The generic nature of the absolute-retardation method of photoelasticity

The method of absolute-retardation measurements does not depend upon the use of any specific interferometer. Any one of the many extended field interferometers can be employed, including the Series, Michelson, Mach-Zehnder and Fizeau types. Where adequate monochromatic purity of light source is available, reflections from the two surfaces of the model can form the interferogram, thus dispensing with the necessity of any separate optical interferometer. The two-dimensional stress-optical relationships are derived in their most general form. The relationships are identical for all instruments or interference systems—only the calibration constants change with different systems. Interferograms from four distinctly different systems are shown. Interference-fringe sharpening is introduced and demonstrated. A laser-light source was used with two systems to provide high monochromatic purity. The interferometric method of Nisida and Saito is correlated with the absolute-retardation method. The opportunity to obtain information for a complete stress solution from one photograph makes the method attractive for both static and dynamic problems.     

Thickness of the film in an elastic hydrodynamic contact

A method is proposed for determining the thickness of the film in a heavily loaded elliptical elastic hydrodynamic contact. The method consists of integration of the Reynolds equation over the region occupied by the film, using the boundary differential equation for the integral of the reduced pressure. To determine the thickness of the film it is sufficient to know only the integral of the reduced pressure along the line of a constant gap. A new formula is obtained for the thickness of the film in an elliptical elastohydrodynamic contact, i.e., for the general case of a heavily loaded Hertzian contact in the presence of a lubricant.     

滑动表面卷吸速度为零时的热弹流润滑分析

提出了接触处两表面等速反向运动的圆柱间在一定条件下赤存在足够厚的稳态热弹流膜,此时固体表面呈现中凹状、且凹陷深度随勒荷的增加而增大,随表面速度的增加而减小。     

谐波振动下线接触弹流润滑的仿真及分析

采用多重网格技术对谐波振动下线接触弹流问题进行了仿真 ,并对不同振动参数下油膜厚度与压力分布的仿真结果进行了分析 .结果表明 :谐波幅值和频率均对弹流膜厚度、形状及压力分布具有重要影响     

Holographic photoelasticity: Determination of absolute retardations by a single hologram

In this paper, real-time holographic interferometry is applied to determine the absolute-retardation fringes in the photoelastic analysis of plane models. The method requires only one hologram recorded with the model unloaded. In the reconstruction process, the mcdel is loaded and the polarizers on the reference and object beams are rotated through the same angle. At the points of the model where the polarization direction is parallel to one of the principal stresses, only the corresponding family of absolute retardations is obtained. The technique is demonstrated experimentally using a deep beam centrally loaded.     

润滑剂边界滑移及其对弹流润滑特性的影响

基于润滑剂在弹性流体动力润滑状态下表现出类似塑件固体的非牛顿特性，根据塑性屈服和流体动力润滑理论，建立了考虑润滑剂在固液界面滑移的线接触弹流润滑失效预测模型。计算结果显示：载荷和滑滚比对润滑油膜厚度影响显著；在一定载荷和滑滚比下，润滑油膜将丧失承载能力而破裂。与现有理论及实验数据对比，线接触弹流润滑失效预测模型的计算结果与实验结果具有较好的一致性。     

有限长滚子线接触热弹流润滑分析

应用多重网格解法 ,求出了有限长滚子线接触热弹流润滑的完全数值解 .结果表明 :在滚子的中部 ,油膜压力、温度和最小膜厚与无限长线接触热弹流润滑的解几乎一致 ;在滚子端部的圆角处 ,油膜压力、温度和最小膜厚与中部均显著不同 ,且最大油膜压力、最大油膜温度和最小油膜厚度均发生在此处 ,端部圆角半径对弹流润滑性能有显著影响 .同时 ,将有限长线接触热解与有限长线接触等温解进行了比较 .     

On the limitations of interferometric methods in three-dimensional photoelasticity

The photoelastic response of tinree different epoxy materials was measured. Tensile strips, beams, disks and spheres were loaded and the deformations “frozen in.” Slices from these models were used to calibrate and analyze the absolute retardation of the materials. It was found that the absolute retardation of light vibrating in a given principal direction was directly proportional to the principal strain in that direction and to the deviatoric components of stress in that direction. This result was a consequence of a unique value of the ratio of the absolute-retardation constants and is contrary to published suggestions that absolute-retardation methods could be used to separate normal stresses in the interior of stress-frozen models.     

表面粗糙度特征对齿轮接触区润滑特性的影响

大部分工程实际粗糙表面符合非高斯分布,并对齿轮接触副润滑特性有重要影响.将渐开线齿轮啮合过程中齿面接触等效为三维无限长线接触,建立了一个可分析直齿轮和斜齿轮的混合弹流润滑计算模型;采用基于快速傅里叶变换的数值仿真方法生成给定参数的非高斯粗糙表面;运用该模型对直齿轮和斜齿轮啮合过程进行分析,求得不同表面粗糙度特征齿轮在各个啮合点的油膜厚度、接触区载荷以及接触区比例的情况.结果表明:对于标准差相等的非高斯粗糙表面,偏度值对齿轮润滑状况的影响与工况紧密相关,在润滑良好的条件下,偏度值越小润滑状况越优;润滑恶劣的条件下,偏度值越大润滑状况越优;而在各种工况下,峰度值对齿轮润滑状况的影响都表现出峰度值越大润滑状况越优的特点.     

关于椭圆接触弹流润滑Hamrock-Dowson膜厚公式的再思考

使用常用的Hamrock-Dowson公式计算椭圆点接触中心油膜厚度时发现:当维持接触区中心赫兹压力为常数,增加椭圆比k_e超过一定值时,得到的中心膜厚不升反降,这与其物理本质相悖. 应用有限单元法重新对等温椭圆接触弹流润滑问题进行了数值计算,提出新的表征椭圆接触的综合几何参数. 在较大的速度和载荷范围内下,依据数值计算结果,拟合出修正端泄因子和修正中心膜厚公式. 修正公式与数值计算结果相吻合,且正确地表达了膜厚与椭圆比的关系.      

Friction in an elastohydrodynamic contact

The problem of the movement of a fluid in an elastohydrodynamic contact is examined in cases of high pressures, high displacement velocities, and low characteristic times, taking into account the nonlinear properties of the fluid — dependence of viscosity on pressure, temperature, and displacement velocity. Simple asymptotic formulas are obtained. The problem is solved numerically in the one-dimensional case. A comparison is made with an experiment on the measurement of the frictional force in an elastohydrodynamic contact.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 135–137, July–August, 1976.The authors wish to thank V. D. Danilova and A. I. Petrusevich for supplying the experimental data.     

基于MEPE和EHL理论的渐开线斜齿轮啮合特性分析

以斜齿轮为研究对象,应用最小弹性势能原理(MEPE)和弹性流体动力润滑理论(EHL),采用多重网格数值求解法获得了斜齿轮在不同啮合位置及沿接触线方向的载荷分布,压力与膜厚分布,并对比分析了不同螺旋角下基于MEPE理论和基于接触线长比例理论的载荷分布模型及数值仿真结果.结果表明:沿啮合线方向,载荷在啮合中间段达到最大值,螺旋角越大,载荷分布趋于平均;受综合曲率半径和载荷分布的影响,压力分布在啮合中间段较高,膜厚沿啮合线缓慢变化,节点处稍有下降;沿接触线方向,载荷变化平缓,近似呈抛物线,最小膜厚单向线性变化,而压力则在两端具有较大值.     

Jacobian-free Newton-Krylov subspace method with wavelet-based preconditioner for analysis of transient elastohydrodynamic lubrication problems with surface asperities

This paper presents an investigation into the effect of surface asperities on the over-rolling of bearing surfaces in transient elastohydrodynamic lubrication(EHL) line contact. The governing equations are discretized by the finite difference method. The resulting nonlinear system of algebraic equations is solved by the Jacobian-free Newtongeneralized minimal residual(GMRES) from the Krylov subspace method(KSM). The acceleration of the GMRES iteration is accomplished by a wavelet-based preconditioner.The profiles of the lubricant pressure and film thickness are obtained at each time step when the indented surface moves through the contact region. The prediction of pressure as a function of time provides an insight into the understanding of fatigue life of bearings.The analysis confirms the need for the time-dependent approach of EHL problems with surface asperities. This method requires less storage and yields an accurate solution with much coarser grids. It is stable, efficient, allows a larger time step, and covers a wide range of parameters of interest.     

两表面速度均为任意方向的非牛顿椭圆接触等温弹流润滑分析

提出了一种简单易行的方法用于进行两表面速度均为任意方向的等温点接触弹流润滑分析;建立了等温非牛顿椭圆接触弹流润滑的数学模型,综合考虑了两表面速度同向、反向及不共线且与椭圆短轴成一定角度的工况,并得到了两表面速度均为任意方向的等温数值解.结果表明:随着两表面速度方向的改变,合卷吸速度的方向不断变化,接触椭圆在计算域内的倾斜角度也随之改变;由于接触椭圆与坐标轴成一定角度,油膜的压力和膜厚不再与Y=0平面对称,Y=0平面内第二压力峰和油膜颈缩出现在出口区,而在X=0平面内第二压力峰和油膜颈缩出现在入口区.     

电阻法检测乳化液润滑状态的变化

用改进的电阻法测定了金属滑动摩擦副在混合润滑状态下发生接触的时间比率，并且检测了环－块试验过程中水包油型乳化液润滑状态的变化，同时还就乳化液中油相的体积分数和载荷等对乳化液成膜能力的影响进行了试验研究．根据测得的金属接触时间比率－滑动速度曲线的变化趋势，可以清楚地判断出润滑状态的转化及对应的临界转化速度．对比相应工况下油膜厚度的理论计算值，可以说明环－块接触区会形成一个基油富集区（油池）．在此区域内，乳化液中油相的体积分数远比其标称值高，乳化液润滑具有油池润滑的特点     

球盘点接触区外润滑油分布的试验研究

利用激光激发荧光技术对球-盘弹流接触区附近以及自由表面上的润滑油分布进行了试验观察,探究了离心力作用下接触区附近以及自由表面上润滑油分布的变化规律. 结果表明:随着速度增大,内外两侧油池及自由表面上的油量分布均有所减少,其中外侧油池及自由表面上外侧油带的变化较明显;在一定工况条件下,外侧油池的大小存在极限,因此速度较大时外侧油池宽度对供油量变化不显著,而该极限由离心力作用和毛细力作用共同决定;在离心力作用下,自由表面上的油带有向外侧铺展的趋势,而接触区周围的油池分布对自由表面上的油带分布起决定作用.      

非牛顿重载滚滑工况有限长线接触热弹流研究

在流速主矢量方向使用Eyring流变模型,用多重网格法求出接触压力高达1.04 GPa的相交圆弧修形滚子的热弹流完全数值解.研究表明:随着Eyring流体非牛顿效应的增强,有限长线接触弹流二次压力峰的高度明显降低,每次工作循环中摩擦副受第二次高压的强度减小;热效应显著减弱,有助于防止由热效应导致的各种形式的失效;最小油膜厚度略有增加,有利于润滑膜的形成.因此,使用Eyring非牛顿流体有利于延长线接触副的寿命.与此同时,使用Eyring非牛顿流体时,非牛顿效应对滚子端部的压力分布影响很小,因此Eyring非牛顿效应对有限长摩擦副的凸度设计无明显影响.     

使用不等距多重网格技术求解线接触热弹流润滑问题

使用不等距多重网格法求解了线接触热弹流润滑问题 .结果表明 :与等距多重网格法相比 ,新解法虽不能提高数值求解的稳定性 ,却能得到更为精确的压力、膜厚及温度分布 ;计算结果表明中载下第二压力峰是光滑的     

Experimental analysis of contact for the indentation of a flat rounded punch

The ‘plane vs. plane’ contact involving flat punches has been the subject of many investigations, even in recent years, mainly due to the crucial role that such components play in phenomena, such as fretting fatigue and indentation tests. While the problem has been deeply approached from a theoretical point of view, there is a noteworthy lack of experimental verifications due to the limited number of laboratory techniques capable of supplying detailed information about contact parameters. In order to make a partial contribution towards gaining an understanding of such problems, this study proposes the investigation of flat rounded punch contact with an ultrasound-based technique, which exploits the properties of ultrasonic waves to be differently reflected by a contact interface depending on its stress state. A suitable setup was built in such a way as to ensure a good level of control of contact conditions, and the interface was scanned with a high-frequency ultrasonic transducer so as to acquire the reflection data. While the graphic processing of the ultrasonic coefficient of reflection may easily be displayed as a ‘contact map’, the quantitative accuracy of the method was also investigated by comparing experimental results with those obtained from a Finite Element model of the system. The results show a good level of agreement between the two approaches, thus confirming that the ultrasonic technique can be effectively employed to investigate many contact problems which to date have never (or scarcely) been experimentally validated.     

自旋对界面滑移弹流油膜的影响

应用旋滑式光干涉弹流薄膜测量系统研究了自旋对界面滑移条件下玻璃盘-钢球形成的反常弹流油膜的影响,通过弹流接触副与玻璃盘旋转中心距离的调节,在弹流润滑中实现不同程度的自旋,即引入不同的旋滑比.结果表明,随着旋滑比的增加,油膜整体厚度减小,油膜形状呈现明显的非对称性,人口凹陷的深度有所减小;最小油膜厚度的速度指数随旋滑比的增加而增加;固定偏心距,随着载荷的增加,最小膜厚先增加后减小,油膜形状的非对称性增强.对上述观察到的试验现象,也进行了相应的理论解释,认为自旋引起的卷吸速度变化及气穴区的不对称是主要诱因.