ABSTRACT
Rheological investigations consist of mechanical excitation of a material under strictly defined conditions. Two basic types of deformation exist: shear strain and extension (elongation) strain. Depending on the stress or strain magnitude, the method of its application and the length of time the stress or strain acts on a material, shear flow or extensional flow of the material can occur. Deformation caused by an external force acting on the material can be large or small. If the deformation is small enough, the structure of the investigated material does not change. Large deformation of complex materials usually causes some changes in their macroscopicscale structure, which can be partially reversible or not.
