The method of strain measurement after annealing is reviewed and found to be unsatisfactory for the materials available in this country. A new, general method is described for the photoelastic determination of the principal stresses at any point of a general body subjected to arbitrary loads. The method has been applied to a sphere subjected to diametral compressive loads. The results show possibilities of high accuracy.
Photoelasticity as an experimental method for analyzing stress fields in mechanics was developed in the early thirties by the pioneering works of Mesnager in France and Coker and Filon in England. Almost concurrently, Föppl, Mesmer, and Oppel in Germany contributed significantly to what turned out to be an amazing development. Indeed, in the fifties and sixties a tremendous number of scientific papers and monographs appeared, all over the world, dealing with various aspects of the method and its applications in experimental stress analysis. All of these contributions were based on the so-called Neumann-Maxwell stress-opticallaw; they were developed by means of the classical methods of vector analysis and analytic geometry, using the conventionallight-vector concept. This way of treating problems of mechanics by photoelasticity indicated many shortcomings and drawbacks of this classical method, especially when three-dimensional problems of elasticity had to be treated and when complicated load and geometry situations existed. Meanwhile, the idea of using the Poincare sphere for representing any polarization profile in photoelastic applications was introduced by Robert in France and Aben in the USSR, in order to deal with problems of polarization oflight passing through aseries of optical elements (retarders andjor rotators). Although the Poincare-sphere presentation of any polarization profile con stitutes a powerful and elegant method, it exhibits the difficulty of requiring manipulations in three-dimensional space, on the surface of the unit sphere. However, other graphical methods have been developed to bypass this difficulty.
Photoelasticity presents the development of photoelasticity. This book discusses the principle of optical equivalence of stressed isotropic bodies. Organized into 29 chapters, this book begins with an overview of the progress in three-dimensional photoelasticity. This text then summarizes the approximate theoretical analysis by the strain-energy technique and derives the basic equations for the evaluation of P and Q by graphical integration. Other chapters consider the importance of stress concentrations in the domain of strength of materials, particularly where fatigue is present. This book discusses a well the various instructive fractures and indicates that the strength of bakelite is determined by the maximum tensile stresses as computed by advanced methods of stress analysis. The final chapter deals with the two fundamental problems in three-dimensional photoplasticity and explains the general stress-optic law under plastic flow without unloading. This book is a valuable resource for designers as well as mechanical and civil engineers.
