''It is true that "Nothing is more practical than a theory" Provided - however - That the assumptions on which the theory is founded Are well understood. - But, indeed, engineering experience shows that "Nothing can be more disastrous than a theory When applied to a real problem Outside of the practicailimits of the assumptions made", Because of an homonymous identity With the problem under consideration. " (J. T. P. ) The primary objective of this work is to present the theories of analytical and optical isodynes and the related measurement procedures in a manner com patible with the modem scientific methodology and with the requirements of modem technology pertaining to the usefulness of the stress analysis proce dures. The selected examples illustrate some major theses of this work and demonstrate the particular efficiency of the isodyne methods in solving the technologically important problems in fracture mechanics and mechanics of composite structures including new materials. To satisfy this objective it was necessary to depart from the common practice of presenting theories and techniques of experimental methods as a compatible system of equations and procedures without mentioning the tacitly accepted assumptions and their influence on the theoretical admissibility of analytical expressions and the reliability of the experimental or analytical results. It was necessary to design a more general frame of reference which could allow to assess the scientific correctness of isodyne methods and the reliability of experimental results.

It is true that "Nothing is more practical than theory" as Boltzmann said. Provided - however - that the assumptions on which The theory is founded are well understood. But. indeed. engineering costly experience shows that "Nothing can be more disastrous than a theory" when applied To a real task outside of practical limits of the assumptions made. Because of an homonymous identity with the considered problem. J.T.P The growing interest in Isodyne Stress Analysis and the related experience of the author show that the major monograph and reference book on the subject, Isodyne Stress Analysis by Jerzy T. Pindera and Marek-Jerzy Pindera, [27], does not of contain sufficiently detailed data on the theories and techniques experimentation. The purpose of this work is to close this gap. Thus, this work is an extension of Isodyne Stress Analysis and complementary to it. Consequently, only a short outline of the theory ofisodynes is given in Chapter 2. Only the basic concepts and relations are presented to provide the link between the underlying analytical and optical theories and the experimental techniques. One of the major purposes of a preface is to formulate and explain the chosen frame of reference in a condensed form, even when some components of it are discussed in the text. A main issue of the underlying frame of reference pertains to the roles of the abstract thinking and of the observation in cognition of reality.

I express my sincere gratitude to NATO Science Committee for granting me the financial award to organize and direct the Advanced Research Workshop on "MULTILAYERED and FIBRE-REINFORCED COMPOSITES: PROBLEMS AND PROSPECTS" that was held in Kiev, Ukraine, during the period of June 2 - 6, 1997, in collaboration with Professor S. A. Firstov of the Frantsevich Institute for Problems of Materials Science, National Academy of Sciences, Kiev, Ukraine. In this context I wish to convey special thanks to Dr. J. A. Raussell-Colom, NATO Programme Director for Priority Area on High Technology, for his kind efforts and continuous guidance in the course of organizing the Workshop. I appreciate sincerely the opportunity of working closely with Professor Firstov and acknowledge with deep gratitude his outstanding contribution in co-directing the Workshop. I wish to express my special thanks to Dr. N. Orlovskaya of the Frantsevich Institute, for her outstanding contribution towards both the organization and conduct of the Workshop. I wish to convey my sincere thanks to Professor V. V. Skorohord, Deputy Director of the Frantsevich Institute, on behalf of the same Institute, for hosting the Workshop and welcoming the participants to l{iev. The very kind efforts of the members of the Scientific Advisory Committee, the Local Organizing Committee and the Staff of the Frantsevich Institute towards the organization and conduct of the Workshop, are gratefully appreciated. I convey my full indebtedness to all researchers who participated in the Workshop.

The desire to understand the mechanics of elastic and plastic solids, new materials and the stability, reliability and dynamic behaviour of structures and their components under extreme environmental conditions has dominated research in structural engineering for many decades. Advances in these areas have revolutionized design methods, codes of practice, and the teaching of structural engineers. In this volume an international body of leading authorities presents some forty papers on current research directions in the specific areas of solid mechanics, structural computation, modern materials and their application, buckling and instability, design of structural systems and components, reliability, seismic analysis, and engineering education. They were presented at a symposium held July 10-12, 1994, at the University of Waterloo, Canada, to honour Professor Archibald Norbert Sherbourne who recently retired from a long and active career of teaching, research and academic administration at this University. The themes of the work contained within this volume reflect Professor Sherbourne's own research interests and will be of interest to both academics and practicing structural engineers.

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