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.

Dynamic compressive tests of alumina samples with different grain sizes obtained by spark plasma sintering (SPS) of submicron- and micron-sized α-Al2O3 powders have been performed. The effect of heating rate (Vh), sintering temperature (Ts), holding time (ts), and cooling rate (Vc) on the hardness, crack resistance, and dynamic ultimate strength (σY) of Al2O3 has been studied. An amorphous layer of a nanometer thickness was on the surface of submicron powders in the initial state. The transformation of an amorphous structure with an excess free volume into a crystalline phase occurs upon the SPS process with the formation of dislocation-type defects at the grain boundaries, which induce long-range internal stress fields. It has been shown that nanopores less than 50–100 nm in size are observed at the grain boundaries of ceramics. It has been shown that the nonmonotonic pattern of the dependence of σY on the temperature and time of the SPS is due to the simultaneous change in the density, the nonequilibrium state of grain boundaries, and the grain size of the ceramic. It has been shown that a decrease in the degree of nonequilibrium of the grain boundaries of alumina due to an increase in the SPS temperature or an increase in the holding time makes it possible to increase the dynamic strength of alumina. It has been established that an increase in the cooling rate leads to the formation of compressive residual stresses and a slight increase in σY of the ceramic. The maximum dynamic strength (σY = 1755 MPa) was reached for the alumina ceramic with an average grain size of 1.6–2 μm obtained by SPS at Vh = 50°С/min, Ts = 1520°С, and ts = 50 min.

Herein, we present the results of an experimental study on the mechanical properties of Fe-C alloys with different carbon contents (0.2, 0.45, and 0.8%) in a wide range of deformation rates (10−3–103 s−1) and abrasive wear resistance, which underwent combined laser thermal (laser surface hardening—LSH) and laser shock wave (Laser Shock Peening—LSP) processing. The combined treatment modes included a different sequence of exposure to laser thermal and laser-induced shock pulses on the material. The amplitude and duration of laser-induced shock waves were measured using a laser Michelson interferometer. The mechanical properties of steel samples were studied under conditions of uniaxial tension under static loads on a standard universal testing machine, the LR5KPlus, and under dynamic loading, tests were carried out on a specialized experimental complex according to the H. Kolsky method using a split Hopkinson rod. The abrasive wear resistance of hardened surfaces was studied using the Brinell–Haworth method. Studies have shown that the use of a combination of LSH and LSP treatments leads to an increase in both the mechanical properties of steels and abrasive wear resistance compared to traditional laser hardening. It has been established that in the combinations considered, the most effective is laser treatment, in which LSP treatment is applied twice: before and after LSH. Thus, after processing steels using this mode, an increase in the depth of the hardened layer was recorded—by 1.53 times for steel 20, by 1.41 times for steel 45, and by 1.29 times for steel U8—as well as a maximum increase in microhardness values by 22% for steel 20, by 27% for steel 45, and by 13% for U8 steel. The use of this mode made it possible to obtain the maximum strength properties of the studied materials under static and dynamic loading, which is associated with an increase in the volume fraction of the strengthened metal and high microhardness values of the strengthened layer of traditional LSH. The dependences of abrasive wear of the studied steels after various combinations of LSP and LSH impacts were established. It is shown that the greatest wear resistance of the studied steels is observed in the case when the LSH pulse is located between two LSP pulses. In this case, abrasive wear resistance increases by 1.5–2 times compared to traditional LSH.

This review considers the state of the art in the field of theoretical and experimental studies of dynamic deformation and destruction of wood materials. The orthogonal properties of wood, features of early and late wood are considered, the dynamic properties of wood are analyzed, as well as the influence of the strain rate during dynamic compression. It is noted that wood of different species is mainly used as one of the materials that dampen dynamic loads as a result of impacts or explosions. For example, it can mitigate the effects of high-velocity impacts on the contents of containers during the transport of hazardous materials by air, road and rail. It has been established that the cause of the effects of internal friction in wood are the areas of lignin, in which bundles of cellulose molecules (microfibrils) with a diameter of 25-30 nm are immersed, which are crystalline in their structure, which leads to viscoelastic behavior - internal damping. To improve the damping properties, it is recommended to choose wood with a low microfibril angle. It is noted that the stress-strain curve under dynamic compression of wood consists of three separate parts: the initial elastic region, the yield region and the compaction region. The main characteristics of compression, that is, the components of the stress-strain curve and the destruction of the fibers, do not depend on temperature. Young's modulus is much larger in the longitudinal direction than in the radial and tangential directions. The rate of deformation, temperature and humidity have a great influence on the strength properties of wood. The features of the mechanical behavior of the zones of early and late wood in the massif of a tree trunk are considered. Late wood is more rigid than early wood. As a result, differences in the mechanical properties of the wood fibers during compression may cause the early wood fibers to be destroyed while the late wood fibers remain intact. Due to the complexity of the wood structure, its reliable description by a numerical model requires complex models that take into account not only the influence of temperature, strain rate, and the type of stress-strain state, but also the angle between the direction of loading and the direction of wood fibers. Two main groups of wood material models are considered: micromechanical models simulating the details of the wood structure, and continuum models simulating the behavior of wood as a whole.

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 present work was aimed at the investigation of the effect of high-energy ball milling (HEBM) time on the sintering kinetics, structure, and properties of the heavy tungsten alloy (HTA) W-7%Ni-3%Fe. The HTA samples were obtained from nanopowders (20–80 nm) using conventional liquid-phase sintering (LPS) in hydrogen and using spark plasma sintering (SPS) in vacuum. The HTA density was shown to depend non-monotonously on the HEBM time that originates from the formation of nonequilibrium solid solutions in the W-Ni-Fe systems during HEBM. The SPS kinetics of the HTA nanopowders was shown to have a two-stage character, the intensity of which depends on the Coble diffusion creep rate and on the intensity of diffusion of the tungsten atoms in the crystal lattice of the γ-phase. The kinetics of sintering of the initial submicron powders has a single-stage character originating from the intensity of the grain boundary diffusion in the γ-phase. The dependencies of the hardness and of the yield strength on the grain sizes were found to obey the Hall–Petch relation. The hardness, strength, and dynamic strength in the compression tests of the fine-grained tungsten alloys obtained using SPS and LPS were studied.

We discuss experimental and numerical studies of the deformation and destruction of fine-grained concrete B22.5 under dynamic loading. The experiments were carried out using the Kolsky (or split-Hopkinson pressure bar) method, and its modifications in the strain rate range from 400 to 2000 s(-1). The rate dependences of ultimate stresses and fracture energy in tension and compression are obtained. Based on experimental data, the identification of the dynamic component of two models from the LS-DYNA computational complex was carried out: *MAT_CONCRETE_DAMAGE and *MAT_CSCM. The results of a comparative analysis of the identified models based on single-element modeling and comparison with experimental data are presented. It is shown that the obtained experimental strain rate dependences of the fracture characteristics can significantly improve the predictive ability of the model compared to the default parameter set. Information about the rate dependence of the fracture energy in *MAT_CSCM model makes it possible to more realistically simulate the behavior of the material beyond the ultimate stress.

This article presents the results of experimental studies concerning the dynamic deformation and failure of a unidirectional carbon fiber reinforced plastic (T700/LY113) under compression. The test samples were manufactured through the filament winding of flat plates. To establish the strain rate dependencies of the strength and elastic modulus of the material, dynamic tests were carried out using a drop tower, the Split Hopkinson Pressure Bar method, and standard static tests. The samples were loaded both along and perpendicular to the direction of the reinforcing fiber. The applicability of the obtained samples for static and dynamic tests was confirmed through finite element modeling and the high-speed imaging of the deformation and failure of samples during testing. As a result of the conducted experimental studies, static and dynamic stress-strain curves, time dependencies of deformation and the stress and strain rates of the samples during compression were obtained. Based on these results, the strain rate dependencies of the strength and elasticity modulus in the strain rate range of 0.001-600 1/s are constructed. It is shown that the strain rate significantly affects the strength and deformation characteristics of the unidirectional carbon fiber composites under compression. An increase in the strain rate by 5 orders of magnitude increased the strength and elastic modulus along the fiber direction by 42% and 50%, respectively. Perpendicular loading resulted in a strength and elastic modulus increase by 58% and 50%, respectively. The average strength along the fibers at the largest studied strain rate was about 1000 MPa. The obtained results can be used to design structural elements made of polymer composite materials operating under dynamic shock loads, as well as to build models of mechanical behavior and failure criteria of such materials, taking into account the strain rate effects.

An experimental study of the dynamic properties of fine-grained concrete reinforced with fine-meshed meshes under dynamic uniaxial compression relative to the original fine-grained concrete has been carried out. Reinforced samples were made by pouring concrete into molds with pre-installed mesh frames. Dynamic tests have been carried out. Dynamic compression tests were carried out using the Kolsky method at strain rates from 30 to 600 s−1. The paper presents the composition of the test material, test parameters, as well as a comparative analysis of the data obtained. The introduction of reinforcing meshes into the original fine-grained concrete increased the dynamic strength of the material. The dependences obtained demonstrate that the maximum breaking stresses achieved in the experiments increase linearly with the growth of the strain rate, as do the corresponding limiting strains. The time before the onset of fracture decreases with increasing strain rate according to a power law.

This paper presents an experimental study of the deformation and energy absorption of fiber-reinforced concretes under compression at different strain rates. Static load tests are carried out using the Zwick-Roell Z100 universal testing machine at a strain rate of 30*10"6 s-1. Dynamic load tests are carried out in the range of strain rates 200-800 s-1 using the Kolsky method, which implies loading of the studied sample in a split Hopkinson pressure bar system. Specimens are made from a concrete mixture with the addition of wavy steel or polypropylene fibers with a volume fraction of 1.5 %. As a result of experiments and processing of the recorded strain pulses of measuring bars, the deformation diagrams and the corresponding diagrams of the specific energy absorption for the fiber-reinforced concretes under study are constructed. For all concretes being studied, the diagrams of deformation and energy absorption have similar trends and show an increase in the strength and energy before fracture initiation with an increase in the strain rate.

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.

An experimental study of the dynamic properties of three types of fiber-reinforced concrete under dynamic uniaxial compression relative to the original fine-grained concrete was carried out. Three types of fiber-reinforced concrete were produced: with polymer fiber, steel fiber, and with a combination of two types of fiber. Static and dynamic tests were carried out. Dynamic compression tests were carried out using the Kolsky method at strain rates from 102 to 103 s−1. The tests were carried out using a FASTCAM Mini UX100 high-speed camera. The paper presents the compositions of the studied materials, test parameters, as well as a comparative analysis of the data obtained. The introduction of a reinforcing fiber into the original fine-grained concrete increased the dynamic strength of the material. The highest strength under dynamic uniaxial compression was shown by fiber-reinforced concrete with steel fiber. The dependences obtained demonstrate that the maximum breaking stresses achieved in the experiments grow linearly with an increase in the strain rate, as do the corresponding limiting strains. The time before the onset of fracture decreases with increasing strain rate according to a power law.

The article describes the development of a modification of the Kolsky method used for testing brittle materials at splitting. The scheme of the experiment involves the application of a dynamic load along diametrically opposite generatrices of the cylindrical surface of the test specimen. At the same time, it is in a biaxial stressed state and fracture into two halves from the action of tensile stresses. The method is based on the assumption that the material under test behaves elastically under equilibrium deformation of the specimen. This modification is proposed to be used to determine the dynamic Young's modulus and Poisson's ratio. The derivation of relations for calculating the indicated mechanical characteristics based on Hooke's law using experimental possibilities is given. Approbation of the proposed scheme for determining elastic constants was carried out when testing specimens of fireclay brick in the Hopkinson split bar system. The deformation impulses of measuring bars were recorded with the help of tensometry to assess the forces acting on the sample and calculate the stresses arising in its center. Deformations of the central part of the specimen were determined using digital image correlation technology. The obtained graphs of stresses and strains versus time had a different time step using the optical method in combination with tensometry. The arrays of the obtained stress and strain values were reduced to a single and constant time interval up to the moment of specimen failure using linear interpolation to process the experimental data based on the derived formulas. The study made it possible to construct graphs of the dynamic Young's modulus and Poisson's ratio versus time at the initial stage of specimen loading and to determine the average values of these elastic mechanical characteristics.

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.

The results of dynamic strength tests of the alumina ceramics with various grain sizes are presented. The ceramics were obtained by Spark Plasma Sintering (SPS) of industrial submicron and fine Al2O3 powders. The heating up was performed with the rate of 10 oC/min; the grain sizes in the ceramics was controlled by varying the SPS temperature and the heating rate as well as by varying the initial sizes of the Al2O3 particles in the powders. The ceramics had a high density (over 98 mean grain sizes varied from 0.8 to 13.4 mkm). The dynamic compressing tests were carried out by modified Kolsky method with using split Hopkinson pressure bar. The tests were performed at room temperature using a 20-mm PG-20 gas gun with the strain rate of  10^3 s-1. The dependence of the dynamic ultimate strength of alumina on the grain size was found for the first time to have a non-monotonous character (with a maximum). The maximum value of the dynamic ultimate compression strength (SY = 1060 MPa) was provided at the mean grain size of  2.9-3 mkm. The reduction of SY for alumina in the range of submicron grain sizes was shown to originate from the reduction of the relative density of the ceramics sintered at lower SPS temperatures.

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.