Plastic Folding of Bar Stocks of Round and Barrel-Shaped Sections

Research has been carried out on the process of plastic folding of bar stocks with round and barrel-shaped cross-sections. The dependence of the movement of the movable tool on the bending angle has been established. The force parameters of the deformation process and the stress-strain state in the bending workpiece are determined based on the results of finite element modeling of plastic bending.

HIGH-TEMPERATURE DEFORMATION BEHAVIOR AND HOT-PROCESSING MAP OF 25CrMo4 AXLE STEEL BASED ON FRICTION CORRECTION

The deformation behavior and microstructure of 25CrMo4 axle steel was systematically investigated by thermal compression deformation. The hot-compression test of a 25CrMo4 axle steel sample was carried out on a Gleeble-3800 thermal mechanical simulation tester. The flow behavior of the alloy was studied at the deformation temperature (900–1200 °C), strain rates (0.01; 0.1; 1.0) s–1 and the maximum deformation of 60 %. The flow curves under different deformation conditions were obtained, and the effects of the deformation temperature and strain rate on the appearance of the flow curves are discussed. The true stress-strain curve obtained by experiment is modified by friction. Based on the corrected experimental data, the activation energy determined by the regression analysis was Q = 311 kJ/mol, and the constitutive model was constructed. The high-temperature flow behavior of the 25CrMo4 axle steel was described by the Zener-Hollomon parameter. The optimum hot-deformation process parameters were determined based on the hot processing maps, followed by the analysis of the microstructure characteristics of the alloys under optimum hot working. The results show that the suitable hot-deformation process parameters of the alloy are as follows: deformation temperature is 1050–1200 °C, and strain rate is 0.01 s–1 to 0.14 s–1.

Analysis of processing variables in Equiangular Channel Press deformations

Equiangular Channel Pressing (ECAP) is by far the most promising technique, by the severe plastic deformation (SPD) method, being able to produce large volumes of materials sufficient for practical applications. The ECAP process can be repeated until refining saturation is reached, leading to large amounts of shear strain. The reason behind the exceptional properties obtained in materials processed by ECAP was attributed to the microstructure of the material obtained in this deformation process. This work investigated the ECAP strain variables in the literature in order to analyze the effect of each of these on the microstructure of processed materials. The articles were collected from the following databases: ScienceDirect and the Scientific Electronic Library Online (SciELO) electronic library, as they include national and international literature. Based on the results found, it could be seen that several parameters must be analyzed to deform pure metals and alloys, to refine the microstructure, such as bending angle and channel angle of the strain matrix, number of passes, and pressing temperature. It was possible to verify that changes in these variables configure changes in the microstructure.

Cylinder sleeve of the internal combustion engine. Mathematical model of the deformation process

During the operation of internal combustion engines, deformation of the cylinder sleeve is possible, which causes its premature wear during the operation of the “piston ring – sleeve” pair. Imagine the sleeve as a two-stage hollow cylinder with forces applied to it, which cause deflection in the section. It can be assumed that if the greatest deformation of the cylinder is in the section of the application of forces, then with distance from this place it will decrease. At some distance from the point of application of forces, the deflection of the sleeve will be equal to zero. It is required to simulate a mathematical formula that would make it possible to evaluate the possibility of estimating the value depending on the basic geometric dimensions of the cylinder sleeve. A mathematical model of the deformation process of a hollow two-stage sleeve of an internal combustion engine has been developed, an analytical dependence has been obtained for the value of the “neutral” section depending on the main geometrical dimensions of the cylinder sleeve of the engine, a rather extensive analysis of the influence of various parameters on the value of the “neutral” section has been carried out.

THE ASPECTS OF ALMG6 ALUMINIUM ALLOY DEFORMATION UNDER EXPLOSIVE WELDING

The paper presents the results of a study of the features of the deformation of the main plate made of AlMg6 in the process of explosion welding (with corrosion-resistant steel 08Cr18Ni10Ti). It was found that the end and edge sections of the main plate undergo severe deformation, as evidenced by the constructed maps of the distribution of residual deformations over the plate area. With an increase in the detonation velocity, an intensification of the deformation process occurs, which leads to the appearance of cracks and local spalling of plate fragments. In addition, the results of measurements of the elongation of the main plate showed that a noticeable longitudinal deformation of the plate begins approximately at a distance equal to 2/3 of the total length of the plate. The measured value of the beginning of elongation (240 ± 10 mm) with an accuracy of 95% converges with the calculated value (229 mm).

Evaluation of the quality of three-layer steel bimetallic strips obtained on a unit of continuous casting and deformation

Today there is an urgency of creating high-performance continuous processes for the production of bimetals. The article describes the main tasks of improving the quality of the materials under consideration. Two stages of the technology for producing steel three-layer bimetallic strips on the unit of a combined continuous casting and deformation process are considered. The authors give recommendations on the conduct of the technological process in order to obtain high-quality bimetallic strips on such unit. The problem statement is presented. The material considers initial data for determining the temperature of the steel base strip and the stress-strain state of the metals of the cladding layers and the strip in deformation center of a three-layer bimetallic ingot. A model for calculating and a method for solving problems of thermal conductivity and elastoplasticity are shown. Regularities of the temperature change of the main steel strip are given during its passage through the molten metal of the cladding layer. Stress-strain state of the metals of the main strip and cladding layers in the deformation center was determined when three-layer bimetallic steel strips were obtained on the unit of combined continuous casting and deformation process. The authors describe the values of compression of the main steel strip and mutual displacement of the layers during compression of the bimetallic ingot by the strikers. Regularities of the distribution of axial and tangential stresses are shown along the contact line of the cladding layer with the striker. The evaluation of the process of obtaining bimetal steel 09G2S - steel 13KhFA - steel 09G2S was made on a pilot unit for continuous casting and deformation. Microstructure of the main strip and cladding layers of a three-layer bimetallic steel strip is shown when a combined continuous casting and deformation process is obtained in one unit.

Finite Element Calculation of the Linear Elasticity Problem for Biomaterials with Fractal Structure

Aims: The aim of this study was to develop the mathematical models of the linear elasticity theory of biomaterials by taking into account their fractal structure. This study further aimed to construct a variational formulation of the problem, obtain the main relationships of the finite element method to calculate the rheological characteristics of a biomaterial with a fractal structure, and develop application software for calculating the components of the stress-strain state of biomaterials while considering their fractal structure. The obtained results were analyzed. Background: The development of adequate mathematical models of the linear elasticity theory for biomaterials with a fractal structure is an urgent scientific task. Finding its solution will make it possible to analyze the rheological behavior of biomaterials exposed to external loads by taking into account the existing effects of memory, spatial non-locality, self-organization, and deterministic chaos in the material. Objective: The objective of this study was the deformation process of biomaterials with a fractal structure under external load. Methods: The equations of the linear elasticity theory for the construction of the mathematical models of the deformation process of biomaterials under external load were used. Mathematical apparatus of integro-differentiation of fractional order to take into account the fractal structure of the biomaterial was used. A variational formulation of the linear elasticity problem while taking into account the fractal structure of the biomaterial was formulated. The finite element method with a piecewise linear basis for finding an approximate solution to the problem was used. Results: The main relations of the linear elasticity problem, which takes into account the fractal structure of the biomaterial, were obtained. A variational formulation of the problem was constructed. The main relations of the finite-element calculation of the linear elasticity problem of a biomaterial with a fractal structure using a piecewise-linear basis are found. The main components of the stress-strain state of the biomaterial exposed to external loads are found. Conclusion: Using the mathematical apparatus of integro-differentiation of fractional order in the construction of the mathematical models of the deformation process of biomaterials with a fractal structure makes it possible to take into account the existing effects of memory, spatial non-locality, self-organization, and deterministic chaos in the material. Also, this approach makes it possible to determine the residual stresses in the biomaterial, which play an important role in the appearance of stresses during repeated loads.

Ultrasonic and Spectroscopic Techniques for the Measurement of the Elastic Properties of Nanoscale Materials

Materials at the nanoscale often have properties which differ from those they have in the bulk form. These properties significantly depend on the production process, and their measurement is not trivial. The elastic properties characterize the ability of materials to deform in a reversible way; they are of interest by themselves, and as indicators of the type of nanostructure. As for larger scale samples, the measurement of the elastic properties is more straightforward, and generally more precise, when it is performed by a deformation process which involves exclusively reversible strains. Vibrational and ultrasonic processes fulfill this requirement. Several measurement techniques have been developed, based on these processes. Some of them are suitable for an extension towards nanometric scales. Until truly supramolecular scales are reached, the elastic continuum paradigm remains appropriate for the description and the analysis of ultrasonic regimes. Some techniques are based on the oscillations of purpose-built testing structures, mechanically actuated. Other techniques are based on optical excitation and/or detection of ultrasonic waves, and operate either in the time domain or in the frequency domain. A comparative overview is given of these various techniques.