Fibre reinforced composite materials are increasingly used in industry; both monolithic and more complex sandwich structures. Their application has spread from high technology industries such as aerospace and defence to other sectors including chemical, offshore, marine, transport and civil applications. Each industry faces different challenges and the materials used and nature of the composite fabrications may differ.
A common feature is that defects and damage can occur, which reduce the strength and stiffness, and determine the safe working life of composite structures. These are complex, various and intricately related to a variety of service conditions and failure modes under many different circumstances. Defects may be introduced during manufacture, accidentally in-service or perhaps unavoidably in design because of the requirement to introduce discontinuities such as cut-outs, ply drops or structural connections.
The uptake of composites in industry has been limited by a perception
that they are difficult to inspect. In some cases this
has lead to over reliance on visual methods at the expense of
component quality. In reality a number of common and established
methods for non-destructive evaluation (NDE) are routinely
available and there have been significant advances in NDE systems
and technology. Newer methods such as laser shearography and
transient thermography are now well accepted in aerospace
and marine sectors and finding applications elsewhere; in many
cases replacing traditional methods such as ultrasonic C-scanning.
In ultrasonic systems the development of modern digital flaw
detectors and improvements like wheel probes have opened up new
avenues of data aquisition and analysis. Although relatively few
NDE methods are practically used on composites by industry, there are
an increasing number of newer and specialised
methods such as microwaves, acoustography and vibro-thermography
which are showing promise in specific applications
In the MMS15 Project an Interactive Knowledge Base IKB has been developed on NDE of composites by AEA Technology's National NDT Centre in partnership with QinetiQ and NetComposites. The Project has benefited from considerable support from industry and input on current and past projects from project partners. The IKB will be made accessible to industry by dissemination through the NetComposites portal with links in the DTI Materials Solutions Portal. The project has been successful in raising industry awareness of newer or more specialised NDE methods that are becoming available. It is considered the project could considerably advance the use of composites in UK and European industry from the knowledge that non-destructive evaluation NDE methods are available. The information in the IKB is likely to benefit UK industry and lead to an improvement in the overall quality of manufactured components. Through the links with the MMS13 project a good link has been established between NDE and application of NDE data in defect assessment of composites.
In the MMS15 project AEA Technology's National NDT Centre (NNDTC) in partnership with QinetiQ and Net Composites and support from Nobletech have developed an Interactive Knowledge Base IKB on non-destructive evaluation (NDE) of composites. The IKB is being made accessible to industry through the NetComposites portal. A link will also be established on the Materials Solutions site which gives access to a range of information tools developed on DTI programmes.
The IKB is designed to provide users of composites with an authoratitive guide as to what NDE techniques are available, what defect types are detectable by or difficult for a particular inspection technique and what information there is available on performance and reliability. This is the beta (pre-release testing) version of an Interactive Knowledge Base (IKB) on non-destructive evaluation and design of composites. The knowledge base contains a vast amount of information on the selection and use of non-destructive evaluation techniques for composites, with a series of comprehensive search and interrogation functions. The IKB allows user to browse for information by NDE method and defect type with data examples and standards sets of information such as defects, examples, pros & cons, equipment, principles and procedures.
To assist users a technique selection tool has been developed that allows users to ask and answer a series of questions (Q&As) that define the nature of their application. The selection tool is designed to indicate techniques that could be suitable. Links allow the user to browse more detailed information on these methods in the IKB. Experience shows the method despite the intrinsic simplicity can be valuable in highlighting methods that an industrial user or experienced NDE practitioner may not have considered. The selection tool uses a simple and transparent scoring system and the scores and comments are available to the user so they can use their judgement on how to proceed. The scores put together from experts and experienced users and subject to audit. The IKB includes other live features including feedback and an NDE Forum that allow dialogue and interaction and the facility to comment and submit new information.
The aim of the MMS15 project was to maximise UK and
European industrial
competitiveness in the composite materials industry, through:
The
project involved the following technical areas:
The main achievements of the MMS15 project were as follows. These are outlined in more detail below.
A review was made of NDE methods for composites, jointly with MMS13
An Interactive Knowledege Base (IKB) has been delivered covering the non-destructive evaluation (NDE) of fibre reinforced composites: monolithic and sandwich structures, GRP, CFRP and Kevlar reinforced.
A Technique Selection process has been developed and integrated in the IKB to assist industry in finding the most practicable NDE methods for their specific application.
Generic knowledge base IKB software has been developed and exploited with a simple and flexible web-based user interface
The project has raised awareness in industry of the NDE methods commonly available and newer or more specialised NDE methods that could assist them in more difficult applications.
Substantive information has been gathered from partners and industry on composite NDE.
There has been useful interaction and exchange with MMS13 linking NDE methods to the requirements of defect assessment.
Active industry participation (25+) companies. Good dissemination through project web site and noticeboard
The user interface has been adapted to make the IKB accessible to industry through the NetComposites site www.netcomposites.com.
A dedicated website has been produced www.mms15.com which gives access to the Interactive Knowledege Base (IKB) , the Development Version and other information arising from the project
Valuable case studies have been undertaken.
MMS15 contributed to a joint review of NDE methods with MMS13 As well as describing common techniques, readily useable by industry, the NDE review detailed a number of more specialised techniques perhaps not so accessible by industry, but that might typically be used to assist defect assessment.. The review assessed issues such as probability of detection (PoD) and described the inspection value method. In addition a number of past reviews were assessed and information summarised including the DTI funded CDP4A, CPD4D and DCC3 programmes, development of ultrasonic C-scan standards and Brite-Euram projects including BE5145.
The main deliverable from MMS15 is the Interactive Knowledge Base IKB on NDE of composites accessible via the Internet. The IKB allows the user to browse for information on NDE methods in different ways and answer questions they may have on NDE of composites. For example:
A state-of-the-art user-interface gives dissemination via the NetComposites portal. The information can be accessed in a number of ways and features include: Browse by NDE method, Browse by Defect Type, Technique Selection, Search and Feedback. A user guide can be accessed as a .PDF file or web pages. The IKB structure is simple and reliable giving a short path to get to useful information.
A module has been written that allows the user to browse for information by NDE method. This is the main route for accessing information in the IKB. To help the user NDE methods are categorised as common, specialised or developmental. Definitions are as follows:
Although common methods may have most resonance to industrial users raising awareness of newer methods was considered a major benefit of the present programme. Modern methods of composite fabrication can pose real problems for inspection where common methods may not always be the most applicable.
The Common NDE methods include: Acoustic Emission (AE) Acoustic Impact (AI) Laser Shearography (LS) Mechanical Impedance (MI) Membrane Resonance (MR) Thermography (TT) Ultrasonic B-Scan (UB) Ultrasonic amplitude C-Scan (UC) Ultrasonic depth scan (2D map of structure, colour represents depth, rather than attenuation) (UD) Ultrasonic thickness (A-scan) or 'Ultrasonic A-Scan' (UA) Visual (included enhanced) (V) X-Radiography (XR). Information on over thirty specialised and developmental techniques is included.
A common need is to identify NDE methods that are most applicable to the type of defects known to cause concern in particular components. For example this could be delaminations, adhesive disbonds or fipre wrinkling or misalignment in more modern moulded components. MMS15 has addressed this need by developing a Browse by Defect Type module. This allows the user to drill down by defect type, find out more about the defect and summarises the NDE methods that could be applicable with examples of data.
There are many factors in composites that may affect the suitability of an NDE method, for example: material, defect type, location, type of composite - sandwich or monolithic, fibre type, thickness, coatings, access, complexity. It would not be simple to address these all by separate browse features. An important achievement of MMS15 is the development of a technique selection tool.
The selection tool allows users to ask and answer a series of questions (Q&As) that define the nature of their application. The Q&As were carefully chosen and agreed by project partners with assistance from the IAG to reflect the main factors that may impact on the suitability of different NDE techniques. The methodology established over several years in other IKB applications such as the HOIS offshore JIP involves multiplying a series of scores or rankings together based on the answers given. These scores vary from 0 to 10. A score of 0 means that that factor rules out that NDE technique, a score of 10 means that the factor has no impact on the effectiveness of the technique. An intermediate score indicates that the capability is reduced slightly, partly or significantly. The system offer much flexibility.
The user can ask and answer as many Q&As as are necessary to define their problem. At any time they can select view results and see an ordered list of techniques that may be applicable and their overall ranking or suitability. The basis of the scores can be seen on a summary table with comments and is transparent to users. The selection tool is designed to indicate techniques that could be suitable. Links take the user to detailed information on the NDE method in the IKB. Experience shows the method despite the intrinsic simplicity can be valuable in highlighting methods that an industrial user or experienced NDE practitioner may not have originally considered.
Scoring and Audit Process
It is important for users to have confidence in the selection tool. With this aim, the original scores were obtained from experts both users, researchers and suppliers of the technology. The full spreadsheet of scores and comments were subject to detailed Audit by Robert Smith from QinetiQ and Steve Burch, Head of the National NDT Centre. The strategy for scoring, audit report and full table of Scores is accessible to users and can also be seen on the dedicated project website www.mms15.com . It is likely that further refinement will occur with use of the IKB and associated feedback.
At the start of the project it was recognised that the major benefit to UK and European industry would come if the information was freely accessible and not hidden behind UserIDs and passwords. This could assist overseas competitors but conversely could provide contacts and a market for UK NDE service companies. It was proposed the main route for access to the IKB would be through the Net Composites Portal one of the most widely accessed internet sites for composite materials.
To facilitate this the IKB software has been integrated with the software on the NetComposites web site and specific software developed to allow the uploading of associated databases and pages of information, taking account differences in database heirarchy and web coding. A separate link will be initiated from the DTI Materials Solutions portal which includes other DTI funded tools for the composites industry. A separate Development Version can be accessed with password on the AEA Technology server. All information can be accessed via a dedicated website www.mms15.com .
Developments in NDE methods continue to occur and users may wish to comment or add to the information on a particular page in the IKB. To help the IKB remain current an interactive Feedback feature is included and a separate conference facility or NDE Forum. By hitting the Feedback option users can send an email to the development team. Importantly the message identifies and gives a link to the precise page the user is looking at when they made the comment. This gives a fast route to correct any errors in the IKB or for users to submit new information or examples for consideration.
A separate NDE Forum has been implemented on the NetComposites site linked to the IKB. This is one of a number of Forums on separate composites issues. Users can register and initiate discussion on new issues or respond to existing issues. The Forum is moderated by NetComposites. The Forum gives an additional source of information and comment to users. The Forum provides another method for updating information on the IKB with time.
An interactive Search facility has been included to help the user go quickly to specific information in the IKB. A ranked list of information is provided dependent on the keywords entered with automatic links to the information, similar to using an Internet Search Engine.
The MMS15 project had a an active Industrial Advisory Group (IAG) jointly with MMS13. Presentations by industrialists and NDE service and equipment suppliers were a common theme of the IAG meetings. A significant number of industrial visits were made during the project as well as presentations at industry working groups including the Harwell Offshore Inspection Service HOIS and offshore composite repair groups. It was evident that this interchange raised awareness of newer NDT methods such as transient thermography and laser shearography as well as more specialised methods such as advanced ultrasonic methods, acoustography and microwave inspection. The availability of the IKB is likely to extend this awareness more broadly within UK industry
In order to evaluate the applicability and performance of NDE
methods in practical situations a number of case studies were
undertaken. A number of these were undertaken jointly with
MMS13 as well as interactions with industry groupings such as the
offshore composite repair group (OCRG). These case studies
included:
The project has also made accessible many case studies from prior DTI programmes such as CPD4D, DCC3 and CPD4A, commercial projects and European projects including BE5145. Specific case studies were also provided by NDE service companies. This information has been made available as examples in the IKB.
The MMS15 Project did not specifically address defect assessment methods but had strong links with MMS13 sharing a common IAG and developing a consistent approach. In MMS13 a defect assessment framework has been established as well as guidance on defect characterisation and defect criticality. In MMS13The National Physical Laboratory (NPL) and AEA Technology have developed a general procedure for the assessment and criticality of defects and damage in composite material systems. The defect criticality framework and assessment procedure is based on the multi-level assessment philosophy contained within API (American Petroleum Industry) 579 - Recommended Practice for Fitness-For-Service and Continued Operation of Equipment. The basis for the framework detailed in this guide is a 3 Level approach which involves increasing levels of sophistication in the assessment procedure, from operator level to specialist. For each level, guidance has been provided on defect characterisation, non-destructive evaluation (NDE) techniques, defect criticality and test methods for materials characterisation data. The procedure is primarily concerned with carbon and glass fibre-reinforced polymer composite material systems, and focuses on crack-like defects such as delamination and matrix micro-cracking.
The Interactive knowledge base software developed in MMS15 is an advance on previous IKB software used developed on HOIS and other projects. The software is very flexible and the subjects and topics used in the Browse facility can be simply edited or used to generate a new IKB for completely different subjects. Simple database editing, association and upload software has been developed.new pages can be simply added by associating the information with relevant subjects in the database and moving in or out of the Topics directory. This makes it very fast to amend, update or remove data from the IKB.
As an example the IKB software has been used in a number of different projects. In the MMS5 project the software has been used to develop an IKB on design of composites under multiaxial loading. The software has been used for the HOIS offshore JIP to develop an IKB on Floating Production, Storage and Offloading Vessels (FPSOs). More recently the software has been adapted for the UK Health and safety Executive to develop an IKB on Gas Turbine Integrity and Maintenance.
The main outputs from the MMS15 Project were as follows:
Interactive Knowledge Base (IKB) on NDE of composites
Software module on Browse by NDE Method
Software Module on Browse by Defect Type
Technique Selection Tool for recommending NDE methods for specific composite applications
Audited scores and comments for the Technique Selection Tool
Generic IKB software and database editing, upload and association tools
User interface and menus for dissemination of IKB through the NetComposites Portal
IKB User guide (HTML and PDF)
Dedicated Project website www.mms15.com giving access to IKB and project output
Separate Development Version of the IKB
Input to MMS13 Project on NDE methods and capabilities and links to defect assessment
Presentations on MMS15 were given at 6 Industrial Advisory Group Meetings (IAG) at several meetings of the Harwell Offshore Inspection Club (HOIS) and at meetings of the Offshore Composite Repair Group. Presentations were given at the QinetiQ course on NDE of Composites in all three years of the MMS15 project 2003 to 2005; this had a wide industry attendance. A significant number of visits were made during the course of the project to industrial users, composite fabricators and NDE service and equipment suppliers. NDE equipment from several suppliers was demonstrated on composite samples at Culham and Harwell. Project staff attended seminars on thermography at Bath University in 2003 and 2005.
This work was funded by the UK Department of Trade and Industry as part of the Measurements for Materials Systems Programme. The considerable body of information and case studies input from the project partners National NDT Centre NNDTC, QinetiQ and Industrial Advisory Group members named below is gratefully acknowledged. The assistance and advice of project partners Net Composites and Nobletech and Jack Stow Software in the development and evolution of the IKB software and menu sytems throughout the project is gratefully acknowledged.
There are many companies whose assistance with this project has been invaluable, including.
Throughout the three year project duration, IAG meetings were held every six months jointly for MMS15 and MMS13, alternating between NPL and AEAT. The contribution of the IAG in providing materials, guidance, case studies, review of documents and attending meetings is gratefully acknowledged.
A fundamental objective of MMS15 was that information should be independent, based on technical considerations, sources of information clearly identified, and not influenced by commercial considerations. The maximum benefit was seen in making the IKB freely accessible and not charging for access. These objectives limit some potential sources of future funding.
As with any knowledge base system it is important that information is updated as technology develops and new experience is gained. A number of routes are envisaged to allow progressive update of information
A three year DTI Technology funded programme, ACLAIM, lead by AEA Technology and with NPL as a major partner was launched in March 2005. The ACLAIM project aims to develop a framework for assessing the integrity of advanced composite structures over the complete life cycle through an integrated approach to structural health monitoring and management. This framework will require development of new multi-functional sensors, improved modelling of defect criticality with these developments validated through laboratory and in-service performance trials culminating in good practice guidance.In addition the use of novel embedded sensors for monitoring the condition of composite material systems will be considered for the next Measurements for Materials Characterisation programme.
An Interactive Knowledge Base IKB has been developed on NDE of composites. The Project has benefited from considerable support from industry and input on current and past projects from project partners. The IKB will be made accessible to industry by dissemination through the NetComposites portal. The project has been successful in raising indutry awareness of newer or more specialised NDE methods that are becoming available. It is considered the project could considerably advance the use of composites in UK and European industry from the knowledge that non-destructive evaluation NDE methods are available. The information in the IKB is likely to benefit UK industry and lead to an improvement in the overall quality of manufactured components. through the links with the MMS13 project a good link has been established between NDE and application of NDE data in defect assessment of composites.
