Experiment And Constitutive Model Study On Cyclic Deformation Of Medium Manganese TRIP Steel

Medium manganese TRIP steel is a typical representative of the third generation of advanced high-strength steels,with high strength and large elongation at the same time.In addition,it also has great advantages over other materials in terms of impact resistance,corrosion resistance and cost.At present,the advanced high-strength steel represented by TRIP steel is an important material in the lightweight design of the automobile industry,and it also has broad application prospects in the fields of national defense industry,railway transportation,and marine navigation.Compared with most traditional low-strength steels,TRIP steel is a multi-phase material.When it is deformed by external loads,it will transform from retained austenite to martensite,so that the material obtains higher strength and plasticity.,but at the same time,the mechanical behavior and microstructure changes of TRIP steel during deformation are more complicated than those of traditional low-strength steel.At the same time,TRIP steel will inevitably be subjected to cyclic loads during processing and actual service.Therefore,it is very necessary to carry out experimental research on the cyclic deformation behavior of TRIP steel to reveal its cyclic deformation characteristics.A cyclic plastic constitutive model of behavior,which has high scientific significance and engineering application value.The main work of this paper is summarized as follows:(1)The uniaxial strain cycling characteristics and ratcheting behavior of mediummanganese-aluminum-containing TRIP steel were systematically investigated at room temperature.The results show that the material has a slight cyclic softening phenomenon in the initial cycle stage,but soon enters the cycle stability stage.The larger the strain amplitude,the smaller the softening degree,and the overall softening rate does not exceed 4%;under different average stress loads,the evolution law of ratchet strain rate is similar,and they all maintain a non-zero constant from large to small.Under lower stress amplitude loads,the ratcheting behavior is similar to the ratcheting characteristics of cyclically stable metal materials.Under higher stress amplitude loads,the ratcheting strain will increase rapidly.That is to say,under different stress amplitude loads,its ratchet strain evolution exhibits two different characteristics.(2)Under the unified cyclic plastic constitutive framework,based on the experimental results and the research ideas of the existing models,the ratchet parameters related to the cumulative plastic strain and the step function are introduced into the kinematic hardening law,and the change of the ratchet parameters is controlled by the step function.Two different ratcheting strain rate evolutions are used to establish an improved cyclic plastic constitutive model.The method for determining the material parameters is given.The comparison between the model simulation results and the experimental results shows that the improved constitutive model can reasonably describe the cyclic deformation behavior of medium-manganesealuminum-containing TRIP steel.(3)The improved constitutive model was implement into the finite element program ABAQUS by user-subroutine UMAT.Based on radial method and back Eular integration,a new implicit stress integration algorithm was proposed.Simultaneously,a new expression of consistent tangent modulus was also derived.After verifying that the transplant is correct,the finite element simulation of the cyclic deformation behavior of the simple structure is carried out.The finite element calculation results of experimental structural components under different mesh densities show that the mesh density has little effect on the deformation prediction results of structural components,and the implicit stress integration algorithm is unconditionally stable.