N. I. Zhigacheva

Turbulence and dissipative structures in shock-loaded copper

Shock-loading tests of polycrystalline copper M3 under conditions of uniaxial deformation at impact velocities of 100 to 700 m/s were performed. It was established that a threshold deformation rate exists above which dissipative structures in the dynamically deformed material arise in the form of local regions of cellular type, with a size of 15–25 μm, separated by shear plastic bands. The basic size of cellular structure domains is on the nanometer scale. The microhardness of the material within the cellular structures is somewhat higher than in the bands of plastic deformation that separate these structures. At threshold deformation rates and above it, the defect of the mass velocity, the difference between the impactor velocity for symmetrical collision and the free surface velocity at the plateau of the compression pulse, increases sharply as does the spall strength of the material.

On the Shock-Induced Structures in Copper

Shock loading of M3 copper within strain rate range of 5·10 6 -5,7·10 6 s -1 reveals a nucleation of structural objects of 5-30 µm in diameter, which present the three dimensional frameworks composed from shear bands of 50-200 nm spacing. The structures are shown to be nucleated by means of interference of longitudinal and periphery release waves. Transition of the material into structure unstable state responsible for the shear banding happens when rate of change of the velocity variance at the mesoscale becomes higher than the rate of change of the mean particle velocity. The sites of nucleation of 3D-structures are speculated to be the staking faults generated under action of chaotic velocity pulsations relevant to dynamic deformation. The physical model for formation of 3D-structures takes into account the intersection of the partial dislocations and Lomer - Cottrell barriers.

Shock-wave behavior of structural nitrogen-bearing steel after heat treatment under various conditions

Abstract04Kh20G11N6M2AFB steel is subjected to shock tests in the following two states: after high-temperature mechanical treatment (HTMT) and after HTMT followed by quenching. The dynamic yield strength, the spall strength, and the structural transition threshold induced by shock loading are determined. It is shown that these parameters weakly depend on the shock loading rate in the steel after HTMT and increase slightly in the steel quenched from a temperature of 1100°C. In both cases, the mass velocity defect at a compression pulse plateau increases sharply beginning from a certain threshold strain rate, which indicates a high energy absorption ability of the steel.

Mechanisms of micro-macro energy exchange and dynamic strength of solids

Two kinds of steel—30CrNi4Mo armor steel and austenitic 04Cr20Ni6Mn11Mo2NVNb (nitrogen) steel—have been taken for comparative experimental studying a shock-wave behavior under uniaxial strain conditions. For the first kind of steel, transferring energy from load to deformed body is found to be realized through intermediate structural scale (mesoscale), whereas for the second kind—directly, i.e. with-out intermediate scale level.

STUDIES ON LOCALIZED STRAIN IN SHEET METALS UNDER IMPACT TENSION AND SHEAR

Results of studies on the microstructure of plane sheet specimens after their impact loading at different rates are discussed. Near the notch tips, in the area of localized strain, several layers of different microstructure were revealed. The formation of fine grains is assumed to be determined by the process of dynamic recrystallization at increased local temperatures due to intensive plastic deformation. The boundaries between the layers of different microstructure as well as increased pore concentrations in the area of localized strain near the outer surface point to the realization of the three-dimensional stress-strain state in the material.

Investigation of plug extrusion processes in counterpropagating waves

The creation of a radially nonuniform stressed state is proposed to achieve intensive shear processes under high-velocity loading of targets with a planar impactor. The technique allows laser differential interferometry to be used to study the microstructure kinetics of the deformable material. Experimental results are described.