A brief review of the recent developments in photo-orthotropic elasticity which covers methods of producing transparent, birefringent orthotropic model materials from glass fibres and plastics is presented. A classical form of the stress-optic law applicable in uniaxial-stress fields is given in which the orthotropic characteristics of the model material are treated by considering the material fringe value fu to be dependent upon fibre orientation. Limitations of the orthotropic model materials are identified and the effects of material non-linearities, fibre debonding and fibre distribution are described. The methods established were used to obtain a solution of the stresses in an orthotropic half-plane loaded with a concentrated force. The experimental results obtained were compared with theoretical results due to Green, and while the agreement was good, errors were considerably larger than those encountered in photo-isotropic elasticity. Finally the methods were applied to the solution of boundary stress on an elliptical hole in a finite-width tension strip.
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