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To study the dynamic strength of pipe steels, a cycle of dynamic tests of three grades of pipeline steels (X80, X90, and X100) was performed, which included three types of experiments based on the Kolsky method: uniaxial tension of smooth specimens, as well as tension of specimens with a V-shaped annular notch and Charpy impact test according to the three-point bending pattern of beam-type specimens with a V-notch. In the last two cases, the fracture force and impact toughness, as well as the nominal fracture stress in the specimen, were determined. To assess the effect of “cold brittleness” and determine the temperature of the ductile-brittle transition, the specified test cycle was carried out in the temperature range from +20°C to –100°C. As shown by the test results, the studied steels have a fairly high ductility: the elongation at break is 25-30%. Therefore, the destruction of specimens directly in the first load cycle is not always possible. The use of an original system for registering additional loading cycles makes it possible to determine in which loading cycle the specimen ruptured. The limiting characteristics of plasticity (ψ and δ) of all tested steel grades are weakly dependent on both the strain rate and temperature (within the range of their variation). Whereas the impact toughness of steels significantly (2-3 times) decreases with a decrease in temperatures from room temperature to –100°C.

The nanocrystalline (NC) and ultrafine-grained (UFG) structures of metallic materials can lead to their extraordinary high strength. However, most of the papers on this topic consider deformation parameters of NC and UFG materials only for the case of quasi-static tensile tests. Characteristics of dynamic strength and fracture of such materials remain unexplored. This paper presents a study of the mechanical behavior of pure titanium Grade 4 with a coarse-grained (CG) and UFG structure under uniaxial compression with different strain rates. The UFG structure was provided using the method of equal-channel angular pressing. The dynamic compression was carried out on a setup with the Split-Hopkinson pressure bar. It is found that in the observed range of strain rates 10–3-3×103 s–1, the yield stress of the CG titanium increases by 20%, and does not exceed the yield stress of the UFG titanium. However, the yield stress of the UFG titanium remains close to a quasi-static value. It is shown that these strain-rate dependencies of the yield strength can be predicted by the incubation time approach. The calculated curves show that at strain rates above 104 s–1 the yield stress of the CG titanium becomes higher than the yield strength of the UFG titanium.

Metallic materials with a nanocrystalline or ultrafine-grained (UFG) structure can exhibit increased strength, albeit with reduced ductility. The behaviour of such materials under high-speed and impact loads has been insufficiently explored. This work presents experimental results on the dynamic response of UFG pure copper (99.95%) processed by equal-channel angular pressing (ECAP) in comparison with its initial coarse-grained (CG) structure. The yield strength in the case of compression tests of cylindrical samples and the energy consumed for deformation and fracture in the case of a three-point bending of a beam with a V-notch are considered. The UFG copper has higher yield strength in compression tests, but its sensitivity to the loading rate is significantly less than that of the CG initial material and depends on the number of ECAP passes. The UFG material shows higher impact toughness KCV and energy consumption for the entire process of deformation and fracture under impact three-point bending.

International audience; Experimental results on assessing the effects of strain and stress rates on the behavior of fine-grain concretes are presented. Specimens of fine-grain and fiberreinforced concretes were dynamically tested using the Kolsky method and its modification, the “Brazilian test”. As a result of the experiments, values of the Dynamic Increase Factor (DIF) were determined for both the materials studied. Their curves as a function of strain and stress rates were constructed. The experimental data is compared with the theoretically obtained values of DIF as a function of strain rate available in the literature

This work presents results of an experimental and theoretical study on dynamic and quasi-static failure of rocks and concrete. The results of dynamic compression and splitting of rocks (gabbro, granite, marble), as well as dry, water-saturated and frozen limestone and concrete are discussed. The tests were conducted using the Split-Hopkinson pressure bar with the diameter of 20 mm. It is shown that one material (or its condition) can have a lower dynamic strength for a higher static strength compared to the other material (or its condition). Also, it is shown a dependence of the threshold limit stress on the stress pulse duration. An unified interpretation of the experimental results, based on the structural–temporal approach is presented.

The paper presents the results of studying the structure and wear resistance of compacts produced from fine dispersed reduced iron powder (average particle size 3– 5 μ m) with the addition of tungsten carbide (WC) nanopowder with the average particle size of 25–30 nm. The mass fraction of tungsten carbide (wolfram carbide) in the powder composition was 5% and 10% of the total mass. Impulse pressing was conducted using the modified Kolsky method at compacting temperatures of 20 °C to 300 °C. The produced compacts had relative density of over 90%. Metallographic studies using the scanning electronic microscopy method on a TESCAN VEGA II electronic microscope have shown that the produced compacts have a fairly homogeneous fine-grained structure, with a uniform pattern of pore distribution, the form of the pores being close to spherical. X-ray microanalysis using an INCA Energy 250 energy-dispersion spectrometer with scanning along the surface line and transversal laps testifies to the fact that, in the considered temperature range, dynamic compaction does not lead to any noticeable changes in the distribution of the Fe, W and C elements over the bulk of the specimens. The conducted measurements of micro-hardness of the compacts have shown that it increases considerably with the pressing temperature. The produced compacts were tested for wear resistance in a dry friction regime, using the ‘rotating disk – stationary specimen’ configuration. Mass loss of the compacts as a function of testing time is presented. Wear resistance of compacts depends on pressing temperature and concentration of the WC powder in the matrix of reduced iron. It has been experimentally determined that maximal wear resistance is observed in the compacts with the mass fraction of WC equal to 10%, produced at a pressing temperature of 300 °C.

Comparison of strength characteristics of engineering materials is usually based on comparison of data from quasi-static tests. However, under dynamic loads, strength characteristics of materials are unstable and the strength ratio of two materials can change dramatically. This paper presents a comparative study of the strain/stress rate dependencies of the critical stresses of various quasi-brittle and ductile engineering materials, as well as their various internal states. A case of continuously increasing load in compression and splitting tests is considered. Experimental results were obtained for bricks, mortar and limestone in dry, saturated and frozen states, copper and titanium in different structural states, and road bitumens with different modifiers. The results show that such dependencies can intersect, thereby realizing a strength competition effect. This means that one material can withstand higher stresses under a quasi-static load and lower stresses under a dynamic load in comparison with another material. Thus, such an intersection suggests that the choice of a material based on quasi-static parameters may be erroneous for structures intended for dynamic modes. The analysis of strain/stress rate dependencies of ultimate or yield strength is carried out on the basis of the incubation time approach. The introduction of dynamic strength characteristics with the dimension of time is considered. This parameter characterizes well the response of the materials to dynamic loading. The calculation results show the possibility of estimating the critical stresses and the strength competition effect at high rate loads using no more than three parameters, which can be easily used in engineering practice.

The pultrusion of large-diameter glass fiber reinforced epoxy rods at high pulling speed is often accompanied by the formation of cracks at the surface of a profile, leading to product rejection. In this study, we investigate the causes of crack formation based on numerical simulations of manufacturing process mechanics, including the temperature distribution, degree of polymerization, and residual stresses. Based on the built model, we solve the problem of temperature condition optimization for maximizing pulling speed. The results show that up to 27% increases in pulling speed are possible provided that the following conditions are met: thermal destruction of the material is avoided; a profile is cooled sufficiently quickly before cut-off; a high degree of polymerization is achieved in a final product; and there are no cracks in a profile.

The dynamic characterization of materials under intermediate and high strain rates is fundamental to understand the material behaviour in case of dynamic loadings. In this study dynamic tests of rocks in compression and splitting by the Kolsky method and its modification were analysed. The time dependence of the critical stress can predict by the incubation time of fracture criterion and these dependencies turned out to be in good agreement with experiments.

This work presents studies the effect of ultrafine-grained (UFG) structure on impact toughness and dynamic compression of pure copper M1 (99.9%). The UFG structure was provided by means of equal-channel angular pressing (ECAP) on the Conform scheme with four and eight passes. Impact toughness tests on samples with U-shaped notch were performed using a drop weight impact machine. Dynamic compression test of cylindrical samples were performed with a setup with the Split-Hopkinson pressure bar (SHPB-20) by the Kolsky method. The results showed that the impact toughness of the UFG copper states was not less than that of the coarse-grained (CG) counterpart. Moreover, the fracture process of the UFG material requires more energy. An increase of compression strain rate by 6 orders resulted in the well-known strain-rate dependence of the yield strength for the CG material and the UFG material after eight ECAP passes. The yield strength of the material after four ECAP passes remained at the level corresponding to a quasi-static loading.

The results of dynamic compression and splitting of dry and water-saturated limestone are presented. The tests have been performed using the Kolsky method and its modification for dynamic splitting. The strength and fracture time of this material at high strain rates have been obtained. It is shown that these characteristics are sensitive to the strain rate. A unified interpretation of these rate effects based on the incubation time approach is presented. Theoretical calculations show that the application of the incubation time concept allows to select the optimal ratio of duration and amplitude of action, which can reduce energy consumption during production and processing of rocks.

This work presents the study of an influence of ultrafine-grained (UFG) structure on impact toughness and dynamic compression of commercially pure titanium Grade 4. The UFG structure was provided by means of equal-channel angular pressing according to the Conform scheme (ECAP-Conform, Ufa) with subsequent heat treatment. Impact toughness tests on samples with U-shaped notch were carried out using a drop weight impact machine. Dynamic compression test of cylindrical samples were carried out on a setup with the Split-Hopkinson pressure bar (SHPB-20) by the Kolsky method. It was found that the impact toughness of the UFG titanium is 15% greater than that of its coarse-grained (CG) counterpart. However, fracture process of the CG material requires 1.5 times more energy. The ECAP treatment significantly increased yield strength of the material. At the same time, an increase of compression strain rate by 6 orders resulted in an increase of yield strength of the CG material by 20%, while yield strength of the UFG titanium remained at the level of a quasi-static load. The UFG material showed a well-expressed strain hardening behaviour for all strain rates.

It is known that experiments with intensive dynamic influences and high-speed deformation of specimens under tension are important in the analysis of deformations and strength of structures and their elements. The most reasonable and widely used method for obtaining dynamic stressstrain curves, characteristics of ultimate strength and deformations is the modified Kolsky method. It should be noted a small number of publications on the analysis of the influence of fillets and the length of the working part of the specimen on the most important mechanical characteristics obtained by this method. This work is aimed at increasing knowledge in this area. By numerical and experimental analysis it was established that when the working part of the specimen has a length of 5 mm, then the uniformity and one-dimensionality of the stressed state are seriously violated. When choosing the length of the specimen in the Kolsky method, there are important limitations: the length of the specimen must be much smaller than the length of the loading pulse. Therefore, in this study, two specimen lengths of 10 and 15 mm were analyzed. In this paper, we give experimental and calculated diagrams and their comparison with each other. It was shown, that for the above-mentioned lengths, the homogeneity and one-dimensionality of the stressed state is substantially improved.

The combined experimental and theoretical approach was applied to the study of high-speed deformation and fracture of the 1810 stainless steel. The material tests were performed using a split Hopkinson pressure bar to determine dynamic stress-strain curves, strain rate histories, plastic properties and fracture in the strain rate range of 102 ÷ 104 s-1. A scheme has been realized for obtaining a direct tensile load in the SHPB, using a tubular striker and a gas gun of a simple design. The parameters of the Johnson-Cook material model were identified using the experimental results obtained. Using a series of verification experiments under various types of stress-strain state, the degree of reliability of the identified mathematical model of the behavior of the material studied was determined.

A description of experimental complexes, methodological and hardware means for determining the mechanical properties of materials under high-speed deformation and fracture is given in the report. Determination of mechanical properties in the strain rate range 5•102÷103 s-1 is the first direction of work in the laboratory of “Dynamic Materials Testing”. These tests are done using automated complexes based on the Kolsky method and its modifications for compression, tension and shearing. It is also possible to determine the fracture toughness, the characteristics of dynamic crack resistance, as well as to obtain stressstrain curves of low-density materials under uniaxial strain. Original gas guns with a caliber of 10, 20 and 57 mm are used for creation a dynamic load. The study of the behavior of materials at strain rates of 105 s-1 and higher is the second direction of work. In this case, the methods of a planewave shock experiment based on gas guns of 57 and 85 mm caliber are used. Manganine and dielectric pressure sensors, as well as laser interferometry are used for measuring the parameters of elastoplastic waves and for determining such important characteristics as impact compressibility, Hugoniot yield strength, spall strength.

The objective of this study was to investigate the compression behaviour of the UHPFRC and its matrix (UHPC) under high strain rate. Two experimental set-ups were used for compression testing: a traditional Split Hopkinson Pressure Bars and a compression version of the Modified Hopkinson Bar. The tests were conducted, in the range of 100–500 s −1 on cylindrical specimens with both diameter and height of 20 mm. Results show significant increases in peak strength and dissipated energy.

A study of the strength and deformation properties of freshwater ice under compression, tension and shear in a wide range of strain rates (10−4 − 3 ⋅ 103 s−1 ) and temperatures of − 5∘ C, − 20∘ C, − 40∘ C and − 60∘ C was performed. Static stress-strain curves of ice under compression were obtained on which the identified strength properties of ice as well as compressive modulus. To determine the mechanical properties of ice at high-speed loading the Kolsky method was used with various embodiments of split Hopkinson bar. The deformation curves were obtained at various loading conditions. Thereon breaking points were defined as well as their dependence on the strain rate and temperature. Also static and dynamic strength properties of ice at splitting and circular shear were defined. Increase in the dynamic strength properties upon the static ones for all loading conditions was marked.

In the present work the combined experimental and theoretical approach has been ap- plied to study high strain rate behavior and failure of titanium alloy Ti-6Al-4V. For modeling con- stitutive material response it has been suggested to use the modified Gurson's plasticity model which takes into account a dependence on the type of loading. Rate dependency effects have been added to the initial constitutive equations. Compressive and tensile tests were carried out by means of Split Hopkinson Pressure Bar for determination of dynamic stress-strain curves, strain rate histories, plasticity and failure properties for strain rate range 10 2 -10 4 s x1 . Parameters of the material model were determined using the obtained experimental results. High strain rate tensile tests of cylindrical V-cut specimens and three point bending (Charpy) experiments were carried out for validation of the model. The numerical simulation of dynamic material response was conducted with implementa- tion of the developed material model for the last test schemes.

High-porosity materials, such as chamotte and mullite, possess a heat of fusion. Owing to their properties, these materials can be used with success as damping materials in containers for airplane, automobile, etc. transportation of radioactive or highly toxic materials. Experimental studies of the dynamic properties have been executed with using some original modifications of the Kolsky method. These modified experiments have allowed studying the dynamic compressibility of high-porosity chamotte at deformations up to 80% and amplitudes up to 50 MPa. The equations of the mathematical model describing shock compacting of chamotte as a highly porous, fragile, collapsing material are presented. Deformation of high-porous materials at non-stationary loadings is usually accompanied by fragile destruction of interpore partitions as observed in other porous ceramic materials. Comparison of numerical and experimental results has shown their good conformity.