Constitutive Model of TRIP-Type Duplex Stainless Steel Under Symmetrical Strain Cyclic Loading Considering the Effect of Martensitic Transformation

During the transformation process, the plasticity and strength of TRIP-type duplex stainless steel are simultaneously enhanced through strain-induced martensitic transformation, which triggers the TRIP effect. Under cyclic loading conditions, the material exhibits both cyclic softening and hardening, affecting its mechanical response. Symmetric strain cycling tests were performed on TRIP-type duplex stainless steel (Fe–19.3Cr–2Ni–2.7Mn–2Si) with strain amplitudes ranging from 0.5 to 1.3 pct, at intervals of 0.2 pct. For each strain amplitude, in-situ measurements of the α ′ martensitic transformation were conducted using a ferrite measurement instrument. A kinetic model was developed to describe the relationship between martensitic transformation and cumulative plastic strain under cyclic loading conditions. Subsequently, a constitutive model for symmetric strain cycling was established by integrating the Ohno–Wang I work hardening model with the Voce isotropic hardening model. Numerical analysis was performed utilizing the UMAT subroutine in the finite element software ABAQUS and a parameter optimization program was created using ISight software to refine the initial model parameters. Finally, a comparative analysis of the strain hysteresis energy, based on experimental and simulated hysteresis curves, was conducted. The results reveal a strong consistency between the numerical simulation results and experimental data, with the best fit occurring at a strain amplitude of 1.1 pct, which exhibited a relative error of only 3.0 pct. The relative errors for strain amplitudes of 0.9 and 1.3 pct were similarly limited to 7 pct, while those for strain amplitudes of 0.5 and 0.7 pct were comparatively larger. This discrepancy can be attributed to the fact that the initial model parameters were derived and optimized at the 1.1 pct strain amplitude, whereas the martensitic transformation at 0.5 and 0.7 pct strain amplitudes was diminished, thus producing a less significant effect.