一种原子尺度应变定义方法及其在识别微观缺陷演化中的应用

doi:10.11900/0412.1961.2019.00343

金属学报

2020, Vol. 56

Issue (8): 1144-1154 DOI: 10.11900/0412.1961.2019.00343

本期目录 | 过刊浏览

一种原子尺度应变定义方法及其在识别微观缺陷演化中的应用

盛鹰¹^,², 贾彬¹^,²(

), 王汝恒¹^,², 陈国平¹^,²

1 西南科技大学工程材料与结构冲击振动四川省重点实验室绵阳 621010
2 西南科技大学土木工程与建筑学院绵阳 621010

The Definition of Atomic Scale Strain and Its Application in Identifying the Evolution of Microdefects

SHENG Ying¹^,², JIA Bin¹^,²(

), WANG Ruheng¹^,², CHEN Guoping¹^,²

1 Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province, Southwest University of Science and Technology, Mianyang 621010, China
2 School of Civil Engineering and Architecture, Southwest University of Science and Technology, Mianyang 621010, China

引用本文:

盛鹰, 贾彬, 王汝恒, 陈国平. 一种原子尺度应变定义方法及其在识别微观缺陷演化中的应用[J]. 金属学报, 2020, 56(8): 1144-1154.
Ying SHENG, Bin JIA, Ruheng WANG, Guoping CHEN. The Definition of Atomic Scale Strain and Its Application in Identifying the Evolution of Microdefects[J]. Acta Metall Sin, 2020, 56(8): 1144-1154.

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摘要:

为探索性地定义原子尺度的应变，本工作提出了可同时适用于原子尺度和连续介质尺度的“变形”的计算方法，采用离散变形梯度表征原子尺度下的“变形”。在此基础上，引入邻域原子影响权函数，定义了原子尺度下的应变张量，建立了计算任一中心原子的综合局部变形梯度和应变张量的加权最小二乘法目标函数，从而将原子尺度应变的计算转化为解决目标函数的最小值优化问题。然后运用改进的自适应多层复形遗传算法即可实现原子尺度应变的计算。最后，以NiTi合金为研究对象，建立了NiTi合金变形与破坏的分子动力学演化模型并计算了各时刻的原子尺度应变云图，通过应变云图观察到了孪晶。经与NiTi合金三点弯曲冲击断裂试件裂纹尖端的微观观察实验作对照，验证了本工作建立的原子尺度应变定义方法的合理性及其在识别微观缺陷演化中的应用意义。

关键词 ：原子尺度应变, 离散变形梯度, 权函数, 目标函数优化, 微观缺陷演化

Abstract：

The strain tensors are commonly defined by the local deformation of continuum. Unlike displacement, strain is not a physical quantity that can be measured directly, and it is calculated from a definition that relies on the gradient of the continuous displacement field. At the microscale, it is difficult to define the local deformation according to the position of each atom which is obtained from the adjacent discrete time interval, so there is no universally accepted definition of strain tensors of atomic scale so far, and none of the molecular dynamics software can be used to calculate the atomic strain until now. In order to define the atomic scale strain, a method for calculating the "deformation" both in the atomic scale and the continuum scale is proposed. In the definition, the discrete deformation gradient is proposed to describe the "deformation" in the atomic scale and the influence weight function of neighborhood atom is introduced. Then the weighted least squares error optimization model is established to seek the optimal coefficients of the weight function and the optimal local deformation gradient of each atom. After that, the advanced multilayer complex genetic algorithm can be used to calculate the atomic strain. Finally, take NiTi alloy as an example, the molecular dynamics evolution model of deformation and failure of NiTi alloy was established. Then the atomic scale strain nephogram at each time was calculated, and the microdefects such as twins were observed by strain nephogram. Compared with the micro-observation experiment of crack tip of NiTi alloy for three-point bending, the rationality of the atomic scale strain definition method established in this study and its application significance in identifying the evolution of microdefects are verified.

Key words： atomic scale strain discrete deformation gradient weight function objective function optimization evolution of microdefect

收稿日期: 2019-10-15

ZTFLH:

O341

基金资助:西南科技大学博士基金项目(17zx7149);工程材料与结构冲击振动四川省重点实验室开放基金项目(18kfgk12)

作者简介: 盛鹰，男，1982年生，博士

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https://www.ams.org.cn/CN/10.11900/0412.1961.2019.00343 或 https://www.ams.org.cn/CN/Y2020/V56/I8/1144

图1 邻域内离散原子的运动示意图

图2 NiTi合金三点弯曲试样断口形貌的SEM像

图3 NiTi合金裂纹表面的TEM像

图4 NiTi合金应力-应变计算曲线

图5 对应图4中关键点1~6的原子构型图

图6 NiTi合金裂尖附近的分子动力学模拟结果

图7 与图6对应的原子尺度应变云图

图8 NiTi合金权函数ωn(r)的函数图

图9 不同截断半径Rcut时NiTi合金权函数ω(r)的函数图

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