Invariant stress state parameters for forging upsetting of magnesium in the shell

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 1 2021 Invariant stress state parameters for forging upsetting of magnesium in the shell Yuriy Loginov 1, 2, a,* , Yuliya Zamaraeva 1, 2, b 1 Ural Federal University named after the fi rst President of Russia B.N. Yeltsin, 19 Mira str., Ekaterinburg, 620002, Russian Federation 2 M.N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, 18 S. Kovalevskaya str., Ekaterinburg, 620137, Russian Federation a https://orcid.org/0000-0002-7222-2521, j.n.loginov@urfu.ru , b https://orcid.org/0000-0002-2620-7064, zamaraevajulia@yandex.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2021 vol. 23 no. 1 pp. 79–88 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2021-23.1-79-88 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 12 January 2021 Revised: 25 January 2021 Accepted: 13 February 2021 Available online: 15 March 2021 Keywords : Magnesium Plasticity Upsetting Value of the stress state Lode coef fi cient Finite element method Funding The reported study was funded by RFBR according to the research project № 20-38-90051. ABSTRACT Introduction. For pressure treatment of low-plastic metals, it is necessary to develop special techniques for increasing plasticity. In the cold state, an increase in plastic properties is possible due to an increase in the level of compressive stresses during deformation. In the processes of upsetting, this is achieved by using shells or clips of various types. At the same time, the con fi guration of the upsetting tool also matters. To create additional compressive stresses and increase the ductility of the metal, the working surface of the tool can be con fi gured differently than with a normal free upsetting, where it is obviously larger than the contact surface area of the workpiece, so that metal broadening can occur. The stress state has a great in fl uence on the plasticity of the processed material. This state is described by methods of tensor representation, but to assess the situation, it is customary to use invariants of tensors in one form or another, which eliminates the in fl uence of coordinates on the results of the analysis. In the sections of deformable body mechanics dealing with the in fl uence of the stress state on plasticity, the fi rst, but sometimes other invariants of the stress tensor are used, the invariants themselves are transformed into the stress state indicator and the Lode coef fi cient. The aim of the work: mathematical evaluation of invariant parameters of the stress state of the magnesium upsetting process at room temperature, according to the results of which it is possible to obtain a positive result in real experiments. Research methods: fi nite element simulation using the DEFORM software module. Results and discussion. The theoretical justi fi cation of increasing the plasticity of the magnesium billet in the process of upsetting in the cage without its compression is carried out. An increase in the stress state index modulo 2...5 times is revealed, which contributes to an increase in the plasticity of the metal. At the same time, a zone with a Lode coef fi cient close to zero is identi fi ed. It is adjacent to the middle of the height of the workpiece at the point of contact with the cage and can be a dangerous cross-section from the position of crack formation. For citation: Loginov Yu.N., Zamaraeva Yu.V. Invariant stress state parameters for forging upsetting of magnesium in the shell. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) =Metal Working andMaterial Science , 2021, vol. 23, no. 1, pp. 79–88. DOI: 10.17212/1994- 6309-2021-23.1-79-88. (In Russian). ______ * Corresponding author Zamaraeva Yuliya V. , Junior researcher M.N. Mikheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, 18 S. Kovalevskaya str., 620137, Ekaterinburg, Russian Federation Tel.: +7-950-200-56-79, e-mail: zamaraevajulia@yandex.ru Introduction The plastic properties of the metal should be considered during developing the manufacturing process of a metal’s pressure shaping. Increasing plasticity in low-plastic metals requires developing special techniques. Basically, efforts are aimed at increasing the level of plastic properties by increasing the temperature. However, this approach does not always suit the developers of the technology since a number of metals begin to oxidize from the surface when the temperature rises, or there occurs the process of gas saturation of the bulk metal. This is especially true for metals such as titanium [1] and magnesium [2]. Therefore, there may also be an approach in which the processing is carried out in a cold state and the plasticity increases due to an increase in the level of compressive stresses [3] during the deformation process.