Issue 38

M. Sokovikov et alii, Frattura ed Integrità Strutturale, 38 (2016) 296-304; DOI: 10.3221/IGF-ESIS.38.40 302 It has been found that the localization of plastic strain occurs in a thin region on the plug formation. It has also been observed that in the areas of strain localization the sub-grains are elongated into bands and then fragmented, forming thus the ultra-crystalline structure with the grain size ~300nm. It is the consequence of the forming of the rotational deformation modes and the high-angle disorientations of grains. M ODELING he mechanisms of plastic shear instability and localization of plastic deformation (in the quasi-uniaxial statement) have been simulated numerically, and the peculiarities of the kinetics of microshear accumulation in the material have been analyzed. We consider the deformation of a plane layer under simple shear loading. One side of the layer is rigidly fixed, and the other side is moving with a constant velocity. During the process of high-speed deformation of the material, a structural transition in the microshear ensemble occurs in the local area. This transition is characterized by the jump in the microshear density parameter (Fig. 11a), which leads to abrupt change in effective characteristics of the material, in particular, to sharp decrease in the effective viscosity, and, as a consequence, to an increase in the plastic deformation and stress relaxation rates, and finally to decrease in the shear resistance in this area (Fig.10b). Twisting deformation of thin-wall cylindrical specimens was simulated numerically according to the experimental scheme of pure shear testing in quasi uni-axial formulation. Fig.12 represents the graph illustrating the distribution of plastic strain localized in the narrow central part of the specimen. Figure 11 : Distribution of a) microshear density parameter, and b) plastic deformation rate. Figure 12 : Evolution of plastic deformation with time along the specimen. Figure 13 : Numerical results. Distribution of microshear density parameter. T a) b)