Variation Coefficient of Metal Yield Strength in New and Long-Used Building Structures

Introduction. Non-destructive methods are most often used to assess the condition of the metal structure. Dangerous stress is determined by the value of the yield strength. This approach has weaknesses. This is, firstly, the probabilistic nature of the methodology (the minimum value of the indicator obtained during laboratory tests is entered into the regulatory and technical documentation). Secondly, the limitations on the number of samples should be overcome. Thirdly, the different duration of operation causes a significant difference in the mechanical characteristics of the metal, which to a certain extent complicates the long-term prediction of the condition of the structure. The presented work is designed to solve these problems within the framework of the study of new and long-operated facilities in the Rostov region. The scientific research objective is to analyze fatigue changes and determine possible degradation of the metal.

Materials and Methods. The mechanical characteristics of the material under study were reliably described by the Weibull distribution law through the shear parameter (the minimum possible value of the characteristic) and the shape parameter (magnitude dispersion). For scientific research, the indentation method based on a modified Rockwell hardness estimation method was used as part of the work. A conical indenter was embedded in the surface, then the reaction of the metal was analyzed. To implement the method, an analog-to-digital converter and a laptop were used. For correlation analysis, intermediate characteristics were taken: depth, maximum and minimum velocities, maximum and minimum acceleration of cone insertion. A correlation was established with the mechanical characteristics determined by standard tensile and hardness tests of the metal.

Results. Objects with zero and long-term operation were studied. The measurements were carried out in a warehouse, production site, stadium, bridge, Palace of Sports and on a power line support. From the group of new and used structures, one was selected for a detailed fixation of the values of yield strength. So, before the start of operation, the condition of three metal trusses of the warehouse was analyzed. It was established that the lowest value of the yield strength here was 240 MPa, the maximum was 345 MPa. On the power transmission line poles, which have been in operation for 43 years, the lowest recorded value of the yield strength was 235 MPa, the highest was 384 MPa. For each of the six structures, the minimum and average distribution of the metal yield strength values was given, and the coefficients of variation of this indicator were given. The recorded values were summarized in the form of a table. The average values for all new and used designs were calculated. Graphically presented data illustrate the growth of the coefficients of variation of the yield strength with increasing service life.

Discussion and Conclusion. A comparative analysis of the obtained values of the yield strength of building structures of approximately the same strength class suggests that the influence of operating time can both increase and decrease the studied indicator. At the same time, long-term operation is a factor that increases the average value of the coefficient of variation. To monitor the strength capabilities of the structure, it is advisable to use a non-destructive method, selectively monitoring the mechanical characteristics of the elements before and during operation.

1. Dotsenko ER, Myndyuk VD, Karpash MO. Otsenka izmenenii mekhanicheskikh svoistv metalla magistral'nykh truboprovodov s ispol'zovaniem metodov nerazrushayushchego kontrolya. In: Trudy VII mezhdunar. nauch.-tekh. konf. po nadezhnosti i bezopasnosti magistral'nogo truboprovodnogo transporta. Novopolotsk: 2011. P. 143–145. URL: https://www.psu.by/images/stories/nauka/tezis_7mntk.pdf

2. Gorynin IV, Timofeev BT. Degradation of properties of structural materials at long time influence of operational temperatures. Voprosy Materialovedeniya. 2011; (1(65)):41–59.

3. Demina Yu. Vliyanie dlitel'noi ekspluatatsii i khraneniya na mekhanicheskie svoistva i mekhanizmy razrusheniya konstruktsionnykh materialov. Avtoref. dis. kand. tekh. nauk. Moscow; 2014. 26 p.

4. Lubenskii SA, Yamnikov SA. Vliyanie dlitel'nosti ekspluatatsii na svoistva metalla trub magistral'nykh truboprovodov. Issues of risk analysis. 2013;10(1):58–63.

5. Bykov IYu, Birillo IN, Kuzbozhev PA. Study of characteristics of mechanical properties of gas-distributing station pipes metal after long-term operation. Oil and Gas Studies. 2015;(2):86–91. https://doi.org/10.31660/0445-0108-2015-2-86-91

6. Bolshakov AM. Analiz razrusheniya i defektov v magistral'nykh gazoprovodakh i rezervuarakh Severa. Gas Industry. 2010;(5(646)):52–53.

7. Syromyatnikova AS. Degradation of physical and mechanical condition of gas pipeline metal during long operation at low climatic temperatures. Tambov University Reports. Series Natural and Technical Sciences. 2013;18(4-2):1746–1747.

8. Nikiforchin GN, Tsirul'nik OT, Zvirko OI, Gredil' MI, Voloshin VA. Degradation of the physical and mechanical properties of steels in long-run gas pipelines. Industrial Laboratory. Diagnostics of Materials. 2013;79(9):48–55.

9. Aneesh Bangia, Raghu V Prakash. Energy Parameter Correlation of Failure Life Data between Cyclic Ball Indentation and Low Cycle Fatigue. Open Journal of Metal. 2012;2(1):31–36. https://doi.org//10.4236/ojmetal.2012.21005

10. Collin M, Parenteau T, Mauvoisin G, Pilvin P. Material Parameters Identification Using Experimental Continuous Spherical Indentation for Cyclic Hardening. Computational Materials Science. 2009;46(2):333–338. https://doi.org//10.1016/j.commatsci.2009.03.016

11. Gorev VV, Uvarov BYu, Filippov VV, Belyi GI, Endzhievskii LV, Krylov II, et al. Metallicheskie konstruktsii. In 3 vol. Vol. 1. Elementy stal'nykh konstruktsii. Moscow: Vysshaya shkola; 1997. 527 p.

12. Pullin R, Holford KM, Lark R, Eaton MJ. Acoustic emission monitoring of bridge structures in the field and laboratory. Journal of Acoustic Emission. 2008;26:172–181.

13. Anastasopoulos AA, Kourousis DA, Cole PT. Acoustic emission inspection of spherical metallic pressure vessels. In: The 2nd International Conference on Technical Inspection and NDT (TINDT2008). Iran, Tehran; 2008. 10 p. URL: http://www.ndt.net/article/tindt2008/papers/177.pdf (дата обращения: 28.05.2023).

14. Pollock, A. Probability of detection for acoustic emission. Journal of acoustic emission. 2007;25:231–237.

15. Polyzos D, Papacharalampopoulos A, Shiotani T, Aggelis DG. Dependence of AE Parameters on the Propagation Distance. Journal of acoustic emission. 2011;29:57–67.

16. Gongtian Shen, Zhanwen Wu. Study on Spectrum of Acoustic Emission Signals of Bridge Crane. Insight — Non-Destructive Testing and Condition Monitoring. 2010;52(3):144–148. URL: http://www.ndt.net/article/ecndt2010/reports/1_07_08.pdf

17. Dirk Aljets, Alex Chong, Wilcox SJ, et al. Acoustic emission source location in plate-like structures using a closely arranged triangular sensor array. Journal of acoustic emission. 2010;28:85–98.

18. Pullin R, Baxter M, Eaton M, Holford KM, Evans S. Novel acoustic emission source location. Journal of acoustic emission. 2007;25:215–223.

19. Wilson JW, Liu Jun, Karimian N, Davis CL, Peyton AJ. Assessment of microstructural changes in Grade 91 power station tubes through permeability and magnetic Barkhausen noise measurements. In: 11th European Conference on Non-Destructive Testing (ECNDT 2014). Czech Republic, Prague; 2014. URL: https://research.manchester.ac.uk/en/publications/assessment-of-microstructural-changes-in-grade-91-power-station-t

20. Hongping Jin, Wenyu Yang, Lin Yan. Determination of residual stresses and material properties by an energy-based method using artificial neural networks. Proceedings of the Estonian Academy of Sciences. 2012;61(4):296–305. https://doi.org//10.3176/proc.2012.4.04

21. Clausnera А, Richterb F. Fundamental limitations at the determination of initial yield stress using nanoindentation with spherical tips. European Journal of Mechanics. 2016;58:69–75. https://doi.org/10.1016/j.euromechsol.2016.01.009

22. Belenkii DM, Nedbailo AA. Sposob opredeleniya mekhanicheskikh kharakteristik i fizicheskogo kriteriya podobiya prochnosti materiala detali. Patent RF, No. 2279657. 2006. 12 p. URL: http://allpatents.ru/patent/2279657.html

23. Beskopylnyi AN, Veremeenko AA, Vernezi NL. Programma dlya EVM № 2015610650 Vektor 2015. Certificate of the Russian Federation on state registration, No. 2014661747. 2015. URL: https://onlinepatent.ru/software/2015610650/

24. Vernezi NL, Veremeenko AA, Valdman DS. Research of strength characteristics of metal fixture of the wooden case of the river mooring. Engineering journal of Don. 2015;(3). URL: http://ivdon.ru/ru/magazine/archive/n3y2015/3231

25. Belen’kii DM, Vernezi NL, Cherpakov AV. Changes in the mechanical properties of butt welded joints in elastoplastic deformation. Welding International. 2004;18(3):213–215. https://doi.org/10.1533/wint.2004.3268