颗粒流润滑的多尺度动力学及剪切膨胀承载机制研究

发布时间：2018-01-09 12:32

本文关键词：颗粒流润滑的多尺度动力学及剪切膨胀承载机制研究　出处：《合肥工业大学》2015年博士论文　论文类型：学位论文

【摘要】：颗粒流润滑是根据颗粒物质系统理论提出的一种新型的润滑方式,其基本的设计思路是将不黏附的硬质固体颗粒作为润滑介质导入到摩擦副间隙中,在润滑过程中利用固体颗粒之间的相互碰撞、滑动、摩擦和滚动等微观运动,以及颗粒自身的弹性变形,减小摩擦副表面之间的相互接触面积,从而实现减小摩擦和起到保护摩擦副的目的。该润滑方式环境适应性强,可以静态承载。对其研究掌握它的多尺度动力学特性和剪切膨胀承载机制,不仅具有重要的基础科学意义,而且具有实际的工程应用价值。首先,基于二元碰撞假设理论建立的碰撞颗粒流润滑控制方程和边值条件,对碰撞颗粒流润滑的流态进行了数值模拟研究。数值分析结果表明：颗粒润滑介质在剪切运动过程中的波动是引起固体体积分数、波动速度和摩擦系数变化的最重要的因素,主要三体参数的变化会改变颗粒润滑介质的波动趋势,从而引起固体体积分数、波动速度和摩擦系数发生改变。其次,采用离散单元法构建了密集颗粒流润滑的理论研究模型,对颗粒润滑介质的速度波动和自扩散特性、动力学特征、力链特征、剪切膨胀现象及承载的力学机制进行了研究。主要研究结果表明：颗粒润滑介质的平均速度和波动速度的变化趋势相反；接触力和接触角均按幂函数规律变化,并且法向接触力的大小要远远的大于切向接触力；颗粒润滑介质的动力学行为具有阻塞态、准静态流、慢速流和快速流四种状态；颗粒润滑介质在剪切运动过程中的剪胀率随时步的变化服从二次多项式规律,整体的剪切膨胀程度会随着剪切速度的增大而减小,压力载荷的减小而增大；颗粒润滑介质剪切膨胀过程中产生的法向作用力也可以有效承载,且承载能力随着剪切速度的增大而减弱,压力载荷的增大而增强等。最后,利用端面摩擦试验机和石墨颗粒对密集颗粒流润滑开展的粘滑运动实验研究表明,运动摩擦副与颗粒润滑介质间的宏观摩擦系数与颗粒润滑介质间形成的细观力链密切相关,细观力链的演变规律决定宏观摩擦系数的变化和演变,而运动摩擦副与颗粒润滑介质间的宏观摩擦系数可以视为细观力链变化趋势的宏观外在反映；颗粒润滑介质的流变特性会随着剪切速度和压力载荷的增大逐渐由粘滑运动状态过渡为滑动状态。通过以上对颗粒流润滑系统的理论和试验研究,阐明了颗粒流润滑的流变机理、剪切膨胀承载机制和粘滑运动机理。在此基础上,建立了考虑颗粒流润滑多尺度动力学和剪切膨胀承载机制的颗粒流润滑理论。该成果一方面对颗粒流润滑的工业应用与发展提供了理论支持,另一方面亦促进了颗粒物质力学的向前发展。
[Abstract]:Particle flow lubrication is a new type of lubrication method proposed according to the theory of particle matter system. The basic design idea is to introduce hard solid particles as lubricating medium into the friction pair clearance. In the process of lubrication, the contact area between the surfaces of friction pairs is reduced by using the micro motion of solid particles such as collision, sliding, friction and rolling, as well as the elastic deformation of particles themselves. Therefore, the purpose of reducing friction and protecting friction pair is achieved. The lubrication mode has strong adaptability to environment and can be statically loaded. Its multi-scale dynamic characteristics and shear expansion loading mechanism are studied and mastered. Not only has important basic scientific significance, but also has the practical engineering application value. First, based on the binary collision hypothesis theory, the governing equation and boundary value condition of the collision particle flow lubrication are established. The numerical simulation results show that the fluctuation of particle lubricating medium in shear motion is caused by the volume fraction of solid. The variation of main three-body parameters, the most important factor of fluctuation velocity and friction coefficient, will change the fluctuating trend of particle lubricating medium, thus causing the volume fraction of solid. The wave velocity and friction coefficient change. Secondly, the theoretical model of dense particle flow lubrication is constructed by discrete element method. The velocity fluctuation and self-diffusion characteristics of particle lubricating medium are studied. The characteristics of force chain, shear expansion phenomenon and mechanical mechanism of loading are studied. The main results show that the average velocity and fluctuation velocity of particle lubricating medium change in the opposite trend. The contact force and contact angle change according to the law of power function, and the normal contact force is far larger than the tangential contact force. The dynamic behavior of granular lubricating medium has four states: blocking state, quasi static flow, slow flow and fast flow. The shear expansion rate of granular lubricating medium in the process of shear motion varies from the quadratic polynomial law. The shear expansion degree of the whole will decrease with the increase of shear velocity and increase with the decrease of pressure load. The normal force produced in the process of shear expansion of granular lubricating medium can also be effectively loaded, and the bearing capacity decreases with the increase of shear speed and the increase of pressure load. Finally. The viscous and slip motion of dense particle flow lubricated by end friction tester and graphite particle is studied. The macroscopic friction coefficient between the moving friction pair and the particle lubricating medium is closely related to the mesoscopic force chain formed between the particle lubricating medium. The evolution law of the mesoscopic force chain determines the change and evolution of the macroscopic friction coefficient. The macroscopic friction coefficient between the moving friction pair and the particle lubricating medium can be regarded as the macroscopic external reflection of the change trend of the mesoscopic force chain. With the increase of shear velocity and pressure load, the rheological properties of particle lubricating medium will gradually change from the viscous state to the sliding state. The theoretical and experimental study on the particle flow lubrication system is carried out. The rheological mechanism, shear expansion load-bearing mechanism and visco-slip motion mechanism of particle flow lubrication are expounded. The theory of particle flow lubrication considering the multi-scale dynamics of particle flow lubrication and the mechanism of shear expansion is established, which provides theoretical support for the industrial application and development of particle flow lubrication on the one hand. On the other hand, it also promotes the development of particle mechanics.
【学位授予单位】：合肥工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TH117

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