Mechanics of nondestructive testing

Mechanics of nondestructive testing

paper describes similar results based on a television system using an X-ray sensing vidicon camera tube, coupled with an image storage tube. Both meth...

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paper describes similar results based on a television system using an X-ray sensing vidicon camera tube, coupled with an image storage tube. Both methods are useful for revealing changes in topography during crystallisation and other phenomena. The next paper in this section describes an automated optical plotter and interferometric device for 3-D imaging. The system provides a three-dimensional spatial distribution of a local parameter such as attenuation coefficient or small differences in the refractive index of objects which are relatively transparent to electromagnetic energy. A computer controlled optical tracing system is used to produce the differing amplitude filters needed for the optical treatment, together with an interferometer device for scanning phase subjects. The remaining paper in this group describes a method of using 0.15 nm thermal neutrons for determining the topography and tomography of crystals. Neutrons extend the diffraction method to larger and thicker crystals than are feasible with X-rays of the same wavelength. The phosphor intensifier technique used is faster than the neutron and film methods previously used; real-time imaging is sometimes possible but the resolution

is not quite so good. The results obtained are described and illustrated. In the last section Mengers describes the design and operation of a digital image processing unit which provides the following improvement capabilities: noise averaging, image differencing or comparison, contrast transfer modification, spatial filtering and edge enhancement. Examples of applications to X-ray and neutron imaging are given, including the processing of very-low-contrast images. Ritman et al describe a prototype multiple X-ray source computerised transaxial tomographic system 'currently being fabricated'. The equipment involves 28 X-ray sources arranged in a semi-circle with 28 corresponding image-intensifier/image isocon chains. It is expected to be particularly useful in the quantification of the dynamic structure, function and perfusion of the heart, lungs or other organs. Ziskin and Philips describe computerised fluorodensitometry with a solid-state matrix camera. The system has lower noise-level relative to other methods, and has been used for measuring pulmonary pulsations in monkeys. Kruger et al discuss their experiences in medical radiography with real-time

Mechanics of nondestructive testing Edited by W.W. Stinchcomb

Plenum Press, New York, 1980 This 405-page hardback volume contains the 19 papers presented at the Conference on the Mechanics of Nondestructive Testing held at Virginia Polytechnic Institute and State University on 10-12 September 1980. The fact that the proceedings were published by the end of October 1980 says much for the speed at which the editor and his three associates from the Materials Response Group at VPISU and the publishers must have worked, to achieve what must be a record in conference proceeding publication. The Conference was sponsored by the Army Research Office, the National Science Foundation and the Virginia State University and its objective was 'to promote an understanding of the mechanics of


nondestructive testing as related to the evaluation of materials response' and to develop the relationships that exist between NDT techniques and the mechanics of materials response to operating variables. The first five chapters are intended as 'overviews' of areas of NDT techniques. They cover optical interference techniques for measuring deformation (Post), wave analysis as a means of source identification in acoustic emission (Green), a survey of electromagnetic methods (Lord), damage measurement by stiffness monitoring (O'Brien) and ultrasonic methods of evaluating the mechanical properties of materials (Vary). Each gives a very readable state-of-the-art survey quaintly but clearly expressed by one author as 'to explain in sufficient detail to generate a comfortable association with the subject'. For the reader not personally caught up in

digital processing of X-ray transmission information taken from the video output of conventional X-ray fluoroscopy and cine-fluorographic systems. Several medical applications are described and illustrated. Sklensky and Buchanan report on their experience with a digital integrator and comment that high-energy real-time radiography now challenges the image quality of film. In their study of missile motors they found that the real-time image gave 1% sensitivity, compared with ½% for film. The equipment is described and results are quoted. As the above brief review of the papers shows, the methods and applications discussed covered an extremely wide spectrum in a highly specialised field. The organisers certainly achieved their aim to provide a record of the state of the art of maximising the minimal image signals. The book is very well produced but, sadly, it is unlikely to have an extensive readership because of its specialised nature. But those closely concerned with the art should certainly obtain a copy somehow!

L. Mullins

the 'nuts and bolts' developments of a particular aspect of NDT that is a perfect and satisfying objective indeed. The same author also saw his overview as an attempt 'to foster understanding and appreciation in order to inspire increased utilization and further development'. Indeed the book, throughout, is overtly aimed at the utilization of NDT in the context of materials performance rather than the mere cataloguing of development and progress in testing technology. After the 'overviews' which occupy just over a third of the book there are six shorter papers on materials property assessment. These are on the use of neutron scatter to monitor changes in microstructure (Glinka et al); materials characterisation by careful analysis of acoustic emission waveforms (Weisinger); determination of critical velocity of plastic strain propagation which differentiates between brittle and ductile fracture behaviour in a material (Pond et al); an ultrasonic


surface wave technique to predict the fracture stress of a solid containing a surface crack (Resch et al); the measurement and theoretical modelling of elastic constant anisotropy in a laminated boron-aluminium composite (Datta et al); and ultrasonic attenuation studies of dislocation behaviour in solids subjected to dynamic stressing by high-power ultrasound (Mignogna et al). The theme of the third session of the Conference was the characterisation of flaws. Chapters in the proceedings relating to this session are on the relatively new technique of vibrothermography, or the assessment of internal defects by the temperature changes they produce at the surface by energy dissipation when a component is subjected to vibrating excitation (Reifsnider et al); dynamic photoelasticity to study the interaction of Rayleigh waves with surface cracks as a basis for better crack sizing (Singh et al); defect characterisation in graphite/aluminium matrix com-

Microfocal radiography Edited by R.V. Ely

Academic Press, London, 1980 (295 pp, £28.80/$66.50) This book has been written by pioneers in all aspects of microfocal radiography and will make a strong appeal to all radiologists, whether or not they are directly concerned with microfocal radiography. It comprises six most authoritative papers relating to microfocal radiographic techniques in medicine and biology as well as in non-destructive testing, and an equally authoritative paper on X-ray microscopy. Each paper is very clearly written, is profusely illustrated and carries a very extensive list of references. In the Foreword, Dr Cosslett, of the Cavendish Laboratory, briefly outlines the history of microfocal radiography and points out that although the first work on the subject was done by R~ntgen himself, followed in 1898 by Heycock and Neville, it was not until the 1950s that substantial progress was


posites by radiographic and ultrasonic C-scan techniques (Romano et al); and the sensitivity of detecting delaminations in graphite/epoxy composite laminates using a variety of transmission and reflection ultrasonic techniques (Schramm et al). The final set of four papers was concerned with the initiation and development of material damage and the associated problem of life prediction. Papers dealt with the influence of initial defect distribution on the expected life of reactor piping systems and its implication regarding NDT test sensitivity and defect statistics (Leis et al); crack monitoring on airframe structures in flight with built-in acoustic emission sensors (Martin); the relationship between variations of mechanical properties such as yield stress and tensile strength with acoustic emission parameters (Pisarenko et al); and the use of acoustic emission, ultrasonic C-scan and ultrasonic attenuation to study the development of fatigue delamina-

made on the equipment side, thanks largely to the design of special micro-focus tubes by Mr Ely. In his Preface, Mr Ely states that the object of the volume is to provide a state of the art report on the subject, to detail the development of the special X-ray equipment and to record the present and potential applications in medicine, biology' and industry. He is to be congratulated in achieving this end so superbly. Although there does not appear to be any standardized definition of microfocal radiography, it is generally taken to mean radiography using an X-ray tube having a focal spot dimension under 100/~m and a comparatively low voltage which seldom exceeds 150 kV. In the type of tube developed by Mr Ely and his colleagues, focal spot sizes as low as 15 ~m have been achieved in tubes operating at 90 kV. These tubes are continuously pumped with demountable gun and targetanode assemblies so that filament replacement and other essential maintenance can be readily carried out. There are many applications where it

tion in unidirectional carbon/epoxy composites (de Charentenay et al)' This is an excellently produced conference proceedings publication which will undoubtedly find its rightful place on bookshelves amongst the profusion of quality books now becoming available as NDT assumes wider importance, attracts greater scientific attention and adopts a less introverted and more complementary role in materials and engineering quarters. As one author stated 'NDT today is the determination of the existence (and degree) of discontinuities and inhomogenieties which will produce an undesired change in mechanical behaviour'. NDX is no longer just concerned with the determination of the existence of discontinuities and inhomogeneities - full stop. The nondestructive tester and the mechanical behaviourist have a lot to learn from each other as they move into timely wedlock. This book is a happy choice of honeymoon reading!

R.S. Sharpe

is preferable to produce magnified radiographs directly, rather than to rely on optical magnification of a 1 : 1 radiograph with the consequent magnification of the grains in the emulsion that ensues. The direct production of such radiographs is only possible if the focal spot has micrometre rather than millimetre dimensions. The microfocal spot also makes it possible to make ordinary 1 : 1 radiographs in regions of restricted access where only very small focusto-film distances are possible. Those readers whose main interest lies in non-destructive testing will find the excellent paper by Sharpe and Parish on engineering applications, of particular interest. This is a fascinating record of the application of microfocal radiography in cases where conventional radiography could not be used for such reasons as restricted access, inability to resolve fine detail sufficiently well, and dynamic studies where the geometrical configuration of microfocal radiography was an essential requisite.

H. L. Carson