Criterion for the occurrence of the macro destruction and formation of breaking during metal deformation

When generalizing the geometrically nonlinear law of Murnaghan elasticity to plasticity, a formally mathematical criterion was introduced for deformational macrofracture (macrocrack appearance) associated with an increase in elastic and plastic anisotropy as a failure cause. The use of the double potentiality of the governing equations in stresses and their velocities made it possible to obtain the reliable information on the structure of the deviatory section of the yield surface, the existence of which is a classical hypothesis in solid mechanics. The normal vector to the surface of the deviatory section is selected from two mutually orthogonal eigenvectors of the constructed operator. There are two families of regular concave surfaces, and a section surface is formed by joining the parts of two representatives of the families at singular points. To select normal vectors, the obtained ratio for them is used for isotropy. In connection with the considered problem of a double simple shift, it is established that multiple eigenvalues appear for the both normal vectors. To unambiguously determine the normal vector at a regular point, it is necessary to exclude the presence of multiple eigenvalues for the both normal vectors at the same time. At a singular point, the appearance of a multiple eigenvalue of one of the normal vectors is still unacceptable. These two conditions are necessary and sufficient to validate the governing equations of the generalized Murnaghan model. Otherwise, a macrocrack occurs. The theoretical construction is supported by the developed software complexes.

Establishment and Analysis of Simulation Model for Single-pass 20 Steel Spinning

With the continuous advancement of computer technology, finite element simulation has been gradually applied to the analysis of plastic deformation of metals. If a strong spinning simulation model of 20 steel cylindrical parts can be established to effectively simulate the stress, strain and surface quality of the metal deformation process, it can provide a scientific basis for the setting of spinning process parameters, thus reducing the number of spinning process experiments to determine spinning process parameters.

DEFORMATION OF ALUMINUM ALLOYS IN ISOTHERMAL CONDITIONS

It has been scientifically proven that aluminum, more than other materials, meets the requirements of production, storage and processing of various foods. Therefore, the prospects for its use in the agro-industrial complex are quite high. At the same time, the process of developing such materials should be improved and promoted. Aluminum alloys are widely used in the aviation industry, in mechanical engineering and in agricultural production, due to their properties and light metal consumption. Alloys are resistant to water, they are not afraid of corrosion, sunlight, easily disinfected. All these properties are best suited for the use of aluminum in the storage of both cereals and livestock products. Moisture, dangerous molds, rodents and various insects are released and absorbed in storage. Aluminum has a high thermal conductivity and reflectivity, which reduce the risk of moisture condensation, which normalizes storage. The smoothness of this material suggests that the walls of aluminum structures collect much less dust. The proposed isothermal method of hot deformation of aluminum alloys in the processing of metals by pressure, differs from traditional deformation, and the temperature of the heated workpiece and the deforming tool is kept constant, close to the upper limit of forging temperatures, throughout the process. The deformation of the metal under isometric conditions and approximate deformations is characterized by an increase in ductility compared with ductility when machined in a cold tool. This is due to the lower rate of deformation, the lower limit of which is limited only by the productivity of the process. As a result, the "filling time" of defects that occur during metal deformation increases, the temperature stress in the workpiece volume decreases, the deformation becomes more uniform.

Seamless Pipes Manufacturing Process Improvement Using Mandreling

The paper discusses the specific aspects of hot rolled seamless pipes manufacture using pipe rolling plants including screw-rolling mills. The method of accuracy enhancement of pipe dimensions, as well as external and internal surface quality improvement, is proposed. The article specifies the results of computer and physical modeling of the pipes mandreling process. The application of the mandreling process within the cage using different diameter mandrels is shown. We managed to decrease the typical mark caused by the metal deformation, due to the screw-rolling mill and to manufacture pipes with more accurate dimensions, as a result of the mandreling process modeling. The results of the physical experiment on mandreling the shell pierced at the screw-rolling mill showed a positive effect from the process of hollow billet cold treatment using the mandrel.

Investigation of the stress-strain state and microstructure transformation of copper busbars in the deformation zone during continuous extrusion

The paper describes an extensive study of features peculiar to physical and mechanical processes occurring in metal in the deformation zone during the continuous extrusion of Cu-ETP rectangular busbars 10×60 mm in size. Finite element computer simulation was used to obtain the values of extrusion power parameters. It was noted that moment and force values increase to the point of filling the press chamber free space with metal reaching a maximum of 12.26 kN·m and 1.54 MN, respectively. The stress-strain state analysis of metal in the deformation zone made it possible to obtain distribution fields of accumulated plastic strain, strain rate intensity and average stresses, and to build the graph of metal temperature variation over time during extrusion. Maximum levels of accumulated plastic strain and compressive stresses are observed in the contact zone of the workpiece with the press container abutment. The most intense metal deformation heating also occurs there. The comparison of modeling and microstructural study results indicate that a significant portion of the cast structure grinding work occurs at the entrance to the deformation zone and at the abutment zone subjected to the highest level of compression stresses. Metal deformation during the die passage leads to an oriented crystal structure formed with a grain size of 25–30 μm. Sample hardness measurement results are consistent with the results of structure analysis in the studied areas of the deformation zone. When the workpiece passes through the compression container abutment section, deformation heating occurs, which leads to a decrease in hardness from 93 to 67 HV. After the metal passes through the die, recrystallization processes continue in it leading to a slight increase in grain size and, accordingly, a decrease in hardness from 79 to 74 HV, which continues until the busbar contacts a cooling medium.

Installation of screw reduction UVO 20-50 for hardening and calibration of cylindrical parts and billets of agricultural machinery

A screw reduction unit UVO 20-50 (diameter of hardened products from 20 mm to 55 mm) with a closed cooling system for hardened rolled products with the ability to integrate equipment into a production line for manufacturing parts was developed. The UVO unit is intended for shaping and hardening of cylindrical parts by high-temperature thermomechanical treatment (HTMT) with metal deformation by screw compression (VO), ensuring the technical characteristics of products. It is known that some thermomechanical methods of hardening and production of rolled products, for example, steels HTMT, in comparison with conventional types of hardening heat treatment, provide a set of higher properties: strength, ductility and fracture resistance. Evaluating the efficiency of us-ing the hardening thermomechanical treatment of long products for highly loaded parts, it is neces-sary to use the criteria of fracture mechanics, to study the resistance to brittle and cyclic fracture of steel under the action of stress concentrators, negative temperatures and other difficult test and op-erating conditions. Taking into account the increased properties of steels with HTMT, it becomes possible to use hollow sections instead of solid billets. The investigated materials and the revealed patterns allow authors to conclude that thick-walled hollow parts, which are used to save metal and lighten the weight of structures, should be considered not only as full-fledged substitutes for solid ones, but also as having an advantage over the latter, mainly due to their better hardenability at sur-face cold working and less sensitivity to stress concentration at cyclic loads, which makes them more reliable in operation. These research results substantiate the wider use of hollow profiles for such parts of agricultural machinery as track pins, shafts, axles, torsion bars and other parts for var-ious purposes.

Force parameters of metal deformation during sheet drawing

The aim of the work. The effect of the curvature of the rounding of torus surfaces during the formation of a cylindrical product (glass) is investigated, taking into account the plastic thinning of the deformable material at the end edges of the matrix and pressing punch. Methods. The existing scheme for determining the power parameters of sheet drawing is analyzed, based on the assumption of the implementation of some abstract stress state in the material; mainly conditional tensile strength. At the same time, the possibility of forming the product without destruction determines the obvious overestimation of the stress level. A mathematical model of the volumetric stress state of the metal is being developed, which makes it possible to assess the deformation and stress state during the formation of a cold-drawn product, i. e. the folding of the sheet blank along the end radius of the rounding of the pressing punch and the steady-state process of drawing the blank into the deformation zone with successive bending/straightening of the material along the edge of the matrix are considered. The level of radial stresses during folding and stretching of sheet material is estimated, taking into account its strain hardening and thinning, which determine the forming force. The obtained results will make it possible to simulate the stress-strain state of the metal during the development of sheet drawing technology: to establish the amount of thinning, to estimate the level of radial stresses in the formation of rounding of torus surfaces along the end edges of the matrix and the pressing punch, as well as to determine the power parameters of the formation, which will prevent the destruction of the pulled part, guaranteeing obtaining high-quality products and more accurately choosing the deforming equipment.