PSI - Issue 23

I.A. Volkov et al. / Procedia Structural Integrity 23 (2019) 316–321 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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State University, in the conditions of hard (strain-controlled) uniaxial tension compression at ambient temperature. The testing program consists of two blocks including monotonic and cyclic loading modes by Kazakov et al (1999): in the first block, the specimen is loaded in compression to the strain of 11 0,01 е  , and then in tension to the strain of 11 0,05 е  ; in the second block, nonsymmetrical hard cyclic loading is realized with the strain range of ( ) ( ) 11 11 11 0,01 е е е       up to failure ( 850 f N  ). At this stage, the setting of the plastic hysteresis loop takes place, and after the 500-th cycle the loop becomes practically symmetrical. The results of numerical analysis of the processes of cyclic plastic deformation and fatigue damage accumulation under hard (controlled strains) block-type nonsymmetrical low-cycle loading are given in the Tables below by Volkov et al (2016). Tables 1 – 3 summarize the main physical-mechanical characteristics and material parameters of the MDM model for steel 12Х18Н9, determined experimentally by Volkov, Коrotkikh (2008) or Volkov, Igumnov (2017), used in computations. Table 1. Physical-mechanical characteristics and parameters of the MDM model of steel 12Х18Н9 . K G o p C , ( МPа ) 1 g , ( МPа ) 2 g 3 g , ( МPа ) 4 g 1 k , ( МPа ) 2 k 1 a 2 a a W f W 165277 76282 190 24090 286 800 2 10000 0,2 5 0 0 800 Table 2. Cyclic hardening modulus 1 max ( ) Q  (МPа) of steel 12Х18Н9 ( 2 0 Q  ). 1 Q , МPа 190 205 210 215 220 225 225 max  , МPа 0 20 40 60 80 100 120 Table 3. Monotone hardening modulus 1 q (МPа) of steel 12Х18Н9 ( 2 0 q  ). 1 q , МPа -5000 -4471 -4188 -3859 -2460 -182 888 1531 1274 913 913 913  0 0,002 0,004 0,006 0,008 0,01 0,015 0,02 0,03 0,04 0,05 0,06 Fig. 1 depicts the process of deformation of steel 12 Х 18 Н 9 in the second loading block (the 500-th cycle). Both qualitative and quantitative agreement of the experimental and numerical data can also be observed. Fig. 2 shows the history of mean stress of the cycle, ( ) 11 m  , in the process of cyclic loading in the second block. It is evident that the used model of thermo-plasticity qualitatively and quantitatively describes the landing process. Fig. 3 shows fatigue life curve of the 12 Х 18 Н 9 stainless steel under hard symmetric cyclic loading. The solid line corresponds to the experimental curve; the full symbols show the numerical results obtained using the MDM model by Volkov, Коrotkikh (2008) or Volkov, Igumnov (2017). Comparison of the numerical and experimental results indicates that the MDM model developed in the present paper describes processes of fatigue life of polycrystalline structural alloys under block-type nonsymmetrical low-cycle loading qualitatively and accurately enough for engineering purposes. 4. Conclusions To describe fatigue life of polycrystalline structural alloys under block-type nonsymmetrical low-cycle loading, the reliability of definition relations of MDM has been assessed by comparing the results of numerical experiments with the test data on plastic deformation and damage accumulation in the 12 Х 18 Н 9 stainless steel under block-type nonstationary nonsymmetrical low-cycle loading, which corroborated the adequacy of modeling with utilization of experimentally determined material parameters. Acknowledgements The work is financially supported by the Federal Targeted Program for Research and Development in Priority Areas of Development of the Russian Scientific and Technological Complex for 2014-2020 under the contract No. 14.578.21.0246 (unique identifier RFMEFI57817X0246).