Microscopic mechanisms of shear band formation in bulk metallic glasses

大块金属玻璃的力学性能与其变形时剪切带的形成密切相关。本项目利用大规模非平衡分子动力学(NEMD)模拟来研究BMG中剪切带的微观机制。简单的模型系统被认为是为了理解玻璃中剪切带状的一般场景。此外，通过从头计算的方法，建立了真实的模型(特别是Pd40Ni40P20)。然后，通过分析剪切带内外的自扩散、应变图和结构各向异性，使用真实模型的NEMD模拟允许与实验项目中获得的结果进行直接比较。该项目的主要重点是深入了解通过局部塑性事件(如剪切变化带)形成剪切带的情况。此外，还应研究剪切带断裂过程的形核。为了实现这一点，系统地改变了模拟的各种参数，使用不同的压缩和剪切协议，考虑了恒定体积和恒压模拟，并考虑了不同冷却速度下淬火产生的玻璃样品。

The mechanical properties of bulk metallic glasses (BMG) are intimately related to the formation of shear bands when these materials are deformed. In this project, large-scale Non-equilibrium Molecular Dynamics (NEMD) simulations are used to study the microscopic mechanisms of shear banding in BMG. Simple model systems are considered to understand generic scenarios of shear banding in glasses. Moreover, realistic models (in particular for Pd40Ni40P20) are developed by means of ab initio calculations. Then, by analyzing self-diffusion, strain maps and structural anisotropies inside and outside the shear bands, NEMD simulations with the realistic models allow for a direct comparison to the results obtained in the experimental project. The project’s primary focus is to give insight into the formation of shear bands via local plastic events (such as shear transformation zones). Furthermore, nucleation of fracture processes from shear banding shall be investigated. To achieve this, various parameters of the simulation are systematically changed, using different protocols of compression and shear, the consideration of simulations at constant volume and constant pressure, and the consideration of glass samples resulting from quenches at different cooling rates.