CDD as a Mesoscopic Field Theory: Dynamic Closure and Multiphysics Extension

在上一报告期内发展起来的CDD是一种介观场理论，它根据类密度场变量描述位错微观结构的演变。由于其与经典位错连续介质理论的关系，CDD可以自然地获得单位错尺度以上的介观内应力。同时，该理论需要动态闭合关系，该关系将局部位错速度表示为位错场的非线性和一般的非局部泛函。在物理方面，这些闭合关系提供了连续环境中个体错位相互作用的平均表示。本项目的第一行研究采用了一种全新的方法来解决动态闭合问题，即脱离常用的现象学近似，转而使用数据驱动的研究范式，根据从大规模离散位错动力学模拟中提取的数据对一般非线性函数进行参数化。该项目的第二项研究将弥合CDD和实验之间的差距，并展示我们模型的直接技术相关性：在多物理场方法的意义上，将CDD与其他介观场理论耦合，可以预测和分析先进合金系统中缺陷和相微观结构的耦合演变。为了描述伽玛/伽玛合金中位错蠕变和定向粗化的耦合应力驱动动力学，将用相场方法来证明CDD的耦合。

CDD as developed in the previous reporting period is a mesoscopic field theory which describes dislocation microstructure evolution in terms of density-like field variables. Due to its relations with the classical continuum theory of dislocations, CDD gives natural access to mesoscopic internal stresses above the single-dislocation scale. At the same time, the theory requires dynamic closure relationships which express the local dislocation velocities as nonlinear and in general non-local functionals of the dislocation fields. In physical terms, these closure relationships provide an averaged representation of the interactions of individual dislocations in a continuum setting.The first line of research pursued in the present project uses an entirely novel approach to the problem of dynamic closure, by departing from commonly used phenomenological approximations and using instead a data-driven research paradigm to parameterise generic nonlinear functions on the basis of data extracted from large-scale discrete dislocation dynamics simulations.The second line of research in this project will bridge the gap between CDD and experiments and demonstrate direct technological relevance of our model: coupling CDD with other mesoscopic field theories in the sense of a multiphysics approach allows e.g. to predict and analyze the coupled evolution of defect and phase microstructures in advanced alloy systems. This will be demonstrated for the coupling of CDD with a phase field approach in order to describe the coupled stress-driven dynamics of dislocation creep and directional coarsening in gamma/gamma´ alloys.