Symmetry classes and harmonic decomposition for photoelasticity tensors

Two different definitions of symmetries for photoelasticity tensors are compared. A count of such symmetries based on an equivalence relation induced on the set of subgroups of SO(3) was presented by Huo and Del Piero, who proved the existence of exactly 12 classes. Here, another viewpoint is chosen, and photoelasticity tensors themselves are divided into symmetry classes, according to a different definition. By use of group theoretical techniques such as harmonic and Cartan decomposition, it is shown that this approach again leads to 12 classes. (C) 1997 Elsevier Science Ltd.