Study of the effect of strain amplitude ratio at two-frequency cyclic loading

The operating modes of loading elements of machines and structures exhibit, as a rule, more complicated character of their loading cycles compared to sinusoidal used in the practice of calculations and experiments. It is noted that in a number of cases the actual conditions of load changing can be schematized by dual-frequency loading modes with superposition of the high-frequency component of the main workload attributed to the effects of vibrations, aero- and hydrodynamic impacts, regulation of the working process, etc. Testing of three steel samples which differ in their cyclic properties has shown that such two-frequency regimes lead to a decrease in the durability in comparison with single-frequency loading, equal in the amplitude of maximum stresses. This reduction depends on the parameters of the basic low-frequency and imposed high-frequency loads. Evaluation of this reduction can be performed both i) using the laws of summation of the damage expressed in the strain terms, and ii) using an analytical expression considered below, which includes calculated or experimentally determined durability for single-frequency loading with the maximum (total) amplitude of the effective stress and durability coefficient, characteristic of each type of material and determined by the ratio of amplitudes and hours of low- and high stresses. A computational-experimental analysis of the effect of the amplitude of low-frequency and superimposed high-frequency loading under two-frequency modes of stress change on the cyclic durability showed that the imposition of the high-frequency component of cyclic deformation on the main low-cycle loading process leads to a significant decrease in the cyclic durability, the level of the decrease correlates with the level of amplitudes and frequencies ratios of the summarized harmonic processes of load application.

1. Kogaev V. P. Strength calculations at variable in time stresses. — Moscow: Mashinostroenie, 1993. — 364 p. [in Russian].

2. Makhutov N. A. Structural strength, resource and engineering safety. In 2 parts. Part 1. Strength and resource criteria. — Novosibirsk: Nauka, 2005. — 494 p. [in Russian].

3. PNAE G-7-002–86. Rules and norms in nuclear energetics. Strength calculation norms for equipment and pipelines of nuclear engine installations. — Moscow: Énergoatomizdat, 1989. — 525 p. [in Russian].

4. Strength and safety problems of water-moderated power reactors. The series «Researches of stresses and strength of nuclear reactors». — Moscow: Nauka, 2008. — 446 p. [in Russian].

5. Carrying capability of steam generators of water-moderated power reactors. The series «Reseacches of stresses and strength of nucleac reactors». — Moscow: Nauka, 2003. — 440 p. [in Russian].

6. Makhutov N. A. Safety and risks: system reseacches and developments. — Novosibirsk: Nauka, 2017. — 724 p. [in Russian].

7. Safety of Russia. Legal, social-economic and scientifically-engineering aspects. Management of service resource for highly risks objects. Functioning and development of complex economic, technical, power, transport systems, communication systems and service lines. Part 1. Theoretical bases of safe functioning of complex technical systems. — Moscow: MGF «Znanie», 1998. — 448 p. [in Russian].

8. Safety of Russia. Legal, social-economic and scientifically-engineering aspects. Management of service resource for highly risks objects. Functioning and development of complex economic, technical, power, transport systems, communication systems and service lines. Part 2. Maintenance of safe functioning of complex technical systems at different stages of life cycle. — Moscow: MGF «Znanie», 1998. — 416 p. [in Russian].

9. Stress-strain states of liquid-fuel rocket engines. The series «Reseacches of rocket engines stresses and strength». — Moscow: Nauka, 2013. — 646 p. [in Russian].

10. Gadenin M. M. Assessing the effect of loading on the terms of attaining the ultimate state of stocks and the assignment of the reserves / Zavod. Lab. Diagn. Mater. 2013. Vol. 79. N 10. P. 65 – 70 [in Russian].

11. Gadenin M. M. Damage and life-time reseacch of the structures in conditions of single- and two-frequency loading modes using strain and energy approaches / Zavod. Lab. Diagn. Mater. 2017. Vol. 83. N 6. P. 44 – 52 [in Russian].

12. The state equations at a low-cycle loading. — Moscow: Nauka, 1981. — 245 p. [in Russian].

13. Gadenin M. M. Peculiarities of strains evolution and damages accumulation at two-frequency low-cycle loading and heightened temperatures / Mashinovedenie. 1976. N 1. P. 69 – 77.

14. Makhutov N., Romanov A., Gadenin M. High temperature low-cycle fatigue resistance under superimposed stresses at two frequencies / Fatigue of Engineering Materials and Structures. 1979. Vol. 1. N 3. P. 281 – 285.

15. Gadenin M. M. Resistance change to low-cycle deformation and fracture for two-frequency process of a loading / Abstracts of the XIII scientific conference «Problems of reliability and durability of structural elements in the engineering and construction industry». — Sverdlovsk: Sverdlovskii oblastnoi Sovet NTO, 1978. P. 5 – 6 [in Russian].

16. Gadenin M. M. Thermal stress and low-cycle fatigue. — Moscow: Mashinostroenie, 1974. — 344 p. [Russian translation].

17. Gadenin M. M. Kinetics of strains and damages accumulation as a result of elastoplastic loading cycle form / Zavod. Lab. Diagn. Mater. 2008. Vol. 74. N 10. P. 61 – 65.