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.     

A surface motor-driven planar motion stage integrated with an XYθZ surface encoder for precision positioning

This paper describes a surface motor-driven XY planar motion stage equipped with a newly developed XYθ_Z surface encoder for sub-micron positioning. The surface motor consists of four linear motors placed on the same surface, two pairs in the XY-axes. The magnetic array and the stator winding of the linear motor are mounted on the platen (the moving element) and the stage base, respectively. The platen can be moved in the X-direction by the X-linear motors, and in the Y-direction by the Y-linear motors. It can also be rotated about the Z-axis if the X- or Y-linear motors generate a moment about the Z-axis. The surface encoder consists of two two-dimensional angle sensors and an angle grid with two-dimensional sinusoidal waves on its surface. The angle grid is mounted on the platen of the stage which is levitated by air-bearings. The angle sensors and the air-bearing pads are fixed on the stage base so that the motion of the platen is not affected by the electronic cables and air hoses. The XY-positions and θ_Z rotation of the platen can be obtained from the angle sensor outputs with resolutions of approximately 20 nm and 0.2′′, respectively. The surface encoder is placed inside the stage so that the stage system is very compact in size. Experimental results indicate that precision positioning can be carried out independently in X, Y and θ_Z with resolutions of 200 nm and 1′′, respectively.     

Soft-tribology: Lubrication in a compliant PDMS–PDMS contact

We investigate the influence of surface roughness and hydrophobicity on the lubrication of a soft contact, consisting of a poly(dimethylsiloxane) (PDMS) sphere and a flat PDMS disk. The full Stribeck curves, showing boundary, mixed and elasto-hydrodynamic (EHL) lubrication, are presented for varying surface roughness and hydrophobicity. It is found that neither surface roughness nor hydrophobicity influence the friction coefficient (μ) within the EHL regime. However, increasing surface roughness decreases μ in the boundary regime, while extending the limits of the boundary and mixed lubrication regimes to larger values of the product of velocity and lubricant viscosity (Uη). The transition from the mixed lubrication to EHL regime is found to take place at lower values of the film thickness parameter Λ for increasingly rough surfaces. We found Λ=0.7 in the case of a root mean square (r.m.s.) surface roughness of 3.6 μm, suggesting that the effective surface roughness in a compliant compressed tribological contact is lower than that at ambient pressures. Rendering the PDMS surface hydrophilic promotes full-film lubrication and dramatically lowers μ in the boundary regime by more than an order of magnitude. This influence of surface wetting is also displayed when examining a range of lubricants using hydrophobic tribopairs, where the boundary μ decreases with decreasing lubricant–substrate contact angle. Implications of these measurements are discussed in terms of the creation of model surfaces for biotribological applications.     

Design-based estimation of surface area in thick tissue sections of arbitrary orientation using virtual cycloids

Surface area is a first‐order stereological parameter with important biological applications, particularly at the intersection of biological phases. To deal with the inherent anisotropy of biological surfaces, state‐of‐the‐art design‐based methods require tissue rotation around at least one axis prior to sectioning. This paper describes the use of virtual cycloids for surface area estimation of objects and regions in thick, transparent tissue sections cut at any arbitrary (convenient) orientation. Based on the vertical section approach of Baddeley et al., the present approach specifies the vertical axis as the direction of sectioning (i.e. the direction perpendicular to the tissue section), and applies computer‐generated cycloids (virtual cycloids) with their minor axis parallel to the vertical axis. The number of surface‐cycloid intersections counted on focal planes scanned through the z‐axis is proportional to the surface area of interest in the tissue, with no further assumptions about size, shape or orientation. Optimal efficiency at each x–y location can be achieved by three virtual cycloids orientated with their major axes (which are parallel to the observation planes) mutually at an angle of 120°. The major practical advantage of the present approach is that estimates of total surface area (S) and surface density (S_V) can be obtained in tissue sections cut at any convenient orientation through the reference space.     

The development of the modified Hurst orientation transform for the characterization of surface topography of wear particles

A modified Hurst orientation transform (HOT) method for characterization of wear particle surfaces is proposed and described in this paper. The method involves the calculation of self-affine Hurst coefficients in all directions and displays the calculated coefficient values in a form of rose plot. The calculation of individual Hurst coefficients, H, is based on the rescale range (r/s) analysis (r(d)/s∼ d ^H ). The rose plot is then used to obtain three texture surface parameters, i.e.: texture aspect ratio, texture minor axis and texture direction. The effectiveness of this modified HOT and resulting surface texture parameters was evaluated. The method was first applied to computer-generated images of isotropic and anisotropic particle fractal surfaces and then to field emission scanning electron microscope images of wear particles found in synovial joints. The ability of the surface parameters to reveal surface isotropy or anisotropy, measure roughness and determine the dominant direction of surface texture was assessed. The effects of measurement conditions such as noise, gain variations and focusing on the surface parameters were also investigated. The results demonstrate that the HOT and surface texture parameters developed can successfully be used in the characterization of wear particle surface topography. This revised version was published online in August 2006 with corrections to the Cover Date.     

Surface roughness and material removal rate of lapping process on ceramics

Lapping is a widely used surface finishing process for ceramics. An experimental investigation is conducted into the lapping of alumina, Ni−Zn ferrite and sodium silicate glass using SiC abrasive to study the effect of process parameters, such as abrasive particle size, lapping pressure, and abrasive concentration, on the surface roughness and material removal rate during lapping. A simple model is developed based on the indentation fracture and abrasive particle distribution in the slurry to explain various aspects of the lapping process. The model provides predictions for the surface roughness,R _a andR _t , on the machined surface and rough estimation for the material removal rate during lapping. Comparison of the predictions with the experimental measurements reveals same order of magnitude accuracy.     

Grindability of high-temperature alloy with ceramic alumina wheels

The grindability of high-temperature alloy by using ceramic alumina wheels is studied on the basis of extensive analysis of the grinding force, grinding temperature, surface roughness and topography of ground surfaces, residual stress, hardness distribution of surface layer, and morphology of the surface layer from a metallographic point of view. The grinding burn mechanism of high-temperature alloy is unveiled and the feasible grinding parameters to avoid burning are analyzed. Some conclusions are obtained as follows. Increasing the grinding depth or the wheel velocity makes grinding temperature and residual tensile stress of the surface rise, which deteriorates the surface topography. Appropriate liner velocity of the wheel is 18–22 m/s and the depth of grinding should not exceed 0.02 mm in grinding GH2132 alloy with ceramic alumina wheels to assure the surface quality. When a _p increases enough to cause grinding burn, the strengthening effect of particles γ′ in γ base decrease and the micro-hardness of the surface is obviously lower than that of the base material, which deteriorates the mechanical properties and heat resistance of GH2132 alloy. Results provide a theoretical and experimental basis for technical optimization in the grinding of high-temperature alloy with high efficiency and high quality.     

Comparisons of the topographic characteristics and electrical charge distributions among Babesia‐infected erythrocytes and extraerythrocytic merozoites using AFM

Tick‐borne Babesia parasites are responsible for costly diseases worldwide. Improved control and prevention tools are urgently needed, but development of such tools is limited by numerous gaps in knowledge of the parasite–host relationships. We hereby used atomic force microscopy (AFM) and frequency‐modulated Kelvin probe potential microscopy (FM‐KPFM) techniques to compare size, texture, roughness and surface potential of normal and infected Babesia bovis, B. bigemina and B. caballi erythrocytes to better understand the physical properties of these parasites. In addition, AFM and FM‐KPFM allowed a detailed view of extraerythrocytic merozoites revealing shape, topography and surface potential of paired and single parasites. B. bovis‐infected erythrocytes display distinct surface texture and overall roughness compared to noninfected erythrocytes. Interestingly, B. caballi‐infected erythrocytes do not display the surface ridges typical in B. bovis parasites. Observations of extraerythrocytic B. bovis, B. bigemina and B. caballi merozoites using AFM revealed differences in size and shape between these three parasites. Finally, similar to what was previously observed for Plasmodium‐infected erythrocytes, FM‐KPFM images reveal an unequal electric charge distribution, with higher surface potential above the erythrocyte regions that are likely associated with Babesia parasites than over its remainder regions. In addition, the surface potential of paired extraerythrocytic B. bovis Mo7 merozoites revealed an asymmetric potential distribution. These observations may be important to better understand the unique cytoadhesive properties of B. bovis‐infected erythrocytes, and to speculate on the role of differences in the distribution of surface charges in the biology of the parasites.     

An algorithm of NURBS surface fitting for reverse engineering

Reverse engineering is an approach for constructing a CAD model from a physical part through dimensional measurement and a surface model. Different from conventional methods, this paper develops a new algorithm by which a desired fitted surface is obtained with less computation. Let selected m×n measured points be control points to construct B-spline or NURBS surface, then modify this constructed surface by using all the measured points and least squares minimization. A new algorithm for parameterization for measured points is also presented in this paper. The effectiveness and efficiency of these proposed algorithms are demonstrated.     

Accuracy Optimisation for Mould Surface Profile Milling

In the profile milling process for mould surfaces, for any type of curve combination, when implementing the milling process on a CNC machine, the surface can be produced from straight lines or curves in a piecewise or continuous milling process. This work employs the features of a CNC machine: 1. To divide the various sizes of curve at different slopes. 2. To use with different milling spindle speeds. 3. To use cutting feeds for actual milling experimentation. The results of the profile dimension accuracy and profile surface roughness from these experiments are then used in a neural network to establish an experiment result and a model for the milling variables. The neural network is composed of a number of functional nodes. Once the milling parameters (spindle speed, feed speed and milling angle) are given, the milling processing performance (the surface roughness, the surface profile-error) can be accurately predicted by the net-work developed. The optimal milling processing parameters can be searched for by a simulation annealing (SA) optimis-ation algorithm with a performance index to obtain a satisfactory mould surface. The experiment is then used to show that improved conditions for mould profile processing can indeed be obtained.     

一个新的泛卡塞格林望远镜系统

将卡塞格林系统的主镜及次镜都取球面,在焦面前加2片以上改正透镜,而将作为密封窗的平行平板的一面加4次方项,可以设计出具有相当大视场,像质优良的新光学系统。平板上的4次方非球面是凹面性质,它的制造,在周边铰支而外加均布载荷时可以加工为球面,释放均布载荷后该面即弹回成所要的4次非球面。所以,此系统从光学工艺角度看只有球面和平面。文中设计了4个不同相对口径系统:F/3,F/5,F/8,F/10。口径和视场相同:φ=300mm,2ω=1°,像质都接近或达到衍射极限。     

Predictive Modeling of Surface Roughness in Grinding of Ceramics

The surface roughness represents the quality of ground surface since irregularities on the surface may form nucleation for cracks or corrosion and thus degrade the mechanical properties of the component. The surface generation mechanism in grinding of ceramic materials could behave as a mixture of plastic flow and brittle fracture, while the extent of the mixture hinges upon certain process parameters and material properties. The resulting surface profile can be distinctively different from these two mechanisms. In this article, a physics-based model is proposed to predict the surface roughness in grinding of ceramic materials considering the combined effect of brittle and ductile material removal. The random distribution of cutting edges is first described by a Rayleigh probability function. Afterwards, surface profile generated by brittle mode grinding is characterized via indentation mechanics approach. Last, the surface roughness is modeled through a probabilistic analysis of ductile and brittle generated surface profile. The model expresses the surface finish as a function of the wheel microstructure, the process conditions, and the material properties. The predictions are compared with experimental results from grinding of silicon carbide and silicon nitride workpieces (SiC and Si₃N₄, respectively) using a diamond wheel.     

Use of the Roughness Parameters Ssk and Sku to Control Friction—A Method for Designing Surface Texturing

The aim of this work was to show that with the use of the surface roughness parameters S_sk and S_ku we can predict tribological behavior of contact surfaces and use these parameters to plan surface texturing. This article presents a continuation of our research on virtual texturing and experimental work on surface textures in the form of channels. For this investigation, steel samples were laser surface textured in the shape of dimples with different spacings between the dimples and different dimple depths. The experimental results confirmed that the parameters S_sk and S_ku can be used to design the surface texturing, where a higher value of S_ku and more negative S_sk lead to lower friction.     

Analytical Surface Roughness Parameters of a Theoretical Profile Consisting of Elliptical Arcs

The closed‐form solutions of surface roughness parameters for a theoretical profile consisting of elliptical arcs are presented. Parabolic and simplified approximation methods are commonly used to estimate the surface roughness parameters for such machined surface profiles. The closed‐form solution presented in this study reveals the range of errors of approximation methods for any elliptical arc size. Using both implicit and parametric methods, the closed‐form solutions of three surface roughness parameters, R _t , R _a , and R _q , were derived. Their dimensionless expressions were also studied and a single chart was developed to present the surface roughness parameters. This research provides a guideline on the use of approximate methods. The error is smaller than 1.6% when the ratio of the feed and major semi‐axis of the elliptical arc is smaller than 0.5. The closed‐form expressions developed in this study can be used for the surface roughness modeling in CAD/CAM simulations.     

Measurement of surface roughness of metals using binary speckle image analysis

In this paper, results from an optical technique for measuring surface roughness using image analysis of speckle pattern images are presented. The technique coined as statistical properties of binary images (SPBI) utilizes the combined effects of speckle and scattering phenomena. The speckle patterns obtained with a He–Ne laser were binarized and examined. The parameters such as bright and dark regions and their ratios obtained from this model to evaluate the surface roughness were compared with the surface roughness parameter R_a obtained from a profilometer. It was found that there is a strong relationship between these parameters and R_a, especially in the range of λ<R_a<2λ where λ is He–Ne laser wavelength. Although, it is a relative method, it has great potential to be used for in-process measurement and automation due to the simplicity of optical system used. The proposed method for the surface roughness combined with a non-contact optical measuring system is applied to samples from 0.5825 to 1.9 μm of steel (CK 45) through CNC face-milling process.     

Fractal model to predict the crack roughness effect on the local bending compliance of circular shafts

In this paper the local compliance due to a transverse fractal crack in a shaft under pure bending is investigated. In a fractal crack, the surface is considered irregular and it is characterized by the presence of nonuniformities at different scales. Therefore, the crack surface can be modeled as a fractal surface with fractal dimension D. An analytical model for the compliance coefficient is presented with and without the effect of the surface roughness. The results obtained shows that as the dimension of the fractal surface increases the compliance increases as well. It is shown that this behavior conforms well with existing experimental results.     

Photoconductivity in a magnetic field and photomagnetic effect in <Emphasis Type="Italic">p</Emphasis>-HgCdTe graded-gap photodetecting film structures

The photomagnetic effect and photoconductivity in a magnetic field are studied at a liquid nitrogen temperature for the Voigt geometry on p-HgCdTe films with graded-gap boundary regions where the content of cadmium (x) is increased above its mole fraction in the central area of the structure with a uniform distribution of x. A case with dominating Shockley-Read recombination is considered. It is demonstrated on the basis of experimental data that the film structure in studying these effects can be replaced by the central area with an identical value of x, by introducing effective velocities of surface recombination and surface generation of excess charge carriers on the interfaces between the central area and the graded-gap regions.     

Method of determination of truncation parameters from measured surface profile

The probability density function of the roughness height of a sliding surface is not always Gaussian like that of a truncated surface caused by running-in or mild wear. Therefore, it is important for obtaining contact pressure or frictional characteristics to estimate the truncation level of the non-Gaussian distribution function. This paper presents a method of determination of the two truncation parameters in the truncation model presented by King et al. [Proceedings of the 4th Leeds–Lyon Symposium on Tribology, MEP, London, 1978, p. 333]. The two truncation parameters p and β can be determined by plotting the values of skewness S_k and kurtosis K obtained from a measured profile of surface roughness on the S_k–K diagram calculated with the truncation model for various given values of parameters p and β. The height distributions reproduced by the truncation model with the truncation parameters p and β identified by the present method is in good agreement with the original ones of the measured surfaces.     

Friction of plastic webs

This paper is about the measurement of the friction of plastic and similar flexible webs in contact with cylindrical surfaces. There are numerous ways for measuring friction coefficients of materials in relative contact, but to be meaningful, the testing technique should simulate the tribosystem of interest. The subject of this paper is the capstan friction test, which simulates the tribosystem of a flexible material with some angle of wrap around a cylinder.It is the purpose of this paper to propose the use of the ASTM G-143 capstan friction test standard, which is the preferred technique to study web transport systems that involve a web in contact with rollers. This tribosystem is used to transport plastic sheets, rubbers, paper, fabrics, wrought metals and many industrial products. If the roller/product friction is too low, there may be transport tracking problems. If the friction is too high, it may lead to breaking of the web or other problems. Transport friction needs to be controlled. This paper presents the equations governing the test, describes the ASTM test procedure, and presents data on the effect of variables on the test.The repeatability of the test was determined to be acceptable in interlaboratory tests; the coefficient of variation was less than 10%. The effects of temperature, humidity, velocity, surface cleanliness and web tension depended on the particular tribosystem. The friction of plastic webs is affected by most of these factors when sliding against themselves or metal rollers. When the tensions in this test are high, the web surface may be damaged. If this happens, the measured friction coefficient becomes quite low (approaching 0.1); the test is no longer measuring friction of surface a sliding on surface b. It is measuring the deformation of surface a by surface b.As with all tribotests, care must be used in interpreting results, but it has been determined that this test correlates with manufacturing web/roller transport systems and its use is recommended for these kinds of application.     

A rabbit maxillary sinus model with simultaneous customized‐implant placement: Comparative microscopic analysis for the evaluation of surface‐treated implants

We describe the use of a rabbit maxillary sinus model, characterized by thin osseous tissue and low bone density, for the evaluation of surface‐treated implants by histologically and histomorphometrically comparing the osseointegration patterns depending on the surface treatment methods. Twenty rabbits were randomly assigned to two groups of 10 animals, one receiving 5 × 3 mm customized implants (machined, MA or sandblasted and acid etched, SLA) placed in sinus and the other receiving implants placed in a tibia. Histological observation of the implant placed in sinus shows relatively more active new bone formation, characterized by trabecular bone pattern underneath the cortical bone in sinus as compared with that in tibia. Histomorphometric analysis in the rabbits receiving implants in a tibia, the NBIC (%) associated with the SLA surface implant was greater than that associated with the MA implant at 2 weeks (55.63 ± 8.65% vs. 47.87 ± 10.01%; P > 0.05) and at 4 weeks (61.76 ± 9.49% vs. 42.69 ± 10.97%; P < 0.05). Among rabbits receiving implants in a sinus, the NBIC (%) associated with the SLA surface implant was significantly greater than that associated with the MA surface implant both at 2 weeks (37.25 ± 7.27% vs. 20.98 ± 6.42%; P < 0.05) and at 4 weeks (48.82 ± 6.77% vs. 31.51 ± 9.14%; P < 0.05). As a result, we suggest that the maxillary sinus model is an appropriate animal model for assessing surface‐treated implants and may be utilized for the evaluation of surface‐treated implants in poor bone quality environment. Microsc. Res. Tech. 78:697–706, 2015. © 2015 Wiley Periodicals, Inc.