非晶合金裂纹尖端场及其塑性内禀关联机制

The poor ductility at room temperature greatly impedes the structural application of metallic glasses (MGs), the underlying physics of ductility is one of the greatest scientific conundrums in the fields of mechanics, material sciences and physics. Despite that considerable progress has been made in the last decades, the micro-mechanisms of ductility and brittleness in MGs and their multi-scale plastic flow mechanisms still need to be clarified. The ductile or brittle fracture behavior of MGs is greatly related to the localized deformation ahead of the crack tip. To this end, a systematic investigation on the dynamic evolution of the crack tip field will be carried out in this research for MGs of different ductility, via experiments, numerical simulation, and theoretical analyses. The stress and strain distribution, and the size of the plastic zone ahead of the crack tip will be quantitatively characterized. The correlation of the activation of the plastic flow units with the formation and evolution of shear bands and micro-cavitation within the plastic zone will be elucidated. The dynamic evolution model of the plastic zone ahead of the crack tip will be developed. Based on the above analyses, the spatiotemporal relationship among the activation of plastic flow unit, the local deformation in front of the crack tip, and the macro-deformation will be further established, and the multi-scale plastic flow mechanisms and the micro-mechanisms of ductility and brittleness will be revealed for MGs. This research may increase our understanding of plastic mechanisms as well as provide theoretical basis for improving the room-temperature ductility in MGs.

室温低延性是非晶合金作为结构材料应用的瓶颈，其背后的物理机制是力学、材料、物理等领域致力解决的重大科学难题之一。尽管过去几十年此方面已取得重要进展，但非晶合金延脆的微观机理及多尺度塑性流动机制仍有待进一步澄清。非晶合金的延脆断裂行为与裂纹尖端场局部变形密切相关。为此，本项目拟通过实验、数值模拟及理论分析相结合，针对宏观延脆存在显著差异的非晶合金，系统深入地研究其裂纹尖端场动态演化过程；定量表征裂纹尖端应力应变分布及塑性区大小；阐明裂纹尖端场塑性区流动单元激活行为与剪切带、微孔洞形成演化的关联；发展裂纹尖端塑性区动力学演化模型；基于上述分析，进一步建立塑性流动单元激活行为、裂纹尖端局部变形与宏观变形的跨尺度时空关联，从而揭示非晶合金多尺度塑性流动机制及延脆的微观机理。本项目的研究将有助于深入理解非晶合金的塑性机制，为改善其室温低延性提供理论基础。

室温低延性是抑制非晶合金作为结构材料应用的瓶颈，其背后的物理机制是力学、材料、物理等领域致力解决的重大科学难题之一。本项目围绕非晶合金裂纹尖端场及其塑性内禀关联，通过实验、数值模拟及理论分析相结合，系统深入地研究了非晶合金裂纹尖端场动态演化过程，定量表征了裂纹尖端应力应变分布、塑性区大小、剪切带形成及演化；阐明了裂纹尖端场塑性区流动单元激活行为与剪切带、微孔洞形成演化的关联；揭示了剪切带形成的应变梯度驱动机制；考虑非晶合金压力敏感、剪胀及微结构演化，结合滑移线场分析及J积分理论，发展了平面应变条件下I型裂纹尖端塑性区动力学演化模型，得到了裂纹尖端塑性区的理论解，揭示了临界塑性区形状因子与宏观延脆性的内在关联；基于上述分析，建立了塑性流动单元激活行为、裂纹尖端局部变形与宏观变形的关联，揭示了非晶合金塑性流动机制及延脆的微观机理。本项目从裂纹尖端场出发，构建了非晶合金宏观延脆性与塑性区、剪切带等微观变形行为之间的关联。相关结果有助于深入理解非晶合金的塑性机制，同时，为改善其室温低延性提供理论基础。