Molecular Dynamics Investigation of Tribological Phenomena in Micro Machining

该研究的目的是建立一个物理模型来描述纳米级材料去除过程中的微观摩擦学现象。这种原子模型使我们能够处理摩擦、磨损和润滑的动态现象，以及表面/界面上的弹塑性变形、断裂和化学反应。主要研究结果如下： 1.基于莫尔斯势假设原子间作用力，对铜单晶的(111)面沿[101]方向进行正交加工。晶体中现有的空位和刃位错导致晶格结构进一步无序并增加切削力。在对完美晶体进行双重加工的情况下，工作原子的位移被限制在成品表面处或略低于成品表面。结论是，工件表面无损伤的先决条件是工件材料应尽可能纯净和完美。工具和工作原子之间的润滑也是一个关键因素。2.采用Bragg和Nye的气泡筏法研究肥皂泡的纳米级切割机制，并与铜单晶的MD模拟进行比较。在基本切削现象方面可以看到定性的一致性，包括切屑形成的表面下损伤，其中通过位错的类似变形机制起着主要作用。刀具与工件之间的相互作用也是纳米级加工的一个关键因素。3.现有的二维MD仿真程序已成功扩展到三维仿真程序，并开发了用于可视化的计算机图形学作为Windows95的应用软件。使用模拟系统，可以阐明更真实的摩擦学现象，例如去除的工作原子向加工表面扩散以及磨损的工具原子重新粘附在工具和工作表面上。

The purpose of the research is to build a physical model that describes microtribological phenomena in a nano-scale material removal process. This atomistic model enables us to deal with dynamical phenomena of friction, wear and lubrication followed by elastic-plastic deformation, fracture and chemical reaction at surfaces/interfaces. The major results obtained are as follows :1.Postulating interatomic force based on the Morse potential, a (111) plane of a copper single crystal is orthogonally machined in the direction of [101]. Existing vacancies and edge dislocations in the crystal result in further disorder of the lattice structure and an increase in cutting forces. In the case of the duplex machining of the perfect crystal, displacement of the work atoms is limited to at or just below the finished surface. It is concluded that a prerequisite for a damage-free surface is that the work material should be as pure and perfect as possible. Lubrication between the tool and work atoms is a crucial factor as well.2.The bubble raft method according to Bragg and Nye has been employed to investigate the nano-scale cutting mechanisms of soap bubbles as well to make a comparison with MD simulations of a copper single crystal. Qualitative agreement can be seen with respect to basic cutting phenomena, including chip formation subsurface damage in which a similar deformation mechanism through dislocations plays a primary role. The interaction between the tool and work is also a key factor in nano-scale machining.3.The existing two-dimensional MD simulation program has successfully been extended to a three-dimensional one in which computer graphics for visualization has also been developed as application software of Windows95. Using the simulation system, more realistic tribological phenomena have been clarified, such as diffusion of the removed work atoms toward the machined surface and re-adhesion of the worn tool atoms on the tool and work surfaces.