高速冲击下纳米颗粒间机械接触的研究

With the development of precision and processing nanotechnology, much progress has been made in the design and fabrication of nanodevices such as nano-electro-mechanical systems (NEMS), nanomotors and even molecular machines. As the size of devices decreases to nanoscale, the effects of intermolecular forces such as van der Waals (vdW) attraction，become more significant than those of gravity and inertia forces. These nanodevices often involve high speed motions of nanoparticles, such as rotation and translation, during which contact deformation arises, thus understanding the high-speed contact mechanics and deformation mechanism at the nanoscale is of both fundamental importance and of practical interest for device design, materials selection, self-assembly and other nano-technological innovation...Previous studies have initiated this topic regarding high-speed contact mechanics. This project aims to unravel the effects of crystallinity (crystalline or amorphous), humidity on nanoparticle's mechanical response (including elastic restoring force, contact radius, maximal contact radius) and materials' macroscopic properties (including elastic-plastic transition, yield strength, hardness) using advanced molecular modelling. This project will expound the inherent relationship between macroscopic properties and the sub-micro-structural changes such as bond length, bond angle, coordination number of atoms, dislocation, etc. The outcomes generated from this proposal are expected to clarify the nanoscale plasticity mechanism from the molecular level and strengthen our capability to perfect the existing continuum theoretical models.

伴随着微纳机电装置逐步降低到纳米尺度，分子间作用力，比如范德华吸引力，发挥着比重力和其他惰性力更明显的作用。在这些微纳米装置中，往往涉及纳米颗粒的高速运动，而动态效应对材料的结构性能的影响并未被完全理解。因此，理解高速接触力学并研究纳米尺度的变形机理不但具有理论价值，而且具有重要的实际意义。前期工作主要开启了动态效应的在纳米尺度上对接触力学的影响这一课题，拟开展的工作将利用分子模拟技术揭示纳米颗粒的不同晶型（非晶和晶体）、空气湿度等对纳米材料的力学响应（弹性恢复力、塑性变形力、接触半径、最大接触半径）和材料结构性能响应(包括弹塑性转变、屈服强度、硬度等宏观性质)的影响规律，阐释材料宏观性能与亚微观结构变化（键长、键角、原子配位数、位错、相转变等）的内在关联，从分子尺度澄清非受限条件下的变形机理并完善已有的连续介质理论模型。

伴随着微纳机电装置逐步降低到纳米尺度，往往涉及纳米颗粒的高速运动，分子间作用力，比如范德华吸引力，发挥着比重力和其他惰性力更明显的作用。因此，理解高速接触力学并研究纳米尺度的变形机理不但具有理论价值，而且具有重要的实际意义。本项目利用分子模拟技术揭示纳米颗粒的不同晶型（非晶和晶体）、反应/非反应力场、空气湿度等对纳米材料的力学响应（弹性恢复力、塑性变形力、接触半径、最大接触半径）和材料结构性能响应(包括弹塑性转变、屈服强度、硬度等宏观性质)的影响规律，阐释了材料宏观性能与亚微观结构变化（键长、键角、原子配位数、位错、相转变等）的内在关联，从分子尺度澄清非受限条件下的变形机理并完善已有的连续介质理论模型。经典的Mindlin-Deresiewicz理论在小的重叠程度上仍然有效; 无定形碳纳米材料，屈服强度σ和杨氏模量E0近似满足σ=E0/10; 在较小的碰撞速度和较小的位移下，连续介质模型Hertz仍然适用；Rosenberg-Dekel模型给出的估计要低得多，但Forrestal-WarrenⅡ模型仍然可以预测纳米尺度下的侵彻深度。颗粒碰撞动力学研究蒋为微纳米技术加工、颗粒多相流、外太空碎片撞击防护、弹体侵彻甚至行星形成演化过程等领域提供理论借鉴。在项目资助下，发表SCI论文11篇，参加国内国际会议10余次，培养博士生1名，硕士生2名。