Papers by Author: Mark J. Eaton

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Authors: Rhys Pullin, Mark J. Eaton, James J. Hensman, Karen M. Holford, Keith Worden, S.L. Evans
Abstract: This work forms part of a larger investigation into fracture detection using acoustic emission (AE) during landing gear airworthiness testing. It focuses on the use of principal component analysis (PCA) to differentiate between fracture signals and high levels of background noise. An artificial acoustic emission (AE) fracture source was developed and additionally five sources were used to generate differing AE signals. Signals were recorded from all six artificial sources in a real landing gear component subject to no load. Further to this, artificial fracture signals were recorded in the same component under airworthiness test load conditions. Principal component analysis (PCA) was used to automatically differentiate between AE signals from different source types. Furthermore, successful separation of artificial fracture signals from a very high level of background noise was achieved. The presence of a load was observed to affect the ultrasonic propagation of AE signals.
Authors: Mark J. Eaton, Karen M. Holford, C.A. Featherston, Rhys Pullin
Abstract: The presence of impact damage in a carbon fibre composite can reduce its capacity to support an in-plane load, which can lead to an unexpected or premature failure. This paper reports on an investigation into two slender carbon/fibre epoxy panels, one un-damaged and one with an artificial delamination introduced using an embedded section of PTFE. The reported tests form part of a larger series of investigations using differing sizes of artificial delamination and real impact damage. An investigation of wave velocity propagation at varying angles to the composite lay up was completed to assist in source location. The specimens were loaded under, uniaxial in-plane loading and monitored using four resonant acoustic emission sensors. A full field optical measurement system was used to measure the global displacement of the specimens. Analysis of AE waveforms and AE hit rate were used to assess the buckling of the panel. The results compared favourably with the optical measurement results.
Authors: Mark J. Eaton, Rhys Pullin, C.A. Featherston, Karen M. Holford
Abstract: Damage detection and location in aerospace composites is currently of great interest in the research community and is being driven by the need to reduce weight of commercial aircrafts and hence make substantial environmental improvements. The increased use of composites as safety critical components has led to the need for development of structural health monitoring (SHM) systems. Acoustic Emission (AE) offers an excellent potential for delivering the necessary information of damage detection to maintenance engineers in terms of location however there are currently no methodologies that can use AE signals to characterise damage sources. This paper explores a methodology for damage characterisation based on measuring the amplitude ratio (MAR) of the two primary plate wave modes, to allow identification of in-plane (matrix cracking) and out-of-plane sources (delamination). Results from a large-scale buckling test show good correlation between signal characterization and observed damage mechanisms.
Authors: Rhys Pullin, Mark J. Eaton, Matthew R. Pearson, Christopher Pollard, Karen M. Holford
Abstract: Composite patch repairs are being increasingly used throughout bridge structures in the UK. These patches offer a convenient and strong repair providing that the bond used to adhere the patch to the structure retains its integrity. Acoustic emission (AE), a passive approach and Acousto-Ultrasonic (AU), an active approach offer two methodologies for monitoring the structural bond and ensuring the patch repair remains effective. An experimental program was developed to assess the suitability of using AE and AU for monitoring the bond. Two concrete beams were manufactured and pre-cracked in three point bending prior to being repaired using a bonded composite patch. Two static tests were then completed to assess the performance of the two techniques for monitoring the bond. Results were compared with strain gauges adhered to the bonded patch and visual observation. For active monitoring a baseline of signals were captured at a known load and post damage a further series was captured at the same load. The signals sets were then compared using a cross correlation function technique. A simple accumulative acoustic energy analysis was then completed for the passive data. Results demonstrated that both techniques can be utilised to monitor the bonded structure. By comparing the results with those recorded by the strain gauges and visual inspection it was possible to demonstrate the successful effectiveness of the techniques for detecting global damage but specific debonding events would require further investigations.
Authors: Rhys Pullin, Matthew R. Pearson, Mark J. Eaton, Carol A. Featherston, Karen M. Holford, Alastair Clark
Abstract: The ability of a Structural Health Monitoring (SHM) system to automatically identify damage in a composite structure is a vital requirement demanded by end-users of such systems. This paper presents the demonstration of a potential method. A composite fatigue specimen was manufactured and initially tested at 1Hz for 1000 cycles. Acoustic emission (AE) signals were recorded for complete fatigue cycles periodically in order to establish a base-line associated with undamaged specimens. The specimen was then subjected to impact damage to create barely-visible impact damage (BVID) and subjected to further fatigue cycles with acoustic emission recorded until failure. The data was subsequently analysed using a range of techniques including basic RMS signal levels and frequency-based analysis. At various stages during the test, C-scanning was used to validate the results obtained. Results demonstrated that AE is capable of detecting BVID in composite materials under fatigue loading. The proposed method has wide applicability to composite structures which are subjected to cyclic loading, such as wind turbine blades.
Authors: Matthew R. Pearson, Mark J. Eaton, Eszter Szigeti, Rhys Pullin, Alastair Clarke, Richard Burguete, Carol A. Feathersto
Abstract: Composite materials are increasingly being used in a wide range of structural applications in place of metallic materials. This presents a new range of challenges when considering the monitoring of damage and failure in complex components. This paper explores these challenges and presents a potential monitoring method using airborne acoustics which is both non-contact and easily implemented. A carbon composite panel was manufactured and statically loaded in tension until failure. During the test, Digital Image Correlation (DIC) was used to measure full field surface strain in the panel. An array of microphones, placed adjacent to the panel, was used to capture airborne acoustic signals between 400Hz and 20kHz during the test. The captured sound waves potentially contain signals originating from a range of sources, such as fibre failures and matrix cracking, but also contain background noise. A range of techniques have been used to examine the signals and determine the onset of failure, including Short-Time Fourier Transforms (STFT). The detection of failure using the airborne acoustic system has been validated using the strain data from the DIC measurements. The results presented demonstrate the applicability of the airborne system to monitoring of composite components.
Authors: James J. Hensman, Rhys Pullin, Mark J. Eaton, Keith Worden, Karen M. Holford, S.L. Evans
Abstract: This paper details progress towards the application of a methodology for Acoustic Emission (AE) detection and interpretation for the monitoring of fatigue fractures in large-scale industrial environments. An artificial acoustic emission source, representative of a fatigue fracture was injected into a test of a substantial landing gear component. An AE monitoring system was then used to successfully locate and identify the source using the new signal processing methodology.
Authors: Rhys Pullin, A. Clarke, Mark J. Eaton, Karen M. Holford, S.L. Evans, J.P. McCory
Abstract: The detection of damage in gear teeth is paramount to any condition monitoring or structural health monitoring (SHM) tool for aerospace power transmissions such as those used in helicopters. Current inspection techniques include vibration analysis and time-inefficient visual inspection. Acoustic Emission (AE) is a very sensitive detection tool that has been successfully used in many SHM systems. Successful application of AE for damage detection in gear teeth will enable the optimisation of gear box design (and hence weight saving) in addition to safety improvements. This paper details a small aspect of a larger project designed to demonstrate automatic detection and location of common gear tooth defects. A novel test rig was designed to allow the fatigue loading of an individual gear tooth which was monitored using AE. The gear tooth was static in order to exclude the detection of AE signals arising from rotation; this allows initial development of the methodology prior to investigating rotating gears. Digital Image Correlation was used to determine the onset of cracking for comparison with the detected AE. Preliminary results of the investigation show that the developed methodology is appropriate for developing an automated gear health monitoring system and that future work should concentrate on the development of sensors and data acquisition methods associated with obtaining signals from rotating machinery.
Authors: Timothy P. Bradshaw, Mark J. Eaton, Rhys Pullin, S.L. Evans, C.A. Featherston
Abstract: Eight composite plates 400x410x2.15mm were fabricated from carbon/epoxy in ((0,90)4)s lay-up. To ensure there was no damage in the plates prior to the impact investigations the plates were C-scanned. A drop test rig was used to apply a low velocity impact to the undamaged plates. A rebound mechanism was employed to prevent secondary impacts. AE sensors were selected for frequency and size due to the limited space on the test rig. Super glue was used both as a couplant and also to secure the sensors in position. During the impact wave streaming, time driven data and hit driven data were used to record the impact simultaneously. One test was conducted on each sample with two impacts completed at 5J, 6J, 8J and 10J (total of 8 samples). The impacts were designed to allow only slight visible impact damage to be formed. After completion of the impact investigation the plates were C-scanned to determine the area of debonded material. Analysis of the data showed the complete record of the impact event from the wave streaming, while the hit driven and time driven absolute energy data provided increasing correlations with the area of composite damaged.
Authors: C.A. Featherston, Mark J. Eaton, S.L. Evans, Karen M. Holford, Rhys Pullin, Matthew Cole
Abstract: The effect of lightning attachment to structures and vehicles is a cause of major concern to a number of different industries, in particular the aerospace industry, where the consequences of such an event can be catastrophic. In 1963, a Boeing 707 was brought down in Maryland killing 81 people on board, triggering the improvement of lightning protection standards. However, commercial jets are still struck on average once every 10,000 hours of flight time and between 1963 and 1989 forty lightning related accidents were recorded within the U.S.A alone. The rapid increase in the use of composite materials in aircraft design and the consequent increase in complexity when determining the effects of a lightning strike, has led to new challenges in aircraft protection and the requirement for improved understanding and standardisation.
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