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Research techniques in nondestructive testing, volume 3
that bond integrity, voids, porosity, and cracks parallel to the substrate may be generally amenable to thermal and ultrasonic methods of examination: ultrasonic pulse-echo absorption and resonance damping are possible candidates for testing for inclusion content, and ultrasonic surface waves and magnetic flux analysis for cracks normal to the substrate. Bucklow also suggested that these techniques are likely to be comparative, and to be most applicable to repetitive work. As one delegate pointed out, however, users are more likely to have confidence in the results of destructive tests on a statistical sample of the components: it is surely in 'one-off' production and reclamation spraying that there is the greatest need for reliable non-destructive test methods.
Answering perhaps the comments of another delegate - "What we want to know about a coating is how thick it is, and is it going to adhere" - Franke and de Gee of Metaalinstituut TNO described an acoustic technique for measuring adhesive bond strength of thermally sprayed non-fused coatings. Their study involved the application of dual transducer (transmission technique) and single transducer (backwall echo and interface echo techniques) methods. It was found that a transmission technique, using transducers with 5 MHz crystals, gave adequate results. Further development work is clearly needed, particularly on calibration, but the technique appears to hold promise for the future. C. Evans
bookreview Research techniques in nondestructive testing, volume 3 Edited by R.S. Sharpe Academic Press, London, New York, San Fransisco (1977) 500 pp, £20.00/$39.00 The two earlier volumes in this series have established themselves as valuable sources of information for industrial and university research workers. The present volume is another tribute to the editorship of Mr Sharpe and is perhaps the most fascinating and thought-provoking book on non-destructive testing to appear in recent years. It is an excellently produced book which in its 500 pages presents fourteen technical papers contributed by 26 internationally-famous authors drawn froha six countries. It includes very extensive references and a very full index. The subject coverage emphasizes ultrasonics but other topics are given a reasonable amount of space. The only minor criticism that can be levelled at the work is that, on the basis of authors, it is 54% American and only 15% British. This is also reflected in the terminology and in the spelling of'nondestructive' without a hyphen, in true American style, even by Mr Sharpe himself! Five of the chapters are devoted to ultrasonic techniques and ultrasonics also figures prominently in two other chapters. This is perhaps only to be expected in a work of this kind, as for many years now, considerable effort has been devoted to improving ultrasonic testing and to the extraction of the maximum amount of information about the nature and dimensions of defects by more and more refinements in data analysis. This subject is well docu-
NDT I N T E R N A T I O N A L . JUNE 1978
mented in the book and in addition to frequency analysis and diffraction effects, there is a paper on the extraction of meaningful defect information from signals almost drowned in noise. The use of electronically-produced steerable ultrasonic beams is by no means new; Bradfield in the mid-50s developed such transducers. However, the way in which such techniques can be applied to automated tube inspection clearly illustrates just how valuable this form of ultrasonic scanning has now become. Ordinary transducers are no less important and for more than a decade ultrasonic practitioners have realised that all was not as it should be in this domain. Mr Sharpe's own laboratories together with those of SCRATA and the CEGB, to name but three, have all played essential roles in bringing this deficiency to light and in signposting the way to a possible improvement in probe quality. A most readable/rod practical chapter of the book is contributed on this subject by a member of the Ispra laboratories of the European Communities. There is also a chapter dealing with computerized data handling in eddy-current systems; here, as in ultrasonics, link-up with a computer enables measurements to be far more sensitive and accurate than would otherwise be possible. 'Dynamic Radiography' is the title of one of the chapters and in this it is stated that "the usual concept of radiation
165
imaging as an absorption-transmission exercise should be replaced by the concept of an image being produced because an object or a system impresses an imprint or signature of its space-time behaviour on an emerging radiation field". If the reader should be wondering what it is all about, it is later made clear that the chapter is concerned with the radiography of parts in motion. Another radiological contribution has the rather indigestible title of: Xonics Electron Radiography for Industrial NDT Application'. When it is described in more conventional English this turns out to be a system for recording X- or gamma-ray images by electronic means in a fashion not unlike that used in xeroradiography. It is claimed that it provides much greater sensitivity than conventional film radiography and requires only 5% of the exposure time. In a paper on the performance of radiographic systems and techniques, the very thought-provoking statement is made that "radiographic quality cannot be expressed as a single figure or parameter, but rather as a set of parameters which must be optimally blended for a certain imaging task". This has often been suspected but it can hardly ever have been stated more succinctly. The paper treats radiography as a communications channel and groups together a number of ideas which have been expressed many times by other authors but seldom in such a readable and concise fashion. A novel and extremely useful chapter presents a mathematical approach for comparing the effectiveness of ndt systems which are based on different physical principles, particularly those based on ultrasonics and penetrating radiation. Next to this comes a contribution which assesses the effectiveness of another essential component
166
in most non-destructive tests - the operator. The rather depressing conclusion is reached that unlike a piece of electronic equipment, the basic characteristics of an operator cannot be extensively modified. The only answer, therefore, is to abolish the operator and go for all-out automation. Although the book does not say this in so many words, the tone of most of its chapters is in line with this approach. Two methods that will be new to most non-destructive testers are entitled 'Positron Annihalation' and 'Exoelectron Emission from Metals'. The first is stated to show promise for the detection of deformation, creep and fatigue damage in metals, while the second is said to have promise in assessing the mechanical performance of metal surfaces. The last chapter of the book is probably the most fascinating. It explains how lasers can be used to generate ultrasound, neutrons and X-rays. This opens up a completely new approach to non-destructive testing which, if successful, could result in the development of a new range of equipment quite different from the conventional singlemethod variety that we are compelled to make do with to-day. The trend towards computers, lasers, automation and robots is the principle theme that binds the fourteen chapters into a coherent whole and whether or not one favours such developments, no forward-looking worker in non-destructive testing can afford to ignore its insistent message. After all, 1984 is now rather less than six years away! HoL. Carson
NDT I N T E R N A T I O N A L . JUNE 1978
Answering perhaps the comments of another delegate - "What we want to know about a coating is how thick it is, and is it going to adhere" - Franke and de Gee of Metaalinstituut TNO described an acoustic technique for measuring adhesive bond strength of thermally sprayed non-fused coatings. Their study involved the application of dual transducer (transmission technique) and single transducer (backwall echo and interface echo techniques) methods. It was found that a transmission technique, using transducers with 5 MHz crystals, gave adequate results. Further development work is clearly needed, particularly on calibration, but the technique appears to hold promise for the future. C. Evans
bookreview Research techniques in nondestructive testing, volume 3 Edited by R.S. Sharpe Academic Press, London, New York, San Fransisco (1977) 500 pp, £20.00/$39.00 The two earlier volumes in this series have established themselves as valuable sources of information for industrial and university research workers. The present volume is another tribute to the editorship of Mr Sharpe and is perhaps the most fascinating and thought-provoking book on non-destructive testing to appear in recent years. It is an excellently produced book which in its 500 pages presents fourteen technical papers contributed by 26 internationally-famous authors drawn froha six countries. It includes very extensive references and a very full index. The subject coverage emphasizes ultrasonics but other topics are given a reasonable amount of space. The only minor criticism that can be levelled at the work is that, on the basis of authors, it is 54% American and only 15% British. This is also reflected in the terminology and in the spelling of'nondestructive' without a hyphen, in true American style, even by Mr Sharpe himself! Five of the chapters are devoted to ultrasonic techniques and ultrasonics also figures prominently in two other chapters. This is perhaps only to be expected in a work of this kind, as for many years now, considerable effort has been devoted to improving ultrasonic testing and to the extraction of the maximum amount of information about the nature and dimensions of defects by more and more refinements in data analysis. This subject is well docu-
NDT I N T E R N A T I O N A L . JUNE 1978
mented in the book and in addition to frequency analysis and diffraction effects, there is a paper on the extraction of meaningful defect information from signals almost drowned in noise. The use of electronically-produced steerable ultrasonic beams is by no means new; Bradfield in the mid-50s developed such transducers. However, the way in which such techniques can be applied to automated tube inspection clearly illustrates just how valuable this form of ultrasonic scanning has now become. Ordinary transducers are no less important and for more than a decade ultrasonic practitioners have realised that all was not as it should be in this domain. Mr Sharpe's own laboratories together with those of SCRATA and the CEGB, to name but three, have all played essential roles in bringing this deficiency to light and in signposting the way to a possible improvement in probe quality. A most readable/rod practical chapter of the book is contributed on this subject by a member of the Ispra laboratories of the European Communities. There is also a chapter dealing with computerized data handling in eddy-current systems; here, as in ultrasonics, link-up with a computer enables measurements to be far more sensitive and accurate than would otherwise be possible. 'Dynamic Radiography' is the title of one of the chapters and in this it is stated that "the usual concept of radiation
165
imaging as an absorption-transmission exercise should be replaced by the concept of an image being produced because an object or a system impresses an imprint or signature of its space-time behaviour on an emerging radiation field". If the reader should be wondering what it is all about, it is later made clear that the chapter is concerned with the radiography of parts in motion. Another radiological contribution has the rather indigestible title of: Xonics Electron Radiography for Industrial NDT Application'. When it is described in more conventional English this turns out to be a system for recording X- or gamma-ray images by electronic means in a fashion not unlike that used in xeroradiography. It is claimed that it provides much greater sensitivity than conventional film radiography and requires only 5% of the exposure time. In a paper on the performance of radiographic systems and techniques, the very thought-provoking statement is made that "radiographic quality cannot be expressed as a single figure or parameter, but rather as a set of parameters which must be optimally blended for a certain imaging task". This has often been suspected but it can hardly ever have been stated more succinctly. The paper treats radiography as a communications channel and groups together a number of ideas which have been expressed many times by other authors but seldom in such a readable and concise fashion. A novel and extremely useful chapter presents a mathematical approach for comparing the effectiveness of ndt systems which are based on different physical principles, particularly those based on ultrasonics and penetrating radiation. Next to this comes a contribution which assesses the effectiveness of another essential component
166
in most non-destructive tests - the operator. The rather depressing conclusion is reached that unlike a piece of electronic equipment, the basic characteristics of an operator cannot be extensively modified. The only answer, therefore, is to abolish the operator and go for all-out automation. Although the book does not say this in so many words, the tone of most of its chapters is in line with this approach. Two methods that will be new to most non-destructive testers are entitled 'Positron Annihalation' and 'Exoelectron Emission from Metals'. The first is stated to show promise for the detection of deformation, creep and fatigue damage in metals, while the second is said to have promise in assessing the mechanical performance of metal surfaces. The last chapter of the book is probably the most fascinating. It explains how lasers can be used to generate ultrasound, neutrons and X-rays. This opens up a completely new approach to non-destructive testing which, if successful, could result in the development of a new range of equipment quite different from the conventional singlemethod variety that we are compelled to make do with to-day. The trend towards computers, lasers, automation and robots is the principle theme that binds the fourteen chapters into a coherent whole and whether or not one favours such developments, no forward-looking worker in non-destructive testing can afford to ignore its insistent message. After all, 1984 is now rather less than six years away! HoL. Carson
NDT I N T E R N A T I O N A L . JUNE 1978