27 21 650 3229; F: +27 21 650 3240; E: profg@ebe.uct.ac.za
This paper reviews digital shearography in its current state of development. The technique was originally proposed as a strain measurement method but has more recently found an equally important role in the field of non-destructive testing. Digital shearography, as nowadays practiced in research laboratories and in industry, reveals defects beneath the surface of an object by identifying anomalies in the field of surface displacement gradients. Shearography as a non-destructive testing tool has found innumerable applications involving a wide range of materials and in particular has had notable success in identifying debonds and delaminations in composite material structures. In the face of distinct advantages over other NDT methods, such as full field view, non-contacting and real time evaluation, and proven in a vast number of applications in the laboratory/field/factory environment, surprisingly it does not yet have a standard, like for example an ISO International Standard. The objective of this paper is a call for the standardisation of digital shearography based on the involvement of interested parties calling for the start of the process, perhaps as is suggested here, by the technical committee TC 135 of the ISO.
Bond strength testing of composite joints using laser speckle shearing interferometry
Dr John R Tyrer
Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU.
Whole-field optical methods using laser speckle shearing interferometry have been used for qualitative assessment of composite structures for over 10 years. These techniques have provided visible detection of delaminations, inclusions, bubbles and dis-bonds.
As user requirements have elevated, information concerning the state of the internal fibre components and the adhesion within the structure have also become imperative. Alternative optical designs have provided the ability to sense the complete defect family within a structure. What is now needed to determine residual lifetime of structures is an ability to quantify the influence of the defect to the overall performance of the structure.
Computer-based modelling of composite components has now reached an adequate level – this paper shows the feedback of quantified optical non-destructive testing into these models which determines the reduction in structural strength and the consequences of the defects to the overall residual lifetime of the structure.
ACLAIM: Advanced Composite Life Assessment and Integrity Management
Graham Bryce
Doosan Babcock Energy Ltd
Advanced composites are used successfully in many industry sectors, including renewable energy (wind and wave), civil infrastructure (new build and repair), off-shore oil and gas (weight reduction and repair), transport (road, rail and air) and chemical process plant. Nevertheless, their full acceptance for use within major installations requires a consistent integrated approach to integrity management in order to improve reliability, extend life, improve safety, minimise failures and reduce maintenance costs.
The ACLAIM project aims to develop a framework for assessing the integrity of advanced composite structures over their complete life cycle through an integrated approach to structural health monitoring and management. This framework requires development of new multi-functional sensors, aided by improved modelling of defect criticality, and their validation through laboratory and in-service performance trials.
ACLAIM brings together a varied group of both industrial and academic partners to undertake a number of tasks and case studies which look at the differing aspects of composite materials and their integrity management requirements. Findings will culminate in good practice guidance for composite life assessment and integrity management.
In addition to providing an overview of the ACLAIM project, this paper highlights the Doosan Babcock led activities investigating the development, integration and exploitation of sensors, and presents a case study looking at pipe repairs.
Further developments in ultrasonic phased array inspection of ageing aircraft
Irene G Pettigrew1, David I A Lines2, Jesse A Skramstad3, Robert A Smith4 and Katherine J Kirk1
1Microscale Sensors, Institute of Physical Research, School of Engineering & Science, University of Paisley, Paisley, PA1 2BE, UK.
2Diagnostic Sonar Ltd, Kirkton Campus, Livingston, EH54 7BX, UK.
3NDT Solutions Inc., 1682 County Road K, New Richmond, WI 54017, USA.
4NDE Group, QinetiQ Ltd, Cody Technology Park, Farnborough, GU14 0LX, UK
The high performance imaging capability of ultrasonic phased arrays has encouraged their recent widespread adoption for inspecting aircraft components. The benefits of Full-Waveform Capture (FWC), where the RF waveform is recorded for every point on the component surface, has been reported[1]. The speed of their electronic scan means that arrays are particularly suited to this technique and a number of such systems are now in use for rapid 100% area coverage.
A further extension of this technique, termed Full Raw Data (FRD) collection and processing, has also been described[2]. FRD collection involves acquiring a coherent RF data set of multiple transmit-receive combinations from different locations along one or more arrays. The increased quantity of data requires special software techniques to maintain inspection speed and these have been implemented in DSL's modular FlawInspecta system. The FRD approach allows many operations, such as beam steering and adjustable aperture sizing, shading and focusing, to be performed offline on captured data when normally their values are fixed at acquisition time. The system is also able to implement novel techniques that are only possible with FRD acquisition, including enhanced resolution by dynamic transmit focusing and non-linear beamforming.
A critical inspection on ageing aircraft is the detection of radial cracks around fasteners and DSL's FlawInspecta system has successfully found 0.5 mm second layer cracks[3]. In a current application the array is mechanically scanned over the fasteners and volumetric FWC data, comprising ultrasonic frames of 45º shear beams, are recorded for each position of the array. Multiple passes with the array skewed at -20º, 0º and 20º are needed to find cracks at the specified orientations. These separate scans can all be generated from a single pass FRD acquisition. The paper reports on this collaborative project involving single pass data acquisition and advanced processing for second layer crack detection. It also reviews the extension of the technique to include a wider range of skew angles.
[1] D I A Lines, J Skramstad, R A Smith, 'Rapid, low-cost full-waveform mapping and analysis using ultrasonic arrays', Proceedings of WCNDT 2004, Montreal, 30 August – 3 September 2004.
[2] D I A Lines, I G Pettigrew, J A Skramstad, K J Kirk, S Cochran, 'Rapid Distributed Data Collection and Processing with Arrays – the next step beyond Full Waveform Capture', Proceedings of Aging Aircraft 2006, Atlanta, 6 – 9 March 2006.
[3] D I A Lines, J M Bending, R A Smith, 'Novel Applications of Ultrasonic Arrays for Aerospace NDT', Proceedings of Aerospace Testing Expo – Europe, Hamburg, 4-6 April 2006.
Automated data analysis for fastener inspection on ageing aircraft structures
Robert Pitts1, Robert A Smith1, Andrew Connor1, Irene G Pettigrew2, Jesse A Skramstad3, David I A Lines4 and Katherine J Kirk2
1NDE Group, QinetiQ Ltd, Cody Technology Park, Farnborough, GU14 0LX, UK
2Microscale Sensors, Institute of Physical Research, School of Engineering & Science, University of Paisley, Paisley, PA1 2BE, UK
3NDT Solutions Inc., 1682 County Road K, New Richmond, WI 54017, USA
4Diagnostic Sonar Ltd, Kirkton Campus, Livingston, EH54 7BX, UK
Developments in acquisition technology have made the capture of ultrasonic data from large areas of aircraft structure increasingly viable[1]. The large volume of data generated necessitates automated data processing techniques to minimise the analysis burden on the operator.
The detection of cracks in multi-layer structures presents particular challenges due to the complexity of the data. Automated techniques have been developed to enhance the distinction between crack indications and potential false calls, reducing the operators workload[2]. This software also sentences each fastener hole using pass/maybe/fail criteria and attempts to size any crack that is found – based on calibration data from an EDM-notched specimen. This paper reports on developments to the software to enable its application to much larger scan areas, containing several thousand fasteners. Operator burden is further reduced by improvements to the graphical user interface.
[1] I G Pettigrew, D I A Lines, J Skramstad, R A Smith and K J Kirk, 'Further Developments in Ultrasonic Phased Array Inspection of Aging Aircraft', Proceedings of NDT 2007, Glasgow, 18 - 20 September 2007.
[2] Robert A Smith, David Edgar, Lyn D Jones and David M Percivall, 'An Ultrasonic Solution For Second-Layer Crack Detection', Proceedings of NDT 2004, pp 223-228, 2004.
Acoustic emission: From aerospace applications to the clinical assessment of arthritis
L-K Shark1, B Mascaro1, J Prior1, J Selfe1, P Cole2, J Stockdale3, R Bury3 and J A Goodacre1,3
1University of Central Lancashire, 2Physical Acoustics Limited, 3Blackpool, Fylde & Wyre NHS Trust
The presentation reviews a range of applications of acoustic emission in the aerospace sector, which include on-line monitoring of tool wear in the manufacturing phase of aircrafts as well as structural health monitoring in the operation phase of aircrafts. The presentation then describes potential new applications of acoustic emission in human health, focusing on its utilisation for assessing the functional integrity of human knee joints in clinical practice and research. This development is based on the use of a common acoustic emission system for monitoring engineering structures. From the description of the distinctive structural and functional features which acoustic measurements need to capture for each application, the equipment set-up, characteristics of the signals acquired, and methodologies adopted for signal processing, the presentation highlights the differences as well as the similarities in applying acoustic emission to rigid aircraft components and flexible human tissues.
Session 4A – Aerospace
Ultrasonic detectability under loaded conditions of potentially closed cracks from cold-worked holes
Luke J Nelson, Ken Brown, Andrew Young, Lyn D Jones and Robert A Smith
QinetiQ Ltd, Farnborough, GU14 0LX, United Kingdom
Many non-destructive inspections for cracks rely on detecting ultrasound scattered or reflected from the crack. Recently, several methods for second-layer ultrasonic crack detection have been developed, sometimes using automated analysis methods to interpret the complex ultrasonic responses from multiple layers. In the validation of these techniques, the assumption is often made that fatigue cracks will reflect as much ultrasound as an artificially introduced EDM notch or saw cut. However, this is not always the case for 'closed' cracks, which can have a very low ultrasonic reflectivity. Of particular concern is the case of cold-worked holes, where a residual compressive stress field exists, extending to approximately one radius from the fastener hole. In addition, if a crack has grown under fatigue loads that include high peak stresses, there can be a closed region in the plastic zone at the crack tip. To complicate matters further, interference-fit fasteners apply an additional tensile stress, which may or may not counteract the cold-worked stress field near to the fastener, depending on the amount of interference.
This problem was encountered whilst validating a two-layer ultrasonic inspection technique on real cracks in a real fatigue-test wing containing cold-worked holes. Inspections were performed at four different remote load levels by stress-jacking the wing. Whilst the ultrasonic indications from some of the cracks grew with increasing remote load, others did not. Some ultrasonic indications grew both towards the fastener and away from it, suggesting that both crack-tip closure and cold-worked crack-root closure were occurring. A possible reason for some cracks not growing is that they were already being held open by interference-fit fasteners.
The aim of this project was to investigate and understand the effects of cold working, interference-fit fasteners and crack-tip closure on the ultrasonic detectability and sizing of cracks. In particular, information was required about the potential improvement in defect detectability by applying a remote tensile load to the structure to overcome the residual compressive stresses. Results will be reported of an experiment designed to grow fatigue cracks to a range of lengths at cold-worked holes in a single specimen, with interference-fit fasteners installed. These cracks could then be inspected ultrasonically at various remote tensile-load levels and the results compared with EDM notches in a similar specimen. Finally, the interference-fit fasteners could be removed and the ultrasonic inspections at the various loads repeated. Initial results have confirmed that ultrasonic indication size and amplitude both increase with remote tensile load but further results will be required to determine the dependence of defect detectability on remote load.
