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

CDD是在前一报告期发展起来的一种介观场论，它用密度类场变量来描述位错微结构的演化。由于它与经典的位错连续理论的关系，CDD给出了单个位错尺度以上的介观内应力的自然通道。同时，该理论要求动力学闭合关系将位错的局域速度表示为非线性的，并且一般是位错场的非局域泛函。在物理方面，这些闭合关系提供了连续体环境中单个位错相互作用的平均表示。本项目中追求的第一条研究线使用了一种全新的方法来解决动态闭合问题，通过偏离常用的唯象近似，而使用数据驱动的研究范式，基于从大规模离散位错动力学模拟中提取的数据来参数化一般的非线性函数。本项目的第二条研究路线将弥合CDD和实验之间的差距，并展示我们模型的直接技术相关性：在多物理方法的意义上将CDD与其他介观场论相结合，可以预测和分析先进合金系统中缺陷和相微结构的耦合演化。为了描述伽马/伽马合金中位错蠕变和定向粗化的耦合应力驱动的动力学，这将在CDD和相场方法的耦合中得到证明。

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.