多晶金属材料动态力学行为的多尺度位错动力学塑性模型

The complex interactions of the evolution of microstructure and dislocations with its influence on plastic deformation induced by multiscale microscopic mechanisms, as well as micro/meso-mechanical modeling for metallic materials, is currently one of the hot research issues in the field of plastic mechanics. The micro-macro characterization and analysis of microstructure of TWIP steel after plastic deformation process is conducted at dynamic strain rates to reveal the interactions of grain boundaries, twinning boundaries with dislocations under dynamic conditions. Based on the discrete dislocation dynamics theory, the complex interactions of dislocation reactions, twinning boundaries, fast moving of short range dislocations and its inertial force are considered to establish a multiscale model which coupling DDD with CPFE via the transmission between discrete dislocations and statistical dislocations. Furthermore, the procedure for simulation and analysis will be developed and implemented based on the implicit algorithm. According to the proposed multiscale model, the evolution law to represent the influence of strain rate and grain size on microstructure and the evolution of macroscopic response will be analyzed and explained. It is important for this project to develop the multiscale modeling approaches for polycrystalline materials under dynamic conditions. This proposed multiscale modeling will lay a significant foundation to accurately simulate the microstructural evolution and to provide a theoretical guidance for optimizing microstructural design, furthermore promoting the material mechanical properties.

金属在位错与各种微结构复杂作用下的塑性变形机理及微细观力学建模是目前塑性力学领域的研究热点之一。本项目拟结合典型TWIP钢高应变速率条件下塑性变形过程的宏微观实验，研究揭示动态条件下晶界、孪晶界与位错交互作用机理；引入孪晶界与位错反应、位错短程剧烈运动及其惯性力的描述，建立基于离散位错与统计位错传递的耦合DDD-CPFE多尺度塑性模型并开发模拟程序；应用于分析并掌握TWIP钢应变率、晶粒尺寸等对微结构演化及其宏观力学响应的影响规律。本项目的意义在于拓展多尺度塑性建模理论，为更精细地模拟微结构的演化奠定基础，并为优化和设计微结构以改善材料力学性能提供理论依据。

多晶体金属动态位错动力学模型对于阐述其在复杂作用下的变形机理有着重要研究意义，实现动态条件下金属力学行为和性能的精确预测需迫切解决动态条件下位错与晶界、孪晶界交互作用机理及其多尺度表征这一基本科学问题。本项目以TWIP钢动态变形条件下位错与晶界、孪晶界相互作用为切入点，结合SHTB动态冲击实验分析了高应变速率下的位错组态与晶界、孪晶界的相互作用机制；发展了考虑“位错流”的三维离散位错动力学（3D-DDD）模型和考虑位错密度和应变率的二维离散位错塑性（2D-DDP）模型；建立了一种描述高应变率下多晶塑性变形的多尺度模型，揭示了动态高应变速率下各种微结构相互作用及其演化规律。取得的主要进展为：（1）典型TWIP钢多晶体材料动态高应变速率实验揭示了材料随动态应变的孪晶体积分数演化规律，阐述了各应变阶段位错滑移和孪晶、孪晶界的相互作用机理，确定了高应变速率下绝热温升对滑移和孪生演化的影响。（2）考虑孪晶、晶界与位错的相互作用，引入孪晶界-位错反应及其拓扑反应准则，建立了耦合孪晶的多晶三维离散位错动力学（3D-DDD）模型，该模型描述了位错间相互作用、位错反应等微观机制演化晶界位错反应及演化过程，定量分析了塑性变形过程中孪晶对流动应力的贡献。（3）基于位错运动的形核、增殖、湮灭等位错反应，引入位错均匀形核和惯性效应机制，建立了高速变形条件二维离散位错动态塑性（2D-DDP）模型，分析了亚微米尺度晶体冲击塑性变形行为，确定了孪晶形核是存在完全位错的扩展；（4）考虑应变率对层错孪晶和流动应力的影响，建立了耦合位错源和位错源激活准则的2D-DDP动态本构模型，得到了应变初始阶段，应变硬化的应变速率敏感性为-192.90 MPa，而在应变后期为-67.39 MPa；确定了位错增殖速率随应变速率降低的演化规律。本项目的意义在于拓展多晶材料多尺度塑性建模理论，为多晶材料极端条件使用性能预测提供理论依据。