Discrete Dislocation Dynamics

离散位错动力学方法将通过分析不同加载条件下位错系的演化，为小尺度试样的塑性研究提供新的思路。重点将放在晶界（GBs）和施加的应力或应变梯度对新出现的位错结构的作用上。在FOR1650报告期1中，已经发现GB的塑性变形-在DDD中建模为不可穿透-只能在假设有限和应变依赖的晶界屈服强度的连续体框架中描述。然而，目前尚不清楚如何制定这样的晶界屈服强度。广泛的离散位错动力学模拟将允许通过相关晶粒的错取向和塑性特性（例如初始位错密度）的系统变化来更好地理解这种行为。相邻晶粒中位错之间的弹性相互作用的作用将被详细地描述。此外，还将探讨位错网络中位错增殖机制的取向和微观结构依赖关系。除了简单的密度测量和“结计数”外，还应发展拓扑和统计方法来定量表征位错微观结构。预期的结果还将指导塑性连续体描述的发展，例如，在位错连续体理论中处理gb和制定滑移系统相互作用所需的关键机制。为了提高计算效率，应该实现DDD代码的MPI并行化，这将允许模拟多晶样品。

The discrete dislocation dynamics method will be used to gain new insight in the plasticity of small scale specimens by analysing the evolution of dislocation ensembles under different loading conditions. The main focus will be on the role of grain boundaries (GBs) and imposed stress or strain gradients on the emerging dislocation structure. In reporting period 1 of FOR1650, it has been found that the plastic deformation of a GB -- modelled as impenetrable in DDD -- can only be described in a continuum framework assuming a finite and strain dependent grain boundary yield strength. However, it is yet unclear how such a grain boundary yield strength can be formulated. Extensive discrete dislocation dynamics simulations will allow to derive a better understanding of this behaviour by a systematic variation of misorientation and plastic properties (e.g initial dislocation density) of the involved grains. The role of the elastic interaction between dislocations in the neighbouring grains shall be characterized in detail. Furthermore the orientation and microstructure dependence of dislocation multiplication mechanisms within a dislocation network will be explored. Topological and statistical measures shall be developed for quantitatively characterizing dislocation microstructures, while going beyond simple density measures and "junction counting". The expected results will also allow guiding the development of continuum descriptions of plasticity, e.g. the handling of GBs and the key mechanism needed for the formulation of the interaction of slip systems in dislocation continuum theories. For improved computational efficiency a MPI parallelisation of the DDD code shall be realized which would allow simulating poly-crystalline samples.