Numerical Simulation of Non-proportional Cyclic Hardening Characteristics of 316L Stainless Steel

The strain-controlled tensile and torsional fatigue tests at room temperature were carried out on 316L stainless steel under the equivalent strain range of 0.7%, and the cyclic hardening characteristics of proportional strain path (uniaxial path and proportional path) and non-proportional strain path (cruciform path and circular path) were discussed. The cyclic characteristics under each path were simulated by AF-OW dynamic hardening model combined with Chaboche isotropic hardening criteria and an improved model by embedding non-proportionality into the isotropic hardening criteria, and the experimental verification was carried out. The results show that 316L stainless steel showed cyclic hardening phenomenon in the early cycle under each path. The cyclic hardening rates were 5.2%, 4.5%, 38.2% and 44.6% under uniaxial path, proportional path, cruciform path and circular path, respectively. Under the non-proportional strain path, the steel showed obvious additional strengthening. The AF-OW model combined with the isotropic hardening criterion could accurately simulate the cyclic hardening characteristics under uniaxial and proportional paths; the simulation did not agree well with the test results under cruciform path and circular path, and the maximum relative errors between the simulated normal stress-normal strain hysteresis loop and test results were both larger than 20%. The modified model could accurately describe the cyclic hardening characteristics under the cruciform path and circular path. The maximum relative errors of the normal stress-normal strain hysteresis loop were 1.3% and 3.2%, and the relative errors of the maximum equivalent peak stress were 1.9% and 1.2% under the cruciform and circular paths, respectively.