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

Experimental studies on the effect of transient heating of the outer surface of radial crack-containing ring specimens from 45 steel on their fracture toughness are described. Such a treatment contributes to an increase in brittle fracture resistance at low temperature. As numerical simulation results demonstrated, transient heating of the outer specimen surface results in localized plastic flow near the crack tip, leading to strain hardening and its blunting

A multichannel system of high-speed recording of strains and loads during fracture toughness tests of materials has been developed. A four-channel analog-to-digital converter was used to record signals. Tests were carried out using a rotary and a vertical impact testing machines at various loading rates and temperatures. Some results are presented for impact testing of Charpy specimens with recording of load variation at supports during tests.Keywords: impact fracture energy, Charpy specimen, load, temperature, multichannel recording system. Introduction.Analysis of the known experimental data has shown that even with a common brittle character of fracture of the material, considerable plastic strains that reach tens and even hundreds of percents are present at the stress raiser (a notch, a crack) apex, the strain localization and shear strips as well as the stretching of crack surfaces and their ductile extension increment are observed. Up to now, there has been no common point of view on the criteria of ductile-to-brittle transition, especially under dynamic loading. The available test results permit no full explanation of this phenomenon, there remain many open questions, in particular a combined effect of the strain rate, temperature and stressed state rigidity on the process of dynamic deformation and fracture of materials.To study the peculiar features of deformation and fracture of materials at both static and dynamic loads, extensive experimental data are required. Standard impact tests of Charpy specimens are widely used in determining the mechanical properties of structural materials, in particular in assessing the embrittlement of the base material and weld metal of NPP reactor pressure vessels, from the shift of the critical temperature of brittleness due to the radiation and thermal effects during operation. However, such tests usually provide rather limited data on the analysis of the effect of various factors on the material behavior. The energy spent for fracture of specimens [1-5] is determined from the test results, whereas the fraction of the ductile component in the fracture or the value of the lateral expansion of the specimen in the fracture zone is determined from the appearance of their fracture surfaces [6].The use of instrumented impact testing machines with the recording of load versus time diagrams makes it possible to determine not only the fracture energy but also a number of such critical parameters as the load corresponding to the general yielding, the maximum load, the levels of loading at the moments of the brittle fracture start and arrest. With the use of load versus time diagrams it is possible to divide the energy spent for the specimen deformation and fracture into the components related to the crack nucleation and propagation.It is possible to increase the amount of information obtained during such tests for its subsequent analysis by way of equipping conventional testing equipment with up-to-date data recording instruments [1-3, 5, 6].Development of the System for Data Rec...

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