基于流变学理论的相变诱导塑性TRIP钢的本构模型研究

This project based on rheology、elastic-plastic theory and micromechanics built uniform rheological constitutive model of transformation-induced plasticity (TRIP) steel for the extreme lack of research on constitutive equation of solid transformation materials during deformation. Firstly, the effects of different phase in TRIP steel like ferrite(soft phase)、 martensite(hard phase) and retained austenite(metastable phase) on the parameters of macroscopic mechanical properties were investigated. Secondly, this paper using the correlation of micromechanics and macroscopic rheology as a bridge studied the work hardening ability induced by transformation from retained austenite to martensite to determine the construct and parameters of elastic、plastic and viscous fluid in the constitutive model during plastic deformation. Lastly, rheological constitutive equations were deduced at different stage of deformation. One dimensional rheological constitutive equations is spreaded to three dimensional state of stress based on the Tensor theory. The relationship of generalized stress relaxation、generalized creep fluid stress、strain and parameters of forming process was analyzed by the model of rheological constitutive equation, which revealed the behavior of work hardening and spring back and also enriched models of constitutive equation of solid transformation material. The establishment of constitutive equation of TRIP steel was beneficial for the reduce of crack and spring back and the increase in finishing product rate.

由于目前对具有固态相变材料本构方程的研究极其匮乏，本项目基于流变学、弹塑性理论，结合微细观力学建立变形过程中具有相变诱发塑性TRIP钢统一的流变学本构模型。首先研究了TRIP钢中铁素体（软相）、马氏体（硬向）及残余奥氏体（亚稳相）等各相对宏观物性参数的影响；然后再研究塑性变形过程中残余奥氏体向马氏体转变引起的应变硬化规律，从而以微细观力学与宏观流变学内在联系为桥梁，确定流变学本构模型中的弹性、塑性及粘性体的结构及参数；推导出TRIP钢成形过程中不同阶段的流变学本构方程，应用张量理论,将单向流变学本构方程扩展到多向应力状态。分析本构模型在广义应力松弛、蠕变下的行为，揭示与描述在成形过程中的加工硬化、卸载后的回弹行为规律，丰富和发展了具有固态相变材料本构模型的研究。有利于减少TRIP钢在成形过程中的开裂，回弹严重等现象，提高了相变诱发塑性TRIP钢成形的成材率。

TRIP钢是一种先进高强汽车钢，具有优良的综合力学性能，目前对具有固态相变材料本构方程的研究极其匮乏。本申请课题基于流变学理论、弹塑性理论，结合微观力学建立变形过程中具有相变诱发塑性TRIP钢统一的流变学本构模型。首先根据TRIP钢组织中各相的在变形过程中的特点，建立了流变学本构模型。对试验钢的蠕变和松弛性能进行研究，对一维状态蠕变和松弛条件下的本构方程进行求解，利用张量理论将单向流变学本构方程扩展到多向应力状态。利用XRD、EBSD、SEM等手段研究了微观组织转变与弹性模量和粘性系数的关系，此外对TRIP钢的非弹性回复行为以及相变诱导塑性钢的粘塑性行为进行分析。利用双向拉伸机和板材成形机对TRIP钢的成形性能进行了研究。最后将建立的本构方程嵌入到有限元软件中，对成形过程进行模拟仿真并与实际成形实验进行对比。通过对本构模型以及成形性能的研究，揭示与描述在成形过程中的加工硬化、卸载回弹行为规律，丰富了具有固态相变材料本构模型的研究，有利于提高相变诱发塑性TRIP钢成型的成材率。