Higher Grade Material Structures

It has been often pointed out, by critics and supporters alike, that the theory of inhomogeneities of Noll [1] and Wang [2] does not enjoy the generality often demanded by those propagating the so-called lattice model. This is because in the structural approach to the theory of continuous distribution of defects it has been suggested that, although the presence of dislocations shows through the non-vanishing torsion of the material connection, disclinations are measured by the curvature of such a connection; see e.g. Anthony [3]. Since any constitutive functional associated with a simple elastic material body induces, by definition, a locally integrable parallelism it appears that the disclinations, and possibly other defects, are ruled out. A structural approach suggests also that bodies with defects, disclinations in particular, are subject to multipolar stresses. Thus, it seems natural to investigate the possibility of describing disclinations in the realm of the higher-grade materials as originally suggested by Elianowski and Epstein [4]