539.4

ultimate strength, actual ultimate strength, ultimate stress, the uniform plastic stability loss, localization of strains.

If a thin-walled pipe loaded with internal pressure and tension allows the appearance of plastic strains takes place, then the uniform plastic stability loss with the emergence of a local plastic deformation zone is considered the limit state, the corresponding stresses are considered as the limit ones. Correct prediction of the stress-strain state at the moment of strain localization requires taking into account the actual size of the loaded pipe and the calculation of true stresses. The article proposes the implementation of the method of predicting the limit values of true stresses that appear in the pipe at different ratios of internal pressure and axial tension. The physical and mechanical properties of the material, the type of stress state and the change in the actual dimensions of the loaded pipe are taken into account. For two grades of steels (carbon steel 45 and alloy steel 10MnН2MoV), an increase in the calculated strength threshold is shown with an insignificant additional load of a pipe loaded with pressure and axial tension. Analysis of the results showed that it is possible to establish a balance between the actual geometry of the element and the load, which will solve the problem of finding the optimal ratio of «weight-strength», important for practical applications in aircraft, rocket and mechanical engineering. The proposed method for finding the limiting values of actual stresses makes it possible to calculate a realistic safety factor and make improved engineering solutions at the design and operation stages of structural elements; to increase the efficiency and safety of using pipeline and shell-type saving systems.

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10. Zhu, Xian-Kui & Leis, Brian. (2011). Evaluation of burst pressure prediction models for line pipes. International Journal of Pressure Vessels and Piping – INT J PRESSURE VESSELS PIPING. P. 89. Doi:10.1016/j.ijpvp.2011.09.007
11. Law, M. (2005). Use of the cylindrical instability stress for blunt metal loss defects in linepipe. International Journal of Pressure Vessels and Piping, 82 (12), 925–928. Doi:10.1016/j.ijpvp.2005.04.002.
12. Kozbur H. Prediction technique for thin-walled cylindrical tubes boundary state. Scientific Journal of TNTU. Tern: TNTU, 2019. Vol. 94. No. 2. P. 145–155. (Mathematical modeling. Mathematics). URL: https://doi.org/10.33108/visnyk_tntu2019.02.145.
13. Kozbur H. Method of predicting necking true stress in a thin-walled tube under a complex stress state. Strojnícky časopis. Journal of Mechanical Engineering. 2020. No. 70 (2), 101–116. URL: https://doi.org/ 10.2478/scjme-2020-0024
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15. Lebedev A. A., Kovalchuk B. I., Giginyak F. F., Lamashevskiy V. P. Mehanicheskie svoystva konstruktsionnyih materialov pri slojnom napryajennom sostoyanii. Pod red. akademika NAN Ukrainyi A. A. Lebedeva. Kiev: Izdatelskiy dom “In YUre”, 2003. 540 p. [Іn Russian].

1. Luchko J., Ivanyk E. Сiagnostics of the main gas pipelines and assessment of their residual life under the conditions of long-term operation. Scientific Journal of TNTU (Tern.) 2017, vol. 87, no. 3, pp. 48–63. URL: https://doi.org/10.33108/visnyk_tntu2017.03.048.
2. Bony, M., Alamilla, J. L., Vai, R., Flores, E. Failure pressure in corroded pipelines based on equivalent solutions for undamaged pipe. ASME. J. Pressure Vessel Technol. 2010, 132 (5): 051001. URL: https://doi.org/10.1115/1.4001801.
3. Hillier M. J. Tensile plastic instability of thin tubes–I. International Journal of Mechanical Sciences, Volume 7, Issue 8, 1965. pp. 531–538, ISSN 0020-7403. Doi: https://doi.org/10.1016/0020-7403(65) 90010-X.
4. Tomita Y., Shindo A., Nagai M. Axisymmetric deformation of circular elastic-plastic tubes under axial tension and internal pressure. International Journal of Mechanical Sciences. Volume 26. Issues 6–8. 1984. Рp. 437–444. ISSN 0020-7403. Doi: https://doi.org/10.1016/0020-7403(84)90033-X.
5. Dilman, V. L., Ostsemin A. A. O vliyanii dvuhosnosti nagrujeniya na nesuschuyu sposobnost trub magistralnyih gazonefteprovodov Izv. RAN. Mehanika tverdogo tela, 2000. No. 5, pp. 179–185. [Іn Russian].
6. Dilman, V. L., Ostsemin, A. A. O potere plasticheskoy ustoychivosti tonkostennyih tsilindricheskih obolochek. Problemyi mashinostroeniya i nadejnosti mashin. 2000. No. 5, pp. 50–57. [Іn Russian].
7. Degtyarev V. P. Deformatsii i razrushenie v vyisokonapryajennyih konstruktsiyah. M.: Mashinostroenie, 1987. 105 p. [Іn Russian].
8. Kollinz Dj. Povrejdenie materialov v konstruktsiyah. Analiz, predskazanie, predotvraschenie. M.: Mir, 1984. 624 p. [Іn Russian].
9. Updike D. P., Kalnins A. Tensile plastic instability of axisymmetric pressure vessels. ASME. J. Pressure Vessel Technol, 120 (1), February 1998. Рp. 6–11. Doi: https://doi.org/10.1115/1.2841888.
10. Zhu, Xian-Kui & Leis, Brian. (2011). Evaluation of burst pressure prediction models for line pipes. International Journal of Pressure Vessels and Piping – INT J PRESSURE VESSELS PIPING. P. 89. Doi:10.1016/j.ijpvp.2011.09.007
11. Law, M. (2005). Use of the cylindrical instability stress for blunt metal loss defects in linepipe. International Journal of Pressure Vessels and Piping, 82 (12), 925–928. Doi:10.1016/j.ijpvp.2005.04.002.
12. Kozbur H. Prediction technique for thin-walled cylindrical tubes boundary state. Scientific Journal of TNTU. Tern: TNTU, 2019. Vol. 94. No. 2. P. 145–155. (Mathematical modeling. Mathematics). URL: https://doi.org/10.33108/visnyk_tntu2019.02.145.
13. Kozbur H. Method of predicting necking true stress in a thin-walled tube under a complex stress state. Strojnícky časopis. Journal of Mechanical Engineering. 2020. No. 70 (2), 101–116. URL: https://doi.org/ 10.2478/scjme-2020-0024
14. Kaminskiy A. A., Bastun V. N. Deformatsionnoe uprochnenie i razrushenie metallov pri peremennyih protsessah nagrujeniya. K.: Nauk.dumka, 1985. 168 p. [Іn Russian].
15. Lebedev A. A., Kovalchuk B. I., Giginyak F. F., Lamashevskiy V. P. Mehanicheskie svoystva konstruktsionnyih materialov pri slojnom napryajennom sostoyanii. Pod red. akademika NAN Ukrainyi A. A. Lebedeva. Kiev: Izdatelskiy dom “In YUre”, 2003. 540 p. [Іn Russian].