Volume 10 Issue 4 March 2012 by Sugumar MP

Volume 10 issue 4 March 2012

from the Chief Editor

The year of 2011 ended with a grand gala NDE2011 which saw more than 200 technical presentations, 120 exhibitors, and about 1000 registered participants that will stay in everyoneâ&#x20AC;&#x2122;s memories for ever. In this issue, these experiences can be shared by all ISNT members with many of the snapshots captured by the organizing team of the NDE2011. The 4 Technical papers in this issue of JNDTE are on a variety of NDE methods with the first one from NML that discusses NDE tool for friction stir welding process. The use of fiber optic sensors for acoustic emission sensing is will described by the authors from IITM and IGCAR. These fiber optics sensors offer a new method of detecting and monitoring acoustic waves with some inherent advantages over the piezo sensors that are currently used for AET. A novel ultrasonic air coupled L-scan mode of inspection for composite materials is discussed in the paper from CNDE at IITM. This method allows for the inspection using non-contact mode (without any coupling material like water) and can be used for inspection and materials characterization. The final paper on ultrasonic modeling and the simulations using the ray based approach is well described for phased array imaging by the team from Dhvani Research. They have obtained excellent comparisons between the experimental data and the simulated data that infuses confidence in the theoretical models and how it can be used by NDT personnel for improving the interpretation and reducing costs for procedure development and validation. The other featured articles such as BASICS, HORIZON, PUZZLE, PROBE, and PRODUCTS AND PATENTS are interesting reading material and it is hoped that more participation in these type of articles, including contributions from ISNT members, would be welcome. The Editorial Board joins me in wishing all the readers a successful and enjoyable 2012. The 18th WCNDT 2012 is in Durban, South Africa between 15-20 April 2012 and there are many participants from India, particularly ISNT members. This growth in the number of participants in India, in both the technical sessions and in the exhibition hall ,is extremely encouraging and hope this trend continues.

Dr. Krishnan B alasubramaniam 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 10 issue 4 March 2012

I S N T - National Governing Council Chapter - Chairman & Secretary President Shri P. Kalyanasundaram President Elect Shri V. Pari Vice-Presidents Shri D.J. Varde Shri Swapan Chakraborty Shri N.V. Wagle Hon. General Secretary Shri R.J.Pardikar Hon.Jt.Secretaries Shri Rajul.R.Parikh Dr.B.Venkatraman Hon. Treasurer Shri S.Subramanian Hon. Co.Treasurer Shri Sai Suryanarayana Immediate Past President Shri K.Thambithurai Past President Shri Dilip.P.Takbhate 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 Prof. G.V.Prabhugaunkar Shri B.K.Pangare Shri M.V.Rajamani Shri Samir K. Choksi Shri B.K.Shah Shri S.V.Subba Rao Shri Sudipta Dasgupta Shri R.K.Singh Shri A.K.Singh(Kota) Shri C.Awasthi Shri Brig. P.Ganesham Shri Prabhat Kumar Shri V.Sathyan Shri P.Mohan Shri R.Sampath Ms. Hemal Thacker Shri A.K.Singhi Shri T.V.K.Kidao Shri B. Prahlad Dr. BPC Rao Dr.Sarmishtha Palit Sagar Permanent Invitees Shri V.A. Chandramouli Prof. S. Rajagopal Shri G. Ramachandran and All Past Presidents, All Chapter Chairmen / Secretaries Ex-officio Members Chairman NCB, Secretary NCB, Treasurer NCB, Controller of Examination NCB, President QUNEST, Secretary QUNEST, Treasurer QUNEST

vol 10 issue 4 March 2012

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 QAS, RAPS - 5 & 6, PO Anushakti Rawatbhata 323 303 abahl@npcil.co.in Shri S.K. Verma, Hon. Secretary, TQAS, RAPS - 5 & 6, PO Anushakti Rawatbhata 323303. surendrakverma@npcil.co.in

Mumbai 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

Bangalore Prof.C.R.L.Murthy, Chairman Dept. of Aerospace Engg, Indian Institute of Science, Bangalore 560012 Email : crlmurty@aero.iisc.ernet.in

Chennai Nagpur

Shri R. Sundar, Chairman Director of Boilers, Tamil Nadu Shri R. Balakrishnan, Hon. Secretary, No.13, 4th Cross Street, Indira Nagar, Adyar, Chennai 600 020 isntchennaichapter@gmail.com

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

Delhi Shri A.K Singhi, Chairman, MD, IRC Engg Services India Pvt. Ltd 612, Chiranjiv Tower 43, New Delhi 110019 ashok.ircengg@gmail.com Shri M.C. Giri, Hon.Secretary, Managing Partner, Duplex Nucleo Enterprise New Delhi 110028 munish.giri@yahoo.com

Pune

Hyderabad

Sriharikota

Shri BK Pangare, Chairman Quality NDT Services, Plot BGA, 1/3 Bhosari, General Block, MIDC, Bhosari, Pune- 411 026 ndtserve@pn3.vsnl.net.in Shri BB Mate, Hon Secretary, Thermax Ltd., D-13, MIDC Ind. Area, RD Aga Road, Chinchwad, Pune- 411 019 bmate@thermaxindia.com

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. isnt@shar.gov.in

Shri M. Narayan Rao, Chairman, Chairman & Managing Director, MIDHANI, Kanchanbagh, Hyderabad 500 058. cmd.midhani@ap.nic.in Shri Jaiteerth R. Doshi, Hon.Secretary, Scientist, Project LRSAM DRDL, Hyderabad 500 058. joshidrdl@gmail.com

Tarapur

Jamshedpur

Shri PG Bhere, Chairman, AFFF, BARC, Tarapur-401 502. pgbehere1@rediffmail.com Shri Jamal Akhtar, Hon.Secretary, TAPS 1 & 2, NPCIL, Tarapur. jakhtar@npcil.co.in

Dr N Parida, Chairman, Senior Deputy Director Head, MSTD, NML, Jamshedpur - 831 007 nparida@nmlindia.org Mr. GVS Murthy, Hon. Secretary, MSTD, NML, Jamshedpur gvs@mnlindia.org / gvsmurthy_mnl@yahoo.com

Tiruchirapalli R.J. Pardikar AGM, (NDTL) BHEL Tiruchirapalli 620 014. rjp@bheltry.co.in Shri L. Marimuthu, Hon. Secretary, HA-95, Anna Nagar Tiruchirapalli 620 026. lmmuthu@bheltry.com

Kalpakkam Dr. B. Venkatraman, Chairman Associate Director, RSEG, & Head, QAD, IGCAR, Kalpakkam 603 102 bvenkat@igcar.gov.in Shri B. Dhananjaykumar, Hon.Secretary Reprocessing Group, IGCAR, Kalpakkam â&#x20AC;&#x201C; 603 102 mdjkumar@igcar.gov.in

Vadodara

Kochi Shri CK Soman, Chairman, Dy. General Manager (P & U), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal 682 302. Kochi somanck@bharatpetroleum.in Shri V. Sathyan, Hon. Secretary, SM (Project), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal-682 302. Kochi sathyanv@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

Shri P M Shah, Chairman, Head-(QA) Nuclear Power Corporation Ltd. npcil.bar@gmail.com M S Hemal Thacker, Hon.Secretary, NBCC Plaza, Opp.Utkarsh petrol pump, Kareli Baug, Vadodara-390018. pmetco@gmail.com

Thiruvananthapuram Dr. S. Annamala Pillai, Chairman Group Director, Structural Design & Engg Group, VSSC, ISRO, Thiruvananthapuram 695022 s_annamala@vssc.gov.in Shri. Binu P. Thomas Hon. Secretary, Holography section, EXMD/SDEG, STR Entity, VSSC, Thiruvananthapuram 695 022 binu_thomas@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 Destructive Testing & Evaluation

Journal of Non Destructive Testing & Evaluation About the cover page:

Volume 10 issue 4 March 2012

Contents Basics -

The cover page depicts the experimentally imaged field characteristics of two immersion ultrasonic transducers, using a reference stainless steel ball as a reflector. Ultrasonic fields can be used to define the performance of the transducer used for inspection. The directivity pattern of the ultrasonic transducer depends on the medium, diameter, shape, frequency, and the lens used, in the inspection. Depending on the ultrasonic field, the interpretation of the test results may vary, and hence the field must be well characterized. The characteristic of an ultrasonic transducer may also not remain the same over extended duration. Hence, periodic characterization of the transducers for the time, frequency, and profile characterizations as per accepted standards is now becoming mandatory in several industries. Standards such as ASTM E 1065-99 are used by the industry to define the procedures for characterisation for both immersion and contact transducers. Several industry requirements such as NADCAP (in aerospace industries) mandate the suppliers to conform to such transducer characterisation standards. (Courtesy: The ultrasonic field images were obtained by the Advanced Systems Laboratory, Hyderabad, using the TraCSS system supplied by Dhvani Research and Development Solutions Pvt Ltd, Chennai)

Horizon -

Chapter News

NDE 2011 Highlights

NDE 2011 Photos

NDT Events

NDT Puzzle

NDT Patents Technical Papers Detection and Quantification of Lack-of-Penetration in Al-Al Friction-Stir Welded Plates using Phased Array Ultrasonic Technique

Rajat Mazumder, N.R. Bandyopadhyay and S Palit Sagar

Transient Response of Fabry-Perot Filter-based Dynamic Interrogator

Harish Achar, Bibin Varghese, G.M. Krishna Chaitanya, S. Sosamma, M. Kasinathan, Anish Kumar, C. Babu Rao, N. Murali, T. Jayakumar and Balaji Srinivasan

Air-coupled L-scan (Lamb wave scan) Imaging and its application in inspection of composite structures

Janardhan Padiyar M, C Ramadas and Krishnan Balasubramaniam

Validation of ray-based ultrasonic simulation tool (simsonic) using conventional and phased array transducers

Padma Purushothaman, Krishnan Balasubramaniam and C.V. Krishnamurthy

Probe

Chief Editor Prof. Krishnan Balasubramaniam e-mail: balas@iitm.ac.in

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

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.

Classifieds Scaanray Metallurgical Services (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 in all the following eleven Methods

Shri. K. Ravindran, Level III RT, UT, MT, PT, VT, LT, ET, IR, AE, NR and VA

vol 10 issue 4 March 2012

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, Govindaraji Naicker Complex, Janaki Nagar, Arcot Road, Valasaravakkam, Chennai 600 087 Tamil Nadu, India Phone : +91 44-2486 4332, 2486 8785, 4264 7537 E-mail: sisins@gmail.com and sisins@hotmail.com Website: www.sisndt.com/www.ndtsis.com/ wwwpdmsis.com

Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

Basics US waves get reflected at materials’ interface where the acoustic impedances do not match resulting in an echo.

Ultrasonic Testing Method

In the example given in Figure 2, a US pulse generated by the probe travels in 100 mm steel specimen and returns to the probe in about 32 microseconds (microsecs). In the same specimen if a flaw is present at 40 mm an echo will be received at 14 microsec. It is this time difference that we discern to locate the flaw.

Dr.Oruganti Prabhakar Proprietor-OP-TECH

INTRODUCTION

BASIC PRINCIPLES

Ultrasonic Testing (UT) is done by first generating high frequency acoustic waves at the outer surface of the component and transmitting these waves through a coupling medium into the component. The flaw indications are indirect unlike Radiographic Testing Method where the silhouette of the discontinuity can be seen on the radiograph. The UT of flat and parallel-sided components for large isolated discontinuities is quite straightforward. However, caution must be exercised in applying UT for complex shapes and for detecting smaller discontinuities. Operator skill would determine the correct interpretation of the results. It is better to restrict UT to materials having an attenuation coefficient less than 0.1 dB/mm to reduce the trust deficit of the management on UT.

PULSE-ECHO TECHNIQUE

TWO PRINCIPLES DEFINE THIS UT TECHNIQUE:

Ultrasonic (US) waves have a fixed phase velocity in a given medium (non-dispersive type) for a given mode.

ACOUSTIC WAVES

Fig. 1 : Types of UT waves

There are many ultrasonic vibration modes that travel through materials. The widely used modes for UT are longitudinal, transverse, surface and plate waves. The directions of particle vibration and wave propagation direction will determine the vibration mode. If they are parallel then it is ‘longitudinal’ and if they are perpendicular to each other then it is ‘shear’ or ‘transverse’ waves. In conventional UT we deal mostly with non-dispersive type of US waves where the phase velocity is independent of frequency and specimen thickness.

Fig. 2 : Pulse-Echo technique principle

vol 10 issue 4 March 2012

In pulse-echo technique we are looking for means to measure times in the microseconds range. So we use a CRT to measure the time of travel of the pulse. This is also known as the “Time of flight” (TOF). We synchronize the electron beam travel

Journal of Non Destructive Testing & Evaluation

Basics

schematic of the method. This technique is employed in the resistance welding of plates and sheets. One uses a continuous train of US waves unlike a pulse in the pulse- technique. OBLIQUE INCIDENCE

Mode conversion takes place as shown in Fig. 7 when a sound beam strikes an interface between two media at an angle other than 90o. The angular relationships between the various modes can be determined by Snellâ&#x20AC;&#x2122;s law given below. Fig. 3 : Block diagram of an ultrasonic Pulse Echo equipment

in the CRT with the US pulse travel in the specimen. Figure 3 shows a schematic block diagram of US pulse echo equipment. Modern equipment are different, however, for training we still use CRT to explain the UT fundamentals. Some typical flaw indications are shown in Figure 4. What one should notice is an echo from the discontinuity should be received by the probe. Otherwise we cannot draw any conclusion. So planar defects like fatigue crack, hot tear, laminations etc. that reflect the US waves nicely back to the probe can be detected easily by UT. Shrinks, pipes etc. are poor reflectors and hence detection is more difficult.

2. ACOUSTIC IMPEDANCE (FIG.5) It is the product of the density and the phase velocity of a material. The degree of mismatch between two materials will determine the amount of pressure transferred from one material to another when in contact. 3. THROUGH TRANSMISSION TECHNIQUE In through transmission technique US energy is transmitted through the zone of interest. The changes in the transmitted energy are taken as a measure of the quality of the zone of interest. Figure 6 shows the

where subscript L= longitudinal, t=Transverse, 1= medium 1 and 2 =medium 2. We generate longitudinal waves in the probe but scan the component using shear waves generated through mode conversion. By clever manipulation we totally eliminate the presence of longitudinal waves in the component. This law is used extensively in UT for testing and probe construction. One should remember while Snellâ&#x20AC;&#x2122;s law indicates angular relationships between various modes, it does not tell us about the pressure distribution amongst these modes. PRESSURE ATTENUATION

Fig. 4 : Typical flaw indicattions Journal of Non Destructive Testing & Evaluation

The gradual loss of intensity of US waves travelling through a specimen is termed as Attenuation. Grain size distribution, micro inclusions and other scatterers influence attenuation. If the scatterer is smaller than the wavelength then the scatterer is practically of no consequence. By employing a lower frequency or a higher wavelength one may reduce the scattering problem. However, lowering the frequency will decrease the sensitivity to detect discontinuities and will also reduce lateral resolution. vol 10 issue 4 March 2012

Basics SENSITIVITY

It is ability to detect the smallest flaw. It is influence by the wavelength or the probe frequency employed in UT. Higher the frequency higher the sensivity of the UT method. The smallest size of the flaw one can detect is half of the wavelength used. This is for spherical type of flaws. In the case of crack like discontinuities the crack thickness can be as low as one tenth of the wavelength or even smaller. RESOLUTION Fig. 5 : Reflection and transmission

Resolution is the ability to separate two signals coming from two defects lying close to each other. Both axial and lateral resolutions are relevant in UT. 6 dB difference may be used to differentiate two closely lying signal. Axial resolution may be altered by changing the damping of the crustal and the pulse voltage applied to the crystal. Lateral resolution is manipulated by changing the beam spread and beam focussing. IMMERSION TECHNIQUE

Fig. 6 : Through transmission technique

Fig. 7 : Mode conversions vol 10 issue 4 March 2012

In this technique water is used as the couplant. The part to be tested in immersed in a water tank during testing. In immersion technique it is possible to use different search units sizes and shapes. The search units are usually focussed probes. The water path and the focussing distance inside the steel specimen are of major concerns in this method. One tends

Fig. 8 : Immersion Technique Journal of Non Destructive Testing & Evaluation

Basics to use scanners in immersion technique. The principle one employs in immersion testing and in any time delay technique in general, is that the second reflection from the water/ specimen interface should come after the first reflection from the backwall of the test specimen. This will ensure easier analysis of the signal patterns. Please see Fig. 8 for a general arrangement used in immersion testing. PROBE TYPES

The following types of probes are used in UT. 1. 2. 3. 4. 5. 6. 7. 8. 9.

Normal Probe Angle Probe T/R Probe Immersion Probe Squirters Bubblers EMAT Laser induced US waves Air coupling Probe

Each type of probe is used depending on the application. The most commonly used probes are the normal, angle and immersion probes. CALIBRATION/REFERENCE BLOCKS

Calibration blocks are used to calibrate the time and the gain of the UT equipment. Two of the commonly

used calibration blocks are shown in Figure 9. Reference blocks are made with a wide variety of reflectors such as notches, flat bottom holes (FBH) and side drilled holes (SDH). FLAW SIZE DETERMINATION

Fracture control and fracture mechanics have placed a great emphasis on the flaw size determination. UT is of great help to determine the flaw size. One employs three methods to assess the flaw size: 1. 6 dB drop method: This is used when the flaw size is bigger than the probe diameter. 2. Distance- Gain-Size diagrams (DGS), Distance-AmplitudeCorrection Curve (DAC), Flat Bottom Holes (FBH) or Side drilled Holes (SDH): This is used when the flaw size is smaller than the probe diameter. 3. Time of Flight: In this method one employs the time of flight to calculate the flaw size instead of the gain used.

Cathode ray tube (CRT)

Cathode ray tube (CRT) is usually employed in UT. The CRT has two sets of plates, one pair â&#x20AC;&#x201C; X-Pair and the other- Y-Pair. Two electrical signals can be fed to these two pairs of plates. The type of scanning is determined by the electrical signals we choose to feed into CRT. A-SCAN:

X-Pair- Time of flight of the US pulse. Y-Pair- Amplification of the US signal, Gain. B-SCAN:

X-Pair- Probe location on the component in one (say x) direction. Y-Pair- Time of flight of the US pulse. So you find that the B-Scan has no information on the gain employed. So this is useful in Time of Flight Diffraction (TOFD), a type of UT which utilizes the diffraction effects of US waves. One may also call Bscan as parallel stacking of A-Scan signals.

SCANNING METHODS

The information obtained in UT can be displayed by three methods: 1. 2.

Meter Strip Chart

C-SCAN:

X-Pair- Probe component in xY-Pair- Probe component in y-

location on the direction. location on the direction.

In the C-Scan the test data like time of flight, gain or phase are displayed as the pixel intensity or depth. TESTING OF CASTINGS

Fig. 9 : V1, V2 reference blocks Journal of Non Destructive Testing & Evaluation

Plain carbon steel or alloy steel castings weighing up to 50 tons are cast in India for many industries including for cement and sugar mills. Heat treatment is an essential feature of these castings. Adequacy of the heat treatment can be in many situations monitored by UT. Ultimately the toughness of the castings is what the engineer vol 10 issue 4 March 2012

focussing on. UT would reveal many factors like inclusions, hot-tears, blow holes, porosity, cracks, hydrogen blisters, hydrogen induced cracking etc. that affect toughness. We should not forget that some critical information on embrittlement including hydrogen or tramp element induced embrittlement, segregation or presence of harmful phases like sigma or Chi phase cannot be obtained by conventional UT on the shop floor. Minimum section thickness of the castings, surface roughness, the orientation of the discontinuities and microstructure are some of the factors that limit the use of UT in the casting industry. Curved surfaces such as the bore of an engine cylinder block would not permit adequate or easy coupling of the probe and so precautions should be taken. Cast iron castings pose a special problem due to the presence of free graphite that damps the US waves. Grades higher than 17 or Spheroidal graphite cast irons may be tested with UT. UT is more useful to assess the structure of cast iron castings than for flaw detection. WELD TESTING

Welds are tested using angle probes as shown in Figure 10.

Basics By its very nature weld cannot be perfect. Welds have defects. Cracks or nicks, residual stresses and variations in microstructure constitute the major issues of concern. Many of the weld defects can be detected by UT and it is the main test method in many situations to accept welds. Hydrogen continues to be a major problem in welds. In its atomic state it can cause embrittlement or coalesce to form blisters. However, in the molecular form coupled with residual stresses can cause delayed cracking. UT is an invaluable tool to detect HIC (hydrogen induced cracks). Mostly angle probes are employed. Once a flaw is detected during scanning, the beam path from the flaw detector and the physical distance measured between the probe and the weld centre line are used to obtain information on the location, size and the nature of flaw. A UT operator has to undergo good practical training to do weld testing reliably. Codes like AWS and ASME are used extensively in the industries to carry out UT. The main principle is that the UT beam should be very nearly at 90o to the flaw to obtain good reflection. So in the case of thick plates one may virtually slice the plates into three

or more zones and use different probes for different zones. This is practised in Automated Ultrasonic Testing (AUT). Just for one type of defect like Lack of side wall fusion (LOF) in thick welds, we may use time of flight diffraction technique which is a slight variation of UT. In TOFD we use the diffracted beam and not the reflected beam. ADVANCES IN UT

Major advances have taken place in UT. Most of these are propelled by improvements in signal and image analysis techniques. Phased array ultrasonic testing (PAUT), Guided wave testing and Time-of-flight diffraction technique are the important modern UT methods. Investments in equipment and manpower training are huge. In India there is a general belief amongst the technologists that more recent the technique the better it is. Remember the days when acoustic emission technique was introduced in early 70â&#x20AC;&#x2122;s and when all the Indian NDT personnel rushed to embrace this technique as a cure all. However, at least one major advanced country has reservations about these modern UT techniques. They feel that conventional UT can do the job adequately and it is mostly the hype that is surrounding these modern techniques. Obviously truth should be lying somewhere between the two extreme views. GENERAL COMMENT

For a successful application of UT in a jobbing environment, time and effort are needed. Reasonable remuneration for UT operators and tightening the certification programs are necessary if the reliability and usefulness of this method are to be further improved in our country. Â&#x201E;

Fig. 10 : Weld Testing vol 10 issue 4 March 2012

Journal of Non Destructive Testing & Evaluation

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Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

Horizon

Imaging 3D objects or extended objects requires a large depth of focus. Likewise, as shown in Figure 2, imaging small objects distributed in the volume at different depths also require a large depth of focus. However, increasing the depth of focus leads to lowering the SNR and increasing the beam waist – the weak focusing regime.

Localized Waves and Imaging Dr. CV Krishnamurthy Centre for NDE and Department of Physics, IIT Madras Chennai 600036 Tamilnadu Email ID: cvkm@iitm.ac.in

When a collimated beam of monochromatic waves propagating along, say, the z-axis is focused by a lens, the beam converges to a narrow waist at the focal point and diverges beyond it. A depth of focus is defined as the spatial extent along the z-axis within which the beam intensity is within 6-dB of the maximum as shown in Figure 1. A measure of the spot size can be obtained if we define a 6-dB width laterally in the xy-plane at each point on the z-axis within the depth of focus.

Ideally objects in the focal plane can be imaged with the highest SNR and the maximum lateral resolution as the beam intensity is the highest and the beam waist is the narrowest at the focal plane. An additional advantage is that the plane wave-fronts at the focal plane enable quantitative interpretation of scattering experiments. Lateral resolution can be improved by reducing the beam waist, and concomitantly increasing the SNR, through appropriate lenses – the strong focusing regime.

Obtaining a large depth of focus without reducing the SNR significantly has been a long-standing objective for the imaging community. It is well known that a beam from an extended source (diameter D, wavelength λ) has an angular width defined by λ/D – traditionally larger apertures were employed to attain “pencil” beams but at the cost of increased sidelobe levels. Fairly sophisticated weightages (nonuniform apertures or apodized apertures) were employed to keep the sidelobe levels under desired levels particularly by the radar community. Efforts to design annular or more complex acoustic transduction mechanisms and design of complex passive elements such as the logarithmic lens (see Figure 3 below) have resulted in attractive options for improving SNR as well as increasing the focal zone.

Fig. 1 : Depth of Focus for a Gaussian Beam

Fig. 2 : Optimal depth-of-field in the aspect of image quality [from Hong and Cho (2010), International Journal of Optomechatronics, vol. 4, 379-396]. vol 10 issue 4 March 2012

Ultrasonic imaging is quite similar to imaging with light except for the fact that true focus falls shorter than the geometric focus with the distinction becoming significant at lower frequencies. When finite bandwidth signals are used as in ultrasound, in the form of pulses, the focal characteristics of the dominant frequency are assumed to prevail although it is a somewhat simplified picture.

Synthetic apertures were proposed and exploited to achieve even narrower beam widths (SAFT) by having simple sources span a larger spatial domain. With the advent of electronically controllable arrays of

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HORIZON

It was shown that an axicon could generate a Bessel beam, the socalled non-diffracting beams, for which the transverse distribution was constant along the propagation direction, theoretically.

Fig. 3 : Typical acoustic lens with axi-symmetric logarithmic profile producing a narrow beam

active radiation elements, it has been possible to achieve better control on beam formation. The central feature of radiation from a “point” source is that it spreads spatially with propagation distance. Radiation from a collection of “point” sources, visualized using Huygen’s wavefront construction, leads to “beams” in the far-field, with fairly well-defined amplitudes and phase fronts in space. The angular dependence of the amplitude (also known as directivity) in the far-field with locally plane phase fronts can also be thought of as a resultant of a superposition of plane waves propagating in different directions. Attempts to produce “pencil” beams with narrow apertures (or slits) fail due to diffraction of the waves. Once launched into a medium, the wave disperses as it propagates governed entirely by local medium properties.

discovered by Ziolkowski who developed a procedure to construct new solutions through the Laplace transform. Durnin et al., in 1987 discovered independently a new exact nondiffracting solution of the free-space scalar wave equation. Hsu et al. realized in 1989 a beam with a narrow band PZT ceramic ultrasonic transducer of non-uniform poling. Durnin et al. showed experimentally that a realistic nondiffraction beam (also called Bessel beam because the lateral beam profile is described by a Bessel function) with wavelength λ = 0 .6328 nm and central spot of 59 mm, passing through an aperture with radius R = 3.5 mm, is able to travel about 85 cm keeping its transverse intensity shape approximately unchanged (in the axial region surrounding its central peak).

By comparison, a Gaussian beam at the same wavelength and central spot dimensions, when passing through an aperture with the radius R = 3.5 mm, doubles its transverse width after 3 cm, and after 6 cm its intensity has already diminished by a factor of 10. In other words, the Bessel beam could travel, approximately without deformation, a distance 28 times longer than that travelled by a Gaussian beam! This remarkable property is due to the fact that, when diffracting, the transverse intensity fields (whose value decreases with increasing radial distance), associated with the rings that constitute the (transverse) structure of the Bessel beam, end up reconstructing the beam itself all along a large depth of field. Fig. 3.2 below shows the experimental setup for launching the Bessel beam in the microwave regime. The Bessel beam is generated by using an axicon using an InP Gunn diode oscillator with output power of 10-20 mW mounted within a resonant cavity with the output tuned from 72 to 95 GHz.

Are there then possibilities for generating a beam that does not disperse as it propagates? BESSEL BEAMS Stratton, as early as in 1941, obtained solutions for the Helmholtz wave equation that had non-dispersive characteristics. In 1983, Brittingham discovered the first localized wave solution of the free-space scalar wave equation and called it a self-focus wave mode. In 1985, another localized wave solution was

Fig. 4 : Axicon generating a Bessel beam. The Bessel beam can be thought of as a superposition of plane waves (wavefronts shown as dotted lines) forming the same angle with the horizontal but propagating in two different directions as shown. The characteristic central non-diffraction spot of the Bessel beam is shown as an image at the right extreme. [from David McGloin, Veneranda Garcés-Chávez, and Kishan Dholakia, oemagazine (SPIE) January 2003]

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Fig. 5 : The Characteristic ring structure of the Bessel beam.[from Florian O. Fahrbach and Alexander Rohrbach, Nature Communications (2011) ]

Fig. 7 : Intensity profile of a microscopic Bessel-like beam. To generate this pattern, the beam of a 10-fs Ti: sapphire laser was spatially multiplexed with an array of Gaussian-shaped thin-film microaxicons (fused silica layer on a substrate of identical material, structure height 5.7μm). The field of view was magnified with a microscopic objective (20 × ) and imaged onto a high-resolution CCD camera. [from Grunwald et al., Ch.11 in Localised Waves (2008) ed. Hugo E. Hernandez-Figueroa, Michel Zamboni-Rached and Erasmo Recami, John Wiley & Sons, Inc.]

by illuminating axicons with plane waves or Gaussian intensity distributions. The propagation zone over which minimum changes in the pattern occurs is extended. X-WAVES Fig. 6 : Experimental configuration for launching a Bessel beam at 90 GHz [from Monk et al. (1999) Opt. Comm. 170, 213-215]

The output signal was fed to a corrugated feed-horn and the beam was directed toward a lens. The lens produced a Gaussian beam with 20-mm waist, which was directed toward 90-mm diameter axicon with angle of 32°. The lens and the axicon were both made from polyethylene with a refractive index of 1.52 and had l/4 in. deep grooves in order to reduce reflections and standing waves. The generated beam was measured using a diode detector mounted on a x-y scanning stage. The measurements indicate a field depth around 70mm and the FWHM of the center spot is 4mm. A Gaussian beam with the same wavelength and vol 10 issue 4 March 2012

FWHM has a field depth of about 10mm. Durnin had termed the new beams “nondiffracting beams” or “diffraction-free beams”. Today they are termed “limited diffraction beams” on the basis that all practical beams will diffract eventually. Theoretically, limited diffraction beams can only be produced with an infinite aperture. In practice, these beams can be closely approximated with a finite aperture over a large depth of field. Bessel-like beams generated by Gaussian phase profiles are quite different from focused Gaussian beams or Bessel-like beams obtained

Bessel beams were generalized into nondiffracting pulses, called X-waves after the shape of the beam as shown in Figure 8 below, with the feature that all the frequency components propagate with the same angle to the beam axis. As all wave components share a common phase velocity along the propagation axis, they keep their mutual interference pattern unchanged. The wave energy is focused onto the axis of propagation, not merely into a single spot as for Gaussian-type waves but along an entire focal line, whose length is determined by the transducer. In comparison to spherical ultrasonic lenses the depth of field is wavelength independent. It is only determined by the radius Rax and the angle ς1 of

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HORIZON

Fig. 8 : Amplitude of the zeroth-order X-wave, in the meridional xz plane. The whole X-wave pattern is rotationally symmetric about z. [from Fagerholm et al., Phys. Rev. E. (1996), 54, 4347-4352 ]

the axicon transducer as given below:

There have been several schemes proposed to generate Bessel beams and X-waves many of which employ axicons or circular diffraction gratings or a combination of the two as shown below: There has been an extensive numerical study on the reflection and transmission properties of X-waves at an interface separating air and a lossy dispersive medium modeling the ground. The results indicate that X-waves can penetrate deeply into the ground while retaining their localization properties. This could certainly have applications in subsurface detection (e.g., land mines). By increasing the field depth, it is possible to use X-waves for subsurface detection, fiber optical communication, secure communications, high-frame rate imaging, non-destructive evaluation, Doppler velocity estimation and pulse-echo imaging. X-Wave timedomain scattering can provide significant advantages over classical frequency-domain methods and recent ultra-short pulse time-domain measurements. The combination of an axicon with a lens is used in laser machining to drill holes. In

fundamental physics, axicons are used to generate an optical trap which guides atoms or molecules. Reflective axicons are used with ultra-short laser pulses to generate and study X-pulses properties.

Photoacoustic imaging with a conical axicon detector has been attempted through simulations and experiments. It was found that axicon-based detection gives images with high depth of field but a relatively high level of artifacts. Figure 13 shows simulated results highlighting the advantages of axicon detector. The axicon detector appeared to favor small, isolated sources and partly rejected signals from planar boundaries. Due to the spatial invariance of the point spread function (PSF) the X-shaped artifacts could be reduced by deconvolution and restoration of the actual source dimensions was accomplished. An intriguing property of X-waves is that they seem to self-reconstruct after being scattered by small objects! This is in contrast with Talbot effect â&#x20AC;&#x201C; spatial and temporal self-

Fig. 9 : Panels (1) and (2): Computer simulations of the zeroth-order (n = 0) band-limited X wave at distances z =170 mm and 340mm, respectively, away from the surface of a 50mm-diameter transducer. An exact X wave aperture shading and a broadband X wave pulse drive of the transducer were assumed. The transmitting transfer function of the transducer was assumed to be the Blackman window function peaked at 2.5 MHz and with -6-dB bandwidth around 2.1 MHz. Panels (3) and (4): Experimental results that correspond to the simulations in (1) and (2), respectively. A 10-element, 50-mmdiameter, 2.5-MHz central frequency, PZTceramic/polymer composite J 0 Besscl transducer with a -6-dB pulse-echo bandwidth about 50% of the central frequency was used. Linear analytic envelope of the real part of the X wave is displayed in all panels. [from Lu and Greenleaf (1992), IEEE Trans UFFC, 39, 441-446] surface give rise to acoustic waves that converge on an axis along a length given by the depth of focus (DOF). [from Passler et. al., (2010) 1, Biomedical Optics Express, 318-323]

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HORIZON

imaging in a periodic manner. Figure 14 shows one of several experiments indicating almost total recovery of the incident beam after getting distorted by an object in its propagation path.

Fig. 10 : Lateral (a2) and axial (a4) beam plots of the X waves shown in Fig. 1 at distances z=340 mm. Full lines, dotted lines, and dashed lines correspond to experiment, simulations with an exact X wave aperture shading and simulations with a piecewise X wave aperture shading, respectively.[from Lu and Greenleaf (1992), IEEE Trans UFFC, 39, 441-446]

Fig. 11 : Schematic of an axicon transducer. Laser pulses absorbed in a black layer on a conical

Ideal diffraction-free waves are characterized by the property that the field, which satisfies the source- free Helmholtz equation, factors in its transverse and longitudinal parts, with the longitudinal part being independent of the propagation distance. An almost limitless variety of diffraction-free patterns and arrays can be produced in the Cartesian coordinate system, while the Bessel beams and other more general rotating and spiraling fields containing, for example, Neumann and Hankel functions are examples of propagation-invariant waves in circular cylindrical coordinates. The Helmholtz equation also separates in appropriate transverse and longitudinal part s in both elliptical and parabolical cylindrical coordinates. Examples of nondiffracting fields in the former coordinate system are the propagation-invariant Mathieu beams whereas in the latter system one obtains propagation- invariant parabolic beams, whereas in the latter system one obtains propagationinvariant parabolic beams. Higher-order doughnut (dark, hollow) beams exhibit helical wavefronts, which correspond to optical vortices (e.g., phase singularities, dislocations). Nondiffracting vortex beams exert radiation pressure and carry orbital angular momentum; they can be used for microparticle trapping (optical tweezers) and rotation (optical spanners).

Fig. 12 : (a) Circular diffraction grating on the surface of an axicon â&#x20AC;&#x201C; a composite optical element, that can be used for generation of localised waves.(b) optical setup for generation of localised waves. A plane-wave pulse is incident on an annular slit. A Bessel X-pulse with cone angle Î¸ behind a Fourier lens (L) is incident on the composite optical element. [from Reivelt and Saari, Ch.7 in Localised Waves (2008) ed. Hugo E. Hernandez-Figueroa, Michel Zamboni-Rached and Erasmo Recami, John Wiley & Sons, Inc.]

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Nonlinear interaction of light with matter appears to give optical pulses surprising and potentially useful properties. When the pulses enter a dispersive medium (say a crystal), nonlinear interactions spontaneously transformed them into a new shape

Journal of Non Destructive Testing & Evaluation

Fig. 13 : Images of three spherical photoacoustic sources lying on a line, calculated (a) for a conical detector, (b) for aspherical detector and (c) for a ring detector. The detectors are scanned along a line perpendicular to its axis.The sketches below the images show the cross sections of the detectors and the three spherical sources.[from Paltauf et al., Proc. of SPIE (2009), 71770S-7]

Fig. 15 : Nonlinear X waves retain their characteristic profiles when measured in Fourier space. To make this image, an X wave was sent through a lens and onto a spectrograph. The horizontal axis is angular frequency and the vertical axis is wave number.[from Charles Day, Physics Today, October 2004]

that in longitudinal cross section looks like an X. Figure 15 shows an example. Fig. 14 : Self-reconstruction of a10-fs Bessel beam after significant distortion during propagation in air. The transversal intensity pattern was detected at different distances z between 2.9 and 9 mm and compared to the undistorted case and a numerical simulalion assuming a realistic spectrum. The beam was shaped by a single microaxicon from a femtosecond Ti : sapphire laser beam after inserting a 30 mm thick gold wire perpendicular to the optical axis (laser: center wavelength 790 nm, pulse duration 12 fs, axicon: fused silica on quartz, sagittal height 5.7 μ m, vertex directed to the detector, detection: time integrated, CCD Camera, 20 × magnification, distance of wire axis from axicon vertex: 2.9 mm, field of view: 320 × 320 μm2) [from Grunwald et al., Ch.11 in Localised Waves (2008) ed. Hugo E. Hernandez-Figueroa, Michel Zamboni-Rached and Erasmo Recami, John Wiley & Sons, Inc.]

Journal of Non Destructive Testing & Evaluation

Because of the intensity dependence of refractive index (nonlinearity), bright light travels more slowly than dim light. As a beam propagates, Kerr focusing occurs - the collapsing of the faster dim outer part around the slower bright spot. When chromatic dispersion is normal, as is the case for optical light in most transparent media, broadening occurs vol 10 issue 4 March 2012

in the time domain and collapse is prevented. The interplay of Kerr nonlinearity and chromatic dispersion is found to be responsible for the nonspreading propagation of Xwaves. It is becoming clear that with diffraction and dispersion effects under control, research in localised waves is opening up newer

possibilities going beyond imaging towards communications, lithography, and manipulation of atoms.

3. J. Lu, Bowtie Limited Diffraction Beams for Low-Sidelobe and Large Depth of Field Imaging, IEEE UFFC (1995), 42, 1050-1063

FOR FURTHER READING:

4. Localised Waves (2008), ed. Hugo E. Hernandez-Figueroa, Michel ZamboniRached and Erasmo Recami, John Wiley & Sons, Inc

1. J.A. Stratton, Electromagnetic Theory, McGraw-Hill, New York, 1941, p356 2. J.Durnin, J.J.Miceli, and J.H.Eberly, Diffraction-free beams, Phys. Rev. Lett. (1987), 58, 1499-1501

5. Kishan Dholakia, Against the spread of the light, Nature (2008), 451, p413

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Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

CHAPTER NEWS · ISNT DELHI CHAPTER 1. 2nd Executive committee held on 23rd Dec 2011 regarding to NDE 2012.Core Committee was Constituted. 2. Core Committee meeting was held on 4th Jan, 2012 at Ansal Imperial Tower, Naraina Vihar, New Delhi .

3. 3rd Executive Committee meeting was Held on 4th Feb, 2012 to discuss THEME/VENUE BOOKING/ OPENING of NDE ACCOUNT were taken. 4. ISNT PT & RT L-II courses and exam conducted From 6th Feb to 25th Feb, 2012

ISNT THIRUVANANTHAPURAM 1. Technical talk: Technical talk by Sri. G. Prasanna, Scientist/ Engineer of Composites Entity VSSC on “Acoustic source location through evolutionary geodesics” organized by Young Scientists Forum of ISNT Thiruvananthapuram Chapter on 25th November 2011 2. One Day National Seminar: One day National Seminar on NDE of composite structures’ on 22nd October 2011 at SP Grand Days, Thiruvananthapuram. The seminar was inaugurated by Dr. A. Jayakrishnan, Vice Chancellor Kerala University & was presided over by Sri. R. Sivaramakrishnan, GM, RPP, VSSC and Chairman, Organizing Committee of the seminar. Dr. S. Annamala Pillai, Chairman, ISNT Thiruvananthapuram chapter

welcomed the delegates and K. R. Mohan Ananthanarayanan, Convener proposed the vote of thanks. Sri. M. Enamuthu, former Deputy Director of Composites Entity, VSSC gave the keynote address Lectures on Advanced Radiographic Techniques by Dr.M T.Shyam Sunder of Global Research, Advanced Ultrasonic Technique by Dr.T.Jayakumar of IGCAR, Optimal Methods by Dr.Annamala Pillai of VSSC, Thermography Techniques by Dr.K.Srinivas of DRDO, Charatecterization of materials using Ultrasonic by Shri S.Adalarasu of VSSC & Acoustic Emission Technique by Dr. Annamala Pillai & Shri Two executive committee meetings were held during October 2011 and November 2011.

3. National Seminar NDE 2011, 11 members of this chapter attended the National Seminar NDE 2011 Eight papers were presented during the seminar The Best Paper Award was received for the paper titled ‘Debond characterization of isogrid-PUIR foam interface using wood pecker instrument’ presented by our chapter member Sri. V. P. Unnikrishnan, VSSC. IMAGE: Technical bulletin of the Chapter Published the technical bulletin IMAGE on October 2011.

ISNT, CHENNAI CHAPTER A Humorous technical talk by Dr.GS Kailash was organized on 8 th January, 2012 on physical health fitness. EC meeting held on 08.01.2012

Dr. Jayakrishnan, VC, University of Kerala delivering the inaugural address.

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Journal of Non Destructive Testing & Evaluation

21 MT & PT Level-II (ASNT) course was conducted from 18.11.2011 to 27.11.2011. Mr.M.V.Rajamani was the course Director and Mr.J.Shanmugam was the examiner. MT Level-II (ASNT) course was conducted from 12.12.2011 to 16.12.2011. Mr.M.V.Rajamani was the course Director and Mr. P.N.Udayasankar was the examiner.

The editorial board and the members of the NGC, ISNT Congratulate Prof. Krishnan Balasubramaniam on assuming Dean IC & SR, IITM, Chennai

RT Level-II (ASNT) course was conducted from 19.01.2012 to 28.01.2012. Mr.M.S.Ramachandran was the course Director and Mr.E.Sathya Srinivasan was the examiner. NDE 2012 seminar and workshop held from 6 th to 10 th December 2011. Total No. of participants for workshop was 265 & for seminar it was 857.

ISNT MUMBAI CHAPTER APCNDT 2013 committee Meeting was held on 23rd December 2011 at ISNT, Mumbai Chapter Office. Ultrasonic Testing Level- II Exam. for IRS was conducted on 31.12.2011 and the Examiner was Mr. S.P Srivastava. Ultrasonic Testing Level- II Course and Examination for ONGC Engineers on 9th Jan. to 14th Jan. 2012 and the examiner was Shri S. P. Srivastava. 4. Welding Inspector Examination on 21st February 2012 for Avishkar Learning Centre at Mumbai and the examiners were Shri L. M. Tolani and Shri Hemant Madhukar.

SRIHARIKOTA: Presentation on Nano X-ray equipment by M/s HEXAA Bytes, Chennai

HYDERABAD CHAPTER: Annual General Body meeting of ISNT Hyderabad Chapter was conducted on 18 Jan 2012 at Sec’bad.

14th APCNDT Asia Pacific Conference on NDT Mumbai-2013

Prof. Dr. Krishnan Balasubramaniam, the Chief Editor of Journal of Non Destructive Testing & Evaluation has assumed office as the Dean, IC & SR, IIT Madras, Chennai. Prof. Krishnan Balasubramaniam has been involved in the field of Non-destructive evaluation for more than Twenty Five years with applications in the fields of maintenance, quality assurance, manufacturing and design. He is currently a Professor in the Department of Mechanical Engineering and serves as the Head of the Centre for Non- Destructive Evaluation. He has over 250 technical publications (including 102 refereed journal papers) and has directed 12 Ph.D student dissertations and 35 MS student theses. He has served as a consultant to many multinational companies including GE, Corning Inc., BF Goodrich, Gillette, Caterpillar, Lockheed-Martin, Nipon TV, Karta Technologies, Sieger Spintech, etc. He is currently a consultant to US Air Force, Timken, Boeing, Astrium, Corning, HAL, Indian Navy, ARDE, GE, BHEL, etc. He is the Principal Investigator in several sponsored research projects funded by DST, DAE, ADA, ISRO and DRDO organizations. He currently serves as the Editor-in-Chief of the Journal for Nondestructive Evaluation, and features in the editorial board of the South-east Asia Editor for the Journal of Nondestructive Testing and Evaluation (Taylor and Francis) and the Journal of Structural Longevity. Of the many awards, two in the field of NDT are “NDT Man of Year” & “ISNT International Recognition Award”. He has also been conferred the “Fellowship of INAE” recently. The Editorial board and members of NGC, Congratulate Prof. Dr. Krishnan Balasubramaniam and wish him the best in his new role as the Dean. Managing Editor, JNDE

Journal of Non Destructive Testing & Evaluation

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Journal of Non Destructive Testing & Evaluation

Highlights

NDE - 2011, Chennai ENRICH & EXCEL IN ENGINEERING THRO’ NDE

The much awaited NDE-2011 Seminar with the above mentioned theme was organized by ISNT-Chennai Chapter from 8th to 10th December, 2011 with the preconference tutorial on 6th & 7th December, 2011. This was possible because of unstinted hard work rendered by the Members of Chennai Chapter. Our sincere thanks to Mr K Thambithurai, the former President, ISNT for providing the opportunity to Chennai chapter and extending good support for the Seminar. Immediately on getting the nod from the NGC, the Chennai Chapter with its dynamic young & energetic force started working on the conductance of this Seminar. To streamline the activities through different forums, the following Committees headed by resource persons were set-up to achieve the desired results. As the theme was apt & relevant to the present day scenario, the response received was overwhelming. The workforce in Industries and the academicians of Educational Institutions in the Seminar which made rich contributions for its glorious success.

ORGANISING COMMITTEE Mr R Sundar, the Director of Boilers of Tamilnadu played a significant role as the Chairman of the NDE 2011 Seminar Organizing committee and he lead the Committee admirably and guided all its committee members in the proper direction. His valuable guidance yielded the beneficial result at the end was beyond excellence. Under his able leadership, the NDE Seminar planning meets were regularly conducted on the planned dates and the role of each committee as listed below was emphasized and their activities were monitored periodically for improvement. The present status & future activities were fully analyzed in each meet and the committee members were enthusiastically encouraged to carry out their planning activities well in advance without facing any hindrances. RESOURCE MOBILISATION It is great honour for Chennai Chapter to have Sri.N.Balakrishnan, the President, M/s. Sundaram fasteners Ltd as Chairman of the Resource Mobilization committee as he has been

National Organising Committee Seminar Organising Committee International Organising Committee Technical Committee Resource Mobilisation Committee Souvenir Committee Exhibition Committee Registration Committee Event Management Committee Entertainment Committee Catering Committee Logistics Committee Public Relations Committee Convener

Shri K. Thambithurai Shri R. Sundar Shri V. Pari Prof Krishnan Balasubramanian Shri N. Balakrishnan Shri RG Ganeshan Shri S. Subramanian Shri SR Ravindran Shri P. Guruprasad Shri S. Swaminathan Shri N. Karunanidhi Shri E. Sathya Srinivasan Shri G. Ramachandran Shri R. Balakrishnan

NDE 2011 TEAM Er.R.Sundar Shri R.Balakrishnan Shri TV Navaneetha Krishnan Dr.Krishnan Balasubramaniam Shri V.Pari Shri N.Balakrishnan Shri RG.Ganesan Shri S.Subramanian Shri R.Vivek Shri S.R.Ravindran Shri P.Guruprasad Shri S.Swaminathan Shri N.Karunanidhi Shri E.Sathya Srinivasan Shri G.Ramachandran Journal of Non Destructive Testing & Evaluation

Chairman Convener Treasurer Technical International Resource Mobilisation Souvenir Exhibition Exhibition Co-chairman Registration Event Management Entertainment Catering Logistics Public Relation

instrumental in bringing sizable fund to the Seminar. The confidence shown by him towards the seminar about fund mobilization boosted every active member to concentrate more. Under his able guidance, the package and benefits to the sponsors & supporters of the event were established and it worked out well in attracting the entry of many reputed manufacturers and organization to the Seminar as sponsors & supporters. We have to thank “M/s FOUR VECTOR” who came first to extend support to the event as a PRIME SPONSOR and it really gave us rich benefits. Indeed their announcement as the PRIME SPONSOR to the event had not only pulled many sponsors into NDE 2011participation but also induced confidence in organizing the seminar as per the expectations. The monetary contributions made by other sponsors as listed below were highly beneficial for the smooth conductance of the seminar without any financial crisis and scripted out a golden record in the history of ISNT. The act of Mr Navaneetha Krishnan in handling the finance as a treasurer of NDE 2011 Seminar added feather to the cap of Resourse Mobilisation committee. EXPOSURE OF NDE 2011 Mr G RAMACHANDRAN ,the Treasurer of NCB and past Vice Chairman and Senior member of Chennai Chapter took keen interest as Chairman of Public Relation committee in spreading out the information of conductance of Seminar to all Oil Companies and other industries by interacting with high level dignitaries and it attracted many leading organization to take part in the seminar. Mr.V Pari, the Chairman of International Committee also played a vital role in spreading out the information to the members of Asia Pacific society and many other countries which attracted reputed NDE experts to participate in the Seminar. About 30 foreigners participated the Seminar. The highlight of the seminar is the participation of 2 foreign NDE manufacturers as Exhibitors and the participation of South Africa, the organizer of World Conference 2012. The experience of Mr V Pari as a convener of NDE 2002 Seminar and his association with many Seminar events helped to organize the events successfully and his contributions were widely applauded. EXHIBITION Exhibition is the real strength of the

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24 Seminar for its successful conductance as it is attractive to the participants of the Seminar as a visual medium. It was also a good platform to NDE equipment manufacturers in selling their products, gave ample opportunity to NDE Service providers and other Seminar Delegates to know about the latest trends of NDE. Mr S Subramanian, the chairman & Mr Vivek Rajamani -Co Chairman of the committee did a splendid work not only in finding the Exhibitors for the seminar but also making them pay their committed contributions in time and this was widely appreciated. Due to their initiatives, the Exhibition Manual was first floated in this seminar which has attracted many exhibitors as it contained all details about the Seminar like Exhibition rules & regulations, accessories requirements etc which were neatly framed and forwarded to all Exhibitors in time. Because of their sincere efforts almost all stalls as per planning were booked in a short period which is a remarkable achievement of the Seminar. The contractor Ms DEKO systems did excellent job on stall management added feather to Exhibition committee. The high light of the Exhibition Committee is the conductance of Exhibition for 4 days which is a record on ISNT Seminar history. TECHNICAL ACTIVITIES The brain of NDE Seminar is Technical sessions which were ably handled by Prof. Dr. Krishnan Balsubramanian, HOD –Applied Mechanics, IIT Chennai, as Chairman for Technical Committee Prof. Krishnan Balasubramanian is the wisdom of Technical activities of ISNT Chennai Chapter and the chapter is very much fortunate and proud to have his association for its Technical activities. His well reputed international recognization and ever appreciable wisdom played a significant part in arranging the Technical papers 210 Nos (Oral-160:poster-50 in Nos ) as received for paper presentation, their Publication in proceedings , identifying the faculty for Workshops as detailed in Table 1, identifying reputed NDE experts from various countries for Memorial& key note addresses, preparing Technical sessions for Seminar days, arrangements of Preconference workshops etc, without any flaw and its quality deliverance astonished every participant of the Seminar and made a high degree of satisfaction to all the participants of the seminar. The No of papers 210 Nos

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as received for oral & poster methods astonished every NDE fraternity for its quality contents. REGISTRATION ACTIVITIES Our Chapter’s appreciations go to Mr S R Ravindran of NPC, the Joint secretary of Chapter and the Chairman of registration committee for his total dedication in carrying out the functions effectively. His well planned activities yielded many members to participate in the seminar and he also made elaborated arrangements for easy and quick registration for the participants at Seminar Venue during the event days. About 250 participants for Preconference workshops and 850 delegates for seminar had been registered. SOUVENIR Mr R G GANESAN, JT. SECRETARY of Chennai Chapter and his involvement made easy in getting about 80 advertisements for the publication in NDE 2011 Souvenir and also his active role in publishing both Souvenir and Technical Papers with Seminar proceedings in time is a remarkable role of his service to Seminar and it is an appreciable one. M/s VRK Printing House had extended their valuable Services in Seminar by printing the Souvenir, Technical Papers abstract & proceedings and deserves appreciation for their excellence in spreading out the message on conductance of seminar throughout the world by web systems and postal communications. CATERING ARRANGEMENTS All the participants of Preconference workshops & Seminar enjoyed the delicious food served by two caterers –GRT during seminar days & Hot Kitchen during preconference workshops. Mr N Karunanidhi, the treasurer of ISNT-Chennai Chapter and the Chairman of catering committee had identified the caterers for the Seminar and also in selecting delicious & suitable food items which delighted all the participants of the Seminar & workshops and presented the highest degree of satisfaction. The food was served for more than 5000 persons in total during the 5 days of the Conference. LOGISTICS ARRANGEMENTS The Committee headed by Mr. Satya Srinivasan played a vital role on logistics arrangements and the transport

facilities were extended to faculty, Chair persons, foreigners and the exhibitors and the needy delegates. Heartfelt thanks to M/s Vellammal Tech Institutions, Chennai for sparing their Buses to drop the delegates during seminar days. ENTERTAINMENT ACTIVITIES The committee headed by Mr S Swaminathan of Q & Q Inspection delivered fragrances to seminar by their excellent identification of Artists Like OM KARA GROUP for cultural Programme. Their delightful performance enthralled the audience and received many applauses and appreciations. EVENTS MANAGEMENT The highlight of the Seminar is the successful exhibition of Events management. Mr. Guruprasad, the Chairman of the committee made a splendid role in planning the events from the day of inauguration to the day of valedictory function in the most befitting way without any lacunae and deserves appreciations. His systematic planning of the programme schedule and compilation of all events were quite exemplary. VENUE ALL IN ONE PLACE IS ALWAYS WELL. The CHENNAI TRADE CENTER at Nandambakkam was fixed as the venue for Seminar as it has salient features in conducting International events and contains the covered space for Inauguration, conductance of parallel technical sessions, Exhibition arrangements and catering arrangements in closed circuit which benefitted many delegates to participate and enjoy their presence without wastage of time and the seminar arrangements were appreciated by one & all. The details of the seminar programme from Inauguration to valedictory function are described in Table III. EXECUTION All the planned actions of NDE Seminar was successfully executed with the help of the secretariat staff – Mr S Swaminathan, Mr S Balakrishnan, Ms Rajeswari, Ms Rosaline and Mr Saravanan and their tremendous hard work and sincere attention in carrying out the instructions of all committee members in time without any second thoughts & this has paved the way of

Journal of Non Destructive Testing & Evaluation

25 Date

Details of the Programme

Chief Guest

6th Dec 2011

Inauguration of Pre Conference workshop

Mr.P.Mannar Jawahar, Vice-chancellor, Anna University

250

7th Dec 2011

Inauguration of Exhibition

Prof.Sridhar Krishnaswamy, Northwestern Univ., Evanston, USA.

125

7th Dec 2011

Evening Inauguration of Seminar

Mr.J.Mahilselvan, Director (Power) Neyveli LigniteCorporation, Neyveli

8th Dec 2011

AK Rao Memorial Lecture - NDE IN WIND ENERGY

8th Dec 2011

Jain Memorial lecture LASER ULTRASONIC METHODS OF NON DESTRUCTIVE MATERIALS CHARACTERIZATION

Delegates

Prof.Christain Boller, IZFP, Saarbrucken, Germany

850

Dr.Heidt.H, BAM, Berlin, Germany.

850

Key Note Address-1 NANO, MICRO OR MACRO PROBLEMS - THE KNOWLEDGE GAP IN NDE

10th Dec 2011

Key Note Address-II Dr. Baldev Raj, NDE APPROACHES FOR ENHANCED PERFORMANCE PSG Institutions, Coimbatore AND HEALTH MONITORING IN CRITICAL TECHNOLOGIES EveningValedictory function

850

Prof.Sridhar Krishnaswamy, Northwestern Univ., Evanston, USA.

9th Dec 2011

10th Dec 2011

850

Dr. Baldev Raj,

850

Workshops

Convener

Total No. of Participants

NDE in Automobile

Dr.O.Prabhakar

NDE in Aerospace

Dr.Shyam Sundar

NDE in Concrete Structure

Dr. Anish Kumar / Mr. S.G.N. Murthy

NDE in Residual Life Assessment of Boilers & Turbines

Er.R.Sundar

Sponsors M/s. Four Vector Engineering Systems P. Ltd M/s. GE India Industrial Pvt. Limited M/s. BGR Energy Systems M/s. Areva NDE – Solutions M/s. Blue Star Limited M/s. Sievert India Private Limited M/s. Sundram Fasteners Limited M/s. P-Met High Tech Co. Pvt. Limited M/s. East West Engineering & Electronics P. Ltd M/s. Electronic Engineering Company India P. Ltd M/s. Mabel Engineering

success. They also deserve for good appreciations for proper execution. Our sincere thanks to ISNT HO for rendering help in the conductance of NDE-2011. Team work and proper coordination are the main tools that were employed for the successful execution of NDE 2011 Seminar activities and I , as Convener enjoyed my role in NDE 2011 Seminar . As all activities were well taken care

of entire NDE work Team, the convener had only little work to spare in seminar activities. I express my sincere thanks to entire team members of the Seminar for their excellent contributions towards Seminar NDE 2011. The Secret of success to the Seminar is finally due to the proper execution of all planned activities as per the following verses of Tamil Vedam Tirukkural

Journal of Non Destructive Testing & Evaluation

Principal Sponsor Platinum Sponsor Gold Sponsor Silver Sponsor Silver Sponsor Silver Sponsor Silver Sponsor Bronze Sponsor Bronze Sponsor Bronze Sponsor Bronze Sponsor

ªð£¼œè¼M è£ô‹ M¬ùJìªù£´ ä‰¶‹ Þ¼œbó ã‡E„ ªêò™ Money and means, time, place and deed Decide these five and proceed for the desired act. R BALAKRISHNAN CONVENER-NDE 2011

vol 10 issue 4 March 2012

Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

NDE events We hope that this new feature added to the journal during the last year has been useful for the readers in planning their activities in terms of paper submissions, registering for seminars, etc. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com April 2012 18th World Conference on NDT (WCNDT18) April 16 - 20, 2012 ; Durban, South Africa http://www.wcndt2012.org.za International Symposium on Ultrasound in the Control of Industrial Processes April 18-20, 2012 : Madrid, Spain http://www.ucip2012.net/ May 2012 International Nondestructive Testing & Quality Summit (INTEQS) April 29 â&#x20AC;&#x201C; May 2, 2012 ; Abu Dhabi, UAE http://www.inteqs.com/index.html Acoustic Emission Working Group (AEWG-54) May 21-22, 2012 ; Princeton, NJ, USA http://www.aewg.org/ 9th International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components May 22-24, 2012 ; Seattle, Washington, USA http://www.9thnde.com/ June 2012 Nondestructive Evaluation of Aerospace Materials and Structures III June 4-5, 2012 ; St. Louis, MO, USA http://www.asnt.org/events/conferences/aero12/ 11th Quantitative InfraRed Thermography Conference June 11-14, 2012 ; Naples, Italy http://www.qirt2012.unina.it/ocs/index.php/2012/QIRT 17th International Workshop On Electromagnetic Nondestructive Evaluation (ENDE2012) June 17-20, 2012 ; Rio de Janeiro, Brazil http://ende2012.metalmat.ufrj.br/ 4th International CANDU In-service Inspection and NDT Conference June 18 - 21, 2012 ; Toronto, Ontario, Canada http://events.cinde.ca/ July 2012 6th European Workshop on Structural Health Management July 3-6, 2012 : Dresden, Germany http://www.ewshm2012.com/ QNDE 2012 - 39th Annual Review of Progress in Quantitative Nondestructive Evaluation July 15-20, 2012 : Denver, Colorado http://www.qndeprograms.org/2012/Conference2012.html ASNT Digital Imaging Conference XV July 16-18, 2012 : Mashantucket, CT, USA http://www.asnt.org/events/conferences/digital/digital.htm vol 10 issue 4 March 2012

Journal of Non Destructive Testing & Evaluation

NDE Puzzle Conceptualized & Created by Dr.M.T.Shyamsunder, GE it appears in the KEYWORD. Each word identified by you should Global Research, Bangalore have a minimum of FOUR letters or more. Your final list should We hope you enjoyed solving the “NDT Crossword Puzzle” have atleast ONE eight letter and ONE nine letter words to which was published in the last issue. We received many entries qualify for the prize. For evaluation purposes, greater weightage from the readers and based on the maximum number of correct will be given to words with more number of letters. words identified, the following is the WINNER N.Narayanankutty, VSSC, Trivandrum

Keyword 1 : NONDESTRUCTIVE (example : SEND, DUCT, COUNT, STUDIO….)

Congratulations to the Winner. They will receive their prizes Keyword 2 : INSPECTION (example : NOTICE, PINS, PEST……) from the Chief Editor of the journal shortly. The correct answers I n s t r u c t i o n s to the Puzzle are published below. Please send your answers by email to In this issue, we have another puzzle to continue stimulating jndte.isnt@gmail.com with your name, organization, contact your brain cells! We hope you will find this section number and email address interesting, educative and fun filled. Please send your Rules & Regulations feedback, comments and suggestions on this section to - Only one submission per person is allowed mandayam.shyamsunder@gmail.com Introduction

In this form of the “Word Search Puzzle”, you have to form “Dictionary acceptable” English words from the KEYWORD listed in bold below. A letter can be used only as many times as

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

The correct answers and the names of the prize winners will be published in the next issue

Answ ers for P d SSear ear ch 4 Answers Prrevious issue - NDT Wor ord earch

NDT WORDSEARCH - 4

Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

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Our Advanced Product Range Our advanced Range of Equipments Laser Shearography The LTI 5100HD offers the ultimate in shearography NDT performance. This operates in all modes, including continuous real time phase maps, real time subtraction, phase stepping and phase reversal. Benefits Large Area Inspection, Real-Time Imaging of: -De-laminations, - Dis-bonds, Ultra High Through-put Applications:Exclusively for Composites

Digital Radiography DR 1200 system is based on computed radiography flexible imaging plates and high performance NDT workstation technology. This system replaces conventional film radiography with flexible reusable digital imaging plates. Features:Integrated Scanner and eraser. YTB/Se 75/Ir gamma radiation source From 10KV to 10.8Mev 10 8Mev X-Ray X Ray energy operation Professional scientific work station Carbon composites inspection

Acoustic Emission Testing Uniscope system is based on Acoustic Emission T h l Technology f assessing for i the th integrity i t it off products. d t Benefits Detection of crack initiations and propagation Detection and location of corrosion, leak and high stress level zones. positioning g and size measurement. Defect p Real-time monitoring & Condition Monitoring of various processes and critical large dimension structures Applications Pipelines, Pressure Vessels, Tanks, Boilers, Derricks, Cranes, Bridges and other objects

NDE patents

Compiled by Dr. M.T.Shyamsunder, GE Global Research, Bangalore, India

We hope that the section on NDE Patents, which featured in the last few issues of this journal has continued to trigger your curiosity on this very important topic of Intellectual property. 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 Continuing our endeavor to provide you updates on NDE and Inspection related patents, listed below are a few patents from areas related to the use of magnetostrictive sensors for a variety of inspection applications which were issued by USPTO in the last few years. 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/

Inventors: Kwun Hegeon; Parvin JR. Albert J.; Laiche Erika Christine Assignee: Southwest Research Institute, San Antonio, USA

UNITED STATES PATENT 20110169486 Magnetostrictive Sensor for Tank Floor Inspection

UNITED STATES PATENT 20100127698 Magnetostrictive Stress Sensor

Inventors: Light Glenn M; Puchot Alan R; Cobb Adam C; Laiche Erika C. Assignee: Southwest Research Institute (San Antonio, TX)

Inventors: Shimada Munekatsu; Sakurai Hiroshi ; Kawashita Yoshio; Uramot; Kiyohiro ; Matsuoka Toshimitsu ; Aihara Masao; Fujita Mitsuaki; Ooshima Masaharu Assignee: NISSAN Motor Co Ltd, Japan

A method of testing for defects in the bottom of an above ground storage tank, the tank bottom having a lip extending outwardly from the tank wall around the circumference of the tank. A special magnetostrictive sensor is designed to be placed on this lip. The sensor is placed over a strip of magnetostrictive material, which generally conforms in length and width to the bottom of the probe, with a couplant being applied between the strip and the lip surface. The sensor is then operated in pulse echo mode to receive signals from defects in the bottom of the tank. It is incrementally moved around the circumference of the tank.

UNITED STATES PATENT 20110025317 MsS Probe for Guided-Wave Inspection of Fuel Rods Inventors: Kwun Hegeon ; Parvin, JR.; Albert Joseph; Glauser; Rolf Assignee: Electric Power Research Institute Inc, Charlote, NC, USA The present application discloses a magnetostrictive sensor (MsS) probe for guided-wave inspection of the entire length of a fuel rod. The probe includes a waveguide adapted to be clamped to a fuel rod, and an MsS adapted to generate guided waves into the waveguide such that the guided waves propagate down the waveguide into the fuel rod and back to the waveguide for detection by the MsS. vol 10 issue 4 March 2012

A magnetostrictive stress sensor includes: a magnetic member having a magnetostriction; a permanent magnet adjacent to the magnetic member; a magnetic sensor for detecting a leak magnetic flux on a side opposite to the permanent magnet with respect to the magnetic member, wherein the leak magnetic flux changes according to a stress acting on the magnetic member and the magnetic sensor detects the change of the leak magnetic flux, to thereby detect the stress acting on the magnetic member, and a direction of the stress acting on the magnetic member is substantially orthogonal to a magnetizing direction of the permanent magnetpresent application discloses a magnetostrictive sensor (MsS) probe for guided-wave inspection of the entire length of a fuel rod. The probe includes a waveguide adapted to be clamped to a fuel rod, and an MsS adapted to generate guided waves into the waveguide such that the guided waves propagate down the waveguide into the fuel rod and back to the waveguide for detection by the MsS.

UNITED STATES PATENT 20100052670 Magnetostrictive Sensor Probe for Guided-Wave Inspection and Monitoring of Wire Ropes/Cables and Anchor Rods

An economical, flexible, magnetostrictive sensor (MsS) probe assembly for use on longitudinal cylindrical structures, for guidedwave, volumetric inspection of the structures is described. The paired flexible plate MsS probes each include a flexible strip of magnetostrictive material that is positioned and/or adhered to the base of a generally flat, flexible, conductor coil assembly, preferably with an elastomeric adhesive. The conductor coil assembly has a core composed of a thin flexible layer of metal and a thin bendable permanent magnet circuit. The flexible core is surrounded by a flat flexible cable (FFC) that is folded and looped over the layers of the core. The exposed conductors at the ends of the FFC are shifted from each other by one conductor spacing and joined together so that the parallel conductors in the FFC form a flat, flexible, continuous coil. The probe assemblies may preferably be utilized in pairs and conformed to match the curved contours of the cylindrical surface of the structure under investigation in a manner that is specifically tailored for wire rope, cable, and anchor rod type applications.

UNITED STATES PATENT 20100052669 Flexible Plate Magnetostrictive Sensor Probe for Guided-Wave Inspection of Structures Inventors: Kwun Hegeon; Parvin Albert J.; Peterson Ronald H. Assignee: Southwest Research Institute, San Antonio, USA An economical, flexible, magnetostrictive sensor probe for use on planar and/or curved structural surfaces, for guided-wave volumetric inspection of the structure is described. The flexible plate MsS probe includes a flexible strip of magnetostrictive material that is adhered to the base of a generally flat, flexible, conductor coil assembly,

Journal of Non Destructive Testing & Evaluation

39 preferably with an elastomeric adhesive (such as silicon) or with double sided tape. The conductor coil assembly has a core that is composed of a thin flexible strip of metal, a layer of an elastomeric material (such as rubber), and a thin permanent magnet circuit. The flexible core is surrounded (top, bottom, and on the longitudinal ends) by a flat flexible cable (FFC) that is folded and looped over the layers of the core. The exposed conductors at the ends of the FFC are shifted from each other by one conductor spacing and joined together so that the parallel conductors in the FFC form a flat, flexible, continuous coil. The entire probe assembly may be bent to match the curved contours of the surface of the structure under investigation.

Inventors: Schmitt Zimmer Juergen

UNITED STATES PATENT 20090021253 Method and device for longrange guided-wave inspection of fire side of waterwall tubes in Boilers

Inventors: Light Glenn M; Kwun Hegeon; Kim, Sang-Young; Spinks Robert L. JR.

Inventors: Kwun Hegeon; Matsumoto Hirotoshi; Crane James F. Assignee: Southwest Research Institute, San Antonio, USA Methods and devices for inspecting waterwall tubes for the detection of fire side damage over a long length of the tube are described. The system of the invention uses a magnetostrictive strip and a flat coiltype plate magnetostrictive sensor (MsS) that are held in place on the waterwall using a specially designed frame and an electromagnetic circuit. The magnetostrictive strip and plate type MsS are positioned against a tube in the waterwall using an elastomeric pad or a fluid filled bladder to achieve close contact and good mechanical coupling between the magnetostrictive strip and the tube surface. When current activated, the electromagnet holds the entire assembly in place and provides a DC bias magnetic field required for plate magnetostrictive sensor probe operation. Long-range guided-waves are pulsed into the tube and reflected signals are detected within the same sensor structure. The received signal data representative of a long section of the tube under investigation is then analyzed for the presence of anomalies and defects. When data acquisition for a particular tube or tube section is completed the electromagnet is turned off and the entire device is moved to the next tube in the waterwall.

UNITED STATES PATENT 20080060443 Sensor and Method for Detecting a Deformation

Stephan;

A sensor has a substrate having a mechanically deformable region, a magnetostrictive spin-valve sensor element being arranged to detect a mechanical deformation of the mechanically deformable region. On the substrate, there is a device for generating a controllable magnetic field by Which a performance of the sensor element is influenced.

UNITED STATES PATENT 20010022514 Method and apparatus for short term inspection or long term structural health monitoring

A method and apparatus is shown for implementing magnetostrictive sensor techniques for the nondestructive short term inspection or long term monitoring of a structure. A plurality of magnetostrictive sensors are arranged in parallel on the structure and includes (a) a thin ferromagnetic strip that has residual magnetization, (b) that is coupled to the structure with a couplant, and (c) a coil located adjacent the thin ferromagnetic strip. By a transmitting coil, guided waves are generated in a transmitting strip and coupled to the structure and propagate along the length of the structure. For detection, the reflected guided waves in the structure are coupled to a receiving strip and are detected by a receiving magnetostrictive coil. Reflected guided waves may represent defects in the structure.

UNITED STATES PATENT 20010019263 Magnetostrictive sensor rail inspection system Inventors: Light Glenn M; Kwun, Hegeon A method and apparatus is shown for implementing magnetostrictive sensor techniques for the nondestructive evaluation of railroad rails. The system includes magnetostrictive sensors specifically designed for application in conjunction with railroad rails and trains that generate guided waves in the railroad rails which travel there through in a direction parallel to the surface of the railroad rail. Similarly structured sensors are positioned to detect the guided waves (both incident and reflected) and generate signals representative of the characteristics of the guided waves detected that are reflected from anomalies in the

Journal of Non Destructive Testing & Evaluation

structure such as transverse defects. The sensor structure is longitudinal in nature and generates a guided wave having a wavefront parallel to the longitudinal axis of the sensor, and which propagates in a direction perpendicular to the longitudinal axis of the sensor. The generated guided waves propagate in the rail within the path of the propagating wave. The reflected waves from these abnormalities are detected using a magnetostrictive sensor. Shear horizontal waves may also be created by rotating the magnetic bias 90.degree. and used for similar inspection techniques.

UNITED STATES PATENT 20080315872 Method and device for longrange torsional guided-wave inspection of piping with a partial excitation and detection around the pipe circumference Inventors: Kwun Hegeon; Matsumoto Hirotoshi; Crane James F. Assignee: Southwest Research Institute, San Antonio, USA Sensor assemblies and methods are described that facilitate the use of a long-range torsional guided-wave inspection system for inspecting pipes, tubes, or other longitudinal cylindrical structures, with a partial excitation and detection around the pipe circumference. The sensor assemblies comprise a plate-type magnetostrictive sensor probe positioned beneath a compressible/ expandable bladder and an inverted U-shaped frame that retain and position the sensor probe against the external wall of the pipe under inspection. Preferably, a magnetostrictive strip is positioned in direct contact with the pipe wall over which the plate magnetostrictive sensor probe is positioned. The probe is preferably curved to match the curvature of the external surface of the pipe. A pad may be positioned between the probe and the magnetostrictive strip to improve compliance with irregular pipe surfaces. The frame (and therefore the sensor assembly) is held in place by a belt that encircles the pipe and may be tensioned in order to pull the frame against the pipe, and through the compressive force associated with the bladder, direct the magnetostrictive sensor probe against the surface of the pipe or against the magnetostrictive strip positioned on the surface of the pipe. Methods are described for placement of the magnetostrictive strip and the positioning of the magnetostrictive sensor probe.

vol 10 issue 4 March 2012

Human hair, image with 5X lens

Plume analysis with gas filters

Stress analysis at high temperature

High speed tire testing

Laser beam profile

Helicopter thermal signature

FLIR Representative:-

Ms. Kaveri Mukherjee, Specialise Instruments Marketing Company E mail - specmco@fastmail.fm * Images herein are for illustrative purpose only. Specifications are subject to change without notice. Terms & Conditions applied.

National NDT Awards

No.

Award Name

Sponsored by

ISNT - EEC National NDT Award (R&D)

M/s. Electronic & Engineering Co., Mumbai

ISNT - Modsonic National NDT Award (Industry)

M/s. Modsonic Instruments Mfg. Co. (P) Ltd., Ahmedabad

ISNT - Sievert National NDT Award (NDT Systems)

M/s. Sievert India Pvt. Ltd., Navi Mumbai

ISNT - IXAR Best Paper Award in JNDE (R & D)

M/s. Industrial X-Ray & Allied Radiographers Mumbai

ISNT - Eastwest

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

ISNT - Pulsecho Best Chapter Award for the Best Chapter of ISNT

M/s. Pulsecho Systems (Bombay) Pvt. Ltd. Mumbai

ISNT - Ferroflux National NDT Award

M/s. Ferroflux Products Pune

(International recognition)

National NDT Award for Young NDT Scientist / Engineer

ISNT - Lifetime Achievement Award

ISNT

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 www.isnt.org.in

vol 10 issue 4 March 2012

Journal of Non Destructive Testing & Evaluation

vol 10 issue 4 March 2012

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Local Conference Secretariat The Conference Company South Africa Tel: 27 31 303 9852 Fax: 27 31 303 9529 Nina Freysen-Pretorius - nina@confco.co.za Deidre Hancke-Haysom - deidre@confco.co.za www.wcndt2012.org.za

Technical Paper

Detection and Quantification of Lack-of-Penetration in Al-Al Friction-Stir Welded Plates using Phased Array Ultrasonic Technique Rajat Mazumder1, N.R. Bandyopadhyay1 and S Palit Sagar,* School of Materials Science and Engineering, Bengal Engineering and Science University, Shibpur, India * CSIR-National Metallurgical Laboratory, Jamshedpur, India Email: sarmi@nmlindia.org

ABSTRACT This paper presents the results of phased array ultrasonic technique to detect the defects in friction stir welded Al-Al plates in three different processing conditions. Results of phased array ultrasonic were validated through ultrasonic C-scan imaging and real-time radiography techniques. From the results it has been observed that the width and depth of the defect like lack-of penetration can be successfully detected and quantified from the images of phased array ultrasonic technique. Keywords: friction stir welding, phased array ultrasonic, ultrasonic C-scan imaging, lack of penetration

1. INTRODUCTION Friction stir welding (FSW) is emerging as a key technology in many industrial applications, especially those involving the joining of light alloys, such as aluminium [1-6]. The increased application of these materials by very demanding industrial sectors, e.g., aerospace, naval, and automotive has generated significant research and development in FSW [7-9]. The reliability of the assembly is the prerequisite for their efficacious use in practical field. The industrial environment in which FSW is applied demands fast (online, if possible) and cost efficient non-destructive testing (NDT) of welds. Due to its solid-state nature, FSW, in most cases, produces weldment properties that are remarkably better than those of traditional arc welds. The solid-state nature of FSW by its inherent nature is able to produce fine grain structure near the interface, alter the characteristic features of second phase distribution and change the defect density. Naturally, apart from a novel approach of fabrication, the technique provides betterment in mechanical properties. Moreover, due to the solid state nature of FSW, FS welds are usually free of imperfections. However, some imperfections may arise due to improper stirring of the parent material, inadequate surface preparation, lack of penetration of the pin, or inadequate axial forging forces. Some typical FS weld imperfections include lack of penetration, root imperfections (weak or intermittent welding), cavities on the advancing side of the weld, and second phase particles and oxides aligned under the shoulder. Because the quality of FS welds impacts manufacturing cost and product quality, appropriate quality control should be implemented to detect these imperfections in friction stir welds. In general, the data available on the application of NDT to FS welds is scarce [10-14]. Moreover there are no universally accepted quality assurance procedures for friction stir welds, they need to be Vol. 10, Issue 4 March 2012

developed, standardised and incorporated into production processes. Among the various non-destructive evaluation (NDE) techniques, acoustic methods are the most frequently used. Recent advances in modern material technology require the development of NDE techniques that quantify microscale damages in a variety of materials, both during their production and life cycle. Ultrasonic waves interact with interface boundaries, grain interstices, pores, inclusions, cracks, etc. and gather substantial information about the details of the geometry and physical properties of the insonified medium. Ultrasonic phased array systems can potentially be employed in almost any test where conventional ultrasonic flaw detectors have traditionally been used. Weld inspection and crack detection are the most important applications, and these tests are done across a wide range of industries including aerospace, power generation, petrochemical, metal billet and tubular goods suppliers, pipeline construction and maintenance, structural metals, and general manufacturing. Phased arrays can also be effectively used to profile remaining wall thickness in corrosion survey applications. The benefits of phased array technology over conventional UT come from its ability to use multiple elements to steer, focus and scan beams with a single transducer assembly. Beam steering, commonly referred to sectorial scanning, can be used for mapping components at appropriate angles. This can greatly simplify the inspection of components with complex geometries. The small footprint of the transducer and the ability to sweep the beam without moving the probe also aids inspection of such components in situations where there is limited access for mechanical scanning. Sectorial scanning is also typically used for weld Journal of Non destructive Testing & Evaluation

48 inspection. The ability to test welds with multiple angles from a single probe greatly increases the probability of detection of anomalies. Electronic focusing permits optimizing the beam shape and size at the expected defect location, thus further optimizing probability of detection. The ability to focus at multiple depths also improves the ability for sizing critical defects for volumetric inspections. This paper describes the use of phased array ultrasonic technique to detect the lack of penetration of the pin in three aluminium-aluminium specimens joined by friction stir welding with different process parameters and the results of PAUT have been validated using conventional ultrasonic C-scan imaging and radiography which are mostly laboratory based techniques.

2. EXPERIMENTAL 2.1 FSW sample preparation

In FSW, a cylindrical-shouldered tool, with a profiled threaded/unthreaded probe (pin) is rotated at a constant speed and fed at a constant traverse rate into the joint line between two pieces of sheet or plate material, which are butted together. The parts have to be clamped rigidly onto a backing bar in a manner that prevents the abutting joint faces from being forced apart. The length of the pin is generally slightly less than the weld depth required and the tool shoulder should be in intimate contact with the work surface. The pin is then moved against the work, or vice versa. Frictional heat is generated between the wear-resistant welding tool shoulder and pin, and the material of the work pieces. This heat, along with the heat generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without reaching the melting point (hence cited a solid-state process), allowing the traversing of the tool along the weld line in a plasticised tubular shaft of metal. As the pin is moved in the direction of welding, the leading face of the pin, assisted by a special pin profile, forces plasticised material to the back of the pin while applying a substantial forging force to consolidate the weld metal. The welding

Technical Paper

of the material is facilitated by severe plastic deformation in the solid state, involving dynamic recrystallization of the base material. Figure 1 schematically represents the FSW technique. In our work, three aluminium-aluminium joined samples were prepared by varying the process parameters of FSW joining. The process parameters of joining of three samples are listed below in table 1. Table 1 : The process parameters of friction stir joining of three samples Parameter

Sample 1

Sample 2

Sample 3

Spindle speed

300 rpm

500 rpm

700 rpm

Travel speed

45mm/min

Tool

5mm

Depth

5.25 mm

Plate thickness

6 mm

Feed rate

2 mm/min

2.2 Phased Array Ultrasonic Technique (PAUT)

Phased array system utilizes the wave physics principle of phasing, varying the time between a series of outgoing ultrasonic pulses in such a way that the individual wave fronts generated by each element in the array combine with each other to add or cancel energy in predictable ways that effectively steer and shape the sound beam. Figure 2a shows the crystal combination for linear array of the phased array probes and Fig. 2b depicts the phased array system used for the experiments (Model: OMNISCAN, make: RD Tech, Canada).

Fig. 2(a): Linear array phased array probe Fig. 1 : Schematic of Friction Stir Weld (FSW) process Journal of Non destructive Testing & Evaluation

Fig. 2(b): OMNISCAN; Phased Array Ultrasonic Testing (PAUT) System Vol. 10, Issue 4 March 2012

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In this work 16 elements linear array probe of frequency 5 MHz was used in the range of 30o â&#x20AC;&#x201C; 70o for sectorial scan (S-Scan). An S-scan image represents a twodimensional cross-sectional view derived from a series of A-scans that have been plotted with respect to time delay and refracted angle. The horizontal axis corresponds to test piece width, and the vertical axis to depth. This is the most common format for medical sonograms as well as for industrial phased array images. The sound beam sweeps through a series of angles to generate an approximately cone-shaped cross-sectional image. Before conducting the measurement, proper velocity, wedge delay and sensitivity calibration has been performed. 2.3 Ultrasonic C-scan Imaging

In ultrasonic c-scan imaging technique, the sample is immersed in water in a tank. Water acts as a couplant and the sample is scanned in a non-contact way. Scanning is normally done in a raster mode. In this work a 15 MHz focussed immersion probe was used to scan the sample with a resolution of 0.5 mm along the joining and 0.3 mm across the joining. Besides scanning the welded zone for defect detection, attenuation of ultrasonic waves across the weld zone has also been determined from the received ultrasonic signal at each position at a distance of 1 mm across the joining.

2.4 Real Time Digital Radiography

Radiography was carried out using the Real Time digital radiography system (Make: AGFA ISO Volt 225). For all the three samples 50 KV voltage and 5 Amp current was used to generating the X-ray from the source and getting the image.

3. RESULTS 3.1 Detection of lack of penetration 3.1.1 Using ultrasonic c-scan imaging

Ultrasonic c-scan imaging in thickness mode was made for all three joined samples and are shown in Figs. 3 a, b, and c respectively. Ultrasonic C-scan images show that at the joining region the thickness is less compared to the parent materials, because the two sheets when joined using a tool of length 5 mm, beyond a certain depth there was no joining. This defect is known as lack of penetration (LOP). The width and depth of LOPs in all three samples were determined by analysing the c-scan images and are listed in Table 2.

Fig. 3 : Ultrasonic C-scan images of (a) sample 1, (b) sample 2 and (c) sample 3 in thickness mode Vol. 10, Issue 4 March 2012

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Table 2 : The width and depth of LOPs in all three samples were determined by analysing the c-scan images Sample

Width of LOP (mm)

Depth of LOP (mm)

Sample 1

0-1.85

1.6

Sample 2

1.25 min â&#x20AC;&#x201C; 2.25 max

2.54

Sample 3

2.5

2.34

3.1.2 Using Phased Array Ultrasonic (PAUT):

PAUT was carried out on the same Al-Al FSW samples along the parallel direction of the joint line and scanned

the whole joined region. Inspection was done using 5 MHz probe with 45Â° wedge. The analysis was done using Tomoview software. S-scan (Sectoral scan) image was captured at different positions for each sample. For all the three joint samples lack of penetration was clearly seen almost throughout the joining line. Images were captured from initial position (34 mm) till 150 mm along the joining. A schematic of joint sample with scanned region is shown in figure 4 below and the corresponding S-scans at 4 different positions within initial and end are shown in Fig. 5 a, b, c and d.

Fig. 4 : Schematic of the joined sample and the scanned region along with the view of sample 1 with probe

Fig. 5 : Phased array s-scan images at different positions of (a) Sample 1, (b) Sample 2 and (c) Sample 3 Journal of Non destructive Testing & Evaluation

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Fig. 6 : Ultrasonic C-scan image of amplitude variation and PAUT image at the initial position of sample 3

Photograph of sample 3, its c-scan image at frequency 15 MHz and the PAUT image of the initial position of sample 3 are shown in Fig. 6. Red portion of the PAUT image corresponds to the edges of the shoulder of the tool which is clearly visible in cscan image too. Hence the portion marked as “region of interest” in the PAUT image was the area to detect any defects in the joined region. The width and depth of LOP in all three samples were measured from the PAUT images and are listed in table 3. Table 3 : The width and depth of LOP in all three samples were measured from the PAUT images Sample

Width of LOP (mm)

Depth of LOP (mm)

Sample 1

1.25

1.68

Sample 2

1.63

2.74

Sample 3

2.55

2.49

3.1.3 Using Real Time Radiography System:

Real time Radiography was performed on the FSW samples to verify the PAUT result. The inspection was done using 50KV and 5Amp current. Variation of thickness around the central line of the welding was clearly shown in the radiographs. The bright portion in the image indicates less thickness compared to the dark portion. The real time Radiography images of the three samples are shown in the Fig. 7.

CONCLUSIONS Ø Phased array ultrasonic technique was used to detect successfully Lack of penetration (LOP) in Al-Al FSW samples Ø Among all three samples, sample #1 having the least rotational speed shows minimum lack of penetration compared to the other two samples. Ø At the end point of the welding a tunnel like defect was observed in C-scan image for sample 2 and 3 which is negligible for sample 1. Ø Depth and width of LOP region as detected by PAUT was compared with C-scan images and found in good agreement with that obtained from C-scan results as listed in Table 4. Table 4 : Comparison of the depth and width of LOP as measured from the images of PAUT and C-scan Sample No.

Lack of penetration (depth)(mm)

Width of the lack of penetrated region by(mm)

C-scan

PAUT

C-scan

PAUT

1.6

1.68

1.85

1.25

2.54

2.74

1.25-2.5

1.63

2.34

2.49

2.5

2.55

This work shows that PAUT which is a portable system can be used onsite for LOP detection in FSW joined sheets

ACKNOWLEDGEMENT Fig. 7 : Real time Radiography images of (a) sample 1, (b) Sample 2 and (c) sample 3 Vol. 10, Issue 4 March 2012

This work is a part of the degree for Master of Technology of the principal author. The principal author is grateful to Journal of Non destructive Testing & Evaluation

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Dr S. Srikanth, Director, CSIR-National Metallurgical Laboratory for his kind approval to carry out the project work at CSIR-NML.

6. Vilaça, P., Quintino, L., Santos, J., Zettler, R., Sheikhi, S., iSTIR, Int. Journal of Materials Science and Engineering: A (Structural Materials: Properties, Microstructure and Processing), 445-446 (2007) 501-508

REFERENCES

7. Y.S. Sato, S.H.C. Park, A. Matsunaga, A. Honda and H. Kokawa: J of Mater Sci., 40 (2005) 637-642.

1. W. M. Thomas, E. D. Nicholas, J. C. Needham, M. G. Murch, P. Templesmith and C. J. Dawes, GB Patent Application No. 9125978.8, December 1991 and US Patent No. 5460317, October 1995 2. L. E. Murr, G. Liu and J. C. McClure, J. Mater. Sci. Lett., 16 (1997) 1801 3. G. Lio, L. E. Murr, C. S. Niou, J. C. McClure and E. R. Vega, Scripta Mater. 37 (1997) 355 4. M. W. Mahoney, C. G. Rhodes, J. G. Flintoff, R. A. Spurling and W. H. Bingel, Metall. Mater. Trans. A 29A (1998) 1955 5. Vilaça, P., Pedrosa, N., Quintino, L., Experimental Activities and Computational Developments of FSW at IST – Technical University of Lisbon, Proceeding of Romania Welding Society (ASR), International Conference: “Welding in Romania on the Edge of Joining the European Union”, Galati – Romania, 2830th, Timisoara, pp.62-77, Set. 2005.

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8. S. Fukumoto, H. Tsubakino, K. Pkita, M. Aritoshi and T. Tomita: Mater. Sci. Technol. 14 (1998)1080-1086. 9. Santos, T., Data Fusion with Fuzzy Logic in Non-Destructive Testing of Friction Stir Welding, MSc Thesis, IST, Technical University of Lisbon, Portugal, 2006. 10. Vilaça, P., Santos, T., Quintino, L., Experimental Analysis, Defect Evaluation and Computational Developments of FSW. Proceeding of IIW South East – European Regional Congress, Timisoara, Romania, 2006. 11. www.qualistir.com 12. Bird, R., Insight, 46 (2004) 31–36 13. Stepinski, T., NDE of friction stir welds, nonlinear acoustics ultrasonic imaging, Technical Report TR-04-03, Svensk Kärnbränslehantering AB, pp.3-14, 2004. 14. Reza, H. et al., NDT&E International, 40 (2007) 337–346

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Technical Paper

Transient Response of Fabry-Perot Filter-based Dynamic Interrogator Harish Achar, Bibin Varghese, 1G.M .Krishna Chaitanya, 1S. Sosamma, 1M. Kasinathan, 1 Anish Kumar, 1C. Babu Rao, 1N. Murali, 1T. Jayakumar and Balaji Srinivasan Indian Institute of Technology Madras, Chennai, India - 600036 1 Indira Gandhi Center for Atomic Research, Kalpakkam, India.

ABSTRACT In this paper, we demonstrate the capability of our home-built dynamic interrogator using Fabry Perot filters based on fiber Bragg Gratings to capture the transient response of acoustic emissions. The signal to noise ratio of the acoustic emission data is improved using adaptive signal processing techniques and the data obtained from standard ball drop tests are found to be consistent with expected values. Keywords: Transient response, Fiber Bragg Gratings, Adaptive Line Enhancement PACS: 43.40. +s

INTRODUCTION Monitoring of acoustic emissions from structures provide critical information on their integrity. Conventionally, piezoelectric transducers (PZTs) have been used for sensing such acoustic emissions spanning a frequency range of 10 kHz to 1 MHz. Unfortunately, PZTs suffer from electromagnetic interference (EMI), heavy cabling, and narrowband response (due to their mechanical resonances). Fiber Bragg gratings (FBGs) are possibly attractive replacements for PZTs in acoustic emission sensing as they do not suffer from EMI and a single fiber can be used for sensing at different points on the sensor which eliminates the need for heavy cabling. Moreover, FBGs have flat frequency response up to several MHz [1, 2]. We have previously demonstrated the use of Fabry-Perot filter based on fiber Bragg gratings (FP filter) for dynamic interrogation of acoustic emissions in the range of 10 kHz to 1 MHz with a sensitivity of less than 1 microstrain [3]. Such sensitivity was achieved using FBG based FabryPerot (FP) filters as not only the interrogator element but also the sensor element. In the present work, we extend the testing to the detection of transient acoustic emissions.

The transient performance of the system has been demonstrated through standard ball drop tests using steel balls of different diameters in the range of 2 - 9 mm. The FBG sensor was pasted on to an aluminum plate using a room temperature curing epoxy and the impact waves were generated in the plate by hitting the plate with the spring loaded steel balls. The data was logged to a personal computer and subsequently plotted to analyze the frequency content of the ball impact. The frequency content of the transient response decreased with increase in the ball diameter and could be quantitatively correlated with the diameter of the ball. As such, the present study demonstrates the applicability of the developed Fabry-Perot filter based acoustic emission sensor as a broad-band detector of transient acoustic emissions.

EXPERIMENTAL SETUP The experimental set up required to capture the acoustic emissions using the FBGs is shown in the Fig. 1. The set up consists of a broadband SLED light source which is fed to the port 1 of the circulator. The port 2 of the circulator is connected to the FP sensor which is pasted on the test bed. The test bed is an aluminum plate which is 2 mm

Fig. 1 : Schematic diagram of the acoustic sensor setup. Vol. 10, Issue 4 March 2012

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54 thick. The FP sensor is pasted on the plate with a room temperature curing epoxy. The light reflected back from the FP sensor passes through the matched FP interrogator connected to the port 3 of the circulator. The spectrum of the FP interrogator might get slightly offset from the FP sensor which is pasted on the plate. In order to match the FP interrogator to the appropriate center wavelength of the sensor the interrogator FP is pasted on a PZT fed by the dc supply. By tuning the PZT with the dc supply voltage the interrogator FP can be matched with the sensor FP. This arrangement takes care of any changes in the FP sensor wavelength due to temperature or static strain. The light is collected by the optical receiver which consists of highly sensitive Avalanche Photodiode integrated with the transâ&#x20AC;&#x201C;impedance amplifier (APD-TIA, oemarket.com). The schematic block diagram of the optical receiver module is shown in the Figure 2. The APD-TIA has a high pass cut off frequency at 10 kHz and it is fiber pig tailed. The signal is then fed to the 16-bit Sigma-Delta over-sampling ADC (Texas instruments, ADS1602) which is used to digitize the signal. Frequency resolution of <1 kHz is obtained. The ADC over samples at a rate of 40 MSa/s and then the signal is down sampled to 2.5 MSa/s to reduce the noise level. The ADC is connected to the processing module through a serial link which can transfer the digitized data to the data processor. Actel ProAsic 3 (A3P1000) FPGA manages the entire module by providing clocking signals to the ADC and synchronizing signals to the other on board processors. The data is processed in Analog Devices digital signal processor called sharc. The data is logged in to the personal computer using a microcontroller (Cypress semiconductor, EZ USB FX2) which can support a high speed USB 2.0 connection. The entire optical module as well as the electrical module has been integrated into a compact, portable box for ease of usage.

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TRANSIENT RESPONSE WITH BALL DROP TEST In order to evaluate the transient response of our dynamic interrogator we performed ball drop experiments with steel balls of different sizes. The test bed consists of an aluminum plate with dimensions 30 cm X 15 cm and having a thickness of 0.02 cm as shown in the Figure 1. A sensor FP filter is pasted to the plate using a room temperature curing epoxy. Steel balls of different diameters are taken and are used for drop ball tests. The time domain data from the dynamic interrogator is logged on to a personal computer and subsequently an Adaptive Line Enhancer (ALE) with an order of 300 is applied to the signals in order to increase the SNR and get a cleaner time domain. In ALE, the signal is split in two components and the present sample is compared with previous sample. The signal components in the delayed and the present samples are correlated whereas the noise is uncorrelated. By comparing the present and the delayed samples the signal can be greatly enhanced and the noise can be suppressed [4, 5]. However, the improvement is achieved at the expense of increased computation cost and processing delay. One of the key requirements for using any signal processing algorithm is to ensure that it does not corrupt the sensitive acoustic signals. In order to verify this, we compared the frequency content of the acoustic signals before and after applying ALE. Fig. 3 and Fig. 4 illustrate the time domain and the corresponding frequency domain data respectively, for a 2 mm drop ball test before and after passing the data through ALE. It can be seen clearly that the frequency content of the two plots are similar indicating that the ALE is not altering the frequency components of the original signal.

Fig. 2 : Schematic diagram of our home built optical receiver. Journal of Non destructive Testing & Evaluation

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Fig. 3 : Plot of signals captured from the drop ball test for 2 mm ball without ALE and with ALE.

Fig. 4 : Plot of frequency spectrum of the signals captured from the drop ball test for 2 mm ball without ALE and with ALE.

In our digital electronics module, we use an Analog Devices Sharc processor which is capable of executing instructions at 250 MIPS, resulting in a processing time of 30 ms for the above operation. Choosing the right delay and filter order is crucial for getting a better performance from the ALE. ALE is typically suitable for enhancing a single frequency compared to a band of frequencies as captured with the acoustic emission sensor. However, through our experiments we find that the de-correlation parameter D being set to 1 gives the best approximation of the noisy periodic sinusoids [5]. The order of transversal filter used for the ALE is 300 with the de-correlation delay of 1 unit and the training parameter Îź is set to a value of 0.01. The order of the transversal filter is chosen such that the ALE provides sufficient gain for the low level signal buried in noise. As the sampling frequency is 2.5 MHz, the filter order of 300 provides a frequency resolution of 8 kHz. The training parameter decides the convergence rate and the steady state error. Higher value of the training parameter ensures faster convergence but it also leads to higher steady state error. We have evaluated the transient response for balls of different sizes and the results are plotted in the Figure 5. ALE is applied on each of the signals and plotted. A key fact to notice from Figure 5 is that the frequencies which are excited in the plate due to the different ball sizes are Vol. 10, Issue 4 March 2012

following a pattern. The frequencies excited are decreasing with the increase in the ball size. This behavior is seen because the time of contact of the ball with the plate due to a drop increases with the increase in ball size. Hence smaller the size of the ball, higher is the frequencies that are excited in the plate. The dominant frequency excited in a plate due a ball drop is proportional to 1/D, where D is the diameter of the ball used for the test. There are many frequency components which are obtained in a drop ball test. In order to plot the dominant frequency against the size of the ball we took the weighted average of the frequency components excited. As can be inferred from the Figure 6, the behavior is seen to be consistent with the expected performance. We tested the transient response of our dynamic interrogator system by also observing the acoustic emissions due to dropping a steel ball of 5 mm diameter on an Al plate from different heights. The SNR of the noisy time domain plots was improved using ALE as explained above. A self trigger mechanism was developed in order to log the data when the event (ball drop) occurs. Figure 7 shows the time domain plots and the corresponding spectrum of the signals captured using the acoustic sensor. We observe an increase in the amplitude of the acoustic emission for higher ball drops, as expected. Another Journal of Non destructive Testing & Evaluation

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Fig. 5 : Plot of time domain signals before and after ALE captured from our home built acoustic sensor along with the frequency spectrum. Journal of Non destructive Testing & Evaluation

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Fig. 6 : Plot of dominant frequency excited in the plate versus the size of the ball used for ball drop.

Fig. 7 : Plot of time domain signals captured for ball drops from different heights. Vol. 10, Issue 4 March 2012

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interesting feature is that the frequency of the acoustic emissions is also increasing with the ball drop height. This may be attributed to the decrease in the contact time experienced by the ball with increasing velocity for higher ball drops, as explained through the Hertz model of colliding surfaces [6].

Balasubramaniam and Mr. Janardhan Padiyar of Machine

CONCLUSIONS

1. M. Serridge, “What makes vibration condition monitoring reliable?” Noise Vibration Worldwide, vol 22 8, pp. 17–24, 1991.

We have demonstrated the ability of our dynamic interrogator to pick transient response from the ball drop tests. We have used different size of balls for the test as well as different ball drop heights and recorded the response by applying adaptive filtering technique. The results captured are consistent with the expected excitation of the drop ball test on the plate. The adaptive line enhancement (ALE) technique is able to increase the SNR by an order of magnitude at the cost of an additional processing delay of 30 ms.

ACKNOWLEDGEMENTS The project is funded by Indira Gandhi Center for Atomic Research. We are grateful to Dr. Krishnan

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Design Section from Mechanical Department of Indian Institute of Technology Madras for useful discussion on the development and testing of dynamic interrogator.

REFERENCES

2. J.R. McEwan (Ed.), “Condition Monitoring”, vol. 3, Gulf Publishing, Houston, 1991. 3. Bibin Varghese, A V Harish and Balaji Srinivasan, “Enhanced Detection of Vibrations Using Fiber Fabry Perot Filters and Spectral Estimation Techniques”, Optical Sensors Conference, June 2011, Toronto, Canada. 4. S. Haykin, “Adaptive filter theory Prentice-Hall”, New Jersey (2002). 5. James R. Zeidler, Edgar H. Satorius, Douglas M. Chabries, Herbert T. Wexler, “Adaptive Enhancement of Multiple Sinusoids in Uncorrelated Noise,” IEEE Transactions on Acoustics, Speech and Signal Processing, Vol ASSP - 26, No. 3, 1978. 6. Rod Cross, “The bounce of a ball”, Am. J. Phys. Vol. 67, No. 3, pp. 222-227, 1999.

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Technical Paper

Air-coupled L-scan (Lamb wave scan) Imaging and its application in inspection of composite structures Janardhan Padiyar Ma, C Ramadasb and Krishnan Balasubramaniama a

Machine Design Section, Center for Nondestructive Evaluation, Dept. of Mech. Engg., Indian Institute of Technology Madras, Chennai, India – 600 036 b Composite Research Center, R&D E (E), DRDO, Pune-411 015, India

ABSTRACT This paper describes the applications of air-coupled ultrasonic imaging method based on Lamb waves for identification of defects in composite structures. First part of the paper discusses the Lamb wave scan (L-scan) using the fundamental Ao Lamb wave mode in through transmission approach. Second part of the paper brings out the characterization of delamination in flat composite laminates using single sided L-scan approach using A0 mode. Experimental study is presented using these two approaches by imaging impact damages and delamination in laminates. The result shows that L-scan is capable of producing 3-6 times higher signal amplitude than the conventional normal incidence C-scan. The limitations of single sided L-scan approach are discussed and recommendations to improve this approach are listed. A simple expression was derived to get the actual size of delaminations for L-scan images. Keywords: Composites, Lamb waves, delamination, L-scan

1. INTRODUCTION Air-coupled ultrasonics imaging (AUI) is an emerging NDE technique for composite structures due to specific advantages like no mechanical contact, liquid coupling or without any surface preparation. Hence AUI is an excellent alternative for replacing the current couplant or squirter based inspection system for composites structures during production or in-service. Advances in piezo-composites transducer technology have further improved signal-to-noise ratios of air-coupled transducers leading to highly efficient transducer designs. Compared to contact based method, AUI has low signal-to-noise ratio of received signal (after transmission through the plate) partially due to high impedance mismatch in the air path and attenuation of ultrasonic wave in composite material. Air-coupled ultrasonic NDT using through transmission employing bulk waves have been widely investigated. Testing of very thin metal plate with air-coupled ultrasonics using Lamb waves was first investigated [1]. In a related work [2,3] authors had used immersion based single sided inspection of composites using S0 symmetric Lamb wave mode .This inspection method was named L-scan which uses raster scanning similar to conventional C-scan but transducer are incident obliquely to excite and receive Lamb waves. Using broad capacitive air-coupled ultrasonic transducer in through transmission mode [4] far greater thickness plate can be inspected by bulk waves if the frequency of excitation of transducer is tuned to match the through thickness resonance of plates. There is large impedance mismatch between air and most solid materials in ‘normal incidence through transmission C-scan’ compared to ‘oblique incidence through transmission Lscan ’. Recently, variants of L-scan method called as Focused Slanted Transmission Mode (FSTM) have been evaluated using focused air-coupled transducers in through Vol. 10, Issue 4 March 2012

transmission mode. Oblique incidence has been employed in the inspection and imaging of composites [5, 6]. Most of the work reported in literature shows that inspections by AUI currently need access to both the sides of the structure for defect characterization. In actual in-service applications most of the composite structures have only single-sided access for inspection. It is therefore of practical importance to develop methods for in-service inspection of defects such as delaminations in composite structures using single sided inspections. In another study [7], authors were first to address singled sided inspection of composites by employing air-coupled transducers using A0 asymmetric Lamb wave mode and the results were also validated with Finite Element (FE) model. Interaction A0 Lamb wave mode with delamination was studied through numerical simulations and this interaction observation was confirmed by experimental study [8]. In the present work, viability of two L-scan approaches namely through transmission oblique incidence and singled sided L-scan are first studied in detail using unfocused air-coupled transducer. Our main contribution is to demonstrate experimentally the improvement in signal-to-noise ratio in images obtained by both the approaches using A0 mode. Furthermore, imaging of delamination with single sided L-scan approach using A0 mode is studied in detail and recommendation for transducer configuration for improved L-scan images are suggested. Additionally simple expression for calculating the exact size of rectangular type delamination in singled sided L-scan is derived.

2. EXPERIMENTAL PROCEDURE 2.1 Through transmission oblique incidence method

In a conventional normal incidence C-scan, a beam of aircoupled ultrasound from the transmitter causes the Journal of Non destructive Testing & Evaluation

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Fig. 1 : Schematic diagram illustrating the orientation of the air coupled transducers in normal incidence and oblique incident through-transmission inspection (a) Carbon fiber composite plate

formation of longitudinal waves in air and this wave travels through the specimen and is received by a receiver on the other side as shown in fig. 1. The received signal contains the information, in terms of amplitude, regarding defects in the material [5]. The oblique incidence set-up enables the generation of Lamb wave modes by phase matching approach. Phase matching allows efficient excitation and propagation of Lamb wave in the plate. The concept of Lscan is illustrated in fig.1. The angle of incidence needed for generation of a particular Lamb mode can be determined by the relation given below. Excitation at this correct angle is the key to increase in amplitude of the received signal.

Equation 1 Excitation angle for generation A0 mode

The concept of acoustic impedance is the foundation for all success in L-scan experiments. . The impedance mismatch is large between air and most materials when air is used as the coupling medium. There is reduction in acoustic impedance at the air material interface when using Lamb waves in L-scan. This is due to lower velocity of Ao mode compared to bulk longitudinal wave used in normal incidence. Low impedance mismatch in L-scan has resulted in increase in amplitude of the received signal. This in turn results in increased amplitude of the received signal. Table1 gives an idea of acoustic impedance for various materials when a longitudinal wave is used. Since Ao mode

(b) Plexiglas plate Fig. 2 : Variation in received signal amplitude for normal incidence and oblique incidence using 200 KHz air-coupled transducers

was employed for L-scan, phase velocity of this mode was considered for computation of acoustic impedance. To examine the amplitude (voltage) of the received signal both in normal incidence and oblique incidence, experiments were conducted on CFRP and Plexiglas samples of various thicknesses. A-scans using air-coupled probes were captured in each sample. Variation in amplitude of the received signal with thickness is shown in fig 2. It is observed that in oblique incidence case, there is a clear

Table 1 : Illustration of acoustic impedance faced by normal and oblique incidence. Material

Density Ď (kg/m3)

Longitudinal Velocity C(m/s)

Acoustic Impedance(normal incidence) Z = Ď C (106 kg/m2s)

Phase Velocity (Vph )A0 Mode (t= 2mm) @ f=200KHz

Acoustic Impedance (oblique incidence) Z = Ď Vph (106 kg/m2s)

CFRP(0/90)s

1500

3670

5.5

1063

1.6

GFRP(0/90)s

1990

2345

4.6

1072

2.1

Plexiglas

1180

2812

3.3

1025

1.2

Aluminium

2700

6320

1747

4.7

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(b)

Fig. 3 : Photograph air-coupled transducers experimental setup used for during scanning (a) Normal incidence(C-scan). (b) Oblique incidence (L-scan).

increase in the amplitude of the received signal for all the thicknesses of plates. In case of Plexiglas plate at 7.5 mm thickness, the amplitude of signal in normal incidence is higher. This is because of thickness mode resonance effect. Note that the thickness mode resonance also depends on the transducer frequency. In order to compare the inspection capabilities of L-scan with C-scan methods for imaging defects, ultrasonic imaging was carried out on various glass/ epoxy, carbon/epoxy composites. Air-coupled transducers were mounted using special holders fabricated from extruded aluminum profiles to ensure light-weight and sturdy construction as shown in Fig.3 2.2 Case study 1-Thin specimen glass fiber composite laminate:

To compare L-scan method with conventional C-scan method, experiments were conducted on Glass Fibre Reinforced Plastic (GFRP) laminate with 60 mm delamination. Fig. 4(a) shows the normal incidence through transmission mode C-scan of a thin laminate of thickness 1.32 mm obtained using air-coupled transducers of 200 kHz frequency with scanning resolution of 0.5 mm. The transducer was excited with a pulse of voltage 400 V and receiver gain of 60 dB to capture the C-scan. Fig. 3(b) shows the oblique incidence through transmission mode L-scan on the same specimen. In this case transducers were oriented at angle of 22 degrees with respect to normal to the specimen and rest of the pulser receiver parameters were maintained same as that during C-scan. The most Vol. 10, Issue 4 March 2012

Fig. 4 : Raster scan image of delamination obtained by (a) Normal incidence (b) Oblique incidence

noticeable feature in oblique incidence L-scan compared to normal incidence C-scan image is that the peak voltage obtained in L-scan is almost 3 times higher than that in normal incidence method. But, the sharpness of edge of defect has reduced in oblique incidence compared to that in normal incidence. 2.3 Case study 2-Low velocity impact damage:

To evaluate the effectives of L-scan on CFRP composite plate, experiments were conducted on a plate of 200 mm length and width and 3.12 mm thickness containing Barely Visible Impact Damages (BVID). Fig. 5(a) illustrates the normal incidence C-scan obtained on a CFRP sample with BVID. Scan was carried out with a resolution of 0.5 mm. Air-coupled probes of 100 kHz were employed. Following were the settings of pulser â&#x20AC;&#x201C; 400 V excitation voltage and 60 dB gain. Fig. 5(b) shows the L-scan on the same CFRP Journal of Non destructive Testing & Evaluation

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plate. The probes were oriented at an angle of 12 degrees with respect to the normal to the plate. From both the images, it is clear that the defect can be found using either of the images. The improvement in SNR can clearly be seen in these images. Speckled appearance is seen in normal incidence method whereas the L-scan image is clear and is twice the amplitude than that of C-scan image. But the defect observed in L-scan is larger in size. 2.4 Case study 3-thick glass fiber composite laminate plate

One more sample, GFRP cross-ply laminate of thickness 16.8 mm, was considered to examine the increase in amplitude of the received oblique incidence compared to normal incidence. Air-coupled probe of 100 kHz with an active diameter of 50 mm was excited by a pulse voltage of 900V with receiver gain set at 60 dB. The fig. 6 shows the A-scans captured in normal and oblique incidences. In oblique incidence the transducer were oriented at an angle of 14 degrees with respect to normal, rest of the pulserreceiver parameters were maintained same in both normal and oblique incidences. The amplitude of the received signal in oblique incidence is twice that of the normal incidence. The air-coupled ultrasound penetrates thick materials easier through L-scan than in normal incidence.

3. SINGLE-SIDE L-SCAN IMAGING

Fig. 5

: Raster scan image of barely visible impact damage obtained by (a) Normal incidence (b) Oblique incidence

In single-side L-scan imaging, transmitter and receiver are on the same side of the structure to be inspected. Transmitter and receiver are oriented at an apt angle to generate and receive Ao mode. Minimum separation distance is fixed between transmitter and receiver assembly (probe unit) and raster scan is carried out over the plate. The image obtained in this technique is named as single side L-scan image. Fig. 7 shows single side L-scan image in composite plate (02/902/902/02) with two delaminations of sizes 50 mm and 40 mm, both were in the second layer from the top surface. This L-scan image was generated using 200 kHz air-coupled transducer with an active diameter of 25 mm and probe separation distance of 70

Fig. 6 : Typical A-Scan at signal in normal incidence vs. oblique incidence in thick CFRP laminate. Journal of Non destructive Testing & Evaluation

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(a)

(b)

Fig. 7 : L-scan imaging with air-coupled ultrasound (a) composite plate with two delamination (b) single side L-scan

mm. Voltage set for excitation of the transmitter was 900 V and receiver gain was set at 60 dB. 3.1 Practical issues with single-side L-scan imaging

Fig 7(b) shows overlapping of boundary of defects. This results in difficulty of sizing of defects. The reason for overlapping of boundary of defects can be attributed to finite size of transducers and the distance of separation of probes. If these points are not considered while scanning (L-scan) a laminate with multiple defects which are nearer to each other, then, L-scan image shows as a bigger defect. This is due to overlapping of the boundaries of the defects. In addition, one more parameter that governs the over sizing of defects in L-scan image is probe lift-off. Lift-off of transducers increases the chances of surface reflection of acoustic wave from plate and interferes with the guided wave signal leaking from the composite plate. All these aspects should be taken into account while sizing the defect using L-scan image. Currently, commercially available lower frequency air-coupled transducers are large in diameter. This poses a difficulty of bringing them closer. When transducers are brought close to each other, acoustic wave propagating through air interferes with Lamb wave propagating in the plate as shown in fig 7(b). To some

extent this interference can be circumvented by selecting high frequency probe and less number of cycles in the excitation. Albeit the smallest diameter probes are chosen, a minimum probe separation distance should always be maintained while capturing L-scan image. These geometric restrictions can be overcome by following the recommendations listed in Table 2. Fig 8 shows L-scan image captured through implementing these recommendations. Air-coupled probes of 500 kHz and active diameters of 13 mm (transmitter) and 9 mm (receiver) were used. It is seen that the size of defect has reduced compared to that in fig 7 and there is a clear separation between the defects. Table 2: Recommendations for carrying out single-sided L-scan for thin composite laminates of less than 5 mm thickness 1

Select smaller diameter probes. Preferably not more than 15mm.

Keep minimum transducer separation distance

Select higher frequency transducer - 400kHz or 500kHz

Keep minimum lift off. Preferably less than 5mm.

3.2 Sizing of delamination in single-sided L-scan imaging

The sizing of imaged delamination in L-scan requires size correction. An expression relating the size of defect in Lscan image (S), probe separation distance (D) and average of diameters of transmitter and receiver (da) is given below. S = P + D â&#x20AC;&#x201C; d a;

Fig. 8 : Schematic of the possible Lamb wave propagation paths in the composite plate in single sided inspection. Vol. 10, Issue 4 March 2012

where, d1 and d2 are diameters of transmitter and receiver. Fig 10(a) shows normal incidence conventional C-scan obtained on a plate containing 50 mm delamination. L-scan image obtained on the same plate is shown in Fig. 10(b). From fig 10(b), size of delamination is 85 mm, diameters of probes were 13 mm and 9 mm and probe Journal of Non destructive Testing & Evaluation

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Fig. 9 : Schematic of air-coupled transducer configuration (a) through transmission (b) single sided L-scan transducer configuration (c) C-scan of composite plate (b) single side L-scan.

Fig. 10 : Imaging with air-coupled ultrasound composite plate (0//90/90/0) with 50mm delamination width (a) Normal incidence through transmission C-scan (b) single side L-scan image

separation distance was 44. From the above expression, the size of delamination works out to be 52 mm, which is in good agreement with the actual value.

4. SUMMARY AND CONCLUSION The present study aimed at understanding two approaches of L-scan using air-coupled ultrasonic transducers. Journal of Non destructive Testing & Evaluation

Experiments were carried out for evaluating the variation in amplitude of received A-scan signal in conventional normal incidence and oblique incidence L-scan in various thicknesses of plates. It was seen that oblique incidence gives higher amplitude in the plate with smaller thickness. When the plate thickness falls near the through thickness resonance of the plate, the amplitude of the received signal increases drastically in normal incidence. L-scans images Vol. 10, Issue 4 March 2012

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obtained for various defects using oblique incidence approach is seen to have higher SNR compared to normal C-scan image. Due to the increased SNR one can produce faster air-coupled scans without averaging the signal during the scanning. Oblique incidence L-scan requires only change in the transducer angle without any changes in the conventional C-scan system. In separate experiments using single sided L-scan it was observed many geometric factors affect the size of delamination. It was observed that there was a clear separation between nearby defects in L-scan image obtained using smaller diameter and higher frequency air-coupled transducer of 500 kHz. Also, the size of defect in L-scan was higher than the actual one. This is due to finite size of transducers. An expression was derived to estimate the size of delamination from L-scan image. The predicted delamination size was found to be in good agreement with the actual delamination size. Thus experimental result shows that the air-coupled single sided L-scan is reliable for characterizing delaminations and holds considerable promise in diagnosing delaminations in thin composite materials. Moreover, the proposed L-scan imaging technique encourages the development of scanning systems with singled sided air-coupled inspection feature for in-service inspection of thin composite structures. The main limitation of L-scan method is that the appearance of defect bigger than the actual one.

ACKNOWLEDGMENTS The authors thank R&DE(E), Pune, for supplying all composite laminates used in the experiments. Also the authors express their sincere thanks to Nikhil Hariharan and Maheswaran, both from NIT, Trichy, for fabricating

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transducer attachment and specimen preparation. The authors thank ADA, Bangalore for partial funding of the research work.

REFERENCES 1. M. Luukkala, P. Heikilla, and Y. Surakka. Plate wave resonanceA contactless test method. Ultrasonics, vol. 9, pp. 201-208, 1971. 2. Kundu T, Ehsani M, Maslov KI and Guo D. C-scan and L-scan generated images of the concrete/GFRP composite interface. NDT&E Int. vol.32, pp. 61-9, 1999. 3. Chimenti D E and Nayfeh A. H. Leaky Lamb waves in fibrous composite laminates. J. Appl. Phys. vol.58 pp. 4531-8,1985. 4. D.W. Schindel, D.A. Hutchins and W.A. Grandia. Capacitive and piezoelectric air-coupled transducers for resonant ultrasonic inspection. Ultrasonics vol.34, pp. 621-627, 1996. 5. I. Yu. Solodov, R. Stoessel and G. Busse. Material characterization and NDE using focused slanted transmission mode of air-coupled ultrasound. Research in Non-Destructive Evaluation, vol. 15, pp. 65-85, 2004. 6. H. N. Bar, V. Dayal, D. Barnard, and D. K. Hsu. Plate Wave Resonance with Air-Coupled Ultrasonics. AIP conference proceedings. Rev. of prog. QNDE vol.29, pp. 1069-1076,2010. 7. Castaings M, Cawley P, Farlow R and Hayward G. Single sided inspection of composite materials using air-coupled ultrasound. J Non-destruct Eval. vol.17, pp. 37-45, 1998. 8. Karthikeyan P, Ramadas C, Bhardwaj MC and Balasubramaniam Krishnan. Non-contact ultrasound based guided Lamb waves for composite structure inspection: some interesting observations. AIP conference proceedings. Rev. of prog. QNDE, vol. 28, pp. 928-935, 2009.

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Validation of ray-based ultrasonic simulation tool (simsonic) using conventional and phased array transducers Padma Purushothaman1, Krishnan Balasubramaniam2 and C.V.Krishnamurthy2 Dhvani Research and Development Solutino Pvt Ltd, Taramani, Chennai, India Centre for Nondestructive Evaluation, Indian Institute of Technology Madras, Chennai, India 1

ABSTRACT A ray-based simulation software SIMSONIC with 2D and 3D ray model is developed to study the propagation of ultrasonic waves in media with simple and complex objects. SIMSONIC accepts any geometry that can be modelled in CAD software in SLP and STL file formats. The ultrasonic beam is modelled as a collection of rays and a cumulative Gaussian distribution is used to distribute the energy among the rays. The primary rays are propagated and new reflected, refracted and mode converted rays are generated at each interface following Snellâ&#x20AC;&#x2122;s law. In this paper, SIMSONIC simulations carried out with Conventional and Phased Array transduction are compared with measurements on simple objects and IIW Calibration blocks The A-scans and the associated B-scans show good agreement with measurements. Keywords: Ultrasonic, Ray Tracing, Modelling, Simulations, Phased Array.

1. INTRODUCTION WHY should a NDE inspector have an NDE Simulator? The use of simulation tools in NDE will allow the user to have the following advantages: (a) New inspection procedures can be developed without the need for expensive and time consuming experimental mock setups, at relatively lower costs and at reduced time. (b) The inspection of complex problems can be investigated and solutions for difficult situations can be developed and validated. (c) Experimentally obtained signals and scans can be interpreted to identify the signals, obtain the sensitivity, resolutions, Probability of Detection (PoD), Probability of Sizing (PoS). etc. (d) The effect of anisotropy, grain noise, surface roughness, etc can be understood. These effects are not yet implemented in SIMSONIC. Simulation tools are increasingly finding application in the inspection processed due to (a) Improved modelling tools that allow faster calculations, (b) user friendly graphical user interface that allows almost anyone to use the simulations, and (c) the faster computational processors, even in the form of a laptop. In an ultrasonic simulators, A-, B-, C-, S-, and other forms of scans on simple and complex shaped components is feasible. Defects can be introduced All simulation tools are based on some theoretical basis, that allow the user to conduct a virtual experiment in a computer and analyze the results to learn more about the generation, propagation, interaction, reception, and Journal of Non destructive Testing & Evaluation

interpretation of ultrasonic waves in components with and/ or without defects. All simulation tools are based on some assumptions, that allow for the reduction in computational effort, but will introduce approximations in the results that must be taken into account while utilizing the results. As the approximations increase, the speed of computation will decrease significantly. A ray-based simulation tool SIMSONIC has been developed to understand the ultrasonic wave propagation through simple and complex objects. Ray modelling is already discussed and presented earlier [1]. Validation of SIMSONIC using conventional transducer was discussed earlier [2]. In this paper, the simulations using Phased Arrays are also included and validated through experiments. Using this simulation tool, frequently encountered problems in ultrasonic inspection like (a) to identify the signal echo from the defect that constitute an A-Scan, (b) Scan path planning, (c) to identify echo in A-scan due to longitudinal and transverse waves. Ray based simulation is an attractive alternative to the computationally intensive simulation models like Finite difference models due to its highly interactive capability and quick assessment of A-scans and B-scans. It is developed in Visual C++ .net environment with OpenGL for visualisation and Measurement Studio for A-scan and B-scan displays.

2. FEATURES OF SIMSONIC The component to be inspected is modelled in CAD software like ProE, SolidWorks or CATIA and saved as triangular meshes in STL or SLP files. These files can be imported in SIMSONIC for Ray-based assessment. The features of SIMSONIC are listed below: Vol. 10, Issue 4 March 2012

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(a) Modes of Inspection – Immersion, Contact and Wedge (b) Transducer Types: Unfocussed, Focussed and Phased Array (c) Pulse-echo and Pitch Catch Simulation modes (d) Input pulse of a Transducer - Internally generated pulse or User-defined Pulse of a transducer (e) Material Manager – Material Library that contains the density, longitudinal and shear velocities of the object material and wedge material, with a provision to update with User-defined material properties. (f) Three dimensional visualisation of Object with ray paths (g) Live Simulated A-Scan and B-Scan visualisation with file saving options (both text and image)

corresponding A-scan will be displayed instantaneously. The A-scan and B-scan data can be stored in text files for further analysis.

VALIDATIONS OF SIMSONIC All the validations are carried out with 3.5 MHz unfocussed transducer in the immersion mode and 5L64 Phased Array. The input pulse of the transducer is measured using a thin copper wire of 0.28mm diameter tied around two blocks with the transducer about 60mm above the copper wire. The measured A-scan is shown in Figure 2. The input pulse of the transducer, which is shown in the expanded scale next to A-scan in figure 2 is used in SIMSONIC for simulations.

(h) Construction of Wedge

3. VALIDATION OF SIMSONIC

(i) Save/Retrieval of input data in xml file format.

3.1 Case 1

(j) Live transducer manipulation using keyboard and mouse (k) Report generation in html file format. All the above features are managed using windows docking/ undocking properties. Figure 1 shows a snap-shot of SIMSONIC. In the graphics window, the transducer can be rotated or moved by using keyboard keys and mouse and the

Pulse-echo B-Scan response of an 5 deg slope bottom Stainless steel block with a rectangular defect using an 3.5 MHz Unfocussed Transducer – Comparison with measurements made at CNDE. Figure 3 shows the Ray picture of SIMSONIC, B-scan of SIMSONIC and measured B-scan images. Only the rays received by the transducer that constitute the Ascan are shown in the ray picture for clarity. The small change in

Fig. 1 : A snap-shot of SIMSONIC Vol. 10, Issue 4 March 2012

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Fig. 2 : A-scan of a thin copper wire measured using an 3.5 MHz Unfocussed Transducer

Fig. 3(a)

Fig. 3(b)

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the front wall signal in the measured B-scan is due to the material kept under the specimen to keep the front wall parallel to the scan path. Due to the flexibility of that material, the front wall is not exactly parallel to the scan path during the measurement.

received signal is maximum and the fall in signal on moving the transducer on both sides is shown in Fig. 4(b). The Bscan of SIMSONIC is compared with Measurements made at CNDE for this case in Fig. 4(c). 3.3

3.2

Case 2

Shear wave inspection on IIW Calibration Block â&#x20AC;&#x201C; To obtain a peak signal from 4" radius curved surface of IIW Type 1 Steel Block. Figure 4(a) shows the received rays that are reflected from the 4" radius curvature of IIW block. At this position, the

Case 3

SimSonic Simulation using Contact Phased Array â&#x20AC;&#x201C; Sectorial Scan on 25mm Aluminium Block with a 2mm Notch. Figure 5(a) shows the 25mm Aluminum Block with 5L64 contact Phased Array probe. The following parameters are used: 16 element aperture (start element:26), 46 Focal laws,

Fig. 4(a)

Fig. 4(b)

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Fig. 5(a)

Fig. 5(b) : SIMSONIC Simulations Measured at CNDE

Fig. 6 : (a) IIW Block is shown as wireframe. For clarity, only receiving rays are shown ; (b) SIMSONIC Simulations corresponding Experimental Validation Journal of Non destructive Testing & Evaluation

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0-45 deg Steering angle, 12.5 mm Focal length. The simulated B-scan is compared with measurements in Figure 5(b). Case 4 : SimSonic Simulation using Contact Phased Array – Linear Scan on IIW Type1 Steel Calibration Block to study the echo from a 0.06" dia hole and 2" dia hole filled with Plexiglass. Figure 6(a) shows the IIW Calibration Block with 5L64 contact Phased Array probe. The following parameters are used: 16 element aperture, 49 Focal laws, Right to Left Scan. 15 mm Focal length. The simulated B-scan is compared with measurements in Fig. 6(b).

4. SUMMARY The use of SIMSONIC simulation tool on several standard samples has been demonstrated. Simulation results compare well with the corresponding experimental results. Some of

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the future additions in the SIMSONIC software that are planned includes: · · ·

TOFD modelling Simulations inside anisotropic weld! Gram noise models

REFERENCES 1. Adarsh Krishnamurthy, Mohan K. Varadarajan, Soumya K., Krishnamurthy Chitti Venkata and Krishnan Balasubramaniam, “A Simulation Tool for Ultrasonic Inspection”, Journal of the Korean Society for Nondestructive Testing, Vol.26, No.3, pp.153161, 2006. 2. Padma Purushothaman, C.V. Krishnamurthy and Krishnan Balasubramaniam, “Validation of Ray-based Ultrasonic Simulation Tool (SIMSONIC) with Measurements”, Proceedings of the National Seminar & Exhibition on Non-Destructive Evaluation, NDE 2011, December 8-10, 2011, available in www.ndt.net.

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PROBE Perception varies not only from person to person but also from time to time for the same person. Perception depends upon the mind which is nothing but accumulation of the past data (experience) as we saw in the earlier issue. As the mind changes due to one’s own experience, the perception also changes. The life’s aim for an ordinary person is to lead peaceful, purposeful, knowledgeful, respectful and contended happy life. As a matter of fact the real happiness springs from within. The happiness that originates from outside (due to material possession – is born out of the notions of I and mine.) is temporary. Happiness that arises from within is like that of water pouring out of a spring and is eternal. On some days, as we get up in the morning for no apparent reason happiness pours out of us and our actions reflects the same and whole day we radiate happiness and a sense of well being. That is our nature. That is the child like quality which is hidden inside us and manifests when our mind is unperturbed by external influences and is in its pristine state- unpolluted. This child quality is altered by external influences and our own experience. Kindly recall what was written in the earlier issue about stimuli and response to the stimuli. The stimuli are of external origin but the response is our reaction to the stimuli. So long as we hold the response we hold our future. It is this gap that decides our future and our circle of influence. Unbelievable? Wait! I can do no better than narrate this incident. Kesavan was an intelligent and incorrigible optimistic young man. His friends have never seen him in wallowing in self pity or in a depressed mood. He was always in a joyous happy and playful mood. His friends used to ask him that how is it that he is never upset and was always happy? For which Kesavan used to reply that happiness is nothing but a frame of mind and you decide what your mind should do. He also said that every day in the morning as soon as he gets up the first thing that he does is to thank GOD for having given yet another day to rejoice and tells his mind that he had chosen to be happy that day. His friends could never understand his philosophy and were waiting for the day when he would be unhappy. It so happened that one night thieves paid a visit to the restaurant while Kesavan was tallying the day’s collection and took away all the cash after stabbing him in the stomach. He was admitted in the hospital and was recuperating after the operation when his friends visited him hoping that at least this time they will find him in a sad mood. But to their surprise they found him as cheerful as ever and when questioned Kesavan said that “When I was wheeled to the operation theatre I was tempted to be sad and was about to ask Why me? And asked the surgeon what were my chances? The surgeon was looking very serious and thoughtful. The surgeon replied that there is nothing serious and I will get through. I told him Doctor but your face does not reflect what you say. Hearing this he burst out laughing and the mood in the theatre took a dramatic turn. Every one put in their best effort and the result is what you see.” Kesavan took his future in his hands and through his response to the stimuli made a positive change in the moods of the people who were present in the theatre and his approach influenced the people surrounding him to produce spectacular result. This could happen to anyone of us. The important thing is the attitude. Please remember that Attitude decides the Altitude.

Ram.

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