Abstract. In 2014–2016 on the Kovdor—Pinozero section of Oktyabrskaya Railway tests were carried out on the impact of cars with axial loads of 245.3 and 264.9 kN on the track in comparison with standard cars with an axial load of 230.5 kN. Test program included trips to five experimental sections of the track with the same construction of the track superstructure, but different parameters of the road bed. Tests carried out on the impact on the track of trains weighing from 2000 to 8000 tons at different axial loads of cars and moving at different speeds made it possible to estimate the dependence of the growth of vertical forces acting on the rail on the duration and frequency of load application. Work on the registration of vertical forces was carried out by the specialists of the Department “Tracks and track facility” of the JSC “VNIIZhT”. On the basis of the results obtained, a mathematical model was developed that describes the effect of increasing the impact of railcars on the track as the load application increases, allowing calculations for various characteristics of the base. In the future, it is planned to use this model to estimate the accumulation of deformations of the track with different characteristics of the base and variants of train load. Obtained results allow stating that the accumulation of track failures depends not only on the level of the axial load and the mass of the train, but also on the duration and frequency of the load application.

In recent years, the method of driving the liner with a magnetic field in a classical Z-pinch scheme has been intensively developed by the world research laboratories. The application of this method with the use of a liner as a cylindrical impactor opens up wide possibilities for studying the dynamic properties of materials under conditions of shock-wave axisymmetric loading. The paper presents the studies of the dynamic properties of various materials in the liner experiments using a helical EMG equipped with an explosive switch as a source of pulsed power. The setup and results of a series of experiments investigating the shear strength of beryllium in the strain rate range of 10(3)-10(4) s(-1) are described. A comparative analysis of applicability of various computational models for a description of the deformation process in axisymmetric geometry has been performed. The results of experiments studying the lead "ejecta" process under conditions of shock-wave loading are presented. The numerical simulation has determined the influence of the ejecta-forming surface profile on the velocity and distribution of particles in a dust cloud by varying the amplitude of the shock wave in the range of 15-40 GPa.

Damage initiation and evolution, failure, and recollection processes under axisymmetric convergence were studied in the Russian-Damage experimental series, a joint effort between the Los Alamos National Laboratory and the All-Russian Institute of Experimental Physics. A helical explosive magnetic generator was used to drive a cylindrical liner shell to produce shock wave loading of a concentric cylindrical target shell. Shock wave amplitude was controlled by the liner-to-target spacing and by the magnetic field amplitude. Variation of the current pulse duration produced either a single impact, to study damage initiation through failure, or a double impact, to study failure with recollection. Both full and partial recollection of the main crack was obtained. By fielding high-precision diagnostics to measure the dynamic drive conditions and material response and by employing post-shot metallographic analysis, this project produced well-characterized experimental data across a range of damage and recollection levels for the chosen material, aluminum. We present selected experimental results to illustrate the methodology and utility of this experimental technique.

To study the peculiarities of initiation, evolution and recollection of spall-type damage under axis-symmetric convergence using the impact method, the test bench with an explosive magnetic pulsed power source (EPPS) on the basis of a helical generator with an explosive opening switch and a current interrupter has been created. The EPPS allows shaping the trapezoidal current pulses with the amplitude from 4 MA to 12 MA, full base duration from 10 to 250 mu s and front rise duration similar to 2 mu s in the load (liner). The magnetic field produced by the EMG current ensures the isentropic drive of a cylindrical liner used to create a shock wave of the required characteristics in the targets. In experiments "R-Damage-8,9" representing the completion stage of the experimental series "R-Damage-0-9" realized jointly by the VNIIEF and LANL teams we used the isentropically driven liners to realize a set of processes of shock-wave compression, evolution of damage and recollection of a damaged matter under axis-symmetric convergence in the extruded aluminum. The features of these processes were recorded with the use of PDV technique due to the time dependencies of the hollow targets' inner surface velocity. The presented method allowed apparently for the first time realizing the full and incomplete recollection of the main crack as the results of metallographic analysis have showed. This result made it possible to verify the numerical models of the damaged medium recollection being developed at the present time.

The paper presents the results for construction of defining relations of beryllium. The phenomenological elastic-plastic relaxation model is utilized to calculate the deviatoric component of a shear stress. A spherical component of stress tensor is expressed through the equation of state in the form of Mie-Gruneisen. Melting temperature dependence on density is determined on the basis of the equation of Lindeman. The model takes account of strain and compression hardening, thermal softening, stress history, as well as relaxation of elastic stress.

The work presents the modification of two-stage kinetic model of spall fracture (NAG model type) concerning the effect of temperature and strain rate on its parameters. It is shown that the proposed modification extends the model’s range of convenience significantly.

The paper describes a new method of research on micro- and mesoscalc high-rate (similar to 10(5)-10(7) s(-1)) deformation of metals. The method consists in studying the collapse of cylindrical holes of initial diameter D(0) = 0.5-2 mm by shock waves of known intensity and duration. The method was tested on annealed coarse-grained MI copper.

The nucleation and evolution of damage in annealed coarsely crystalline M1-type copper subjected to fast loading to a pressure P ∼ 32 GPa, followed by the action of tensile stresses σ p with an intensity of ≈−2.0 GPa for a time t ≈ 0.3–1.5 μs, have been investigated numerically and experimentally. It has been shown that, at a specific combination of amplitude-time characteristics of the tensile stress pulse, damage localization in some cases at t < 1 μs has been observed in zones (∼10–14 mm in size) alternating with “dead” zones (∼3–5 mm in size) containing no visible damages. Pores are connected by “yield streamlets.” The existing multistage models of fracture kinetics have neither explained nor predicted the formation of a “band” damage structure or the presence of “yield streamlets” in specimens.

For development of models of strength and compressibility of metals in wide range of pressures (up to several megabar) and strain rates ~ 1÷108 s−1, the method of dynamic tests is used. Since direct measurement of strength is impossible under complicated intensive high-rate loading, a formal model is created at first, and then it is updated basing on comparison with many experiments, which are sensitive to shear strength. Elastic-plastic, viscous-elastic-plastic and relaxation integral models became nowadays most commonly used. The basic unsolved problems in simulation of high-rate deformation of metals are mentioned in the paper.

The perturbation method is employed in an experimental-numerical study of the behavior of Ta subjected to both shock and shockless (approximately quasi-isentropic) loading. The loading produces large deformation plastic flow, pressures on the order of 10-80 GPa, and strain rates on the order of 10(5)-10(9) s(-1). Metallographic analysis is used to assess microstructural changes. Perturbation growth is reasonably well predicted with the use of a finite element continuum code and the Steinberg-Glushak model. Perturbation growth in Ta is compared to that of Al and Cu. Observations are made concerning fundamental differences in the behavior of fcc versus bcc materials subjected to the studied load environment. Ramifications of these differences on model development is discussed.

This work presents a newly developed experimental method. The method is simple, relatively inexpensive, and expected to be exceedingly useful in studies of material behavior at strain rates on the order of 10(5)-10(7) s(-1). Application of this method as a tool for validation is likely to be exceedingly advantageous in the development of predictive models applicable to flow in this strain rate regime. The method focuses on the convergence of cylindrical holes fabricated into specimens subjected to shock loading. The method is applied herein to M1 Cu. Hole convergence is observed to be accompanied by two forms of mesoscopic heterogeneous deformation: intergranular grain sliding, and intragranular deformation localization (likely due to twin formation). It is possible that the present work represents the first time that intragranular deformation localization structures have been seen to develop in Cu under such low intensity shock loading (sigma(x) similar to 1.6 GPa; (epsilon) over dot(i) similar to 10(5)-10(7) s(-1)).

A phenomonological elastic-viscoplastic constitutive model is developed that accounts for variations in initial grain morphology and for changes to grain morphology under load.

Results are presented of a study of the conditions under which microstructural changes involving the formation of complex bi-periodic twin structures occurs in copper during shock wave and high strain rate (epsilon > 10(7) s(-1)) shock-less loading. We have observed that the formation of these bi-periodic twin structures results in an initial loss of shear strength that is significant over a time period of about 0.2 to 0.4 mu s.

The paper presents the results of application of the explosive magnetic pulsed power source (EMPPS), in the first experiments studying the spallation mechanisms of the solid substances damage under conditions of converging axisymmetric geometry of loading of samples by the impact of the cylindrical liner driven to a velocity of 0,2-1 km/s.

The paper presents results of studies of shear strength of copper having various grain sizes under quasi-isentropic and shock-wave loading up to pressures P >> AO GPa and P >> 70 GPa. The studies were performed for copper M1; large-grain copper with grain size d >> 100 mm; and ultradispersed copper with grain size d >> 0.5 mm. Basing on results of the experiments, the relaxation models of shear strength were developed. The model of shear strength of large -grain copper takes account for deformation heterogeneity. The first experimental data on strength properties of copper at pressure up to P >> 300 GPa were obtained by the perturbation method.

This paper presents the computational analysis of an experimental three-layer liner system, Al-polyethylene-Cu and Al-water-Cu, designed for the study of dynamic strength of low-density and high-density materials using the perturbation growth caused by the Rayleigh-Taylor instability. Copper and polyethylene dynamic strength models developed by VNIIEF are used. Comparison between computations and experiments showed good agreement with a model for copper obtained previously from analysis of high-pressure explosive driven shock-free experiments. The data also allowed us to refine a model for polyethylene obtained from the analysis of previous experiments.