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The Charpy impact tests were carried out at different temperatures and loading rates. The temperature dependences of crack initiation and propagation in carbon steels 45 and St. 3 under impact testing were determined from the obtained force variation plots. The effect of the impact velocity in the range from 1 to 4.4 m/s on the fracture toughness temperature dependence is estimated.Keywords: carbon steels, Charpy specimen, instrumented impact testing machine, fracture toughness, crack initiation and propagation energy, ductile-brittle transition temperature.Introduction. One of the main characteristics of materials in the assessment of the strength and reliability of structures and constructions is the ductile-brittle transition temperature (DBTT). In order to determine it, various testing methods are used, of which the Charpy impact testing is the most simple and widespread. Usually, as a result of such testing, the temperature dependences of fracture toughness are determined, and by their processing, there are determined the ductile-brittle transition temperatures [1][2][3]. In so doing, it should be taken into account that the fracture toughness is an integrated characteristic that includes the specimen deformation energy, crack initiation and propagation energy.The use of instrumented impact testing machines makes it possible to record force versus time plots during testing and thus to get much more information on the material behavior [1,[4][5][6][7]. The use of modern high-speed digital recording systems increases considerably the capabilities of processing of the obtained data. These data permit analyzing various approaches to determination of the ductile-brittle transition temperature and the energy spent at different stages of deformation and fracture of Charpy specimens under impact testing [2].The goal of the present work was to study the behavior of carbon steels, such as St. 3 and 45, at different temperatures and loading rates using an instrumented vertical impact testing machine.Testing Procedure and Processing of the Results. Impact testing of steels was carried out using an instrumented vertical impact testing machine equipped with a multichannel system for high-speed recording of forces and strains (the sampling frequency is 20 MHz) and a system for cooling and heating specimens in the temperature range T = from −150 to 400°C [8]. Standard Charpy specimens of steels St. 3 and 45 of 55 10 10 × × mm in size served

We investigate the structure, hardness, strength, plasticity and fracture character of Cu-Cr microlayer composite material for electric contacts with prescribed microlayered structure and chemical composition in the temperature range from 290 to 1070 K. The correlation relationships between the hardness and strength characteristics have been established. Notation σ u -ultimate strength, MPa σ 0 2 . -offset yield stress, MPa δ -relative elongation, % δ pr -relative uniform elongation, % ψ -reduction of the cross-sectional area, % HV -Vickers hardness, MPa T -thermodynamic temperature, K U -plastic strain activation energy (enthalpy), eV ′ A -constant characterizing the material and strain rate c -proportionality factor, c H = σ H -hardness, MPa σ -characteristic of strength, MPa k -the Boltzmann constant G -shear modulus, MPa HV m -mean value of Vickers hardness, MPa S -root-mean-square deviation, MPa w -coefficient of variation, % ΔHV -reliable estimate at a 0.95 confidence level, MPa a b , -regression coefficientsIntroduction. Copper and chrome composites are widely used as the most efficient electric contact materials for arcing contacts of arc-extinguishing chambers in vacuum circuit breakers. In addition to the conventional methods of powder metallurgy, these materials are produced by high rate electron-beam evaporation/condensation of copper and chrome from separate water-cooled crucibles and layer-by-layer condensation on a metal substrate (a rotating steel disc). The electron-beam physical vapor deposition (EBPVD) technology makes it possible to produce, within one production cycle, sheet copper-chrome composite materials with a given microlayer structure and chemical composition, and condensates with the content of gaseous impurities no higher than that in the initial material, even in the case of evaporation of active metals such as chrome. One more peculiar feature of this method is that it allows the creation of combined contacts with a working layer of an arc-extinguishing composite material obtained by physical vapor deposition, which is cohesive with the copper substrate that provides heat removal from the working layer.The optimum content of chrome in these composites that provides the most favorable combination of electrical, mechanical and chemical characteristics of the material is from 30 to 40 mass%, the tensile strength of composites being 400 to 550 MPa, hardness from 1600 to 1800 MPa, and the resistivity not exceeding 2 5 10 8 . ⋅ − Ω ⋅ m. A high-temperature annealing of the condensed materials Cu-(30 to 40 mass%) Cr is responsible for the decrease in their strength and resistivity down to 30%, but, in fact, does not influence the hardness. Owing to the specific structure of these materials, their unique physico-mechanical and operating characteristics are formed. At present, condensed Cu-Cr microlayer composite materials have been produced as pilot lots by the "Gekont" Research and Production Enterprise (Vinnytsya, Ukraine) [1][2][3][4][5][6][7].In the process of operation, materials of co...

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