平均分子动力学模拟研究金属的慢应变率行为
Averaging Molecular Dynamics simulations to study the slow-strain rate behavior of metals
AI总结：
采用实用时间平均（PTA）框架，通过定义慢变量为快原子动力学的时间平均观测量，模拟准静态加载下的晶体固体，实现比传统分子动力学低数个数量级的应变率模拟。
摘要：
分子动力学（MD）模拟在准静态加载中的应用受到原子振动时间尺度与实验相关变形速率之间巨大分离的严重限制。在这项工作中，我们采用实用时间平均（PTA）框架来克服这一限制，并实现准静态加载条件下晶体固体的原子模拟。PTA通过将慢变量定义为快原子动力学的时间平均观测量及其在慢加载时间尺度上的演化，利用固有的时间尺度分离，从而避免对快动力学的显式积分。使用这种方法，我们模拟了4至20 nm立方体面心立方铝纳米晶体在接近准静态条件的施加应变率下的单轴拉伸和压缩变形。我们将慢变量定义为加载方向上的平均动能、势能和法向应力，并追踪它们在慢时间尺度上的演化。应力-应变曲线显示屈服接近均匀成核的理论应力，随后是由位错成核、运动以及从自由表面退出引起的连续载荷下降和上升。从应力-应变响应以及屈服应力随样品尺寸的变化中，“越小越硬”效应明显。响应中的锯齿状波动对于较小样品更为明显。还研究了施加应变率和初始温度的影响。该方法还通过追踪时间平均原子位置，捕捉了慢时间尺度上复杂位错微结构的演化。PTA框架使得模拟应变率比传统MD可达到的低数个数量级，在保持完整原子分辨率的同时，展示了计算时间上的显著加速。
英文摘要：
The application of molecular dynamics (MD) simulations to quasistatic loading is severely limited by the large separation between atomic vibration timescales and experimentally relevant deformation rates. In this work we employ the Practical Time Averaging (PTA) framework to overcome this limitation and enable atomistic simulations of crystalline solids under quasistatic loading conditions. PTA exploits the intrinsic separation of timescales by defining slow variables as time-averaged observables of the fast atomistic dynamics and their evolution on the slow loading timescale, thereby avoiding explicit integration of the fast dynamics. Using this approach, we simulate uniaxial deformation, in both tension and compression, of 4 to 20 nm cubic specimens of face centered cubic aluminum nanocrystals at applied strain rates approaching quasistatic conditions. We define slow variables as the averaged kinetic energy, potential energy, and normal stress in the loading direction, and track their evolution on the slow timescale. The stress-strain curves show yielding close to the theoretical stress for homogeneous nucleation, followed by successive load drops and rises caused by dislocation nucleation, motion, and exit from free surfaces. The "smaller is harder" effect is evident from the stress-strain response and from the variation of yield stress with sample size. Serrations in the response are more pronounced for smaller samples. The effects of applied strain rate and initial temperature are also studied. The method also captures the evolution of intricate dislocation microstructures on the slow timescale by tracking time-averaged atomic positions. The PTA framework enables simulations at strain rates several orders of magnitude lower than those accessible to conventional MD, demonstrating significant speedup in computational time while retaining full atomistic resolution.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
