MMS15 Interactive Knowledge Base (IKB) NDE of Composites

Strategy and validation for Technique Selection Tool and  IKB Data

This strategy was established at a meeting of project partners at QinetiQ on  at Qinetiq on 21 September 2004 This includes validation of information in the IKB and ranking of techniques for the technique selection feature, referred to previously as recommend-a-technique (RAT). Those present included: Martin Wall, Richard Lee AEA Technology; Robert Smith, Anne Birt Qinetiq; and Gordon Bishop, Paul Knight NetComposites.  A PDF or WORD version of  this document can be accessed by clicking the following links:

• MMS15 Auditing of Technique Selection Scores and IKB Content.pdf   
• MMS15 Auditing of Technique Selection Scores and IKB Content.doc  

 Principles

1.             The rankings used in the  Technique Selection Tool should be transparent.  It should be well documented how the rankings were arrived at, who by and any auditing and cross-checking carried out. This would allow the user to make an appropriate judgement on how to use the recommendations.

2.             In drawing up this strategy, various issues regarding the scoring process were considered.  Should the starting point be a blank page or a spreadsheet already populated by the project partners? Who should be approached? How should the inputs be assessed?  Should simple averaging be used or results weighted differently for experts and suppliers? Could manufacturers be trusted to be unbiased? Should an open note be sent with respondents, asked to give answers where they felt they had valid expertise?  What arbritration process  should there be to handle any objections to the ranking process.

3.             It was considered that different phrasing of the questions may be needed for the people doing the rankings to the questions that appeared in the IKB.

4.             The delineation of NDE techniques in the IKB is common, specialised, and  developmental. This approach had been suggested and supported by the IAG.  The techniques included in each category can be found below in Table 1.

5.             There was a discussion of the definitions of common, specialised and developmental and the relevance of these to industrial users.  The following definitions were agreed;

Common  Well established methods, routinely applied to composite materials.
Specialised Newer methods, requiring more specialised skills to apply or only applied in specific industries. Equipment is out there. The methods have been practically applied to real problems
Developmental Methods currently still at a developmental stage. Equipment usually not available to practically apply the technique in real situations. There may be a significant experimental background of development and trials.

6.             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.

Basis of Selection Tool

7.             The Technique Selection Tool allows users to ask and answer a series of questions (Q&As) that define the nature of their application.  The Q&As have been carefully chosen and agreed by project partners to reflect the main factors that may impact on the suitability of different NDE techniques: material, defect type, thickness, structure, access, coatings etc.

8.             The methodology established over several years in other IKB applications such as HOIS involves multiplying a series of scores or rankings together based on the answers given. These scores vary from 0 to 1. A score of 0 means that that factor rules out that NDE technique, a score of 1 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 As the scores are multiplied, a series of low scores for individual answers will lead to a low overall score..

9.             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 and is transparent to users.

10.        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.

Ranking process

11.        There was a concern that including the full range of methods equally in the recommend ranking may be confusing to users who may not easily distinguish common methods from those requiring more specialised application. Also that ranking of developmental methods may be less objective because of the limited experience of their application. The tool needed to be useful and reliable from the start to gain acceptance. Methods of making the ranking simpler and more transparent to users were discussed with the objective of getting a good reliable tool in a reasonable timescale.

12.        As experience of specialised and developmental techniques is more limited than those used commonly, it is not possible to rank these with the same precision as for common techniques.  To provide the most practical and reliable tool to users. The following was agreed:

·        Full ranking between 0 and 1 would be restricted to the common methods.

·        Specialised and developmental methods would not be formally ranked or audited. A score of 0 would be given to any answer that would rule out the technique or limit it to such an extent that it was not a practical proposition (showstoppers).  The score would be left at 1 for other answers. In scoring there would be the option to add a comment, indicate with a question mark (?) Adjacent to the score if there was any uncertainty. The scorer could also indicate (S) if they felt the answer would significantly limit the technique.

·        The results from the Technique Selection (RAT) process would be a ranked listing with supporting tables and comments of common techniques applicable to the defined problem. 

·        A separate column would list specialised or developmental methods that had not been ruled out with the following comment ‘ Our experts also suggest you should look at the following techniques’. Users would be guided to look in the main IKB for more information. This second column would be in alphabetical order and not ranked.

·        For example:

13.        Core thickness Issues should be dealt in main text under limitations.

14.        A spreadsheet would be drawn up for the common techniques.  Selected columns would be sent to experts to rank.

Table 1. Provisional List of experts to involve in the ranking process

G  General   U User    S Supplier    E Expert

Validation of IKB Content

15.        A discussion was held on the validation of IKB content. It was agreed to approach the IAG in this context. There are 4 issues:

·        Populated

·        Structure right

·        At right Level

·        Is it technically correct

The IAG would be split into the same categories as above. Two people from the IAG would be asked to review each technique section.

16.        Content audit is important.  The content would initially be audited by the project partners to fill in any gaps

Adjudication of Technique Scores

17.        It was agreed that adjudication of the RAT rankings would be done by Steve Burch (AEAT) assisted by Robert Smith (QinetiQ).  Robert and Steve would meet to try out the ranking process for common methods and assess how easy this would be.  They would also have a first cut at allocation scores (0 or 1) to specialised and developmental techniques as described above.

v 1.0 DRAFT 1 October 2004  Martin Wall Project Manager

Annex 1

MMS15 List Of NDE Methods

Revised 21 September 2004

The list of NDE methods to be included in the IKB was discussed and revised at a meeting of MMS15 project partners at Qinetiq on 21 September 2004.  The IKB and content spreadsheet will be updated to reflect these new definitions.

Notes

1. The list should be limited to individual NDE methods

2.      Grouped methods such as optical, ultrasonic, vibrational should be removed. Relevant information can be included under specific techniques or included as background information.

3. It was agreed to stick to Common, Specialised, Developmental as the categories. This categorisation had been suggested by the IAG as simpler and more practical than ordering by type of non-destructive method. Recognised that there may be some debate as to where techniques should lie.  For a method to be included as specialised rather than developmental, there should be equipment available and the method should have been practically applied to real situations.
4. Manual versus automated inspection is a separate issue common to a number of techniques.   This issue should be covered separately and not treated as different techniques.
5. Acoustic Impact is a subset of vibrational. Tap and Coin Testing is a subset of Acoustic impact.  This excludes membrane resonance which is a continuous wave

Categories

It was recognised that there are other ways to categorise the NDE methods, for example by type of method.

·                   Ultrasonics

·                   Vibration Methods

·                   Radiographic Methods

·                   Optical Methods

·                   Thermal Methods

·                   Acoustic Methods

It was agreed to stick to the present categorisation of common, specialised and developmental. A fourth category of other may be considered to encompass methods that had specific applications, for example to composite overwrap repairs but not applied to composites.

List of NDE Methods

The following revised list of NDE methods was agreed:

Common

These techniques are commonly used and do not require specialised application

·        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

Specialised

These methods need more specialised expertise to apply. To be included the methods need to have been practically applied to composite inspection and there needs to be equipment out there that can be used.

·        Acousto Ultrasonics (AU)

·        Angle Probe Ultrasonics (AP)

·        Dielectric (DI)

·        Eddy Current Methods (ET)

·        Lamb and Guided Waves (LW)

·        Laser Ultrasound (LU)

·        Microwave (MW)

·        Polar Ultrasonic Scan (PU)

·        TOFD (TO)

·        Ultrasonic Backscattering (UK)

·        Ultrasonic Spectroscopy (US)

·        UT C-Scan Image Processing (UI)

·        Velocimetric (VE)

·        Velocity Measurement (Vm)

·        X-Ray Tomography (XT)

As previous list with following changes to names and definition:

Acousto Ultrasonics Now specialised

Angle probe ultrasonics For matrix cracking, remote access

Polar ultrasonic scan Refers here to use of polar scan methods with ultrasonic shear wave  probes.  The term polar scan is used more widely.

Velocimetric                          Vibration

Optical Holography  Better in as developmental. Is kit really available?

Image Processing Refers to evaluating ply orientation by processing of Ultrasonic C-scan data. A particular technique for looking at ply orientation

+ Ultrasonic Spectroscopy

+ Dielectric 

+ Microwaves - various people have used to inspect for delaminations. Qinetiq have a small scanning system, with a microwave antenna (low Energy) linked to ANDscan. The method checks for transparency as well as Integrity. In stealth applications use to check radar cross section as well as integrity.

Developmental

As the current list except with Ultrasonic Spectroscopy moved to Specialised as equipment is available and used.

·        CHIME Head Wave (CH)

·        Gamma Radiography (GR)

·        Lock-In Thermography (LT)

·        Optical Holography (OH)

·        Vibro Thermography (VT)

·        X-Ray Backscatter (XB)

·        X-Ray Refractometry (XR)