Influence of polymeric fluid additives in EHL rolling/sliding line contacts

The effect of polymeric fluid additives on EHL behavior of rolling/sliding line contacts is investigated numerically at low as well as high loads. The polymer-modified oil is represented by a homogeneous mixture of Newtonian base oil and power law fluid with varying concentration, viscosity ratio and power law index. The Reynolds equation incorporating the mixed rheological fluid model is derived using perturbation method. The EHL characteristics computed for polymer-modified oils are found to depend upon the effective viscosity of the lubricant mixture which is governed by the superposition of shear thinning behavior and piezo-thickening effect of the polymeric fluid additive. Since the reference viscosity of polymeric fluid additives is much higher than that of base oil, therefore, polymer-modified oils are shown to yield thicker fluid films in most of the cases. The results show a significant variation in maximum fluid pressure and minimum fluid film thickness with the volume fraction, reference viscosity ratio and power law index of the polymeric fluid additive.     

Coupled effects of surface roughness and flow rheology on elastohydrodynamic lubrication

The coupled effects of surface roughness and flow rheology on elastohydrodynamic lubrication (EHL) circular contact problems are analyzed and discussed. The averaged type Reynolds equation utilizing the average flow model on the interactions between couple stress fluids and surface roughness, the elastic deformation equation, the viscosity–pressure and density–pressure relations equations, and the force balance equation are solved numerically by the multilevel multi-integration (MLMI) algorithm to calculate the pressure distributions and film thickness shapes. The results show that the transverse type roughness and standard deviation of composite roughness enhance the pressure and film thickness in the central contact region. Moreover, the longer the characteristic length of the couple stress fluids is, the smaller the pressure distribution is in the central contact region and the greater the film thickness is in all regions.     

Elastohydrodynamic lubrication of circular contacts at pure squeeze motion with non-Newtonian lubricants

In this study a numerical method for general applications with non-Newtonian fluids is developed to investigate the pure squeeze motion in an isothermal elastohydrodynamic lubricated spherical conjunction under constant load conditions. The coupled transient modified Reynolds, the elasticity deformation, and the load equilibrium equations are solved simultaneously. Computer simulation is carried out to investigate the effects of flow rheology and operations on the relationship between the pressure and film thickness distributions. The simulation results reveal that the larger the flow index (n), the larger the film thickness and the smaller the maximum central pressure. This results in larger time needed to obtain maximum central pressure. In addition, the elastic deformation is more significant for the lower flow index. Therefore, the smaller the flow index becomes, the greater the difference between the hydrodynamic lubrication (HL) solution and elastohydrodynamic lubrication (EHL) solution becomes.     

Study of surface roughness effects in elastohydrodynamic lubrication of rolling line contacts using a deterministic model

A sinusoidal surface roughness model is adopted for the analysis of the effects of roughness amplitude and wavelength on pressure profile, film shape, minimum film thickness and coefficient of friction in a steady state EHL line contact. The influence coefficients used for the evaluation of surface displacements are calculated by utilizing a numerical method based on Fast Fourier Transform. Significant reduction is observed in the minimum film thickness due to surface roughness. Such reduction is quantified by roughness correction factor, C_R, and a relationship between C_R and non-dimensional surface roughness amplitude A is derived as: C_R=1−0.7823A^0.8213. This equation may prove to be of interest from designer's viewpoint. The friction coefficient is found to increase appreciably with increasing amplitude and decreasing wavelength of surface roughness.     

Experimental study of real roughness attenuation in concentrated contacts

The understanding of the processes involved in the in-contact deformation of surface roughness represents one of key factors in increasing lubrication capabilities of highly loaded machine components. Two main approaches have been developed in an effort to understand the changes of initial surface topography within highly loaded contacts to provide detailed information about lubrication film thickness and pressure distribution in the vicinity of roughness features. The first approach considers the real surface topography while the other uses the simplified topography features. Numerical solutions based on measured topography data can provide the film thickness and pressure distribution around asperities of realistic scale; nevertheless, obtained results are typically limited to the specific topography configuration measured from a very small area of rubbing surface. That is why some researchers have considered harmonic features of various wavelength and amplitudes to explain the behaviour of real roughness.This study is focused on the experimental validation of an approach based on Fourier decomposition of the surface roughness into harmonic components. Two optical measurement techniques—phase shifting interferometry and thin film colorimetric interferometry are combined to provide the undeformed surface topography and film thickness data within the elastohydrodynamic contact formed between a smooth disk and a ball having a real rough surface. The results obtained under pure rolling conditions not only confirmed the general principle that roughness deformation is component dependent and that long wavelengths deform more than short wavelengths, also the observed deformation for different components agreed well with the data predicted by the theory.     

Effect of waviness and roughness components on transverse profiles of turned surfaces

This paper presents the authors method of simultaneous analysis of roughness and waviness irregularity components, with the aim of better defining the key qualities and characteristics.     

Experimental study of real roughness attenuation in rolling/sliding concentrated contacts

A surface roughness attenuation approach based on the Fourier decomposition of surface roughness into harmonic components may allow predictions of the behavior of real rough surfaces within concentrated lubricated contacts. Recent experiments performed under pure rolling conditions have shown an amplitude reduction of different components that agreed well with the data predicted by the theory. This study represents the next step in the experimental verification of the surface roughness attenuation approach under rolling-sliding conditions. Obviously, the behavior of roughness in the rolling-sliding elastohydrodynamic (EHD) contacts is more complex than for pure rolling. It has been theoretically suggested by other researchers that the modification of the original roughness alone cannot explain all of the major effects that significantly affect film thickness, and a model was proposed in which, along with the roughness attenuation, a complementary wave was generated in the inlet region and moved at the entrainment speed. This paper is focused on the possibility of extracting complementary waves from experiments with real rough surfaces conducted under rolling-sliding conditions and of determining whether the amplitudes of the complementary wave can be determined. This represents the first attempt to study both effects of rough surface behavior separately. The complementary wave was extracted from the measured data by subtracting the attenuated original roughness from the measured film thickness. Although the experimental results were quite scattered, a trend similar to that of the theoretical curves was observed. Based on the results, it can be suggested that the significance of the complementary wave is comparable to the attenuation principle.     

Effect of surface roughness on elastohydrodynamic traction: Part 1

The effect of surface roughness on traction performance was experimentally studied using a two‐roller tester. The nature of the contact was investigated using electrical resistance and electrical capacitance methods. Increased shear stress was observed in the viscous region, which could be attributed to a higher average shear rate and to greater viscosity under EHD contact conditions due to pressure fluctuations caused by the surface texture.     

Influence of surface roughness on pressure distribution and film thickness in EHL-contacts

To better understand the effect of surface roughness and texture on the formation of a lubricating oil film the mean film thickness and pressure distribution in the Hertzian contact zone were systematically investigated with an FZG twin-disk test rig. The pressure distribution was measured using thin film sensors. The influence of roughness and surface texture was investigated as a function of load and sum velocity. Different types of surfaces were produced by circumferential and transverse grinding as well as structuring by etching.     

Effect of surface roughness on elastohydrodynamic traction. Part 2

To investigate the performance of a traction‐drive toroidal continuously variable transmission, the traction characteristics under partial elastohydrodynamic lubrication contact were calculated theoretically based on roller test results. A calculation model was constructed for considering the effects of surface roughness on performance. The model incorporated a viscoelastic and elastic‐plastic model using a nonlinear Maxwell model to represent the rheological behaviour of the traction fluid. The validity of the model was confirmed by its good agreement with the experimental results described in Part 1 of this paper. Various calculations were made to investigate the effect of surface roughness on traction under the operating conditions of an actual traction drive. The results indicated that the effect of surface roughness on durability could not be ignored.     

Experimental and numerical investigation on the behavior of transverse limited micro-grooves in EHL point contacts

This study presents experimental and numerical investigations on the effects of transverse limited micro-grooves on the behavior of film thickness and friction in EHL point contacts. The tribological performance has been compared for smooth and textured surfaces in sliding and reciprocating motion and under starvation. The measurements were conducted by using a ball-on-disk tribometer equipped with a high speed camera and torque sensor. The results show that the transverse shallow micro-grooves with a length less than the diameter of the Hertzian contact are efficiently able to enhance the film thickness under different operating conditions. The beneficial effect under starved lubrication requires a mechanism for filling the depleted micro-grooves entering the contact with fresh lubricant. This mechanism can be attributed to the capillary effect in the inlet zone under starvation. The numerical simulation of the transient behavior of transverse limited micro-grooves shows agreement with experimental results. On the other hand, introducing micro-grooves as closed texture cells on one of rubbing surfaces results in a friction reduction in the reciprocating motion. The reduction of friction is substantially attributed to the film thickness enhancement.     

Investigating the Effect of Surface Finish on Mixed EHL in Rolling and Rolling-Sliding Contacts

Surface finish may significantly affect the lubrication performance of a tribological interface through the influence of topography on micro/nanoscale fluid flows around localized contacts at surface asperities. This paper aims to study the mixed lubrication performance of a group of engineered surfaces, including turned, isotropically finished, ground, and dimpled surfaces, under different operation conditions by means of a deterministic mixed elastohydrodynamic lubrication (EHL) model. The honed surface was used to mate with other surfaces. The results indicate that a longitudinal contact ellipse favors longitudinally oriented mating surface roughness and that a transverse contact ellipse, as well as a line contact, prefers a transversely orientated mating surface roughness for lubrication enhancement.     

Drag reducing effects of polymer additives on Coal-Water Mixture in rotating disk system

Using a rotating disk apparatus, the concept of drag reduction produced by polymer additives is applied to Coal-Water Mixture(CWM) transport. Experiments were undertaken for a wide range of polymer concentrations of poly(ethylene oxide: PEO), poly(acrylamide: PAAM), coal concentrations and rotating disk speeds. Drag reduction decreased with higher coal concentrations, and increased with higher polymer concentrations up to 150 wppm for PEO. Further increases in the PEO concentration led to lower drag reduction. Howere, PAAM produced higher drag reduction which remained almost constant over a wide range of concentrations. The effect of polymer degradation was also investigated and it was found that PAAM is a better drag reducer than PEO when applied to long time transportation of CWM.     

The influence of surface roughness in elliptical contacts

The influence of surface roughness on contact behaviour is of great importance in many tribological situations. In the last decade several methods to calculate the pressure distribution and the real contact area in contacts between rough surfaces have been described. A problem arising for slender elliptical contacts, such as between gear teeth, roller and raceway, cam and follower, etc., is that the size of the contact is much greater than the size of the asperities. Accordingly the number of contact nodes necessary for an accurate solution to the problem becomes excessively large. This paper describes a method to calculate the influence of three-dimensional surface roughness in contacts that are very long in one direction. The method is based on restricting the calculations to a subpart of the real contact area, while the rest of the contact is taken into account by mirroring techniques. The results show that the real contact area is very sensitive to the amplitude of the roughness, while the waviness is less important. An equation is suggested from which the real area can be calculated if the smooth case contact parameters and two roughness parameters are known.     

液体调速离合器中摩擦副热效应的简化分析

液体粘性调速离合器是利用多个摩擦圆盘间的油膜剪切力来传递动力，并通过改变油膜厚度实行无级调速。由于近来工程中广泛采用聚α-稀烃型，聚酯型等合成油作润滑剂，液体粘性调速离合器在调速范围内，其摩擦副往往工作在流体润滑、混合润滑、边界润滑直到直接接触的工况。基于这些特点，笔者采用了幂律型非牛顿流体模型、Patir—Cheng的平均流量模型、GT两粗糙平面接触模型，并计入油膜的惯性影响，建立了热简化研究模型，对液体粘性调速离合器中的摩擦副进行了流体混合润滑状态下的数值计算与分析。     

On Prediction of Wear Coefficients in Sliding Wear

The wear rates and wear coefficients of metals are analytically predicted based on the delamination theory of wear when the wear rates are controlled by the subsurface crack propagation rate. The wear rate and the wear coefficient are predicted to be directly proportional to the depth of crack location and the crack growth rate. The numerical values of wear coefficients are obtained through finite element analysis of crack propagation in elastoplastic solids. The agreement between typical experimental results and theoretical prediction is excellent.     

基于声发射信号的铣削加工表面粗糙度预测技术研究

使用声发射技术对铣削过程进行监测,通过对声发射信号进行频域分析,比较不同频段的能量比来在线预测加工后的表面粗糙度.     

AutoCAD二次开发中表面粗糙度的智能化标注

针对在使用AutoCAD进行绘图时，表面粗糙度标注不方便的问题，提出了利用VBA进行AutoCAD二次开发的方法。充分考虑到了一般用户的使用习惯，实现了标注的智能化。     

Tactile perception: Finger friction, surface roughness and perceived coarseness

Finger friction measurements performed on a series of printing papers are evaluated to determine representativeness of a single individual. Results show occasionally large variations in friction coefficients. Noteworthy though is that the trends in friction coefficients are the same, where coated (smoother) papers display higher friction coefficients than uncoated (rougher) papers. The present study also examined the relationship between the measured friction coefficients and surface roughness to the perceived coarseness of the papers. It was found that both roughness and finger friction can be related to perceived coarseness, where group data show that perceived coarseness increases with increasing roughness.     

An investigation of surface roughness of burnished AISI 1042 steel

The aim of this study is to analyse the evolution of surface roughness finished by burnishing. Burnishing is done on a surface that was initially turned or turned and then ground.It has been noted that burnishing an AISI 1042 steel offers the best surface quality when using a small feed value. This finishing process improves roughness and introduces compressive residual stresses in the machined surface. So, it can replace grinding in the machining range of the piece.Also, an analytical model has been defined to determine the R_t factor in relation to the feed. Good correlations have been found between the experimental and analytical results.