含增粘剂润滑油非线性本构方程的探讨

本文针对含增粘剂润滑油的流变特性，将线性多组元粘弹性模型在特殊的共转坐标系下推广，得到了能同时反映含增粘剂润滑油剪切稀化及其粘弹性的本构方程。将该本构关系给出的表现粘度与实验结果进行了对比，证明该本构关系能够较全面含增粘剂润滑油的流变特性且形式简单便于工程应用。     

HKD型航空润滑油本构方程的确定及拖动力计算

测量了HKD型航空润滑油的拖动力,确定了该油的本构方程,给出了本构方程中各种流变参数的计算方法并拟合出了计算公式,给出了拖动力的计算方法。结果表明:该油在试验条件下表现为粘弹性;拖动力的理论预测值与试验测量值之间误差较小,曲线形状一致,本构方程正确合理;流变参数的拟合公式精度较高。     

低温工况润滑脂流变特性及本构方程研究

润滑脂流变学行为与温度紧密相关,而流变行为决定润滑脂的本构方程。首先分别在不同温度工况下进行流变试验获得润滑脂流变学特性,并对低温工况进行研究;其次,基于Herschel-Bulkley、Power Law与Bingham本构方程对流变数据进行回归分析;最后,基于三种本构方程采用CFD方法深入分析润滑脂在管内的压力损失、粘度分布及速度分布规律。结果表明:在低剪切速率下,低温工况的剪切应力出现峰值,且润滑脂承受的最大剪切速率减小;不同工作温度下,三种本构方程回归精度均大于92%;Herschel-Bulkley本构方程粘度与速度计算结果均小于Power Law与Bingham本构方程;基于三种本构方程计算的速度在管道中心均出现明显的核流区域;Herschel-Bulkley本构方程压降计算结果最小。     

Fe-3.0%Si-0.09%Nb取向硅钢的高温流变应力

通过热模拟试验机测定了Fe-3.0%Si-0.09%Nb取向硅钢在不同变形温度和应变速率下的真应力-真应变曲线,分析了变形参数对流变应力的影响规律,通过线性回归分析计算出该取向硅钢的热变形应力指数n以及变形激活能Q,并构建了流变应力本构方程。结果表明:该取向硅钢的真应力-真应变曲线为动态回复型,其变形时的流变应力主要取决于变形温度和应变速率;当应变速率一定时,流变应力随着变形温度的升高而减小;变形温度一定时,流变应力随着应变速率的增大而增大;用构建的Fe-3.0%Si-0.09%Nb取向硅钢流变应力本构方程计算得到的流变应力与通过试验测得的结果相吻合。     

GH4169合金高温变形过程本构方程

使用MMS-300热模拟实验机对GH4169合金在变形温度950℃,980℃,1000℃,1020℃,1040℃,1060℃,1100℃及变形速率0.01mm/s,0.1mm/s,1mm/s,10mm/s条件下进行压缩实验。其中,压下率为50%。在热压缩变形过程中,当温度升高或变形速率减小时,流变应力降低。根据不同的热变形参数对流变应力的影响,利用线性回归的方法分析了Arrhenius形式的本构方程,并求出激活能Q=505.649kJ/mol。最终,建立描述GH4169合金热变形规律的本构方程并分析其预测精度。结果表明:在不同热变形参数下,其流变应力的预测值与实验值的符合程度良好,平均相对误差为5.13%,线性相关度为0.977。     

2219铝合金热压缩时的流变应力本构方程

采用Gleeble-3180型热模拟试验机对2219铝合金进行单道次热压缩试验,研究了该铝合金在温度为200~350℃、应变速率为0.1~10.0s-1条件下的流变行为,建立了2219铝合金热压缩时的流变应力本构方程,并进行了试验验证。结果表明:2219铝合金的流变应力随应变速率的增大或变形温度的降低而增加;由Fields-Backofen本构方程计算得到的2219铝合金应力的变化规律与试验得到的相同,且应力计算值与试验值的相对误差小于5%,该本构方程可以较准确地描述2219铝合金的高温流变行为。     

基于Johnson-Cook模型构建M50NiL齿轮钢的流变应力本构方程

利用Gleeble-3500型热模拟试验机,研究了M50NiL齿轮钢在变形温度为1 123.15~1 423.15K、应变速率为0.005~10s-1条件下的变形行为,并对实测流变曲线进行了摩擦修正;基于应变速率和变形温度对金属高温变形的耦合效应,建立了基于Johnson-Cook(J-C)模型的耦合流变应力本构方程并进行了验证。结果表明:对试验钢流变曲线摩擦修正后,得到的流变应力比实测值小;经变形参数耦合修正后的J-C耦合本构方程计算得到的流变应力与摩擦修正后流变应力的平均相对误差为3.08%,其预测精度高于传统J-C本构方程(平均相对误差为14.31%)的。     

FV520B马氏体不锈钢的热变形行为和本构关系

采用Gleeble-3500型热模拟试验机对FV520B马氏体不锈钢进行了单道次等温热压缩试验,研究了该不锈钢在变形温度为850~1 150℃和应变速率为0.005~5.000s~(-1)条件下的热变形行为,根据应力-应变曲线并基于Zener-Hollomon参数和Arrhenius双曲正弦方程,建立了该不锈钢在高温压缩时的本构方程,并对该本构方程进行了修正和试验验证。结果表明:FV520B马氏体不锈钢的流变应力随着变形温度的升高或应变速率的减小而降低;在0.005s~(-1)、1 000~1 150℃或0.050~5.000s~(-1)、1 075~1 150℃条件下,该不锈钢发生了较明显的动态再结晶;在0.005s~(-1)、850℃,5.000s~(-1)、850℃和5.000s~(-1)、925℃条件下,由建立的本构方程计算得到的流变应力与试验值存在较大的误差;对本构方程进行修正之后,流变应力的预测值与试验值的相关系数为0.997 88,平均相对误差为2.225%,修正后的本构方程可以准确地预测该不锈钢的热变形流变应力。     

基于改进温度模型的300M钢本构方程参数识别

为了提高通过切削实验获取材料本构方程参数的精度,提出了将基于移动热源理论的温度分布模型沿剪切面积分计算剪切区平均温度的方法,结合不等距剪切区模型求得等效应变和应变率,建立了材料Johnson-Cook(J-C)本构方程参数的求解模型。根据切削实验获取的切削力和切屑厚度数据并采用遗传算法求得了300M钢J-C本构方程参数。与AdvantEdge FEM软件自带的300M钢本构模型相比,用所求模型参数仿真得到的主切削力、进给力和切屑厚度的精度有显著提高,验证了所建本构方程参数求解模型的有效性。     

60钢热压缩变形行为及其变参数Arrhenius本构方程

采用Gleeble-1500型热模拟试验机对60钢进行不同温度(730,750,800,850,900,1 000℃)和不同应变速率(0.01,0.1,1,5,10 s^-1)的热压缩试验,总真应变为0.8,分析了60钢在热压缩过程中的变形行为;引入变参数Arrhenius模型,采用五阶多项式对模型中各参数随应变的变化关系进行拟合,构建出60钢高温变形本构方程,并对方程的精确性进行了评估。结果表明：变形温度越高,应变速率越低,60钢的流变应力越小;在较低温度和较高应变速率下,60钢热压缩变形的软化机制主要为动态回复,在较高温度和较低应变速率下则主要为动态再结晶;建立的变参数Arrhenius本构方程对流变应力的预测值与试验值的拟合相关系数达到0.994 597,说明该本构方程可以较好地描述60钢的高温变形行为。     

The non-Newtonian effect of temperature on hydrodynamic lubrication failure

The influence of temperature on the rheological characteristics of lubricants has been investigated by analysing the viscosity-temperature relationship and energy equation of lubricants. The constitutive equation, which describes the non-Newtonian properties of lubricants caused by thermal effects, is founded and coupled with equations of continuity and momentum of the fluid to calculate the load-carrying capacity in hydrodynamic lubrication. The numerical solutions show that lubricants have ultimate shear strength as a result of the non-Newtonian effect of temperature, which leads to the oil film having limiting load-carrying capacity. The mechanism of film failure in hydro-dynamic lubrication is also studied preliminarily in this paper.     

环形金属橡胶隔振器弹性参数的确定

以实验研究为基础，通过对大量实验结果的分析，借助于金属元件抗拉弹性模量和剪切模量的计算方法，推导出环形金属橡胶隔振器在承受扭剪应力时，抗拉弹性模量以及扭剪弹性模量与金属丝直径、环形隔振器的几何参数、金属橡胶元件的相对密度之间的关系的理论计算公式。研究结果证明，利用该计算公式和有限元计算方法，可以直接求得具有不同结构参数的相应形状金属橡胶隔振器的弹性性能参数，所得计算结果与实验结果具有良好的一致性，因而大大减少了实验工作量，为金属橡胶隔振器的系列化生产奠定了基础。     

CONSTITUTIVE EQUATION OF A NEW AVIATION LUBRICATING OIL

The traction of a new aviation lubricating oil was measured on a self-made test rig. The calculating formulae of the rheological parameters of the oil such as Erying stress, limiting shear stress and shear elastic modulus were obtained under the condition of the high shear strain rate in elastohydrodynamic lubrication(EHL). The constitutive equation of this oil was determined and verified by test The results of experiments show that the behavior of the new aviation lubricating oil behaves as visco-elastic fluid and the theoretical value agrees fairly well with the measured data, which implies that the constitutive equation of this oil is correct and feasible.     

Stability analysis of rough journal bearings under TEHL with non-Newtonian lubricants

The combined effects of surface roughness and lubricants rheology on stability of a rigid rotor supported on finite journal bearing under thermal elastohydrodynamic lubrication have been investigated using the transient method. The newly derived time dependent modified Reynolds and the adiabatic energy equations were formulated using a non-Newtonian Carreau viscosity model. The simultaneous systems of modified Reynolds equation, elasticity equation, energy equation, and the rotor motion equation with initial conditions were solved numerically using multigrid multi-level method with full approximation technique. From the characteristic equation, the instability threshold is then obtained with various surface roughness parameters and the elastic modulus of the bearing liner materials. The results show that stability of the bearing system deteriorates with decreasing both the power law exponent and the elastic modulus of bearing liner material. The rough surface journal bearing with transverse pattern under TEHL regime exhibits better stability when compared with the rough surface journal bearing with longitudinal pattern.     

Analysis of hydrodynamic journal bearings having non-Newtonian lubricants

Commercial lubricants, due to the presence of different types of additives, behave like non-Newtonian fluids. The effect of this nonlinear behaviour on the performance characteristics of finite-width journal bearings is investigated using the Eyring model for the shear stress and shear strain rate. the finite element method using Galerkin's technique has been used to solve the momentum equations and the continuity equation in cylindrical coordinates, representing the flow field in the clearance space of a journal bearing system using Newtonian fluids; the non-Newtonian effect is introduced by modifying the viscosity term for the model in each iteration. The results of static performance characteristics for finite-width journal bearings having non-Newtonian lubricants have been obtained.     

The influence of the viscoplastic and viscoelastic character of a lubricant on elastohydrodynamic lubrication

The non-newtonian constitutive equation proposed by Johnson and Winer is discussed. Derivations of the lubrication equations suitable for the viscoplastic rheological model and the viscoelastic model are presented. The full numerical elastohydrodynamic lubrication solutions for the viscoplastic model and the viscoelastic model are obtained in order to observe the effects of the elastic shear modulus of the fluid and the limiting shear stress on the pressure distribution, film thickness and coefficient of friction.     

悬索式跨越架用纤维绳索非线性本构关系试验研究

悬索式跨越架在跨越电力线路施工中应用广泛,其承载索及封网绳多采用超高分子量聚乙烯纤维绳索和聚酯纤维绳索.由于进行悬索式跨越架动力学仿真计算纤维绳索所涉及的非线性本构关系尚无公开资料,各单位在进行仿真计算时采用弹性模量固定值来替代非线性应力—应变关系曲线,导致计算结果与实际情况不符.针对上述问题,对这两种常用规格的纤维绳...     

A simple non-linear constitutive equation for elastohydrodynamic oil films

In this paper a hypothetical constitutive relation for EHL oil films is proposed which combines a linear elastic response with a non-linear shear thinning viscous response. This model reduces to a linear Maxwell fluid for small strains. It is shown that provided the recoverable elastic strains are kept small (<0.3), which is generally the case for EHL contacts, the ambiguity of stress rate usually encountered with large total strains in viscoelasticity can be avoided. Hence this proposed constitutive law provides a simple Theologically acceptable basis for interpreting large strain EHD traction experiments.     

Rheological behavior’s effect on the work performance of oil film

A 3D model of hydrostatic turntable’s oil chamber is established to investigate the lubricants performance with different rheological properties by using FLUENT software and the finite volume method. Newtonian oil and non-Newtonian oil’s performance under varied speeds are compared on the large size hydrostatic turntable system considering the temperature-viscosity relationship and pressure-viscosity relationship. The results show that the property of non-Newtonian fluid viscosity influenced by shear rate largely affects the lubricants performance for most oil added polymer additives. Lubricants cannot simply be regarded as Newtonian fluid. The shear thickening non-Newtonian fluid has a better work property. The results are important to design a large size and high-speed hydrostatic support system, choose lubricant oils, and investigate oil film’s work properties.