Digital Photoelasticity

Abstract

The stated objectives of this book are: to provide an introduction to the basic concepts and methodologies for digital photoelasticity; to develop a foundation on which the future researcher and student can develop his own new and fruitful ideas; to promote research in the formulation of digital photoelasticity and to promote the application of these techniques to industries. It succeeds in its first objective but falls short of the others; in particular, almost no illustrative industrial applications are included. Each chapter has a comprehensive reference list which will allow the reader to pursue the topics in more detail. The fundamentals of transmission and reflection photoelasticity are described in the opening two chapters. There is a long section on fringe ordering, which is surprising given that many digital photoelastic techniques eliminate the need for it. Digital image processing is introduced at a level that will be useful for stress engineers who have not been formally trained in the subject. Topics including image sensing, display, perception, and storage and software operations including image acquisition, enhancement, segmentation and filtering are discussed. This chapter will be useful to researchers, students and practicioners, but the hardware section is likely to be out of date quite quickly. Early techniques of automated photoelasticity are dealt with together and comprehensively in a chapter entitled: Fringe Multiplication, Fringe Thinning and Fringe Clustering, and the subject of fringe ordering is discussed again. The major techniques of modern digital photoelasticity, phase shifting, polarization and Fourier transform methods are dealt with in a single chapter. In this arrangement the phase-stepping method received the majority of the attention including detailed discussion of its variants and the sources and treatment of errors. Polarization stepping and Fourier methods are treated as poor relations, which might be justified in terms of current popularity but seems inappropriate for a textbook on digital photoelasticity. The process of phase unwrapping is described in a separate chapter, together with optical tiling, but the issues of demodulation of the isoclinic and isochromatic data are not discussed. This emission leaves the student unequipped to construct their own algorithms. Colour image processing, focused principally on the red, green and blue (RGB) method, and spectral content analysis are explained, together with the associated hardware and its limitations. The chapter describing the evaluation of contact and fracture mechanics is narrow in its coverage of the field. The application of the techniques to a spur gear provides an opportunity, which is missed, to deal with the issues associated with interacting contact and crack-tip singularities. The treatment of stress separation is similarly poor, with historical issues dealt with comprehensively but modern developments ignored or only given brief attention. The inclusion of rapid prototyping might at first seem out of place, but this is an enabling and digital technology for model making which is an integral part of photoelasticity. This chapter provides a valuable insight for those new to the subject. Readers looking for a vision of the future in the closing chapter on recent developments and future trends will be disappointed; instead it appears more like a collection of loose ends or after-thoughts. Integrated photoelasticity and dynamic photelasticity are reviewed and identified as fertiles areas of future research, but several research groups are already making progress here so the chapter will be out of date very quickly. Photoelasticians brought up on Frocht's books will find the quality of the photographs in this book poor. This reviewer found the CD-ROM supplied with the book of little value because only two executable programs are supplied and the remainder of the programmes require compiling by the reader using a turbo C or turbo C++ compiler that is not supplied. One of the executable programs did not work, and the other simply showed a set of images for different phase-stepping algorithms, which could be readily included with the book. Each chapter contains exercises at the end, which will be useful for students and teachers. Some of the exercises are linked to the uncompiled programs on the CD-ROM. This is the first monograph in its field and forms a useful contribution despite falling short of its objectives in some areas. E A Patterson