热流变润滑理论及其在弹流研究中的应用

发布时间：2018-02-01 19:35

本文关键词： 热楔 Eyring流变模型剪稀效应广义粘度粘压关系滑滚比微弹流　出处：《青岛理工大学》2016年博士论文　论文类型：学位论文

【摘要】：热效应、流变效应、粗糙度效应和时变效应是现代弹性流体动力润滑理论中重要的研究内容。本学位论文的目的是围绕热流变润滑理论,由单一到复合,深入厘清各效应对特定工况下润滑油膜摩擦学行为的影响。本论文先从牛顿流体入手,对刚性固体光滑表面间的平行间隙内的润滑油膜开展了温度分布与热效应对油膜承载力影响的研究,即对热楔承载机理的研究。分析指出:热楔包括热密度楔与热粘度楔两个组成部分,热密度楔对承载力的贡献始终为正但效果很小,起主导作用的则是热粘度楔。分析进一步指出:热粘度楔效应有两个来源,即固体表面的温度差异和油膜内部的温度梯度。这些结论丰富了五十多年前由英国学者Cameron提出的粘度楔润滑理论。另外,通过固液界面上不同温度边界条件下的数值解,揭示了在流体动力润滑状态下几何楔和热楔各自对滑块轴承承载力的贡献大小。接下来,面向非牛顿流变模型,明确了广义粘度的物理意义,重新推导并改进了广义Reynolds方程。对Eyring流变模型的本构方程给出了一个新的表达形式,使得数值求解时可通过牛顿粘度和剪应变率直接计算广义粘度,从而极大提高了流变分析的计算效率。通过具体算例及对尺度效应的研究指出,广义粘度的高低和摩擦系数的大小是由热稀效应和剪稀流变效应共同决定的。剪稀效应在重载小滑滚比条件下就会发生,而大滑滚比条件下热稀效应更为强烈。使用“同一油品相同的密度对应相同的粘度”的假说,提出了一个由密度求粘度的新粘压关系式,该关系式不仅可以与实验测得的粘度变化高度吻合,且通过Dowson-Higginson密度公式可以把Barus粘度、Doolittle粘度以及Roelands粘度在形式上统一起来,从而在更深的层次上揭示了粘度与密度的关系。新粘度公式被成功应用到点接触Eyring热弹流润滑分析中,摩擦系数的数值解与实验结果吻合良好,这不仅验证了新公式的准确性,也证实了所用密度和粘度关系假说的合理性。在本论文的最后两章,按先易后难的顺序,把前面关于稳态润滑问题的工作推广到因粗糙表面的运动而存在时变效应的点接触Eyring非牛顿流体的热弹流数值仿真之中。先分析了高速滚滑条件下固体材料的热导率、滑滚比的大小和正负、单个横向粗糙峰谷的相对位置等对接触区压力、膜厚、温度、流变行为及摩擦力的影响,接着探讨了两固体表面各有一列粗糙峰时粗糙轮廓之间相互作用的规律,揭示了粗糙度波长和接触固体尺度等参数与摩擦系数的关联,从而丰富了微弹流润滑的知识体系。这无论在学术上,还是对工程设计都有一定的参考价值。
[Abstract]:Thermal effect, rheological effect, roughness effect and time-varying effect are important research contents in modern elastohydrodynamic lubrication theory. The effects of various effects on the tribological behavior of lubricating oil film under specific conditions are thoroughly clarified. This paper begins with Newtonian fluid. The effects of temperature distribution and thermal effect on the bearing capacity of lubricating oil film in parallel gap between smooth surfaces of rigid solids were studied. It is pointed out that the hot wedge consists of thermal wedge and viscosity wedge. The contribution of thermal wedge to bearing capacity is always positive but the effect is very small. The thermal viscosity wedge plays a leading role. The analysis further points out that there are two sources of thermal viscosity wedge effect. These conclusions enrich the viscosity wedge lubrication theory put forward by British scholar Cameron more than 50 years ago. The contribution of geometric wedge and hot wedge to bearing bearing capacity under hydrodynamic lubrication is revealed by numerical solution under different temperature boundary conditions at solid-liquid interface. Next, non-Newtonian rheological model is introduced. The physical meaning of generalized viscosity is clarified, the generalized Reynolds equation is rederived and improved, and a new expression of constitutive equation of Eyring rheological model is given. The generalized viscosity can be directly calculated by Newtonian viscosity and shear strain rate, which greatly improves the computational efficiency of rheological analysis. The generalized viscosity and the friction coefficient are determined by the thermal dilute effect and the shear-dilute rheological effect. The thermal thinning effect is stronger under the condition of large slip ratio. Using the hypothesis that "the same density of the same oil corresponds to the same viscosity", a new visco-pressure relation is proposed, in which the viscosity is calculated by the density. The formula can not only accord with the viscosity measured by experiment, but also can be used to calculate the viscosity of Barus by Dowson-Higginson density formula. Doolittle viscosity and Roelands viscosity are unified in form. The new viscosity formula has been successfully applied to point contact Eyring thermal elastohydrodynamic lubrication analysis. The numerical solution of friction coefficient is in good agreement with the experimental results. This not only verifies the accuracy of the new formula, but also verifies the rationality of the hypothesis of density and viscosity. The previous work on steady state lubrication is extended to the thermal elastohydrodynamic simulation of point contact Eyring non-Newtonian fluid with time-varying effect due to the motion of rough surface. Firstly, the solid is analyzed under the condition of high speed rolling and sliding. Thermal conductivity of bulk materials. The influence of the ratio of slip to roll, the relative position of a single transverse rough peak and valley on the contact pressure, film thickness, temperature, rheological behavior and friction force. Then, the interaction of rough profiles with a series of rough peaks on two solid surfaces is discussed, and the correlation between the parameters such as roughness wavelength, contact solid scale and friction coefficient is revealed. It enriches the knowledge system of micro elastohydrodynamic lubrication, which has certain reference value in both academic and engineering design.
【学位授予单位】：青岛理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TH117.2

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