Prof. Krishnan Balasubramaniam has been involved in the field of Non-destructive evaluation for more than Twenty Six 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 also serves as the Head of the Centre for Nondestructive Evaluation. He graduated from Drexel University, Philadelphia, from the department of Mechanical Engineering a Ph. D. in the year 1989. Before joining IIT Madras in 2000, he was employed as an Associate Professor with the Department of Aerospace Engineering and Mechanics at Mississippi State University. He has over 280 technical publications (including 122 refereed journal papers) and has directed 15 PHD student dissertations and 42 MS student theses. He has also 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 currently the Principal Investigator in several sponsored research projects funded by DST, DAE, ADA, ISRO and DRDO organizations. He is an active member of ISNT, ASNT, SAMPE, ASME, UIA and ASA and has organized several international symposiums and workshops. He currently serves as the Editor-in-Chief of the Journal for Nondestructive Testing and Evaluation (ISNT), and as the South-east Asia Editor for the Journal of Nondestructive Testing and Evaluation (Taylor and Francis). He is also in the editorial board of the Journal of Structural Longevity.

Abstract

Air Coupled Ultrasonic NDT and its applications

The use of Air Coupled Ultrasonics, particularly for industry applications, is fast becoming a reality largely due to the advent of highly efficient transducers and the selection of wave modes that have lower acoustic impedances. The coupling through air allows for a wider use of the ultrasonic NDT technologies when compared with the conventional couplant based methods. The increased speed of inspection, the portability of the systems (since couplants are not required), the sensitivity to defects, inspection of hidden regions, etc. are some of the key advantages of the air coupled ultrasonic techniques. The dis-advantages of the technique include the limitation of the frequency of operation and the requirement of high voltage for excitation. In this paper, the application of Longitudinal, Shear, and Lamb wave modes that are excited and received by air coupled ultrasound transducers will be discussed. The technique is applied to aerospace components, composite pipes, adhesive bonded components, among others. The defects considered include weld inspection, delamination characterisation in composite structures, interfacial weakness in bonded components, etc. that are made with metals and or composites.