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To describe the uniaxial mechanical behavior of 316LN stainless steel more accurately, a polycrystalline cyclic plasticity constitutive model is constructed based on the Ahmadzadeh-Varvani (A-V) kinematic hardening rule in the framework of the rate‑dependent crystal plasticity theory. The constitutive model is implemented to the finite element software ABAQUS through the UMAT, and a two‑dimensional polycrystalline finite element model is established through Voronoi diagrams. And then the deformation behavior of 316LN stainless steel is simulated under different loading rates, strain cycles and asymmetric stress cycles, respectively. The simulated results compared with the experimental data show that under the uniaxial tensile condition, the stress errors of both fluctuate around±0. 9%, and the maximum stress error is only 1. 9%; under the strain cycle condition, the maximum stress error between the two appears in the 5th cycle, with 11. 4% and 12. 2% errors in the tensile and compression phases, respectively, and 7. 4% and 7. 9% errors in the tensile and compression phases, respectively, after cycle stabilization. Under the asymmetric stress cycle condition, the errors of both mainly appear in the hysteresis loop width, the simulated hysteresis loop width is narrower, but the error of the hysteresis loop evolution trend is smaller. [ABSTRACT FROM AUTHOR]

In order to better describe the uniaxial ratcheting behavior of Z2CDN18.12N austenitic stainless steel, the Abdel-Karim-Ohno model was improved under the framework of the unified viscoplastic cyclic constitutive theory. By introducing a plastic strain memory surface into the isotropic hardening rule, the model parameters were determined. Further, the Abdel-Karim-Ohno model and the improved Abdel-Karim-Ohno model were used to predict the uniaxial ratcheting effect behavior of Z2CDN18.12N austenitic stainless steel at the room temperature. The influences of mean stress, stress amplitude, stress rate and loading history on the uniaxial ratcheting strain of Z2CDN18.12N austenitic stainless steel were studied by the two models, respectively. The uniaxial ratcheting strain level increased with the increasing mean stress and stress amplitude, decreased with the increasing stress rate, being more sensitive to the lower stress rate, and the loading history had great influence on the ratcheting behavior. Comparison of the prediction results of the two models with the experimental data proved the effectiveness of the improved model. [ABSTRACT FROM AUTHOR]

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Taking advantage of the EUM-25 K20 tension-torsion fatigue testing machine by CARE,the cryogenic uniaxial ratcheting tests were carried out for the S30408 specimens with and without weld,and with 0%,8%,and 12% pre-strains at110 K. It is shown that ratcheting behavior of specimens with and without weld is closely related to mean stress,amplitude stress and loading history. Because of the softening effect of a small amount of ferrite in weld metal,the initial ratcheting strain of weld specimen and ratcheting strain of weld specimen under small cyclic stress is larger than that of base metal. However,with the increase of plastic deformation,the higher content of alloying elements in weld metal has a more obvious strengthening effect,which makes the subsequent ratcheting strain of weld specimens with a certain number of cycles smaller than that of base metal under larger cyclic stress. The ratcheting strain of specimens with and without weld decreases with the increase of the pre-strain at cryogenic temperature. The accumulation of ratcheting strain can be completely restrained by pre-strain at a small cyclic stress level. S30408 is rate-dependent material at 110 K,and ratcheting strain decreases with the increase of loading rate.