基于分子动力学-格林函数法的微凸体接触数值分析

NUMERICAL ANALYSIS OF ASPERITY CONTACT MODEL BASED ON MOLECULAR DYNAMICS-GREEN'S FUNCTION METHOD

表面接触是摩擦的先决条件,其真实接触面积、压应力大小、空间分布等一直是接触力学关注的核心问题.采用分子动力学-格林函数法(GFMD)模拟粗糙面的接触过程,验证了其在大规模接触分析中的高效及准确性,同时探讨了由微球体组成的粗糙面的接触力学特性,并分析了分子尺度下的结果和传统力学模型计算结果的差异.结果表明,单个微凸体接触结果和分子动力学-格林函数法模拟所得非常接近,误差在5%以内.数值模拟发现,在微凸体高度符合高斯分布的情况下,接触面积和接触力成线性关系;在相同接触面积下,微凸体模型得出的接触力偏高,是上限值.微凸体模型没有考虑微凸体间的相互影响,实际是高估了弹性体的刚度;实际接触过程中微凸体相互影响,微凸体对临域形变影响尤其大,使接触区域更加离散.GFMD模型可以准确计算数十亿量级别分子、原子接触过程中真实接触面积及分布,为后续摩擦、滑移等分析提供可靠的参考.

Rough contact is a prerequisite for surface friction.The rough contact behaviour such as the contact area,the pressure distribution and spatial distributions has been one of the core issues in contact mechanics and tribology.In this paper,the molecular dynamics-Green's function method(GFMD)is used to simulate the contact mechanism of the rough surface,where the asperity model is used for the rough surface,i.e.,the surface is composed of numerous spherical asperities.Starting with the atomic or molecular force filed to consider the rough contact behaviour,the molecular dynamics-Green's function method is able to capture the mechanisms such as super-lubrication and multi-scale e_ect behaviour,which are not found in traditional continuum mechanics.The molecular dynamics-Green's function method demonstrates its high e_ciency in large scale molecular dynamics simulations and is able to simulate the system composed of billions of atoms.The results of single asperity contact based on Hertz contact theory are very close to those simulated by the molecular dynamics-Green's function method,and the di_erence is less than5%.It is found by numerical simulation that the contact area is linearly related to the contact force if the asperity heights follow the Gaussian,and the contact force obtained by the asperity model is the upper limit given the same contact area.Although Asperity model is fast,it overestimates the sti_ness of the elastomer due to the neglection of the interaction between the asperities.In real contact process,asperities have considerable e_ects on each other,especially on the deformation of the adjacent area,which makes the contact spots more discrete.The information of the real contact area and its spatial distributions,is of importance for the following simulation on surface friction.