Research techniques in nondestructive testing

Research techniques in nondestructive testing

BOOK REVIEWS R e s e a r c h Techniques in Nondestructive Testing ed by R. S. Sharpe, Academic P r e s s , London 1970, £ 8.00, 492 + x i i p. This bo...

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BOOK REVIEWS R e s e a r c h Techniques in Nondestructive Testing ed by R. S. Sharpe, Academic P r e s s , London 1970, £ 8.00, 492 + x i i p. This book touches the subjects of most pertinent i n t e r e s t for the future advances in nondestructive testing. The s h o r t preface written by R. S. Sharpe c l e a r l y laid out the way in which the book was intended to p r e s e n t new trends in nondestructive testing for a wide s p e c t r u m of engineers, technologists, scientists and teachers. The preface is followed by 14 chapters written by authors f r o m England and the United States. The f i r s t chapter of P. H. Hutton and R. N. Ord (USA) on 'Acoustic e m i s s i o n ' gives potential applications of this testing technique. These are continuous s u r veillance of p r e s s u r e vessels, detecting and m o n i t o r ing of cracking and, last but not least, the investigations of f r a c t u r e m e c h a n i s m s . The theoretical a s p e c t s and physical principles a r e treated in a descriptive way and one feels the lack of more fundamental ' s t o n e s ' , even though the technique which p r o v e s to be useful can be still regarded as a state of art. The list of r e f e r e n c e s on this is v e r y powerful instrument of p r e s e n t and future nondestructive t e s t ing also s e e m s to be short. The second chapter on 'Ultrasonic s p e c t r o s c o p y ' , written by O. R. Gericke (USA) begins with the explanation that s p e c t r o s c o p y is the analysis of frequency components in ultrasonic signals used in nondestructive testing of m a t e r i a l s . The author briefly r e m a r k s on the methods by which the pulse s p e c t r u m can be analysed and recognized. He goes on to the theory beginning with the description of output s p e c t r u m of the g e n e r a t o r exciting the t r a n s d u c e r and the f r e quency r e s p o n s e c h a r a c t e r i s t i c s of the t r a n s d u c e r itself. The successful application and utilisation of analysing the frequency s p e c t r u m of reflected and t r a n s m i t t e d pulses seem to p r o m i s e m o r e i n f o r m a tion on the s t r u c t u r e of m a t e r i a l s and inherent flaws in the m a t e r i a l . If suitable c i r c u i t r y is used and t r a n s d u c e r frequency r e s p o n s e known then one can observe the frequency distribution changing f r o m one kind of m a t e r i a l to another depending on grain size etc. Defect g e o m e t r y can also be observed to some extent. In chapter 3 on 'Ultrasonic imaging systems' written by J. E. Jacobs (USA) the brief theory and practical applications are presented. Four groups of processes are described to give a full picture of the ultrasonic field (eg chemical effects, thermal, optical and mechanical or electronic techniques). A short summ a r y of each of the above mentioned techniques or effects is given. The author states that acoustic impedance is probably the most significant factor influencing the transmission and reflection of sound waves and presents s o m e of the possible applications of ultrasound imaging systems. The hope was also expressed that the development of holographic techniques holds some promise in extending the usefulness of the system to biological applications. In chapter 4 on 'Ultrasonic critical angle r e f l e c t i v i t y ' the authors F. L. Becker and R. L. Richardson (USA) s t a r t with the statement that the c l a s s i c a l non-attenuating model fails in the range of critical angle r e f l e c tion. They propose a model which includes the effects

of attenuation and show its validness, advantages and limitations, in o r d e r to take account of the damping of vibrations in solids a linear relation between s t r e s s , strain and its f i r s t time derivative is introduced and generalised for three dimensions. After extensive calculations the authors obtain the generalised Shell's law. The critical proof of the model leads to the conclusion that the minimum reflection depends principally on shear attenuation, i n c r e a s i n g with increasing attenuation. Also the shear wave velocity affects the position of minimum reflectivity to a much s t r o n g e r degree than the changes in longitudinal wave velocity. F r o m these considerations s e v e r a l applications in nondestructive testing arise, such as measuring the shear wave attenuation, the surface l a y e r s (internal s t r e s s e s ) etc. Chapter 5 on 'Ultrasonic holography' written by E . E . Aldridge (England) gives a short theoretical introduction on how a hologram is created. The author then d i s c u s s e s ultrasonic holograms, dividing them into two classes, namely those which have analogues in optical methods and those which make use of e l e c tronic methods. A short description of the method using optical analogues is followed by the description of electronic methods. Chapter 6 written by A. E. Ennos (England) is on 'Optical holography and coherent light techniques'. Optical holography involves an extension of applications of optical methods. In holography use is made of amplitude and phase of wave motion such as light. It differs f r o m other methods where only intensity or amplitude of wave motion a r e used. The image formation and reconstruction is presented in a descriptive way and followed by simple mathematical explanations. Much attention is paid to applications such as deformation studies, inspection of shape, vibration analysis and possibilities of fatigue detection are even pointed out. Limitations are also briefly mentioned. Chapter 7, written by C. W. Cox (USA) on 'Data handling techniques' states that with the growing trend towards automation the p r o b l e m s in data p r o c e s s i n g a r e inevitable. A basic difficulty that is still encountered, is that rich information is contained in signals which are quite difficult to translate in o r d e r to make use of them. The chapter is divided into 12 p a r t s and p r e s e n t s a very valuable introduction for those who wish to get acquainted with this tool of data interpretation. It requires, however, some knowledge of probability and statistical theory in o r d e r to follow and understand the considerations. Extensive r e f e r e n c e s help to promote further studies in this direction. Chapter 8 written by R. Halmshaw (England) on 'Direct view radiological s y s t e m s ' considers types of s y s t e m s such as image intensifier tubes, sensitive television c a m e r a s , special television tubes with a pick-up surface sensitive to x - r a y , and image intensifier 'panels' where use is made of photoconductive o r e l e c t r o l u m i n e s c e n t l a y e r s . The short description of the principle of image intensifier s y s t e m s is followed by extensive considerations on the determination of p e r f o r m a n c e of these s y s t e m s . The chapter is closed with short notes on industrial applications and possible lines of future development. non-destructive testing June 1971


Chapter 9 on 'Neutron r a d i o g r a p h y ' written by H. Berger (USA) d i s c u s s e s in detail the neutron r a d i o graphy techniques starting with extensive treatment of sources for neutron radiography and detectors used. The chapter also contains some examples of neutron radiography applications.

Science of Materials), a s e r i e s of advanced text books, which implies that this book is mainly intended for instruction at u n i v e r s i t i e s and technical colleges. The author has tried to p r e s e n t the e s s e n t i a l s of a complex subject in a comprehensible and concise f o r m , without sacrificing scientific principles.

Chapter 10 on 'A communications network approach to submilimetric wave techniques in nondestructive testing' written by W. H. B. Cooper (England) t r i e s to supply a general point of view on wave-like phenomena (such as e l e c t r o m a g n e t i c and ultrasonic waves) which are used in ndt to gather information about the properties of media. The author shows in the chapter how use can be made of the concepts such as the 'field impedance' and the ' t r a n s f e r function' in the wave-like p r c c e s s of ndt. A discussion on s e v e r a l transport p r o c e s s e s is given. The chapter closes with some e l e c t r i c a l analogues of the t r a n s p o r t p r o c e s s e s described e a r l i e r in the chapter.

The book c o v e r s p r i m a r i l y the three main nondestructive testing methods, ie, radiography and ultrasonic and magnetic testing, the latter being subdivided into general magnetic and e l e c t r o - m a g n e t i c induction methods.

Chapter 11 on ' M u l t i p a r a m e t e r eddy c u r r e n t concepts' written by H. L. Libby (USA) outlines the possibilities of m u l t i p a r a m e t e r eddy c u r r e n t tests. It gives the principles of this new concept as well as showing the potential possibilities of this method in c o n t r a s t to commonly used single frequency tests. The d e s c r i p tion of the instrumentation is followed by a demonstration of the application of a two-frequency tubing test s y s t e m and a f o u r - f r e q u e n c y thickness test s y s tem with a tubing c r o s s section display. Chapter 12 by D. L. Waidelich is on ' P u l s e d eddy c u r r e n t s ' . After stating the advantages of pulsed eddy c u r r e n t s in c o m p a r i s o n with sinusoidal eddy c u r r e n t s the author gives s h o r t r e m a r k s on early works and goes on to d i s c u s s the use of s e v e r a l pulse methods such as the applications of masked probes, reflection s y s t e m s , correlation, filtering methods and field analysis. It is hoped that the pulse s y s t e m s will find a considerable number of applications having definite advantages over sinusoidal eddy c u r r e n t s in coming y e a r s . Chapter 13 on 'Microwave techniques' written by D. S. Dean and L. A. Kerridge (England) contains the description of microwave propagation, and the c o m ponents such as g e n e r a t o r s and waveguides, isolators, attenuators etc. Techniques such as t r a n s m i s s i o n , reflection and scattering are discussed. There is a short note on visualisation techniques which rely on heating effects and holographic techniques Chapter 14 on ' I n f r a r e d techniques' is written by W. D. Lawson and J. W. Sabey (England). It outlines the basic concepts of i n f r a r e d radiation, t r a n s m i s s i o n , and detection as well as i n f r a r e d s y s t e m s . The broad objective of the book reviewed, makes it a very valuable information s o u r c e for large numbers of scientists, engineers and m a n a g e r s in industry. The editor, R. S. Sharpe, is to be congratulated for the right choice of new r e s e a r c h techniques in ndt and for making the book as informative as possible. Z. Pawlowski

ZerstSrungsfreie Werkstoffpriifung (Non-Destructive Testing of Materials) by Dr. Werner Kurzmann, VEB Deutscher Verlag ffir Grundstoffindustrie, Leipzig 1970, 275 pp. This book appeared recently as Volume VI of ' E i n f(ihrung in die Werkstoffkunde' (Introduction to the 206

non-destructive testing June 1971

In presenting the individual methods, the author f i r s t d i s c u s s e s physical principles. In accordance with the book's introductory nature, physical laws and theory are described only in so far as is n e c e s s a r y for an understanding of the functioning of the equipment and aids and their scopes and limitations. Next, the testing p r o c e s s e s and equipment are dealt with. F r o m the wide range of possibilities only the p r o c e s s e s and equipment which the author considers important in industrial testing practice are detailed. Specific details, such as the electronic design of the equipment, a r e generally omitted. A third section under each heading is dedicated to test p r o c e d u r e s , r a n g e s of application and, in p a r t i c u lar, special aspects of the individual tests, (for example, calibration in ultrasonic testing) and an app r a i s a l of the information value obtainable. A concluding chapter on other testing methods r e f e r s to p r o c e s s e s which, in the a u t h o r ' s opinion, are still at the development stage but likely to achieve considerable importance in industrial testing in the f o r e s e e a b l e future. Although i n f r a r e d and m i c r o wave testing, neutron t r a n s m i s s i o n and t h e r m o e l e c t r i c methods may fall into this category, penetrent dye tests and e l e c t r i c a l m e a s u r e m e n t of c r a c k depth are already widely used in the industries. The chapters on the principal non-destructive test methods a r e supplemented by a review of promising new methods such as c o l o u r - r a d i o g r a p h y , x e r o - r a d i o graphy and the c - s c a n - m e t h o d in ultrasonic testing. While the betatron is mentioned and described, no r e f e r e n c e is made to the i n c r e a s i n g importance of the linear a c c e l e r a t o r . Apart f r o m the uses of these p r o c e s s e s for flaw detec tion, the possibilities of using non-destructive techniques to determine the condition of m a t e r i a l s and their strength are discussed. This includes the m e a s u r e m e n t of sound velocity and ultrasonic attenuation and the use of magnetic particle and magneto-induction p r o c e s s e s to determine the alloy and m i c r o s t r u c t u r e s of metals. Reference is made to the possibilities of automating radiographic, ultrasonic and magnetic inspection to eliminate subjective evaluation of tests. The author concludes that, although production p r o c e s s e s in many branches of industry are being automated to a g r e a t extent nowadays, automation of the testing p r o c e s s e s is not keeping pace. In the section on ultrasonic testing t h e r e is for the f i r s t time a c l e a r verdict on the health hazard in ultrasonic testing which the author d e c l a r e s is p e r fectly h a r m l e s s to human beings. A subject index, bibliography and a list of periodicals reporting r e g u l a r l y or occasionally on new experiences and p r o c e s s e s in n o n - d e s t r u c t i v e testing c o m plete the work. H. J. Meyer