非晶合金剪切带涌现的內禀动力学机制

The physical origin of the emergence of nanoscale shear bands in amorphous alloys with long-range disorder atomic packing character has been one of the long standing obssessing issues in the fields of mechanics, material sciences and physics.In spite of the considerable progress has been made during past decades,the structural origin, the spatial-temporal feature and the intrinsic kinetics of the nanoscale shear bands induced by activation and self-assembly of microscopic atomic flow units (like shear transformation zone or STZ ) in the material under the stimulus of external loads still remain elusive. To this motivation, in this proposal a series of amorphous alloys with distinct macroscopic ductility will be selected as the researching materials,and then the "deforming frozen" tests at different loading conditions, the characterization of the structural relxation dynamics of deformed amorphous alloys and large-scale molecular dynamics simulation will be made to reveal the micro-heterogeneity in the atomic structure , the dynamic charater of the activation and the spatial-temporal evolution of flow units. Furthermore, a physically self-consistent microsopic flow unit model, the collective evolution dynamics equation characterizing the cooperatvie interaction of microscopic flow units and a trans-scale mechanics model bridging microscopic flow unit dynamics and macroscopic continnum mechanics will be developed to unravel the physical origin and inrinsic kinetics of the emergence of shear banding induced by the activation and evolution of flow units in amorphous alloys. The present research is intended to provide valuble clues for disentangling the physical origin of the emergence of shear banding and for structure designing of amorphous alloys.

原子排列长程无序的非晶合金纳米尺度剪切带涌现的物理起源是力学、材料、物理等相关领域长期困惑的重大科学难题之一。尽管过去几十年中外学者在此方面已取得长足进展，但在外载激励下材料内部微观原子流动单元（如剪切转变区-STZ等）激活、自组装诱发纳米尺度剪切带的结构起源、时空特征、內禀的动力学机制等一系列基础性问题仍相当模糊。为此，本项目拟以宏观塑性有显著差异的不同非晶合金体系为对象，系统开展不同加载条件下的"变形冻结"实验和结构弛豫动力学实验，结合大规模分子动力学模拟，获得材料微观原子结构不均匀性及流动单元激活、时空演变动力学特征；发展物理自洽的微观流动单元力学模型，建立微观流动单元群体协同演化的动力学方程及其与宏观连续介质力学方程相耦合的跨尺度力学模型；揭示流动单元激活、演化诱致剪切带涌现的物理途径及內禀动力学机制。本研究可望为厘清非晶合金剪切带涌现的物理起源及非晶材料结构设计提供有价值的线索。

原子排列长程无序的非晶合金纳米尺度剪切带涌现的物理起源是力学、材料、物理等相关领域长期困惑的重大科学难题之一。尽管过去几十年中外学者在此方面已取得长足进展，但在外载激励下材料内部微观原子流动单元（如剪切转变区-STZ 等）激活、自组装诱发纳米尺度剪切带的结构起源、时空特征、內禀的动力学机制等一系列基础性问题仍相当模糊。为此，本项目发展了剪切变形可控“冻结”的切削技术和剪切带内部原子尺度微结构演变在位检测的声发射技术，首次捕捉到剪切带从萌生到演化终止过程中原子尺度体积膨胀的变化规律，揭示了剪切带演化程度与体积膨胀的关联性质，提出了剪切带延脆转变准则，揭示了剪切带内部原子尺度体胀累积是延-脆剪切带转变的物理起源。以宏观塑性有显著差异的不同非晶合金体系为对象，系统开展了结构弛豫动力学实验，揭示了非晶合金锯齿流变行为、应变速率敏感性及剪切带涌现与结构驰豫的关联规律。结合大规模分子动力学模拟，获得了非晶合金微观原子结构不均匀性及流动单元激活、剪切带时空演化动力学特征；发展了物理自洽的微观流动单元力学模型，建立了微观流动单元群体协同演化的动力学及其与宏观连续介质力学相耦合的跨尺度力学模型，揭示了剪切带应变梯度驱动的内禀动力学机制。本研究为厘清非晶合金剪切带涌现的物理起源及非晶材料结构设计提供了有价值的线索。