Abstract: In order to study the influences of the grain sizes on the contact mechanics properties of the materials， the contact and separation processes of the diamond indenter and the copper substrate with different grain sizes were investigated at the atomic scale， where the molecular dynamics method was utilized and the elastoplastic deformations of the polycrystalline copper substrates were considered. The results show that with different grain sizes， the maximum adhesion force during the adhesive contact processes of the polycrystalline coppers remains unchanged basically， and the maximum normal contact force shows a trend of first increasing and then decreasing with the decrease of the grain sizes. Moreover， the nano-hardness and contact stiffness are respectively related to the changes of the plastic energy and elastic energy during the contact processes， and the change of the nano-hardness possesses a negative relation with that of the contact stiffness generally. Finally， based on common neighbor analysis method， a study of the elastoplastic deformation processes of the polycrystalline copper substrates was conducted， and it is found that the number of grain boundaries strongly influences the nano-hardness of materials， and then further affects the contact mechanics properties. 

Key words: polycrystalline copper, nano-hardness, contact stiffness, contact mechanics, elastoplastic deformation

摘要： 为研究晶粒尺寸对材料接触力学特性的影响，考虑多晶铜基体弹塑性变形情况，基于分子动力学方法，在原子尺度下模拟了金刚石压头与不同晶粒尺寸的铜基体的接触与分离过程。研究结果表明：在不同晶粒尺寸下，多晶铜黏着接触过程中的最大黏着力基本保持不变，最大法向接触力随晶粒尺寸的减小表现出先增大后减小的趋势。纳米硬度和接触刚度分别与接触过程中的塑性能和弹性能的变化相关，且纳米硬度与接触刚度的变化总体成负相关。最后，采用公共近邻分析方法研究了多晶铜基体弹塑性变形过程，研究发现晶界数量对材料的纳米硬度有重要影响，并进一步影响其接触力学特性。

关键词: 多晶铜, 纳米硬度, 接触刚度, 接触力学, 弹塑性变形