Kinetic equations of creep and damage for description of materials with non-monotonic dependence of fracture strain on stress

OBRABOTKAMETALLOV Vol. 23 No. 3 2021 152 MATERIAL SCIENCE References 1. Volegov P.S., Gribov D.S., Trusov P.V. Damage and fracture: classical continuum theories. Physical Mesomechanics , 2017, vol. 20, pp. 157–173. DOI: 10.1134/S1029959917020060. Translated from Fizicheskaya Mezomekhanika , 2015, vol. 18, no. 4, pp. 68–87. 2. Lokoshchenko A.M. Polzuchest’ i dlitel’naya prochnost’ metallov [Creep and long-term strength of metals]. Moscow, Fizmatlit Publ., 2016. 504 p. ISBN 978-5-9221-1645-9. 3. Meng Q., Wang Z. Creep damage models and their applications for crack growth analysis in pipes: A review. Engineering Fracture Mechanics , 2019, vol. 205, pp. 547–576. DOI: 10.1016/j.engfracmech.2015.09.055. 4. Skrzypek J.J., GanczarskiA.W. Modeling of material damage and failure of structures: theory and applications . Berlin, Springer, 1999. 326 p. ISBN 3-540-63725-7. Kinetic equations of creep and damage for description of materials with non-monotonic dependence of fracture strain on stress Inna Banshchikova * Lavrentyev Institute of Hydrodynamics of the Siberian Branch of the RAS, 15 Ac. Lavrentieva ave., Novosibirsk, 630090, Russian Federation https://orcid.org/0000-0002-4045-7975, binna@ngs.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2021 vol. 23 no. 3 pp. 139–154 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2021-23.3-139-154 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 16 June 2021 Revised: 05 July 2021 Accepted: 30 July 2021 Available online: 15 September 2021 Keywords : Creep Kinetic equations Non-monotonic dependence Fracture strain Normalized accumulation damage curve Tension of rod Rational deformation modes Acknowledgements Research were partially conducted at core facility “Structure, mechanical and physical properties of materials” ABSTRACT Introduction. Reducing the level of damage accumulation during pressure treatment of materials at elevated temperatures in creep and close to superplasticity modes in the manufacture of parts can signi fi cantly increase its service life in the cold state. Finding temperature and power conditions leading to a reduction in damage of material during the production process and operation is an important task. The purposes of the work: 1) to show the possibility of using the Sosnin-Gorev creep and damage model for alloys with a non-monotonic dependence of strain at fracture on diagrams with creep curves; 2) to carry out comparative analysis of damage accumulation under conditions of uniaxial tension at constant stress and at constant strain rates for alloy with such a dependence. Research methods. Used scalar damage parameter is equated to the normalized deformation, i.e. to the ratio of the current strain to the fracture strain. To fi nd the coef fi cients of relations creep and damage, the similarity of the creep curves in the normalized values “normalized strain – normalized time”, i.e. the presence of single normalized curve of damage accumulation is checked. The least squares method is used to approximate the experimental data. Numerical integration methods are used for comparative analysis of deformation modes. Results and discussion. Determination of the parameters of the creep and damage equations by the method of a single normalized curve is carried out on the example of experimental data for steel 12Kh18N10T (12Cr18Ni10Ti) at 850 °C, which has a minimum of fracture strain in diagrams with creep curves. Analysis of the static and kinematic modes of deformation for studied material showed that damage accumulation in both cases is practically the same for stresses close to the stress at which this minimum is reached. If the stresses are lower, then the lower level of damage accumulation will be in the kinematic mode; if the stresses above the minimum value, then the static mode will lead to a lower level of damage accumulation. Application. The obtained results can be useful when choosing rational modes of forming structural elements from alloys with a non-monotonic dependence of the fracture strain on stress, as well as in evaluating it for long-term strength during operation. For citation: Banshchikova I.A. Kinetic equations of creep and damage for description of materials with non-monotonic dependence of fracture strain on stress. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2021, vol. 23, no. 3, pp. 139–154. DOI: 10.17212/1994-6309-2021-23.3-139-154. (In Russian). ______ * Corresponding author Banshchikova Inna A., D.Sc. (Physics and Mathematics), Senior researcher Lavrentyev Institute of Hydrodynamics of Siberian Branch of RAS, 15, Ac. Lavrentieva ave., 630090, Novosibirsk, Russian Federation Tel.: 8 (383) 333-27-50, e-mail: binna@ngs.ru