1
from the Chief Editor
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.
Dr. Krishnan Balasubramaniam Professor Centre for Non Destructive Evaluation IITMadras, Chennai balas@iitm.ac.in jndte.isnt@gmail.com
URL: http://www.cnde-iitm.net/balas Journal of Non Destructive Testing & Evaluation
vol 9 issue 4 March 2011
2
I S N T - National Governing Council Chapter - Chairman & Secretary President Shri K. Thambithurai President-Elect Shri P. Kalyanasundaram Vice-Presidents Shri V. Pari Swapan Chakraborty Shri D.J.Varde
Ahmedabad
Kota
Shri D.S. Kushwah, Chairman, NDT Services, 1st Floor, Motilal Estate, Bhairavnath Road, Maninagar, Ahmedabad 380 028. dskushwah@icenet.net Shri Rajeev Vaghmare, Hon. Secretary C/o Modsonic Instruments Mfg. Co. Pvt. Ltd. Plot No.33, Phase-III, GIDC Industrial Estate Naroda, Ahmedabad-382 330 modsonic@modsonic.com
Shri R.C. Sharma, Chairman Associate Director (QA), Rawatbhata 323 307 rlsharma@npcilraps.com Shri S.V.Lele, Hon. Secretary, T/IV – 5/F, Anu Kiran Colony, PO Bhabha Nagar, Rawatbhata 323 307. svlele@npcil.co.in
Mumbai Bangalore
Hon.General Secretary Shri R.J.Pardikar
Dr. M.T. Shyamsunder, Chairman, NDE Modelling & Imaging Lab., Cassini Building, GE Global Research, John F. Welch Technology Center EPIP Phase 2, Whitefield Road, Bangalore-560066. Mt.shyamsunder@ge.com
Hon. Treasurer Shri T.V.K.Kidao Hon. Joint Secretaries Shri Rajul R. Parikh
Nagpur Chennai
Immediate Past President Shri Dilip P. Takbhate Past President Shri S.I.Sanklecha Members Shri Anil V. Jain Shri Dara E. Rupa Shri D.K.Gautam Shri Diwakar D. Joshi Dr. Krishnan Balasubramaniam Shri Mandar A. Vinze Shri B.B.Mate Shri G.V.Prabhugaunkar Shri B.K.Pangare Shri M.V.Rajamani Shri P.V. Sai Suryanarayana Shri Samir K. Choksi Shri B.K.Shah Shri S.V.Subba Rao Shri Sudipta Dasgupta Shri N.V.Wagle Shri R.K.Singh Shri A.K.Singh (Kota) Shri S. Subramanian Shri C. Awasthi Brig. P. Ganesham Shri Prabhat Kumar Shri P. Mohan Shri R. Sampath Ex-officio Members Managing Editor, JNDT&E Shri V. Pari Chairman, NCB & Secretary, QUNEST Dr. Baldev Raj
Shri T.V.K. Kidao, Chairman Madras Metallurgical Services Pvt. Ltd. 14, Lalithapuram Street, Royapettah Chennai – 600 014 mmspl@vsnl.net Shri R. Balakrishnan, Hon. Secretary, No.13, 4th Cross Street, Indira Nagar, Adyar, Chennai 600 020. rbalkrishin@yahoo.co.in
President, QUNEST Prof. Arcot Ramachandran All Chapter Chairmen/Secretaries Permanent Invitees Shri V.A.Chandramouli Prof. S. Rajagopal Shri G. Ramachandran & All Past Presidents of ISNT
Shri Pradeep Choudhari, Chairman Parikshak & Nirikshak, Plot M-9, Laxminagar Nagpur - 440 022 Mr. Jeevan Ghime, Hon. Secretary, Applies NDT & Tech Services, 33, Ingole Nagar, B/s Hotel Pride, Wardha Road, Nagpur 440 005. antstg_ngp@sancharnet.in
Pune Delhi Shri B.S.Chhonkar, Chairman, 90A, Pocket-1, Mayur Vihar - 1 New Delhi 110 091 chhonkar@gmail.com Shri Dinesh Gupta, Hon.Secretary, isntdelhi@gmail.com
Hyderabad Shri G. Narayanrao, Chairman, Chairman & Managing Director, MIDHANI, Kanchanbagh, Hyderabad 500 058. cmd.midhani@ap.nic.in Shri J.R. Doshi, Hon.Secretary, Scientist, Project LRSAM DRDL, Hyderabad 500 058. joshidrdl@in.com
Shri PV Dhole, Chairman NDT House, 45 Dr Ambedkar Road, Sangam Bridge, Pune- 411 001 info@technofour.com Shri VB Kavishwar, Hon Secretary, NDT House, 45 Dr Ambedkar Road, Sangam Bridge, Pune- 411 001 eddysonic@gmail.com
Sriharikota Shri S.V. Subba Rao, Chairman, General Manager, Range Operations SDSL, SHAR Centre Sriharikota 524124. svsrao@shar.gov.in Shri G. Suryanarayana, Hon. Secretary, Dy. Manager, VAB, VAST, Satish Dhawan Space Centre, Sriharikota-524 124. gsurya@shar.gov.in
Tarapur Jamshedpur Mr J. C. Pandey, Chairman, Researcher, R&D, TATA Steel, P. O. Burmamines, Jamshedpur - 831 007 jcpandey@tatasteel.com Mr. M K Verma, Hon. Secretary, Manager, SNTI, TATA Steel N-Road, Bistupur, Jamshedpur - 831 001 mk.verma@tatasteel.com
Kalpakkam
Controller of Examination, NCB Dr. B. Venkatraman
Shri YC Manjunatha, Chairman Director ESG, IGCAR, Kalpakkam – 603 102 ycm@igcar.gov.in Shri BK Nashine, Hon.Secretary Head, ED &SS, C&IDD, FRTG IGCAR, Kalpakkam – 603 102 bknash@igcar.gov.in
Kochi Shri John Minu Mathew, Chairman, General Manager (Technical), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal 682 302. Kochi johnminumathew@bharatpetroleum.in Shri K.D.Damien Gracious, Hon. Secretary, CM (Advisory Services), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal-682 302. Kochi damiengraciousk@bharatpetroleum.in
Kolkata Shri Swapan Chakraborty, Chairman Perfect Metal Testing & Inspection Agency, 46, Incinerator Road, Dum Dum Cantonment, Kolkata 700 028. permeta@hotmail.com Shri Dipankar Gautam, Hon. Secretary, 4D, Eddis Place, Kolkata-700 019. eib1956@gmail.com
vol 9 issue 4 March 2011
Shri R.S. Vaghasiya, Chairman, B 4/7, Sri Punit Nagar, Plot 3, SV Road, Borivile West, Mumbai 400 092. ravji.vaghasiya@gmail.com Shri Samir K. Choksi, Hon. Secretary, Director, Choksi Brothers Pvt. Ltd., 4 & 5, Western India House, Sir P.M.Road, Fort, Mumbai 400 001. Choksiindia@yahoo.co.in
Journal of Non Destructive Testing & Evaluation
Shri PG Behere, Vice Chairman, AFFF, BARC, Tarapur-401 504. pgbehere@rediffmail.com Shri R. Murali, Hon.Secretary, rmurali@npcil.co.in
Tiruchirapalli Shri V Thyagarajan, Chairman General Manager (WRI & Labs) BHEL Tiruchirapalli 620014 isnt_try@sancharnet.in Shri A.K.Janardhanan, Hon. Secretary, C/o NDTL Building 1, H.P.B.P., BHEL, Tiruchirapalli 620 014. akjn@bheltry.co.in
Vadodara Shri P M Shah, Chairman, Head-(QA) Nuclear Power Corporation Ltd. npcil.bar@gmail.com M S Hemal Mehta, Hon.Secretary, NBCC Plaza,Opp. Utkarsh petrol pump, Kareli Baug, Vadodara-390018. pmetco@gmail.com
Thiruvananthapuram Dr. V.R. Ravindran, Chairman Division Head, Rocket Propellant Plant, VSSC, ISRO, Thiruvananthapuram - 695 022 drvrravi@yahoo.co.in Shri. Imtiaz Ali Khan Hon.Secretary, Engineer, Rocket propellant Plant, VSSC, Thiruvananthapuram 695 013 imtiaz_ali@vssc.gov.in
Visakhapatnam Shri Om Prakash, Chairman, MD, Bharat Heavy Plate & Vessels Ltd. Visakhapatnam 530 012. Shri Appa Rao, Hon. Secretary, DGM (Quality), BHPV Ltd., Visakhapatnam 530 012
Journal of Non Destructive3 Testing & Evaluation About the cover page:
Volume 9 issue 4 March 2011
Contents
The image in the Front Cover Page is an ultrasonic C-Scan Image using 15 MHz highly focused beam on a Steel billet that was sectioned (Courtesy: R&D and SS Division, Tata Steel, Jamshedpur). During the continuous casting process, due to the differential cooling from the outside surface to the inside, the grain structure is expected to take the distribution as represented by the classic schematic. Here, the chill zone (A) is found on the outer most layer that is in contact with the coolant. The anisotropic columnar grain structure (B) is found below the chill zone. The inside regions are found to be equiaxed (C). The relative area of the 3 Zones will depend on the processing conditions. At Tata Steel the high frequency ultrasonic C-scan imaging is used to optimize the electro-magnetic stirring process parameters in order to improve the quality of steel (billet) manufacturing. The cross-sectional plane C-scan image on a typical as-cast billet is shown in the cover page clearly indicating the 3 zones. The Journal is for private circulation to members only. All rights reserved throughout the world. Reproduction in any manner is prohibited. Views expressed in the Journal are those of the authors' alone. Published by Shri RJ Pardikar, General Secretary on behalf of Indian Society for Non Destructive Testing (ISNT) Modules 60 & 61, Readymade Garment Complex, Guindy, Chennai 600032 Phone: (044) 2250 0412 Email: isntheadoffice@gmail.com and Printed at VRK Printing House 3, Potters Street, Saidapet, Chennai 600 015 vrkonline@gmail.com Ph: 09381004771
5
NCB Announcement
9
Chapter News
11
Basics
17
Horizon
23
NDT Puzzle
25
IQ Forum
27
NDE events
29
Producs & Patents
34
NDE 2011 Highlights Technical Paper
42
Fatigue Crack Growth Monitoring in Ti-6Al-4V Alloy Using Acoustic Emission Technique and Digital Image Correlation Shivanand Bhavikatti, M R Bhat and CRL Murthy - Page 43
47
Development of an Acoustic Emission Condition Monitoring system for use in IC Engines. Sreedhar P, JanardhanPadiyar M, R Maharajan and Krishnan Balasubramaniam
53
Signature Analysis of Failure Modes in Composites using Acoustic Emission M. Ramesh kumar and M.R. Madhava
60
An empirical approach for the burst prediction of GFRP pressure bottles using acoustic emission technique R.Joselin , T.Chelladurai, M.Enamuthu, K.M. Usha and E.S. Vasudev
Chief Editor Prof. Krishnan Balasubramaniam e-mail: balas@iitm.ac.in
Co-Editor Dr. BPC Rao bpcrao@igcar.gov.in
Managing Editor Sri V Pari e-mail: scaanray@vsnl.com
Topical Editors Dr D K Bhattacharya Electromagnetic Methods
Dr T Jayakumar, Ultrasonic & Acoustic Emission Methods
Sri P Kalyanasundaram Advanced NDE Methods
Sri K Viswanathan Radiation Methods
Editorial Board Dr 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 Panel Prof 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
Objectives The Journal of Non-Destructive Testing & Evaluation is published quarterly by the Indian Society for Non-Destructive Testing for promoting NDT Science and Technology. The objective of the Journal is to provide a forum for dissemination of knowledge in NDE and related fields. Papers will be accepted on the basis of their contribution to the growth of NDE Science and Technology.
Journal of Non Destructive Testing & Evaluation
vol 9 issue 4 March 2011
4
Classifieds Scaanray Metallurgical Services
Transatlantic Systems
(An ISO 9001-2000 Certified Company)
NDE Service Provider Process and Power Industry, Engineering and Fabrication Industries, Concrete Structures, Nuclear Industries, Stress Relieving Call M. Nakkeeran, Chief Operations, Lab: C-12, Industrial Estate, Mogappair (West), Chennai 600037 Phone 044-2625 0651 Email: scaanray@vsnl.com ; www.scaanray.com
Electro-Magfield Controls & Services & LG Inspection Services We manafucture : Magnetic Crack Detectors, Demagnetizers, Magnetic Particles & Accessories, Dye Penetrant Systems etc Super Stockist & Distributors: M/s Spectonics Corporation, USA for their complete NDT range of productrs, Black Lights, Intensity Meters, etc. Plot 165, SIDCO Industrial Estate, (Kattur) Thirumullaivoil, Vellanur Village, Ambattur Taluk Chennai 600062 Phone 044-6515 4664 Email: emcs@vsnl.net
Madras Metallurgical Services (P) Ltd Metallurgists & Engineers
Metallography Strength of Materials Non Destructive Testing Foundry Lab
Serving Industries & Educational Institutes for the past 35 years
24, Lalithapuram street, Royapettah, Chennai 600014 Ph: 044-28133093 / 28133903 Email: mmspl@vsnl.com
OP TECH ASNT Level III Intensive Taining Educational CDs PT, UT, RT, MT, ET, Basic Metallurgy and Mechanical Testing Call 93828 12624 Land 044 - 2446 1159
B Ram Prakash A 114, Deccan Enclave, 72, T M Maistry Street, Thiruvanmiyur, Chennai 600 041
Southern Inspection Services NDT Training & Level III Services in all the following ten NDT Methods
Support for NDT Services NDT Equipments, Chemicals and Accessories Call DN Shankar, Manager 14, Kanniah Street, Anna Colony, Saligramam, Chennai 600093 Phone 044-26250651 Email: scaanray@vsnl.com
Betz Engineering & Technology Zone An ISO 9001 : 2008 Company 49, Vellalar Street, near Mount Rail Station, Chennai 600088 Mobile 98401 75179, Phone 044 65364123 Email: betzzone@vsnl.net / rg_ganesan@yahoo.com
International Training Division 21, Dharakeswari Nagar, Tambaram to Velachery Main Road, Sembakkam, Chennai 600073 www.betzinternational.com / www.welding-certification.com
KIDAO Laboratories NABL Accredited Laboratory carrying out Ultrasonic test, MPL and DP tests, Coating Thickness and Roughness test. We also do Chemical and Mechnical tests
A-3, Mogappair Indl. Area (East) JJ Nagar, Chennai 600037 Phone 044-26564255, 26563370 Email: kidaolab@giasmd01.vsnl.net.in; kidaolabs@vsnl.net www.kidaolabs.com
Dhvani R&D Solutions Pvt. Ltd 01J, First Floor, IITM Research Park, Kanagam Road, Taramani, Chennai 600113 India Phone : +91 44 6646 9880
• Inspection Solutions • Software Products • Training • Services & Consultancy
CUPS, TAPS, CRISP, TASS SIMUT, SIMDR Guided Waves, PAUT, TOFD Advanced NDE, Signal Processing C-scans, On-line Monitoring
E-mail: info@dhvani-research.com
www.dhvani-research.com
No.2, 2nd Floor, Govindappa Naicker Complex, Janaki Nagar, Arcot Road, Valasaravakkam, Chennai-600 087 Tamil Nadu, India
Shri. K. Ravindran, Level III RT, VT, MT, PT, NR, LT, UT, ET, IR, AE
vol 9 issue 4 March 2011
-
Journal of Non Destructive Testing & Evaluation
Phone : 044-2486 8785, 2486 4481 E-mail: sisins@gmail.com and sisins@hotmail.com Website: www.sisndt.com
5
National Certification Board Indian Society for Non Destructive Testing
ANNOUNCEMENT ASNT NDT Level III Examination Bangalore 23, 24 & 25 May 2011 The Indian Society for Non - Destructive Testing (ISNT), the National Sponsoring Organization of the American Society for Non – Destructive Testing (ASNT) is pleased to announce that the ASNT NDT Level III Examination of 2011 (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 by NCB-ISNT. NDT Level III certification by ASNT (which is given only by examination) will help NDT personnel and the organizations that employ them, in promoting global acceptance of their Products and Services. The importance and the 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, refresher courses in various methods will be conducted under the arrangement of ISNT –Bangalore Chapter. The details of the fee structure applicable for the Examination and Refresher Courses are given in Table-I and Table -II respectively. All correspondences on the subject and request for application forms may please be addressed to: Dr. B. Venkatraman ASNT Level III Examination Coordinator,NCB – ISNT, Modules 60 & 61, Readymade Garment Complex, SIDCO Industrial Estate, Guindy, Chennai 600 032, India Ph:91 44 22500412 & 91 44 42038175 91 44 27480500 Ext.22306 E Mail: isntheadoffice@gmail.com Alternate E Mail: ncbisnt@gmail.com Applications for the Examinations duly completed in all respects along with requisite supporting documents and applicable 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. 2. 3. 4. 5. 6.
Basic Radiographic Testing Magnetic Particle Testing Ultrasonic Testing Liquid Penetrant Testing Eddy Current Testing
7. 8. 9. 10. 11.
Neutron Radiographic Testing Leak Testing Visual Testing Acoustic Emission Testing Thermal / Infrared Testing
It may please be noted that the basic examination by itself is not considered as a method. Basic and method examination(s) must be taken to become eligible to receive a certificate for that method(s). The maximum number of examinations that can be taken is six during the three days of the Examination. Journal of Non Destructive Testing & Evaluation
vol 9 issue 4 March 2011
6 The fees payable to ASNT and ISNT for the NDT Level III Examination are given in the following table: Table - I Examinations (Basic or Method)
ASNT Examination Fee
Surcharge
USD
USD
ASNT membership fee for the year *
ASNT Fee Total *
ISNT Fee
USD
USD
INR
1.
First time exam / Adding method exam / Renewal of certification exam One Examination 260 40 Two Examinations 520 40 Three Examinations 780 40 Four Examinations 1040 40 Five Examinations 1300 40 Six Examinations 1560 40
75 75 75 75 75 75
375 635 895 1155 1415 1675
12000 12000 12000 12000 12000 12000
2.
Retaking Failed Examination One Examination Two Examinations Three Examinations Four Examinations Five Examinations Six Examinations
75 75 75 75 75 75
300 485 670 855 1040 1225
11,000 11,000 11,000 11,000 11,000 11,000
1.
2.
3.
4.
185 370 555 740 925 1110
40 40 40 40 40 40
*Please see Instructions 2 below. INSTRUCTIONS: The amount shown under ISNT fees includes the courier charges for the examination booklet(from and to ASNT), lunch, refreshments and all other administrative expenses to be incurred by ISNT in this connection. Those who are not current members of ASNT at the time of examination (i.e. as on May 2011) shall include membership fee of USD 75 along with relevant ASNT examination fee and the surcharge. Those who are current member at the time of examination and wishing to renew the membership for one year shall include membership fee of USD 60 (refer examination documents). Those who do not include the membership fee along with examination fee shall positively give their current ASNT membership number and the expiry date. The total ASNT fee including surcharge and membership fee as applicable shall be sent in the form of a crossed
5.
6.
7.
cheque in US Dollars favoring “American Society for Nondestructive Testing” and payable in USA. Those who are applying from within India may get the necessary foreign exchange in USD from a scheduled bank. The ISNT fees (and the course fees if opted), shall be paid only by crossed demand draft in Indian Rupees favoring “NCB-ISNT”, payable at Chennai. Cheques will not be accepted. Completed application form along with enclosures and the relevant ASNT and ISNT fees shall be sent to ASNT Level III Exam Coordinator at the address given in the first page, before the due date. NO APPLICATION WITH DD DATED AFTER THE DUE DATE WILL BE ACCEPTED. Candidates may kindly fill up the application form as per instructions given. Incomplete application forms or those without requisite enclosures and fees will not be accepted.
ASNT NDT Level III Refresher Courses AT BANGALORE, INDIA To assist the candidates in preparing for the May 2011 Examinations, refresher courses will be conducted at Bangalore; the details along with fees for the courses are given below. Table II Method
Course Duration
Dates
Fees for the 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
18 May to 21 May 2011
Radiographic Testing
4 days
Eddy Current Testing**
4 days
7,500
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 courses on Visual Testing and Eddy Current Testing should intimate their intention sufficiently in advance to facilitate scheduling the courses. They may also inform the details of other courses they wish to attend.
vol 9 issue 4 March 2011
Journal of Non Destructive Testing & Evaluation
7
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: asnt2011.refresher@gmail.com 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 be given to the participants on the first day of the course. If it is needed earlier, it can be sent to the participants, at their specific request to the examination coordinator, by courier service, at their cost. In case the candidate withdraws from the course with an advance intimation of three working days, the course fee would be refunded to him after deducting 10% of the fees towards administrative charges. Any cancellations for the course should however be informed prior to May 01, 2011. No refund would be given to candidates thereafter. Also once the candidates have received the course material, on no account the course fee will be refunded. The course syllabus will be as per ASNT SNT-TC-1A 2006 requirement. The candidates can opt for one or more of the above courses as desired by them. The course fee should be sent by a crossed demand draft drawn in favor of “NCB-ISNT� payable at Chennai 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 the American Society for Non-Destructive Testing (ASNT) is pleased to announce that the ASNT NDT Level II Examination of 2011 directly by the ASNT will be held at Chennai during July, 18-20, 2011. Application deadline 8th May 2011. The examinations will be conducted under the auspices of the American Society for Non-destructive Testing, USA by NCB-ISNT. ASNT NDT Level II Examination will be conducted in the following methods:
Radiographic Testing
Leak Testing
Magnetic Particle Testing
Visual Testing
Ultrasonic Testing
Acoustic Emission Testing
Liquid Penetrant Testing
Thermal / Infrared Testing
Eddy Current Testing Please visit our website isnt.org.in for application and further details For further queries, please contact: Dr. B. Venkatraman ASNT Level III Examination Coordinator, NCB-ISNT, Modules 60 & 61, Readymade Garment Complex, SIDCO Industrial Estate, Guindy, Chennai 600 032, India Ph: 91 44 22500412 & 91 44 42038175 91 44 27480500 Ext.22306 E-mail: isntheadoffice@gmail.com Alternate E-mail: ncbisnt@gmail.com Journal of Non Destructive Testing & Evaluation
vol 9 issue 4 March 2011
EPOCH 600
ULTRASONIC FLAW DETECTOR
Economical Size, Quality Performance The EPOCH 600 Digital Ultrasonic Flaw Detector combines Olympus’ industry leading conventional flaw detection capabilities with the efficiency of a highly portable, intuitive instrument. The EPOCH 600 is an exciting new addition to the Olympus flaw detector product line, incorporating quality flaw detection features for any level of user. • • • • • • • •
Compact and rugged, weighs only 1.68 kg (3.72 lb.) Vibrant full VGA sunlight viewable display PerfectSquare™ tunable square wave pulser Intuitive user interface EN12668-1 compliant Digital high dynamic range receiver Digital filtering enhances signal-to-noise ratio Two hardware configurations: - Adjustment Knob (designed for IP66 rating) - Navigation Pad (designed for IP67 rating)
EPOCH 600 and EPOCH 1000 Series
Exclusive Distributor in India: Blue Star Limited Tel: +91 444-244-4000 • ndtenquiry@bluestarindia.com For worldwide representation visit www.olympus-ims.com • info@olympusNDT.com
9
CHAPTER NEWS Mumbai Chapter APCNDT 2013 committee Meeting was held on 21st December 2010 UT Level II course & Examination for ONGC Engineers on 3-8, January, 2011 at IQM, Jogeshwari (W), Mumbai. Course Director was Shri N. Sadasivan and Examiners were Shri S.P. Srivastava and Shri Luke Pinenta Welding Inspector examination at ITT, Mahim on 8th January 2011, and the Examiner was Shri L. M. Tolani. RT Level II course & Examination for ONGC Engineers on 1015, January 2011 at IQM, Jogeshwari (W), Mumbai. Course Director was Shri L.M. Tolani and Examiners were Shri S.P. Srivastava and Shri Sanjay Narang. APCNDT 2013 committee Meeting was held on 14th January 2011. EC Meeting to be held on 28th January 2011
Vadodara Chapter The activity was a Lecture by Air Marshall Shri P.K. Desai (Retd.) on”NDT for Maintenance of various Aircrafts of Indian Air Force during Peace Period and War Period”. The lecture was well attended and also was participated by Indian Air Force personnel. The lecture gave insight and indication to theparticipants on requirement of NDT science and NDT technology to ensuresafety of pilots as well as to ensure maintenance of air armaments in evergreen stage. The interested aspect of this lecture was evaluation on extension of lives of planes - a system developed
jointly by Indian Air Force with the scientists and technologists of Kalpakkam group who are also members of ISNT “Shri P.M. Shah – Chairman ISNT Vadodara Chapter welcomed the Chief Guest and Ms. Hemal Mehta - Hon. Secretary ISNT Vadodara Chapter introduced Chief Guest; Shri Nayak – Vice Chairman ISNT Vadodara Chapter gave vote of thanks”
Kolkata Chapter ISNT-NDE-2010 -National Seminar,jointly organized by Jamshedpur and Kolkata Chapter during 9-11th.Dec,2010 at Science City , Kolkata. There were two pre seminar Tutorial on 7th & 8th.Dec,2010 on Digital Radiography and Thermal Imaging and on Signal Analysis,simulation and Modeling. The workshop on Advance NDE for structural intigrity assessement. Pre tutorial and workshos were conducted on three parallal session and more than 90 participants mainly students, Research Scholars and from industries attended the pre-tutorial and work shop. On 9th.Dec’2010 inagural ceremony was held. Mr.Rajiv Kaul,Industrialist was chief guest and Vice chancellor of Bengal Engineering and Science University was Guest of Honour. More than 500 delegates attended the seminar. There were more than forty two exhibitors. NDT equipment manufacturers exibited their products. Exhibitors were from Germany, Ukraine, China, Checkoslovakia, USA and Indian manufacturers.M/s.GE Sensing & Inspection Technologies was main sponsor, M/S. Bluestars Ltd was Co-Sponsor and M/S. East West Engineering & Electronics Pvt.Ltd, M/S. Godavari Technical Services, M/s.Sivert India were the Associate sponsors. WCNDT participated the seminar and they were provided with a complementary stall. Photographs of NDE 2010 is printed elsewhere in the journal.Swapan Chakraborty, Convener NDE 2010.
National NDT Awards
No.
Award Name
Sponsored by
1.
ISNT - EEC National NDT Award (R&D)
M/s. Electronic & Engineering Co., Mumbai
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ISNT - Modsonic National NDT Award (Industry)
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3.
ISNT - Sievert National NDT Award (NDT Systems)
M/s. Sievert India Pvt. Ltd., Navi Mumbai
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ISNT - IXAR Best Paper Award in JNDE (R & D)
M/s. Industrial X-Ray & Allied Radiographers Mumbai
5.
ISNT - Eastwest Best Paper Award in JNDE (Industry)
M/s. Eastwest Engineering & Electronics Co., Mumbai
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ISNT - Pulsecho Best Chapter Award for the Best Chapter of ISNT
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Note-1: The above National awards by ISNT are as a part of its efforts to recognise and motivate excellence in NDT professional enterpreneurs. Nomination form for the above awards can be obtained from ISNT head office at Chennai, or from the chapters. The filled 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: isntheadoffice@gmail.com
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BASICS Basics of Microfocal Radiography V. Manoharan1 and Neuser Ebherhard2 1
GE India Technology Center, Bangalore, India 2 GE Energy Services, Wunstorf, Germany Email: Manoharan.v@ge.com ; ebherhard.neuser@ge.com
Edited by Prof. O. Prabhakar, OP Tech, Chennai. Geometric unsharpness and magnification are the two issues that are of concern in conventional radiography. Particularly in areas like microelectronics, materials technology, biomedical applications and medicine fine details have to be observed. By reducing the area from which the X-rays are generated (Focal spot) one can improve the resolution and the magnification of the conventional radiography. Due to its importance in modern NDT, the fundamentals of micro-focal radiography are explained in this article by Dr Manoharan and Dr Eberhard, experts in this field.
If the focal spot size is less than 100 microns, then the radiographic inspection is termed as Microfocal radiography. Micro focal radiography systems with focal spot of size 1 to 100 microns has opened the way for the detection of micro defects of the order of few microns in critical engineering components as smaller focal spot allows image magnification. For example, the internals of an Integrated Circuit can be clearly seen as shown in Fig.1. This would have been very difficult to achieve using conventional radiography. Microfocal radiography Systems coupled with state-of-the-art digital radiography systems are today being widely used in the aerospace, automotive, power and electronic industries for automated 2D inspection and 3D imaging of critical components.
1. INTRODUCTION Radiographic inspection can be classified in many ways e.g. based on type of radiation sources used, type of detection medium , applications and etc. Conventional and Microfocal radiography are classifications based on focal spot sizes of x-ray generation devices. The focal spot is defined as an area on the target where x-rays are generated. If the focal spot size is greater than 100 microns, then the radiographic inspection is generally termed as conventional radiography. Ever since the discovery of x-rays, conventional radiography has been used for many industrial applications such as inspection of welds, castings, composites and other engineering materials. However, the larger focal spot sizes in conventional radiography produces blurring of images and thus does not allow projection radiography (image magnification). Therefore, there is a limitation of detecting micro defects using conventional radiography. With the development of new materials and an increased stringent requirement of specifications, the emphasis shifted from the detection of macro defects to micro defects, thus resulting in the demand and development of microfocal radiography.
Fig. 1 : Microfocal Radiography of Integrated Circuit
2. PHYSICS OF MICROFOCAL RADIOGRAPHY The main advantage of Microfocal radiography is that it allows projection radiography (image magnification). Let us try and understand the requirements of projection radiography. The object needs to be placed away from the detector as shown in Fig. 2 for image magnification. The magnification (M) is given by M = FDD / FOD
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BASICS due to geometric magnification. Thus one can attain very high magnification with minimum unsharpness using Microfocal x-ray sources when compared to conventional ones. 3. MICROFOCAL X-RAY SOURCES As we know that only 1- 3% of the kinetic energy of electrons is converted into x-rays and rest is dissipated as heat, the heat energy generated over very small area in micrococcus x-ray sources can melt the target. This is a huge challenge in the designing of micro focus xray sources and it limits the power of microfocus x-ray sources. A typical construction of microfocus x-ray sources is shown in Fig. 4.
Fig. 2 : Illustration of geometric magnification
Fig. 3 : Illustration of geometric unsharpness
where FDD is the Focal spot to Detector Distance and FOD is Focal spot to Object Distance. Hence, for larger magnification, the Object to Detector Distance (ODD) needs to be larger. However, We know that, geometric unsharpness will be more if ODD is more as the geometric unsharpness (Ug) is given by Ug = f x ODD / FOD
(2)
Where f is the focal spot size. It is evident that the focal spot size and ODD are important factors in determining the geometrical unsharpness. The variation of geometrical unsharpness with focal spot size and ODD is illustrated in 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 sources can compensate the increase in geometric unsharpness vol 9 issue 4 March 2011
Fig 4 : Construction of microfocus x-ray source
The microfocus x-ray tube consists of an evacuated tube, tungsten filament, a target and electro magnetic lenses to focus electrons. Electrons are generated by thermionic emission by heating the filament and accelerated towards target by a potential difference between cathode and anode as in conventional x-ray sources. The filament current is controlled by means of the Wehnelt grid, which is held at a negative potential (voltage UG). The beam passes through a hole in the anode and is then directed onto an electromagnetic lens by a series of deflecting magnets where it is then collimated and focused onto the target. X-rays are emitted when accelerated electrons are decelerated upon striking a target. There are two types of targets used in microfocus x-ray tubes, the Transmission and Directional type. The transmission target consists of a thin layer of tungsten on a plate of light metal. In case of transmission targets, the X-ray
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source is located very close to the outer wall of the microfocus X-ray tube allowing the user to bring samples very close to the source ensuring highest magnifications. The directional type directional type targets enables more power and suitable for inspection thicker and denser components. Transmission and directional type microfocus x-ray sources are illustrated in Fig.5. Fig. 5 : Transmission and Directional Targets
Microfocus x-ray sources with kV of the order of 220 kV are commercially available and 300 kV sources are also introduced in the market. The target to window distance is one of the key specification of microfocus xray sources, which determines how closely object can be placed near the focal spot and achieve larger magnification. The micro focus x-ray sources are also classified as sealed sources and de-mountable source based on how vacuum is maintained in them. Sealed sources have permanently vacuum-sealed x-ray tube head. The advantage of sealed sources is that it is maintenance free and has high power. A demountable x-ray tube consists of an open type X-ray tube head, which consists of continuously pumped vacuum system. The advantage of demountable tube is that opening the x-ray tube head; we can replace the faulty filament and target. Its limitation is frequent maintenance requirements of vacuum systems and time taken to achieve vacuum during operation. Some of the micro focal x-ray systems have rod anode, which is used, for inspection of welds in smaller diameter tubes. The rod anode can be inserted inside tube and panoramic exposure cab be carried out with geometric magnification. Different types of rod anode configurations are given in Fig. 6. 4. MICROFOCAL X-RAY SYSTEMS There are integrated microfocal x-ray systems, which consist of a microfocus x-ray source, a manipulator to handle objects, a digital detector array, a radiation shielded cabinet and software to control manipulator/ source & detector and image analysis tools to process x-
Fig. 6 : Type of rod anodes
Fig. 7 : A typical integrated Micro focus x-ray inspection system Journal of Non Destructive Testing & Evaluation
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BASICS
ray images. These systems are used for inspection of small parts automatically in a production line. A typical such system is shown in Fig.7. Micro tomography is another type of integrated x-ray system, which has 3D imaging capability with resolution of the order of few microns. 5. RECENT ADVANCES X-ray sources with focal spot size of less than 1 micron are developed and are commercially available in the market. These nanofocus x-ray sources extend the resolution capability of 2D and 3D x-ray imaging systems significantly. Nanofocus x-ray sources enables the level contrast and resolution required for the inspection of low-density structures and very small features common in miniature electronic components such as optoelectronics, Microelectromechanical systems and micro-opto-electromechanical systems.
3D micro tomogram of Automotive Metal foam
6. APPLICATIONS PRINTED CIRCUIT BOARD ASSEMBLY
Micro focus radiography is extensively used in Electronics and semiconductor industries for inspection of Printed Circuit Board Assembly (PCBA), Multi layer circuit board, power electronic components and integrated circuits. Defects solder joints such as Missing solder fillets, Voids, blisters; Solder bridges and Nonwetting defects in PCBAs can be easily detected by high-resolution micro focal radiography. MULTILAYERED CIRCUIT BOARD
In multilayer circuit board manufacturing, high-resolution microfocal radiography is mainly used to determine the layer offset and minimum annular width and detecting flaws such as short circuits caused by etching or layout defects and defective conductor tracks.
Power Transistor on a printed circuit board
SEMICONDUCTORS
As electronic components are becoming increasingly miniaturized, high-resolution and magnification X-ray technology provides the means necessary to inspect components such as Inspection of bond wires and bonding areas, Void analysis of conductive and nonconductive die bonds, inspection of flip-chip solder joints in processor cases and Analysis of discrete components such as capacitors and inductors.
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Fig. 8 : Applications of microfocal Radiography
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Solder Joint
3D Micro tomography is used for inspection of gas turbine blades, Aluminium castings, composites, sintered ceramic materials and geological specimens, In plastics engineering, high-resolution X-ray technology is being used to optimize the casting and spraying process by
PCBA-Faulty
MICRO TOMOGRAPHY APPLICATIONS
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Tube-to-Tube sheet welds
Fig. 9 : Microfocal Radiography of tube-to-tube sheet weld (Ref.5)
The tube-to-tube sheet weld inspection in heat exchangers of nuclear reactors is another critical application of microfocal radiography. There are many references available for tube-to-tube sheet inspection, which is given in the references. Here a rod anode is used and panoramic exposure of entire circumference of tube-totube sheep weld is radiographed with ~ 2X magnification. An example of tube-to-tube sheet inspection is given Fig. 9. 7. ADVANTAGES & LIMITATIONS The advantages of micro focal radiography are as follows: 1.
It allows projection radiography (image magnification) and makes it possible to detect defects of the order of few microns
2.
It reduces scattered radiation reaching the detector, as the distance 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 of a few microns
The advantages of microfocal radiography are illustrated in Fig. 10. Some of the key limitations of micro focal x-ray systems are its limited power arising from the heat load in small x-ray focal spots, limited area coverage per exposure and the difficulties in inspecting thick & high-density materials 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, High Definition Radiography of Tube to Tube Sheet Welds of Steam Generator of Prototype Fast Breeder Reactor, Insight, 37,1995,pp-189-192.
Fig. 10 : Advantages of Microfocal Radiography
detecting contraction cavities, blisters, weld lines and cracks, and to analyze flaws. Industrial X-ray computed tomography (CT) provides three-dimensional images of object characteristics such as grain-flow patterns and filler distribution as well as imaging of low-contrast defects. 3D metrology with industrial CT is the only technique allowing non-destructive measurements of the interior of complex objects. Typical examples of applications are given in Fig. 8.
3. B.Venkataraman, V.Manoharan, P.Kalyanasundaram, Baldev Raj and V.K.Sethi, N.V.Wagle, Radiographic Sensitivity of Microfocal and Thulium Sources, Proc. of National seminar on 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 NonDestructive Testing, Naraosa Publications 6. Dr. Holger Roth, Stuttgart, Fundamentals of x-ray inspection, GE MCS-Phoenix x-ray, Internal Presentation
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Contact Mr. D. Simon Amallaraja |
0 9866343309,9848043309|amallraja@fourvector.com
Ms.Gomathi Ramasamy |
0 7702733309 | gomathi@fourvector.com
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0 8978517118 | frankedwinz@fourvector.com
HORIZON
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T-rays Where will it lead us?
Between the microwave and the infrared regions of the electromagnetic spectrum, lies the terahertz (THz) region characterised by the now not-so-mysterious T-rays (see Figure 1). It remained nearly untapped for a long time, as neither electronic nor optical sources could illuminate this shadowy region. Terahertz (THz) frequency domain is usually defined as the portion of the submillimetre-wavelength electromagnetic spectrum between approximately 1mm (300 GHz, ~ 0.4 meV) and 30ĂŹm (10 THz, ~ 40 meV). T-rays have several advantages over x-rays, one being that they have low photon energies (for example, 4 meV at 1 THz) and therefore do not subject a biological tissue to harmful radiation. In comparison, typical x-ray photon energy is in the range of keV, which is 1 million times higher than that of a T-ray photon. T-ray imaging provides spectroscopic information within the terahertz frequency range, unlike microwave and xray imaging modalities which produce density pictures. The rotational, vibrational and translational responses of materials (molecular, radicals and ions) within the THz range provide information that is generally absent
C.V. Krishnamurthy Department of Physics Indian Institute of Technology, Madras Chennai 600036, Tamilnadu, India e-mail: cvkm@iitm.ac.in
in optical, x-ray and NMR images. In principle, these transitions in THz frequency are specific to the molecule and therefore enable THz wave fingerprinting. T-rays can easily penetrate and image inside most dielectric materials and polymers, which may be opaque to visible light and low contrast to x-rays, making T-rays a useful and complementary imaging source in this context. As a quasi-optical beam, a T-ray can be reflected and collimated by metallic mirrors and focused by a plastic or high-resistivity silicon lens. Imaging with optical and near-infrared waves entails large amounts of Rayleigh scattering which tend to spatially smear out the objects to be imaged. T-rays, due to their longer wavelengths, can provide significantly enhanced contrast because of low Rayleigh scattering. At microwave frequencies, compact electronic devices are typically used as high-power sources. But at frequencies substantially above 100 GHz, as the transit times of electrons in devices become shorter and capacitative effects are more dominant, it becomes increasingly difficult to generate large output powers. Conversely, approaching the terahertz frequency range
Fig. 1 : Electromagnetic spectrum highlighting the Terahertz region. Journal of Non Destructive Testing & Evaluation
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from the visible side of the electromagnetic spectrum, it becomes progressively more difficult to engineer and maintain a population inversion between two states in a laser, as their energy separation becomes closer and closer to kBT (where kB is Boltzmann’s constant and T is temperature). For these reasons, most uses of terahertz waves have been demonstrated with broadband terahertz spectroscopy systems that are based on femtosecond lasers. GENERATION AND RECEPTION
Electrically biased photoconductor generates a THz pulse when a femtosecond laser pulse induces its conductivity changes. Transient photoconductivity, a highly complex phenomenon, includes optical generation of hot electrons and holes, their rapid thermalization, ballistic acceleration of the electrons, velocity-overshoot on a subpicosecond time scale and fast screening of the internal electric field. It is important that the energy bandgap of the semiconductor εgap is smaller than the laser photon energy hí, so that the photons will be absorbed and electron and hole pairs will be created.
In 1995, Binbin Hu and Martin Nuss at Lucent Technologies’ Bell Laboratories created a terahertz imaging system and coined the term T-ray for these short, broadband terahertz pulses.
A split antenna is fabricated on a semiconductor substrate to create a switch (see Fig. 2). A dc bias is placed across the 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 vol 9 issue 4 March 2011
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laser pulse combination allows electrons to rapidly jump the gap, and the resulting current in the antenna produces a terahertz electromagnetic wave. This radiation is collected and collimated with an appropriate optical system to produce a beam. This switch generates a train of pulses, whose repetition frequency is the same as that of the femtosecond pump laser. Pulse widths are on the order of 100 fs, with average powers of a few microwatts and a frequency spread of >500 GHz. The pulse bandwidth 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 and pump-laser power, pulse width, and configuration. Coherent THz wave signals are detected in the time domain by mapping the transient of the electric field in amplitude and phase. This gives access to absorption and dispersion spectroscopy. The terahertz pulse is distorted by selective absorption as it passes through a sample, causing delays in its arrival time at the detector. The transmitted beam is then focused onto a detector, which is essentially identical to the emitter except that it is unbiased. By varying the time at which the sample pump pulse arrives at the detector, successive portions of the terahertz pulses can be detected and built into a complete image of the pulse in terms of its delay time, or time domain. The data are then processed by fast Fourier transform analysis in order to convert the delay time into the frequency of the terahertz signal that arrives at the detector. Continuous wave (CW) THz systems are preferred when spectral resolution is the primary concern, e.g., to study sharp absorption lines of gases. In contrast to pulsed THz systems, no femtosecond lasers are required. As shown in the Fig. 3, the output of two frequency stabilized laser diodes is spatially overlapped in a beam combiner and focused onto a photoconductive antenna (PCA) with an optimized electrode geometry. Instead of the ultrafast carrier dynamics employed in the pulsed case, mixing of the two incident waves is exploited to generate a continuous THz wave, which oscillates with the difference frequency of the two incoming waves. By detuning one of the laser diodes, the emission frequency can be swept in a wide spectral range. A second PCA is employed for coherent sampling of the incoming THz radiation. Even though pulsed systems are decreasing in price, CW systems are still less expensive and feature a frequency resolution down to 2MHz. APPLICATIONS THz offers a non-invasive, non-contact, non-ionizing method of assessing composite part condition and could
Fig. 4 : THz images resolving 0.4 mm fibre, 0.25 mm mass and 0.24 mm specks from a phantom.
Fig. 5 : A THz image and a photograph of an air-bag cover made of a low-absorbing polymer. All elements that are visible in the photograph can also be easily resolved in the THz image, including ribs, edges, paper stickers marked with (1) or even slightly thicker regions marked with (2), which are merely seen in the photograph.
overcome some of the short-comings of other nondestructive techniques such as x-rays, ultrasound, video inspection, eddy currents, and thermographic techniques. With wavelengths in the sub-millimeter domain, high resolution THz imaging extending to micron range appears feasible. Since most polymers are transparent to T-rays, nondestructive testing in the plastics industry appears to be a very promising commercial application. This includes the in-line monitoring of polymeric compounding processes and flaw detection, as well as a 100% quality control inspection of plastic parts manufactured by injection molding. THz can penetrate glass fiber without contacting it, with submillimeter resolution, and can detect surface defects, hidden voids, delaminations, and bending damage in composites. Additionally, it can also be used to evaluate whether the aircraft composite has been chemically altered from engine burn damage by measurement of its index of refraction and absorption coefficient spectrum. The absorption coefficient for liquid water is as high as 150 cmâ&#x20AC;?1 at 1 THz. This strong absorption limits the sensing and imaging in water-rich samples for most terahertz applications and prohibits transmission-mode imaging through a thick tissue. However, THz wave
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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 image on the left shows a good quality tablet. The second and third images on the right show tablets with integrity problems.
Fig. 6 : Examples of THz imaging of tablet characteristics (from http://www.teraview.com/terahertz/)
transmission changes of 1% have been demonstrated so much so that absorption even by minute amounts of water or small changes in water concentration can be reliably detected. As physical and mechanical properties of polymers are severely influenced by its water content, THz sensing appears promising. Perhaps the greatest potential for new applications lies in the strong spectral dependence of the interaction with materials, where resonant absorption by the molecular structure of targets provides information on their composition, and hence the target identity, not readily available by other remote sensing methods. Terahertz imaging applications in pharmaceuticals, particularly in characterizing tablet integrity, enteric coating parameters, adhesion quality between the layers in the tablet core, tablet dissolution rates have begun on a commercial basis. Transform-limited pulses with terahertz bandwidth have durations <1ps, and corresponding pulse lengths of <0.3mm, so terahertz radar is capable of probing the
detailed structure of multi-component targets on a submillimetre scale while being able to distinguish between materials in terms of the spectral dependence of dielectric constant or absorption. Weapons or personnel can be detected through camouflage or thin foliage, and targets can be discriminated from background on the basis of spectral response. There is also scope for the detection, identification and tracking of chemical and biological weapons in the atmosphere. Unique THz chemical signatures of war gases due to rotational spectral lines, and phonon excitations of biological warfare agents can be detected in the low-THz range by high-resolution spectroscopy. While state-of-the-art quality control systems can easily detect metallic contaminations in food products, nonmetallic contaminations are often hard to find. Existing approaches, such as ultrasonic or x-ray scans, fail when the density difference or the dielectric contrast between the material and the contamination is low. As THz scans consider not only the absorption spectrum but also the phase information due to the underlying coherent emission and detection scheme, many parameters can be employed for the identification of undesired inclusions. RECENT TRENDS
Fig. 7 : Near-field THz imaging showing enhanced lateral resolution. vol 9 issue 4 March 2011
An alternative to using photoconductive switches or semiconductor surfaces has been to employ noncentrosymmetric nonlinear optical crystals. This approach offers both controllability of the spectrum and amplitude of the emitted THz pulses by varying experimental parameters, such as the wavelength and duration of the generating laser pulse, and crystal thickness. DAST (4N, N-dimethylamino-4â&#x20AC;&#x2122;-Nâ&#x20AC;&#x2122;-methyl stilbazolium tosylate) is a well-known organic optical crystal with low dielectric
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Los Alamos National Laboratory and Boston University (see Fig. 8). Metamaterials are composites, engineered on the micron-scale, that use unique metallic contours in order to produce responses to light waves, giving each metamaterial its own unique properties beyond the elements of the actual materials in use. The team incorporated semiconducting materials in critical regions of tiny elements – in this case metallic split-ring resonators – that interact with light in order to tune metamaterials beyond their fixed point on the electromagnetic spectrum that allowed them to tune terahertz resonance across a range of frequencies in the far-infrared spectrum. One recent enabling technology is that of the T-ray transceiver. This technique utilizes the reciprocal relationship between optical rectification and electrooptic detection to allow a single ZnTe crystal for both emission and detection of THz pulses. In principle, such a transceiver could be made as small as 1 mm2 and mounted at the end of an optical fibre for endoscopic applications. There is no doubt that THz wave imaging is an attractive technique with enormous potential in military and biomedical applications on the one hand and in inspecting plastic and composite materials on the other. It has a number of important advantages over competing techniques that may give rise to a number of niche applications. Fig. 8 : Scanning electron microscopy (SEM) images of the frequency-tunable planar metamaterial. An individual unit cell (a), and periodically patterned square array (b). All dimensions are shown in microns and materials are indicated in the images. The polarization of the incident linearly-polarized THz radiation is also indicated in (b). Source URL: http://www.sciencedaily.com /releases/2008/ 04/080415185016.htm
constant and high nonlinear response. In such a noncentrosymmetric nonlinear optical material, an ultrashort laser pulse (< 150 fs) induces a quasistatic polarization, which follows in time the amplitude of the pump pulse and thus acts as a source for the THz pulse. A tunable metamaterial that can be used over a range of frequencies in the so-called “terahertz gap” has been engineered by a team of researchers from Boston College,
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 terahertz pulses through optical rectification in organic DAST crystals: theory and 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 using transmissive terahertz time domain spectroscopy, Optics Express 16 (2008) 170039- 170051 Rafal Wilk et al., Continuous wave terahertz spectrometer as a noncontact thickness measuring device, Applied Optics 47 (2008) 3023-3026 Christian Jansen et al, Terahertz imaging: applications and perspectives, Applied Optics 49 (2010) E48 – E57
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A new feature in the Journal of NDT & E
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ndt puzzle Starting from this issue, we are introducing a new section “ NDT Puzzle”, which will stimulate your brain cells, help spend some time usefully and of course enhance your knowledge. And what is more ! You will get paid for having FUN by way of attractive prizes !! To start with we have for you a ‘Word Search Puzzle’. We hope you will find this section interesting, educative and fun filled. In the forthcoming issues, you can expect Crosswords, Anagrams, and more. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com
Conceptualized & Created by Dr. M.T. Shyamsunder, GE Global Research, Bangalore
Introduction The “Word Search Puzzle”, contains fifty (50) words related to Nondestructive Testing. These include techniques, terminologies, phenomenon, famous people, etc. These words are hidden in the puzzle and may be present horizontally, vertically, diagonally in a forward or reverse manner but always in a straight line. Instructions All you have to do is identify these words and mark them on the puzzle with a black pen -Preferably you may take a photocopy of the Puzzle sheet and mark your
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answers on that (see the marked example) -Once completed please scan your answered puzzle sheet as a PDF file and email the scanned sheet to jndte.isnt@gmail.com with your name, organization, contact number and email address Rules & Regulations -Only one submission per person is allowed -The marked answers should be legible and clear without any scratching or overwriting -The decision of the Editor-in-Chief, Journal of NDT &E is final and binding in all matters -First three correct entries will receive suitable rewards and will be announced in next issue.
PHONE
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NDT WORDSEARCH - 1
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IQ forum Problem: 03-2011
Absence of Back-wall echo
“To establish a connect between the Researchers and Practitioners in NDE, this new forum INDUSTRIAL QUERY (IQ) FORUM is being created in our journal.
Posted by: Prof. O. Prabhakar
We wish to bring together the underlying scientific principles, engineering and technological aspects and the most probable solutions for a NDT problem posed by our readers and members.”
Casting: The steel casting, weighing about 15 tonnes, was made in two segments and welded together. Later the casting was cleaned, fettled and normalized. Subsequently, PT and UT were done as shown in Fig. 1.
If you are in the industry and have a IQ, send an MSWord document with associated drawings to jndte.isnt@gmail.com with subject title “IQ Problem” for consideration for publication in a future issue. Also include any attempts at solving this problem.
Industry: Steel Foundry
Ultrasonic Testing: No clear flaw echo was obtained during UT of the weld and near the welded portions. Also, the back-wall echo was absent in the casting near weld portions. UT was done with a normal probe in both the directions as shown in the Fig. 2. The 2/4 MHz probes with a large diameter were employed. The problem posed was why the back-wall echo was absent.
If you have a suggestion or solution for this, issue of IQ, please send it to jndte.isnt@gmail.com with subject title “IQ Solution- 03-2011” along with your contact information. Selected responses will be published in the June 2011 issue. All responses will be forwarded to the person posing the IQ. “Readers are welcome to contribute their own experiences in this kind of problems. ISNT would select the best answer for a possible reward.” -Prof. O. Prabhakar -Prof. Krishnan Balasubramaniam
Fig. 1 : PT being done on the actual casting.
Solution I: Usually cast structure shows coarse grains and a good normalizing treatment is essential before UT is carried out. In addition if the cooling rate is very high during heat treatment, structure would show Widmanstaetten structure which would also hinder UT. So the first suggestion given was to repeat the Normalizing heat treatment. Result: UT results did not improve. Still the back-wall echo was absent. Solution II: A small portion was cut out near the weld zone and metallographically studied. The specimen was found to have numerous small tight cracks, which on separation showed silver foil appearance. This is typical of hydrogen cracking. CONCLUSION: Steel castings are prone to hydrogen embrittlement due to pick up of hydrogen either during casting or welding. This would result in poor fracture toughness. When this material is subjected to residual stresses, hairline cracks would appear. This is a very dangerous situation that could lead to catastrophic failure in service. In this case, the welding process provided the required stresses and the hydrogen was picked up either during casting or welding. Hence absence of back-wall echo is a serious indication and should be further probed.
Fig. 2 : Steel Casting Journal of Non Destructive Testing & Evaluation
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A new feature in the Journal of NDT&E
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NDE events
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 such as 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 mandayam.shyamsunder@gmail.com
MARCH 2011
Annual Conference and Exhibition of the French Society for NDT (COFREND) - May 24 to 27, 2011, Dunkirk, France
16th International Workshop on Electromagnetic NDE (ENDE 2011) -March 10 â&#x20AC;&#x201C; 12, 2011 ; IIT, Madras, Chennai,INDIA
http://www.cofrend.com/2011/
http://www.igcar.gov.in/seminars/
JUNE 2011
ASNT Annual Research Symposium & Spring Conference -March 21 â&#x20AC;&#x201C; 25, 2011 ; San Francisco, USA
International Chemical and Petroleum Industry Inspection Technology XII Conference - June 8-11, 2011 ; Houston, Texas, USA
http://www.asnt.org/events/conferences/sc11/sc11.htm 10th International Exhibition and Conference for Non-Destructive Testing and Technical Diagnostics March 22 to 14, 2011 ; Moscow, Russia http://ndt-russia.primexpo.com/
http://www.asnt.org/events/conferences/icpiit/ abstracts.pdf 12th Int. Symposium on Nondestructive Characterization of Materials (NDCM-XII) - June 19 to 24, 2011 ; Blacksburg, VA, USA
APRIL 2011
http://www.cpe.vt.edu/NDCM-XII/
12th National NDT Conference and Exhibition DEFEKTOSKOPIA 2011 - April 5 to 7, 2011 ; Slovakia
International symposium on Digital Industrial Radiology and Computed Tomography - June 20 to 22, 2011 ; Berlin, Germany
http://www.defektoskopia.eu
http://www.dir2011.com/
BINDT Aerospace Forum 2011 April 13-14, 2011 ; Bristol, UK h t t p : / / w w w. b i n d t . o rg / E v e n t s / NDT_Conferences_&_Seminars/ BINDT_Aerospace_Forum_2011 24 th Brazilian National Congress on NDT and Inspection - May 10 to 13, 2011 ; Brazil http://www.abende.org.br
The Eighth International Conference on Condition Monitoring and Machinery Failure Prevention Technologies - 20-22 June 2011 ; Cardiff, UK h t t p : / / w w w. b i n d t . o rg / E v e n t s / CM_Conferences_&_Seminars/ CM_2011_and_MFPT_2011 JULY 2011 38th Annual Review of progress in Quantitative NDE July 17 to 22, 2011 ; Burlington, VT, USA
MAY 2011 NDTMS 2011 International Symposium on NDT of Materials & Structures - May 15 to 18, 2011 ; Istanbul, Turkey
http://www.qndeprograms.org/2011/Conference2011.html
http://www.ndtms.itu.edu.tr/0.2/
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“WCAE-2011” World Conference on Acoustic Emission–2011 Beijing (WCAE-2011) is organized by the Chinese Society for Nondestructive Testing (ChSNDT) and undertaken by Technical Committee on Acoustic Emission of ChSNDT (TCAE). Conference Date Venue
August 24 to 26, 2011 Beijing International Convention Center and Beijing Continental Grand Hotel No.8 Beichen Dong Road, Chaoyang District, Beijing 100101, P.R. China Room Reservations: Tel: ++86-10-84980105 ; Fax: ++86-10-84970106 E-mail: bcgh@bcghotel.com Website: www.bcghotel.com ; www.bicc.com.cn
Call for Papers
The papers are sought in all areas related to acoustic emission such as follows: z AE signal detection and processing z AE behavior of materials z AE in pressure equipment z AE in structures z AE in civil engineering and geology z AE in transportation engineering z AE in condition monitoring and diagnosis for mechanics z AE in medical science z AE standardization z AE instrument and new developments z AE and applications in other fields
Key Dates
Abstract submission April 30, 2011 Notification of acceptance May 15, 2011 Submission of full papers June 30, 2011 Registrationf and payment of registration fee July 15, 2011 Registration Fees (including: Welcome Party, Welcome Dinner and three Lunches) General: 450 US$ ; Student: 300 US$
Contact
Conference-secretariat and Mailing Address Mr. Zhanwen Wu, WCAE-2011 Secretariat China Special Equipment Inspection and Research Institute Building 2, Xiyuan, Hepingjie, Chaoyang District, Beijing 100013, China Email:wcae2011@vip.csei.org.cn
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Managing Editor Journal of Non Destructive Testing & Evaluation Modules 60 & 61, Readymade Garment Complex, Guindy, Chennai 600032 Phone: (044) 2250 0412 vol 9 issue 4 March 2011
Journal of Non Destructive Testing & Evaluation
29
NDE P A T E N T S
Compiled by Dr. M.T. Shyamsunder GE Global Research, Bangalore
We hope that the inaugural section on NDE Patents, which featured in the December 2010 issue of this journal, has triggered your thoughts and has provided enough motivation to consider patenting your ideas. We continue this section with a few more facts on patents and a listing of a few selected NDE patents. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com
In this issue, we will take our discussion forward on Patents and the different aspects and elements of it with a few more points of relevance. A patent provides protection for the invention to the owner of the patent. The protection is granted for a limited period, generally 20 years. Patent protection means that the invention cannot be commercially made, used, distributed or sold without the patent ownerâ&#x20AC;&#x2122;s consent. These patent rights are usually enforced in a court, which, in most systems, holds the authority to stop patent infringement. Conversely, a court can also declare a patent invalid upon a successful challenge by a third party. A patent owner has the right to decide who may - or may not - use the patented invention for the period in which the invention is protected. The patent owner may give permission to, or license, other parties to use the invention on mutually agreed terms. The owner may also sell the right to the invention to someone else, who will then become the new owner of the patent. Once a patent expires, the protection ends, and an invention enters the public domain, that is, the owner no longer holds exclusive rights to the invention, which becomes available to commercial exploitation by others. Patents provide incentives to individuals by offering them recognition for their creativity and material reward for their marketable inventions. These
incentives encourage innovation, which assures that the quality of human life is continuously enhanced. Patented inventions have, in fact, pervaded every aspect of human life, from electric lighting (patents held by Edison and Swan) and plastic (patents held by Baekeland), to ballpoint pens (patents held by Biro) and microprocessors (patents held by Intel, for example). All patent owners are obliged, in return for patent protection, to publicly disclose information on their invention in order to enrich the total body of technical knowledge in the world. Such an ever-increasing body of public knowledge promotes further creativity and innovation in others. In this way, patents provide not only protection for the owner but valuable information and inspiration for future generations of researchers and inventors [Source : http:// www.wipo.int] Listed below are a few selected patents in the area of Ultrasonic Testing, which were issued by USPTO in 2010. If any of the patents are of interest to you, a complete copy of the patent including claims and drawings may be accessed at http://ep.espacenet.com/ UNITED STATES PATENT 7,650,790
Method of inspecting a component and an apparatus for inspecting a component Inventors: Wright David C
Assignee: Rolls-Royce (London, GB)
PLC
Abstract : An apparatus for ultrasonically inspecting a component comprises a first ultrasonic transducer for transmitting an ultrasonic signal into a component having rotational symmetry and a second ultrasonic transducer for detecting the reflected, or transmitted, ultrasonic signal. A motor and a turntable produce relative rotation between the rotationally symmetrical component and the first and second transducers. Motors, a carriage and tracks on a frame provide relative radial motion between the rotationally symmetrical component and the first and second transducers to scan the whole of a surface of the rotationally symmetrical component. An ultrasonic signal analyzer analyses the detected ultrasonic signal by monitoring for ultrasonic signals having an amplitude above a predetermined amplitude and not having rotational symmetry and a display provides an indication that any detected ultrasonic signals above the predetermined amplitude and not having rotational symmetry is a potential flaw in the component. UNITED STATES PATENT 7,647,829
Steam generator nondestructive examination method Inventors: Junker Warren R., Lareau John P.
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vol 9 issue 4 March 2011
30 Products & Patents
Assignee: Westinghouse Electric Co. LLC (Cranberry Township, PA, USA) Abstract : A method of examining a steam generator heat exchange tube from the outside surface employing ultrasonic nondestructive inspection techniques. An ultrasonic transducer contacts the outside surface of the tube and transmits a pseudo helical Lamb wave into the wall of the tube chosen to have a mode that does not significantly interact with water in the tube. The reflected waves are then analyzed for changes in modes to identify defects in the wall of the tube. UNITED STATES PATENT 7,644,618
Apparatus and method for nondestructive inspection of parts Inventors: Fetzer Barry A, Walters William O., Bui Hien T. Assignee: The Boeing Company (Chicago, IL, USA) Abstract : A method of inspecting a radius area of composite parts with an ultrasonic inspection system, the system includes at least one ultrasonic probe, an upper sliding surface, a lower sliding surface, an adjustable guide rail, and an adjustable encoder wheel rotatable coupled to a rotary encoder, is provided. The method includes generating a high frequency sound wave using the probe including a radius of curvature extending from a center point, the sound wave travels partially through the part, adjusting the guide rail to align the center point of the probe with a center axis of a part corner portion, sliding the part through the inspection system to inspect the corner portion using the sound wave by rotating the wheel and rotary encoder such that the accurate distance of the part is recorded, adjusting the wheel to avoid any apertures defined within the part, and vol 9 issue 4 March 2011
processing information.
the
sound
wave
UNITED STATES PATENT 7,640,810
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 inspecting a structure are provided that use a pedestal robot mounted on a rail system, a probe extension coupler, and an inspection probe capable of performing pulse echo ultrasonic inspection. A probe may also include sled appendages and an axial braking system to inspect over holes and off edges. A probe may also include an ultrasonic pulse echo transducer array for high rate inspection; the transducer array may be mounted in a bubbler shoe for individually coupling each of the transducers in the array. A rail system may also include an optical encoder for providing location information for the robot and axial braking system. A probe extension coupler presses the inspection probe against the structure for adjusting to changes in surface contours. UNITED STATES PATENT 7,640,809
Spot welding inspecting apparatus Inventors: Shibata Kaoru, Shigematsu Noriaki, Igaue Mitsutaka, Kurimoto Noriko Assignee: Honda Motor Co., Ltd. (Tokyo, Japan) Abstract : A spot welding inspecting apparatus is provided with: a gun chip; a signal transmitting part; an ultrasonic sensor; an inner cylinder; a through hole; a partitioning cylinder; a first flow path; a second
Journal of Non Destructive Testing & Evaluation
flow path; and a third flow path. The inner cylinder is inserted to an outer cylinder of spot welding gun and holds the ultrasonic sensor. The through hole is provided on the inner cylinder. The partitioning cylinder surrounds the through hole and is inserted into a gap between the ultrasonic sensor and the outer cylinder. The first flow path is formed between the inner cylinder and the partitioning cylinder by passing the through hole from an inner portion of the inner cylinder. The second flow path is formed at the gun chip to be circulated around a front end of the partitioning cylinder. The third flow path is formed between the outer cylinder and the partitioning cylinder. A cooling agent flows in an order of the first flow path, the second flow path and the third flow path. UNITED ST ATES PA TENT STA PATENT 7,849,748
Method of and an apparatus for in situ ultrasonic rail inspection of a railroad rail Inventors:
Havira Robert Mark
Assignee: Sperry Rail, Inc. (Danbury, CT, USA) Abstract : An ultrasonic railroad rail inspection system, apparatus and method for in situ rail inspection including a wheel assembly containing a fluid-filled tire and an ultrasonic transducer mounted within the wheel assembly. The transducer is supported in the tire such that the ultrasonic beam generated by the transducer has a beam axis that intersects a head of a railroad rail at a position offset from the longitudinal median plane of the rail to the side of the head penetrated by the ultrasonic beam. The ultrasonic beam is reflected by flaws in the rail in the form of echoes. The echoes return to the transducer identifying the location of flaws.
31 UNITED STATES PATENT 7,841,237
Ultrasonic testing apparatus for turbine forks and method thereof Inventors: Suzuki Yutaka, Koike Masahiro, Matsui Tetsuya, Kodaira Kojirou, Isaka Katsumi, Odakura Mitsuru, Tayama Kenji, Suzuki Kazuhiro, Kumasaka Kenji, Adachi Yuuji Assignee: Hitachi, Ltd. (Tokyo, Japan) Hitachi Engineering & Services Co., Ltd. (Ibaraki, Japan) Abstract : An ultrasonic testing apparatus for a turbine fork of a turbine blade joined to a turbine disc, comprising: an ultrasonic testing sensor; a sensor mounting apparatus for mounting the ultrasonic testing sensor on a flat portion on a side surface of the turbine fork with the turbine blade joined to the turbine disc; and an ultrasonic testing apparatus for inspecting internal and external surfaces of the turbine fork by using reflected waves, which is received by the ultrasonic testing sensor, from the internal surface of the turbine fork. UNITED STATES PATENT 7,823,454
Ultrasonic inspection method Inventors: MacLauchlan Daniel T., Cox Bradley E. Assignee: Babcock & Wilcox Technical Services Group, Inc. (Lynchburg, VA, USA) Abstract : A method for ultrasonically inspecting components with wavy or uneven surfaces. A multi-element array ultrasonic transducer is operated with a substantial fluid layer, such as water, between the array transducer and the component surface. This fluid layer may be maintained by immersing the component in liquid or by using a captive couplant column between the probe and the component surface. The component is scanned, measuring the two dimensional
surface profile using either a mechanical stylus, laser, or ultrasonic technique. Once an accurate surface profile of the componentâ&#x20AC;&#x2122;s surface has been obtained, data processing parameters are calculated for processing the ultrasonic signals reflected from the interior of the component that eliminate beam distortion effects and reflector mislocation that would otherwise occur due to the uneven surfaces. UNITED STATES PATENT 7,817,843
Manufacturing process or in service defects acoustic imaging using sensor array Inventors: Senibi Simon D, Banks David L, Carrell Chris K, Curry Mark A Assignee: The Boeing Company (Chicago, IL, USA) Abstract : A mobile platform is provided which has at least one component having an array of distributed piezoelectric transmitters and an associated array of distributed receivers. The receivers are configured to receive ultrasonic transmissions from the transmitters. Data from the receivers is stored in memory and processed through an algebraic reconstruction tomography algorithm which forms an image of the defect within the component. An algorithm is used to determine the position and size of the defect. UNITED STATES PATENT 7,798,000
Non-destructive imaging, characterization or measurement of thin items using laser-generated lamb waves Inventors: Murray Todd W., Prada Claire, Balogun Oluwaseyi Assignee: Trustees of Boston University (Boston, MA, USA) Abstract : A laser-based ultrasonic technique for the inspection of thin plates and membranes employs an amplitude-modulated laser source to
excite narrow bandwidth Lamb waves. The dominant feature in the acoustic spectrum is a sharp resonance peak that occurs at the minimum frequency of the first-order symmetric Lamb mode, where the group velocity of the Lamb wave goes to zero while the phase velocity remains finite. Experimental results with the laser source and receiver on epicenter demonstrate that the zero group velocity resonance generated with a low power modulated excitation source can be detected using an optical probe such as a Michelson interferometer coupled to a lock-in amplifier. This resonance peak is sensitive to the thickness and mechanical properties of plates and may be suitable, for example, for the measurement and mapping of nanoscale thickness variations. UNITED STATES PATENT 7,783,433
Automated defect detection of corrosion or cracks using SAFT processed Lamb wave images Inventors: Gordon Grant A., Hedl, Radek Assignee: Honeywell International Inc. (Morristown, NJ, USA) Abstract : A system, method and computer program product is provided for automated defect detection of corrosion or cracks using synthetic aperture focusing technique (SAFT) processed Lamb wave images. The method comprises processing the first image using a synthetic aperture focusing technique (SAFT) to enhance a resolution and a signal to noise ratio of a first extracted ultrasonic image, applying a systemic background noise suppression algorithm to the first extracted ultrasonic image to render a second extracted ultrasonic image having reduced noise, and applying a deconvolution linear filtering process to the second extracted ultrasonic image to render a third extracted ultrasonic image.
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Technical Paper
Fatigue Crack Growth Monitoring in Ti-6Al-4V Alloy Using Acoustic Emission Technique and Digital Image Correlation Shivanand Bhavikatti, M R Bhat and CRL Murthy Department of Aerospace Engineering, Indian Institute of Science, Bangalore, INDIA E-mail : bkatti@aero.iisc.ernet.in
ABSTRACT Crack growth due to fatigue loading can be monitored using the accurate measurement of surface displacement and hence strains during deformation using Digital image correlation (DIC). While other techniques require point-by-point scanning over the area to be tested for the object, a whole field strain measurement can be made in one go both inside as also on the surface of the specimens by DIC. Thus, DIC could provide less expensive and fast testing technique for crack propagation. DIC works by measuring stain by interfering a reference image with images taken at different loads from the surface of the structure. Through the study presented in this paper an attempt is made to establish correlation between Acoustic Emission Data and strain measured by DIC for detecting crack initiation and monitoring its propagation for prediction of failure of a structural component under fatigue loading. Experiments have been carried out on a set of Ti-6Al-4V alloy specimens subjected to constant amplitude fatigue loading with continuous AE monitoring. The results obtained show that DIC can be a reliable off-line tool to validate AE data for establishment of the technique. Thus, the objective of experiments has been to identify and validate genuine AE signals due to fatigue damage and characterize them to identify progressive stages leading to the final failure.
1. INTRODUCTION Fatigue tests typically require long testing times. This is due to periodic interruption of the fatigue test to manually measure crack lengths which can be avoided by using DIC where in the measurements are made without interrupting the test. Recently several researchers reported the use of DIC for transient fracture [1]. The use of highspeed and high resolution cameras, thus, enables new possibilities for DIC testing. The idea behind the method is to measure the displacement of the material under test by tracking the deformation through painted spots applied to the component’s surface and obtain the speckle patterns from digital images acquired during loading. Over the past few decades acoustic emission (AE) monitoring has been explored as an effective nondestructive technique for the detection, location and monitoring of active defects and dynamic processes in a variety of structures including full scale tests of airframes, petro chemical components and civil structures. This method has enormous potential as a tool for structural integrity evaluation, extraction of useful information from complex data which include various extraneous noise is a real challenge [2,3]. AE technique is based upon the detection of elastic waves generated when a material undergoes plastic deformation and/or cracking during which rapid release of energy from a localized source within a stressed material occurs[4,5]. These transient elastic waves can be detected by highly sensitive piezoelectric sensors. While the sources of interest of acoustic emission are defect related processes such as crack propagation and plastic deformation of material, background Journal of Non destructive Testing & Evaluation
noises that normally exist in laboratory environment and field conditions pose a major problem for extraction of true AE activity. AET has very attractive advantages such as the capability to not only detect active microscopic and macroscopic failure mechanisms but also to obtain the location of these energy releasing sources in a larger structural components without scanning the entire component surface[6]. These are the features which still lure the structural engineers to try the technique to study the complex fatigue and fracture phenomena in critical structural components in different engineering fields. Thus, this attempt is to utilize the AET as an on-line monitoring tool to study the fatigue crack initiation and propagation in Titanium alloy extensively used in aerospace structural components.
2.
EXPERIMENTS
Fatigue tests were carried out on Ti-6Al-4V alloy choosing three point bend as test configuration; geometrical dimensions of specimen are shown in Fig. 1. Specimen preparation includes scribing of graduated scale on the surface to facilitate crack length measurements in increments of 1mm from notch to 50% of the depth of crack propagation in the specimen. A high speed camera with 12 megapixel is used to take the snaps for DIC. Fatigue tests were carried out using INSTRON-1341 configured with ± 100 KN capacity, ± 50 mm stroke, computer controlled servo hydraulic dynamic testing machine. Fatigue test parameters were also chosen based on the preliminary tests carried out in the laboratory, loading frequency of 18 Hz, amplitude range of 7kN-1.4kN with Vol. 9, Issue 4 March 2011
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Technical Paper
characteristics of signal are later used as inputs to the system which establishes location of active AE source and its characteristics.
3. RESULTS AND DISCUSSION
Fig. 1 : Schematic Three point bend Ti-6Al-4V Specimen, dimensions in mm
stress ratio of 0.2 is maintained for all the samples[7]. A 10 X magnification lens was used to trace the crack growth to the subsequent divisions. Acoustic emission data from all the test specimens was continuously acquired and recorded using multi-channel acoustic emission monitoring system with sensors, associated preamplifiers and accessories. Two peak resonant type acoustic emission sensors with highest sensitivity around 300kHz were used in the linear location mode for detection for AE events due to crack initiation and propagation in the specimen. The sensors were bonded to the specimen surface using adhesive tape with high vacuum silicon grease as the couplant interface between the sensor and the specimen surface. Preamplifiers with 40 dB fixed gain and a band pass filter in the range of 200- 400 KHz were used along with the AE sensors. Acoustic emission data measured and recorded includes hits (emission detected by a single sensor), events (emissions detected and located by two sensors), energy, time of the event, rise time, parameter (load), duration and amplitude throughout the experiment. Through a set of preliminary tests, threshold of 55dB was found to be optimum under laboratory test environment. AE sensors have been bonded on the specimen to locate crack initiation and propagation. Notched sample is preferred as it is obvious that the crack initiation has to take place from the high stressed zone at the notch tip. The emphasis has been on AE signal generated from this region. Non-metallic liners with a combination of Glass Fiber Reinforced Plastic and Teflon film were used as contact interfaces in between loading points and the specimen surface to avoid noise generated due to friction being picked by the sensors. The AE monitoring system was calibrated for linear location of AE source by breaking a 2H, 0.5-mm-diameter pencil lead at each side of the center notch. The method of using a pencil lead break to calibrate AE transducer and system sensitivities is detailed in ASTM E 647â&#x20AC;&#x201C;05 [8], Standard Guide for Determining the Reproducibility of Acoustic Emission Sensor Response. Breaking pencil lead at tip of the notch generates pulse signal that is similar to AE signal generated during crack growth. AE monitoring system records signal arrival time, parameters and calculate the difference of arrival time Î&#x201D;t, between the two sensors. Obtained Î&#x201D;t value and other Vol. 9, Issue 4 March 2011
Figure 2(a) shows the overall distribution of the AE activity recorded during the fatigue tests. It is clearly seen in Fig2(a) that majority of AE events were generated in the notched region. Cumulative AE activity in this region with reference to number of applied fatigue cycles is presented in Fig. 2(b) and the clear change in slope corresponding to the initiation of crack at the notch tip can be observed. This is verified with optical aid. Significant rise in AE activity during crack initiation is observed in all the samples tested. Eventually once crack is initiated, crack propagation enters stable crack growth stage, here AE activity exhibits reduced emission rate. Loading was stopped when crack propagated 50% of the depth. AE data at crack initiation and at crack propagation for each specimen was analyzed and the AE profile for crack initiation phase was discriminated from the complete AE data profile in the play back mode. This was done primarily on the basis of the cumulative count plot against the time scale (indirectly reflecting the load cycles by multiplying with the corresponding load cycle frequency). Time domain parameter analysis of AE Signals in correlation to fatigue process
Fig. 2 : Distribution of AE (a) Events Vs location (b) Cumulative Counts Vs Time Journal of Non destructive Testing & Evaluation
44 Figure 2(b) shows Cumulative counts vs Time, from this graph it can be observed that crack was initiated very much prior to visual observation. Crack initiation was observed visually at around 1300 sec. Considering time, crack was actually initiated at around 300 sec to 1100 sec. So it is necessary to find out at which point crack has started. While the detection of crack initiation and identification of stable crack growth was possible through simple approach of monitoring overall AE activity generated with reference to number of fatigue load cycles applied. Further signal analysis revealed advanced information in terms of characteristic signatures of AE in these stages. It is clearly evident from Fig. 2(b) that crack initiated at the centre of notch along the width is well in advance compared to initiation observed on surface, which can be substantially explained referring to Fig. 3(a) and Fig. 3(b). Experiments were conducted using identical set of samples to verify crack observed on surface of the specimen applying fatigue load. Fig. 3(a) shows truncated specimen in which crack initiation was observed and three points namely a, b, and c are marked. Significance of a, b and c are as follows. As can be seen from Fig.3(b), crack first initiates at â&#x20AC;&#x2DC;aâ&#x20AC;&#x2122; due to plain strain condition and extends
Technical Paper
within the thickness until it reaches the surface at points b and c which can be observed from the width of the crack at the points a, b and c. Digital Image Correlation (DIC)
Digital image correlation (DIC), sometimes called electronic speckle photography, digital image processing was used to solve the crack identification problem. A DIC software VIC2D from Correlated Solutions[9] has been used for obtaining the strain change on the surface specimen through speckle interferometry. The camera was positioned approximately 500 mm from the three point bend specimen in the loading position as shown in Fig. 4, perpendicular to facing the specimen. The camera was carefully focused and Images have been obtained and analyzed using VIC2D software. By using this technique full field measurements made on the specimen can be analyzed. Images were taken after every 150 cycles over the full test and the data thus recorded has been analyzed using VIC2D. Once calibrated, the DIC software is able to calculate the displacement field of a specimen at any point during loading with a corresponding image. A strain field is obtained by differentiation of the associated displacement field. The
Fig. 4 : Schematic of Digital Image correlation
displacement field is calculated by comparing the loaded and reference images. The amount of crack growth between any two intervals of 150 cycles loading points was determined by the shift between their associated strain fields in front of the crack tip by displacement vector.
Fig. 3 : (a) Fatigue Crack Initiation as observed on the Surface of the Specimen, (b) Distribution of AE Cumulative Counts Vs Time before Crack propagation Journal of Non destructive Testing & Evaluation
Mathematically, this is accomplished by finding the region in a deformed image that maximizes the normalized crosscorrelation co-efficient with regard to a small subset of the images taken while no load was applied. By repeating this process for a large number of subsets, full-field deformation data can be obtained. The DIC method does not require the use of lasers and the specimen can be illuminated 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 the specimen before the test. Among the many methods for Vol. 9, Issue 4 March 2011
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Technical Paper
(a)
(b)
Fig. 5 : DIC (a) Strain in specimen at crack tip (b) enlarged view of crack Tip Fig. 7 : Strin vs. No of Cycles using DIC
(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 crack tip
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 base image with the unloaded specimen was selected. Using the software tool, a quadrilateral area of interest was chosen on the specimen in order to reduce computation time and define the region to be analyzed. Finally, the rest of images of the specimen over the entire loading sequence, called the deformed images, were selected for comparison with the base image for calculation of each of their respective strain fields which can be seen in Fig. 5(a) near the crack tip. 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 interval of 10000 cycles can be observed. i.e. the plastic zone after 10000 cycles is almost nil, and after 40000 cycles itâ&#x20AC;&#x2122;s about 1mm along the loading direction. As we are interested in plastic zone ahead of the crack tip which can be precisely measured with DIC Technique. With this Fig. 6 (d) clearly shows a high strain in at the notch compared to other images and it has been observed manually the crack has initiated on the surface. From this it is evident that crack tip strains increased after some number of cycles leading to crack initiation. The DIC tools, such as Correli-Q4 [10,11,12] that are used here, are more effective when the images are made of random patterns. At the macroscopic level, one can use Vol. 9, Issue 4 March 2011
painting in order to add an artificial speckle to the surface of the specimen to find displacement. A number of strain plotting tools are available in the VIC-2D software. One was a line-plotter, which plots the values of strain for a selected line on the base image for all of the deformed images as shown in Fig. 7- Strain Vs No of Cycles. Here strain are less than 300 micro strain before the crack starts and once the crack starts it is of the order of 500 micro strains or more. The plot shows sudden change in strain at about 30000 cycles, which means that the crack has started at the surface of the specimen. Whereas from Fig. 2(b) one can see the sudden increase in cumulative counts at same number of cycles from AE data. Thus we can compare the data from AE counts with DIC strain values. Fig. 7 shows the axial strain (ĂĽyy) in the direction of loading along the crack-line for a series increasing crack lengths. The strain profiles along the un-cracked line were high near the crack tip and decreased as function a distance away from the perceived crack tip.
4. CONCLUSION Acoustic Emission Technique results from experiments carried out are used as an on-line monitoring tool to study fatigue crack initiation and propagation. Along with this, a semi on-line DIC tool has been used to monitor the strain associated with number of cycles on the surface of the specimen. The main objective of the investigations carried out and presented in this paper aim at developing AE as an online predictive tool at the very early stages of crack initiation and growth in Ti6Al4V material. Consequently crack growth experiments have been carried on a set of three point bend specimens and AE data recorded and analyzed. One most interesting aspect that has been observed is that while AE data could be recorded even before the crack appears on the surface, proof of crack initiation and growth show confirmation through a complementary method, which can register and trace the crack growth while the phenomenon had been occurring within the thickness of the specimen. Thus, surface strains measured all though the fatigue crack growth experiments confirm that AE data obtained before the crack appears on the surface is due to crack growth within the thickness of the specimen. Journal of Non destructive Testing & Evaluation
46 REFERENCES 1. M.S. Kirugulige, H. Tippur and T. Denney, Measurement of transient deformations using digital image correlation method and high-speed photography: application to dynamic fracture. Appl Opt, 46(22) (2007) 5083–96. 2. Carle. Hartbower, et al , Acoustic emission from low-cycle highstress-intensity fatigue, Engineering Fracture Mechanics 5 (1973) pp. 765-789. 3. J.R. Kennedy, Acoustic emission during deformation of Ti-6Al4V, Scripta Metallurgica, 16 (1982) 525 – 530. 4. D.H. Kohn and P. Ducheyne, Sources of acoustic emission during fatigue of Ti-6Al-4V: Effect of micro structure, Journal of material science, 27 (1992), 1633- 1641. 5. D.H. Kohn and P. Ducheyne, Acoustic emission during fatigue of Ti-6Al-4V: Incipient fatigue crack detection limits and generalized data analysis methodology, Journal of material science, 27 (1992) 3133-3142.
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Technical Paper 6. T.M. Morton, R.M. Harrington and J.G. Bjeletich, Acoustic emissions of fatigue crack growth, Engineering Fracture mechanics, 5 (1973) 691-697. 7. Avraham berkovits and Daining fang, study of fatigue crack characteristics by acoustic emission, Engineering fracture mechanics, 51(3) ( 1995) 401-416, 8. Standard Test Method for Measurement of Fatigue Crack Growth Rates, 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 analysis from digital images : application to Portevin-Le Châtelier bands. Expl Mechanics, 46(6) 789–804, 2006. 12. SteveVanlanduit et al, A digital image correlation method for fatigue test experiments, Optics and Lasers in Engineering, 47 (2009) 371–378
Vol. 9, Issue 4 March 2011
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Technical Paper
Development of an Acoustic Emission Condition Monitoring system for use in IC Engines. Sreedhar P, JanardhanPadiyar M, R Maharajan and Krishnan Balasubramaniam Centre 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 identifying these warnings can lead to identification of faults in early stages and hence minimize the damage. The major challenge lies in detecting such faults in their early stages of occurrence in a nonintrusive way. This paper tries to show the development of an Acoustic Emission (AE) Test system for condition monitoring of critical IC Engine parts. The objective of the work is to develop an efficient and cost effective acoustic emission system with custom signal conditioning unit that can continuously monitor â&#x20AC;&#x2DC;onlineâ&#x20AC;&#x2122; the AE generated during the piston movement with no modification to the engine. Furthermore it is proposed to conduct various studies for evaluating the performance of the sensor developed for this purpose.
1.
INTRODUCTION
Predictive maintenance is highly economical and efficient in cases where machinery are concerned. The monitoring of the engines for early detection of failures and taking appropriate action can make a considerable difference in terms of cost incurred as well as instil confidence in the customers. The failures that occur commonly in an engine give a characteristic indication before transforming into non-repairable faults. The major challenge lies in detecting such faults in the early stages of occurrence in a nonintrusive way. Currently techniques like vibration monitoring, strain monitoring, oil debris analysis etc are being used in industries. Studies over the past few years have shown Acoustic Emission to be a very dependable tool for condition monitoring of Engines. Acoustic emission (AE) is the propagation of transient elastic waves that are generated within or on the surface of a material by fundamental processes that define friction and wear such as deformation and micro fracture. AET offers the advantage of earlier failure detection due its inherent higher sensitivity as compared to the low frequency vibration signals. (1)(2). This paper explains in detail the development of an efficient and cost effective acoustic emission system with custom signal conditioning unit which can be used for the continuous online monitoring of the AE generated in the engine without any modification to its basic construction.
2.
ACOUSTIC EMISSION SOURCES IN AN ENGINE
Any kind of dynamic machinery such as Engines has plenty of moving parts which are excellent sources of AE. Since friction is a major source of AE, it can be utilized as a very efficient tool in studying the condition of any moving part non-intrusively. Of course, this is possible Vol. 9, Issue 4 March 2011
only if there is a provision for the sensor to be mounted in a suitable position to pick up the emissions. The major sources 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 generated for Bearing Condition monitoring.(3) , Gear Box condition monitoring (4)and to detect exhaust valve leakage (5). Also, extensive work has already been carried out to study the piston ring and cylinder liner condition using AE.
3. OBJECTIVE At present, the AE sensors and measurement systems available in market are costly and found not feasible for growing automobile industries. Studies conducted with Kistler made Piezotron 8152B111 probes with 16 channel 8 bit digitizer and external power supply system to probes showed that the system was impractical for On-line monitoring due to various reasons1) These sensors cannot be mounted without tampering with the engine. 2) These sensors are not designed to work efficiently at the temperatures expected. 3) The system requires a 30-40V DC supply to power the Pre-amplifier. 4) Cost of each sensor is anywhere between 75,000 to 100,000 INR. These factors led to the need for development of a cost effective system that can be easily integrated with the engine in a non-intrusive way. Journal of Non destructive Testing & Evaluation
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4. ACOUSTIC EMISSION SYSTEM DEVELOPMENT i)
Transducer Development
Feasibility of employing various piezo-electric crystals was studied. These sensors were used to collect AE Data from a four stroke Petrol engine. Mainly two types of piezoelectric crystals were used in this study. 1. Piezo Wafer Active Sensor(PWAS) crystal(0.2 mm thick) 2. PZT (Lead Zirconium Titanate) Crystal(2 mm thick) Initially, experiments were done with the crystal bonded to the engine fin of a four stroke petrol engine using Superglue. Figure 1 (a) and 1(b) respectively shows the mounted PWAS and PZT sensors.
Fig. 2 : (a) Cut section view of the stainless steel casing (b) Final Assembly
to act as a wave guide. And the casing here gives a protective cover to the sensor. The cut section view of the solid model of the casing is provided in Fig.2 (a). ii)
Fig. 1 : Sensor mounted on the engine (a) : PWAS; (b) : PZT crystal
This study showed that the active elements were less effective in detecting signal transients when mounted directly on the engine. Moreover, uncovered soldered joints of PWAS and PZT can pick up EMI (Electro Magnetic Interference) from sparkplug cable, if they are near the sparkplug. With these problems in mind, a casing was designed to enclose the sensor and thus effectively isolate it from the heat and EMI. A typical Acoustic Emission sensing element has a wear plate and casing for it. In our case wear plate is designed Journal of Non destructive Testing & Evaluation
Development of Signal Conditioning Unit (SCU)
An acoustic emission sensor is essentially a piezoelectric sensor that generates potential difference (voltage) across its terminals when subjected to mechanical stress. They are essentially capacitive in nature and have high impedance. Hence a signal conditioning circuit having a high input impedance preamplifier is needed [6, 7]. The received signal is usually of the order of micro volts and contains signals over a wide band of frequencies .The purpose of the signal conditioning circuit is to amplify this low amplitude signal and also limit the bandwidth of the signals coming into the circuit. In order to successfully extract and analyze the signal output by the sensor, an Op Amp with high input impedance has to be selected. In this work we have used a commercial off-shelf amplifier for designing the preamplifier circuit. Generally, two preamplifier topologies are used for piezoelectric sensors charge amplifier and voltage amplifier. In the present work a voltage-feedback amplifier with two stage design using very low-noise, wideband variable gain operational amplifiers has been used. The parameters for selection of Op Amps for preamplifier design used in this work are shown in Table 1. Vol. 9, Issue 3 March 2011
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Fig. 3 : Block diagram of Custom Pre-Amplifier Unit.
Table1 : Suggested Commercial IC Selection parameters for Acoustic Emission Preamplifier Primary Parameters
Limiting Value
Secondary parameters
Limiting Value
High Input Impedance
> 106 Ohms
Input Bias Currents
< 10 μA
High Gain (linear)
>40 dB
Slew rate
> 300 V/μs
Low input voltage noise
<4n V/sqr(Hz) quiescent current
< 15 mA
Low input Current noise
10p A/sqr(Hz)
Table 2. Since Op Amp circuits requires ±5V a -5V a DCDC converter (NDTD0505) which accepts 4.5V-7V as input and delivers isolated 5V±3% with about 75% effi ciency at 200mA. The preamplifier designed is having a estimated peak power consumption of approx120mA Ceramic capacitors are provided at input and output of the DC-DC converter to reduce ripple, switching noise in the output voltage and to reduce the surge current drawn from the input.
5. ACOUSTIC EMISSION TESTING PROCEDURE
Low Offset Voltage < 500 μV
The success of a precision preamplifier depends largely on the choice of the input stage. In this preamplifier circuit, the first stage is optimized so as to achieve low noise, at the same time give a very high gain of 100 times (40dB). For boosting the signal further, the second stage is also designed for high linearity in the range of 10 times thus having a combined gain of 60 dB which is sufficient for the measurement by a digital to analog convertor. While receiving low-level signals, it is necessary to limit the bandwidth of the incoming signals into the system . The simplest way to accomplish this is to place a high pass RC filter at the non inverting terminal and low pass RC filter at the output of the second stage. Capacitors are placed in series after each stage to reduce the dc offset caused due to input offset voltage and bias current. The power supply pins to the preamplifier circuit are decoupled with capacitors to reduce noise. A multilayer PCB board is designed with power supply and ground planes.
First, a trial was conducted using commercially available AE Sensor. The Studies revealed that most of the main emissions were in the 50-300 kHz band. So the crystals with a narrow frequency band with resonant frequency at 250 kHz were selected for this study. The transducers were bonded to the fin of a 4 stroke petrol engine using bonding agent. The data was acquired from the sensor using National Instruments Data Acquisition system and saved in a Laptop with the help of a custom developed Lab VIEW program as GUI. Engine was run in the idling condition and data was collected. Then the sensor with casing was mounted on the fin of the engine as shown in Fig.4.The Experimental setup used for this purpose is illustrated in Fig.5. The same experiment was repeated for this configuration. Data was acquired at a sampling frequency of 1 MHz. The signal conditioning
Table 2 : Specification of Op Amp used PZT Input Maximum Input Driver Impedance Gain Voltage IC noise nV/sqr (Mohms) (dB) (Hz) VCA810
1
OPA657
10 6
40 40
Input Current Noise pA/sqr (Hz)
(mVpp)
2.1
0.35
3.5 4.8
1.3
x10-6
Low Offset Voltage
2.5
Our application demands the use of a small portable preamplifier for which a battery power supply have to used. The specifications of the Op Amp are given in Vol. 9, Issue 4 March 2011
Fig. 4 : Sensor mounted on the engine Journal of Non destructive Testing & Evaluation
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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
unit gave 80 dB output, two channels, two stages (each 40 dB) with a low pass filter of 1MHz. The unit was powered by a 5 V supply from a portable battery. Similar set of experiments were conducted with and without the signal conditioning unit to study its effect on the signal.
6. EXPERIMENTAL RESULTS The data acquired from the crystals were plotted using a LabVIEW program. Figure 6 shows the AE signal over a period of 0.1 seconds as obtained from the PWAS transducer without using the SCU. The signal was found to conform with signals obtained in test on such engines according to literature. Journal of Non destructive Testing & Evaluation
The FFT plotted for this signal indicated that most of the events generated emissions of frequency band of 100300 kHz. Figure 7 shows the frequency distribution for the above signal. The results obtained on using 80 dB amplifier for the same set up indicated that it was not suitable for use with the PWAS crystal. The frequency plot for this signal indicated a domination of low frequency noise in the signal. The signal and the corresponding frequency distribution plots can be found in Fig. 8(a) and 8(b) respectively. The results from the test using PZT crystal showed that the signal had frequencies varying from 20-250 kHz. The Signal and frequency distribution are shown in Fig. 9. The results obtained from our sensor were compared with a commercially available KistlerPiezotron 8152B111 sensor. Vol. 9, Issue 3 March 2011
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Fig. 8 : (a) Signal from PWAS crystal on using 80 dB gain; (b) Frequency distribution for signal shown in Fig.8(a)
Fig. 9 : (a) Signal obtained from the PZT crystal using 60 dB gain (b) Frequency distribution for the signal shown in Fig. 9(a) Vol. 9, Issue 4 March 2011
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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.
Fig. 10 shows the comparison of signals from the two sensors. The experiments using the sensors with stainless steel casing revealed a considerable reduction in noise. The various events were clearly distinguishable in the signal. Figure 11 shows the raw data obtained while the engine was running in its fourth gear.
CONCLUSION Experimental tests conducted using two crystals PWAS and PZT with 60dB gain showed similar signals. But the PZT being thicker is easy to handle and hence is preferred over thin PWAS. The stainless steel casing designed for the crystal was found to reduce the EMI noise and also insulate the crystal from the heat dissipated by the engine. The EMI noise was found to reduce from 5 V to 5 mV on using the casing. The sensor was also able to pick up the various events with sensitivity comparable with a commercially available sensor. The major benefit of the system is the cost effectiveness and its feasibility for on road testing due to its portability.
ACKNOWLEDGEMENTS The Authors would like to thank TVS Motor Company Ltd., Hosur. for providing the Engine and for their wholehearted assistance during the data acquisition for this experiment
Journal of Non destructive Testing & Evaluation
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 emission and 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 Planned Maintenance, Reliability and Quality, University of Oxford, England, 2–3 April 1998. 3) C James Li, S Y Li , Acoustic Emission Analysis for Bearing Condition 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 artificially induced gear cracks utilizing on-line vibration and acoustic emission 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 leakage detection in large diesel engines, Condition Monitoring and Diagnostic Engineering Management, COMADAM, Clayton, Australia 1 (1998) 269–278. 6) A. Turoa and J. Salazar, Ultra-low noise front-end electronics for air-coupled ultrasonic non-destructive evaluation, NDT&E International, 36 (2003) 93–100. 7) Yanez Y, Garcia – Hernandez M J, Salazar J, Turo A, Chavez J A, Designing amplifiers with very low output noise for high impedance piezoelectric transducers. NDT&E International, 38, (2005) 491-496.
Vol. 9, Issue 3 March 2011
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Technical Paper
Signature Analysis of Failure Modes in Composites using Acoustic Emission Ramesh kumar. M* and Madhava. M.R+ *Advanced composites division, National Aerospace Laboratories, Bangalore – 560017 + Retired, NAL, Bangalore – 560017 E-mail : rameshrk@nal.res.in
ABSTRACT During static structural qualification tests, it is always preferable to monitor the structural health in real time by non destructive manner. In the event of any premature failure occurring during loading, it is preferred that this it is detected immediately at an early stage to prevent the catastrophic failures in service at an appropriate time. Acoustic Emission (AE) is the only proven technique 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 information about the damage initiation and source location and also essential to identify more information about the nature of failures in the composite structure as the failure modes in composites are more complex. This paper briefs about identification of signatures of 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 use of composites has increased due to distinct advantages they offer over metals. Prior to the clearance for airworthiness, the components are subjected to static structural integrity and qualification tests to demonstrate and prove the competence to sustain various load cases as per design requirements. Failure modes in composites used in aircraft structures can be more complex when compared to conventional metal alloys [1,2,3]. This research work was carried out to identify the characteristic signatures of failure modes in composites which enable us to predict the nature of failure, if any during full scale component testing. To satisfy the basic requirement of the composites for qualification and acceptance as a material of construction, the following tests are conducted. They are Tensile, Compression, Flexure and Lap shear [4,5] tests. Once the basic material was qualified through such tests the component or the structure can be fabricated out of it wherein component or structure [6] would be subjected to Design Limit Load (DLL), Design Ultimate Load (DUL) to qualify for structural integrity. The first component fabricated would be subjected to various tests. Considering the advantages of the AE technique, it was decided to use an NDE tool for structural health monitoring during static testing [7,8]. AE is increasingly used in the aviation industry [9,10] during fatigue loading for the damage detection and growth in a structure for life extension studies [11,12,13]. In the initial phase of loading, failure mechanisms may be at a micro level that may Vol. 9, Issue 4 March 2011
subsequently lead to catastrophic failure, which can be detected using other Non-Destructive Testing (NDT) techniques. During the testing process the most common composite 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 expected failure modes in composites structural [17, 18] components. AE would be an ideal NDE technique to identify such failure modes in composites, whereas other methods such as thermography, radiography, ultrasonics, etc., fail to detect during structural testing. Researchers have shown that each type of defect exhibits different AE characteristics [19, 20, 21]. Many techniques such as Visual and Graphical methods have been applied on AE data for pattern recognition. The specimens that can simulate three different types of failure mechanisms in composites [22] were fabricated using Glass-Epoxy pre-pregs (GFRP) [23] and cured in an autoclave as per a given cure cycle. Test samples were prepared according to the ASTM standards. (1) For matrix failure (in-plane shear) mode – the prepregs were stacked in ± 45 deg.(cross-ply), of 2 mm thick. The samples were fabricated and tested as per ASTM D 3518 standard. (2) For delamination failure mode – DCB samples (Double Cantilever Beam) of 1.2mm thick having an inclusion at the tip side in the middle of the thickness to initiate the delamination upon loading. The samples were fabricated and tested as per ASTM D 5528 (mode 1) standard. (3) For debond failure mode – samples of 2 mm thick were bonded with an adhesive film (Redux 319) having Journal of Non destructive Testing & Evaluation
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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 using Universal Testing Machine (UTM) (Fig. 1) and acoustic emission monitoring system, MISTRAS 2000 equipment (Fig. 2) was used to acquire the emission from the samples while testing. GFRP samples were prepared (width of the specimen is 25mm) according to the standard and end tabs are bonded (only for tensile load) to the specimen on either side which will avoid slipping of the specimens from the grip in the UTM. Acquire acoustic emission signal at the time of testing through mechanical load, AE sensor was fixed on the specimen little below the centre of the specimen. The MISTRAS hardware parameters and a signalprocessing filter were selected as described below: 1. Test threshold = Fixed 45 dB. 2. Signal processing filter = 10 - 1200 kHz
2.3 Experimental Procedure
In (1) matrix failure mode, the specimen was tested in a similar fashion of a tensile specimen test. AE signals was acquired and stored in the MISTRAS system at the time of mechanical test was conducted. (2) The second type of test is the delamination in the Double Cantilever Beam (DCB) specimen. An inclusion was introduced in the mid plane of the thickness, to initiate the delamination easily when the load was applied on the specimen. Metallic hinges are bonded on the top and bottom side of the specimens (Fig.3) to initiate the delamination and propagate the growth towards the mid plane of the specimen. When the delamination was initiated and the growth started propagating due to mechanical load, the acoustic emissions were captured in these stages for further analysis. The hinges help the specimen to take the different shapes like L to V (Fig. 3). The AE sensor was bonded in the middle of the specimens for acquiring acoustic emission signal. (3) Lap shear test was conducted for debond / disbond studies in the specimens prepared by bonding the adherents with an adhesive material in the lap area. The length of the specimen is 110mm, bonded using adhesive film Redux 319 in the lap joint method. An acoustic emission sensor was fixed on one side of the lap joint to acquire the AE
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 the pencil lead break on the structure around the sensor locations. Between two sensors the pencil lead break response in terms of amplitude value should be above 70% and the threshold value will be selected based on the noise level in the structure. The pre-amplifier gain of 20dB may be selected based on the distance between the component and the AE system. The band pass filter was selected to eliminate the unwanted noise during testing.
Fig. 1 : Universal Testing Machine
2.2 AE Sensors
R15D AE sensor is manufactured by Physical Acoustics Corporation (PAC). An R15D sensor was used and its resonance frequency is 150 KHz. These sensors have an external preamplifier, making their size smaller than the other sensors. The R15D sensor and the external preamplifier are suitable for in-situ application. Journal of Non destructive Testing & Evaluation
Fig. 2 : Acoustic Emission System Vol. 9, Issue 3 March 2011
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Fig. 3 : DCB Specimen in testing condition
Fig. 4 : Tested Lap Shear Specimen
signal from the joint during mechanical loading. Fig. 4 shows the failure of lap joint specimen.
Algorithm was written to develop the software program in the Labview environment for signal processing. In the initial step the converted ‘ASCII’ data (acoustic emission data) was read by the program and displayed in the Labview platform (Fig. 5), the continuous signal (all hits) received during the single test were display in the software using ‘History’ command. This will enable to analyze and identify the maximum amplitude and the corresponding hit number and time.
These raw acoustic emission data were filtered and processed in the acoustic emission system. Post processing capability is not available in MISTRAS system. In view of this problem a signal analysis tool was developed to get the signatures of different types of failure modes in composites.
3.
SOFTWARE DEVELOPMENT
To carry out analysis on stored raw data, the raw data should be converted to a form which was accessible in other platforms. The acoustic emission signals are converted to ‘ASCII’ format, enable us to read the signal in the post processing software for signature analysis.
The user friendly software enables the user to select the required data and set/change the threshold value during the time of analysis. The noise levels (due the gripping or unwanted mechanical noises) were eliminated by fixing a proper threshold on the signal (hit). This threshold can be applied to each hit (discrete waveform of the test) and the signal above the threshold were extracted and displayed.
Fig. 5 : Post processing software developed for AE signal analysis showing all the hits (top) of a single specimen Vol. 9, Issue 4 March 2011
Journal of Non destructive Testing & Evaluation
56 The spectral analysis of the extracted waveform was used to find out the 6dB bandwidth (BW) of the particular waveform. Also, other parameters like duration, count, rise time and peak amplitude were calculated and displayed which enable in arriving at the signature of the failure modes. The above steps were repeated on each hit of the same test and iterated to all the samples for three different types of test conducted on this experimental work.
4. RESULTS AND DISCUSSION The acquired waveforms are further post processed using the Labview software for analysis of three different failure modes. Each failure modes were analysed individually to arrive at the parameters towards the AE signatures of failure modes. 4.1 Matrix failure
All the individual test specimen data was displayed using the Labview post processing software for analysis on each hit was carried out to identify the parameters like duration, count, rise time, peak amplitude and bandwidth. Select the hit number in order and carry out post processing to identify the above parameters on each hit on the first test specimen. This Iteration has to be continued till the last hit number of the first specimen. Each hit AE parameters are recorded and the average value of the hits for a particular specimen was recorded in tabular form. Then the second specimen data was read by browsing the ‘File
Technical Paper
Path’ in the Labview analysis software and the above iteration procedures to be followed. Similarly the same procedure had been followed for all the five tested specimens. Table 1 gives the values of AE parameters of the matrix failure modes. The threshold voltage for this analysis was 1.0 mv. At the time of matrix failure initiation the AE data had high amplitude of the order of 80 dB. But towards the end of the test the fibre and matrix were slipping and the amplitude values are diminishing to very low of 25dB. Figure 6 shows the signal of matrix failure specimen, tent-2 of hit no. 49. The signal of matrix failure had consistent value of AE parameters like duration between 30 to 40 μs, count range from 4 to 7 Nos., peak amplitude is more than 85dB and Bandwidth (BW) varied between 40 to 50 KHz. Table 1 : Analysis of Matrix failure ±45° (In-plane shear) specimens Specimen Duration Name (μs)
Count Rise Time Peak (Nos) (μs) Amplitude (dB)
Bandwidth (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 Journal of Non destructive Testing & Evaluation
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4.2 Delamination failure
Software analysis procedure should be followed as same as mentioned above (Matrix Failure) for delamination failure mode analysis. Browse the ‘File path’ and select the folder of the delamination test data and pick the first hit for analysis. The analysis procedure should be followed (mentioned above) to identify the AE parameters. Each hit was iterated following the same procedure for all the test specimens to arrive at the values of AE parameters for delamination failure modes. The value of threshold voltage for analysis was 2.0 mv. Table 2 shows the AE analysis values of the delamination test specimens, for failure modes of all the specimens. The signals of delamination (DCB) specimens signal endurance for longer duration was noticed. Table 2: Analysis of delamination (DCB) specimens Specimen Duration Name (μs)
Count Rise Time Peak (Nos) (μs) Amplitude (dB)
Band width (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 had consistent value of AE parameters, duration between 100 to 200 μs, count range from 20 to 30 Nos., peak amplitude had an average value of 65dB and BW varied between 12 to 25 KHz. 4.3 Debond failure
Similar analysis procedure followed above had been used for the lap shear test specimens. Table 3 provides the values of AE parameters from the bonded test specimen, tested for debond failure modes. The threshold voltage for these lap shear analysis was 2.0 mv. Table 3 : Analysis of Lap shear specimens Specimen Duration Name (μs)
Count Rise Time Peak (Nos) (μs) Amplitude (dB)
Bandwidth (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 Vol. 9, Issue 4 March 2011
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Fig. 8 : AE Signal of debond failure mode
had consistent value of AE parameters showing count ranges from 8 to 12 Nos., the rise time varied from 6 to 12 μs and peak amplitude value < 80dB and BW varied between 27 to 35 KHz. All five specimen test values were averaged to arrive at AE test parameters, helped to identify the signature of failure modes from the test results.
5. CONCLUSIONS The AE signature of all the failure modes were summarised as : (I) For Matrix failure, the average values from the post processed AE signal parameters : duration range from 30 – 40 μs, the count was 4 – 7 numbers, the rise time 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 the tested specimens, the AE parameters were : duration range between 100 – 200 μs, the count from 20 – 30 numbers, the rise time between 15 – 40 μs, the peak amplitude was 60 – 70 dB and the band width lie between 12 – 25 KHz. (III) Debond failures, the signatures were arrived from the raw AE signals : the duration between 40 – 50 μs, the count numbers between 8 – 12, the rise time varied 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 were obtained from the test results of the GFRP specimens. Journal of Non destructive Testing & Evaluation
These signatures were very much useful for the static structural analysis and to study the post test evaluation of structural health and integrity of the structure. This makes it an ideal tool for finding the AE Signature parameters for inspection.
ACKNOWLEDGEMENT Thanks are due to Mr. D. Karuppanan, Mr. S. Sanjeev Kumar, Mr. H.V. Ramachandara, Mr. M.C Devaiah Mr. V. Srinivasa, for the extensive support during the work. We are 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 frequency content 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 an acoustic emission, Composite Structures, 75 (2006) 163-169 3. Rongsheng Geng. Modern acoustic emission technique and its application in aviation industry, Ultrasonics, 44 (2006) 10251029 4. H.Suzuki, T.Kinjo, N. Saito, M. Takemoto, K.Ono. Integrity evaluation of glass-fibre composites with varied fibre/matrix interfacial strength using acoustic emission, NDT&E International, 33 (2000) 173-180
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Technical Paper 5. A.G. Magalhaes, M.F.S.F. de Moura. Application of acoustic emission to study creep behavior of composite bonded lap shear joints, NDT&E International, 38 (2005) 45-52 6. Mikael Johnson, Peter Gundmundson. Broad-band transient recording and characterization of acoustic emission events in composite laminates, Composites Science and Technology, 60 (2000) 2803-2818 7. Joung-Man Park, Sang-II Lee, Oh-Yang Kwon, Heung-Soap Choi, Joon-Hyun Lee. Comparison of nondestructive micro failure evaluation of fibre-optic Bragg grating and acoustic emission piezoelectric sensors using fragmentation test, Composites PartA, 34 (2003) 2003-216 8. Chandrashekhar Bhat, M.R Bhat, C.R.L Murthy. Acoustic emission characterization of failure modes in composites with ANN, Composites Structures, 61 (2003) 213-220 9. Y. Mizutani, K. Nagashima, M. Takemoto. K. Ono. Fracture mechanism characteristic of cross-ply carbon-fibre composites using acoustic emission analysis, NDT& E Int., 33 (2000) 101110 10. Yiannis Z. Pappas, Vassilis Kostopoulos. Toughness Characteristic and acoustic emission monitoring of a 2-D carbon/carbon composites, Engineering Fracture mechanics, 68 (2001) 15571573 11. M. Bourchak, I. R Farrow, I.P Bond, C.W Rowland, F. Menan. Acoustic emission energy as a fatigue damage parameter for CFRP 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 composites under quasi-static loading using time/frequency analysis of acoustic emission monitored waveforms, Composites Sc. and Technology, 66 (2006) 1366-1375 13. Xingmin Zhuang, Xiong Yan. Investigation of damage mechanisms in self reinforced polyethylem composites, Composites Sc. and Technology, 66 (2006) 444-449 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 by simultaneous measurement of ultra-small-angle scattering and acoustic emission during the deformation. II. Evaluation of the interface strength, J. Macromol. Science-Phy, (1999) 913-929
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59 15. F.E Silva, L.L Goncalves, D.B.B Fereira, J.M.A Rebello. Characterization of failure mechanism in composite materials through fractal analysis of acoustic emission signals, Chaos Solitons & fractals, 26 (2005) 481-494 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 by simultaneous measurement of ultra-small-angle scattering and acoustic emission during the deformation. I. Method, J. Macromol. Science-Phy, (1999) 901-912 17. A. Velayudham, R. Krishnamurthy, T. Soundrapandian. Acoustic emission based drill condition monitoring during drilling of glass/ phenolic polymeric composite using wavelet packet transform, Material Sc. and Engineering A, 412 (2005) 141-145 18. Amilcar Quispitupa, Basir Shafiq, Frederick Just, David Serrano. Acoustic emission based tensile characteristics of sandwich composites, Composites Part B, 35 (2004) 563-571 19. Tadej Kosel, Igor Grabec, Franc Kosel. Time-delay estimation of acoustic emission signals using ICA, Ultrasonics, 40 (2002) 303306 20. N.Godin, S.Huguet, R. Gaertner. Influence of hydrolytic ageing on the acoustic emission signatures of damage mechanisms occurring during tensile test on the polyester composites : Application of a Kohonenâ&#x20AC;&#x2122;s map, Composite structures, 72 (2006) 79-85 21. R.Hill, R.Brooks, D.Kaloedes. Characterization of transverse failure in composites using acoustic emission, Ultrasonics, 36 (1998) 517-523 22. Mikael Johnson, Peter Gudmundson. Experimental and theoretical characterization of acoustic emission transients in composites laminates, Composites Sc. and Tech., 61 (2001) 1367-1378 23. H.N Bar, M.R. Bhat, C.R.L Murthy. Identification of failure modes in GFRP using PVDF sensor : ANN approach, Composites Structures, 65 (2004) 231-237 24. Annual Book of ASTM Standards, Section â&#x20AC;&#x201C; 15, Vol. 15.03 & Section-3, Vol. 03.01
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An empirical approach for the burst prediction of GFRP pressure bottles using acoustic emission technique R.Joselin1 , T.Chelladurai2, M.Enamuthu3, K.M. Usha4 and E.S. Vasudev5 1
2
Research scholar, JNTU Hyderabad, Hyderabad -500085, A.P., India. 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:joselinjerish@yahoo.co.in
ABSTRACT Acoustic Emission (AE) is an upcoming NDT technique gaining ground in different fields as an on-line monitoring method for detection, location and characterization of various kinds of active degradations. This method has also made an impact as a tool for structural integrity evaluation and failure prediction. AE has been growing vigorously in recent times and has been used in wide range of applications in aerospace, nuclear and chemical engineering fields. AE technique is highly sensitive and can detect degradations in FRP structures viz delamination, fibre crack, debonding, matrix crazing etc well before occurrence of any catastrophic failure under dynamic service condition. In the present study, five identical GFRP hardware were taken up for the study and acoustic emission data is analyzed thoroughly and a lucid empirical relation is developed to predict their burst performance. 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 prediction of composite pressure vessels. This innovative methodology illustrates the structural behavior of GFRP pressure bottles in terms of AE parameters and its derivatives. In this approach AE data is acquired only upto 50% of the theoretical burst pressure and then the bottles are pressurized to failure. An empirical relation was generated for the GFRP bottle which is subjected to cyclic proof pressure cum burst test on the basis of governing AE parameters viz, ring down counts, event duration, peak amplitude and felicity ratio. This methodology can possibly predict in real time the burst pressure of similar hardware if extended to other material systems. Keywords: Acoustic emission, GFRP pressure bottles, structural integrity, empirical relation, AE parameters, prediction.
1. INTRODUCTION Acoustic Emission Technique (AET) is widely used for both materials research and structural integrity monitoring applications because of its unique potential for detection and location of dynamic defects under operating stresses. In the past two decades, AE has been mostly used for testing pressure bottles undergoing proof/acceptance tests [1,2]. In aerospace composite structures, pressurised systems are made with low margins with their attendant light weight construction [3]. With the rapid advances taking place in this area, there is a strong need for an NDT technique which can indicate the degradation that takes place during the course of the proof or acceptance testing of pressurised systems. There are cases reported in the literature that composite hardware that have successfully undergone proof pressure tests did fail during their actual test. In this respect, AE technique has assumed a unique role. More than evaluating the structural integrity of pressurised systems it has the capability to predict the burst pressure within certain limits. It is well known that GFRP pressure bottles undergo degradation during acceptance/proof pressure test in view of resin crazing,delamination,fibre fracture, fibre pullout and debonding between the layers etc. Such degradations can Journal of Non destructive Testing & Evaluation
be indicated through major AE parameters and their derivatives. A methodology is being developed in this paper to estimate the residual strength of GFRP pressure bottles.
2. GFRP HARDWARE DETAILS AND AE INSTRUMENTATION AE studies have been performed on five numbers of similar Glass epoxy pressure bottles. In which, E-Glass fibres impregnated with epoxy resin are wound over an inner liner made of polypropylene. The bottles are built up of hoop layers and polar layers alternately placed in groups.The dome openings are equal and are closed with flat plates or special closures, as the case may be, for the pressure test purposes. The thickness of the composite wall is 5mm. The sensitiveness of AE sensors is verified and adjusted frequently at the end of every cycle with the use of HsuNielsen pentel pencil-break technique. The PAC-Disp 4 AE work station is used to monitor in conjunction with AE sensors R15(150 KHz,resonant type)and matching preamplifiers 40 dB with high pass analog filter range 20 KHz -400 KHz. Radiography (X-ray) test is conducted on each of the bottles to verify the uniformity in thickness of composite walls. Initially the threshold 45dB is set during the starting in order to avoid the system collapse. Vol. 9, Issue 3 March 2011
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3.
AE MONITORING DURING HYDROSTATIC PRESSURE TEST
The emissions are captured with the use of four AE sensors.These AE sensors are mounted as per standard procedure [ASTM,1986], connecting co-axial cables with AE system. The deformation of the bottle is identified by fixing single element 350Ω strain gauges (ranges 018000με) and their locations are shown in the Fig.1. The pressure cycle is carried out upto 50% of their theoretical burst pressure in a cyclic mode. The pressure is brought down to zero after every cycle. The pressure rate is maintained at 20 bar/min throughout the test. As to GFRP02 bottle test during pressurisation the hardware failed due to adaptor failure. In order to avoid this nature of failure, the remaining four hardware were gently machined
steps upto 200 bar and the remaining hardware were pressurised upto 150 bar only. An air assisted hydraulic pump is used to pressurise upto 150 bars and for the higher pressurisation a mechanical pump is used. The incremental pressure was 25 bar in all cases.The first time holds at various incremental pressures were for a minimum period of 1 min until the event rate declines. The maximum hold shall be for a period of 3 mins. In this paper, the emissions were studied only for repeat cycles. For every cycle, the AE parameters just before pressure hold are taken into consideration for developing the empirical relation predicting the burst pressure. In all cases, AE parameters were studied for a maximum pressure of 125 bar except for the first hardware. In the first hardware, cycling was done upto 175 bar.
5. EMPIRICAL RELATION The empirical relation is nothing but a equation connecting the dominant AE parameters with expected burst pressure and internal pressure at which the prediction is attempted. This relation is developed in the first hardware itself, after that, the same will be refined after every remaining hardware test. The general form of empirical equation is assumed as: Fig. 1 : SG/AE instrumentation on GFRP pressure bottle
N-α x D-β x A-γ x Ra = F x P-b
Where, N D A R F P
= = = = = =
Ring down Counts Event Duration in μs Peak Amplitude in dB Felicity Ratio Tentative burst pressure in bars The internal pressure (in bars) at which prediction is attempted α, β, γ, a, b are Empirical constants
6. AE PARAMETERS
Fig. 2 : Experimential setup
at the cylindrical portion by 1 mm depth. The schematic view of experimental setup is shown in Fig.2. 6-Nos of strain gauges and three Nos linear potentiometers are mounted to find out the deformations and axial/diametrical dilations of the hardware. These data are acquired and analyzed for further developments of this research.
4.
PRESSURISATION AND PRESSURE HISTORY
Two sets of pressure schemes are used to pressurise 6litre capacity,150 mm dia cylindrical GFRP pressure bottles5 nos.Initialy the first hardware is pressurised in cyclic Vol. 9, Issue 4 March 2011
In this analysis the major derived AE parameters chosen were ring down counts, event duration, peak amplitude and Felicity ratio(F.R). The pressure at which significant emissions start during first repeat cycle is considered as ‘P1’. The maximum pressure reached during the previous cycle is say, ‘P2’. Thus F.R=P1/P2. F.R is arrived at from the AE response graphs as well as from the statistics of the first repeat cycle. The other parameters are chosen just before the pressure hold that follows during the first repeat cycle. The solution of each hardware is found out by MAT LAB software. The unknown exponents are arrived at by substituting all the major AE parameters into the empirical relations. In any hardware, the tentative burst pressure is arrived at by substituting the other hardware’s exponents. In respect of GFRP-02 bottle, initially the emissions were very low. Therefore, the equation is formed from 75 bar pressure cycle onwards. The authors also observed that the machined hardware exhibit burst earlier than the first hardware failure. Journal of Non destructive Testing & Evaluation
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Table 2 : Prediction using GFRP -2 constants
7. RESULTS AND DISCUSSION In the case of one of the hardware,say,GFRP-02, for the first repeat cycle at 75 bar, the values of derived AE parameters and pressure at which prediction was attempted are substituted into their equations corresponding to 75, 100, 125, 150 & 175 bars respectively. The solution initially gave low burst values in comparison with the actual burst pressure of 299.5 bar. In the pressure 125 bar, it gave reasonable percentage of error, say, 2.67%. The chosen values are also verified with the sixth equation at 200 bar. In this case, it indicates the values of burst pressure with an error margin of -1.42%. Using these equations one could find out the constants with the help of MAT lab software. This software displays the output for any {mxn} matrix, where m=n. Similarly, for the other hardware the AE parameters are acquired from 25 bar internal pressure onwards at an incremental pressure rise of 25 bar. The mathematical procedure is same for all the hardware. For each of the pressure bottles the dominant AE parameters preceding failure can be detected at around 75% of MEOP. From the acquired data, a set of multiple parameters can be developed with a small error margin. The initial emissions are more for all the bottles except for the unmachined bottle. The prediction attempted in the GFRP03 pressure bottle gave the percentage error from -6.11 to 3.22% at 100 bar pressure cycle. Its exponents gave a prediction of -15.37 to 21.9% at 100 bar pressure cycle. The exponents of GFRP-01 and GFRP-05 pressure bottles exhibit reasonably low error margins at -0.64 to 3.22% and -19.2 to 6.43% respectively at 75 bar cycle. GFRP04 pressure bottle failed at very low pressure (125 bar) compared to all the remaining hardware. Substituting the GFRP-02 hardware exponents/constants gave a prediction for this hardware with an error margin of 16.9% at 75 bar cycle. This particular hardware failed during the 3 mins hold period. E.V.K.Hill and T.J.Lewis [4] already found the characteristic of bad pressure vessel. The continuance of AE activity during the pressure hold would indicate a bad vessel creeping to failure and could cause huge error margin. This methodology can be extended for other types of hardware like Kevlar- epoxy, Carbon- epoxy etc. The results comparison of all the hardware is given in Tables 1 to 5. Table 1 : Prediction using GFRP -1 constants Bottle no.
Bottle no.
Actual Predicted Percentage Prediction Remarks burst burst error attempted pressure pressure pressure (bar) using (bar) empirical relation (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
Table 3 : Bottle no.
Prediction using GFRP -3 constants Actual Predicted Percentage Prediction Remarks burst burst error attempted pressure pressure pressure (bar) using (bar) empirical relation (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
Table 4 : Prediction using GFRP -4 constants Bottle no.
Actual Predicted Percentage Prediction Remarks burst burst error attempted pressure pressure pressure (bar) using (bar) empirical relation (bar)
GFRP-1 263.6
217.492
-17.5
125
machined
GFRP-2 299.5
179.84
-39.9
125
unmachined
125
machined
GFRP-3
274
198.037
-27.72
GFRP-4
125
124.966
-0.03
50
machined
GFRP-5
260
214.98
-17.3
100
machined
Table 5 : Prediction using GFRP -5 constants
Actual Predicted Percentage Prediction Remarks burst burst error attempted pressure pressure pressure (bar) using (bar) empirical relation (bar)
Bottle no.
Actual Predicted Percentage Prediction Remarks burst burst error attempted pressure pressure pressure (bar) using (bar) empirical relation (bar)
GFRP-1 263.6
263.66
+0.02
100
machined
GFRP-1 263.6
280.539
+6.43
50
machined
GFRP-2 299.5
307.51
+2.67
125
unmachined
GFRP-2 299.5
241.86
-19.2
50
unmachined
GFRP-3
274
288.823
+3.22
100
machined
GFRP-3
274
279.976
+2.18
100
machined
GFRP-4
125
173.99
+39.2
75
machined
GFRP-4
125
176.133
+40.9
125
machined
GFRP-5
260
259.9833
-0.64
75
machined
GFRP-5
260
259.958
-0.02
75
machined
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If one compares the performance of all the hardware it can be identified that the failure of GFRP hardware is preceded by high count rate, large number of long duration events, high amplitude rate and a very low felicity ratio. The authors observed from the mathematical analysis that the predicted burst pressure error margin is high at lower pressure and it is reasonable in the range 75 bar to 100 bar.
to predict the burst strength and can send out warning signals well ahead of failure.
8. CONCLUDING REMARKS
REFERENCES
The authors have clearly verified that the prediction of burst pressure is possible in the case of GFRP pressure bottles with a lucid empirical relation. The correlation of all the five hardware is reasonably better with an acceptable error margins at –0.64% to 2.18% and for the worst case the percentage of error prediction is -19.2% to 16.9% at around 75% of MEOP. The major AE parameters like ring down counts, event duration, peak amplitude and felicity ratio exhibited during first repeat cycle could substantially facilitate accurate prediction of failure. This innovative approach can be extended to any other material systems
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ACKNOWLEDGMENTS The authors would like to thank the Senior Scientists of Composite Entity, VSSC, Thiruvananthapuram for the suggestions and encouragements given.
1. Schliessmann J A, Pressure Vessel Proof Test Variables and Flaw Growth, Journal of materials, JMLSA, 7(4) (1972) 465-469. 2. Dai Guang., Xu Yan Ting.,Wang Ya Li., Zhang Bao Qi and Han Wan Xue., AE Monitoring and Data Analysis for Large Spherical Tanks, NDT &E International, 26(6) (1993) 287-290. 3. Jessen,E.C., Spanheimer,H and De Herrera, A.J., Prediction of Composite 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 a Filament-Wound Composite Rocket Motor Case during Hydro Proof, Journal of Material Evaluation, 43 (1985) 861.
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PROBE
AYURVEDA
and
CHANAKYA
By B. Ramprakash 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 same way according to the nature of the diet – satva, rajas, or tamas- we produce results.
Chanakya These lines establish the connection between food and mind. As per me the food for mind is the thoughts that 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. When it is tuned to a certain frequency the waves floating around in that frequency is collected. Controlling the radio 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 bigger things (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 smooth life. “Noyatra vazhve kuraivatra selvam”. Which in English means that “a life without disease is perfect wealth”. By exercising the control over our senses we are able to set an example for others and are able to influence others surrounding us (example Mahatma Gandhi). Our circle of influence increases. Success is a measure of the circle of influence. Going back to the analogy of radio we can control the choice of frequency. We have the choice of choosing the frequency. Similarly we can choose the thoughts that reach us. Great inventions have taken place in a flash because the inventor was tuned to that frequency. We are the masters of our minds. Quote “Five years ago, I had a beautiful experience which set me on road that has led to writing of this book. I was sitting by the ocean one late summer afternoon, watching the waves rolling in and feeling the rhythm of my breathing, when I suddenly became aware of my whole environment as being engaged in a gigantic 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 only discoveries! 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 into silence we become the seer instead of the seen. It is an elimination process. Start from outward but go inward and you will learn the art of allowing it to happen
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