G. V. Garkushin
Russian Academy of Sciences
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Featured researches published by G. V. Garkushin.
Physics of the Solid State | 2012
S. V. Razorenov; G. I. Kanel; G. V. Garkushin; O. N. Ignatova
This paper presents the results of measurements of the strength properties of technically pure tantalum under shock wave loading. It has been found that a decrease in the grain size under severe plastic deformation leads to an increase in the hardness of the material by approximately 25%, but the experimentally measured values of the dynamic yield stress for the fine-grained material prove to be less than those of the initial coarse-grained specimens. This effect has been explained by a higher rate of stress relaxation in the fine-grained material. The hardening of tantalum under shock wave loading at a pressure in the range 40–100 GPa leads to a further increase in the rate of stress relaxation, a decrease in the dynamic yield stress, and the disappearance of the difference between its values for the coarse-grained and fine-grained materials. The spall strength of tantalum increases by approximately 5% with a decrease in the grain size and remains unchanged after the shock wave loading. The maximum fracture stresses are observed in tantalum single crystals.
Physics of the Solid State | 2012
G. V. Garkushin; G. I. Kanel; S. V. Razorenov
This paper presents the results of measurements of the dynamic elastic limit and spall strength under shock wave loading of specimens of the magnesium alloy Ma2-1 with a thickness ranging from 0.25 to 10 mm at normal and elevated (to 550°C) temperatures. From the results of measurements of the decay of the elastic precursor of a shock compression wave, it has been found that the plastic strain rate behind the front of the elastic precursor decreases from 2 × 105 s−1 at a distance of 0.25 mm to 103 s−1 at a distance of 10 mm. The plastic strain rate in a shock wave is one order of magnitude higher than that in the elastic precursor at the same value of the shear stress. The spall strength of the alloy decreases as the solidus temperature is approached.
Jetp Letters | 2015
G. I. Kanel; A. S. Savinykh; G. V. Garkushin; S. V. Razorenov
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.
Physics of the Solid State | 2010
G. V. Garkushin; G. I. Kanel; S. V. Razorenov
The results of measurements of the dynamic elastic limit and spall strength under shock-wave loading of aluminum samples AD1 of thicknesses between 0.5 and 10.0 mm at room temperature and at temperature increased up to 600°C are presented. The anomalous thermal hardening of aluminum under high strain rate has been confirmed. An analysis of the decay of precursors at temperatures of 20 and 600°C has shown that the change in the main mechanism of drag of dislocations occurs at a strain rate equal approximately to 5 × 103 s−1, which agrees with the results of measurements by the Hopkinson split bar method. The results of measurements of the spall strength in a wide range of strain rates add the previously obtained data and agree with them.
Physics of the Solid State | 2014
G. I. Kanel; S. V. Razorenov; G. V. Garkushin; S. I. Ashitkov; P. S. Komarov; M. B. Agranat
The results of measurements of the decay of an elastic precursor in iron at the distances from 0.13 to 10 mm and the spall strength of the samples with such thicknesses have been compared with similar data for the nanometer-scale samples. The decay has been described by a unique dependence whose differentiation gives the relationship between the initial plastic strain rate in the range from 103 to 109 s−1 and the compression stress in the elastic shock wave from 1.5 to 27.5 GPa. The dynamic breaking strength (spall strength) varies in this range of shock-wave load time from 1.5 to 20 GPa.
Physics of the Solid State | 2008
G. V. Garkushin; S. V. Razorenov; G. I. Kanel
The dynamic yield stress and the dynamic strength were measured for D16T aluminum alloy samples loaded by plane shock waves of submicrosecond duration. The temperature was varied from 20 to 470°C. It is established that the dynamic yield stress of the alloy decreases upon heating due to annealing. The dynamic yield stress of annealed samples increases with temperature, a fact that was observed earlier for aluminum. The dynamic strength of the alloy in the initial state decreases significantly upon heating, while the strength of the annealed material varies only slightly with temperature.
Mechanics of Solids | 2010
G. V. Garkushin; O. N. Ignatova; G. I. Kanel; Lothar W. Meyer; S. V. Razorenov
We present the results of measuring the strength properties of metals and alloys with face-centered cubic lattice (copper, aluminum), body-centered cubic structure (Armco iron, tantalum), hexagonal close-packed structure (titanium and titanium alloy BT6) in the original coarse-grained and submicrocrystalline state under shock-wave loading. The grain dimension of the materials under study was changed by intensive plastic deformation. The influence of the grain dimensions on the dynamic yield stress does not always agree with the data of low-rate test even in sign, which is interpreted in the framework of general laws of the strain rate influence on the metal and alloy flow stress. As the grain dimension decreases, there is an increase in the compression rate in the plastic shock wave, a small increase in the fracture strength (spall strength), and an increase in the spall fracture rate.
Technical Physics | 2008
G. V. Garkushin; S. V. Razorenov; G. I. Kanel
The dynamic yield strength and tensile (spall) strength of the D16T aluminum alloy are measured when samples are loaded by submicrosecond plane shock waves. The initial (unannealed) and annealed material is studied, and alloy samples subjected to multiple forging at elevated temperatures are also examined. The loading direction with respect to the texture of the material and the shock-compression pulse duration and shape are varied. The difference in the spall strengths measured along the rolling direction and normal to this direction is close to the dynamic yield strength of the material.
Physics of the Solid State | 2011
S. V. Razorenov; G. V. Garkushin; G. I. Kanel; O. A. Kashin; I. V. Ratochka
The behavior of the Ti51.1Ni48.9 and Ti49.4Ni50.6 alloys with shape memory effects has been studied under submicrosecond shock wave loading in the temperature range from −80 to 160°C, which includes both the regions of the stable state of the specimens in the austenite and martensite phases and the regions of thermoelastic martensitic transformations. The grain size of the studied alloys varies from initial values 15–30 to 0.05–0.30 μm. The dependences of the dynamic elastic limit on the temperature and on the elemental composition are similar to the dependences of the yield stress of these alloys under low strain rate loading. The rarefaction shock wave formation as a consequence of the pseudoelastic behavior of the alloy during a reversible martensitic transformation has been revealed. A decrease in the grain size leads to an increase in the dynamic elastic limit and decreases the temperatures of martensitic transformations.
SHOCK COMPRESSION OF CONDENSED MATTER - 2011: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter | 2012
S. V. Razorenov; G. V. Garkushin; G. I. Kanel; Olga Nikolaevna Ignatova
The VISAR free surface velocity histories have been measured for commercial grade coarse grain (CG, 50 – 60 m) and ultra fine grained (UFG, ~0.5 m grain size) after severe plastic deformation tantalum and for comparison tantalum single crystals, at peak stresses around 12-14 GPa and strain rates of 10 5 –10 6 s -1 . The decrease in the grain size, which resulted in ~25 % increase of the hardness did not cause any significant influence on the HEL, the value of which is ~2 GPa, but increases slightly the spall strength of the UFG tantalum (7.4 GPa) in comparison with the CG samples (~7 GPa). In both cases the spall strength does not noticeably vary with increase of the peak shock stress up to 70 GPa. The experiments using samples precompressed at 40 and 100 GPa peak pressure have confirmed weak influence of preceding shock compression on the tantalum spall strength. The tantalum single crystals display the highest spall strength equal to ~10 GPa. The influences of the grain size on static and dynamic yield stresses are discussed in terms of general strain rate effects. Introduction It is well known that dynamic deformation leads to hardening of metals and alloys due to storage of defects [1] and reduction of grain sizes under severe plastic deformation [2]. On the other hand, the data on the influence of these factors on flow stresses and material strength under high strain rates is very sparse and often contradictory [3,4]. The interest in the dynamic strength of tantalum is connected with its industrial applications under strong impulse stresses. Tantalum has a high density (16.65 g/cm 3 ), melting temperature (2996 0 C) and is unique in it’s combination of high hardness with high plasticity. Extensive research and publications are dedicated to investigations of the elastic-plastic properties and spall fracture of tantalum under shock-wave loading [5-9], but the question about the influence of structural factors on these processes remains unanswered. In this work, the VISAR free surface velocity histories have been measured for commercial grade tantalum with various grain sizes and structural defects, and for comparison, tantalum single crystals to get information about the elastic-plastic transition and the resistance to spall fracture. Material and experiment The tantalum samples in as-received state (CG) had an average grain size ~50-60 m. The ultrafine grain structure (UFG) was obtained by forging in three directions at decreasing temperature starting from 800C. As a result of severe plastic deformation, a uniform structure was achieved with an average grain size ~0.5 – 0.7 m. The microstructure of CG and UFG tantalum samples are presented in Figure 1. It is seen from these pictures, that the deformed samples have rather uniform structure without strongly marked zones of different granularity. However, as the electron microscopy displays, the structure contains less than 1 % of larger extended grains with the size up to 4 m. After the three-dimensional forging the twins in the grain structure of tantalum are not observed. a b Fig.1. Microstructures of as-received (a) and ultra fine grain (b) tantalum tested. The unsoundness of CG and UFG tantalum samples was varied by means of shock wave of ~40 and ~100 GPa intensity. Figure 2 presents the photograph of microstructure of as-received tantalum sample recovered after shock loading of ~25 GPa intensity. Fig.2. Microstructure of as-received tantalum sample subjected by shock wave loading of 25 GPa amplitude. As it can see from this figure, the forming of the bands of local deformations (twins) is observed practically in all grains. Metallography of recovered preshock samples has shown up the twin structure of 10-20% concentration at 40 – 60 GPa, which decreased under pressure growth due to the annealing of material with increasing of shock temperature. In UFG samples, the concentration of twins was found close to zero. Dislocation density increased from 0.5×10 10 cm -2 to 2×10 10 cm -2 at 100 GPa. A few experiments were done with tantalum single crystals of uncertain orientation. The data about hardness measured for all tantalum samples tested are presented in Table 1. From Table it is clear, that both severe static plastic deformation and preshock deformation increase hardness of CG samples by ~25%, but the preshock deformation did not change the hardness of UFG samples. Table 1. The hardness of tantalum in various structural states. Sample Hardness, HRB As-received (CG) (grain size ~55 μm) 76 – 79 Ultra-fine grained (UFG) (~0.5 μm) 103 – 104 Shock precompressed CG (~40 GPa) 103 Shock precompressed CG (~100 GPa) 97 – 99 Shock precompressed UFG (~40 GPa) 104 – 105 Shock precompressed UFG (~100 GPa) 103 – 105