Ratcheting Constitutive Model Description Of Nuclear Stainless Steel And Ratcheting Effect Of Pressurized Pipe

Nuclear energy is widely concerned as a kind of clean energy.The safety,reliability,and fatigue life assessment of pressurized vessels and pipes in nuclear power plants has become a hot topic for researchers all over the world.These equipment are working a long time in a bad environment such as high-pressure and high-temperature cyclic loading,it is inevitable that ratcheting effect may occur.The ratcheting effect can reduce the fatigue life or cause large deformation of the structures/components,which is one of the important problems that must be considered in the practical engineering structure design.The research on the ratcheting constitutive model of material/structure is of great significance for the prediction of the ratcheting effect of material/structure.Take Z2CND18.12N austenitic stainless steel for the primary loop pipe in nuclear power plants as the object of this study,the influence of mean stress,stress amplitude,stress ratio,and loading history on ratcheting effect of Z2CND18.12N austenitic stainless steel is studied.The Ahmadzadeh-Varvani（A-V Ⅰ）model is modified and implemented by MATLAB and ABAQUS respectively,to predict uniaxial and multiaxial ratcheting effects of materials/structures.The main contents of the study are as follows:（1）Based on the incremental theory and Euler backward method,the A-V Ⅰ model is implemented by MATLAB and ABAQUS.The uniaxial tension,strain cycle,and the cyclic plastic behavior of the ratcheting effect of the material are simulated.（2）Based on the framework of the A-V Ⅰ model,the parameter γ₂ is modified.The Ramberg-Osgood（R-O）model and isotropic hardening rule are considered in the A-V Ⅰ model.The evolution of parameters γ₂ with cumulative plastic strain p is given in the study,an improved uniaxial A-V model is proposed.The results show that the predicted results of the improved uniaxial A-V model are in good agreement with the experimental data.The average error is less than 10%.（3）Based on the A-V model and the improved uniaxial A-V model,the ratcheting strain of Z2CND18.12N stainless steel is predicted by MATLAB and ABAQUS,respectively.The results show that the improved uniaxial A-V model can more accurately predict the uniaxial ratcheting strain of Z2CND18.12N stainless steel at room and high temperature.The effects of different mean stress,stress amplitude,stress ratio,and loading history on uniaxial ratcheting are also analyzed.The results show that the ratcheting strain increases with the increase of mean stress and stress amplitude,and the effect of the stress ratio on the ratcheting strain is not significant.（4）To overcome the difficulty of ratcheting strain rate control in the A-V Ⅱ model,the evolution of multiaxial parameter A with cumulative plastic strain p is introduced.The dynamic recovery term of the Hamidinejad-Varvani（A-V Ⅱ）model is modified,an improved multiaxial A-V model is proposed.Based on the improved multiaxial A-V model,the experimental data and predicted results of the multiaxial ratcheting effect of Z2CND18.12N stainless steel at room temperature and high temperature are simulated.The results show that the predicted results of the improved multiaxial A-V model are in good agreement with the experimental data.（5）The ratcheting effect of pressurized pipe is predicted by the improved multiaxial A-V model.The effects of internal pressure,bending moment,and loading path on the ratcheting effect are discussed.The results show that the ratcheting strain increases with the increase of internal pressure and bending loading,and the effect of load path ratcheting strain is very significant.