Vladimir Milyavskiy

Numerical study of converging shock waves in porous media

The dependences of the solutions to the hydrodynamic equations of compressed media that describe converging shock waves on the density of a substance ahead of a wave front are studied. The properties of Hugoniot adiabats that can explain the qualitatively different characters of these dependences for the equations of state of perfect gas and condensed matter are analyzed. The one-dimensional problems of converging shock waves in graphite and aluminum are considered, and the two-dimensional problem of the compression of graphite in a steel target with a conical cavity is solved. The latter problem is also investigated in terms of a simple model for a deformable solid that takes into account shear stresses.

Shock response and structure of yttria-doped tetragonal zirconia

The ceramics on the basis of the partially stabilized zirconia was produced, and some characteristics of the ceramics, such as density, bending strength, crack resistance, Rockwell hardness, microhardness, porosity, etc. were determined. Microstructure and phase composition of the ceramics as well as the phase transformations under mechanical fracture were studied. Hugoniot elastic limit and spall strength of the ceramic specimens were measured.

INFLUENCE OF STRUCTURE AND ORIENTATION OF GRAPHITE ON ITS POLYMORPHIC TRANSFORMATION UNDER SHOCK COMPRESSION

Measurements of the transition pressure and rate under shock compression of different graphites at different sample orientations have been carried out with the goal to verify possible mechanisms of the graphite‐diamond transformation. The materials tested were highly orientated pyrolytic graphite (HOPG) plates and pressed samples of several kinds of natural and synthetic graphite. It has been found the shock direction significantly affects the detected pressure of the transformation and its rate. The effect is more pronounced in more ordered graphite. The transition pressure and rate depend also on the crystallite size and the grain size. Content of rhombohedral phase (up to 30%) does not strongly influence the transformation parameters.

PHASE TRANSITIONS OF C70 FULLERITE UNDER STEP‐LIKE SHOCK COMPRESSION

Shock‐induced phase transitions of C70 fullerite with hexagonal close‐packed structure were experimentally studied with use of recovery assemblies of planar geometry at pressures 8 to 36 GPa. It was found that C70 fullerite undergoes a series of polymorphic transitions in conditions of step‐like shock compression. Hexagonal close‐packed structure of C70 fullerite remained practically unchanged at shock pressure 8 GPa. Shock‐induced transformation of the hexagonal structure into face centered cubic structure was fixed at pressures in the range 8 to 23.5 GPa. Depth of this transformation was increasing with growth of shock pressure. With further growth of shock pressure the destruction of C70 molecules occurs. This destruction is accompanying with a formation of graphite‐like carbon.

SHOCK COMPRESSION AND EQUATION OF STATE OF C60 FULLERITE

Hugoniot of C60 fullerite and sound velocity in shock‐compressed fullerite were experimentally studied at the pressure range up to P∼60 GPa. The results of the shock‐wave measurements were used for the semi‐empirical description of thermodynamic properties of simple cubic phase of C60 fullerite.