NDTnet - November 1997, Vol.2 No.11
Improving the Reliability, Quality and Cost-effectiveness
by the programme partners:
of the Inspection of Safety Critical Structures
(BE 5145 Final Report)
Chris Hobbs (Co-ordinator), AEA Technology, Culham, United Kingdom;
Peter Conroy and Geoff Worrall, AEA Technology, Risley, United Kingdom;
John Hewitt, Airbus Industrie, Toulouse, France;
Claudio Sabatino, Antonio Ciliberto and Giovanni Cavaccini, Alenia Aeronautica, Naples, Italy;
Fernando Serafini, Alitalia, Rome, Italy;
Charlie Ross, British Aerospace Airbus, Bristol, United Kingdom;
Wolfgang Bisle and Dieter Schiller, Daimler-Benz Aerospace Airbus, Bremen, Germany;
Friedhelm Schur, Lufthansa Technik, Hamburg, Germany;
Phil Hall, Monarch Aircraft Engineering, Luton, United Kingdom;
Eugenio Chaveiro, OGMA, Alverca, Portugal;
Magnus Engstrom, Saab/CSM Materialteknik, Linkoping, Sweden;
Tom Cairnduff, Short Brothers, Belfast, Northern Ireland, United Kingdom;
Pat Mallon, University of Limerick, Limerick, Ireland
See also SUMMARY REPORT
BRITE/EuRAM programme BE5145 has focused on the issues concerning the provision of more reliable, more cost-effective inspection of aircraft structures. It has done this by addressing the whole of the inspection process as applied to carbon-composite and metal-to-metal bonded structures.
The project has used a set of specimens containing controlled defects to measure the reliability of a number of present inspection techniques, using the concept of inspection validation. The programme has developed a number of evolving techniques that possibly offer more reliability and/or more cost-benefit to the inspection community. These have been assessed in the same validation environment. This has permitted a direct comparison of the present techniques, and resulted in objective statements of what defect conditions can be reliably detected, where there have been improvements, and also where further work should now be focused.
In parallel, the issue of non-destructive testing (NDT) inspection procedures has been addressed. It has been shown that two new procedures, developed under this programme (and therefore termed 'BRITE/EuRAM procedures'), and which aimed to amalgamate and improve on specific inspection problems, are superior to present practice. This improvement has been quantified through validation. The work has also provided guidelines on how the writing of procedures may be used to increase the reliability of any inspection technique.
TABLE OF CONTENTS
BRITE/EuRAM programme BE5145 has been concerned with the development of improved inspection methods for safety critical 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. One generic benefit of BE5145 is that, by applying the systems approach to a particular topical safety critical inspection case, namely that of airframe inspection, and having demonstrated its worth, this programme has provided key evidence of the viability of such an approach that would be equally valid for a number of similar inspection issues within the European community.
To ensure that all aspects of the inspection process were taken into account equally, the consortium has included representatives from all aspects of the aircraft industry, manufacturers, operators and maintenance organisations, including some of the most prominent companies in Europe (figure 1). Each partner has shown the necessary commitment of manpower and facilities to ensure the success of the programme.
The programme has made use of four key developments to improve current inspection practice. These have been :
- i) research and development of advanced technology to address the specific issues of carbon-composite and metal-metal bond inspection
- ii) development and validation of standardised inspection procedures to minimise the risk of human error
- iii) development of manufacturing methods for realistic test specimens
- iv) implementation of Inspection Validation to ensure maximum reliability, functionality and applicability of the technologies and procedures developed in (i) and (ii).
Specific objectives of the programme 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.
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.
The technical programme was designed to focus on well-defined, current practical problems, ensuring that the developments were of direct relevance to industrial needs and therefore that implementation of the results generated into day-to-day practice is as rapid as possible. Whilst it is inevitable that one or two industrial sectors will benefit from this programme before others, there is no doubt that the multisectorial nature of some of the partners in the programme will lead to spin-off benefits in other industries in the medium term.
Development of Evolving Technologies
The partners in the programme selected three technologies which they considered to offer the most potential for the development of systems which can improve the reliability of inspection and be integrated into the shop floor in the short term. These were an optical based system, thermal inspection, and ultrasonics. The choice was based on the partners' experience of the current capabilities of the techniques, the financial commitment needed for further research and development and the potential cost and safety benefits to be accrued from improvements in these inspection capabilities.
Optical inspection, based on shearography, offers an innovative approach to the inspection of advanced polymer composite materials and novel constructions. Its applications, prior to the programme, had largely been in the USA for advanced military aircraft such as the Stealth bomber. One of the partners in this programme had taken the lead to introduce the technique into Europe via an earlier BRITE programme. It is thus good to see this previous expertise being furthered through the work performed under this contract and specifically, the development of the technique into a usable system which can be applied to the inspection of composite materials in the near future. The potential for application is such that the partners have aimed to improve and extend the performance of the shearography system while validating its effectiveness through the Inspection Validation process. It is envisaged that this will enable Europe to maintain or improve its profile in this technology against strong competition from the USA.
Thermal inspection has the potential to become one of the most cost-effective and widely-used methods of inspection. Since it is a rapid, non-contacting technique, and does not require reagents such as coupling fluids, it is both cost-effective and environmentally friendly. Two of the partners in this programme have been leading the developments in this technology and hold a number of key patents addressing specific aspects of the technique. By combining the facilities of the partners and linking them to current inspection situations, the development and application of the technology has been greatly accelerated.
Ultrasonics is widely used in many industries (e.g. nuclear, offshore oil and gas, petrochemical, aerospace) as a standard inspection tool but currently has significant limitations when dealing with complex constructions such as advanced composites and bonded joints. However, there is extensive scope for improved performance of ultrasonics through the development of new scanning and signal processing methods as well as removing the subjectivity of interpretation of data.
Development and Validation of Standardised Inspection Procedures
The benefits which can be accrued from any inspection technology are dependent on, among others, the skill and experience of the operator, the efficiency of the technique and the procedure by which it is applied. The partners in this programme have a wide range of experience in both writing and applying inspection procedures for many types of NDT technique. There is a real problem with the range of types of procedure produced for similar inspection tasks and the ways in which they are interpreted by the users. This can be particularly true of new technology, where the application of the technique may require different manipulative and interpretative skills than are necessary for traditional methods. Based on the experience gained by some of the programme partners in the nuclear and aerospace industry, it was proposed to carry out a detailed analysis of the limitations of currently written procedures to identify both the key reliability and efficiency issues and where human error is most likely to occur. This analysis identified the shortfalls in written procedures which could then be addressed by drawing up codes of practice for standard inspection procedures. These can then be implemented, or their effects assessed in the Inspection Validation environment.
Development of Manufacturing Methods for Realistic Test Specimens
During the research and development of inspection techniques and procedures, the specimens for demonstration, calibration and validation play a vital role in enabling the assessment of the reliability, applicability and efficiency of a novel technique. Suitable specimens are difficult to obtain, particularly if they have to be samples of advanced materials containing defects of a known size, location and type. The objective of this part of the programme was to develop methods for the reliable and reproducible production of test and validation specimens in advanced materials and complex geometries. As well as providing specimens for the technique development and validation phases, this part of the programme provided a unique, pioneering venture to place the 'green-fingered' art of 'defective-sample' production onto a much more scientific and rigorous basis and has thus offered benefit to every industry where non-destructive inspection has a role.
Implementation of Inspection Validation
One of the major innovations in this programme has been the integration of an independent, objective and quantitative system for validating the performance of the inspection techniques into the technology research and development phase. Usually, inspection technology is evaluated on small test samples containing known defects under laboratory conditions; this situation generally leads to an assessment of the sensitivity of the technique under ideal conditions and in the hands of a highly trained expert, but it says nothing about its efficiency or reliability in practice. After all, it is very easy to detect a defect condition in a small calibration sample if one knows that the specimen does actually contain a defect; it is much more difficult to test a new technique on a large specimen where defects may or may not be present. This issue was recognised by the nuclear power industry in Europe in the early 1980's. In order to meet increasingly stringent licensing requirements, a unique methodology, known as Inspection Validation, was developed by one of the partners. This methodology is now being adopted by the nuclear industry throughout the world and is becoming the basis for the independent and quantitative assessment, standardisation and certification of inspection technologies for the nuclear industry.
Similar stringent requirements are now being imposed on other industries such as offshore oil exploration, petrochemical plant and aerospace where catastrophic failures have had severe human, economic and political costs. The programme partners have demonstrated that the concepts and systems used in Inspection Validation can be applied to analogous situations in other industries. It has also been demonstrated that inclusion of the concept from the beginning of the R&D phase of inspection technology, provides inspection systems which are 'fit-for-purpose' first time and which can be implemented on the shop floor in the minimum possible timescale. This approach to technology development is being explored in the USA where the Federal Government is investing $15M to begin the process of establishing a similar centre of excellence at Sandia National Laboratory (ref. 1). The timeliness and value of the work in BE5145, to retain a European lead in this field, is thus self evident.
Initial discussions have been held with other organisations not involved in the current programme and it was agreed in principle that companies who design, build and sell inspection equipment could interface with the project directly, but at their own expense, for Inspection Validation exercises. This has a major spin-off benefit for the partners in the programme as they can gain access to a wide range of 'off-the-shelf' technology which can be validated at no expense to the CEC or the partners themselves. The equipment company also benefits by gaining the opportunity to have their technology independently validated.
The project has provided results from all four key areas of work - samples, validation, technology and procedures.|
The project has expended a considerable effort to generate test specimens with suitably qualified artificial defects. Consequently, a key result is the development of methods that permit the manufacture of realistic test specimens, of carbon fibre composite and metal sandwich structures, containing defect simulations. This knowledge was built upon the state-of-the-art experience of the partners at the commencement of the programme. The research and development to provide the breadth of the defect population has been a key new development in the NDT field. This resulted in a set of 16 purpose built test specimens, with the materials used encompassing examples of monolithic carbon composites and carbon composites with Nomex and metal cores, and metal to metal bonded structures including metal skin to metal honeycombs (both single and double bondlines). Overall, the set of specimens present a variety of skin thickness, curing mechanism, reinforcing and honeycomb thickness (ref. 2). The samples presented approximately 500 defects spanning 19 different defect types. The range of metal-to-metal bonded constructions is shown in figure 2.
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 :
Fig 2: The metal-to-metal bonded constructions for the Validation Work.
Task 8: Design and Maufacture of Validation Specimens Metallic Bonded Structure
- 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 results of the work (shown in progress in figure 3, with results summarised in figure 4), are based on about 1200 defect-operator interactions from 61 independent operator-panel inspections at an average scanning rate of 1.8 specimens per (8-hour) day. These data have been used to determine the following :
- Visual inspection was shown to be capable of the detection of impact damage sites on all of the structures tested
- Tap testing was shown to be capable of the detection of disbonds between the near skin and honeycomb core of the Metal Single Skin Honeycomb (MSSH) structures
- Bond testing was shown to be capable of the detection of disbonds between the skin and doubler (including regions under the stringer) in the sheet metal to sheet metal (SMS) structures. In addition, moderate success was demonstrated in the detection of disbonding between the doubler and stringer of SMS structures and also the near skin (inspection side) doubler and honeycomb core of the Metal Single Skin Honeycomb (MSSH) structures
- Manual ultrasonic inspection was demonstrated to be moderately effective in the detection of disbonds in the Monolithic Carbon Composite (MCC) structures. Some success was also displayed in the detection of delaminations in both MCC structures and the near skin of Carbon Composite Honeycomb (CCH) structures
- None of the techniques tested were shown to be effective in the detection of disbonds between either the near skin or far skin (opposite inspected side) and the honeycomb of the CCH structures
- None of the techniques tested were shown to be effective in the detection of delaminations in the far skin of the CCH structures
- None of the techniques tested were shown to be effective in the detection of disbonds between either the far skin and the honeycomb core of the MSSH structures, or the far skin doubler and the honeycomb core of the Metal Double Skin Honeycomb (MDSH) structures
- None of the techniques tested were shown to be effective in the detection of disbonds between the far skin and the far skin doubler of the MDSH structures.
The area 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 (for example, see those listed above). Shearography, thermography and specific ultrasonic variants have received attention. Building on the validation theme, these too 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. The results of the validation efforts are summarised below, but specifically, the "Technology" area can be seen as delivering :
- The development of shearography, thermography, Lamb-wave (broad-brush) ultrasonics, add-on units (for ultrasonics) and an automated NDI system, all of which offer possible advantages to airframe inspection
- A host of evidence relating to each technique, including :
- catalogue of typical defect responses to shearography applied on aerospace components
- examples of defect responses to thermography
- influence of image colouration on detection levels (reliability)
- signal processing and enhancement routines
- standardisation of thermographic inspection parameters
- issues of the detection of fluid-filled disbonds
- operational procedures and reporting sheets for shearography, thermography and Lamb-wave ultrasonics.
The validation process (ref. 2) has been applied to these evolving technologies at a point in time where they have been developed toward their goal of a realistic front-line inspection tool. An example of this work is shown in figure 5. The results of the work, summarised in figure 6, are based on about 700 defect-operator interactions from 37 independent operator-panel inspections at an average scanning rate of 3.4 specimens per (8-hour) day. These data have been used to determine the following :
- Automated pulse echo ultrasonics (UT) was effective in the detection of both disbonds and delaminations in MCC structures, delaminations within the near skin of CCH structures and impact damage in both MCC and CCH structures
- Automated bond testing was effective in the detection of all types of disbond in the SMS structures, disbonds between the near skin and doubler of the MDSH structures and also impact damage in MDSH and MSSH structures
- Lamb-wave ultrasonics was effective in the detection of disbonds between the skin and doubler (under the stringer), and also disbonds between the doubler and stringer in SMS structures
- Thermography was marginally effective in the detection of impact damage in both MCC and CCH structures
- Lamb-wave ultrasonics and automated bond testing were both marginally effective in the detection of disbonds between the skin and doubler in the SMS structures
- Lamb-wave ultrasonics was marginally effective in the detection of impact damage in the SMS structures
- Automated bond testing was marginally effective in the detection of disbonds between the near skin and honeycomb core of the MSSH structures
- All of the techniques developed and subsequently tested in the validation environment were ineffective in the detection of :
- Disbonds between either the near skin and core or far skin and core of the CCH structures
- Disbonds between the near skin doubler and honeycomb core of the MDSH structures
- Delaminations within the far skin of the CCH structures
- Disbonds between either the far skin and honeycomb core or the far skin and doubler of the MSSH structures, or the far skin doubler and honeycomb core of the MDSH structures
- Impact damage on the SMS structures
- Bond testing was marginally effective in providing a signal from core splices although core splices so detected were not reported as such.
The project has consolidated the performance demonstrations of both present and evolving technologies and is able to detail the following specific conclusions :
- 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.
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). Specific deliverables have been :
- Production of a 'BRITE/EuRAM' standardised procedure for Rotating Probe Eddy-Current (RPEC) inspection of (fastener) holes. This work has proven that this 'BRITE/EuRAM' procedure, which includes the novel design of a conical 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 (figure 7)
- 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.
FIGURE FROM FINAL REPORT
Table 1 & 2
The Results of the Validation Work on Evolving Inspection Technologies
| Table 1
Best Overall Detection Performance Demonstrated by Task 4 and the Associated Technique(s) Responsible
| DEFECT DESCRIPTION || BEST RESULT|
|DETECTION TECHNIQUE ||SMALLEST DEFECT DETECTED/mm2||LARGEST DEFECT|
|H ||IMPACT DAMAGE ||100 ||VISUAL ||225|| -
|I ||DISBOND BETWEEN SKIN AND DOUBLER ||100 ||BT (Shurtronics) ||400 ||-
|L ||DISBOND BETWEEN NEAR SKIN AND HONEYCOMB CORE ||100 ||TAP|| 625 ||-
|R ||IMPACT DAMAGE|| 100|| VISUAL ||254 ||-
|S ||IMPACT DAMAGE ||100 ||VISUAL/BT (Sondicator S2B) || 133 ||-
|CORE SPLICE ||REPAIR TO HONEYCOMB SECTION ||100|| BT (Sondicator S2B) ||9075 ||-
|G ||IMPACT DAMAGE ||93 ||VISUAL|| 100 ||400
|J ||DISBOND BETWEEN SKIN AND DOUBLER (UNDER STRINGER) ||93 ||BT (Fokker Bond Tester80L) ||225 ||225
|K ||DISBOND BETWEEN DOUBLER AND STRINGER ||83|| BT (Fokker Bond Tester 80L) || 225 ||784
|A ||DISBOND BETWEEN LAYERS|| 80 ||UT (Krautkramer USD10) ||56 ||169
|N ||DISBOND BETWEEN NEAR SKIN AND DOUBLER ||75|| BT (Fokker Bond Tester 80L) ||400|| 1400
|D ||DELAMINATION WITHIN LAYER|| 65 ||UT (USIP 12) ||100|| 625
|E ||DELAMINATION WITHIN LAYER OF NEAR SKIN|| 60|| UT (Krautkrainer USD 10) || 100|| 225
|P ||DISBOND BETWEEN NEAR SKIN DOUBLER AND HONEYCOMB CORE ||50 ||BT(Shurtronics) ||900 ||2500
|F ||DELAMINATION WITHIN LAYER OF FAR SKIN|| 9 ||BT(Sliurtronics) ||400|| 625
|C ||DISBOND BETWEEN FAR SKIN AND HONEYCOMB CORE || 6 ||BT(Sliurtronics) ||400 ||625
|B || DISBOND BETWEEN NEAR SKIN DOUBLER AND HONEYCOMB CORE || 3 || VISUAL ||225 ||491
|M|| DISBOND BETWEEN FAR SKIN DOUBLER AND HONEYCOMB CORE ||2 ||BT(Sliurtronics) || 1400 ||3600
|Q || DISBOND BETWEEN FAR SKIN DOUBLER AND AND DOUBLER||0||-||-||-
|Q ||DISBOND BETWEEN FAR SKIN DOUBLER AND HONEYCOMB CORE ||0||-||-||-
** Note the observed results for the detectionof schedule B and C defects have been interchanged in order to correct for an error in recorded position of these defect in the
definitive data records.
Best Overall Detection Performance Demonstrated by Task 8 and the Associated Technique(s) Responsible
| DEFECT DESCRIPTION || BEST RESULT|
|DETECTION TECHNIQUE ||SMALLEST DEFECT DETECTED/mm2||LARGEST DEFECT|
|D ||DELAMINATION WITHIN LAYER LAYER ||100 ||UT ||100||-
|E|| DELAMINATION WITHIN LAYER LAYER OF NEAR SKIN ||100 ||UT||56.3||-
|G|| IMPACT DAMAGE ||100 ||UT||400||-
|H|| IMPACT DAMAGE ||100 ||UT ||196 ||-
|I||DISBOND BETWEEN SKIN AND DOUBLER ||100 || BT ||225 ||-
|J|| DISBOND BETWEEN SKIN AND (UNDER STRINGER) || 100|| LAMB WAVE & BT ||225 & 400 ||-
|K|| DISBOND BETWEEN DOUBLER AND STRINGER ||100|| LAMB WAVE & BT|| 225 & 400 ||-
|N|| DISBOND BETWEEN NEAR SKIN AND DOUBLER ||100|| BT ||625||-
|S|| IMPACT DAMAGE ||100|| BT ||572.6 ||-
|A|| DISBOND BETWEEN LAYERS ||90|| UT ||100 ||56.3
|L|| DISBOND BETWEEN NEAR SKIN AND IIONEYCOMB CORE ||87.5 ||BT ||225 ||225
|R|| IMPACT DAMAGE ||80 ||LAMB WAVE|| 490.9 ||254.5
|B||DISBOND BETWEEN NEAR SKIN AND HONEYCOMB CORE|| 40|| UT ||256|| 225
|P|| DISBOND BETWEEN NEAR SKIN DOUBLER AND HONEYCOMB CORE ||25 ||BT|| 2500|| 1750
|M|| DISBOND BETWEEN FAR SKIN AND HONEYCOMB CORE||6|| LAMB WAVE ||1750 ||3600
|M||DISBOND BETWEEN FAR SKIN AND HONEYCOMB CORE ||2 ||THERMOGRAPHY ||490.9 ||625
|F|| DELAMINATION WITHIN LAYER OF FAR SKIN ||0|| ALL ||-|| 625
|O|| DISBOND BETWEEN FAR SKIN AND DOUBLER ||0 ||ALL ||- ||3600
|Q|| DISBOND BETWEEN FAR SKIN DOUBLER AND HONEYCOMB CORE|| 0 ||ALL|| - ||3600
The programme aimed to improve the reliability, quality and cost-effectiveness of the in-service inspection of aircraft structures made of carbon-composite and metal to metal bonded materials. Inspection Validation has been used as a management tool both to quantify and compare the performance (reliability/quality) and cost-effectiveness (speed) of a number of present day and evolving inspection techniques. The improvements have come from a number of areas. These major steps forward in technical excellence can be summarised as
- The 'BRITE/EuRAM' RPEC procedure is a qualified improvement over present inspection practice. Employment of the SC2S and the inclusion of the section on "evaluation" have been the main reasons for these improvements
- Present techniques (visual, tap-testing, resonance methods and manual ultrasonics), supplemented by evolving technologies (shearography, thermography, Lamb-wave ultrasonics and automated NDI systems), have sufficient reliability to detect a large range of defects in carbon-composite and metal-bonded structures including (technique(s) offering best compromise of reliability and cost-effectiveness shown in italics in brackets) :
- impact damage sites (visual/automated ultrasonics/automated bond-testing)
- disbonds in the near-skin of MSSH structures (tap-testing)
- disbonds between skin and doubler of SMS structures (manual bond testing)
- disbonds/delaminations in MCC structures (automated ultrasonics)
- delaminations in CCH structures (automated ultrasonics)
- disbonds of all types in SMS structures (automated bond-testing)
- disbonds between the near-skin and doubler of MDSH structures (automated bond-testing)
- disbonds between skin and doubler of SMS structures (Lamb-wave ultrasonics)
- disbonds between doubler and stringer of SMS structures (Lamb-wave ultrasonics)
- The present techniques and evolving technologies noted above are not reliable enough to detect certain types of defect including :
- disbonds between (near or far) skin and honeycomb core in CCH structures
- delaminations in the far-skin of CCH structures
- disbonds between near-skin doubler and honeycomb core in MDSH structures
- disbonds between far-skin and honeycomb of MSSH structures
- disbonds between far-skin doubler and honeycomb core in MDSH structures
- disbonds between far-skin and doubler in 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 certain types of defect despite their promising inspection rates (cost-effectiveness) and their good performances demonstrated on some realistic structure/defect configurations. Improvements could be possible through control of the excitation processes involved in shearography and thermography.
In addition to the references above, the consortium would like all readers to note the following. 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, or through the offices of the project co-ordinator at the address below.
- 'The Aging Aircraft Non-destructive Inspection Development and Demonstration Centre',
P Walter, Proceedings of the 3rd International Conference on Aging Aircraft, Washington, November 1991.
- 'Demonstrating the Reliability of Aircraft Inspection - the Validation Phase of BE5145',
C P Hobbs, R L Smith and P J Conroy, Insight 36(10), 738-740 (1994).
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 : email@example.com
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For more information see: NDT in Aerospace - UTonline 11/97
© Copyright 1. Nov 1997 Rolf Diederichs,
/DB:Article /SO:EU /AU:et_al /CT:NDT /CT:composite /CT:aerospace /ED:1997-11