A. S. Savinykh

Dynamic strength of tin and lead melts

The dynamic tensile strength (spall strength) of tin and lead melts has been measured by a found method. Comparison with similar measurements of the spall strength of these metals at room temperature shows that melting reduces the spall strength by at least an order of magnitude. The spall strength of liquid metals is a smaller fraction of the extremely possible (“ideal”) strength than that for water and organic liquids.

Evolution of shock waves in SiC ceramic

The evolution of a shock compression wave in SiC ceramic is measured for determining the possible contribution of relaxation processes to the high-rate straining. No appreciable decay of the elastic precursor and other features of stress relaxation are revealed when the sample thickness changes from 0.5 to 8.3 mm, and the evolution of the compression wave corresponds to a simple wave. The measured values of the Hugoniot elastic limit (σHEL = 8.72 ± 0.17 GPa) and spall strength (σsp = 0.50–0.62 GPa) with allowance for the density of the ceramic are in conformity with the available data.

Submicrosecond polymorphic transformations accompanying shock compression of graphite

The effect of the structure factors and temperature on the transformation of shock-compressed graphite to diamond or a diamond-like phase has been investigated. It has been revealed a significant effect of the shock compression direction with respect to the crystallographic planes of graphite on the detected pressure and rate of the transformation. The effect is more pronounced in more ordered graphite. The main structure parameter determining the transformation rate is the degree of the three-dimensional ordering of graphite. The transformation pressure decreases with heating. The extrapolation of the results to the high-temperature region and their comparison with the data on the direct transformation of statically compressed graphite to diamond indicate that the “above-barrier” state should be apparently reached to ensure the irreducible transformation to cubic diamond.

Peculiarities of the elastic-plastic transition and failure in polycrystalline vanadium under shock-wave loading conditions

Specific features in the deformation of polycrystalline vanadium under shock-wave loading conditions have been studied by experimental and theoretical methods. Analysis of the full wave profiles was used to determine the dynamic elastic limit and spall fracture stress in a range of stain rates of 105–107 s−1. The laws of elastic–plastic transition at the shock-wave front, mechanisms of elastic precursor relaxation, and spall fracture development are discussed.

Large Tensions and Strength of Iron in Different Structure States

Results of shock‐wave experiments with iron single crystals, ultra‐fine grain and as‐received Armco‐iron, at load durations of ∼20 ns to 200 ns are presented. No evidence of the expected formation of rarefaction shock waves, as predicted by the ab initio calculations, was observed in the range of attained tensile stresses down to −7.6 GPa. The tensile fracture stresses achieved 25–50% of the theoretical iron ultimate strength for a load duration of ∼10−8 s. The spall strength of a coarse‐grain Armco‐iron is much less than that of single crystals whereas an intensively deformed Armco‐iron with a sub‐micron grain size demonstrates nearly the same spall strength as the crystals do.

A ceramic based on partially stabilized zirconia: Synthesis, structure, and properties under dynamic load

A ceramic based on zirconia partially stabilized by yttrium oxide has been prepared. The main properties of the prepared ceramic have been characterized: density, ultimate strength under twisting, microhardness, elasticity coefficients, etc. The microstructure and phase composition of the ceramic and its phase transformations under mechanical action have been studied. The properties of the ceramics under dynamic load have been studied, and the values of the dynamic elastic limit and splitting strength have been obtained. The results have been compared with the literature data.

PHENOMENOLOGICAL DESCRIPTION OF THE FAILURE WAVES IN GLASSES

A combustion‐like model of failure wave has been developed accounting for new data on the response of intact and comminuted glass to longitudinal and bulk compression and release. The bulk compressibility of soda‐lime glass was measured by the mixture method. It has been found that, under uniaxial compression, the Poissons ratio increases up to the value close to 0.5. The strong dependence of the Poissons ratio on deviatoric stress results in increase of average unloading impedance of cracked glass that explains small value of the recompression signal. The failure wave model includes equations of state of intact and comminuted glass, a criterion of compressive fracture, and an equation that relates damage accumulation rate to the damage parameter gradient. Computer simulations with this model reproduce well all details of observed behavior of the glass.

Influence of the temperature-induced martensitic-austenitic transformation on the strength properties of high-alloy steels under dynamic loading

The dynamic elastic limit and spall strength of high-alloy chromium-manganese-nickel steel in the martensitic-austenitic transformation induced by a change in the temperature from −120 to 200°C is measured by recording the complete wave profiles with a VISAR laser interferometer and subsequently analyzing them. The spall strength of the investigated steel in the martensitic phase is found to be 25–30% higher than the strength of steel in the austenitic phase. In this case, the strength decreases in a stepwise manner in a narrow temperature range approximately from −50 to 20°C, where, apparently, basic changes in the internal structure of steel occur due to the martensitic-austenitic transformation. The measured values of the dynamic elastic limit of high-alloy steel have a sufficiently large scatter and hardly decrease with increasing temperature without any features associated with the martensitic-austenitic transformation of the structure.

Response of magnesium single crystals to shock-wave loading at room and elevated temperatures

A series of magnesium single crystals, from 0.2 to 3 mm thick, were shock loaded along specific axes, a and c, of the hexagonal closed packed (hcp) structure. Other experiments involved loading at 45 degrees to these principal axes. Shock compression along the c-axis causes inelastic deformation by means of pyramidal slip and twinning and is associated with the largest Hugoniot elastic limit (HEL) for this material. The low-energy basal slip was activated by shock loading along the inclined direction and has he smallest HEL. In all cases, we observe the decay of the elastic precursor wave and growth of the HEL with increasing temperature. For the c-orientation this change is caused by a decrease of elastic constants, not an increase of shear stress along the pyramidal slip planes. For the other orientations the shear stress on the slip planes increased with temperature. For the inclined shock compression, after the HEL, two plastic waves were found: the stress level of the first plastic wave depends on the ultimate shock stress. Finally, the largest spall strength was along the a-axis and the smallest in the off-axis direction.

Strength and failure of LK7 borosilicate glass under shock compression

The Hugoniot elastic limit (HEL), the spall strength, the failure threshold, and the failure wave velocity in LK7 glass during shock compression are measured. The HEL estimated from the profiles of compression waves of various intensities is 7.1 ± 0.1 GPa. The spall strength exceeds 7 GPa during shock compression in the elastic range and remains high when passing through the HEL. Failure waves form in the stress range from 5.7 to 10.3 ± 0.5 GPa.