Sun Kun, Chen Juan, Wu Bingjie, Wang Liubing, Fang Liang
State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, China.
School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, China.
Materials (Basel). 2020 Nov 12;13(22):5110. doi: 10.3390/ma13225110.
Uniaxial tension tests were performed for amorphous SiO nanowires using molecular dynamics simulation to probe the size effect on the mechanical properties and plastic deformation by varying the length of nanowires. The simulation results showed that the Young's modulus of SiO nanowires increased with the decrease of nanowires length due to its higher surface stress. The corresponding deformation of SiO nanowires during tension exhibited two periods: atomic arrangement at small strain and plastic deformation at large strain. During the atomic arrangement period, the percentage variations of atom number of 2-coordinated silicon and 3-coordinated silicon (PCN2 and PCN3) decreased, while the percentage variations of atom number of 4-coordinated silicon, 5-coordinated silicon (PCN4 and PCN5) and the Si-O bond number (PCB) rose slightly with increasing strain, as the strain was less than 22%. The situation reversed at the plastic deformation period, owing to the numerous breakage of Si-O bonds as the strain grew beyond 22%. The size effect of nanowires radius was considered, finding that the Young's modulus and fracture stress were higher for the larger nanowire because of fewer dangling bonds and coordinate defeats in the surface area. The elastic deformation occurred at a small strain for the larger nanowire, followed by the massive plastic deformation during tension. A brittle mechanism covers the fracture characteristics, irrespective of the nanowire size.
使用分子动力学模拟对非晶态SiO纳米线进行单轴拉伸试验，通过改变纳米线的长度来探究尺寸对其力学性能和塑性变形的影响。模拟结果表明，由于SiO纳米线表面应力较高，其杨氏模量随纳米线长度的减小而增大。SiO纳米线在拉伸过程中的相应变形表现为两个阶段：小应变时的原子排列和大应变时的塑性变形。在原子排列阶段，随着应变小于22%，2配位硅和3配位硅的原子数百分比变化（PCN2和PCN3）减小，而4配位硅、5配位硅的原子数百分比变化（PCN4和PCN5）以及Si-O键数（PCB）随应变增加略有上升。在塑性变形阶段情况相反，因为当应变超过22%时，Si-O键大量断裂。考虑了纳米线半径的尺寸效应，发现较大纳米线的杨氏模量和断裂应力更高，这是因为其表面积中的悬空键和配位缺陷较少。较大纳米线在小应变时发生弹性变形，随后在拉伸过程中出现大量塑性变形。无论纳米线尺寸如何，断裂特征均呈现脆性机制。
