边界层效应及其诱发的力链演变对颗粒流润滑的影响

Granular lubrication,which is effective in extreme environment, is developed in recent years as a new lubrication method, while the boundary-layer effects are an urgent obstacles remains unsolved in fully understanding the granular lubrication theory. First, the project intends to explore the in-situ tribological test technology of granular lubrication, while using Raman spectroscopy and optical microscopy to achieve in-situ analysis of the boundary-layer behavior. By this way, the rule of boundary-layer behavior and its effects coupled with the rough surface will be systematic studied for clarifying the physical mechanism during the formation and variation process like boundary slip and so on. Then, by introducing the boundary-layer effects on the interaction between the granules, the modified granule contact model will be constructed. The strain evolution of the force chain topology, the structure evolving of the force chain and corresponding characterization method will be investigated under the presence of the boundary slip. A multi-scale model coupled with discrete-element and finite-element method will be proposed with the consideration of boundary layer effects. And the model will be used to analyze the rheological behavior of granular lubrication interface, to obtain the stress-strain relationship, and eventully to build the constitutive equation introducing boundary slip、shear rate and force chain characteristics. Finally, the relationship between boundary layer effect and granular lubrication will be linked by force chain. Combining with the tribological experiments, the load carrying and velocity adaptation mechanism of granular lubrication under the effects of boundary layer behaviour will be revealed. With above achievements, an equation model for fully predict the granular lubrication performance could be established.Theoretical research and the corresponding experimental validation will run through the entire research process which will ensure the rules and features of the granular lubrication affected by the boundary layer behavior are accurately revealed. Eventually, this project will promote the development of granular lubrication theory.

颗粒流润滑是近年来发展起来的新型润滑方法，边界层效应是进一步完善颗粒流润滑理论亟待解决的问题。本项目拟首先探索颗粒流润滑的原位试验技术，同时利用拉曼光谱法和显微光学法实现对边界层行为的原位分析，系统研究边界层行为规律及其与粗糙表面的耦合作用，阐明边界层滑移等形成和变化的物理机制。然后，引入边界层行为对颗粒间相互作用的影响，研究边界滑移等存在条件下力链拓扑的应变演化、力链构型演变及相应的表征方法。建立考虑边界层效应的有限元-离散元多尺度模型，分析颗粒流润滑的界面流变行为，获得应力-应变关系，进而构建引入边界层滑移和力链特性的本构方程。最后，结合摩擦学实验，建立润滑模型,实现以力链为纽带的边界层效应与颗粒流润滑特性的关联 。理论研究和相应的实验验证将贯穿整个研究过程，最终准确揭示边界层效应对颗粒流润滑承载和速度适应机制的影响机理，促进颗粒流润滑理论的发展。

由于颗粒物质的非连续性，以及颗粒流润滑边界层形态的复杂性，颗粒流润滑的速度适应机制的多样性，颗粒流边界层的变化、迁移，以及破坏对颗粒流润滑的摩擦学性能是复杂多变的，颗粒材料的离散型导致其具有特殊且多样的速度适应机制。通过边界层的形态观察，模拟中力链结构的分析，从一定程度上解释了部分机制对颗粒流润滑宏观特性的影响，为完善颗粒流润滑理论提供了借鉴。.通过原位的粉末颗粒润滑试验，研究了摩擦界面受限颗粒介质微区的形成机理和分布规律，分析了摩擦过程颗粒在粗糙表面铺展、迁移、分区演化的动态过程。获得了颗粒流润滑界面的摩擦系数，结合颗粒流润滑边界层的演化观察，发现摩擦系数等参数伴随着颗粒流润滑边界层的变化规律，良好的边界层形态能够带来较好的摩擦学性能，边界层的破坏与摩擦学性能的恶化有关。阐明了颗粒流润滑边界层行为规律及其与摩擦副表面因素的耦合作用对颗粒流润滑的摩擦学性能的影响。.结合接触分析和三体界面力学分析，研究了存在边界滑移等效应时颗粒间力的传递机制，同时研究了介观力链结构及其随边界摩擦、滑移、颗粒运动、外部载荷的演变规律，以及力链形成和破坏在颗粒流润滑中的持续性和多样性。阐明了摩擦界面颗粒系统在剪切变形时边界摩擦、滑移对力链演变的作用以及力链演变如何影响宏观的流变学性质，进而揭示了边界层效应对颗粒流润滑承载和速度适应机制的影响机理。.通过软三体混合润滑模型，建立了考虑边界层效应、剪切速率、力链特性、颗粒物理特性等影响的广义本构模型，结合有限元-离散元多尺度模拟，建立本构方程。实现了以力链为纽带的边界层摩擦、滑移特性与宏观颗粒流润滑特性的关联，给出考虑边界层效应影响的分析结果。分析了实际工况下颗粒流-液体润滑的接触多样性，进行了接触模型建模及气泡效应的力学分析。针对具体摩擦副，并通过密集颗粒体摩擦测试仪等摩擦学试验机对颗粒流润滑摩擦系数等参数进行了试验验证和修正。