1.Department of Mathematics, Shanxi Agricultural University, Jinzhong 030801, China 2.Department of Applied Mathematics, Northwestern Polytechnical University, Xi’an 710129, China 3.School of Applied Mathematics, Guangdong University of Technology, Guangzhou 510520, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant No. 11902081), the Science and Technology Innovation Foundation of Higher Education Institutions of Shanxi Province, China (Grant No. 2020L0172), and the Science and Technology Innovation Foundation for Young Scientists of Shanxi Agricultural University, China (Grant No. 2020QC04)
Received Date:03 August 2020
Accepted Date:07 December 2020
Available Online:16 April 2021
Published Online:05 May 2021
Abstract:In this paper, the effects of a Gaussian white noise excitation on the one-dimensional Frenkel-Kontorova (FK) model are studied by the stochastic Runge-Kutta method under two different types of substrate cases, i.e. incommensurate case and commensurate case. The noise excitation is considered through the inclusion of a stochastic force via a Langevin molecular dynamics approach, and we uncover the mechanism of nano-friction phenomenon in the FK model driven by the stochastic force. The relationship between the noise intensity and the nano-friction phenomenon, such as hysteresis, maximum static friction force, and the super-lubricity, is investigated by using the stochastic Runge-Kutta algorithm. It is shown that with the increase of noise intensity, the area of the hysteresis becomes smaller and the maximum static friction force tends to decrease, which can promote the generation of super-lubricity. Similar results are obtained from the two cases, in which the ratios of the atomic distance to the period of the substrate potential field are incommensurate and commensurate, respectively. In particular, a suitable noise density gives rise to super-lubricity where the maximum static friction force vanishes. Hence, the noise excitation in this sense is beneficial to the decrease of the hysteresis and the maximum static friction force. Meanwhile, with the appropriate external driving force, the introduction of a noise excitation can accelerate the motion of the system, making the atoms escape from the substrate potential well more easily. But when the chain mobility reaches a saturation state (B = 1), it is no longer affected by the stochastic excitation. Furthermore, the difference between the two circumstances lies in the fact that for the commensurate interface, the influence of the noise is much stronger and more beneficial to triggering the motion of the FK model than for the incommensurate interface since the atoms in the former case are coupled and entrapped more strongly by the substrate potential. Keywords:Frenkel-Kontorova model/ Gaussian white noise/ hysteresis/ super-lubricity
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2.理论模型基于确定性的一维FK模型[12-14], 本文进一步考虑高斯白噪声激励下由N个原子构成的随机FK模型, 模型中第i$(1 \leqslant i \leqslant N)$个原子满足如下运动方程:
图1和图2描述了在非公度情形下, 随着噪声强度D的增大, 系统机动性能B随着外力绝热增加和减小而改变的规律. 此部分以黄金分割为例, 在数值模拟过程中, 取$a = 1$, $b/a = 144/233$, $c = a/\beta = 144/89$[8,12], 此时链长$L = 144$, 原子个数$N = 233$. 图 1D = 0, 0.005, 0.010时, 非公度情形下系统机动性能B随外力F的改变的变化规律(图中三角形和原点分别表示外力F绝热增加和减小的过程) Figure1. Noise effects on static friction and hysteresis of the $B(F)$ characteristics for the incommensurate case when D = 0, 0.005, 0.010. Triangles and circles denote, respectively, the adiabatic increasing and decreasing process of F.
图 2D = 0.1, 0.2, 0.5时, 非公度情形下系统机动性能B随外力F的改变的变化规律 Figure2. Noise effects on static friction and hysteresis of the $B(F)$ characteristics for the incommensurate case when D = 0.1, 0.2, 0.5.
为验证噪声对系统纳米摩擦现象的影响. 此部分将在公度情形下, 研究随机因素影响下, 系统的纳米摩擦现象随着噪声强度的增大而变化的规律. 其中$a = 1$, $c = a/\beta = 30/24$, 此时, 链长$L = 140$, 原子个数$N = 140$[8,12]. 图4和图5描述的是系统的机动性能B随着外力F绝热增大和减小而发生变化的过程. 图 4D = 0, 0.005, 0.010时, 公度情形下系统机动性能B随外力F的改变的变化规律(图中三角形和原点分别表示外力F绝热增加和减小的过程) Figure4. Noise effects on static friction and hysteresis of the $B(F)$ characteristics for the commensurate case when D = 0, 0.005, 0.010. Triangles and circles denote, respectively, the adiabatic increasing and decreasing process of F.
图 5D = 0.1, 0.2, 0.5时公度情形下系统机动性能B随外力F的改变的变化规律 Figure5. Noise effects on static friction and hysteresis of the $B(F)$ characteristics for the commensurate case when D = 0.1, 0.2, 0.5.