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Long Range Ultrasonic Inspection of Aircraft Wiring

Final Report Summary - SAFEWIRE (Long Range Ultrasonic Inspection of Aircraft Wiring)

Executive Summary:
Due to the aging/degradation process in aircraft wiring which consequently can lead to serious wiring fault. Studies have shown that numerous aircraft incidents (many involves fatalities) between the years 1972 and 2000 found more than 400 wire related incident which triggered a renewed interest in portable testing devices for use during in-service (routine maintenance) inspection.

The aim of the SAFEWIRE project seeks to develop a novel wiring inspection technique based on the use of Long Range Ultrasonic Testing (LRUT) technique which can be used to detect defects in the insulation of the aircraft wiring. In this project, we are attempting to circumvent the shortcomings of traditional inspection methods (i.e. visual) by adopting a novel Long Range Ultrasonic Test technique. The motivation in this project is to exploit the LRUT technologies to detect and characterise damages on the insulation of aircraft wiring in which the area may not be easily accessible by the operator.

The proposed probe utilizes an array of Macro Fibre Composites (MFC) transducers which will conform to the circumference of the cable under test in order to perform the inspection. The array of sensors will be mounted onto the probe holder which will aid in the ease of positioning of the sensors to inspect a cable length of at least 10 m. All prototype software is expected to execute on the MATLAB® platform which is also used to interface with the hardware. The complete LRUT system will provide the user with a two-dimensional image showing the critical defects which may be present in the insulation of the cable section that is tested. Finally the performance of the complete SAFEWIRE system will be evaluated in a field trial.

The challenge in this project is how to offer a feasible solution based on LRUT technologies to increase the Probability of defect Detection (PoD) whilst keeping the virtues of low cost, fast inspection speed and portability (<10 kg). Benefits which will be gained from the SAFEWIRE project are manifold:

1) Reduced risk of human error (i.e. defect missed by visual inspection).
2) Improved quality and safety assurance in aircraft wiring.
3) Require just one (pulse-echo) or two (pitch catch) points access of the cable to carry out the entire length of cable inspection.
4) The transducer array can be made conformable to cope with curvature of the circumference of the cable.
5) No couplants are required which is hazardous in testing live cable.
6) The portable system will aim towards an easy clamping system (couple the transducers to the cable) which will reduce set-up time.
7) High spatial resolution aim towards achieving position accuracy of 100 mm (related to excited frequencies).
8) User friendly software to control the pulser/receiver and displaying the results (post processed by advance signal processing and defect recognition algorithms) to the operator.
9) Reduced operating and maintenance costs.
10) Open new NDT product market.

However, in order for this technique to be fully implemented in a ‘real-world’ setting, there are a number of technical barriers that need to be overcome:

Because of the complexity of wire bundles (multiplicity of materials and irregular shape), no sensor system exists enabling these bundles to be sonified).
Existing LRUT systems require a large heavy pulser/receiver and a laptop computer. No light weight (handheld) 1 or 2 channel unit exists combining the roles of pulser/receiver and computer to control the sensor array, analyse of data and display the results.
It is also necessary to develop defect recognition software enabling LRUT tests of wire bundles to be controlled and interpreted.

At the time of writing, this concept is novel.

Project Context and Objectives:
The SAFEWIRE project seeks to develop a novel wiring inspection technique based on the use of Long Range Ultrasonic Testing (LRUT) technique which can be used to detect defects in the insulation of the aircraft wiring. These defects constitute a serious risk to the aviation industry due to the degradation of the aircraft wiring over time. The proposed project is based on the application of an ultrasonic transducer operating at typical guided waves frequencies (10 – 500 kHz) in which the cable act as a waveguide. The SAFEWIRE project is focussed, at the stage of reporting, upon the development of a reliable LRUT system to detect critical defects. The project envisages developing a portable inspection system which is able to detect insulation defects over a range of commonly used aircraft wiring through advanced signal processing and pattern recognition techniques.

Overall specification of the SAFEWIRE project detailing aerospace industry (including both military and commercial) requirement and the individual module (i.e. building blocks) of SAFEWIRE system are critically reviewed and documented (see D1.1). These are performed in consultation with End Users and SMEs via initial communication during the kick-off meeting and follow up by detailed questionnaires for their input. Subsequently, a range of suitable cables (test specimens) have been acquired, which subsequently will be used throughout the duration of the project. These samples were provided by Marshalls which has extensive knowledge of the cables (i.e. compositions, material, geometry etc…) which are applicable in the aerospace industry.

The objective of the project is to perform inspection in wire bundles. However due to the complexity and impracticality, the study is restricted to the modelling of single wire with both single and multiple cores. In addition, feedback from the end user (Marshall) also revealed that guided waves inspection technique can be conveniently applied to inspect the wires individually. Modelling of guided waves in wire using commercial available Finite Element Method software COMSOL® was performed (see D2.1). The dispersion curve results of simple geometry (benchmark model) are compared with dedicated commercial software (Disperse®) for obtaining dispersion curves, and the results agree very well. More complex geometries of cables (i.e. R015 cable provided by Marshall) were modelled using COMSOL® software since there are limitations in Disperse®. Numerical studies were also performed to determine the influence of dispersion curves by varying model parameters such as material, geometry and adding insulation. Transient analyses were also developed using COMSOL® to analyse wave propagation in R015 cable with and without defect.

Validation of the numerical results for both benchmark and complex cables were also investigated with laboratory experiment using 3D laser scanning vibrometer. The results also showed reasonable agreement between the measured and simulated dispersion curves. Transducers analysis have also been performed as well using the 3D laser scanning vibrometer technique and the experiment concluded that all the transducers were found to be moving predominantly in the y-axis. Laboratory measurement (pulse-echo and pitch-catch) using Teletest system (with existing MFC transducers and holders) has been performed on R105 cable (provided by Marshalls) for various lengths (up to 15 m). Baseline (defect free) and total of 5 defects (including cuts and an area of insulation loss) measurements were performed. Results were sent to Certh for further analysis using advance signal processing and defect recognition algorithms.

Characterisation of the proper test setup has been performed in order to develop a guided wave test procedure. MFCs transducer’s holder has been designed and sent for manufacturing. Specification of the pulser-receiver system (i.e. power source, 7” touch screen and operating system etc…) has been clearly defined. The electronic circuitry of the handheld pulser-receiver unit which consists of two transmitting and receiving channels capable of handling frequency range of 10 kHz and 500 kHz (optimum frequency range is around 15 to 30 kHz for our LRUT application) is designed. Tests have been conducted for the dual channel transmit circuit. The schematics for the receive circuits was finalised in month 9 and its PCB will be ready for test in month 11. The circuit has also been tested with the heaviest load of the transmit circuit for optimising the size of the high voltage power supply that provides ±400 VDC. A suitable battery had been chosen (15 VDC Nom.; 5.3 Ah with 10A protection circuit and status monitor) and evaluated using a dummy load. An external charger will be provided for charging the battery from the mains supply (240V; 50 Hz). Further laboratory experiment works have been carry out to deduce the UGW technique capability with regard to the test range (i.e. length of cable) and sensitivity to well classified damages on the wire insulation. Currently, the maximum length of cable tested is 15 m. The results obtained shown that the proposed technique is capable of detecting insulation defects of at least 10 mm in length from the raw pulse echo data. The knowledge built up from these characterisation test form the basis for subsequent experiment work procedure.

A new transducer system prototype capable of exciting ultrasonic waves into the electrical aircraft wire of various types and detecting signals reflected from potential discontinuities / defects in the insulation of the wire has been developed. In addition, the performance of the prototype has been examined by putting it under test with arrangements for single transducer and an array of two transducers excitation. The transducer array prototype (probe) has been manufactured which aims to provide a very convenient handheld probe use during actual operations. Further experiments have been carried out with this new transducer system prototype and the results demonstrated the sufficient coupling and therefore strong excitation of signal to the wire under test.

A handheld pulsar-receiver had been prototyped. It consists of two transmit channels and four receive channels. The unit is integrated with an off the shelf Single Board Computer (SBC) and an 8” resistive touch screen for portability and making it standalone. An integrated 15V (Nom.); 5.3 Ah rechargeable Li-Ion battery provides primary power to this unit. This unit is capable of sufficiently exciting piezoelectric transducer array/s prototyped for Safewire application at excitation frequency ranging from 5 kHz to 500 kHz at excitation voltage 400 Vpeak-peak (Default: 300 Vpeak-peak). All four receive channels simultaneously sample/ digitise receive data (12bit; 4 MHz) before storing it in the on-board memory (64 GB – Compact flash) for data analysis by the Safewire defect detection software developed. The receive circuits are also implemented with configurable gain (20 dB to 100 dB in 1 dB steps) and filter settings to signal conditioning the useful receive data. The unit supports both pulse-echo and pitch-catch mode ultrasonic guided wave applications. The unit weighs 3.4 kg and measures 330 mm x 250 mm x 80 mm in dimension.
A computational efficient as well as powerful automated defect detection system has been designed. Various feature extraction techniques have been designed and implemented to extract the most informative parameters/measures from the collected signals. Different types of characteristics (time-domain and frequency-domain) were extracted from the ultrasonic signals so as to provide an improved data representation and improve the detection capabilities of the applied techniques. Feature families that were investigated: first-order statistics from time domain, power spectral density (PSD) measures, short time Fourier transform (STFT) and wavelet features (WF). An efficient feature selection technique was employed to reduce the high-dimensionality of the recorded ultrasonic signal and provide a more descriptive and compact signal representation. In addition to enhanced accuracy rates and dimensionality reduction, the method was proved to have reasonably low computational demands, being able to cope with the high-dimensional feature space. An integrated pattern recognition system was developed to automate the flaw detection task. The system was based on advanced non-linear SVM classification models that were trained and tested on the four aforementioned experimental scenarios. A novel hybrid defect discrimination tool was also developed that improves considerably the Signal-to-Noise ratio (SNR), eliminating all the background noisy components and thus forming a valuable tool for defect detection, mapping and sizing. A top level GUI (based on Matlab) that facilitates inputting LRUT specific test data, initiating data collection and view/display test results was implemented. Touch screen size and its resolution were tested for the ease of use. A compromise had been made on screen size for achieving specified/acceptable weight and size of the handheld unit. Suitable connectors and cable for interconnections between the unit and the transducer array (WP3) have been identified.

An application specific Graphical User Interface (GUI) named as Safewire-Application had been developed for bringing all constituent hardware and software components (Safewire defect detection software and guided wave research software) of the Safewire system together such that the complete Safewire system can be operated from a single user interface. An executable file of this Matlab based GUI is installed in the integrated SBC of the handheld pulsar-receiver unit. A Safewire user can invoke this application, input experimental parameters and initiate Safewire inspections from the handheld unit’s desktop: a built in 8”; 800 x 400 resolution LCD touch screen. A purpose built tool lead provides interconnection between the pulsar-receive and the transducer array/s.

A user guide and operation manual for the SAFEWIRE system prototype to inspect bundled-cable has been produced (see D7.1).

The laboratory trials were carried out on a variety of single wire and wires bundle (up to 4 wires in a bundle) of gradually increasing complexity and containing a range of representative defects in the insulation and broken conductors. The test is also performed on a representative mock up (as advised by end-user) and the applicability of the proposed ultrasonic guided wave system is determined. The performance indicators of the system are evaluated in these trials such as defect sensitivity, accuracy of defect detection, effective range of inspection, probability of defect detection, ease of operation and ruggedness of equipment. In addition, the performance of each existing prototype has been examined by putting it under test with various arrangements and types of specimens. The prototype system shows very encouraging results to detect small insulation defect (i.e. a quarter slit) for a single and bundled-cable of several lengths (more than 10 m) with the Combined Hybrid Defect Detection (CHDD) algorithm.

A field trial at Marshall is conducted on a cable bundle set up on a section of an aircraft wing. It is shown that the current SAFEWIRE system with the proposed technology of ultrasonic guided waves is applicable to detect small insulation defect for cable bundle in a well-representative aircraft environment. New and different types of defects (i.e. chaffing and parallel slit) were investigated in this trial in which the results indicates a promising system to detect chaffing for R015 (37 strands) cable. An official trial is performed with the presence of an independent NDT Centre in which the procedure of inspection has been overseen with a view of building a safety case. The independent inspectors have also participated by performing a visual inspection in the trial. The SAFEWIRE project has taken the exploitable results to minimum Technology Readiness Level (TRL) 4.

Initial research has been performed to determine the available options to get the system certified for use (see D8.8). This has been done in consultation with the Dutch government agency Inspectie Leefomgeving en Transport (Inspection for Environment and Transport) who has confirmed the initial findings and provided referral to type certificate holders. Further discussions with the engineering department of Fokker Services, who are type certificate holders revealed that it will be less complex in the certification process of ground equipment rather than used in flight. Further Research has been performed to determine what activities have to be done to get the system certified for use. Further activities have been performed to seek information from organizations who have strong business links to aerospace manufacturer and Maintenance, Repair and Operation (MRO) activities such as Spectrum Technologies PLC, AXON’ CABLE Ltd, TWI Ltd (Transport Industry Sector), TWI Ltd (Adhesives, Composites & Sealants Section) and Civil Aviation Authority (CAA). Such equipment is instead certified by type certificate holders, such as EADS and Boeing. A safety case document is also reported by an independent NDT centre’s specialist, Graham Edwards, (see D7.3 Appendix B) in which compliments this task.

A draft Plan for use and Dissemination of the Foreground (PUDF) has been initially produced (see D8.3). The PUDF includes the potential to attract investment for the SAFEWIRE technology beyond the duration of the project. Subsequently, a final Plan for the Use and Dissemination of the Foreground (PUDF) has been produced. The final PUDF described shows a way forward for developing the Safewire system from a prototype to an commercial system which is certified by various certification authorities from aerospace industry. Up to TRL6 the Technology Push of a research and development takes place and later on, i.e. beyond TRL6, it is replaced by the Market Pull of production engineering to meet specific commercial demands.

A peer-reviewed conference paper has been published, T. Parthipan, P. Jackson, A. Chong, M. Legg, V. Kappatos, A. Mohimi, C. Selcuk, T.H. Gan, S. Moustakidis, K. Hrissagis, “Long Range Ultrasonic Inspection of Aircraft Wiring – Technique and hardware development”, IEEE Industrial Electronics (ISIE), 1289, Jun 2014. DOI: 10.1109/ISIE.2014.6864800.

Project flyers have also been distributed in 2014 Aerospace Workshop organised by the British Institute of Non-Destructive Testing (BINDT) on 29/4/2014 and at the 7th International Symposium on NDT in Aerospace on 12- 14/11/2014. The project flyer has also been circulated to external parties by partners in order to create awareness for this project.
Creating awareness of the project through formal presentations to the following organizations who have strong business links to aerospace manufacturer and Maintenance, Repair and Operation (MRO) activities such as Spectrum Technologies PLC, AXON’ CABLE Ltd, TWI Ltd (Transport Industry Sector), TWI Ltd (Adhesives, Composites & Sealants Section) and Civil Aviation Authority (CAA).

The website for SAFEWIRE is accessible on the public domain using the following URL: http://www.safewire.eu It is used as a medium to disseminate knowledge and news bulletin for those interested in the technology. There is also a secure area where partners are able to exchange materials of confidential nature. There is a provision for public to give feedback in the website. This website will be updated during the progress of the project and beyond.

An approximately 6 minutes video has been created which capture the importance, aim, scope, operations (laboratory and field trial) and results of project SAFEWIRE. This video is accessible in YouTube via invitation only (i.e. video setting as private).

Total of 4 face-to-face project meetings and 5 web meetings have been organized in the second reporting period. Meeting minutes were circulated to all partners after each face to face meeting. Meeting organized as follows:

The 12-month project and 9-month project review meeting took place in Brussels, Belgium on 4th and 5th Dec 2013, hosted by Hortec and REA respectively. The 18-month project meeting took place in Athens, Greece on 19th Jun 2014, hosted by CERETH. System integration work and testing were performed by RTDs prior to this meeting. The final trial and 24-month project meeting took place in Cambridge, United Kingdom on 2nd Dec 2014, hosted by UBRUN. System integration work and fine tuning of the system were performed by RTDs prior to this meeting. 16th Dec 2014, final field trial conducted at Marshall Aerospace and Defence Group, Cambridge, United Kingdom.

In addition, regular meetings are held on a monthly basis between RTDs and PSC to discuss progress, deviations (if any) and potential project continuation for improvement etc…. Other partners are invited to join as necessary.

All technical and financial reports throughout the project duration have been closely monitored, aiming to submit them in a timely manner.

Project Results:
WP1:
Task 1.1 Critical review of requirement Month 1- 3

This task is 100% complete in month 9. A critical review of the SAFEWIRE system requirements has been carried out for each individual work package. In addition, this task involved the consultation of all SMEs and End Users (who are familiar with what is desired for the industry) within the consortium via a questionnaire. The questionnaire aims to identify the technical aspects of most significance that need to be agreed upon in order for the project to tackle relevant problems encountered in the aerospace industry. The questions focused on the followings;

i) technical performance
ii) hardware requirements and
iii) software requirements

which takes accounts of initial discussions at the project kick-off meeting and subsequent meetings with the End users. These forms the building blocks of the main components of the SAFEWIRE system. A literature review for common causes of defects in aircraft wiring and current common methods of wire inspection is also performed.

Overall specification of the SAFEWIRE project detailing industry requirement and the SAFEWIRE system have also been critically reviewed and documented. The complete Guided Ultrasonic Wave (GUW) system will aim to provide the operator with a two-dimensional image showing the critical defects which may be present in the cable. The challenge in this project is how to offer a feasible solution based on GUW technologies to increase the Probability of defect Detection (PoD) in aircraft cable whilst keeping the virtues of low cost, low power consumption and portability. Initially, 2 types of test wire specimens consisting of different wiring size (AWG 10 and 22) of the single core sunscreen type wire (without defect) were sourced and described in D1.1 section 2.1. Subsequently, various lengths of 5 and 15 m for each type of cable are also provided. Information of the material composition for the cables (i.e. cross link modified ETFE use for the insulation and tin coated copper use for the wire) are also provided from the data sheet. A plan has been has been formulated to study wave propagation in simple and complex wire to determine the dispersion curves using both computational modelling and experiment techniques (for WP2). In view of the computational modelling, two commercially available software Disperse® and COMSOL® will be used. Subsequently, the predicted dispersion curves results will be validated using scanning vibrometry. Various types of transducers (i.e. Shear type contact transducer, Electromagnetic Acoustic Transducer (EMAT) and Macro-Fibre Composite (MFC)) were compared and based on the prior knowledge on using MFC for inspection of wire as well as the benefits (i.e. low costs, light weight, easily conformable, extendable to an array and closely match acoustic impedance etc…), consensus of the consortium has been reached to utilised it (for WP3). Preliminary specifications of the hardware and software (i.e. electrical, mechanical, size, weight and potential operating system) of the pulser/receiver module has been defined. Also the descriptions and functionality and user interface are also illustrated (for WP4). A variety of signal processing algorithms will be designed including pre-processing techniques, classification and post processing analysis. A 2D visualisation of the defect display for the operator is also proposed (for WP5). In addition, concept for the overall system based on the pulse-echo and pitch-catch modes are defined (for WP6). The field trials are expected to be carried out at the End User (Marshall Aerospace and Defence Group) facilities. The trials will either be carried out on a C-130 airplane, depending on their availability at the time of site trials, or alternatively on section of a C-130 wing (for WP7).

Task 1.2 Design test specimens Month 1-3 and Task 1.3 Acquire test specimens ONGOING TASK
This task is 100% complete in month 9. Wire samples suitable for both military and commercial aircrafts were sourced following discussions with the SMEs/End Users partners. These samples were provided by Marshalls who has extensive knowledge of aircraft wiring (i.e. material, wire configurations, common securing techniques etc…) which are applicable in the aerospace industry. During the Kick-off meeting, consensus was reached for all partners that the project should start with investigation of a simple case (i.e. a rod). Once knowledge has been built up, more complicated configurations will be studied. Also information of the damaged samples (i.e. types of defects, size and location) should be known to allow more control in the studies. Real (unclassified) defects can be attempted at a later stage. As such a copper rod will be used initially to build the modelling and experimental procedure as part of a benchmarking exercise. Subsequently, the selected wire samples will be put through the developed procedure to investigate wave propagation and defect detection.

WP2:
Task 2.1 Modelling of guided waves in wire bundle Month 2 – 9

This task is 100% complete in Month 9. The objective of this WP is to perform modelling of guided waves in wire bundles. However due to the complexity and impracticality, the study is restricted to the modelling of single wire with both single and multiple cores. In addition, feedback from the end user (Marshall) also revealed that guided waves inspection technique can be conveniently applied to inspect the wires individually.

Analytical and Finite Element methods have identified at least three fundamental wave modes for single core wire structures (longitudinal, torsional, flexural) existing in the guided wave operating range. These techniques have also identified that the fundamental Torsional mode (T(0,1)) is the least dispersive mode, regardless of change in material or geometry properties. The longitudinal mode (L(0,1)), was determined to experience minimal dispersive effects. It is known that the longitudinal mode is generally less attenuative than other modes, and is more sensitive to transverse defects (due to their mode shapes), therefore it can be suggested that L(0,1) will be the most appropriate mode for inspection. The effects of material and geometry parameters on dispersive behaviour were also characterized. The attenuation effects on sound energy due to distance travelled was found to be insignificant when determining a dispersion curve. This indicates that the FEM and analytical techniques assume ideally elastic materials, with no loss due to scattering, from travelled distance. The changes in radius were found to alter the shape of a waveguide, resulting in changes to flexural and longitudinal modes. Changes in density were found to affect the inertial resistance to the motion of a mechanical stress wave. Finally Elastic changes were shown to affect the ability of particles to transfer elastic energy, (stimulated by stress waves) between each other, and had inverse effects to changes in density.
From these observations, it can be predicted that changes in the number of single cores would result in similar effects seen by the change in radius (i.e. a purely geometrical change) in dispersive behaviour. Adding insulation will likely be a complex function of geometry, Material and Impedance mismatch contributions. Transient analysis has been made for R015 cable with and without a defect showing the wave propagating within the cable through time. Experiments have been performed to validate the dispersion curves for cables using a scanning laser vibrometer. The results showed reasonable agreement between the measured and simulated dispersion curves. In addition, the transducer analysis have been performed as well and all the transducers were found to be predominantly moving in the y-axis.

Task 2.2 Development of test procedure Month 2 – 12

This task is now 100% completed. Laboratory measurements have been conducted using the MFC transducers coupled to the cables under test (provided by Marshalls) for various lengths (up to 15 m). The test is carried out for cable with defect free and also well classified defects (i.e. cut or section removal of cable insulation specified by cross section area loss). The commercial available Teletest unit is initially used to perform the measurements. A tone bursts was employed to generate signals with frequency sweeps in the frequency range 10 kHz – 30 kHz with a step of 1 kHz. A total of 30 repetition is performed for each setup to improve the signal to noise ratio (SNR) initially using existing transducer’s holder which requires careful setup by the operator. A better version of the transducer’s holder has been designed (i.e. taking account of ease of usage, flexibility of pressure control, weight etc…) and manufactured as described in the task 3. However the concept of mounting the transducer to the cable is still the same and in view of this, proper characterisation of how the MFC transducer is to be mounted on to the cable under test has been performed using the existing holder. The procedure for the proposed inspection technique based on ultrasonic guided wave (UWG) has been characterised (i.e. the standard for setting up the inspection equipment/apparatus). Laboratory studies were carried out to deduce the UGW technique capability with regard to the test range (i.e. length of cable) and sensitivity to well classified damages on the wire insulation. Currently, the maximum length of cable tested is 15 m. The results obtained shown that the proposed technique is capable of detecting insulation defects of at least 10 mm in length from the raw pulse echo data. The influence of the excitation frequency was also investigated and the suitable range of frequencies (sensitive to insulation damage at >10 m cable length) agrees well with the previous dispersion curve results. In addition, the coupling of the transducer to the cable has also been characterised. It is worth to emphasized that consensus has been reached by the consortium and REA that the proposed technique will aim to inspect wires individually in a bundle due to the complexity of the wave propagation mode in a wire bundle. Based on the information from the End-User (Marshall), such an inspection technique can be implemented in the field as the cables are uniquely marked along their entire length. The knowledge built up from these characterisation test form the basis for subsequent experiment work. See deliverable D2.2 for details.

WP3:
Task 3.1 Guided wave probe design Month 4 – 12

This task is now 100% completed. The first prototype of the transducer probe holder has been designed consists of an array of two MFC transducers which allow proper coupling to the cable under test. The design take accounts of the functionality, ease of clamping/removing to the cable under test, maximum blocking force (87 N) for the specific type of MFC transducer (Type P1), electrical interference, durability, size, weight etc… for the initial design. The design has been circulated to all project partners within the consortium for further comments/input before engaging the manufacturing process. Subsequently, a new transducer system prototype capable of exciting ultrasonic waves into the electrical aircraft wire of various types and detecting signals reflected from potential discontinuities / defects in the insulation of the wire has been developed. In addition, the performance of the prototype has been examined by putting it under test with arrangements for single transducer and an array of two transducers excitation. The details of the design of the transducers probe are also included in this document.

Task 3.2 Prototype transducer array manufacture Month 10 – 18
This task is now 100% complete. The first prototype of the transducer probe holder has been sent for manufacturing by external manufacturer. A Non-Disclosure Agreement (NDA) has been signed by the external manufacturing company (C J Engineering) before communicating the details of the technical drawings on the transducer probe holder. The transducer array prototype (probe) has been manufactured which aims to provide a very convenient handheld probe use during actual operations. The experiment results demonstrated the sufficient coupling and therefore strong excitation of signal to the wire under test.
A number of findings have been extracted which include:
• An array of MFC transducers simultaneously excited provides more signal energy into the
cable.
• Higher performance of the signal (i.e. energy level) can be achieved with probe 2 as
compared with its predecessor (probe 1). Also less fiddling for an operator to mount probe 2
to the cable under test is experienced.
• At a later stage, further refinement/optimisation for this first prototype have also been performed to include a force meter in order to have a means to quantify the coupling force.

WP4:
Task 4.1 Pulser/receiver design Month 2 – 12 This task has now been completed. The handheld pulsar-receiver had been developed to support medium frequency LRUT that allows components to be non-destructively tested by means of ultrasonic wave in the frequency range of 5 kHz and 500 kHz. The handheld unit consists of two transmit channels and four receive channels. Each transmit channel permits exciting piezoelectric transducer array of two MFC transducers of type P1 at a maximum excitation voltage of +/-200V (Default: +/-150V). This excitation voltage amplitude is made scalable from 10% to 100% of +/-150 V. The excitation waveform in a typical application can be a windowed-sine wave (Von-Hann or tone-burst) or chirp envelop of frequency ranging from 5 kHz and 500 kHz at a pulse repetition rate of 10 Hz. The receive channels are designed to handle RF signals of maximum peak to peak amplitude of 500 mV and of frequency ranging from DC to 500 kHz. Its features includes a configurable receive gain from 20 dB to 100 dB in 1 dB step; 12 bit resolution and 4 MHz sampling. The unit is integrated with a 15V (Nom.) 5.3 Ah rechargeable Lithium Ion battery as a primary power source. An off the shelf single board computer running on Windows Embedded 8 Pro together with a 8” touch screen had been integrated in this handheld device for providing computing power and interfacing. Both pulse-echo and pitch-catch mode are supported.
Task 4.2 Prototype pulser/receiver assembly Month 12 – 18
This work now has been completed. The assembly of constituent subsystems of the pulser-receiver are integrated together with the single board computer and the touch screen to form the handheld pulsar-receiver unit. The unit is provided with a port for the tool lead and peripheral ports for external interfacing such as external display, remote access via Ethernet, and USB ports for keypad, mouse and storage devices as enhanced features. This hardware is packaged in an enclosure of size 330 mm x 250 mm x 80 mm. The overall weight of this handheld pulsar-receive unit is 3.4 kg. Further optimisation of the size and weight is possible by customising the enclosure.

WP5:
Task 5.1 Optimise signal generation techniques and signal processing algorithms (M4-M16)
This task is 100% complete. A variety of signal processing algorithms were implemented to meet the objectives of Task 5.1. A list of them is given in the following:
- DC offset correction
- Energy based normalization
- Curve fitting algorithms (linear, quadratic, piecewise linear interpolation, smoothing splines)
- Signal transformations based on the outcome of the curve fitting algorithm application
- Wavelet based denoising
- Auto-correlation measures computation
The aforementioned techniques and algorithms were implemented and validated on real case scenarios where cables of varying lengths were utilized. Artificial cuts of increasing size were created on the insulation of the cable and the efficiency of the aforementioned signal processing techniques was assessed in terms of their ability to improve the Signal-to-Noise Ratio (SNR). To optimise the signal generation process, an enriched and extensive data acquisition protocol was adopted. A significant number of measurements was conducted for each setup (for the defect free cable and the 5 defect categories). A series of tone bursts of gradually changing frequency was employed to generate signals with frequency sweeps in the frequency range 10kHz – 30kHz with a step of 1kHz. The application of the signal processing techniques on this initial dataset contributed to extracting the first findings regarding the optimal frequency and the optimum signal generation process.
A novel hybrid Defect Discrimination (DD) tool was also developed that improves considerably the Signal-to-Noise ratio (SNR), eliminating all the background noisy components and thus forming a valuable tool for defect detection, mapping and sizing. The developed hybrid DD measure formed a novel sophisticated tool for defect identification and localization in aircraft wiring. In comparison with the commonly used baseline subtraction and cross-correlation analysis, the proposed technique accomplished considerable higher SNR being able to identify all the defect sizes under investigation. The effectiveness of the proposed analysis suggested that the DD measure could be efficiently used, not only for wiring inspection but also for other large and complex infrastructures such as pipes, ship hull, bridges etc.

Task 5.2 Defect detection, sizing and characterisation algorithms Month 6 – 18
This task is 100% complete. A computational efficient as well as powerful automated defect detection system has been designed whereas a significant number of the required software components have been already developed:
-Pre-processing tools: a non-linear median filtering technique has been developed for noise reduction and SNR improvement. As it has been mentioned in the paragraph above (Task 5.1) various data analysis and pre-processing tools are also available for signal enhancements and correction.
-Feature extraction: Various feature extraction techniques have been designed and implemented to extract the most informative parameters/measures from the collected signals. Different types of characteristics (time-domain and frequency-domain) were extracted from the ultrasonic signals so as to provide an improved data representation and improve the detection capabilities of the applied techniques. Feature families that were investigated: first-order statistics from time domain, power spectral density (PSD) measures, short time Fourier transform (STFT) and wavelet features (WF).
- Feature selection: An efficient feature selection technique was employed to reduce the high-dimensionality of the recorded ultrasonic signal and provide a more descriptive and compact signal representation. In addition to enhanced accuracy rates and dimensionality reduction, the method was proved to have reasonably low computational demands, being able to cope with the high-dimensional feature space. The generated FS algorithm was proved capable to select the most informative features from the pool of the extracted parameters that can be used to discriminate between defective and defect-free samples as well as classify the type, severity or extent of the defect.
- Classification: An integrated pattern recognition system was developed to automate the flaw detection task. The system is based on advanced non-linear SVM classification models that were trained and tested on various experimental scenarios. The trained SVM model accomplished efficiently the classification task being able to alert the operator to any defects and give indications for the defect severity.

WP6:
Task 6.1 Develop graphic user interface Month 6 – 20
This work has now been completed fully. A Matlab based top level GUI that integrates the Safewire defect detection software developed in WP5 and Plant Integrity Ltd.’s proprietary GW research software had been developed. The GUI acts as a dash-board for Safewire experiments providing menus/fields for inputting inspection specific parameters, initiating inspection, processing the collected data and displaying the processed and/or raw data. An execution file of the developed Matlab code for this GUI named as Safewire Application was generated and installed in the single board computer to form a standalone unit.

Task 6.2 System Build Month 6 – 20
The system build that integrates the prototyped sub-systems of Safewire system: handheld pulser-receiver unit and the transducer array has now been 100 % completed and demonstrated. A custom made tool lead is provided with the hardware for interconnecting the sub systems. The unit is built in with a battery status monitor and an external charger is provided to charge the integrated battery.

WP7:
Task 7.1 Prepare inspection procedure Month 11-12
This task is 100% complete. A user guide and operation manual for the SAFEWIRE system prototype to inspect bundled-cable has been produced (see D7.1).

Task 7.2 Laboratory trial Month 12 – 20
This task is 100% complete. The laboratory trials were carried out on a variety of single wire and wires bundle (up to 4 wires in a bundle) of gradually increasing complexity and containing a range of representative defects in the insulation and broken conductors. The test is also performed on a representative mock up (as advised by end-user) and the applicability of the proposed ultrasonic guided wave system is determined. The performance indicators of the system are evaluated in these trials such as defect sensitivity, accuracy of defect detection, effective range of inspection, probability of defect detection, ease of operation and ruggedness of equipment. In addition, the performance of each existing prototype has been examined by putting it under test with various arrangements and types of specimens as detailed reported in D7.2. The prototype system shows very encouraging results to detect small insulation defect (i.e. a quarter slit) for a single and bundled-cable of several lengths (more than 10 m).

Task 7.3 Blind trials on full scale aircraft harness Month 18 – 24
This task is 100% complete. A field trial at Marshall is conducted on a cable bundle set up on a section of an aircraft wing. It is shown that the current SAFEWIRE system with the proposed technology of ultrasonic guided waves is applicable to detect small insulation defect for cable bundle in a well-representative aircraft environment. New and different types of defects (i.e. chaffing and parallel slit) were investigated in this trial in which the results indicates a promising system to detect chaffing for R015 (37 strands) cable. An official trial is performed with the presence of an independent NDT Centre in which the procedure of inspection has been overseen with a view of building a safety case. A safety case document is reported by Graham (see Appendix B) with the aim to compliments the deliverable D8.1. The independent inspectors have also participated by performing a visual inspection in the trial. See D7.3 for details.

WP8:
Task 8.1 Draft safety case for certification for submission to EASA Month 18 – 23
Research has been performed to determine what activities have to be done to get the system certified for use. The investigation has lead to insights that there are no specific EASA or FAA rules concerning the certification of test equipment. Further activities have been performed to seek information from organizations who have strong business links to aerospace manufacturer and Maintenance, Repair and Operation (MRO) activities such as Spectrum Technologies PLC, AXON’ CABLE Ltd, TWI Ltd (Transport Industry Sector), TWI Ltd (Adhesives, Composites & Sealants Section) and Civil Aviation Authority (CAA). Such equipment is instead certified by type certificate holders, such as EADS and Boeing. A safety case document is also reported by an independent NDT centre’s specialist, Graham Edwards, (see D7.3 Appendix B) in which compliments this task.

Task 8.2 Plan for the Use and Dissemination of the Foreground (PUDF) Month 1 – 24
A final Plan for the Use and Dissemination of the Foreground (PUDF) has been produced (see D8.4). The SAFEWIRE project has identified Exploitation and Dissemination Manager, Dr. Rafal Lopatka of Polkom, who will assume responsibility for coordination of the project management and exploitation, with the full support of the Project Steering Committee (PSC). The final PUDF described shows a way forward for developing the Safewire system from a prototype to an commercial system which is certified by various certification authorities from aerospace industry. Success will relies on much on closing the funding gap for system development beyond finish of the project. It also captures all dissemination and exploitation activities which have been undertaken by the Project partners.

Task 8.3 Awareness events and conferences Month 1 – 24

A peer-reviewed conference paper has been published, T. Parthipan, P. Jackson, A. Chong, M. Legg, V. Kappatos, A. Mohimi, C. Selcuk, T.H. Gan, S. Moustakidis, K. Hrissagis, “Long Range Ultrasonic Inspection of Aircraft Wiring – Technique and hardware development”, IEEE Industrial Electronics (ISIE), 1289, Jun 2014. DOI: 10.1109/ISIE.2014.6864800.

Project flyers have also been distributed in 2014 Aerospace Workshop organised by the British Institute of Non-Destructive Testing (BINDT) on 29/4/2014 and at the 7th International Symposium on NDT in Aerospace on 12- 14/11/2014. The project flyer has also been circulated to external parties by partners in order to create awareness for this project.
Creating awareness of the project through formal presentation to the following organizations who have strong business links to aerospace manufacturer and Maintenance, Repair and Operation (MRO) activities such as Spectrum Technologies PLC, AXON’ CABLE Ltd, TWI Ltd (Transport Industry Sector), TWI Ltd (Adhesives, Composites & Sealants Section) and Civil Aviation Authority (CAA).

Task 8.4 Advertising and promotion Month 1 – 14
The website for SAFEWIRE is accessible on the public domain using the following URL: http://www.safewire.eu
It is used as a medium to disseminate knowledge and news bulletin for those interested in the technology. There is also a secure area where partners are able to exchange materials of confidential nature. There is a provision for public to give feedback in the website. This website will be updated during the progress of the project and beyond. A project flyer has also been designed in order to disseminate them to external parties to create awareness.

An approximately 6 minutes video has been created which capture the importance, aim, scope, operations (laboratory and field trial) and results of project SAFEWIRE. This video is accessible in YouTube via invitation only (i.e. video setting as private).

WP9:
Task 9.1 Progress meetings Month 1 – 24
Total of 4 face-to-face project meetings and 5 web meetings have been organized in the second reporting period. Meeting minutes were circulated to all partners after each face to face meeting. Meeting organized as follows:

The 12-month project and 9-month project review meeting took place in Brussels, Belgium on 4th and 5th Dec 2013, hosted by Hortec and REA respectively.
The 18-month project meeting took place in Athens, Greece on 19th Jun 2014, hosted by CERETH. System integration work and testing were performed by RTDs prior to this meeting.
The final trial and 24-month project meeting took place in Cambridge, United Kingdom on 2nd Dec 2014, hosted by UBRUN. System integration work and fine tuning of the system were performed by RTDs prior to this meeting.
16th Dec 2014, final field trial conducted at Marshall Aerospace and Defence Group, Cambridge, United Kingdom.

In addition, regular meetings are held on a monthly basis between RTDs and PSC to discuss progress, deviations (if any) and potential project continuation for improvement etc…. Other partners are invited to join as necessary.

Task 9.2 Progress report Month 1 – 24

Monitor all technical and financial reports throughout the project duration, aiming to submit them in a timely manner (see D9.1).

Potential Impact:
The European Aviation Safety Agency has reported that 15% of fatalities are attributed to aircraft engineering failure in the period between 1997 and 2009. By effecting a step change in the probability of defect detection in aircraft wiring using the proposed portable LRUT technique, the SAFEWIRE project will aim to provide a tangible contribution to aviation safety. It is anticipated that the SAFEWIRE system will provide increased reliability in detecting defects in the insulation of the cable. This inspection system will not only be applied in the aerospace sector but can also be extended to other safety critical industries such as automotive and marine. This is viewed as an attractive market opportunity and a long term objective. In the short term, the market pull in the aerospace sector is significant where the need is to develop more reliable NDT techniques for aircraft wiring. This represents a business growth opportunity for the SAFEWIRE SMEs and improves their competitiveness as it is estimated that worldwide air traffic will treble in the next 20 years. As a consequence, the aircraft fleet will double in the same period which would require more maintenance, repair and overhaul (MRO).
List of Websites:
http://www.safewire.eu/

Relevant contact details:

Bart de Vries, Hortec B.V.
Tel: +31 541 531775
Fax: +31 541 535608
E-mail: devries@hortec.nl