In classical photoelasticity of transparent isotropic materials, the Brewster law states
that the difference in principal refraction index (birefringence) is proportional to the
difference in principal stress. Here we show that such a relation can be generalized to
anisotropic crystals only for the high-symmetry classes of the cubic group
and for a specific plane stress, also for the high-symmetry classes of the
trigonal, tetragonal, and hexagonal groups. No further generalizations are
possible.
Dipartimento di Ingegneria Civile,
Edile e Architettura
Centro Interdipartimentale di Analisi Globale dei
Cristalli
Università Politecnica delle Marche
Ancona
Italy
