Theory of elastoplastic media with mesostructure

It is known for a long time that under elastoplastic deformation, solid matter develops certain internal structures that can be observed with instruments which make it possible to look into the interior of the solids. Such a behavior is particularly pronounced in crystalline materials in which the plastic deformation occurs by sliding over crystallographic glide planes. Internal structure or microstructure may have a different appearance on several scale levels. Hence, it is also common to speak of multilevel structures. These structures and their influence on the material behavior is the subject of this investigation. It is argued that a continuum theory of elastoplasticity with dislocations is possible only on the microscopic scale where dislocations of opposite sign are considered. The macroscopic dislocation theory takes into account only the excess dislocations of one sign per unit macro-volume. It results in a great loss of information. This means that the macroscopic dislocation theory must be classified as a mean field theory as in statistical physics. The theory can be extended by application of correlation functions. Two examples for the development of a three level structure will be discussed.