采用分子动力学方法研究了不同含水条件下单晶Cu纳米压入过程中的应力松弛和弹性恢复行为。结果表明，恒定变形量下单晶Cu承受的应力减小，发生应力松弛现象，水膜存在时单晶Cu的应力松弛量大于无水情况。纳米压入过程中Cu原子间距随压入深度增加而快速减小，应力松弛阶段Cu原子间的最邻近距离未有明显变化，卸载初期Cu原子间距因变形区域弹性能及位错能的释放而迅速增大。含水条件下单晶Cu内部形成的位错明显多于无水情况，说明不可恢复性变形量因水膜的出现而加剧；卸载结束时部分变形得以释放，促进了部分位错消失，水膜的存在阻碍了弹性恢复和塑性变形的释放。

The stress relaxation and elastic recovery have an important effect on the mechanical and electrical properties of metallic crystal materials, which restricts the range of application and working life of materials. However, during plastic deformation of materials, the relaxation and elastic recovery behaviors are still not very clear at the nanoscale. In this work, the stress relaxation and elastic recovery of monocrystalline Cu under water environment is studied by molecular dynamics simulation. The results indicate the stress acting on Cu surface decreases at constant strain, meaning the occurrence of stress relaxation phenomenon. The stress relaxation increases with water film thickening compared with no-water environment. The separation between Cu atoms dramatically decreases with the increasing indentation depth at indenting stage, and there is no clear change in the nearest interatomic separation at stress relaxation stage, but the separation increases rapidly due to the release of elastic energy and dislocation energy at the unloading stage. The nucleated dislocations within Cu coated by water film are obviously more than that without water, which suggests the water film increases the unrecovered deformation in the total nanoindentation process. During unloading, partial dislocations disappear because of the deformation energy release, while the water film impedes the elastic recovery and plastic release.