Transverse isotropy
That is the material has one plane of symmetry or the transverse. This transverse plane has infinite plane of symmetry. Another word, the material behaves in isotropic manner within that plane. This is called transversely isotropic material. The number of independent constants reduces to five.
Failed to parse (unknown function \begin): left( \begin{array}{cccccc} C_{11}&C_{12}&C_{13}&0&0&0\\ &C_{11}&C_{13}&0&0&0\\ &&C_{33}&0&0&0\\ &&&C_{44}&0&0\\ &symmetric&&&C_{44}&0\\ &&&&&(C_{11}-C_{12}) \end{array} \right)
