''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.

1. Purpose. Approach. Methodology.- 1.1 Concept of isodynes.- 1.2 Scientific framework.- 1.3 Synthesis.- 1.4 References.- 2. Basic theoretical issues of stress analysis. Accepted models.- 2.1 Introduction.- 2.2 Underlying physical and mathematical models of stress states in plates.- 2.3 Local effects.- 2.4 Practical conclusions.- 2.5 References.- 3. Theory of analytical isodynes.- 3.1 Introduction.- 3.2 Concept of plane analytical isodynes.- 3.3 Determination of integration functions. Boundary conditions.- 3.4 Properties of plane analytical isodynes.- 3.5 The concept of differential analytical isodynes.- 3.6 References.- 4. Models of interaction between radiation and matter.- 4.1 Introduction.- 4.2 Basic components of pertinent elementary physical and mathematical models of interaction between radiation and matter.- 4.3 Transmission photoelasticity.- 4.4 References.- 5. Theory of optical isodynes.- 5.1 Concept of plane optical isodynes.- 5.2 Concept of differential optical isodynes.- 5.3 References.- 6. Theory of isodyne experiments.- 6.1 Actual constitutive relations for viscoelastic materials used in isodyne measurements.- 6.2 Responses of isodyne measurement systems. Transfer functions.- 6.3 References.- 7. Experimental techniques of isodynes.- 7.1 Basic techniques.- 7.2 Particular techniques of isodynes.- 7.3 References.- 8. Perspectives.- 8.1 Stress state approach.- 8.2 Deformation state approach.- 9. Two-dimensional stress states.- 9.1 Introduction.- 9.2 Beam loaded by concentrated forces.- 9.3 Circular disk loaded by concentrated forces.- 9.4 Closing comments.- 9.5 References.- 10. Contact problems.- 10.1 Introduction.- 10.2 Experimental investigation.- 10.3 Two beams in contact.- 10.4 Three beams in contact.- 10.5 Closing comments.- 10.6 References.- 11. Three-dimensional local effects.- 11.1 Introduction.- 11.2 Four-point bending of a notched beam.- 11.3 Three-point bending of an unnotched beam.- 11.4 References.- 12. Stresses in composite structures.- 12.1 Introduction.- 12.2 Three-ply structure with a transverse crack.- 12.3 Laminated beam with interlaminar disbonds.- 12.4 References.- Name index.