TRIP钢多尺度晶体塑性本构模型及其高效数值算法研究

Accurate constitutive model and efficient algorithm are important factors in the simulation of TRIP steels' forming. TRIP steel has complex microstructures, and the investigations of finite deformation law and interactions between phases have been concerned by scholars all the time. This project considers TRIP steels' crystalline microstructures, and the TRIP phenomenon during the finite deformation process is studied by theoretical and numerical methods. Theoretical aspects: Based on crystal plasticity and thermodynamics, a constitutive model of retained austenite single crystal is presented by considering laminated martensitic microstructures. This study focus on the effects of properties and evolutions of laminated martensitic microstructures on the TRIP phenomenon during different temperatures and different stress states. The polycrystalline finite element computational model is presented by considering the effect of ferrite matrix. The effects of different loading paths, different grain sizes and different grain orientations on macroscopic mechanical properties of TRIP steels are also studied. Algorithm aspects: To reduce difficulties of numerical simulation resulting from non-linearity of governing equation, several important variables, reflecting plasticity slip and phase transformation, are transformed by discrete Fourier transformation. A high efficient algorithm combining discrete Fourier transformation with finite element method is founded using these transformed variables. This project will reveal the effect of microstructures on transformation induced plasticity, and the constitutive model is faster solved in metal forming, which can provide the scientific foundations for theory and algorithm in TRIP sheet metal forming.

准确的本构模型和高效的计算方法是TRIP钢成形仿真的关键因素。TRIP钢组织结构复杂，各相的变形规律及其相互间的作用关系一直为研究者所关注。本项目考虑TRIP钢各相的晶体结构，对变形中产生的相变诱导塑性现象进行理论研究和数值计算。理论方面：基于晶体塑性和热力学理论，考虑相变产生的马氏体层状微观结构，建立残余奥氏体的单晶本构模型。重点研究不同温度以及应力状态下层状微观结构的特性及其演化对TRIP效应的影响。考虑铁素体基体的影响，建立多晶有限元模型，分析不同加载路径，晶粒尺寸和取向等因素对材料宏观力学性能的影响。算法方面：对本构模型中描述塑性滑移和相变的关键变量进行离散傅里叶变换，降低控制方程非线性造成的数值计算困难，并结合有限元构建耦合算法，以提高计算的效率。本项目预期将揭示微观组织结构对相变诱导塑性的影响，并实现本构模型在成形计算中的快速求解，为TRIP钢成形仿真提供理论和算法上的依据。

本项目针对TRIP钢以及高熵合金等多晶体材料在不同加载条件下出现的相变诱导塑性和孪生诱导塑性现象进行了实验和数值计算分析。具体内容如下：. 1.多晶体材料三维微观组织表征建模：多晶体材料的晶粒取向，大小和形貌等微观组织特性决定了材料的宏观力学性能，基于Voronoi划分原理对单相以及多相材料构建了代表性体积单元作为后续数值计算的基础。同时，利用EBSD，TEM等测试技术对初始以及有限变形后多晶体材料微观结构演化的特点进行了定量的实验分析。. 2.多尺度本构模型的建立：基于晶体塑性理论，分别建立了考虑位错，孪生以及相变等主要塑性变形机制的本构模型，利用晶体塑性有限元定量计算了变形孪晶的形核、长大、以及马氏体体积分数演化等与位错滑移之间的相互作用关系，分析了导致材料强度以及塑性提升的原因。. 3.不同应变率效应和复合加载等工况研究：基于实验定量分析的位错密度，织构演化，孪晶体积分数等微观信息，结合建立的本构模型，对应变率敏感性、复杂的应力状态等进行了计算分析，揭示了微观结构特点与宏观塑性各向异性演化之间的关系。