The method of upsetting of large ingots has been investigated in this work. The proposed method consists in upsetting of profiled workpieces with concave faces. An angle of the concave faces was 150°. A relative depth of the concave faces has been varied in range 15%…25% from workpiece's diameter. Strains effective and mean stresses in the longitudinal cross-section of the workpiece with concave faces after upsetting have been determined by FEM. A value of compressive stresses has been determined based on a parameter of the stress state. FEM allowed to find what a rational depth of the concave faces should be, which has to be 15 % from workpiece's diameter. Maximum closing of the internal defect take place for this depth of the concave faces. Results of the FEM have been tested by experimental investigations. It has been established that upsetting of the four-beam workpieces improved a quality of the massive parts.

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Improvement of upsetting process of four-beam workpieces based on computerized and physical modeling

Material embrittlement is often encountered in machining, low-temperature, and heat treatment conditions among which machining is strain-rate related. In addition to machining, material embrittlement can also occur in the processes of, for example, projectile penetration, explosion, and tunnel boring, because of the high strain-rates in the processes. Many researchers recognize that strain rate can cause material embrittlement. However, the strain-rate evoked material embrittlement is not fully understood, and its fundamental mechanisms are to be investigated. This paper is focused on the material embrittlement mechanisms of engineering materials subjected to loading at high strain rates. Based on the previous research, this paper identifies that the strain rate can lead to an increase in material strength and reduction in toughness, which is an important cause of material embrittlement. Strain-rate sensitivity ks proposed in this study provides a guide for the determination of material embrittlement in terms of strain rate. The paper elucidates that stress wave propagation and reflection is another mechanism that directly contributes to material embrittlement and fragmentation at a high strain-rate. The paper also investigated the critical conditions for ductile to brittle transition of ductile materials based on the strain-rate effect. Finally, the effects of strain rate on the nucleation and propagation of a crack are discussed in terms of dislocation kinetics. It provides guidance to predicting the material embrittlement and fragmentation at a high strain-rate for applications ranging from the machining, tunnel boring, and armor protection of engineering materials.

https://iopscience.iop.org/article/10.1088/2631-7990/ab263f/pdf

Material embrittlement in high strain-rate loading

Technologies for the production of multilayered spherical bottoms and cylindrical shells of quasi-layered material and compaction of the multilayered wall of military equipment elements are developed. The need for these studies is associated with increasing survivability and eliminating fragmentation effects of multilayered structures on manpower and equipment that use pressure vessels (submarines, flamethrower vessels, elements of armored vehicles).Operating conditions for the most efficient use of structures made of layered structural materials are presented. Their advantages in operation and production are described. The highest efficiency is achieved with firm adhesion of structural layers or with the use of quasi-layered materials. The solution to this problem is possible using the energy of high explosives. It is experimentally found that explosive loading leads to an increase in toughness and ballistic resistance of treated materials. Analysis of various methods of multilayered wall compaction is carried out and the most effective technologies are proposed.As a result of the research, process parameters, requirements for process equipment are established.The importance of the presented studies is associated with increasing the fighting efficiency, survivability of military equipment and personnel

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A search for technologies implementing a high fighting efficiency of the multilayered elements of military equipment

The simulation of the process of combined radial reverse extrusion of hollow parts with a flange has established two fundamentally different, in terms of the components of the kinematic modules, calculation schemes CDZ-1.i and CDZ-2.j, taking into consideration the possible shape of the boundary of the section of a metal flow inside a workpiece. The comparison of the dependences of the optimal relative rate of metal outflow in the opposite direction for different schemes indicates significant differences in the resulting values in the course of the deformation process. The relevance of this study is due to making it easier to evaluate the use of the combined extrusion process to produce hollow parts with a flange while maintaining the required dimensions compared to simple deformation schemes. We have identified the lack of detailed studies into the technologies for the introduction of combined extrusion schemes, as well as the absence of technological recommendations for determining the force regime and the shape formation of a semi-finished article. The process of the combined extrusion of hollow parts with a flange was investigated, thereby selecting different types based on the nature of the metal flow depending on the geometric ratios of the deformation process. We have obtained experimental data on the gradual shape formation of a semi-finished product in the process of deformation at different geometric ratios. The limits of using estimation schemes of the process have been defined to obtain data on the increments in a semi-finished product, including in terms of predicting the formation of a shrinkage cavity in the bottom part. It is recommended that a condition of selecting the appropriate scheme should be the condition for a minimum value of the reduced pressure of deformation  p i < p j . The resulting recommendations make it easier to predict the shape formation and the force mode of extrusion (a deviation from experimentally obtained data can be reduced to 10 %), which would contribute to evaluating the rationality of the combined extrusion processes while ensuring the required dimensions of a part

/pdf/predicting-the-shape-formation-of-hollow-parts-with-a-flange-2g0sx135ax.pdf

Predicting the shape formation of hollow parts with a flange in the process of combined radial-reverse extrusion

Modeling Dynamic Parameters of Hard Alloys during Shock Wave Regeneration

It is shown that when modeling the processes of forging and stamping, it is necessary to take into account not only the hardening of the material, but also softening, which occurs during hot processing. Otherwise, the power parameters of the deformation processes are precisely determined, which leads to the choice of more powerful equipment. Softening accounting (processes of stress relaxation) will allow to accurately determine the stress and strain state (SSS) of the workpiece, as well as the power parameters of the processes of deformation. This will expand the technological capabilities of these processes. Existing commercial software systems for modeling hot plastic deformations based on the finite element method (FEM) do not allow this. This is due to the absence in these software products of the communication model of the component deformation rates and stresses, which would take into account stress relaxation. As a result, on the basis of the Maxwell visco-elastic model, a relationship is established between deformation rates and stresses. The developed model allows to take into account the metal softening during a pause after hot deformation. The resulting mathematical model is tested by experiment on different steels at different temperatures of deformation. The process of steels softening is determined using plastometers. It is established experimentally that the model developed by 89 ... 93 % describes the rheology of the metal during hot deformation. The relationship between the components of the deformation rates and stresses is established, which allows to obtain a direct numerical solution of plastic deformation problems without FED iterative procedures, taking into account the real properties of the metal during deformation. As a result, the number of iterations and calculations has significantly decreased.

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Alexander Shapoval

Papers

Improvement of upsetting process of four-beam workpieces based on computerized and physical modeling

A search for technologies implementing a high fighting efficiency of the multilayered elements of military equipment

Predicting the shape formation of hollow parts with a flange in the process of combined radial-reverse extrusion

Modeling Dynamic Parameters of Hard Alloys during Shock Wave Regeneration

Development of the Metal Rheology Model of High-Temperature Deformation for Modeling by Finite Element Method