316L不锈钢随动强化模型改进研究

本文对316L不锈钢进行了单轴与多轴非比例路径下的应力控制棘轮试验，考察了应力幅值、平均应力和加载历程对棘轮特性的影响。同时进行了应变控制循环试验以研究材料的应力松弛特性。试验结果表明轴向棘轮效应在对称剪切荷载下效果明显,同时棘轮应变随应力幅值和平均应力的增加而增加。研究了Chen-Jiao随动强化模型与Jiang-Sehitoglu随动强化模型采用的单轴与多轴参数对背应力分量增量方向的影响，将Chen-Jiao模型中的多轴系数替换为界面饱和率，并在此基础上引入新的参数对塑性模量系数进行修正，计算结果表明修正后的模型能提升应力控制下多轴棘轮的预测精度，并能很好的预测应力松弛现象，表明了新模型的正确性与有效性。

The improvement of kinematic hardening rule of 316L stainless steel

316L stainless steel can produce kinematic hardening effect under cyclic loading, resulting in the accumulation of ratcheting strain and thus greatly reducing the fatigue life of the material. The generation of kinematic hardening can be considered as the movement of the yield surface in the stress space during the loading process, which leads to the asymmetry of the yield strength in tension and compression. Based on the results of cyclic loading tests, many kinematic hardening rules have been proposed. Some rules are suitable for the simulation of uniaxial cycle loading case. However, for the multiaxial non-proportional variable amplitude histories, the calculation results of existing models have large overestimation compared with test results. In this work, the evolution of back stress of several classic kinematic hardening models are studied. And the moving direction of back stress is discussed as well. The stress-controlled ratcheting experiments of 316L stainless steel under uniaxial and multiaxial loading paths are conducted to verify the influences of mean stress, stress amplitude and loading history. The strain-controlled cyclic loading is also conducted to verify the stress relaxation. It is demonstrated that the axial ratcheting is obvious under symmetrical shear loading path, and the ratcheting strain increases with the increasing stress amplitude and mean stress. The influences on the direction of back stress component increment, which are induced by the uniaxial and multiaxial parameters in Chen-Jiao and Jiang-Sehitoglu kinematic hardening rules, are discussed. Based on the experimental results, Chen-Jiao’s kinematic hardening rule is improved by replacing the multiaxial parameter with a surface saturated ratio, and a new parameter is introduced for correcting the plastic modulus coefficients. The calculated results show that the improved rule predicts a similar mean stress with Chen-Jiao’s rule, and coincides with experimental data much better than Chen-Jiao’s kinematic hardening rule under multiaxial loading case, which also proves the improvement is correct and valid.