JNDE

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vol 9 issue 4 March 2011Journal of Non Destructive Testing & Evaluation

from the Chief Editor

Dr. Krishnan BalasubramaniamProfessor

Centre for Non Destructive EvaluationIITMadras, Chennai

[email protected]

[email protected]: http://www.cnde-iitm.net/balas

The first issue of 2011 brings forth five more new sections that will significantly

interest the readers, in addition to the three sections introduced in the previous

issue. The COVER STORY expands on the description of the cover page image. In this

issue, a remarkably clear image obtained using ultrasonic C-scan technique from Tata

Steel is described. The IQ FORUM has now been introduced to bring the INDUSTRY

QUERIES to the researchers and solution developers. A sample problem with solution

is provided in this issue and will be coordinated by Prof. O. Prabhakar and me. We

welcome new problems to be posed by the subscribers from industries and solutions

from readers in the forthcoming issues. The NDT PUZZLE section, coordinated by Dr.

MT Shyamsunder, will challenge you to test your knowledge and skills. I encourage

you to send in your responses as early as possible in order to be eligible to win

exciting rewards. The EVENTS section provides information on the conferences,

seminars, etc, in the forthcoming months. Finally, we bring back a non-technical, but

thought provoking section called PROBE, which is contributed by Mr. B. Ramprakash.

In this edition, he brings Ayurveda and Chanakya together in the most interesting

manner. In this edition of HORIZONS, the focus is of a new a rather forgotten region

of the electromagnetic spectrum called as Terahertz regime. The BASICS section, Dr.

V. Manoharan educates the readers on the fundamentals of microfocal radiography .

The 4 Technical papers in this issue of JNDTE are all on the Acoustic Emission

technique. The first paper from IISc discusses the monitoring of fatigue crack growth

in aerospace Ti alloy using both AE and DIC techniques. This is followed by a technical

contribution from IITM on the development of an indigenous AE sensor that was

employed to monitor the emissions from a high speed motorcycle engine. The

identification of the AE signatures from composite materials, during failure, has been

reported by NAL. Finally, the prognosis of failure of a GFRP pressure bottle using AE

has been discussed in the final article.

This issue also carries a report and wonderful pictures of the ISNT event NDE2010

conducted in the Science City, in Kolkatta. The Editorial Board joins me in wishing all

the readers a successful and enjoyable 2011.

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vol 9 issue 4 March 2011 Journal of Non Destructive Testing & Evaluation

PresidentShri K. Thambithurai

President-ElectShri P. Kalyanasundaram

Vice-PresidentsShri V. Pari

Swapan ChakrabortyShri D.J.Varde

Hon.General SecretaryShri R.J.Pardikar

Hon. TreasurerShri T.V.K.Kidao

Hon. Joint SecretariesShri Rajul R. Parikh

Immediate Past PresidentShri Dilip P. Takbhate

Past PresidentShri S.I.Sanklecha

MembersShri Anil V. Jain

Shri Dara E. RupaShri D.K.Gautam

Shri Diwakar D. JoshiDr. Krishnan Balasubramaniam

Shri Mandar A. VinzeShri B.B.Mate

Shri G.V.PrabhugaunkarShri B.K.PangareShri M.V.Rajamani

Shri P.V. Sai SuryanarayanaShri Samir K. Choksi

Shri B.K.ShahShri S.V.Subba Rao

Shri Sudipta DasguptaShri N.V.WagleShri R.K.Singh

Shri A.K.Singh (Kota)Shri S. Subramanian

Shri C. AwasthiBrig. P. GaneshamShri Prabhat Kumar

Shri P. MohanShri R. Sampath

Ex-officio MembersManaging Editor, JNDT&E

Shri V. Pari

Chairman, NCB &Secretary, QUNEST

Dr. Baldev Raj

Controller of Examination, NCBDr. B. Venkatraman

President, QUNESTProf. Arcot Ramachandran

All Chapter Chairmen/Secretaries

Permanent InviteesShri V.A.Chandramouli

Prof. S. RajagopalShri G. Ramachandran

& All Past Presidents of ISNT

I S N T - National Governing Council

Chapter - Chairman & SecretaryAhmedabadShri D.S. Kushwah, Chairman,NDT Services, 1st Floor, Motilal Estate,Bhairavnath Road, Maninagar,Ahmedabad 380 028. [email protected] Rajeev Vaghmare, Hon. SecretaryC/o Modsonic Instruments Mfg. Co. Pvt. Ltd.Plot No.33, Phase-III, GIDC Industrial EstateNaroda, Ahmedabad-382 330 [email protected]

BangaloreDr. M.T. Shyamsunder, Chairman,NDE Modelling & Imaging Lab.,Cassini Building, GE Global Research,John F. Welch Technology CenterEPIP Phase 2, Whitefield Road,Bangalore-560066. [email protected]

ChennaiShri T.V.K. Kidao, ChairmanMadras Metallurgical Services Pvt. Ltd.14, Lalithapuram Street, RoyapettahChennai – 600 014 [email protected] R. Balakrishnan, Hon. Secretary,No.13, 4th Cross Street, Indira Nagar,Adyar, Chennai 600 020. [email protected]

DelhiShri B.S.Chhonkar, Chairman,90A, Pocket-1, Mayur Vihar - 1New Delhi 110 [email protected] Dinesh Gupta, Hon.Secretary,[email protected]

HyderabadShri G. Narayanrao, Chairman,Chairman & Managing Director, MIDHANI,Kanchanbagh, Hyderabad 500 [email protected] J.R. Doshi, Hon.Secretary,Scientist, Project LRSAMDRDL, Hyderabad 500 [email protected]

JamshedpurMr J. C. Pandey, Chairman,Researcher, R&D, TATA Steel,P. O. Burmamines, Jamshedpur - 831 [email protected]. M K Verma, Hon. Secretary,Manager, SNTI, TATA SteelN-Road, Bistupur, Jamshedpur - 831 [email protected]

KalpakkamShri YC Manjunatha, ChairmanDirector ESG, IGCAR, Kalpakkam – 603 [email protected] BK Nashine, Hon.SecretaryHead, ED &SS, C&IDD, FRTGIGCAR, Kalpakkam – 603 102 [email protected]

KochiShri John Minu Mathew, Chairman,General Manager (Technical),Bharat Petroleum Corporation Ltd. (Kochi Refinery),PO Ambalamugal 682 302. [email protected] K.D.Damien Gracious, Hon. Secretary,CM (Advisory Services),Bharat Petroleum Corporation Ltd. (Kochi Refinery),PO Ambalamugal-682 302. [email protected]

KolkataShri Swapan Chakraborty, ChairmanPerfect Metal Testing & Inspection Agency,46, Incinerator Road, Dum Dum Cantonment,Kolkata 700 028. [email protected] Dipankar Gautam, Hon. Secretary,4D, Eddis Place, Kolkata-700 [email protected]

KotaShri R.C. Sharma, ChairmanAssociate Director (QA),Rawatbhata 323 307 [email protected] S.V.Lele, Hon. Secretary,T/IV – 5/F, Anu Kiran Colony, PO Bhabha Nagar,Rawatbhata 323 307. [email protected]

MumbaiShri R.S. Vaghasiya, Chairman,B 4/7, Sri Punit Nagar, Plot 3, SV Road, Borivile West,Mumbai 400 092. [email protected] Samir K. Choksi, Hon. Secretary,Director, Choksi Brothers Pvt. Ltd.,4 & 5, Western India House, Sir P.M.Road,Fort, Mumbai 400 001. [email protected]

NagpurShri Pradeep Choudhari, ChairmanParikshak & Nirikshak, Plot M-9, LaxminagarNagpur - 440 022Mr. Jeevan Ghime, Hon. Secretary,Applies NDT & Tech Services,33, Ingole Nagar, B/s Hotel Pride, Wardha Road,Nagpur 440 005. [email protected]

PuneShri PV Dhole, ChairmanNDT House, 45 Dr Ambedkar Road,Sangam Bridge, Pune- 411 [email protected] VB Kavishwar, Hon Secretary,NDT House, 45 Dr Ambedkar Road,Sangam Bridge, Pune- 411 [email protected]

SriharikotaShri S.V. Subba Rao, Chairman,General Manager, Range OperationsSDSL, SHAR CentreSriharikota 524124. [email protected] G. Suryanarayana, Hon. Secretary,Dy. Manager, VAB, VAST, Satish Dhawan SpaceCentre, Sriharikota-524 124. [email protected]

TarapurShri PG Behere, Vice Chairman,AFFF, BARC, Tarapur-401 [email protected] R. Murali, Hon.Secretary,[email protected]

TiruchirapalliShri V Thyagarajan, ChairmanGeneral Manager (WRI & Labs)BHEL Tiruchirapalli 620014 [email protected] A.K.Janardhanan, Hon. Secretary,C/o NDTL Building 1, H.P.B.P., BHEL,Tiruchirapalli 620 014. [email protected]

VadodaraShri P M Shah, Chairman,Head-(QA) Nuclear Power Corporation [email protected] S Hemal Mehta, Hon.Secretary,NBCC Plaza,Opp. Utkarsh petrol pump, Kareli Baug,Vadodara-390018. [email protected]

ThiruvananthapuramDr. V.R. Ravindran, ChairmanDivision Head, Rocket Propellant Plant,VSSC, ISRO, Thiruvananthapuram - 695 [email protected]. Imtiaz Ali KhanHon.Secretary, Engineer, Rocket propellant Plant,VSSC, Thiruvananthapuram 695 [email protected]

VisakhapatnamShri Om Prakash, Chairman,MD, Bharat Heavy Plate & Vessels Ltd.Visakhapatnam 530 012.Shri Appa Rao, Hon. Secretary,DGM (Quality), BHPV Ltd., Visakhapatnam 530 012

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Contents

Chief EditorProf. Krishnan Balasubramaniame-mail: [email protected]

Co-EditorDr. BPC [email protected]

Managing EditorSri V Parie-mail: [email protected]

Topical EditorsDr D K BhattacharyaElectromagnetic MethodsDr T Jayakumar,Ultrasonic & Acoustic EmissionMethodsSri P KalyanasundaramAdvanced NDE MethodsSri K Viswanathan

Radiation Methods

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NCB Announcement

Chapter News

Basics

Horizon

NDT Puzzle

IQ Forum

NDE events

Producs & Patents

NDE 2011 Highlights

Technical Paper

Fatigue Crack Growth Monitoring in Ti-6Al-4V Alloy UsingAcoustic Emission Technique and Digital Image CorrelationShivanand Bhavikatti, M R Bhat and CRL Murthy - Page 43

Development of an Acoustic Emission Condition Monitoringsystem for use in IC Engines.Sreedhar P, JanardhanPadiyar M, R Maharajan andKrishnan Balasubramaniam

Signature Analysis of Failure Modes in Composites usingAcoustic EmissionM. Ramesh kumar and M.R. Madhava

An empirical approach for the burst prediction of GFRPpressure bottles using acoustic emission techniqueR.Joselin , T.Chelladurai, M.Enamuthu, K.M. Usha and E.S. Vasudev

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About the cover page:

Editorial BoardDr N N Kishore, Sri Ramesh B Parikh,Dr M V M S Rao, Dr J Lahri,Dr K R Y Simha, Sri K Sreenivasa Rao,Sri S Vaidyanathan, Dr K Rajagopal,Sri G Ramachandran, Sri B Ram Prakash

Advisory PanelProf P Rama Rao, Dr Baldev Raj,Dr K N Raju, Sri K Balaramamoorthy,Sri V R Deenadayalu, Prof S Ramaseshan,Sri A Sreenivasulu, Lt Gen Dr V J Sundaram,Prof N Venkatraman

ObjectivesThe Journal of Non-Destructive Testing &Evaluation is published quarterly by the IndianSociety for Non-Destructive Testing for promotingNDT Science and Technology. The objective ofthe Journal is to provide a forum fordissemination of knowledge in NDE and relatedfields. Papers will be accepted on the basis oftheir contribution to the growth of NDE Scienceand Technology.

Journal of Non DestructiveTesting & Evaluation

Published byShri RJ Pardikar,General Secretary on behalf ofIndian Society for Non Destructive Testing (ISNT)

The Journal is for private circulation to membersonly. All rights reserved throughout the world.Reproduction in any manner is prohibited. Viewsexpressed in the Journal are those of the authors'alone.

Modules 60 & 61, Readymade GarmentComplex, Guindy, Chennai 600032Phone: (044) 2250 0412Email: [email protected] at VRK Printing House3, Potters Street, Saidapet,Chennai 600 015 [email protected]: 09381004771

Volume 9 issue 4March 2011

The image in the Front Cover Page is anultrasonic C-Scan Image using 15 MHz highlyfocused beam on a Steel billet that wassectioned (Courtesy: R&D and SS Division,Tata Steel, Jamshedpur). During thecontinuous casting process, due to thedifferential cooling from the outside surfaceto the inside, the grain structure is expectedto take the distribution as represented bythe classic schematic.Here, the chill zone (A) is found on the outermost layer that is in contact with thecoolant. The anisotropic columnar grainstructure (B) is found below the chill zone.The inside regions are found to be equiaxed(C). The relative area of the 3 Zones willdepend on the processing conditions.At Tata Steel the high frequency ultrasonicC-scan imaging is used to optimize theelectro-magnetic stirring process parametersin order to improve the quality of steel(billet) manufacturing. The cross-sectionalplane C-scan image on a typical as-cast billetis shown in the cover page clearly indicatingthe 3 zones.

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Email: [email protected];[email protected] www.kidaolabs.com

KIDAO Laboratories

Scaanray Metallurgical Services(An ISO 9001-2000 Certified Company)

NDE Service ProviderProcess and Power Industry, Engineering andFabrication Industries, Concrete Structures,

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Electro-Magfield Controls & Services &LG Inspection Services

Plot 165, SIDCO Industrial Estate, (Kattur)Thirumullaivoil, Vellanur Village, Ambattur Taluk

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We manafucture : Magnetic Crack Detectors, Demagnetizers, MagneticParticles & Accessories, Dye Penetrant Systems etc

Super Stockist & Distributors: M/s Spectonics Corporation, USA fortheir complete NDT range of productrs, Black Lights, Intensity Meters,

etc.

Betz Engineering &Technology Zone

An ISO 9001 : 2008 Company

Call M. Nakkeeran, Chief Operations,Lab: C-12, Industrial Estate, Mogappair (West), Chennai 600037

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Support for NDT ServicesNDT Equipments, Chemicals and Accessories

Call DN Shankar, Manager14, Kanniah Street, Anna Colony, Saligramam,

Chennai 600093Phone 044-26250651 Email: [email protected]

49, Vellalar Street, near Mount Rail Station, Chennai 600088Mobile 98401 75179, Phone 044 65364123Email: [email protected] / [email protected]

International Training Division21, Dharakeswari Nagar, Tambaram to Velachery Main Road,Sembakkam, Chennai 600073www.betzinternational.com / www.welding-certification.com

NABL Accredited Laboratory carrying out Ultrasonic test,MPL and DP tests, Coating Thickness and Roughness test.

We also do Chemical and Mechnical testsMetallographyStrength of MaterialsNon Destructive TestingFoundry Lab

Shri. K. Ravindran, Level IIIRT, VT, MT, PT, NR, LT, UT, ET, IR, AE

Southern Inspection ServicesNDT Training & Level III Services in all the

following ten NDT Methods

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Classifieds

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National Certification Board

Indian Society for Non Destructive Testing

ANNOUNCEMENTASNT NDT Level III Examination

Bangalore23, 24 & 25 May 2011

The Indian Society for Non - Destructive Testing (ISNT), the National Sponsoring Organization of the AmericanSociety for Non – Destructive Testing (ASNT) is pleased to announce that the ASNT NDT Level III Examination of2011 (by the ASNT) in various methods is scheduled to be held at Bangalore, India on 23rd, 24th & 25th of May 2011.The examinations will be conducted under the auspices of the American Society for Nondestructive Testing, USA byNCB-ISNT.

NDT Level III certification by ASNT (which is given only by examination) will help NDT personnel and theorganizations that employ them, in promoting global acceptance of their Products and Services. The importance andthe necessity for Indian Industry to compete in the International arena need not be over-emphasized.

In order to assist the intending aspirants in preparing for the May 2011 ASNT NDT Level III examinations, refreshercourses in various methods will be conducted under the arrangement of ISNT –Bangalore Chapter. The details of thefee structure applicable for the Examination and Refresher Courses are given in Table-I and Table -II respectively. Allcorrespondences on the subject and request for application forms may please be addressed to:

Dr. B. VenkatramanASNT Level III Examination Coordinator,NCB – ISNT,

Modules 60 & 61, Readymade Garment Complex,SIDCO Industrial Estate, Guindy,

Chennai 600 032, IndiaPh:91 44 22500412 & 91 44 42038175

91 44 27480500 Ext.22306E Mail: [email protected]

Alternate E Mail: [email protected]

Applications for the Examinations duly completed in all respects along with requisite supporting documents andapplicable fees (ASNT & ISNT) shall be sent to the Examination Coordinator mentioned above.

The last date for receipt of completed application forms is March 14, 2011

The last date for receipt of nominations for the Refresher Course along with course fee is April 15, 2011

ASNT NDT Level III Examination will be conducted in the following methods:

1. Basic 7. Neutron Radiographic Testing2. Radiographic Testing 8. Leak Testing3. Magnetic Particle Testing 9. Visual Testing4. Ultrasonic Testing 10. Acoustic Emission Testing5. Liquid Penetrant Testing 11. Thermal / Infrared Testing6. Eddy Current Testing

It may please be noted that the basic examination by itself is not considered as a method. Basic and methodexamination(s) must be taken to become eligible to receive a certificate for that method(s). The maximum number ofexaminations that can be taken is six during the three days of the Examination.

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The fees payable to ASNT and ISNT for the NDT Level III Examination are given in the following table:

Table - I

Examinations ASNT Surcharge ASNT ASNT(Basic or Method) Examination Fee membership fee Fee Total

for the year * * ISNT Fee

USD USD USD USD INR

1. First time exam / Adding method exam / Renewal of certification examOne Examination 260 40 75 375 12000Two Examinations 520 40 75 635 12000Three Examinations 780 40 75 895 12000Four Examinations 1040 40 75 1155 12000Five Examinations 1300 40 75 1415 12000Six Examinations 1560 40 75 1675 12000

2. Retaking Failed ExaminationOne Examination 185 40 75 300 11,000Two Examinations 370 40 75 485 11,000Three Examinations 555 40 75 670 11,000Four Examinations 740 40 75 855 11,000Five Examinations 925 40 75 1040 11,000Six Examinations 1110 40 75 1225 11,000

*Please see Instructions 2 below.INSTRUCTIONS:

1. The amount shown under ISNT fees includes the couriercharges for the examination booklet(from and to ASNT),lunch, refreshments and all other administrative expensesto be incurred by ISNT in this connection.

2. Those who are not current members of ASNT at the timeof examination (i.e. as on May 2011) shall includemembership fee of USD 75 along with relevant ASNTexamination fee and the surcharge. Those who are currentmember at the time of examination and wishing to renewthe membership for one year shall include membershipfee of USD 60 (refer examination documents).

3. Those who do not include the membership fee along withexamination fee shall positively give their current ASNTmembership number and the expiry date.

4. The total ASNT fee including surcharge and membershipfee as applicable shall be sent in the form of a crossed

cheque in US Dollars favoring “American Society forNondestructive Testing” and payable in USA. Those whoare applying from within India may get the necessaryforeign exchange in USD from a scheduled bank.

5. The ISNT fees (and the course fees if opted), shall be paidonly by crossed demand draft in Indian Rupees favoring“NCB-ISNT”, payable at Chennai. Cheques will not beaccepted.

6. Completed application form along with enclosures and therelevant ASNT and ISNT fees shall be sent to ASNT LevelIII Exam Coordinator at the address given in the firstpage, before the due date.NO APPLICATION WITH DD DATED AFTER THEDUE DATE WILL BE ACCEPTED.

7. Candidates may kindly fill up the application form as perinstructions given. Incomplete application forms or thosewithout requisite enclosures and fees will not be accepted.

ASNT NDT Level III Refresher CoursesAT BANGALORE, INDIA

To assist the candidates in preparing for the May 2011 Examinations, refresher courses will be conducted at Bangalore; thedetails along with fees for the courses are given below.

Table II

Method Course Dates Fees for theDuration Courses in INR

Liquid Penetrant Testing 3 days 04 May to 06 May 2011 5,500

Magnetic Particle Testing 3 days 07 May to 09 May 2011 5,500

Ultrasonic Testing 4 days 10 May to 13 May 2011 7,500

Basic 4 days 14 May to 17 May 2011 7,500

Radiographic Testing 4 days 18 May to 21 May 2011 7,500

Eddy Current Testing** 4 days 7,500

Visual Testing** 3 days 5,500

* Venue will be intimated individually later

** These courses will be conducted and scheduled on the basis of responses received. Those who intend to attend the courseson Visual Testing and Eddy Current Testing should intimate their intention sufficiently in advance to facilitate schedulingthe courses. They may also inform the details of other courses they wish to attend.

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Programme Director

Shri. V. Manoharan, Senior Technologist, Cassini building, John F Welch Technology Center, 122, EPIP, Phase-2,Whitefield Road, Bangalore-560066, India - Phone: +919740643152 Email: [email protected]

The course fee includes study material, lunch and tea. Candidates will have to make their own arrangement for boarding,lodging and other expenses during their stay at Bangalore, both for the examination and the courses. Course material will begiven to the participants on the first day of the course. If it is needed earlier, it can be sent to the participants, at their specificrequest to the examination coordinator, by courier service, at their cost. In case the candidate withdraws from the course with anadvance intimation of three working days, the course fee would be refunded to him after deducting 10% of the fees towardsadministrative charges. Any cancellations for the course should however be informed prior to May 01, 2011. No refund would begiven to candidates thereafter. Also once the candidates have received the course material, on no account the course fee willbe refunded.

The course syllabus will be as per ASNT SNT-TC-1A 2006 requirement. The candidates can opt for one or more of the abovecourses as desired by them. The course fee should be sent by a crossed demand draft drawn in favor of “NCB-ISNT” payable atChennai and sent to the Coordinator at the address given in first page.

American Society for Non-Destructive Testing (ASNT)NDT Level II Examination

(First Time in India - as per SNT-TC-IAI2006)

Certification directly by ASNT

A unique opportunity for you and your organization to avail

The Indian Society for Non-Destructive Testing (ISNT), the National Sponsoring Organization of theAmerican Society for Non-Destructive Testing (ASNT) is pleased to announce that the ASNT NDT Level IIExamination of 2011 directly by the ASNT will be held at Chennai during July, 18-20, 2011. Applicationdeadline 8th May 2011.

The examinations will be conducted under the auspices of the American Society for Non-destructiveTesting, USA by NCB-ISNT.

ASNT NDT Level II Examination will be conducted in the following methods:

Radiographic Testing

Magnetic Particle Testing

Ultrasonic Testing

Liquid Penetrant Testing

Eddy Current Testing

Leak Testing

Visual Testing

Acoustic Emission Testing

Thermal / Infrared Testing

Please visit our website isnt.org.in for application and further details

For further queries, please contact:

Dr. B. VenkatramanASNT Level III Examination Coordinator, NCB-ISNT,

Modules 60 & 61, Readymade Garment Complex,SIDCO Industrial Estate, Guindy,

Chennai 600 032, IndiaPh: 91 44 22500412 & 91 44 42038175

91 44 27480500 Ext.22306E-mail: [email protected]

Alternate E-mail: [email protected]

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CHAPTER NEWSMumbai Chapter

APCNDT 2013 committee Meeting was held on 21st December2010

UT Level II course & Examination for ONGC Engineers on3-8, January, 2011 at IQM, Jogeshwari (W), Mumbai. Course Directorwas Shri N. Sadasivan and Examiners were Shri S.P. Srivastava andShri Luke Pinenta

Welding Inspector examination at ITT, Mahim on 8th January2011, and the Examiner was Shri L. M. Tolani.

RT Level II course & Examination for ONGC Engineers on 10-15, January 2011 at IQM, Jogeshwari (W), Mumbai. Course Directorwas Shri L.M. Tolani and Examiners were Shri S.P. Srivastava andShri Sanjay Narang.

APCNDT 2013 committee Meeting was held on 14th January2011.

EC Meeting to be held on 28th January 2011

Vadodara ChapterThe activity was a Lecture by Air Marshall Shri P.K. Desai (Retd.)

on”NDT for Maintenance of various Aircrafts of Indian Air Forceduring Peace Period and War Period”.

The lecture was well attended and also was participated by IndianAir Force personnel. The lecture gave insight and indication totheparticipants on requirement of NDT science and NDT technologyto ensuresafety of pilots as well as to ensure maintenance of airarmaments in evergreen stage. The interested aspect of this lecturewas evaluation on extension of lives of planes - a system developed

National NDT Awards No. Award Name Sponsored by 1. ISNT - EEC M/s. Electronic & Engineering Co., Mumbai

National NDT Award (R&D)

2. ISNT - Modsonic M/s. Modsonic Instruments Mfg. Co. (P) Ltd.,National NDT Award (Industry) Ahmedabad

3. ISNT - Sievert M/s. Sievert India Pvt. Ltd., Navi MumbaiNational NDT Award (NDT Systems)

4. ISNT - IXAR M/s. Industrial X-Ray & Allied RadiographersBest Paper Award in JNDE (R & D) Mumbai

5. ISNT - Eastwest M/s. Eastwest Engineering & Electronics Co.,Best Paper Award in JNDE (Industry) Mumbai

6. ISNT - Pulsecho M/s. Pulsecho Systems (Bombay) Pvt. Ltd.Best Chapter Award for Mumbaithe Best Chapter of ISNT

7. ISNT - Ferroflux M/s. Ferroflux ProductsNational NDT Award (International recognition) Pune

8. ISNT - TECHNOFOUR M/s. TechnofourNational NDT Award for PuneYoung NDT Scientist / Engineer

9. ISNT - Lifetime Achievement Award

Note-1: The above National awards by ISNT are as a part of its efforts to recognise and motivate excellence in NDT professionalenterpreneurs. Nomination form for the above awards can be obtained from ISNT head office at Chennai, or from the chapters. Thefilled application are to be sent to Chairman, Awards Committee, Indian Society for Non-destructive Testing, Module No. 60 & 61,Readymade Garment Complex, SIDCO Ind. Estate, Guindy, Chennai-600 032. Telefax : 044-2250 0412 Email: [email protected]

jointly by Indian Air Force with the scientists and technologists ofKalpakkam group who are also members of ISNT

“Shri P.M. Shah – Chairman ISNT Vadodara Chapter welcomedthe Chief Guest and Ms. Hemal Mehta - Hon. Secretary ISNTVadodara Chapter introduced Chief Guest; Shri Nayak – ViceChairman ISNT Vadodara Chapter gave vote of thanks”

Kolkata ChapterISNT-NDE-2010 -National Seminar,jointly organized by

Jamshedpur and Kolkata Chapter during 9-11th.Dec,2010 at ScienceCity , Kolkata. There were two pre seminar Tutorial on 7th &8th.Dec,2010 on Digital Radiography and Thermal Imaging and onSignal Analysis,simulation and Modeling. The workshop on AdvanceNDE for structural intigrity assessement. Pre tutorial and workshoswere conducted on three parallal session and more than 90 participantsmainly students, Research Scholars and from industries attended thepre-tutorial and work shop.

On 9th.Dec’2010 inagural ceremony was held. Mr.RajivKaul,Industrialist was chief guest and Vice chancellor of BengalEngineering and Science University was Guest of Honour. More than500 delegates attended the seminar. There were more than forty twoexhibitors. NDT equipment manufacturers exibited their products.Exhibitors were from Germany, Ukraine, China, Checkoslovakia,USA and Indian manufacturers.M/s.GE Sensing & InspectionTechnologies was main sponsor, M/S. Bluestars Ltd was Co-Sponsorand M/S. East West Engineering & Electronics Pvt.Ltd, M/S. GodavariTechnical Services, M/s.Sivert India were the Associate sponsors.

WCNDT participated the seminar and they were provided with acomplementary stall.

Photographs of NDE 2010 is printed elsewhere in thejournal.Swapan Chakraborty, Convener NDE 2010.

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Basics of Microfocal RadiographyV. Manoharan1 and Neuser Ebherhard2

1 GE India Technology Center, Bangalore, India2 GE Energy Services, Wunstorf, Germany

Email: [email protected] ; [email protected]

Edited byProf. O. Prabhakar,

OP Tech, Chennai.

Geometric unsharpness and magnification are thetwo issues that are of concern in conventionalradiography. Particularly in areas likemicroelectronics, materials technology,biomedical applications and medicine fine detailshave to be observed. By reducing the area fromwhich the X-rays are generated (Focal spot) onecan improve the resolution and the magnificationof the conventional radiography. Due to itsimportance in modern NDT, the fundamentals ofmicro-focal radiography are explained in thisarticle by Dr Manoharan and Dr Eberhard,experts in this field.

1. INTRODUCTION

Radiographic inspection can be classified in many wayse.g. based on type of radiation sources used, type ofdetection medium , applications and etc. Conventionaland Microfocal radiography are classifications based onfocal spot sizes of x-ray generation devices. The focalspot is defined as an area on the target where x-rays aregenerated. If the focal spot size is greater than 100microns, then the radiographic inspection is generallytermed as conventional radiography. Ever since thediscovery of x-rays, conventional radiography has beenused for many industrial applications such as inspectionof welds, castings, composites and other engineeringmaterials. However, the larger focal spot sizes inconventional radiography produces blurring of imagesand thus does not allow projection radiography (imagemagnification). Therefore, there is a limitation ofdetecting micro defects using conventional radiography.With the development of new materials and an increasedstringent requirement of specifications, the emphasisshifted from the detection of macro defects to microdefects, thus resulting in the demand and developmentof microfocal radiography.

If the focal spot size is less than 100 microns, then theradiographic inspection is termed as Microfocalradiography. Micro focal radiography systems with focalspot of size 1 to 100 microns has opened the way forthe detection of micro defects of the order of few micronsin critical engineering components as smaller focal spotallows image magnification. For example, the internalsof an Integrated Circuit can be clearly seen as shown inFig.1. This would have been very difficult to achieveusing conventional radiography. Microfocal radiography

Systems coupled with state-of-the-art digital radiographysystems are today being widely used in the aerospace,automotive, power and electronic industries forautomated 2D inspection and 3D imaging of criticalcomponents.

2. PHYSICS OF MICROFOCALRADIOGRAPHY

The main advantage of Microfocal radiography is that itallows projection radiography (image magnification). Letus try and understand the requirements of projectionradiography. The object needs to be placed away fromthe detector as shown in Fig. 2 for image magnification.

The magnification (M) is given by

M = FDD / FOD (1)

Fig. 1 : Microfocal Radiography of Integrated Circuit

BASICSBASICSBASICSBASICSBASICS

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due to geometric magnification. Thus one can attainvery high magnification with minimum unsharpnessusing Microfocal x-ray sources when compared toconventional ones.

3. MICROFOCAL X-RAY SOURCES

As we know that only 1- 3% of the kinetic energy ofelectrons is converted into x-rays and rest is dissipatedas heat, the heat energy generated over very small areain micrococcus x-ray sources can melt the target. Thisis a huge challenge in the designing of micro focus x-ray sources and it limits the power of microfocus x-raysources. A typical construction of microfocus x-raysources is shown in Fig. 4.

where FDD is the Focal spot to Detector Distance andFOD is Focal spot to Object Distance. Hence, for largermagnification, the Object to Detector Distance (ODD)needs to be larger. However, We know that, geometricunsharpness will be more if ODD is more as thegeometric unsharpness (Ug) is given by

Ug = f x ODD / FOD (2)

Where f is the focal spot size. It is evident that the focalspot size and ODD are important factors in determiningthe geometrical unsharpness. The variation of geometricalunsharpness with focal spot size and ODD is illustratedin Fig.3. We can derive another formula for

Ug= f (M-1) (3)

from equation (1) and (2).

This shows that using a smaller focal spot x-ray sourcescan compensate the increase in geometric unsharpness

Fig. 3 : Illustration of geometric unsharpness

Fig. 2 : Illustration of geometric magnification

The microfocus x-ray tube consists of an evacuated tube,tungsten filament, a target and electro magnetic lensesto focus electrons. Electrons are generated by thermionicemission by heating the filament and accelerated towardstarget by a potential difference between cathode andanode as in conventional x-ray sources. The filamentcurrent is controlled by means of the Wehnelt grid, whichis held at a negative potential (voltage UG). The beampasses through a hole in the anode and is then directedonto an electromagnetic lens by a series of deflectingmagnets where it is then collimated and focused ontothe target. X-rays are emitted when accelerated electronsare decelerated upon striking a target. There are twotypes of targets used in microfocus x-ray tubes, theTransmission and Directional type. The transmissiontarget consists of a thin layer of tungsten on a plate oflight metal. In case of transmission targets, the X-ray

Fig 4 : Construction of microfocus x-ray source


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source is located very close to the outer wall of themicrofocus X-ray tube allowing the user to bring samplesvery close to the source ensuring highest magnifications.The directional type directional type targets enables morepower and suitable for inspection thicker and densercomponents. Transmission and directional typemicrofocus x-ray sources are illustrated in Fig.5.

Microfocus x-ray sources with kV of the order of 220kV are commercially available and 300 kV sources arealso introduced in the market. The target to windowdistance is one of the key specification of microfocus x-ray sources, which determines how closely object canbe placed near the focal spot and achieve largermagnification.

The micro focus x-ray sources are also classified assealed sources and de-mountable source based on howvacuum is maintained in them. Sealed sources havepermanently vacuum-sealed x-ray tube head. Theadvantage of sealed sources is that it is maintenancefree and has high power. A demountable x-ray tubeconsists of an open type X-ray tube head, which consistsof continuously pumped vacuum system. The advantageof demountable tube is that opening the x-ray tube head;we can replace the faulty filament and target. Itslimitation is frequent maintenance requirements ofvacuum systems and time taken to achieve vacuum duringoperation. Some of the micro focal x-ray systems haverod anode, which is used, for inspection of welds insmaller diameter tubes. The rod anode can be insertedinside tube and panoramic exposure cab be carried outwith geometric magnification. Different types of rodanode configurations are given in Fig. 6.

4. MICROFOCAL X-RAY SYSTEMS

There are integrated microfocal x-ray systems, whichconsist of a microfocus x-ray source, a manipulator tohandle objects, a digital detector array, a radiationshielded cabinet and software to control manipulator/source & detector and image analysis tools to process x-

Fig. 5 : Transmission and Directional Targets

Fig. 6 : Type of rod anodes Fig. 7 : A typical integrated Micro focus x-ray inspection system


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ray images. These systems are used for inspection ofsmall parts automatically in a production line. A typicalsuch system is shown in Fig.7. Micro tomography isanother type of integrated x-ray system, which has 3Dimaging capability with resolution of the order of fewmicrons.

5. RECENT ADVANCES

X-ray sources with focal spot size of less than 1 micronare developed and are commercially available in themarket. These nanofocus x-ray sources extend theresolution capability of 2D and 3D x-ray imaging systemssignificantly. Nanofocus x-ray sources enables the levelcontrast and resolution required for the inspection oflow-density structures and very small features commonin miniature electronic components such asoptoelectronics, Microelectromechanical systems andmicro-opto-electromechanical systems.

6. APPLICATIONS

PRINTED CIRCUIT BOARD ASSEMBLY

Micro focus radiography is extensively used inElectronics and semiconductor industries for inspectionof Printed Circuit Board Assembly (PCBA), Multi layercircuit board, power electronic components andintegrated circuits. Defects solder joints such as Missingsolder fillets, Voids, blisters; Solder bridges and Non-wetting defects in PCBAs can be easily detected byhigh-resolution micro focal radiography.

MULTILAYERED CIRCUIT BOARD

In multilayer circuit board manufacturing, high-resolutionmicrofocal radiography is mainly used to determine thelayer offset and minimum annular width and detectingflaws such as short circuits caused by etching or layoutdefects and defective conductor tracks.

SEMICONDUCTORS

As electronic components are becoming increasinglyminiaturized, high-resolution and magnification X-raytechnology provides the means necessary to inspectcomponents such as Inspection of bond wires andbonding areas, Void analysis of conductive and non-conductive die bonds, inspection of flip-chip solder jointsin processor cases and Analysis of discrete componentssuch as capacitors and inductors.

MICRO TOMOGRAPHY APPLICATIONS

3D Micro tomography is used for inspection of gasturbine blades, Aluminium castings, composites, sinteredceramic materials and geological specimens, In plasticsengineering, high-resolution X-ray technology is beingused to optimize the casting and spraying process by Fig. 8 : Applications of microfocal Radiography

BASICSBASICSBASICSBASICSBASICSS

older Join

tPC

BA

-Fau

lty

Power Transistor on a printed circuit board

3D micro tomogram of Automotive Metal foam

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Tube-to-Tube sheet welds

The tube-to-tube sheet weld inspection in heat exchangersof nuclear reactors is another critical application ofmicrofocal radiography. There are many referencesavailable for tube-to-tube sheet inspection, which is givenin the references. Here a rod anode is used andpanoramic exposure of entire circumference of tube-to-tube sheep weld is radiographed with ~ 2X magnification.An example of tube-to-tube sheet inspection is givenFig. 9.

7. ADVANTAGES & LIMITATIONS

The advantages of micro focal radiography are asfollows:

1. It allows projection radiography (image magnification) andmakes it possible to detect defects of the order of few microns

2. It reduces scattered radiation reaching the detector, as thedistance between object and detector is more

3. It makes it possible to have uniform depth of focus and

4. It is possible to do 3D micro tomography with resolutions ofa few microns

The advantages of microfocal radiography are illustratedin Fig. 10.

Some of the key limitations of micro focal x-ray systemsare its limited power arising from the heat load in smallx-ray focal spots, limited area coverage per exposureand the difficulties in inspecting thick & high-densitymaterials because of limited x-ray intensities.

REFERENCES

1. Microfocal Radiography by R. V. Ely, Academic press

2. B.Venkatraman, V.K. Sethi, T.Jayakumar and Baldev Raj, HighDefinition Radiography of Tube to Tube Sheet Welds of SteamGenerator of Prototype Fast Breeder Reactor, Insight,37,1995,pp-189-192.

3. B.Venkataraman, V.Manoharan, P.Kalyanasundaram, BaldevRaj and V.K.Sethi, N.V.Wagle, Radiographic Sensitivity ofMicrofocal and Thulium Sources, Proc. of National seminaron NDE (in CD), Mumbai Dec. 2001.

4. http://www.ge-mcs.com/en/phoenix-xray.html

5. Baldev Raj, T.Jayakumar and M.Thavasimuthu, Practical Non-Destructive Testing, Naraosa Publications

6. Dr. Holger Roth, Stuttgart, Fundamentals of x-ray inspection,GE MCS-Phoenix x-ray, Internal Presentation


Fig. 9 : Microfocal Radiography of tube-to-tube sheet weld (Ref.5)

Fig. 10 : Advantages of Microfocal Radiography

detecting contraction cavities, blisters, weld lines andcracks, and to analyze flaws. Industrial X-ray computedtomography (CT) provides three-dimensional images ofobject characteristics such as grain-flow patterns andfiller distribution as well as imaging of low-contrastdefects. 3D metrology with industrial CT is the onlytechnique allowing non-destructive measurements of theinterior of complex objects. Typical examples ofapplications are given in Fig. 8.

Contact

Mr. D. Simon Amallaraja | 0 9866343309,9848043309|

Ms.Gomathi Ramasamy | 0 7702733309 |

Mr. Frank Edwin Vedam | 0 8978517118 |

[email protected]

[email protected]

[email protected]

HORIZONHORIZONHORIZONHORIZONHORIZON

T-raysWhere will it lead us? C.V. Krishnamurthy

Department of PhysicsIndian Institute of Technology, MadrasChennai 600036, Tamilnadu, Indiae-mail: [email protected]

Between the microwave and the infrared regions of theelectromagnetic spectrum, lies the terahertz (THz) regioncharacterised by the now not-so-mysterious T-rays (seeFigure 1). It remained nearly untapped for a long time,as neither electronic nor optical sources could illuminatethis shadowy region.

Terahertz (THz) frequency domain is usually defined asthe portion of the submillimetre-wavelengthelectromagnetic spectrum between approximately 1mm(300 GHz, ~ 0.4 meV) and 30ìm (10 THz, ~ 40 meV).T-rays have several advantages over x-rays, one beingthat they have low photon energies (for example, 4 meVat 1 THz) and therefore do not subject a biological tissueto harmful radiation. In comparison, typical x-ray photonenergy is in the range of keV, which is 1 million timeshigher than that of a T-ray photon.

T-ray imaging provides spectroscopic information withinthe terahertz frequency range, unlike microwave and x-ray imaging modalities which produce density pictures.The rotational, vibrational and translational responsesof materials (molecular, radicals and ions) within theTHz range provide information that is generally absent

in optical, x-ray and NMR images. In principle, thesetransitions in THz frequency are specific to the moleculeand therefore enable THz wave fingerprinting. T-rayscan easily penetrate and image inside most dielectricmaterials and polymers, which may be opaque to visiblelight and low contrast to x-rays, making T-rays a usefuland complementary imaging source in this context.

As a quasi-optical beam, a T-ray can be reflected andcollimated by metallic mirrors and focused by a plasticor high-resistivity silicon lens. Imaging with optical andnear-infrared waves entails large amounts of Rayleighscattering which tend to spatially smear out the objectsto be imaged. T-rays, due to their longer wavelengths,can provide significantly enhanced contrast because oflow Rayleigh scattering.

At microwave frequencies, compact electronic devicesare typically used as high-power sources. But atfrequencies substantially above 100 GHz, as the transittimes of electrons in devices become shorter andcapacitative effects are more dominant, it becomesincreasingly difficult to generate large output powers.Conversely, approaching the terahertz frequency range

Fig. 1 : Electromagnetic spectrum highlighting the Terahertz region.

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HORIZON

from the visible side of the electromagnetic spectrum, itbecomes progressively more difficult to engineer andmaintain a population inversion between two states in alaser, as their energy separation becomes closer andcloser to k

BT (where k

B is Boltzmann’s constant and T

is temperature). For these reasons, most uses of terahertzwaves have been demonstrated with broadband terahertzspectroscopy systems that are based on femtosecondlasers.

GENERATION AND RECEPTION

In 1995, Binbin Hu and Martin Nuss at LucentTechnologies’ Bell Laboratories created a terahertzimaging system and coined the term T-ray for these short,broadband terahertz pulses.

Electrically biased photoconductor generates a THz pulsewhen a femtosecond laser pulse induces its conductivitychanges. Transient photoconductivity, a highly complexphenomenon, includes optical generation of hot electronsand holes, their rapid thermalization, ballistic accelerationof the electrons, velocity-overshoot on a subpicosecondtime scale and fast screening of the internal electricfield. It is important that the energy bandgap of thesemiconductor ε

gap is smaller than the laser photon energy

hí, so that the photons will be absorbed and electronand hole pairs will be created.

A split antenna is fabricated on a semiconductor substrateto create a switch (see Fig. 2). A dc bias is placed acrossthe antenna, and an ultrashort pump-laser pulse(<100 fs) is focused in the gap in the antenna. The bias–

Fig. 2 : Schematic of a typical setup with the PCA switch and its emission spectrum.

Fig. 3 : Schematic of a cw THz system

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HORIZON

laser pulse combination allows electrons to rapidly jumpthe gap, and the resulting current in the antenna producesa terahertz electromagnetic wave. This radiation iscollected and collimated with an appropriate opticalsystem to produce a beam. This switch generates a trainof pulses, whose repetition frequency is the same as thatof the femtosecond pump laser. Pulse widths are on theorder of 100 fs, with average powers of a few microwattsand a frequency spread of >500 GHz. The pulsebandwidth is typically centered at about 1 to 2 THz.The details of the spectrum can vary significantly,however, depending on the design of the switch andpump-laser power, pulse width, and configuration.Coherent THz wave signals are detected in the timedomain by mapping the transient of the electric field inamplitude and phase. This gives access to absorptionand dispersion spectroscopy.

The terahertz pulse is distorted by selective absorptionas it passes through a sample, causing delays in its arrivaltime at the detector. The transmitted beam is then focusedonto a detector, which is essentially identical to theemitter except that it is unbiased. By varying the timeat which the sample pump pulse arrives at the detector,successive portions of the terahertz pulses can be detectedand built into a complete image of the pulse in terms ofits delay time, or time domain. The data are thenprocessed by fast Fourier transform analysis in order toconvert the delay time into the frequency of the terahertzsignal that arrives at the detector.

Continuous wave (CW) THz systems are preferred whenspectral resolution is the primary concern, e.g., to studysharp absorption lines of gases. In contrast to pulsedTHz systems, no femtosecond lasers are required. Asshown in the Fig. 3, the output of two frequencystabilized laser diodes is spatially overlapped in a beamcombiner and focused onto a photoconductive antenna(PCA) with an optimized electrode geometry.

Instead of the ultrafast carrier dynamics employed inthe pulsed case, mixing of the two incident waves isexploited to generate a continuous THz wave, whichoscillates with the difference frequency of the twoincoming waves. By detuning one of the laser diodes,the emission frequency can be swept in a wide spectralrange. A second PCA is employed for coherent samplingof the incoming THz radiation. Even though pulsedsystems are decreasing in price, CW systems are stillless expensive and feature a frequency resolution downto 2MHz.

APPLICATIONS

THz offers a non-invasive, non-contact, non-ionizingmethod of assessing composite part condition and could

overcome some of the short-comings of other non-destructive techniques such as x-rays, ultrasound, videoinspection, eddy currents, and thermographic techniques.

With wavelengths in the sub-millimeter domain, highresolution THz imaging extending to micron rangeappears feasible.

Since most polymers are transparent to T-rays, non-destructive testing in the plastics industry appears to bea very promising commercial application. This includesthe in-line monitoring of polymeric compoundingprocesses and flaw detection, as well as a 100% qualitycontrol inspection of plastic parts manufactured byinjection molding.

THz can penetrate glass fiber without contacting it, withsubmillimeter resolution, and can detect surface defects,hidden voids, delaminations, and bending damage incomposites. Additionally, it can also be used to evaluatewhether the aircraft composite has been chemicallyaltered from engine burn damage by measurement of itsindex of refraction and absorption coefficient spectrum.

The absorption coefficient for liquid water is as high as150 cm”1 at 1 THz. This strong absorption limits thesensing and imaging in water-rich samples for mostterahertz applications and prohibits transmission-modeimaging through a thick tissue. However, THz wave

Fig. 4 : THz images resolving 0.4 mm fibre, 0.25 mm mass and0.24 mm specks from a phantom.

Fig. 5 : A THz image and a photograph of an air-bag cover madeof a low-absorbing polymer. All elements that are visiblein the photograph can also be easily resolved in the THzimage, including ribs, edges, paper stickers marked with(1) or even slightly thicker regions marked with (2), whichare merely seen in the photograph.

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HORIZON

detailed structure of multi-component targets on a sub-millimetre scale while being able to distinguish betweenmaterials in terms of the spectral dependence of dielectricconstant or absorption.

Weapons or personnel can be detected throughcamouflage or thin foliage, and targets can bediscriminated from background on the basis of spectralresponse. There is also scope for the detection,identification and tracking of chemical and biologicalweapons in the atmosphere. Unique THz chemicalsignatures of war gases due to rotational spectral lines,and phonon excitations of biological warfare agents canbe detected in the low-THz range by high-resolutionspectroscopy.

While state-of-the-art quality control systems can easilydetect metallic contaminations in food products, non-metallic contaminations are often hard to find. Existingapproaches, such as ultrasonic or x-ray scans, fail whenthe density difference or the dielectric contrast betweenthe material and the contamination is low. As THz scansconsider not only the absorption spectrum but also thephase information due to the underlying coherentemission and detection scheme, many parameters canbe employed for the identification of undesiredinclusions.

RECENT TRENDS

An alternative to using photoconductive switches orsemiconductor surfaces has been to employ non-centrosymmetric nonlinear optical crystals. This approachoffers both controllability of the spectrum and amplitudeof the emitted THz pulses by varying experimentalparameters, such as the wavelength and duration of thegenerating laser pulse, and crystal thickness. DAST (4-N, N-dimethylamino-4’-N’-methyl stilbazolium tosylate)is a well-known organic optical crystal with low dielectric

transmission changes of 1% have been demonstrated somuch so that absorption even by minute amounts ofwater or small changes in water concentration can bereliably detected. As physical and mechanical propertiesof polymers are severely influenced by its water content,THz sensing appears promising.

Perhaps the greatest potential for new applications liesin the strong spectral dependence of the interaction withmaterials, where resonant absorption by the molecularstructure of targets provides information on theircomposition, and hence the target identity, not readilyavailable by other remote sensing methods.

Terahertz imaging applications in pharmaceuticals,particularly in characterizing tablet integrity, entericcoating parameters, adhesion quality between the layersin the tablet core, tablet dissolution rates have begun ona commercial basis.

Transform-limited pulses with terahertz bandwidth havedurations <1ps, and corresponding pulse lengths of<0.3mm, so terahertz radar is capable of probing the

Fig. 6 : Examples of THz imaging of tablet characteristics (from http://www.teraview.com/terahertz/)

Fig. 7 : Near-field THz imaging showing enhanced lateralresolution.

THz imaging maps the coating thickness,uniformity and region of tablet failure.

Nondestructive cross sections clearly identify cracks at depth within the tablet core. The imageon the left shows a good quality tablet. The second and third images on the right show tabletswith integrity problems.

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Los Alamos National Laboratory and Boston University(see Fig. 8). Metamaterials are composites, engineeredon the micron-scale, that use unique metallic contoursin order to produce responses to light waves, givingeach metamaterial its own unique properties beyond theelements of the actual materials in use. The teamincorporated semiconducting materials in critical regionsof tiny elements – in this case metallic split-ringresonators – that interact with light in order to tunemetamaterials beyond their fixed point on theelectromagnetic spectrum that allowed them to tuneterahertz resonance across a range of frequencies in thefar-infrared spectrum.

One recent enabling technology is that of the T-raytransceiver. This technique utilizes the reciprocalrelationship between optical rectification and electro-optic detection to allow a single ZnTe crystal for bothemission and detection of THz pulses. In principle, sucha transceiver could be made as small as 1 mm2 andmounted at the end of an optical fibre for endoscopicapplications.

There is no doubt that THz wave imaging is an attractivetechnique with enormous potential in military andbiomedical applications on the one hand and in inspectingplastic and composite materials on the other. It has anumber of important advantages over competingtechniques that may give rise to a number of nicheapplications.

REFERENCES

X-C Zhang, Terahertz wave imaging: horizons and hurdles, Phys.Med. Biol. 47 (2002) 3667–3677

Eric R. Mueller, Terahertz Radiation: Applications and Sources,The Industrial Physicist (2003) August/September Issue

A. Schneider, M. Neis, M. Stillhart, et al. Generation of terahertzpulses through optical rectification in organic DAST crystals: theoryand experiment. J. Opt. Soc. Am. B. (2006), 23, 1822-1835.

Christopher D. Stoik, Matthew J. Bohn and James L. Blackshire,Nondestructive evaluation of aircraft composites usingtransmissive terahertz time domain spectroscopy, Optics Express16 (2008) 170039- 170051

Rafal Wilk et al., Continuous wave terahertz spectrometer as anoncontact thickness measuring device, Applied Optics 47 (2008)3023-3026

Christian Jansen et al, Terahertz imaging: applications andperspectives, Applied Optics 49 (2010) E48 – E57

Fig. 8 : Scanning electron microscopy (SEM) images of thefrequency-tunable planar metamaterial. An individual unitcell (a), and periodically patterned square array (b). Alldimensions are shown in microns and materials areindicated in the images. The polarization of the incidentlinearly-polarized THz radiation is also indicated in (b).Source URL: http://www.sciencedaily.com /releases/2008/04/080415185016.htm

HORIZON

constant and high nonlinear response. In such a non-centrosymmetric nonlinear optical material, an ultrashortlaser pulse (< 150 fs) induces a quasistatic polarization,which follows in time the amplitude of the pump pulseand thus acts as a source for the THz pulse.

A tunable metamaterial that can be used over a range offrequencies in the so-called “terahertz gap” has beenengineered by a team of researchers from Boston College,

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Starting from this issue, we areintroducing a new section “ NDT Puzzle”,which will stimulate your brain cells, helpspend some time usefully and of courseenhance your knowledge. And what ismore ! You will get paid for having FUNby way of attractive prizes !! To startwith we have for you a ‘Word SearchPuzzle’. We hope you will find this sectioninteresting, educative and fun filled. Inthe forthcoming issues, you can expectCrosswords, Anagrams, and more.Please send your feedback, commentsand suggestions on this section [email protected]

ndt puzzle Conceptualized & Created byDr. M.T. Shyamsunder, GE Global Research, Bangalore

NDT WORDSEARCH - 1

NAME : ___________________________

ORGANIZATION : ___________________________

IntroductionThe “Word Search Puzzle”, contains fifty(50) words related to NondestructiveTesting. These include techniques,terminologies, phenomenon, famouspeople, etc. These words are hidden inthe puzzle and may be presenthorizontally, vertically, diagonally in aforward or reverse manner but alwaysin a straight line.

InstructionsAll you have to do is identify these wordsand mark them on the puzzle with ablack pen

-Preferably you may take a photocopyof the Puzzle sheet and mark your

answers on that (see the markedexample)

-Once completed please scan youranswered puzzle sheet as a PDF fileand email the scanned sheet [email protected] with your name,organization, contact number and emailaddress

Rules & Regulations-Only one submission per person is allowed

-The marked answers should be legible andclear without any scratching or overwriting

-The decision of the Editor-in-Chief, Journal ofNDT &E is final and binding in all matters

-First three correct entries will receive suitablerewards and will be announced in next issue.

PHONE : ___________________________

EMAIL ID : ___________________________

A new feature in the Journal of NDT & E

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IQ forumProblem: 03-2011

Absence of Back-wall echo

Industry: Steel Foundry

Posted by: Prof. O. Prabhakar

Casting: The steel casting, weighing about 15 tonnes,was made in two segments and welded together. Laterthe casting was cleaned, fettled and normalized.Subsequently, PT and UT were done as shown in Fig. 1.

Ultrasonic Testing: No clear flaw echo was obtainedduring UT of the weld and near the welded portions.Also, the back-wall echo was absent in the casting nearweld portions. UT was done with a normal probe inboth the directions as shown in the Fig. 2. The 2/4 MHzprobes with a large diameter were employed. Theproblem posed was why the back-wall echo was absent.

Fig. 1 : PT being done on the actual casting.

Fig. 2 : Steel Casting

Solution I: Usually cast structure shows coarse grainsand a good normalizing treatment is essential beforeUT is carried out. In addition if the cooling rate is veryhigh during heat treatment, structure would showWidmanstaetten structure which would also hinder UT.So the first suggestion given was to repeat theNormalizing heat treatment.Result: UT results did not improve. Still the back-wallecho was absent.

Solution II: A small portion was cut out near the weldzone and metallographically studied. The specimen wasfound to have numerous small tight cracks, which onseparation showed silver foil appearance. This is typicalof hydrogen cracking.

CONCLUSION: Steel castings are prone to hydrogenembrittlement due to pick up of hydrogen either duringcasting or welding. This would result in poor fracturetoughness. When this material is subjected to residualstresses, hairline cracks would appear. This is a verydangerous situation that could lead to catastrophicfailure in service. In this case, the welding processprovided the required stresses and the hydrogen waspicked up either during casting or welding. Henceabsence of back-wall echo is a serious indication andshould be further probed.

“To establish a connect between the Researchers andPractitioners in NDE, this new forum INDUSTRIALQUERY (IQ) FORUM is being created in our journal.

We wish to bring together the underlying scientificprinciples, engineering and technological aspects andthe most probable solutions for a NDT problem posedby our readers and members.”

If you are in the industry and have a IQ, send anMSWord document with associated drawings [email protected] with subject title “IQ Problem”for consideration for publication in a future issue. Alsoinclude any attempts at solving this problem.

If you have a suggestion or solution for this,issue of IQ, please send it to [email protected] subject title “IQ Solution- 03-2011” alongwith your contact information. Selected responseswill be published in the June 2011 issue. Allresponses will be forwarded to the person posingthe IQ.

“Readers are welcome to contribute their ownexperiences in this kind of problems.

ISNT would select the best answer for a possiblereward.”

-Prof. O. Prabhakar-Prof. Krishnan Balasubramaniam

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NDE events

A new feature in the Journal of NDT&E

Conceptualized & Created by Dr. M.T. Shyamsunder, GE Global Research, Bangalore

Starting from this issue, we are introducing a new section, which will list some of the important events suchas seminars, workshops, conferences that are scheduled to take place in the next few months around the world.We hope this feature will enable you to plan, submit papers and participate in these events more effectively.

Please send your feedback, comments and suggestions on this section to [email protected]

MARCH 2011

16th International Workshop on Electromagnetic NDE(ENDE 2011) -March 10 – 12, 2011 ; IIT, Madras,Chennai,INDIA

http://www.igcar.gov.in/seminars/

ASNT Annual Research Symposium & SpringConference -March 21 – 25, 2011 ; San Francisco, USA

http://www.asnt.org/events/conferences/sc11/sc11.htm

10th International Exhibition and Conference forNon-Destructive Testing and Technical Diagnostics -March 22 to 14, 2011 ; Moscow, Russia

http://ndt-russia.primexpo.com/

APRIL 2011

12th National NDT Conference and ExhibitionDEFEKTOSKOPIA 2011 - April 5 to 7, 2011 ; Slovakia

http://www.defektoskopia.eu

BINDT Aerospace Forum 2011April 13-14, 2011 ; Bristol, UK

h t t p : / / w w w . b i n d t . o r g / E v e n t s /N D T _ C o n f e r e n c e s _ & _ S e m i n a r s /BINDT_Aerospace_Forum_2011

24th Brazilian National Congress on NDT andInspection - May 10 to 13, 2011 ; Brazil

http://www.abende.org.br

MAY 2011

NDTMS 2011 International Symposium on NDT ofMaterials & Structures - May 15 to 18, 2011 ; Istanbul,Turkey

http://www.ndtms.itu.edu.tr/0.2/

Annual Conference and Exhibition of the FrenchSociety for NDT (COFREND) - May 24 to 27, 2011,Dunkirk, France

http://www.cofrend.com/2011/

JUNE 2011

International Chemical and Petroleum IndustryInspection Technology XII Conference - June 8-11,2011 ; Houston, Texas, USA

http:/ /www.asnt.org/events/conferences/icpii t /abstracts.pdf

12th Int. Symposium on NondestructiveCharacterization of Materials (NDCM-XII) - June 19to 24, 2011 ; Blacksburg, VA, USA

http://www.cpe.vt.edu/NDCM-XII/

International symposium on Digital IndustrialRadiology and Computed Tomography - June 20 to22, 2011 ; Berlin, Germany

http://www.dir2011.com/

The Eighth International Conference on ConditionMonitoring and Machinery Failure PreventionTechnologies - 20-22 June 2011 ; Cardiff, UK

h t t p : / / w w w . b i n d t . o r g / E v e n t s /C M _ C o n f e r e n c e s _ & _ S e m i n a r s /CM_2011_and_MFPT_2011

JULY 2011

38th Annual Review of progress in Quantitative NDEJuly 17 to 22, 2011 ; Burlington, VT, USA

http://www.qndeprograms.org/2011/Conference2011.html

28


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“WCAE-2011”World Conference on Acoustic Emission–2011 Beijing (WCAE-2011) is organized by the Chinese Society for Non-destructive Testing (ChSNDT) and undertaken by Technical Committee on Acoustic Emission of ChSNDT (TCAE).

Conference Date August 24 to 26, 2011

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AE signal detection and processing AE behavior of materials AE in pressure equipment AE in structures AE in civil engineering and geology AE in transportation engineering AE in condition monitoring and diagnosis for mechanics AE in medical science AE

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29


NDENDENDENDENDEP A T E N T S

We hope that the inaugural section on NDE Patents, which featuredin the December 2010 issue of this journal, has triggered your thoughtsand has provided enough motivation to consider patenting your ideas.We continue this section with a few more facts on patents and alisting of a few selected NDE patents. Please send your feedback,comments and suggestions on this section [email protected]

Compiled byDr. M.T. ShyamsunderGE Global Research,Bangalore

Assignee: Rolls-Royce PLC(London, GB)

Abstract : An apparatus forultrasonically inspecting acomponent comprises a firstultrasonic transducer for transmittingan ultrasonic signal into a componenthaving rotational symmetry and asecond ultrasonic transducer fordetecting the reflected, ortransmitted, ultrasonic signal. Amotor and a turntable producerelative rotation between therotationally symmetrical componentand the first and second transducers.Motors, a carriage and tracks on aframe provide relative radial motionbetween the rotationally symmetricalcomponent and the first and secondtransducers to scan the whole of asurface of the rotationallysymmetrical component. Anultrasonic signal analyzer analysesthe detected ultrasonic signal bymonitoring for ultrasonic signalshaving an amplitude above apredetermined amplitude and nothaving rotational symmetry and adisplay provides an indication thatany detected ultrasonic signals abovethe predetermined amplitude and nothaving rotational symmetry is apotential flaw in the component.

UNITED STATES PATENT7,647,829

Steam generator nondestructiveexamination method

Inventors: Junker Warren R.,Lareau John P.

incentives encourage innovation,which assures that the quality ofhuman life is continuouslyenhanced. Patented inventions have,in fact, pervaded every aspect ofhuman life, from electric lighting(patents held by Edison and Swan)and plastic (patents held byBaekeland), to ballpoint pens(patents held by Biro) andmicroprocessors (patents held byIntel, for example). All patent ownersare obliged, in return for patentprotection, to publicly discloseinformation on their invention inorder to enrich the total body oftechnical knowledge in the world.Such an ever-increasing body ofpublic knowledge promotes furthercreativity and innovation in others.In this way, patents provide not onlyprotection for the owner but valuableinformation and inspiration forfuture generations of researchersand inventors [Source : http://www.wipo.int]

Listed below are a few selectedpatents in the area of UltrasonicTesting, which were issued byUSPTO in 2010. If any of the patentsare of interest to you, a completecopy of the patent including claimsand drawings may be accessed athttp://ep.espacenet.com/

UNITED STATES PATENT7,650,790Method of inspecting a componentand an apparatus for inspecting acomponent

Inventors: Wright David C

In this issue, we will take ourdiscussion forward on Patents andthe different aspects and elements ofit with a few more points ofrelevance.

A patent provides protection for theinvention to the owner of the patent.The protection is granted for alimited period, generally 20 years.Patent protection means that theinvention cannot be commerciallymade, used, distributed or soldwithout the patent owner’s consent.These patent rights are usuallyenforced in a court, which, in mostsystems, holds the authority to stoppatent infringement. Conversely, acourt can also declare a patentinvalid upon a successful challengeby a third party. A patent owner hasthe right to decide who may - ormay not - use the patented inventionfor the period in which the inventionis protected. The patent owner maygive permission to, or license, otherparties to use the invention onmutually agreed terms. The ownermay also sell the right to theinvention to someone else, who willthen become the new owner of thepatent. Once a patent expires, theprotection ends, and an inventionenters the public domain, that is,the owner no longer holds exclusiverights to the invention, whichbecomes available to commercialexploitation by others. Patentsprovide incentives to individuals byoffering them recognition for theircreativity and material reward fortheir marketable inventions. These

30


Products & Patents

flow path; and a third flow path. Theinner cylinder is inserted to an outercylinder of spot welding gun andholds the ultrasonic sensor. Thethrough hole is provided on the innercylinder. The partitioning cylindersurrounds the through hole and isinserted into a gap between theultrasonic sensor and the outercylinder. The first flow path isformed between the inner cylinderand the partitioning cylinder bypassing the through hole from aninner portion of the inner cylinder.The second flow path is formed atthe gun chip to be circulated arounda front end of the partitioningcylinder. The third flow path isformed between the outer cylinderand the partitioning cylinder. Acooling agent flows in an order ofthe first flow path, the second flowpath and the third flow path.

UNITED STUNITED STUNITED STUNITED STUNITED STAAAAATES PATES PATES PATES PATES PATENTTENTTENTTENTTENT7,849,7487,849,7487,849,7487,849,7487,849,748

Method of and an apparatus for insitu ultrasonic rail inspection of arailroad rail

Inventors: Havira Robert Mark

Assignee: Sperry Rail, Inc.(Danbury, CT, USA)

Abstract : An ultrasonic railroad railinspection system, apparatus andmethod for in situ rail inspectionincluding a wheel assemblycontaining a fluid-filled tire and anultrasonic transducer mounted withinthe wheel assembly. The transduceris supported in the tire such that theultrasonic beam generated by thetransducer has a beam axis thatintersects a head of a railroad rail ata position offset from thelongitudinal median plane of the railto the side of the head penetrated bythe ultrasonic beam. The ultrasonicbeam is reflected by flaws in the railin the form of echoes. The echoesreturn to the transducer identifyingthe location of flaws.

processing the sound waveinformation.


Ultrasonic inspection apparatus,system, and method

Inventors: Kennedy James C.,Little Mark L., Uyehara Clyde T.

Assignee: The Boeing Company(Chicago, IL, USA)

Abstract : Improved apparatus,systems, and methods for inspectinga structure are provided that use apedestal robot mounted on a railsystem, a probe extension coupler,and an inspection probe capable ofperforming pulse echo ultrasonicinspection. A probe may also includesled appendages and an axial brakingsystem to inspect over holes and offedges. A probe may also include anultrasonic pulse echo transducerarray for high rate inspection; thetransducer array may be mounted ina bubbler shoe for individuallycoupling each of the transducers inthe array. A rail system may alsoinclude an optical encoder forproviding location information forthe robot and axial braking system.A probe extension coupler pressesthe inspection probe against thestructure for adjusting to changes insurface contours.


Spot welding inspecting apparatus

Inventors: Shibata Kaoru,Shigematsu Noriaki, IgaueMitsutaka, Kurimoto Noriko

Assignee: Honda Motor Co.,Ltd. (Tokyo, Japan)

Abstract : A spot welding inspectingapparatus is provided with: a gunchip; a signal transmitting part; anultrasonic sensor; an inner cylinder;a through hole; a partitioningcylinder; a first flow path; a second

Assignee: W e s t i n g h o u s eElectric Co. LLC (CranberryTownship, PA, USA)

Abstract : A method of examining asteam generator heat exchange tubefrom the outside surface employingultrasonic nondestructive inspectiontechniques. An ultrasonic transducercontacts the outside surface of thetube and transmits a pseudo helicalLamb wave into the wall of the tubechosen to have a mode that does notsignificantly interact with water inthe tube. The reflected waves arethen analyzed for changes in modesto identify defects in the wall of thetube.


Apparatus and method fornondestructive inspection of parts

Inventors: Fetzer Barry A,Walters William O., Bui Hien T.


Abstract : A method of inspecting aradius area of composite parts withan ultrasonic inspection system, thesystem includes at least oneultrasonic probe, an upper slidingsurface, a lower sliding surface, anadjustable guide rail, and anadjustable encoder wheel rotatablecoupled to a rotary encoder, isprovided. The method includesgenerating a high frequency soundwave using the probe including aradius of curvature extending froma center point, the sound wavetravels partially through the part,adjusting the guide rail to align thecenter point of the probe with acenter axis of a part corner portion,sliding the part through theinspection system to inspect thecorner portion using the sound waveby rotating the wheel and rotaryencoder such that the accuratedistance of the part is recorded,adjusting the wheel to avoid anyapertures defined within the part, and

31


excite narrow bandwidth Lambwaves. The dominant feature in theacoustic spectrum is a sharpresonance peak that occurs at theminimum frequency of the first-ordersymmetric Lamb mode, where thegroup velocity of the Lamb wavegoes to zero while the phase velocityremains finite. Experimental resultswith the laser source and receiveron epicenter demonstrate that thezero group velocity resonancegenerated with a low powermodulated excitation source can bedetected using an optical probe suchas a Michelson interferometercoupled to a lock-in amplifier. Thisresonance peak is sensitive to thethickness and mechanical propertiesof plates and may be suitable, forexample, for the measurement andmapping of nanoscale thicknessvariations.

UNITED STATES PATENT7,783,433Automated defect detection ofcorrosion or cracks using SAFTprocessed Lamb wave images

Inventors: Gordon Grant A.,Hedl, Radek

Assignee: Honeywell InternationalInc. (Morristown, NJ, USA)

Abstract : A system, method andcomputer program product isprovided for automated defectdetection of corrosion or cracksusing synthetic aperture focusingtechnique (SAFT) processed Lambwave images. The method comprisesprocessing the first image using asynthetic aperture focusing technique(SAFT) to enhance a resolution anda signal to noise ratio of a firstextracted ultrasonic image, applyinga systemic background noisesuppression algorithm to the firstextracted ultrasonic image to rendera second extracted ultrasonic imagehaving reduced noise, and applyinga deconvolution linear filteringprocess to the second extractedultrasonic image to render a thirdextracted ultrasonic image.

surface profile using either amechanical stylus, laser, or ultrasonictechnique. Once an accurate surfaceprofile of the component’s surfacehas been obtained, data processingparameters are calculated forprocessing the ultrasonic signalsreflected from the interior of thecomponent that eliminate beamdistortion effects and reflector mis-location that would otherwise occurdue to the uneven surfaces.

UNITED STATES PATENT7,817,843Manufacturing process or in servicedefects acoustic imaging usingsensor array

Inventors: Senibi Simon D,Banks David L, Carrell Chris K,Curry Mark A


Abstract : A mobile platform isprovided which has at least onecomponent having an array ofdistributed piezoelectric transmittersand an associated array of distributedreceivers. The receivers areconfigured to receive ultrasonictransmissions from the transmitters.Data from the receivers is stored inmemory and processed through analgebraic reconstruction tomographyalgorithm which forms an image ofthe defect within the component. Analgorithm is used to determine theposition and size of the defect.

UNITED STATES PATENT7,798,000Non-destructive imaging,characterization or measurementof thin items using laser-generatedlamb waves

Inventors: Murray Todd W.,Prada Claire, Balogun Oluwaseyi

Assignee: Trustees of BostonUniversity (Boston, MA, USA)

Abstract : A laser-based ultrasonictechnique for the inspection of thinplates and membranes employs anamplitude-modulated laser source to

UNITED STATES PATENT7,841,237Ultrasonic testing apparatus forturbine forks and method thereof

Inventors: Suzuki Yutaka, KoikeMasahiro, Matsui Tetsuya,Kodaira Kojirou, Isaka Katsumi,Odakura Mitsuru, Tayama Kenji,Suzuki Kazuhiro, KumasakaKenji, Adachi Yuuji

Assignee: Hitachi, Ltd. (Tokyo,Japan) Hitachi Engineering &Services Co., Ltd. (Ibaraki, Japan)

Abstract : An ultrasonic testingapparatus for a turbine fork of aturbine blade joined to a turbine disc,comprising: an ultrasonic testingsensor; a sensor mounting apparatusfor mounting the ultrasonic testingsensor on a flat portion on a sidesurface of the turbine fork with theturbine blade joined to the turbinedisc; and an ultrasonic testingapparatus for inspecting internal andexternal surfaces of the turbine forkby using reflected waves, which isreceived by the ultrasonic testingsensor, from the internal surface ofthe turbine fork.

UNITED STATES PATENT7,823,454Ultrasonic inspection method

Inventors: MacLauchlan DanielT., Cox Bradley E.

Assignee: Babcock & WilcoxTechnical Services Group, Inc.(Lynchburg, VA, USA)

Abstract : A method forultrasonically inspecting componentswith wavy or uneven surfaces. Amulti-element array ultrasonictransducer is operated with asubstantial fluid layer, such as water,between the array transducer and thecomponent surface. This fluid layermay be maintained by immersing thecomponent in liquid or by using acaptive couplant column between theprobe and the component surface.The component is scanned,measuring the two dimensional

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42 Technical Paper

Journal of Non destructive Testing & Evaluation Vol. 9, Issue 4 March 2011

Fatigue Crack Growth Monitoring in Ti-6Al-4V AlloyUsing Acoustic Emission Technique and Digital Image

Correlation

Shivanand Bhavikatti, M R Bhat and CRL MurthyDepartment of Aerospace Engineering, Indian Institute of Science, Bangalore, INDIA

E-mail : [email protected]

ABSTRACT

Crack growth due to fatigue loading can be monitored using the accurate measurement of surface displacement and hence strainsduring deformation using Digital image correlation (DIC). While other techniques require point-by-point scanning over the areato be tested for the object, a whole field strain measurement can be made in one go both inside as also on the surface of thespecimens by DIC. Thus, DIC could provide less expensive and fast testing technique for crack propagation. DIC works bymeasuring stain by interfering a reference image with images taken at different loads from the surface of the structure. Throughthe study presented in this paper an attempt is made to establish correlation between Acoustic Emission Data and strain measuredby DIC for detecting crack initiation and monitoring its propagation for prediction of failure of a structural component underfatigue loading. Experiments have been carried out on a set of Ti-6Al-4V alloy specimens subjected to constant amplitude fatigueloading with continuous AE monitoring. The results obtained show that DIC can be a reliable off-line tool to validate AE datafor establishment of the technique. Thus, the objective of experiments has been to identify and validate genuine AE signals dueto fatigue damage and characterize them to identify progressive stages leading to the final failure.

1. INTRODUCTION

Fatigue tests typically require long testing times. This isdue to periodic interruption of the fatigue test to manuallymeasure crack lengths which can be avoided by usingDIC where in the measurements are made withoutinterrupting the test. Recently several researchers reportedthe use of DIC for transient fracture [1]. The use of high-speed and high resolution cameras, thus, enables newpossibilities for DIC testing. The idea behind the methodis to measure the displacement of the material under testby tracking the deformation through painted spots appliedto the component’s surface and obtain the speckle patternsfrom digital images acquired during loading.

Over the past few decades acoustic emission (AE)monitoring has been explored as an effective non-destructive technique for the detection, location andmonitoring of active defects and dynamic processes in avariety of structures including full scale tests of airframes,petro chemical components and civil structures. Thismethod has enormous potential as a tool for structuralintegrity evaluation, extraction of useful information fromcomplex data which include various extraneous noise is areal challenge [2,3]. AE technique is based upon thedetection of elastic waves generated when a materialundergoes plastic deformation and/or cracking duringwhich rapid release of energy from a localized sourcewithin a stressed material occurs[4,5]. These transientelastic waves can be detected by highly sensitive piezo-electric sensors. While the sources of interest of acousticemission are defect related processes such as crackpropagation and plastic deformation of material, background

noises that normally exist in laboratory environment andfield conditions pose a major problem for extraction oftrue AE activity. AET has very attractive advantages suchas the capability to not only detect active microscopic andmacroscopic failure mechanisms but also to obtain thelocation of these energy releasing sources in a largerstructural components without scanning the entirecomponent surface[6]. These are the features which stilllure the structural engineers to try the technique to studythe complex fatigue and fracture phenomena in criticalstructural components in different engineering fields. Thus,this attempt is to utilize the AET as an on-line monitoringtool to study the fatigue crack initiation and propagationin Titanium alloy extensively used in aerospace structuralcomponents.

2. EXPERIMENTS

Fatigue tests were carried out on Ti-6Al-4V alloy choosingthree point bend as test configuration; geometricaldimensions of specimen are shown in Fig. 1. Specimenpreparation includes scribing of graduated scale on thesurface to facilitate crack length measurements inincrements of 1mm from notch to 50% of the depth ofcrack propagation in the specimen. A high speed camerawith 12 megapixel is used to take the snaps for DIC.

Fatigue tests were carried out using INSTRON-1341configured with ± 100 KN capacity, ± 50 mm stroke,computer controlled servo hydraulic dynamic testingmachine. Fatigue test parameters were also chosen basedon the preliminary tests carried out in the laboratory, loadingfrequency of 18 Hz, amplitude range of 7kN-1.4kN with

43Technical Paper

Vol. 9, Issue 4 March 2011 Journal of Non destructive Testing & Evaluation

stress ratio of 0.2 is maintained for all the samples[7]. A10 X magnification lens was used to trace the crackgrowth to the subsequent divisions. Acoustic emissiondata from all the test specimens was continuously acquiredand recorded using multi-channel acoustic emissionmonitoring system with sensors, associated preamplifiersand accessories. Two peak resonant type acoustic emissionsensors with highest sensitivity around 300kHz were usedin the linear location mode for detection for AE events dueto crack initiation and propagation in the specimen. Thesensors were bonded to the specimen surface usingadhesive tape with high vacuum silicon grease as thecouplant interface between the sensor and the specimensurface. Preamplifiers with 40 dB fixed gain and a bandpass filter in the range of 200- 400 KHz were used alongwith the AE sensors. Acoustic emission data measuredand recorded includes hits (emission detected by a singlesensor), events (emissions detected and located by twosensors), energy, time of the event, rise time, parameter(load), duration and amplitude throughout the experiment.Through a set of preliminary tests, threshold of 55dB wasfound to be optimum under laboratory test environment.AE sensors have been bonded on the specimen to locatecrack initiation and propagation. Notched sample ispreferred as it is obvious that the crack initiation has totake place from the high stressed zone at the notch tip.The emphasis has been on AE signal generated from thisregion. Non-metallic liners with a combination of GlassFiber Reinforced Plastic and Teflon film were used ascontact interfaces in between loading points and thespecimen surface to avoid noise generated due to frictionbeing picked by the sensors. The AE monitoring systemwas calibrated for linear location of AE source by breakinga 2H, 0.5-mm-diameter pencil lead at each side of thecenter notch. The method of using a pencil lead break tocalibrate AE transducer and system sensitivities is detailedin ASTM E 647–05 [8], Standard Guide for Determiningthe Reproducibility of Acoustic Emission Sensor Response.Breaking pencil lead at tip of the notch generates pulsesignal that is similar to AE signal generated during crackgrowth. AE monitoring system records signal arrival time,parameters and calculate the difference of arrival time Δt,between the two sensors. Obtained Δt value and other

characteristics of signal are later used as inputs to thesystem which establishes location of active AE source andits characteristics.

3. RESULTS AND DISCUSSION

Figure 2(a) shows the overall distribution of the AE activityrecorded during the fatigue tests. It is clearly seen inFig2(a) that majority of AE events were generated in thenotched region. Cumulative AE activity in this region withreference to number of applied fatigue cycles is presentedin Fig. 2(b) and the clear change in slope correspondingto the initiation of crack at the notch tip can be observed.This is verified with optical aid. Significant rise in AEactivity during crack initiation is observed in all the samplestested. Eventually once crack is initiated, crack propagationenters stable crack growth stage, here AE activity exhibitsreduced emission rate. Loading was stopped when crackpropagated 50% of the depth. AE data at crack initiationand at crack propagation for each specimen was analyzedand the AE profile for crack initiation phase wasdiscriminated from the complete AE data profile in theplay back mode. This was done primarily on the basis ofthe cumulative count plot against the time scale (indirectlyreflecting the load cycles by multiplying with thecorresponding load cycle frequency).

Fig. 1 : Schematic Three point bend Ti-6Al-4V Specimen,dimensions in mm

Fig. 2 : Distribution of AE (a) Events Vs location (b) CumulativeCounts Vs Time

Time domain parameter analysis of AE Signalsin correlation to fatigue process

44 Technical Paper


Figure 2(b) shows Cumulative counts vs Time, from thisgraph it can be observed that crack was initiated verymuch prior to visual observation. Crack initiation wasobserved visually at around 1300 sec. Considering time,crack was actually initiated at around 300 sec to 1100sec. So it is necessary to find out at which point crackhas started. While the detection of crack initiation andidentification of stable crack growth was possible throughsimple approach of monitoring overall AE activity generatedwith reference to number of fatigue load cycles applied.Further signal analysis revealed advanced information interms of characteristic signatures of AE in these stages.It is clearly evident from Fig. 2(b) that crack initiated atthe centre of notch along the width is well in advancecompared to initiation observed on surface, which can besubstantially explained referring to Fig. 3(a) and Fig. 3(b).

Experiments were conducted using identical set of samplesto verify crack observed on surface of the specimenapplying fatigue load. Fig. 3(a) shows truncated specimenin which crack initiation was observed and three pointsnamely a, b, and c are marked. Significance of a, b andc are as follows. As can be seen from Fig.3(b), crackfirst initiates at ‘a’ due to plain strain condition and extends

within the thickness until it reaches the surface at pointsb and c which can be observed from the width of thecrack at the points a, b and c.

Digital Image Correlation (DIC)

Digital image correlation (DIC), sometimes called electronicspeckle photography, digital image processing was usedto solve the crack identification problem. A DIC softwareVIC2D from Correlated Solutions[9] has been used forobtaining the strain change on the surface specimen throughspeckle interferometry. The camera was positionedapproximately 500 mm from the three point bend specimenin the loading position as shown in Fig. 4, perpendicularto facing the specimen. The camera was carefully focusedand Images have been obtained and analyzed using VIC2Dsoftware. By using this technique full field measurementsmade on the specimen can be analyzed. Images weretaken after every 150 cycles over the full test and the datathus recorded has been analyzed using VIC2D. Oncecalibrated, the DIC software is able to calculate thedisplacement field of a specimen at any point during loadingwith a corresponding image. A strain field is obtained bydifferentiation of the associated displacement field. The

Fig. 3 : (a) Fatigue Crack Initiation as observed on the Surface ofthe Specimen, (b) Distribution of AE Cumulative CountsVs Time before Crack propagation

Fig. 4 : Schematic of Digital Image correlation

displacement field is calculated by comparing the loadedand reference images. The amount of crack growthbetween any two intervals of 150 cycles loading pointswas determined by the shift between their associated strainfields in front of the crack tip by displacement vector.

Mathematically, this is accomplished by finding the regionin a deformed image that maximizes the normalized cross-correlation co-efficient with regard to a small subset ofthe images taken while no load was applied. By repeatingthis process for a large number of subsets, full-fielddeformation data can be obtained. The DIC method doesnot require the use of lasers and the specimen can beilluminated by means of a white-light source. However,the specimen surface must have a fairly random pattern,which can either be naturally occurring or applied to thespecimen before the test. Among the many methods for

45Technical Paper


painting in order to add an artificial speckle to the surfaceof the specimen to find displacement. A number of strainplotting tools are available in the VIC-2D software. Onewas a line-plotter, which plots the values of strain for aselected line on the base image for all of the deformedimages as shown in Fig. 7- Strain Vs No of Cycles. Herestrain are less than 300 micro strain before the crackstarts and once the crack starts it is of the order of 500micro strains or more. The plot shows sudden change instrain at about 30000 cycles, which means that the crackhas started at the surface of the specimen. Whereas fromFig. 2(b) one can see the sudden increase in cumulativecounts at same number of cycles from AE data. Thus wecan compare the data from AE counts with DIC strainvalues. Fig. 7 shows the axial strain (åyy) in the directionof loading along the crack-line for a series increasingcrack lengths. The strain profiles along the un-crackedline were high near the crack tip and decreased as functiona distance away from the perceived crack tip.

4. CONCLUSION

Acoustic Emission Technique results from experimentscarried out are used as an on-line monitoring tool to studyfatigue crack initiation and propagation. Along with this, asemi on-line DIC tool has been used to monitor the strainassociated with number of cycles on the surface of thespecimen. The main objective of the investigations carriedout and presented in this paper aim at developing AE asan online predictive tool at the very early stages of crackinitiation and growth in Ti6Al4V material. Consequentlycrack growth experiments have been carried on a set ofthree point bend specimens and AE data recorded andanalyzed. One most interesting aspect that has beenobserved is that while AE data could be recorded evenbefore the crack appears on the surface, proof of crackinitiation and growth show confirmation through acomplementary method, which can register and trace thecrack growth while the phenomenon had been occurringwithin the thickness of the specimen. Thus, surface strainsmeasured all though the fatigue crack growth experimentsconfirm that AE data obtained before the crack appears onthe surface is due to crack growth within the thicknessof the specimen.

pattern application are self-adhesive, pre-printed patterns,stamps and application of paint speckles with air-brushes,spray cans or brushes.

Using the software, first a reference image, called a baseimage with the unloaded specimen was selected. Usingthe software tool, a quadrilateral area of interest was chosenon the specimen in order to reduce computation time anddefine the region to be analyzed. Finally, the rest of imagesof the specimen over the entire loading sequence, calledthe deformed images, were selected for comparison withthe base image for calculation of each of their respectivestrain fields which can be seen in Fig. 5(a) near the cracktip. and Fig. 5(b) the enlarged view near the crack Tip.Fig. 6 shows the strain in the specimen after 10000,20000, 30000 and 40000 cycles, as indicated (a), (b), (c),(d) respectively and gradual increase in the strain at intervalof 10000 cycles can be observed. i.e. the plastic zoneafter 10000 cycles is almost nil, and after 40000 cyclesit’s about 1mm along the loading direction. As we areinterested in plastic zone ahead of the crack tip which canbe precisely measured with DIC Technique. With this Fig.6 (d) clearly shows a high strain in at the notch comparedto other images and it has been observed manually thecrack has initiated on the surface. From this it is evidentthat crack tip strains increased after some number ofcycles leading to crack initiation.

The DIC tools, such as Correli-Q4 [10,11,12] that areused here, are more effective when the images are madeof random patterns. At the macroscopic level, one can use

(a) (b)

Fig. 5 : DIC (a) Strain in specimen at crack tip (b) enlarged viewof crack Tip

(a) (b) (c) (d)

Fig. 6 : Estimated x-direction strain after (a) 10000, (b) 20000,(c) 30000 and (d) 40000 cycles at the region near to cracktip

Fig. 7 : Strin vs. No of Cycles using DIC

46 Technical Paper


REFERENCES

1. M.S. Kirugulige, H. Tippur and T. Denney, Measurement oftransient deformations using digital image correlation method andhigh-speed photography: application to dynamic fracture. ApplOpt, 46(22) (2007) 5083–96.

2. Carle. Hartbower, et al , Acoustic emission from low-cycle high-stress-intensity fatigue, Engineering Fracture Mechanics 5 (1973)pp. 765-789.

3. J.R. Kennedy, Acoustic emission during deformation of Ti-6Al-4V, Scripta Metallurgica, 16 (1982) 525 – 530.

4. D.H. Kohn and P. Ducheyne, Sources of acoustic emissionduring fatigue of Ti-6Al-4V: Effect of micro structure, Journalof material science, 27 (1992), 1633- 1641.

5. D.H. Kohn and P. Ducheyne, Acoustic emission during fatigueof Ti-6Al-4V: Incipient fatigue crack detection limits andgeneralized data analysis methodology, Journal of material science,27 (1992) 3133-3142.

6. T.M. Morton, R.M. Harrington and J.G. Bjeletich, Acousticemissions of fatigue crack growth, Engineering Fracturemechanics, 5 (1973) 691-697.

7. Avraham berkovits and Daining fang, study of fatigue crackcharacteristics by acoustic emission, Engineering fracturemechanics, 51(3) ( 1995) 401-416,

8. Standard Test Method for Measurement of Fatigue Crack GrowthRates, ASTM standard Designation: E 647 – 05

9. Correlated Solutions- www.correlatedsolutions.com

10. Marion Risbet et al., Digital Image Correlation technique:application to early fatigue damage detection in stainless steel,Procedia Engineering, 2 (2010) 2219–2227

11. G. Besnard, et al. Finite-element, displacement fields analysisfrom digital images : application to Portevin-Le Châtelier bands.Expl Mechanics, 46(6) 789–804, 2006.

12. SteveVanlanduit et al, A digital image correlation method forfatigue test experiments, Optics and Lasers in Engineering, 47(2009) 371–378

47Technical Paper


Development of an Acoustic Emission ConditionMonitoring system for use in IC Engines.

Sreedhar P, JanardhanPadiyar M, R Maharajan and Krishnan BalasubramaniamCentre for Nondestructive Evaluation and Department of Mechanical Engineering,

Indian Institute of Technology Madras, Chennai, India 600036.

ABSTRACT

Most failures occurring in an IC Engine will have a characteristic indication that can serve as a warning. Effectively identifyingthese warnings can lead to identification of faults in early stages and hence minimize the damage. The major challenge lies indetecting such faults in their early stages of occurrence in a nonintrusive way. This paper tries to show the development ofan Acoustic Emission (AE) Test system for condition monitoring of critical IC Engine parts. The objective of the work is todevelop an efficient and cost effective acoustic emission system with custom signal conditioning unit that can continuouslymonitor ‘online’ the AE generated during the piston movement with no modification to the engine. Furthermore it is proposedto conduct various studies for evaluating the performance of the sensor developed for this purpose.

1. INTRODUCTION

Predictive maintenance is highly economical and efficientin cases where machinery are concerned. The monitoringof the engines for early detection of failures and takingappropriate action can make a considerable difference interms of cost incurred as well as instil confidence in thecustomers. The failures that occur commonly in an enginegive a characteristic indication before transforming intonon-repairable faults. The major challenge lies in detectingsuch faults in the early stages of occurrence in anonintrusive way. Currently techniques like vibrationmonitoring, strain monitoring, oil debris analysis etc arebeing used in industries. Studies over the past few yearshave shown Acoustic Emission to be a very dependabletool for condition monitoring of Engines.

Acoustic emission (AE) is the propagation of transientelastic waves that are generated within or on the surfaceof a material by fundamental processes that define frictionand wear such as deformation and micro fracture. AEToffers the advantage of earlier failure detection due itsinherent higher sensitivity as compared to the lowfrequency vibration signals. (1)(2).

This paper explains in detail the development of an efficientand cost effective acoustic emission system with customsignal conditioning unit which can be used for thecontinuous online monitoring of the AE generated in theengine without any modification to its basic construction.

2. ACOUSTIC EMISSION SOURCES IN ANENGINE

Any kind of dynamic machinery such as Engines hasplenty of moving parts which are excellent sources of AE.Since friction is a major source of AE, it can be utilizedas a very efficient tool in studying the condition of anymoving part non-intrusively. Of course, this is possible

only if there is a provision for the sensor to be mountedin a suitable position to pick up the emissions. The majorsources of AE in an IC Engine are:

i. Engine piston movement inside the cylinder

ii. Gear meshing

iii. Bearing movement

iv. Engine valves opening and closing events and so on.

Previously, work has been done to study the AE generatedfor Bearing Condition monitoring.(3) , Gear Box conditionmonitoring (4)and to detect exhaust valve leakage (5).Also, extensive work has already been carried out to studythe piston ring and cylinder liner condition using AE.

3. OBJECTIVE

At present, the AE sensors and measurement systemsavailable in market are costly and found not feasible forgrowing automobile industries. Studies conducted withKistler made Piezotron 8152B111 probes with 16 channel8 bit digitizer and external power supply system to probesshowed that the system was impractical for On-linemonitoring due to various reasons-

1) These sensors cannot be mounted without tamperingwith the engine.

2) These sensors are not designed to work efficiently atthe temperatures expected.

3) The system requires a 30-40V DC supply to powerthe Pre-amplifier.

4) Cost of each sensor is anywhere between 75,000 to100,000 INR.

These factors led to the need for development of a costeffective system that can be easily integrated with theengine in a non-intrusive way.

48 Technical Paper


4. ACOUSTIC EMISSION SYSTEMDEVELOPMENT

i) Transducer Development

Feasibility of employing various piezo-electric crystals wasstudied. These sensors were used to collect AE Data froma four stroke Petrol engine. Mainly two types of piezo-electric crystals were used in this study.

1. Piezo Wafer Active Sensor(PWAS) crystal(0.2 mmthick)

2. PZT (Lead Zirconium Titanate) Crystal(2 mm thick)

Initially, experiments were done with the crystal bondedto the engine fin of a four stroke petrol engine usingSuperglue. Figure 1 (a) and 1(b) respectively shows themounted PWAS and PZT sensors.

to act as a wave guide. And the casing here gives aprotective cover to the sensor. The cut section view ofthe solid model of the casing is provided in Fig.2 (a).

ii) Development of Signal Conditioning Unit (SCU)

An acoustic emission sensor is essentially a piezoelectricsensor that generates potential difference (voltage) acrossits terminals when subjected to mechanical stress. Theyare essentially capacitive in nature and have high impedance.Hence a signal conditioning circuit having a high inputimpedance preamplifier is needed [6, 7]. The receivedsignal is usually of the order of micro volts and containssignals over a wide band of frequencies .The purpose ofthe signal conditioning circuit is to amplify this lowamplitude signal and also limit the bandwidth of the signalscoming into the circuit. In order to successfully extractand analyze the signal output by the sensor, an Op Ampwith high input impedance has to be selected. In thiswork we have used a commercial off-shelf amplifier fordesigning the preamplifier circuit. Generally, two pre-amplifier topologies are used for piezoelectric sensors -charge amplifier and voltage amplifier. In the present worka voltage-feedback amplifier with two stage design usingvery low-noise, wideband variable gain operationalamplifiers has been used. The parameters for selection ofOp Amps for preamplifier design used in this work areshown in Table 1.

This study showed that the active elements were lesseffective in detecting signal transients when mounteddirectly on the engine. Moreover, uncovered soldered jointsof PWAS and PZT can pick up EMI (Electro MagneticInterference) from sparkplug cable, if they are near thesparkplug. With these problems in mind, a casing wasdesigned to enclose the sensor and thus effectively isolateit from the heat and EMI.

A typical Acoustic Emission sensing element has a wearplate and casing for it. In our case wear plate is designed

Fig. 1 : Sensor mounted on the engine (a) : PWAS; (b) : PZTcrystal

Fig. 2 : (a) Cut section view of the stainless steel casing (b) FinalAssembly

49Technical Paper


Table1 : Suggested Commercial IC Selection parameters forAcoustic Emission Preamplifier

Primary Limiting Secondary LimitingParameters Value parameters Value

High Input > 106 Ohms Input Bias < 10 μAImpedance Currents

High Gain >40 dB Slew rate > 300 V/μs(linear)

Low input <4n V/sqr(Hz) quiescent < 15 mAvoltage noise current

Low input 10p A/sqr(Hz)Current noise

Low Offset Voltage < 500 μV

The success of a precision preamplifier depends largelyon the choice of the input stage. In this preamplifier circuit,the first stage is optimized so as to achieve low noise, atthe same time give a very high gain of 100 times (40dB).For boosting the signal further, the second stage is alsodesigned for high linearity in the range of 10 times thushaving a combined gain of 60 dB which is sufficient forthe measurement by a digital to analog convertor. Whilereceiving low-level signals, it is necessary to limit thebandwidth of the incoming signals into the system . Thesimplest way to accomplish this is to place a high passRC filter at the non inverting terminal and low pass RCfilter at the output of the second stage. Capacitors areplaced in series after each stage to reduce the dc offsetcaused due to input offset voltage and bias current. Thepower supply pins to the preamplifier circuit are decoupledwith capacitors to reduce noise. A multilayer PCB boardis designed with power supply and ground planes.

Table 2 : Specification of Op Amp used

PZT Input Maximum Input Input LowDriver Impedance Gain Voltage Current OffsetIC noise Noise Voltage

nV/sqr pA/sqr(Mohms) (dB) (Hz) (Hz) (mVpp)

VCA810 1 40 3.5 2.1 0.35

OPA657 106 40 4.8 1.3 x10-6 2.5

Our application demands the use of a small portablepreamplifier for which a battery power supply have toused. The specifications of the Op Amp are given in

Table 2. Since Op Amp circuits requires ±5V a -5V a DC-DC converter (NDTD0505) which accepts 4.5V-7V asinput and delivers isolated 5V±3% with about 75% efficiency at 200mA. The preamplifier designed is having aestimated peak power consumption of approx120mACeramic capacitors are provided at input and output of theDC-DC converter to reduce ripple, switching noise in theoutput voltage and to reduce the surge current drawnfrom the input.

5. ACOUSTIC EMISSION TESTINGPROCEDURE

First, a trial was conducted using commercially availableAE Sensor. The Studies revealed that most of the mainemissions were in the 50-300 kHz band. So the crystalswith a narrow frequency band with resonant frequency at250 kHz were selected for this study. The transducerswere bonded to the fin of a 4 stroke petrol engine usingbonding agent. The data was acquired from the sensorusing National Instruments Data Acquisition system andsaved in a Laptop with the help of a custom developedLab VIEW program as GUI. Engine was run in the idlingcondition and data was collected.

Then the sensor with casing was mounted on the fin ofthe engine as shown in Fig.4.The Experimental setup usedfor this purpose is illustrated in Fig.5. The same experimentwas repeated for this configuration. Data was acquired ata sampling frequency of 1 MHz. The signal conditioning

Fig. 3 : Block diagram of Custom Pre-Amplifier Unit.

Fig. 4 : Sensor mounted on the engine

50 Technical Paper


Fig. 5 : Experimental Set-up

Fig. 6 : Signal from PWAS sensor using 60 dB gain

Fig. 7 : Frequency distribution for signal shown in Fig. 6

The FFT plotted for this signal indicated that most of theevents generated emissions of frequency band of 100-300 kHz. Figure 7 shows the frequency distribution forthe above signal.

The results obtained on using 80 dB amplifier for thesame set up indicated that it was not suitable for use withthe PWAS crystal. The frequency plot for this signalindicated a domination of low frequency noise in the signal.The signal and the corresponding frequency distributionplots can be found in Fig. 8(a) and 8(b) respectively.

The results from the test using PZT crystal showed thatthe signal had frequencies varying from 20-250 kHz. TheSignal and frequency distribution are shown in Fig. 9.

The results obtained from our sensor were compared witha commercially available KistlerPiezotron 8152B111 sensor.

unit gave 80 dB output, two channels, two stages (each40 dB) with a low pass filter of 1MHz. The unit waspowered by a 5 V supply from a portable battery.

Similar set of experiments were conducted with andwithout the signal conditioning unit to study its effect onthe signal.

6. EXPERIMENTAL RESULTS

The data acquired from the crystals were plotted using aLabVIEW program. Figure 6 shows the AE signal over aperiod of 0.1 seconds as obtained from the PWAStransducer without using the SCU. The signal was foundto conform with signals obtained in test on such enginesaccording to literature.

51Technical Paper


Fig. 9 : (a) Signal obtained from the PZT crystal using 60 dB gain (b) Frequency distribution for the signal shown in Fig. 9(a)

Fig. 8 : (a) Signal from PWAS crystal on using 80 dB gain; (b) Frequency distribution for signal shown in Fig.8(a)

52 Technical Paper


Fig. 10 shows the comparison of signals from the twosensors.

The experiments using the sensors with stainless steelcasing revealed a considerable reduction in noise. Thevarious events were clearly distinguishable in the signal.Figure 11 shows the raw data obtained while the enginewas running in its fourth gear.

CONCLUSION

Experimental tests conducted using two crystals PWASand PZT with 60dB gain showed similar signals. But thePZT being thicker is easy to handle and hence is preferredover thin PWAS. The stainless steel casing designed forthe crystal was found to reduce the EMI noise and alsoinsulate the crystal from the heat dissipated by the engine.The EMI noise was found to reduce from 5 V to 5 mVon using the casing. The sensor was also able to pick upthe various events with sensitivity comparable with acommercially available sensor. The major benefit of thesystem is the cost effectiveness and its feasibility for onroad testing due to its portability.

ACKNOWLEDGEMENTS

The Authors would like to thank TVS Motor CompanyLtd., Hosur. for providing the Engine and for theirwholehearted assistance during the data acquisition forthis experiment

REFERENCES

1) G.D. Neill, S. Benzi, J.D Gill, P.M. Sandford, E.R. Brown, J.A.Steel and R.L. Reuben. The relative merits of acoustic emissionand acceleration monitoring for detection of bearing faults.COMADEM, 1998.

2) J.D. Gill, R.L. Reuben, M. Scaife, E.R. Brown and J.A. Steel,Detection of diesel engine faults using acoustic emission,Proceedings of the Second International Conference on PlannedMaintenance, Reliability and Quality, University of Oxford,England, 2–3 April 1998.

3) C James Li, S Y Li , Acoustic Emission Analysis for BearingCondition Monitoring, Wear, 185 (1995) 67-74.

4) T.H. Loutas, G. Sotiriades, I. Kalaitzoglou and V. Kostopoulos,Condition monitoring of a single-stage gearbox with artificiallyinduced gear cracks utilizing on-line vibration and acousticemission measurements, Applied Acoustics, 70 (2009) 1148–1159.

5) T.L. Fog, E.R. Brown, H.S. Hansen, L.B. Madsen, P.S. Rensen,J.A. Steel, R.L. Reuben and P.S. Pedersen, Exhaust valve leakagedetection in large diesel engines, Condition Monitoring andDiagnostic Engineering Management, COMADAM, Clayton,Australia 1 (1998) 269–278.

6) A. Turoa and J. Salazar, Ultra-low noise front-end electronicsfor air-coupled ultrasonic non-destructive evaluation, NDT&EInternational, 36 (2003) 93–100.

7) Yanez Y, Garcia – Hernandez M J, Salazar J, Turo A, ChavezJ A, Designing amplifiers with very low output noise for highimpedance piezoelectric transducers. NDT&E International, 38,(2005) 491-496.

Fig. 10 : Comparison of the new sensor with commercial Kistler Sensor

Fig. 11 : The engine events with respect to crank angle The red lines indicate the typically expected positions of the events.

53Technical Paper


Signature Analysis of Failure Modes in Compositesusing Acoustic Emission

Ramesh kumar. M* and Madhava. M.R+

*Advanced composites division, National Aerospace Laboratories,

Bangalore – 560017+Retired, NAL, Bangalore – 560017

E-mail : [email protected]

ABSTRACT

During static structural qualification tests, it is always preferable to monitor the structural health in real time by non destructivemanner. In the event of any premature failure occurring during loading, it is preferred that this it is detected immediately atan early stage to prevent the catastrophic failures in service at an appropriate time. Acoustic Emission (AE) is the only proventechnique that is presently available for the detection and to monitor the growth of defect in real time. Acoustic Emission (AE)technique can provide in-situ information of such behavior as mentioned above. It is not only sufficient to obtain the informationabout the damage initiation and source location and also essential to identify more information about the nature of failures inthe composite structure as the failure modes in composites are more complex. This paper briefs about identification of signaturesof failure modes.

Keywords: Non-Destructive Evaluation, Acoustic Emission, Parameters, Composite Failure Modes, Matrix Failures, Delamination,Lap Shear, Debond

1. INTRODUCTION

In the recent aircraft development programmes, the useof composites has increased due to distinct advantagesthey offer over metals. Prior to the clearance forairworthiness, the components are subjected to staticstructural integrity and qualification tests to demonstrateand prove the competence to sustain various load cases asper design requirements. Failure modes in composites usedin aircraft structures can be more complex when comparedto conventional metal alloys [1,2,3]. This research workwas carried out to identify the characteristic signatures offailure modes in composites which enable us to predictthe nature of failure, if any during full scale componenttesting.

To satisfy the basic requirement of the composites forqualification and acceptance as a material of construction,the following tests are conducted. They are Tensile,Compression, Flexure and Lap shear [4,5] tests. Once thebasic material was qualified through such tests thecomponent or the structure can be fabricated out of itwherein component or structure [6] would be subjectedto Design Limit Load (DLL), Design Ultimate Load (DUL)to qualify for structural integrity. The first componentfabricated would be subjected to various tests.

Considering the advantages of the AE technique, it wasdecided to use an NDE tool for structural health monitoringduring static testing [7,8]. AE is increasingly used in theaviation industry [9,10] during fatigue loading for thedamage detection and growth in a structure for lifeextension studies [11,12,13]. In the initial phase of loading,failure mechanisms may be at a micro level that may

subsequently lead to catastrophic failure, which can bedetected using other Non-Destructive Testing (NDT)techniques. During the testing process the most commoncomposite failure modes [14,15,16] like matrix cracking(the failure due to shear load), delamination, debond, etc.,may initiate in the structure. These are the most expectedfailure modes in composites structural [17, 18]components. AE would be an ideal NDE technique toidentify such failure modes in composites, whereas othermethods such as thermography, radiography, ultrasonics,etc., fail to detect during structural testing. Researchershave shown that each type of defect exhibits different AEcharacteristics [19, 20, 21]. Many techniques such asVisual and Graphical methods have been applied on AEdata for pattern recognition.

The specimens that can simulate three different types offailure mechanisms in composites [22] were fabricatedusing Glass-Epoxy pre-pregs (GFRP) [23] and cured inan autoclave as per a given cure cycle. Test samples wereprepared according to the ASTM standards.

(1) For matrix failure (in-plane shear) mode – the pre-pregs were stacked in ± 45 deg.(cross-ply), of 2 mmthick. The samples were fabricated and tested as perASTM D 3518 standard.

(2) For delamination failure mode – DCB samples (DoubleCantilever Beam) of 1.2mm thick having an inclusionat the tip side in the middle of the thickness to initiatethe delamination upon loading. The samples werefabricated and tested as per ASTM D 5528 (mode 1)standard.

(3) For debond failure mode – samples of 2 mm thickwere bonded with an adhesive film (Redux 319) having

54 Technical Paper


lap length of 12.5 mm. ASTM D 1002-94 standard[24] was followed for the lap tests.

2. EXPERIMENTS

2.1 AE Instrumentation

The different types of AE specimens were tested usingUniversal Testing Machine (UTM) (Fig. 1) and acousticemission monitoring system, MISTRAS 2000 equipment(Fig. 2) was used to acquire the emission from the sampleswhile testing. GFRP samples were prepared (width of thespecimen is 25mm) according to the standard and endtabs are bonded (only for tensile load) to the specimen oneither side which will avoid slipping of the specimensfrom the grip in the UTM. Acquire acoustic emissionsignal at the time of testing through mechanical load, AEsensor was fixed on the specimen little below the centreof the specimen.

The MISTRAS hardware parameters and a signal-processing filter were selected as described below:

1. Test threshold = Fixed 45 dB.

2. Signal processing filter = 10 - 1200 kHz

3. Pre-amplifier gain = 20 dB

4. Sample rate = 4 MHz

5. Pre-trigger = 20 microseconds

6. Threshold = 2 Volts

7. Rate = 1000 microseconds

8. Energy Ref. gain = 20 dB

9. Peak definition time = 200 microseconds

10. Hit definition time = 600 microseconds

11. Hit lockout time = 800 microseconds

The threshold and gain values were selected based on thepencil lead break on the structure around the sensorlocations. Between two sensors the pencil lead breakresponse in terms of amplitude value should be above70% and the threshold value will be selected based on thenoise level in the structure. The pre-amplifier gain of 20dBmay be selected based on the distance between thecomponent and the AE system. The band pass filter wasselected to eliminate the unwanted noise during testing.

2.2 AE Sensors

R15D AE sensor is manufactured by Physical AcousticsCorporation (PAC). An R15D sensor was used and itsresonance frequency is 150 KHz. These sensors have anexternal preamplifier, making their size smaller than theother sensors. The R15D sensor and the externalpreamplifier are suitable for in-situ application.

2.3 Experimental Procedure

In (1) matrix failure mode, the specimen was tested in asimilar fashion of a tensile specimen test. AE signals wasacquired and stored in the MISTRAS system at the timeof mechanical test was conducted. (2) The second typeof test is the delamination in the Double Cantilever Beam(DCB) specimen. An inclusion was introduced in the midplane of the thickness, to initiate the delamination easilywhen the load was applied on the specimen. Metallic hingesare bonded on the top and bottom side of the specimens(Fig.3) to initiate the delamination and propagate the growthtowards the mid plane of the specimen. When thedelamination was initiated and the growth startedpropagating due to mechanical load, the acoustic emissionswere captured in these stages for further analysis. Thehinges help the specimen to take the different shapes likeL to V (Fig. 3). The AE sensor was bonded in the middleof the specimens for acquiring acoustic emission signal.(3) Lap shear test was conducted for debond / disbondstudies in the specimens prepared by bonding the adherentswith an adhesive material in the lap area. The length of thespecimen is 110mm, bonded using adhesive film Redux319 in the lap joint method. An acoustic emission sensorwas fixed on one side of the lap joint to acquire the AE

Fig. 1 : Universal Testing Machine

Fig. 2 : Acoustic Emission System

55Technical Paper


signal from the joint during mechanical loading. Fig. 4shows the failure of lap joint specimen.

These raw acoustic emission data were filtered andprocessed in the acoustic emission system. Post processingcapability is not available in MISTRAS system. In view ofthis problem a signal analysis tool was developed to getthe signatures of different types of failure modes incomposites.

3. SOFTWARE DEVELOPMENT

To carry out analysis on stored raw data, the raw datashould be converted to a form which was accessible inother platforms. The acoustic emission signals areconverted to ‘ASCII’ format, enable us to read the signalin the post processing software for signature analysis.

Algorithm was written to develop the software program inthe Labview environment for signal processing. In theinitial step the converted ‘ASCII’ data (acoustic emissiondata) was read by the program and displayed in the Labviewplatform (Fig. 5), the continuous signal (all hits) receivedduring the single test were display in the software using‘History’ command. This will enable to analyze and identifythe maximum amplitude and the corresponding hit numberand time.

The user friendly software enables the user to select therequired data and set/change the threshold value duringthe time of analysis. The noise levels (due the gripping orunwanted mechanical noises) were eliminated by fixing aproper threshold on the signal (hit). This threshold can beapplied to each hit (discrete waveform of the test) and thesignal above the threshold were extracted and displayed.

Fig. 3 : DCB Specimen in testing condition Fig. 4 : Tested Lap Shear Specimen

Fig. 5 : Post processing software developed for AE signal analysis showing all the hits (top) of a single specimen

56 Technical Paper


The spectral analysis of the extracted waveform was usedto find out the 6dB bandwidth (BW) of the particularwaveform. Also, other parameters like duration, count,rise time and peak amplitude were calculated and displayedwhich enable in arriving at the signature of the failuremodes. The above steps were repeated on each hit of thesame test and iterated to all the samples for three differenttypes of test conducted on this experimental work.


The acquired waveforms are further post processed usingthe Labview software for analysis of three different failuremodes. Each failure modes were analysed individually toarrive at the parameters towards the AE signatures offailure modes.

4.1 Matrix failure

All the individual test specimen data was displayed usingthe Labview post processing software for analysis oneach hit was carried out to identify the parameters likeduration, count, rise time, peak amplitude and bandwidth.Select the hit number in order and carry out post processingto identify the above parameters on each hit on the firsttest specimen. This Iteration has to be continued till thelast hit number of the first specimen. Each hit AE parametersare recorded and the average value of the hits for aparticular specimen was recorded in tabular form. Thenthe second specimen data was read by browsing the ‘File

Path’ in the Labview analysis software and the aboveiteration procedures to be followed. Similarly the sameprocedure had been followed for all the five testedspecimens. Table 1 gives the values of AE parameters ofthe matrix failure modes. The threshold voltage for thisanalysis was 1.0 mv. At the time of matrix failure initiationthe AE data had high amplitude of the order of 80 dB. Buttowards the end of the test the fibre and matrix wereslipping and the amplitude values are diminishing to verylow of 25dB.

Figure 6 shows the signal of matrix failure specimen,tent-2 of hit no. 49. The signal of matrix failure hadconsistent value of AE parameters like duration between30 to 40 μs, count range from 4 to 7 Nos., peak amplitudeis more than 85dB and Bandwidth (BW) varied between40 to 50 KHz.

Table 1 : Analysis of Matrix failure ±45° (In-plane shear)specimens

Specimen Duration Count Rise Time Peak Band-Name (μs) (Nos) (μs) Amplitude width

(dB) (KHz)

Tent-1 30 - 44 5 - 7 7 – 19 76 – 88 40 - 52

Tent-2 31 – 40 5 – 7 8 – 12 80 – 90 38 - 50

Tent-3 30 – 35 3 – 6 6 – 12 80 – 90 41 - 52

Tent-4 25 – 30 4 – 6 6 – 19 85 – 96 39 - 50

Tent-5 31 – 40 4 – 7 6 – 26 85 – 90 41 - 51

Fig. 6 : AE Signal of matrix failure mode

57Technical Paper


4.2 Delamination failure

Software analysis procedure should be followed as sameas mentioned above (Matrix Failure) for delamination failuremode analysis. Browse the ‘File path’ and select the folderof the delamination test data and pick the first hit foranalysis. The analysis procedure should be followed(mentioned above) to identify the AE parameters. Each hitwas iterated following the same procedure for all the testspecimens to arrive at the values of AE parameters fordelamination failure modes. The value of threshold voltagefor analysis was 2.0 mv. Table 2 shows the AE analysisvalues of the delamination test specimens, for failure modesof all the specimens. The signals of delamination (DCB)specimens signal endurance for longer duration wasnoticed.

Table 2: Analysis of delamination (DCB) specimens

Specimen Duration Count Rise Time Peak BandName (μs) (Nos) (μs) Amplitude width

(dB) (KHz)

Dcb-1 65-170 15-33 11-47 56-70 12-23

Dcb-2 75-200 15-35 24-62 60-71 10-24

Dcb-3 100-200 26-50 15-48 70-75 13-27

Dcb-4 120-215 18-42 25-57 60-70 12-26

Dcb-5 130-210 20-30 30-46 55-70 11-25

Figure 7 shows the signal of delamination specimen,dcbt-1 of hit no. 29. The delamination failure signal hadconsistent value of AE parameters, duration between 100to 200 μs, count range from 20 to 30 Nos., peak amplitudehad an average value of 65dB and BW varied between 12to 25 KHz.

4.3 Debond failure

Similar analysis procedure followed above had been usedfor the lap shear test specimens. Table 3 provides thevalues of AE parameters from the bonded test specimen,tested for debond failure modes. The threshold voltage forthese lap shear analysis was 2.0 mv.

Table 3 : Analysis of Lap shear specimens

Specimen Duration Count Rise Time Peak Band-Name (μs) (Nos) (μs) Amplitude width

(dB) (KHz)

Lap-1 38-50 6-11 6-12 70-80 25-34

Lap-2 40-47 5-12 5-15 70-83 25-37

Lap-3 40-55 8-12 8-25 70-80 26-39

Lap-4 35-50 8-15 5-12 68-83 27-35

Lap-5 35-55 7-15 5-10 70-83 29-36

Figure 8 shows the signal of debond failure (lap shear)specimen, lapt-2 of hit no. 52. The debond failure signal

Fig. 7 : AE Signal of delamination failure

58 Technical Paper


had consistent value of AE parameters showing countranges from 8 to 12 Nos., the rise time varied from 6 to12 μs and peak amplitude value < 80dB and BW variedbetween 27 to 35 KHz.

All five specimen test values were averaged to arrive atAE test parameters, helped to identify the signature offailure modes from the test results.

5. CONCLUSIONS

The AE signature of all the failure modes were summarisedas :

(I) For Matrix failure, the average values from the postprocessed AE signal parameters : duration range from30 – 40 μs, the count was 4 – 7 numbers, the risetime 6 – 12 μs, the peak amplitude varies from 80 –90 dB and the band width between 40 – 50 KHz.

(II) In Delamination failure, the average values from thetested specimens, the AE parameters were : durationrange between 100 – 200 μs, the count from 20 – 30numbers, the rise time between 15 – 40 μs, the peakamplitude was 60 – 70 dB and the band width liebetween 12 – 25 KHz.

(III) Debond failures, the signatures were arrived fromthe raw AE signals : the duration between 40 – 50 μs,the count numbers between 8 – 12, the rise timevaried from 6 – 15 μs, the peak amplitude was 70 –80 dB and the band width range from 27 – 35 KHz.The repeated AE parameter values of signatures wereobtained from the test results of the GFRP specimens.

These signatures were very much useful for the staticstructural analysis and to study the post test evaluationof structural health and integrity of the structure. Thismakes it an ideal tool for finding the AE Signatureparameters for inspection.

ACKNOWLEDGEMENT

Thanks are due to Mr. D. Karuppanan, Mr. S. SanjeevKumar, Mr. H.V. Ramachandara, Mr. M.C Devaiah Mr. V.Srinivasa, for the extensive support during the work. Weare also grateful to Mr. P. Senthil Kumar, Dr. G.M. Kamath,Mr. H.N. Sudheendra for many useful discussions.

REFERENCES

1. C.R. Ramirez-Jimenez, N. Papadakis, N. Reynolds, T.H Gan, P.Purnell, M. Pharaoh. Identification of failure modes in glass/polypropylene composites by means of the primary frequencycontent of the acoustic emission event, Composites Sc. & Tech.,64 (2004) 1819-1827

2. Yeun-Ho Yu, Jin-Ho Choi, Jin-Hew Kweon, Dong-Hyun Kim.A study on the failure detection of composite materials using anacoustic emission, Composite Structures, 75 (2006) 163-169

3. Rongsheng Geng. Modern acoustic emission technique and itsapplication in aviation industry, Ultrasonics, 44 (2006) 1025-1029

4. H.Suzuki, T.Kinjo, N. Saito, M. Takemoto, K.Ono. Integrityevaluation of glass-fibre composites with varied fibre/matrixinterfacial strength using acoustic emission, NDT&E International,33 (2000) 173-180

Fig. 8 : AE Signal of debond failure mode

59Technical Paper


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7. Joung-Man Park, Sang-II Lee, Oh-Yang Kwon, Heung-Soap Choi,Joon-Hyun Lee. Comparison of nondestructive micro failureevaluation of fibre-optic Bragg grating and acoustic emissionpiezoelectric sensors using fragmentation test, Composites Part-A, 34 (2003) 2003-216

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11. M. Bourchak, I. R Farrow, I.P Bond, C.W Rowland, F. Menan.Acoustic emission energy as a fatigue damage parameter forCFRP components, Int. Journal of Fatigue, 29 (2007) 457-470

12. T.H Loutas, V.Kostopoulos, C. Ramirez-Jimenez, M. Pharaoh.Damage evolution in center-holed glass/polyester compositesunder quasi-static loading using time/frequency analysis ofacoustic emission monitored waveforms, Composites Sc. andTechnology, 66 (2006) 1366-1375

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14. S.Minko, A.Karl, V. Senkovsky, T. Pomper, S. Cunis, R. Gehrke,G.V. Krosigk, U. Lode, I. Luzinov, A. Voronov, W. Wilke.Investigation of failure mechanisms in polymer composites bysimultaneous measurement of ultra-small-angle scattering andacoustic emission during the deformation. II. Evaluation of theinterface strength, J. Macromol. Science-Phy, (1999) 913-929

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16. S.Minko, A.Karl, V. Senkovsky, T. Pomper, S. Cunis, R. Gehrke,G.V. Krosigk, U. Lode, I. Luzinov, A. Voronov, W. Wilke.Investigation of failure mechanisms in polymer composites bysimultaneous measurement of ultra-small-angle scattering andacoustic emission during the deformation. I. Method, J. Macromol.Science-Phy, (1999) 901-912

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24. Annual Book of ASTM Standards, Section – 15, Vol. 15.03 &Section-3, Vol. 03.01

60 Technical Paper


An empirical approach for the burst prediction ofGFRP pressure bottles using acoustic emission

technique

R.Joselin1 , T.Chelladurai2, M.Enamuthu3, K.M. Usha4 and E.S. Vasudev5

1 Research scholar, JNTU Hyderabad, Hyderabad -500085, A.P., India.2 Principal, James College of Engineering and Technology, Nagercoil-629 852,Tamilnadu.

3 Deputy Director, CMSE, VSSC/ISRO, Thiruvananthapuram-695 013.4 Division Head, CCTD/CCQG/CMSE, VSSC/ISRO, Thiruvananthapuram-695 013.

5 Scientist/Engineer, CMSE, VSSC/ISRO, Thiruvananthapuram-695 013.

Email:[email protected]

ABSTRACT

Acoustic Emission (AE) is an upcoming NDT technique gaining ground in different fields as an on-line monitoring method fordetection, location and characterization of various kinds of active degradations. This method has also made an impact as a toolfor structural integrity evaluation and failure prediction. AE has been growing vigorously in recent times and has been used inwide range of applications in aerospace, nuclear and chemical engineering fields. AE technique is highly sensitive and can detectdegradations in FRP structures viz delamination, fibre crack, debonding, matrix crazing etc well before occurrence of anycatastrophic failure under dynamic service condition. In the present study, five identical GFRP hardware were taken up for thestudy and acoustic emission data is analyzed thoroughly and a lucid empirical relation is developed to predict their burstperformance. Moreover, in this approach, failure is significant even at 50 to 60 % of maximum expected operating pressure(MEOP) with a reasonable error margin. Till date there is no method spelt out in the open literature for burst pressure predictionof composite pressure vessels. This innovative methodology illustrates the structural behavior of GFRP pressure bottles in termsof AE parameters and its derivatives. In this approach AE data is acquired only upto 50% of the theoretical burst pressure andthen the bottles are pressurized to failure. An empirical relation was generated for the GFRP bottle which is subjected to cyclicproof pressure cum burst test on the basis of governing AE parameters viz, ring down counts, event duration, peak amplitudeand felicity ratio. This methodology can possibly predict in real time the burst pressure of similar hardware if extended to othermaterial systems.

Keywords: Acoustic emission, GFRP pressure bottles, structural integrity, empirical relation, AE parameters, prediction.

1. INTRODUCTION

Acoustic Emission Technique (AET) is widely used forboth materials research and structural integrity monitoringapplications because of its unique potential for detectionand location of dynamic defects under operating stresses.In the past two decades, AE has been mostly used fortesting pressure bottles undergoing proof/acceptance tests[1,2]. In aerospace composite structures, pressurisedsystems are made with low margins with their attendantlight weight construction [3]. With the rapid advancestaking place in this area, there is a strong need for anNDT technique which can indicate the degradation thattakes place during the course of the proof or acceptancetesting of pressurised systems. There are cases reportedin the literature that composite hardware that havesuccessfully undergone proof pressure tests did fail duringtheir actual test. In this respect, AE technique has assumeda unique role. More than evaluating the structural integrityof pressurised systems it has the capability to predict theburst pressure within certain limits. It is well known thatGFRP pressure bottles undergo degradation duringacceptance/proof pressure test in view of resincrazing,delamination,fibre fracture, fibre pullout anddebonding between the layers etc. Such degradations can

be indicated through major AE parameters and theirderivatives. A methodology is being developed in this paperto estimate the residual strength of GFRP pressure bottles.

2. GFRP HARDWARE DETAILS AND AEINSTRUMENTATION

AE studies have been performed on five numbers of similarGlass epoxy pressure bottles. In which, E-Glass fibresimpregnated with epoxy resin are wound over an innerliner made of polypropylene. The bottles are built up ofhoop layers and polar layers alternately placed in groups.Thedome openings are equal and are closed with flat plates orspecial closures, as the case may be, for the pressure testpurposes. The thickness of the composite wall is 5mm.The sensitiveness of AE sensors is verified and adjustedfrequently at the end of every cycle with the use of Hsu-Nielsen pentel pencil-break technique. The PAC-Disp 4 AEwork station is used to monitor in conjunction with AEsensors R15(150 KHz,resonant type)and matching pre-amplifiers 40 dB with high pass analog filter range 20 KHz-400 KHz. Radiography (X-ray) test is conducted on eachof the bottles to verify the uniformity in thickness ofcomposite walls. Initially the threshold 45dB is set duringthe starting in order to avoid the system collapse.

61Technical Paper


3. AE MONITORING DURING HYDROSTATICPRESSURE TEST

The emissions are captured with the use of four AEsensors.These AE sensors are mounted as per standardprocedure [ASTM,1986], connecting co-axial cables withAE system. The deformation of the bottle is identified byfixing single element 350Ω strain gauges (ranges 0-18000με) and their locations are shown in the Fig.1. Thepressure cycle is carried out upto 50% of their theoreticalburst pressure in a cyclic mode. The pressure is broughtdown to zero after every cycle. The pressure rate ismaintained at 20 bar/min throughout the test. As to GFRP-02 bottle test during pressurisation the hardware faileddue to adaptor failure. In order to avoid this nature offailure, the remaining four hardware were gently machined

steps upto 200 bar and the remaining hardware werepressurised upto 150 bar only. An air assisted hydraulicpump is used to pressurise upto 150 bars and for thehigher pressurisation a mechanical pump is used. Theincremental pressure was 25 bar in all cases.The first timeholds at various incremental pressures were for a minimumperiod of 1 min until the event rate declines. The maximumhold shall be for a period of 3 mins. In this paper, theemissions were studied only for repeat cycles. For everycycle, the AE parameters just before pressure hold aretaken into consideration for developing the empirical relationpredicting the burst pressure. In all cases, AE parameterswere studied for a maximum pressure of 125 bar exceptfor the first hardware. In the first hardware, cycling wasdone upto 175 bar.

5. EMPIRICAL RELATION

The empirical relation is nothing but a equation connectingthe dominant AE parameters with expected burst pressureand internal pressure at which the prediction is attempted.This relation is developed in the first hardware itself, afterthat, the same will be refined after every remaininghardware test. The general form of empirical equation isassumed as:

N-α x D-β x A-γ x Ra = F x P-b

Where, N = Ring down Counts

D = Event Duration in μs

A = Peak Amplitude in dB

R = Felicity Ratio

F = Tentative burst pressure in bars

P = The internal pressure (in bars) at whichprediction is attempted

α, β, γ, a, b are Empirical constants

6. AE PARAMETERS

In this analysis the major derived AE parameters chosenwere ring down counts, event duration, peak amplitudeand Felicity ratio(F.R). The pressure at which significantemissions start during first repeat cycle is considered as‘P1’. The maximum pressure reached during the previouscycle is say, ‘P2’. Thus F.R=P1/P2. F.R is arrived at fromthe AE response graphs as well as from the statistics ofthe first repeat cycle. The other parameters are chosenjust before the pressure hold that follows during the firstrepeat cycle. The solution of each hardware is found outby MAT LAB software. The unknown exponents arearrived at by substituting all the major AE parameters intothe empirical relations. In any hardware, the tentative burstpressure is arrived at by substituting the other hardware’sexponents. In respect of GFRP-02 bottle, initially theemissions were very low. Therefore, the equation is formedfrom 75 bar pressure cycle onwards. The authors alsoobserved that the machined hardware exhibit burst earlierthan the first hardware failure.

Fig. 1 : SG/AE instrumentation on GFRP pressure bottle

Fig. 2 : Experimential setup

at the cylindrical portion by 1 mm depth. The schematicview of experimental setup is shown in Fig.2. 6-Nos ofstrain gauges and three Nos linear potentiometers aremounted to find out the deformations and axial/diametricaldilations of the hardware. These data are acquired andanalyzed for further developments of this research.

4. PRESSURISATION AND PRESSUREHISTORY

Two sets of pressure schemes are used to pressurise 6-litre capacity,150 mm dia cylindrical GFRP pressure bottles-5 nos.Initialy the first hardware is pressurised in cyclic

62 Technical Paper



In the case of one of the hardware,say,GFRP-02, for thefirst repeat cycle at 75 bar, the values of derived AEparameters and pressure at which prediction was attemptedare substituted into their equations corresponding to 75,100, 125, 150 & 175 bars respectively. The solution initiallygave low burst values in comparison with the actual burstpressure of 299.5 bar. In the pressure 125 bar, it gavereasonable percentage of error, say, 2.67%. The chosenvalues are also verified with the sixth equation at 200 bar.In this case, it indicates the values of burst pressure withan error margin of -1.42%. Using these equations onecould find out the constants with the help of MAT labsoftware. This software displays the output for any mxnmatrix, where m=n. Similarly, for the other hardware theAE parameters are acquired from 25 bar internal pressureonwards at an incremental pressure rise of 25 bar. Themathematical procedure is same for all the hardware. Foreach of the pressure bottles the dominant AE parameterspreceding failure can be detected at around 75% of MEOP.From the acquired data, a set of multiple parameters canbe developed with a small error margin. The initialemissions are more for all the bottles except for theunmachined bottle. The prediction attempted in the GFRP-03 pressure bottle gave the percentage error from -6.11 to3.22% at 100 bar pressure cycle. Its exponents gave aprediction of -15.37 to 21.9% at 100 bar pressure cycle.The exponents of GFRP-01 and GFRP-05 pressure bottlesexhibit reasonably low error margins at -0.64 to 3.22%and -19.2 to 6.43% respectively at 75 bar cycle. GFRP-04 pressure bottle failed at very low pressure (125 bar)compared to all the remaining hardware. Substituting theGFRP-02 hardware exponents/constants gave a predictionfor this hardware with an error margin of 16.9% at 75 barcycle. This particular hardware failed during the 3 minshold period. E.V.K.Hill and T.J.Lewis [4] already foundthe characteristic of bad pressure vessel. The continuanceof AE activity during the pressure hold would indicate abad vessel creeping to failure and could cause huge errormargin. This methodology can be extended for other typesof hardware like Kevlar- epoxy, Carbon- epoxy etc. Theresults comparison of all the hardware is given in Tables1 to 5.

Table 1 : Prediction using GFRP -1 constants

Bottle Actual Predicted Percentage Prediction Remarksno. burst burst error attempted

pressure pressure pressure(bar) using (bar)

empiricalrelation

(bar)

GFRP-1 263.6 263.66 +0.02 100 machined

GFRP-2 299.5 307.51 +2.67 125 unmachined

GFRP-3 274 288.823 +3.22 100 machined

GFRP-4 125 173.99 +39.2 75 machined

GFRP-5 260 259.9833 -0.64 75 machined




empiricalrelation

(bar)

GFRP-1 263.6 243.584 -7.59 100 machined

GFRP-2 299.5 299.286 -0.07 125 unmachined

GFRP-3 274 257.268 -6.11 125 machined

GFRP-4 125 146.17 +16.9 75 machined

GFRP-5 260 243.287 -6.43 100 machined




empiricalrelation

(bar)

GFRP-1 263.6 319.72 +21.289 125 machined

GFRP-2 299.5 281.72 -5.937 100 unmachined

GFRP-3 274 274.23 +0.08 75 machined

GFRP-4 125 68.143 -45.486 100 machined

GFRP-5 260 220.04 -15.369 100 machined




empiricalrelation

(bar)

GFRP-1 263.6 217.492 -17.5 125 machined

GFRP-2 299.5 179.84 -39.9 125 unmachined

GFRP-3 274 198.037 -27.72 125 machined

GFRP-4 125 124.966 -0.03 50 machined

GFRP-5 260 214.98 -17.3 100 machined




empiricalrelation

(bar)

GFRP-1 263.6 280.539 +6.43 50 machined

GFRP-2 299.5 241.86 -19.2 50 unmachined

GFRP-3 274 279.976 +2.18 100 machined

GFRP-4 125 176.133 +40.9 125 machined

GFRP-5 260 259.958 -0.02 75 machined

63Technical Paper


to predict the burst strength and can send out warningsignals well ahead of failure.

ACKNOWLEDGMENTS

The authors would like to thank the Senior Scientists ofComposite Entity, VSSC, Thiruvananthapuram for thesuggestions and encouragements given.

REFERENCES

1. Schliessmann J A, Pressure Vessel Proof Test Variables and FlawGrowth, Journal of materials, JMLSA, 7(4) (1972) 465-469.

2. Dai Guang., Xu Yan Ting.,Wang Ya Li., Zhang Bao Qi and HanWan Xue., AE Monitoring and Data Analysis for Large SphericalTanks, NDT &E International, 26(6) (1993) 287-290.

3. Jessen,E.C., Spanheimer,H and De Herrera, A.J., Prediction ofComposite Pressure Vessel Performance by Application of the‘Kaiser Effect’ in Acoustic Emission, AET corporation, USA,(1974).

4. E.V.K. Hill and T.J Lewis, Acoustic Emission Monitoring of aFilament-Wound Composite Rocket Motor Case during HydroProof, Journal of Material Evaluation, 43 (1985) 861.

If one compares the performance of all the hardware itcan be identified that the failure of GFRP hardware ispreceded by high count rate, large number of long durationevents, high amplitude rate and a very low felicity ratio.The authors observed from the mathematical analysis thatthe predicted burst pressure error margin is high at lowerpressure and it is reasonable in the range 75 bar to 100bar.

8. CONCLUDING REMARKS

The authors have clearly verified that the prediction ofburst pressure is possible in the case of GFRP pressurebottles with a lucid empirical relation. The correlation ofall the five hardware is reasonably better with an acceptableerror margins at –0.64% to 2.18% and for the worst casethe percentage of error prediction is -19.2% to 16.9% ataround 75% of MEOP. The major AE parameters like ringdown counts, event duration, peak amplitude and felicityratio exhibited during first repeat cycle could substantiallyfacilitate accurate prediction of failure. This innovativeapproach can be extended to any other material systems

64 Technical Paper


What you eat, becomes your mind;/As is the food, so is your mind.By the purity food follows the purity of inner nature.

Ayurvedic texts.

When diet is wrong medicine is of no use;When diet is correct medicine is of no need.

Ayurvedic Proverb.

The lamp eats up the darkness and therefore it produces lamp black; in the sameway according to the nature of the diet – satva, rajas, or tamas- we produceresults.

Chanakya

These lines establish the connection between food and mind. As per me the food for mind is the thoughtsthat occur. All of us are clear that we are not our mind. Mind is flow of thoughts. We are like radio receivers.An assembly of inanimate objects when electricity (life energy) is given is ready to collect the waves. Whenit is tuned to a certain frequency the waves floating around in that frequency is collected. Controlling theradio is through the knobs and buttons. Controlling of the mind is through the five sensory organs.

Control is the main factor. Our senses can be controlled by ourselves. Collectively we can control little biggerthings (flow of a river by building a dam etc.), but much bigger things cannot be controlled even collectively(tsunami, floods etc). By controlling our senses we control our body functions, thereby pave way for a smoothlife. “Noyatra vazhve kuraivatra selvam”. Which in English means that “a life without disease is perfectwealth”.

By exercising the control over our senses we are able to set an example for others and are able to influenceothers surrounding us (example Mahatma Gandhi). Our circle of influence increases. Success is a measureof the circle of influence. Going back to the analogy of radio we can control the choice of frequency. Wehave the choice of choosing the frequency. Similarly we can choose the thoughts that reach us. Greatinventions have taken place in a flash because the inventor was tuned to that frequency. We are the mastersof our minds.

Quote “Five years ago, I had a beautiful experience which set me on road that has led to writing of thisbook. I was sitting by the ocean one late summer afternoon, watching the waves rolling in and feeling therhythm of my breathing, when I suddenly became aware of my whole environment as being engaged in agigantic cosmic dance.”

Fritjof Capra. (The Tao of Physics.)

There are several instances like this one. Then does it mean that there are no inventions but onlydiscoveries! There may be an existence of “Thought Field” similar to that of “Magnetic Field”.

Meditation is a method of focusing on to a particular frequency, thoughts. By sitting still and going intosilence we become the seer instead of the seen. It is an elimination process. Start from outward but goinward and you will learn the art of allowing it to happen

AYURVEDA and CHANAKYABy B. Ramprakash

PROBE

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