RHEOLOGICAL MODEL OF FLOW OF A MATERIAL WITH A VARIABLE STRUCTURE UNDER SUPERPLASTIC DEFORMATIONM. A. Tsepin, Jeng Syn, N. L. Lisunets, and A. V. Chekin UDC 621.7.043:539.374 Versions of rheological models describing the phenomenological behavior of materials in the superplasticity state with allowance for the elastic component and without allowance for it have been presented. Consideration has been given to the basic indications of manifestation of superplastic properties from the viewpoint of the influence of the dimensions of the structural components on them. Analytical dependences of the governing relations of the mechanics of a deformable rigid body, which allow for the influence of the applied stresses, the structure, and the temperature on the rate of superplastic deformation (SPD) and enable one to calculate the shear viscosity and the rheological dependences of SPD for deformable aluminum alloys AMg4 and AMg6 with a prepared ultrafine-grained structure, have been given. Moscow State Institute of Steel and Alloys (Technological University), Moscow, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 76, No. 3, pp. 131-134, May-June, 2003. Original article submitted September 6, 2002.