纳观单晶铜表面粘着接触失效的分子动力学模拟

Molecular Dynamics Simulation of Failure in Adhesive Contact with Single Crystal Copper

目的为提高微纳米器件的接触性能。方法在考虑粘附力﹑单晶铜基体弹塑性形变,及忽略各向异性影响的条件下,基于分子动力学法,采用混合势函数(EAM和Morse)和Verlet算法,动态模拟了探针与单晶铜基体的粘着接触与分离过程,对接触与分离过程的接触力进行了分析。通过计算原子中心对称参数,描述了接触区域的原子破坏和迁移轨迹的变化情况。结果在下压接触中,因接触力不断增加,接触区域两侧相继出现滑移带,并向两侧方向逐渐扩张,且滑移带与探针下压方向成45?,分离后,受基体弹塑性恢复和能量耗散的影响,接触区域两侧的滑移带由开始扩张逐渐缩小。完全分离后,因粘附力的存在,基体部分原子粘附于探针底表面,探针与基体间形成明显的"缩颈"现象,且发生明显的粘着滞后现象,是接触表面发生粘着失效形式的主要原因。在整个接触与分离过程中,接触区域点阵原子断裂堆积呈"V"字形状。结论粘着影响使基体部分原子易粘附于探针底表面上,形成粘着滞后现象,这是导致微纳米机械易发生粘着接触失效的主要原因。

The work aims to improve contact behavior of micro/nano devices. Allowing for influences of adhesive force, elastic-plastic deformation of single crystal copper substrate, and neglecting anisotropy, adhesion contact and separation process of probe and single crystal copper was simulated dynamically, contact force during contact and separation process was analyzed in molecular dynamics method based on mixed potential function （EAM and Morse） and Verlet algorithms. Atomic destruction and migration path changes in contact area were analyzed based on center-symmetric parameters. During pushing contact processes, slip bands successively appeared on both sides of the contact area and gradually expanded in both directions as con- tact force increased. Besides, angle between slip band and probe pressing direction was 45~. After separation, under the effects of elastic-plastic recovery and energy dissipation of substrate, slip zone on either side of slip band first expanded and then grad- ually narrowed. After complete separation, atoms on copper substrate stuck to the surface of probe bottom, ＂shrink neck＂ and hysteretic displacement, as well as adhesion delay were obviously observed between the probe and substrate, which were the main cause of adhesion failure on contact surface. What＇s more, lattice atoms in contact area fractured and accumulated in ＂V＂ shape during the whole contact and separation process. The adhesion influence makes atoms on substrate stick to the probe bot- tom surface, leading to adhesion delay, which is the main reason of adhesion failure on micro-nano machinery.