TABLE OF CONTENTS



• Objectives
• Technical Description
• Development of Evolving Technologies
• Development and Validation of Standardised Inspection Procedures
• Development of Manufacturing Methods for Realistic Test Specimens
• Implementation of Inspection Validation
• Results
• Conclusions
• Acknowledgements
• References

OBJECTIVES

BRITE-EuRAM programme BE5145 has been concerned with the development of improved in-service inspection methods for safety - critical aircraft structures. To achieve this the programme has used a systems approach to the development of inspection methodologies. This has incorporated all aspects of the inspection process, technology, procedures and human factors, with the specific inclusion of the development of the concept of using inspection validation as an independent and objective mechanism for assessing the fitness for purpose of inspection methodologies. The systems approach has been able to demonstrate that the inspection method can be optimised with respect to reliability and cost-effectiveness. This programme has provided the evidence of the viability of such a systems approach, that would be equally beneficial to a range of inspection issues within the European Community. Specific objectives have been:

to develop rapid, reliable inspection technology for advanced composite material and bonded joints to introduce and demonstrate the use of Inspection Validation as a management support system capable of providing independent and objective evaluation of inspection capabilities to minimise the subjectivity of inspection, and improve the man-machine interface.

TECHNICAL DESCRIPTION

In order to permit the rapid introduction of inspection techniques, suited to in-service inspection, with reliabilities proven within the programme, the consortium has used a combination of :

validation of present in-service inspection techniques, to understand their reliability and limitations improvement of these techniques, through the issues of procedure, equipment and human factors development of evolving inspection techniques, followed up by validation, and a comparison with present in-service inspection.

As a result, the programme can be considered as four key areas whose results are intimately linked. These were 'Procedures', 'Samples', 'Technology' and 'Validation'.

The area termed 'Procedures' has entailed the assessment of key NDT procedures for airframe inspection, in order to ascertain the optimum means of reliable inspection through adherence to standardised, improved procedures. The programme has established two improved "BRITE-EuRAM" procedures, one for rotating-probe eddy-current (RPEC) for hole inspection, and one for ultrasonic inspection applied to carbon-composites. These new procedures have been tested against present state-of-the-art techniques. The validation process has quantified their relative performance. This has been allied to a series of discussions with organisations at facilities around the world in order to generate a guidance document that specifies how procedures might be improved (including listing of possible failure routes).

The area termed 'Samples', has considered the production of a set of specimens that could permit the testing of current in-service inspection techniques, and also the evaluation of the evolving techniques that were to be developed within the programme. Consequently, this task began with a careful agreement of the defect conditions that should be simulated in those materials key to airframe construction, namely carbon-composites and metal-bonded structures. The result was a set of 16 validation samples containing controlled defects, and manufactured in monolithic carbon-composite, carbon-composite with Nomex or metal cores, and metal-to-metal bonded structures.

Key to the whole project has been the theme of 'Validation', it is all well and good to develop new techniques, and profess their worth, but the only true test of improvement is through quantified, objective assessment and comparison. This was provided through Inspection Validation. The samples, employed in a secure environment, have been used to detail the performance of several typical inspection techniques presently applied to the aforementioned structures. These have included

visual inspection tap testing resonance methods manual ultrasonics.

The validation work has enabled the project to quantify the reliability of these current inspection practices and measure reliability relative to defect-size, defect-type and structure. It has also provided evidence of true inspection rate (cost-effectiveness).

The fourth area, that of 'Technology', has developed evolving inspection techniques which may offer improved inspection, whether it be through faster, or more complete (100%) coverage, or an ability to detect defects that are presently invisible to current methodologies. Shearography, thermography and specific ultrasonic variants have received attention. Building on the validation theme, these two have been subjected to a process of validation, using the same specimens in the same scientifically secure environment. This has permitted not only their relative reliability and inspection rates to be quantified, but has also enabled the consortium the luxury of direct comparison to present everyday practice. Obviously, this highlights those areas where improvements have been made, and others where present techniques offer adequate performance, and of course those areas requiring further work. These are summarised below in the results. However, it is interesting that specific partners are introducing these new technologies into routine process control and inspection fields.

RESULTS AND CONCLUSIONS

The project has provided eight key results which are listed below. The conclusions follow.

Production of a set of 16 specimens containing qualified defect conditions Production of a 'BRITE-EuRAM' standardised procedure for Rotating Probe Eddy-Current (RPEC) inspection of (fastener) holes. This work has proven that this BE procedure, which includes the novel design for the calibration standard (see below) has an improved reliability over versions of the procedure presently used in-service Design of the Split-Conical Calibration Standard (known as the SC2S) for the BRITE-EuRAM RPEC procedure Production of a 'BRITE-EuRAM' standardised procedure for the ultrasonic inspection of carbon composite material. The work has shown that this procedure has an improved reliability over present ultrasonic inspection methods used in-service Production of a guidance document detailing the new procedures and their improvements over present in-service practice. It also details other mechanisms which could further enhance the reliability of procedures, as determined by discussions with NDT personnel from a variety of aerospace facilities The development of shearography, thermography, broad-brush (Lamb-wave) ultrasonics and an automated NDI system, that offer possible advantages to airframe inspection A catalogue of typical defect responses to shearography applied on aerospace components. The validation of current and evolving technologies, including visual inspection, tap-testing, resonance methods, manual ultrasonics, shearography, thermography Lamb-wave ultrasonics and the use of automated NDI systems.

Specific conclusions have been :

The BRITE-EuRAM RPEC procedure is a qualified improvement over present in-service inspections Most of the defects in the samples could be reliably detected using the present inspection techniques (visual inspection, tap-testing, resonance methods or manual ultrasonics) or the evolving ones (shearography, thermography, Lamb-wave ultrasonics or an automated NDI ultrasonic/resonance system) developed within the programme All of the techniques were ineffective in the detection of disbonds in Carbon-Composite Honeycomb (CCH) structures, delaminations in the far skin of the CCH structures, disbonds between the far skin and honeycomb core of the Metal Single-skin Honeycomb (MSSH) structures, disbonds between the far skin and doubler of the Metal Double-skin Honeycomb (MDSH) structures, and disbonds between the far skin doubler and honeycomb core of the MDSH structures There is a need to further examine the role of the evolving technologies to understand and overcome their unusually low showings of reliability for some specific defect-structure combinations despite promising inspection rates (cost effectiveness) and proven capabilities on some real structures tested within the project There is a need to further investigate and determine the best simulation methods of defects for non-ultrasonic methodologies.

COLLOBORATIONS SOUGHT

The consortium is confident that most results can be exploited by the present group. Some will be through single companies, while other exploitation will follow from the partnerships taken from the Consortium. However, the results of the evolving technologies, bar the automated NDT system, have not been as good as originally anticipated. It is suggested that further work should focus or key issues such as reliable defect simulation, the influence of material parameters and geometries on the suitability (or otherwise) of shearography, thermography and Lamb-wave ultrasonics. It is here where the collaboration of interested parties is most sought. It is also suggested that further work on the newer technologies could be used to extend their field of application and suitable collaborators for this are sought.

EXPLOITATION PLANS AND ANTICIPATED BENEFITS

The consortium have put in place a very thorough exploitation plan. The benefits anticipated are listed below

The improvement of inspection reliability through the application of the BRITE-EuRAM RPEC procedure and CFRP ultrasonics procedure The improvement of inspection reliability through the consideration of comments by inspection facilities on the use of the procedures in practice The application of shearography, thermography and ultrasonic variants to a variety of problems in composite materials for which there are no reliable present inspection techniques The use of validation as a means of quantifying inspection performance objectively, allied with immediate introduction of those procedures and techniques with proven reliability and data on cost-effectiveness.

There are also benefits from the knowledge gained in the manufacture of the validation specimens.

FIVE KEYWORDS:
Aircraft Inspection, Non-destructive Testing (NDT), Validation ,Bonded Structure

OBTAINING COPIES OF FINAL REPORT

In view of the positive nature of the results, and the need to ensure that they are used quickly to the benefit of the whole European inspection community, the consortium has decided that the final report on this project is an open-publication, available to all. Interested parties can obtain copies of the report from any partner, whose addresses are listed overleaf, or through the offices of the project co-ordinator at the address below.

Project Co-ordinator BE5145 : AEA Technology, UK
Contact : Dr Chris Hobbs, AEA Technology, E1 Culham, Abingdon , OX14 3DB. UK.
Tel : + 44 1235 463978
Fax : + 44 1235 463799
E-mail : chris.hobbs@aeat.co.uk

NAMES AND ADDRESSES

AEA Technology (Co-ordinator)/ Chris Hobbs
E1 Culham, Abingdon , OX14 3DB. UK.

Airbus Industrie/ John Hewitt
Customer Services Directorate, Headquarters, 1 Rond Point Maurice Bellonte BP 33, 31707 BLAGNAG, Cedex. France.

Alenia Aeronautica/ Antonio Ciliberto
Ingegneria Velivoli da Trasporto, Office : Tecnologia dei controlli - NDT Technology, Viale dell'Aeronautica, 80033 Pomigliano d'Arco (NA), Italy.

Alitalia/ Fernando Serafini
00050 Rome-Fiumincino, Leonardo da Vinci Airport, DOT CCT-FCO, ROME, Italy.

British Aerospace Airbus Ltd/ Charlie Ross
Test & Development Engineering, Materials Laboratory, Filton, BRISTOL, BS99 7AR. England.

Daimler-Benz Aerospace Airbus GmbH/ Wolfgang Bisle
EV37 Materials and Processes, Hunefeldstrasse 1-5, 28183 BREMEN, Germany.

Lufthansa Technik AG/ Friedhelm Schur
Dep. WD 64, Weg beim Jager 193, D-22335, HAMBURG, Germany.

Monarch Aircraft Engineering/ Phil Hall
Luton Airport, LUTON, Bedfordshire. LU2 9LX. England.

OGMA/ Eugenio Chaveiro
OGMA, 2615 Alverca, Portugal.

CSM Materialteknik/ Magnus Engstrom
Box 13200, S-580 13, LINKOPING, Sweden.

Short Brothers plc/Tom Cairnduff
NDI Dept (NAB), PO BOX 241, Airport Road, BELFAST, BT3 9DZ. Northern Ireland.

University of Limerick/ Pat Mallon
University of Limerick, College of Engineering and Science, LIMERICK, Ireland.

CEC officer/ Dr H L Schmidt
EUROPEAN COMMISSION, DG XII/C-1/2, BRITE/EURAM PROGRAMME, 200 Rue de la Loi, B-1049 BRUSSELS. Belgium.

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For more information see: NDT in Aerospace - UTonline 11/97