We compare two methods of millimeter radio interferometry with and without frequency conversion using as an example experimental measurements of the transverse deformation magnitude of a metal rod under dynamic load. We reveal a good agreement between the results, demonstrating a possibility of measuring the surface deviations within times of about 1 μs with micron precision.

A novel experimental laboratory technique for the flow of miniature cumulative jet of copper and without using explosives, is described. To perform the microcumulative tests, miniature cylindrical specimens with conical pits were used. The dynamic loading of the specimens was performed using a gas gun with a striker accelerated up to speeds of 800 m/s. The optimal specimen geometry and testing regimes, including the focal distance during microcumulation testing, were then determined. The influence of the structural condition of the sample material on the parameters of the cumulative jet has been demonstrated A preliminary analysis of the effects of copper purity and processing regimes on the ultimate dynamic plasticity characteristics was performed Keywords: High-speed deformation, cumulative jet flow, copper, ultimate dynamic plasticity, light-gas gun.

We describe the principle of operation of the radio interferometer, which is used to detect the displacement and determine the velocity of the free surface of a sample in the plane-wave experiment. Several measurement schemes are compared experimentally. For some of them, good agreement of the results with the data of the independent measurements is revealed, which demonstrates the possibility of measuring the free-surface velocity with a time resolution of about 0.1 μs and a margin of error of about 10 m/s.

A millimeter wave interferometer based on a Ka-band CW signal generator and a high-speed oscilloscope has been implemented, which makes it possible to carry out measurements without frequency conversion. The experimental measurements of the amplitude of transverse deformations of a metal rod caused by impact loading have been carried out. A good agreement between the calculated and measured data was revealed, demonstrating the possibility to measure microsecond-duration surface deviations with an accuracy of about 1 μm and a relative error of about 8

The aim of the study is to develop a methodology for assessing changes in the microstructure of aluminum under dynamic deformation in a rather wide range of the strain rate and strain degree. The distribution of the microstructure and the strength properties in the cross-section of pure aluminum samples (A99) after dynamic deformation according to the Taylor test were studied. The tests were carried out at room temperature using a PG-20 light-gas cannon, at sample throwing speeds of 127 and 165 m/sec. An interference microscope (Leica IM DRM) and a scanning electron microscope (Jeol JSM-6490) were used to study the aluminum microstructure; the microhardness measurements were carried out on an HVS-1000 device to study the uniformity of the strain distribution in samples. It is shown that three characteristic areas can be distinguished in aluminum samples after Taylor test: the elastic deformation zone, the plastic deformation zone, and the zone of severe plastic deformation, which is located in the area of collision of the sample with a steel barrier. It is shown that dynamic deformation reduced the grain structure from 1 – 1.1 mm to 2.5 – 3 μm at high impact velocities. An elongated grain shape is observed in the collision zone. The proposed method provided determination of the critical strain degree necessary for the onset of grain fragmentation and allowed us to explain the formation of zones of weak and severe plastic deformation. It is shown that the critical strain degree corresponding to the beginning of grain fragmentation increases from 0.18 to 0.21 with an increase in the throwing speed of the sample from 127 to 165 m/sec. In the zone of weak deformation, plastic deformation proceeds by intragrain riveting and the initial stages of grain fragmentation. In the zone of severe plastic deformation, a fine-grained microstructure is formed, which leads to an increase in the microhardness of aluminum in accordance with the Hall – Petch equation.

A novel experimental laboratory technique for evaluating the ultimate dynamic plasticity of materials, under the conditions of cumulative jet flow and without using explosives, is described. To perform the microcumulative tests, miniature cylindrical specimens with conical pits were used. The dynamic loading of the specimens was performed using a gas gun with a striker accelerated up to speeds in the range of 600-800 m/s. The optimal specimen geometry and testing regimes, including the focal distance during microcumulation testing, were then determined. The flow speed of the microcumulative jet was found to be equal to its theoretical value calculated within the framework of the Lavrent'ev hydrodynamic theory. The novel technique was demonstrated to enable the study of the relationship between the initial specimen microstructure and the ultimate dynamic plasticity magnitude at the cumulative jet flow using high-purity copper as an example. The penetration depth of the cumulative microjet into a steel barrier was shown to depend on the parameters of the copper microstructure. A preliminary analysis of the effects of copper purity and processing regimes on the ultimate dynamic plasticity characteristics was performed.

The results of experimental studies of the impact interaction of hemispherical and conical heads with a granular layer are presented. The granular layer consists of steel and lead balls. An experimental technique of inverted experiment is used. The technique for measuring the resistance force using a measuring rod is designed to determine the integral loads at the initial penetration site. A container filled with steel or lead balls is accelerated in a gas-dynamic gun to a speed of 100-200 m/s and strikes a fixed head of a hemispherical or conical shape. The material properties of the rod are such that no plastic deformations occur in it. An elastic compression impulse is formed in the rod, which is recorded by glued strain gauges. To prevent the scattering of metal balls and parts of the container, the impact occurs in a vacuum chamber. The presented results are averaged over the number of experiments performed for each type of head. The resistance of steel ball granular media is significantly higher than that of lead ball media. The shape of the striker has a significant influence on the behavior of the resistance forces. Experimentally obtained deformation diagrams of granular layers in static and dynamic loading modes are also presented. The curves for all loading modes of lead balls are non-linear and irreversible. At high loads, not only the repacking of particles occurs, but also a strong plastic flow of the material. For steel balls in the considered load range, strong plastic flow of the material is not observed. In the future, the experimental results will be used for numerical simulation of the penetration of strikers of various shapes into granular layers of metal balls.

Tests of dry clay were carried out in a uniaxial stress state using the experimental setup which implements the split Hopkinson pressure bar method. Based on the results of these experiments, the compressive strength of clay was determined as an important element of S.S. Grigoryan's model of the soil medium. In addition, the parameters of this model are determined from the results of experiments using the modified Kolsky method with a sample enclosed in a rigid cage. To verify the model of the soil medium, special experiments were carried out on the penetration of striker with conical tips into dry clay in a reversed settings. Using this identified model in the LS-Dyna software package, numerical simulation of penetration into clay was carried out under conditions similar to those carried out the reversed experiments. Comparison of the results of physical and numerical experiments showed their satisfactory agreement at a dry friction coefficient of 0.5.

Despite significant research on spallation, there are still unexplored gaps such as the spall fracture delay. In this case, fracture occurs not at the growth stage of tensile stress in a spall section but at the stage of stress stabi-lization or reduction. However, no attention was paid to this effect. In this paper, we present an experimental and theoretical study to verify the existence of the delay effect. The experiments were carried out on steel specimens under the action of threshold and overloaded impulses. It was found that the spall fracture delay can be realized at the threshold fracture impulses. In order to calculate the fracture stress, the stress history should be considered correctly. For this purpose, the incubation time approach was employed. The incubation time criterion allowed calculating the stress rate dependence of fracture stress and time to fracture taking into account the spall fracture delay at threshold impulses. The calculated curves are in good agreement with the experimental points.

A novel experimental laboratory technique for the flow of miniature cumulative jet of copper and without using explosives, is described. To perform the microcumulative tests, miniature cylindrical specimens with conical pits were used. The dynamic loading of the specimens was performed using a gas gun with a striker accelerated up to speeds of 800 m/s. The optimal specimen geometry and testing regimes, including the focal distance during microcumulation testing, were then determined. The influence of the structural condition of the sample material on the parameters of the cumulative jet has been demonstrated A preliminary analysis of the effects of copper purity and processing regimes on the ultimate dynamic plasticity characteristics was performed.

The effects of the strain rate and degree on the scale of the strain aging effect in carbon steel U8 with lamellar pearlite microstructure, which is a eutectoid mixture of ferrite plates and brittle plates of secondary cementite Fe3C have been investigated. The microstructure and properties of Russian steel U8 after quasistatic compression, dynamic compression (shock processing), and explosion processing have been investigated. A low-temperature annealing (150–500 °C) of the non-deformed steel U8 has been shown to result in a monotonous reduction of hardness. The quasistatic compression and shock processing of the carbon steel were found to result in the strain aging manifested as an increasing hardness at annealing of the deformed steel U8. The increasing of the deformation degree and strain rate was accompanied by the increasing of hardness of the annealed steel. The explosion treatment was shown not to result in a notable improvement of the mechanical properties of carbon steel as well as in a change of the morphology of cementite plates. The deformation aging effect in steel U8 after the explosion loading was absent. The strain aging effect in U8 steel after quasistatic compression and dynamic loading was suggested to originate from an increasing of the lattice dislocation density, the long-range internal stress fields from which lead to the dissociation of the cementite Fe3C plates and to increasing of the concentration of carbon atoms in the ferrite crystal lattice. The absence of the strain aging effect in the carbon steel after the explosion loading is due to a small degree of the explosion deformation that doesn't allow providing an essential increasing of the lattice dislocation density in ferrite.

The results of tests for ballistic resistance of ceramic samples based on aluminum oxide (Al2O3 + 0.25MgO) obtained by high-speed electric pulse plasma sintering (EIPS) are presented. Samples 30 mm in diameter, 6.5 and 7 mm thick had a high relative density (more than 99%), a uniform fine-grained microstructure (average grain size ~1–1.5 mm), and increased hardness (more than 17 GPa). Using the finite element method, using the ANSYS Workbench package, it is shown that during rapid cooling at a rate of 50 °C/min, an uneven temperature field is formed in the samples and a difference in temperatures arises on two opposite sides of the ceramic samples. It has been established that non-uniform cooling during SPS leads to the formation of compressive internal stresses (up to –450 MPa), and there is a significant difference in the magnitude of internal stresses on opposite sides of ceramic samples. The differences in the parameters of the microstructure and microhardness on opposite sides of the samples are insignificant. Ballistic resistance tests were carried out at a speed of 700 m/s, using cylindrical-conical impactors made of hardened steel 52100. The ballistic resistance of the ceramics was evaluated by the anti-barrier action, i.e., the penetration depth of the striker into the aluminum witness sample located behind the tested ceramic plate. It is shown that the barrier action during testing of a ceramic plate with a large value of compressive internal stresses (from –390 to –450 MPa) is 1.5–2 times less than during ballistic testing of a ceramic plate, in the surface layer of which internal compressive stresses are small (from –60 to –90 MPa). The results obtained for the first time demonstrated the importance of the formation of compressive fields of internal stresses in ceramics, which makes it possible to further increase the ballistic resistance of protective ceramic plates.

Solutions of the problem on constant-velocity expansion of a spherical cavity into a soil medium are analyzed. The cavity expands from a point in the half-space occupied by an elastoplastic soil medium. The previously obtained linearized analytical solution of this problem that was obtained under the assumption that the medium behind the shock wave front was incompressible is presented. Having performed the comparison with the results of the numerical solution of the problem in the full formulation, it is shown that the approximate solution is reasonable for the dependence of the pressure at the boundary of the cavity on the velocity of its expansion. The linearized solution is applied to calculate the force of resistance to the penetration of a rigid sphere into soft soil. The dynamic compressibility and shear resistance are characterized by the Rankine-Hugoniot relations and the Mohr-Coulomb-Tresca yield criterion. The results of analytical and numerical calculations are compared with the known experimental data, presented in the form of dependences on the impact velocity of the force of resistance to the penetration of spheres (impactors) into water-saturated sand. A good agreement between theoretical and experimental data has been demonstrated.

This work presents experimental data pertaining to the determination of the ultimate strength of frozen soil under uniaxial compression in the range of strain rates of 400–2700 s-1. Finite expressions are obtained for quadratic approximation coefficients that depend on the impact velocity of a stress normal to the impactor surface and the experimentally determined physical and mechanical parameters of the soil, namely shock adiabat and the dynamic strength in compression. The resulting expressions are verified by comparing them with known experimental data related to the penetration of a steel impactor into frozen sandy soil. It is shown that a difference between the results of two-sided estimates and the experiments does not exceed 15%.

A one-dimensional problem of a spherical cavity expanding at a constant velocity from zero initial radius in an infinite granular medium, which has the first-kind self-similar solution, is considered. We are solving this dynamic spherical cavity-expansion problem to model rigid spheres penetrating into a granular media. Elastic–plastic deformation of the granular media is described in a barotropic approximation, using the high-pressure equation of state and Mohr–Coulomb Tresca’s limit yield criterion. The medium is assumed to be incompressible behind the shock wave front propagating through the unperturbed medium. The problem in this formulation was solved analytically. Besides, a generalized solution of the problem was obtained numerically, which involves transition of a continuous elastic–plastic wave into a plastic shock wave when pressure grows with the cavity expansion velocity. The comparison of the analytical and numerical solutions shows that a linearized analytical solution is a good approximation of the pressure along the boundary of the cavity as a function of its expansion, except for low velocities. The linearized rigid plastic solution can be used for analyzing resistance to a rigid sphere that penetrates into the granular media. The computational results are compared with known experimental relations for resistance to spherical projectiles penetrating dry and water-saturated sand. Good agreement between the numerical and experimental results is obtained without any correction factors.

For the most complete study of the laws of shock interaction of solids with soil barriers, further development of experimental techniques for recording the parameters of the interaction process in direct and inverse experiments is necessary. In this work, to determine the parameters of the movement of the projectile (displacement and speed) in a direct experiment, a millimeter-wave radio interferometer is used. This method allows continuous recording of the movement of the rear end of the striker with high accuracy over a wide range of movements. Using the proposed technique, experiments were carried out to record the motion parameters of cylindrical impactors made of steel and aluminum alloy when interacting with an obstacle made of dry sand. At the same time, the movement of the rear end of the striker was also controlled using high-speed filming until the full immersion of the striker. The experiments showed that the measurement results obtained using two methods coincide within the measurement error. Based on the experiments, it can be concluded that the methodology for determining the displacement and velocity of a projectile in a ballistic experiment using a millimeter-wave radio interferometer allows continuous measurement of large displacements (100 mm or more), including when completely immersed in a target with sufficient practical goals accuracy. Based on the results of the experiments, the dependences of the movement of the projectile and its speed on time are constructed. A change in the penetration law was found with a decrease in the penetration velocity to values less than 100 m/s.

The paper presents the results of a study of the dynamic properties of 3M titanium alloy under tension, carried out using the Kolsky method, as well as the results of determining the spall strength obtained using a VISAR laser interferometer. The experiments using the split Hopkinson pressure bar were carried out in the range of strain rates of 700 - 1500 s_1. In this experiments, dynamic strain diagrams were obtained, according to which the yield strength σ0.2 and the tensile strength were determined. The yield strength of the studied material increases with increasing strain rate from 700 MPa to 800 MPa. Since the 3M alloy does not experience hardening with increasing strain, fracture begins at stress close to yield strength. The tensile strength of this alloy under uniaxial tension (temporary tensile strength) also grows slightly from 700 MPa to 800 MPa with increasing strain rate. The ultimate plastic fracture characteristics of a titanium alloy (elongation and relative narrowing after rupture) are practically independent of the strain rate. In plane-wave experiments, spall strength was studied in the range of strain rates of 2 · 104 - 5 · 104s-1. The obtained values of spall strength lie in the range of 1.6 - 4 GPa, which significantly exceeds the values obtained under static loading and the values obtained in experiments using the Kolsky method, which is apparently associated with both the influence of the strain rate and the influence volumetric stress state in a plane-wave experiment.

The work presents experimental and numerical results on dynamic fracture of PMMA plates subjected to impact loading. The experimental tests were conducted using steel cylinder-shaped projectile accelerated using a gas gun. In order to evaluate performance of the tested specimens, residual impactor velocity was assessed using high-speed photography setup. Square-shaped PMMA specimens with three thicknesses were investigated using various projectile velocities. For all the three specimen types the ballistic limits were experimentally obtained. The conducted experiments were numerically simulated using finite element method with explicit time integration scheme and incubation time fracture model for the material failure prediction. Experiments with all three specimen configurations were successfully simulated using one parameter - incubation time, which was evaluated from existing experimental data on the dynamic fracture of PMMA. In addition to the simulations of the real experiments estimates on performance of a sample with a virtual geometry were made using the developed numerical approach.

A new method is proposed for determining the dynamic Poisson's ratio of both isotropic and anisotropic materials. The sample was loaded with a pulsed compressive load on a setup that implements the Kolsky technique using a split Hopkinson bar. The development in time of the longitudinal compressive deformation of the sample was determined by the signals recorded with the help of low-base strain gauges glued to the measuring bars. A millimeter-wave interferometer was used to measure the development of the radial components of the sample deformation in time. To assess the possible asymmetry of the radial expansion of the sample, measurements were carried out using two independent channels irradiating diametrically opposite zones of the lateral surface of the sample. The tests were carried out on a sample of pine with air humidity in the form of a cylinder 54 mm in diameter and 30 mm in height. A pulsed compressive load was loaded along the fibers. Using two channels of the radio interferometer, the separate displacement of the lateral surfaces of the sample was recorded both along and across the annual layers. It was determined that the displacements of the regions of the lateral surface of the sample during expansion along the annual layers are quite close, while during expansion across the annual layers they are very different. The relative transverse deformation of the sample in both cases was determined as the sum of lateral displacements divided by the sample diameter. As a result, two components of the dynamic Poisson's ratio were obtained, which amounted to ~0.2 (in the direction along the annual layers) and ~0.24 (in the direction across the annual layers).

Experimental dependences of the strength of frozen sandy soil on strain rate are analyzed using a structural–temporal approach. Results of dynamic uniaxial compression tests at a temperature of −18°C and strain rates of 400 to 2600 s −1 of frozen sandy soil specimens of two types with an ice mass fraction of 10 and 18% measured at room temperature are presented. The strain rate dependence at different freezing temperatures of frozen sand with an ice mass fraction of 30% is studied using known experimental data.