This paper presents research of the impact toughness and hardness distribution in specific zones of a ‘single V’butt multiple-pass welded joints of the high-strength low-alloyed steels. Obtained values of the impact toughness are analyzed in correlation with a microstructure in specific zones of the welded joint, together with the micro hardness distribution found in the related zones. Based on the carried out analysis and results obtained in experiments, the applied technology of welding was evaluated. The original conclusions on influence of the selected welding procedure manual metal arc (MMA) for the root passes and metal active gas (MAG) for the filling and covering passes) on impact toughness of the high-strength low-alloyed steels are drawn. The paper also presents discussion on the valid standards and recommendations related to welding of those steels, from the aspect of applications in design of steel welded constructions.

Post-mortem characterisation is a pivotal tool to trace back to the origin of structural failures in modern engineering analyses. This work compared both the crack propagation and rupture roughness profiles based on areal parameters for total fracture area. Notched and smooth samples made of weather-resistant structural steel (10HNAP), popular S355J2 structural steel and aluminium alloy AW-2017A under bending, torsion and combined bending–torsion were investigated. After the fatigue tests, fatigue fractures were measured with an optical profilometer, and the relevant surface parameters were critically compared. The results showed a great impact of the loading scenario on both the local profiles and total fracture areas. Both approaches (local and total fracture zones) for specimens with different geometries were investigated. For all specimens, measured texture parameters decreased in the following order: total area, rupture area and propagation area.

The Ukrainian energy sector is one of the most inflexible energy sectors in the world as a result of the almost complete depreciation of the equipment of the main sources of power supply: nuclear, thermal, and hydropower. In connection with existing problems, there is a need to develop and use new energy-saving technologies based on renewable energy sources. In this proposed research, a regression model of renewable energy growth in the energy sector of Ukraine was developed. The studied literature reveals that the independent use of individual functioning elements of renewable energy sources function as the primary power source that is not an optimal solution for stable energy supply. This study proposes the use of hybrid renewable energy systems, namely a combination of two or more renewable energy sources that will help each other to achieve higher energy efficiency, accelerate the growth of renewable energy in the share of the Ukrainian energy sector and/or improve functioning with battery energy storages. Moreover, the use of hybrid renewable energy systems in Ukraine will reduce the human impact on the environment, realize the potential of local renewable energy resources and also increase the share of electricity generation from renewable energy sources. Therefore, mechanisms for managing state regulation of stimulating the development of hybrid renewable energy systems have been developed.

In this paper we focus on the application of a mixed time partitioning methods to raise efficiency of the solidification kernel in the NuscaS system. We are proposing using a fixed time step in the casting and its integer multiple in other parts of mould because the time step size determines the accuracy of the simulation results. By means of numerical experiments we show that our approach allows for up to about three times performance improvement as compared to the standard approach without loosing precision of results. Moreover, this methods will be extended to 3D numerical simulation in a future work. We notice also that our method can be combined with parallel processing to further improve performance of solidification kernels.

The article presents the modeling of temporary temperature and phase share calculations during SAW (submerged arc welding) overlaying of steel elements. The input heat of a melted electrode and the heat of direct electric arc impact have been taken into consideration in the temperature field solution. The characteristic areas (fusion, full and incomplete transformation), have been determined by solidus, A3 and A1 temperatures, respectively. The limit temperatures of the phase trandformations during cooling, based on the cooling rate in the temperature range 800–500 °C according to S355 steel time-temperature-transformation welding diagram, have been determined. The JMAK (Johnson–Mehl–Avrami–Kolmogorov) law and KM (Koistinen–Marburger) formula were used in the phase change kinetic description. Theoretical considerations were illustrated with examples of temperature and phase share computations for welding overlaid S355 steel plate. The analysis of the history of changes in temperature and structural components (phases) was carried out based on the results of numerical simulations as well as metallographic examination after SAW overlaying. The dimensions of the HAZ (heat-affected zone), obtained experimentally, and the structure types confirmed the results of the computation.