Showing papers on "Surface roughness published in 1988"

Capillary Waves on the Surface of Simple Liquids Measured by X-Ray Reflectivity

Abstract: The properties of the liquid-vapor interface for three simple liquids (water, carbon tetrachloride, and methanol) have been measured using x-ray reflectivity. The measured surface roughness is interpreted using a model that combines the effects of thermally induced capillary waves and the dimensions of the constituent molecules.

The formation of areally‐averaged roughness lengths

Abstract: It is argued that the best area average of the roughness length zo in heterogeneous terrain is that which, if it applied in homogeneous terrain, would produce the correct spatial average value of the surface stress. A heuristic argument is presented to show that this effective value of z0, zeff0, can be obtained by averaging drag coefficients based on a ‘blending’ height. The blending height of about L/200, where L is the horizontal scale of the roughness variations, is the characteristic height at which the flow changes from equilibrium with the local surface to independence of horizontal position. These calculations are compared with numerical simulations of planetary boundary layer flow over variations in roughness length and show good agreement. The values of surface stress which result are always greater than those which would be deduced by assuming a local flow equilibrium through the whole depth of the boundary layer. For variations of z0 on short length scales, zeff0 approaches the largest values of z0 within the averaging area.

Static Friction Coefficient Model for Metallic Rough Surfaces

Abstract: Modele de calcul du coefficient de frottement statique dans le cas de surfaces rugueuses metalliques

Fractal surface finish.

Abstract: Surface finish measurements are usually fitted to models of the finish correlation function which are parametrized in terms of root-mean-square roughnesses, σ, and correlation lengths, l. Highly finished optical surfaces, however, are frequently better described by fractal models, which involve inverse power-law spectra and are parametrized by spectral strengths, Kn, and spectral indices, n. Analyzing measurements of fractal surfaces in terms of σ and l gives results which are not intrinsic surface parameters but which depend on the bandwidth parameters of the measurement process used. This paper derives expressions for these pseudoparameters and discusses the errors involved in using them for the characterization and specification of surface finish.

Roughness and wear during brittle faulting

Abstract: In many natural fault systems, the thickness of gouge and breccia increases approximately linearly with displacement. In contrast, many experimental faults show non linear thickness/displacement relationships. The linear relationship for natural faults has been explained in the past using engineering models for adhesive or abrasive wear. Non linear relationships for experimental faults have not been explained. A model for wear during brittle faulting which considers the scaling of surface roughness can successfully describe the difference between wear on experimental faults and wear on natural faults. We suggest the linear relationship for natural faults results from the approximately self-similar roughness of the fault surfaces. Experimental faults do not generally follow linear relationships because the roughness of ground surfaces normally used in experimental studies scales differently than the roughness of natural rock surfaces. A simple model which assumes that the volume of wear material created is proportional to the volume of mismatch between the surfaces can explain the differences between wear on experimental faults and wear on natural faults. For ground surfaces of experimental samples, the volume of mismatch is independent of the total slip because at the largest scales these surfaces are flat. In contrast, for natural, self-similar surfaces the volume of mismatch increases with slip, because slip isolates larger and larger asperities from their original positions in the opposite surface. Natural and experimental faults evolve differently because of the difference in scaling of their respective surface roughnesses.

Adhesion Model for Metallic Rough Surfaces

Abstract: An improved DMT adhesion model in conjunction with an elastic-plastic contact model is used to study adhesion of contacting metallic rough surfaces The effects of surface roughness and surface energy of adhesion on the pull-off force and on the significance of the adhesion force are investigated It is shown that for clean surfaces the adhesion is quite large even for relatively rough surfaces Adhesion is negligible only for contaminated rough surfaces or at very high external loading

Influence of land surface roughness on atmospheric circulation and precipitation - A sensitivity study with a general circulation model

Abstract: The influence of land surface roughness on the large scale atmospheric circulation and rainfall is examined by comparing three sets of simulations made with a general circulation model in which the land surface roughness length, z(0), was reduced from 45 cm to 0.02 cm. It is found that the reduced surface roughness produced a two-fold increase in the boundary layer wind speed, a two-fold decrease in the magnitude of the surface stress, and almost no change in the surface evaporation and surface sensible heat flux. It is suggested that the height of the earth's vegetation cover has a large influence on the boundary layer water vapor transport convergence and the rainfall distribution.

The Influence of Longitudinal and Transverse Roughness on the Elastohydrodynamic Lubrication of Circular Contacts

Abstract: Influence de la rugosite transversale et longitudinale sur la lubrification elastohydrodynamique d'un contact ponctuel circulaire

Dipolar magnetic surface anisotropy in ferromagnetic thin films with interfacial roughness

Abstract: The demagnetizing field and magnetostatic energy of a thin film with surface roughness has been calculated. It is shown that the surface roughness gives rise to an effective perpendicular anisotropy whose order of magnitude is evaluated as a function of the parameters characterizing the roughness. The results are discussed in connection with experimental situations.

Magnetic surface anisotropy of cobalt and surface roughness effects within Neel's model

Abstract: Neel's phenomenological model of magnetic surface anisotropy is generalised to hexagonal close-packed structures in order to determine the magnetic surface anisotropy of cobalt. The results obtained are in fair agreement with experimental values for the Au(111)/Co interface. It is also shown that Neel's model allows the surface roughness to be easily taken into account.

Quantification of surface damage of tool steels after EDM

Abstract: The surface transformation and damage in AISI O1, A2, D2 and D6 tool steels after EDM were investigated. The results show that the recast layer is composed of two distinct layers: a topmost layer solidifying inwards from the specimen surface and an intermediate layer solidifying outwards from the base of the molten metal. The depth of surface cracks is found to correlate well with the thickness of the white layer, the latter being a layer of rapidly solidified material which, depending on the tool steel material, may consist either primarily of the topmost recast layer, or both the topmost and a large part of the intermediate recast layer. The density of surface cracks, however, correlates better with the thickness of the overall recast layer. Attempts were made to quantify the depth of white (or damaged) layer with respect to the process parameters and surface roughness after EDM. It is found that with a fixed dielectric and flushing condition, the damaged layer correlates well with the pulse energy irrespective of the tool steel material. On the other hand, even though the thickness of the white layer increases with the surface roughness, the result shows considerably more scatter. Based on the present findings, ways of estimating the depth of the damaged layer produced by EDM are proposed.

Surface Roughness of Orthodontic Archwires via Laser Spectroscopy

Abstract: Using specular reflectance, the surface roughness of six representative orthodontic archwire products was determined. Among the four alloy groups which are commonly used in orthodontics, stainless steel appears the smoothest, followed by cobalt-chrome, beta titanium, and nickel-titanium. A clearer understanding of the parameters which contribute to sliding mechanics will be possible when these results are combined with future experiments on the coefficient of friction.

Measurements of the mean force on a particle near a boundary in turbulent flow

Abstract: The transport of particles through gaseous systems is controlled by three factors: their arrival to the surface; whether or not they bounce upon impact; and when (if ever) they are resuspended from the surface. One of the parameters required in determining whether or not a particle is suspended is the lift force acting on the particle. We demonstrate that the fluid lift forces acting on particles as small as 1 μm in diameter can be modelled by particles of several mm in diameter. However, the forces involved in modelling such small particles are around 10−8 N, which is several orders of magnitude smaller than reported in published measurements of fluid lift forces. A system to determine such lift forces has been developed and is described. Measurements of the mean force acting on particles on both rough and smooth surfaces are presented.The data recorded here for the mean fluid lift force on a sphere on a smooth surface are in good agreement with the relationship \[ F^{+} = (20.90\pm 1.57)(a^{+})^{2.31\pm 0.02}, \] where F+ is the non-dimensional force and a+ the non-dimensional particle radius scaled on fluid-boundary-layer parameters. It was observed that surface roughness can change the force by up to a factor of six.

Effect of Surface Roughness on the Point Contact EHL

Abstract: Influence de la rugosite de surface sur la lubrification elastohydrodynamique d'un contact ponctuel

Structure of rough-wall turbulent boundary layers

Abstract: Recent experiments have shown that, in rough-wall turbulent boundary layers, drag varies systematically with the spanwise aspect ratio lambda(z) (span/height) of roughness elements. In this paper, the effect of lambda(z) on turbulence structure has been examined. Based on lambda(z), the roughness in a transversely grooved surface with lambda(z) much greater than 1 is the opposite extreme of model plant canopies with lambda(z) much less than 1, studied in wind tunnels, whereas sandgrain is an intermediate type. Second-, third-, and fourth-order turbulence moments have been measured in turbulent boundary layers over transversely grooved and smooth surfaces and compared with available turbulence structure measurements over other types of surfaces. The near-wall turbulence structure is found to vary with lambda(z). The instantaneous motions involved in the flux of shear stress near the wall in smooth and transversely grooved surfaces are opposite in sign to those in three-dimensional roughness. The former is explained in terms of hairpin vortices alone, while the latter group is modeled to have an additional vortex (the so-called necklace vortex which straddles a three-dimensional roughness element near its base).

Venus: Surface electromagnetic properties

Abstract: Pioneer Venus high-angle radar imaging data are used here to correct values of the specular power reflection coefficient for the effects of diffusely scattering small-scale surface roughness. A value of 5.0 + or - 0.9 is found for the average dielectric permittivity of the rolling plains and lowlands, suggesting that most of the Venus surface is overlain by at most only a few cm of soil or dust. The unexpectedly high values of power reflection coefficient are confirmed by observations of correspondingly low values of radiothermal emission. Thus there can be little doubt that most of the highlands contain significant amounts of a conducting mineral near the surface.

Optical constants for thin films of C, diamond, Al, Si, and CVD SiC from 24 Å to 1216 Å

Abstract: A method for deriving optical constants from reflectance vs angle of incidence measurements using a nonlinear least-squares curve-fitting technique based on the chi(2) test of fit is presented and used to derive optical constants for several thin-film materials. The curve-fitting technique incorporates independently measured values for the film surface roughness, film thickness, and incident beam polarization. The technique also provides a direct method for estimating probable errors in the derived optical constants. Data are presented from 24 A to 1216 A for thin-film samples of C, synthetic diamond, Al, Si, and CVD SiC. Auger electron spectroscopy depth profiling measurements were performed on some of the samples to characterize sample composition including oxidation and contamination.

Excimer laser patterning of a novel resist

Abstract: A dual layer resist configuration is employed for photopatterning high resolution conductive patterns on underlying polymeric or ceramic substrates, particularly substrates exhibiting surface roughness and non-planar design features such as channels, bosses and ridges. More particularly, a thin underlayer of ablatable photoabsorptive polymer is disposed on a metal coated substrate, after which a thicker layer of substantially transparent material is disposed over the polymer. A beam of laser energy, such as that produced by an ultraviolet excimer laser, is directed through the upper layer and is absorbed by the lower layer which is ablated and simultaneously removes the thick layer above it. This results in the ability to etch high resolution features on polymeric and other substrates, particularly copper coated polyetherimide circuit boards. The resist system is also applicable to VLSI wafers even though such wafers usually do not exhibit surface roughness on the scale generally considered herein. It is also equally applicable in various high density interconnect systems used for the direct connection of chip devices. A mask for patterning and a method for making it are also seen to be desirable because of the high laser energy densities generally desired for thorough ablation.

Effects of surface roughness (hairiness) of latex particles on their electrokinetic potentials

Abstract: In a previous paper, we demonstrated that the electric properties of the bitumen/water and crude oil/water interfaces could be explained by the dissociation of carboxyl groups belonging to natural surfactants present in bitumen. Electrophoresis of bitumen-in-water emulsions indicated very high zeta potentials (−100 mV in 10−2M NaCl) especially when compared to a carboxylated latex (−50 mV in 10−2 M NaCl) having similar surface charge density. This difference was attributed to the surface roughness of the latex particle, which results in a larger value for the location of the shear plane resulting in a smaller value for the zeta potential. To test this hypothesis we modified the surface roughness of the latex by heating it above its glass transition temperature. The heat treatment resulted in a significant increase of the zeta potentials calculated from the measured electrophoretic mobilities. This observation suggests that surface roughness is one of the most important factors in determining zeta potentials from electrophoresis. Results of electrophoretic mobilities of the original and heat-treated latexes will be shown as a function of pH in a wide range of NaCl concentrations, and will be compared with those predicted by the Ionizable Surface-Group model. In addition, results of measured mobilities of the heat-treated latex in NaCl, CaCl2, and La(NO3)3 below 10−4 M suggest that the computer solution of O'Brien and White overestimates the electrokinetic relaxation effect of itκa < 100, where κ is the reciprocal Debye-Huckel length and a is the particle radius.

Effects of ball burnishing parameters on surface finish—A literature survey and discussion

Abstract: Ball burnishing, a plastic deformation process, is becoming more popular as a finishing operation. A literature survey and discussion on the effects of the various types of burnishing (normal, vibratory and ultrasonic) and related parameters—force, speed, feed-rate, lubrication, ball material and diameter, workpiece material, pre-machined roughness and frequency of oscillation—on the final surface roughness are presented. The effect is an interaction between the process parameters with burnishing force and feed-rate as the two most significant factors. A particular surface finish can be obtained by appropriate selection of the parameters

The dependence of sea surface slope on atmospheric stability and swell conditions

Abstract: A tower-mounted optical device is used to measure the two-orthogonal components of the sea surface slope. The results indicate that an unstable stratification at the air-sea interface tends to enhance the surface roughness. The presence of a long ocean swell system steers the primary direction of shortwave propagation away from wind direction, and may increase or reduce the mean square slope of the sea surface.

Adhesion of spheres by thin liquid films

Abstract: Thin liquid films may produce significant adhesion between solid bodies, such as powder agglomerates and ultra-flat surfaces. The adhesive force can be split into two components; the meniscus force and a viscous component which, at sufficiently high deformation rates, will become dominant. This paper presents an analysis for the viscous component of adhesion acting between spheres coated by thin liquid layers, which is expressed as the impulse required to separate the spheres. This impulse depends on the radii and surface roughness of the spheres, and the fluid viscosity and thickness. The dependence on the roughness and quantity of fluid is unexpectedly weak (i.e. logarithmic). The predictions of the analysis are confirmed by direct experiment using a simple force pendulum.

Noise reduction in Eden models: II. Surface structure and intrinsic width

Abstract: For pt.I see ibid., vol.20, p.257 (1987). The authors suggest a picture of the intrinsic surface width in Eden models and show that it is a major source of corrections to scaling of the surface roughness. Using the multiple-hit noise reduction method, they can control the intrinsic width and thereby improve the scaling behaviour systematically as is demonstrated in detailed calculations on the square lattice. They calculate the number of excess perimeter sites as a function of time and find that its asymptotic value decays with a power law as a function of increasing hitting number. Substrate effects and anisotropy become more apparent if noise reduction is applied.

An analysis of fretting fatigue

Abstract: This thesis describes a series of fretting fatigue experiments carried out under closely controlled conditions of partial slip. These experiments confirm the existence of a size effect whereby the fretting fatigue life of an aluminium alloy is shown to vary with contact size. The configuration chosen, of cylindrical fretting pads contacting a plane specimen is amenable to classical stress analysis and the surface tractions between the contacting bodies are derived. The effects of tension in the specimen, finite specimen thickness, differing elastic constants, and surface roughness are all investigated and incorporated into the analysis where appropriate. A technique is then developed to calculate stress intensity factors for plane cracks growing under the contact load at an arbitrary angle to the free surface. The analysis is then applied to the experimental results and three possible explanations for the size effect are proposed, based on statistical effects, crack arrest, and crack initiation. These are examined in the light of the experimental evidence and it is proposed that the variation of fatigue life with contact size is due to an increase in the amount of fretting damage above a threshold level for crack initiation. A composite parameter is chosen to characterise the severity of fretting conditions and this is shown to describe the experimental results accurately. Finally, the use of this parameter in design calculations is discussed.

Flattening of grooves on a crystal surface: a method of investigation of surface roughness

Abstract: The decay of a profile artificially produced on a crystal surface below its roughening transition is studied by means of a qualitative theory. In the case of a bidirectional modulation the height h(t) is a linear function of time t and the lifetime τ is proportional to λ 3 h(0), where λ is the wavelength. As suggested by Bonzel et al. the formation of facets is a sensitive information to determine whether a surface is below its roughening temperature. Near the flat part the profile has a (x-x 0 ) 3/2 singularity as in a crystal at equilibrium. The case of a unidirectionnel modulation is still open although some heuristic give a qualitative agreement with experimental results Etude theorique et qualitative de l'evolution de sillons creuses a la surface d'un monocristal en dessous de sa temperature de transition rugueuse

Effect of testing conditions and microstructure on the sliding wear of graphite fibre/PEEK matrix composites

Abstract: The sliding friction and wear behaviour of unreinforced polyetheretherketone (PEEK) matrix and its unidirectional continuous and two-dimensional woven graphite fibre-reinforced composites were investigated. The operating wear mechanisms, as evinced by scanning electron microscopy of the worn surfaces, and the coefficients of friction and the wear rates changed considerably with the fibre reinforcement form and orientation. Sliding wear rates, on account of their extreme sensitivity to the microstructure of the interacting surfaces at the sliding interface, were found to be a function of not only the surface roughness, but also of the sliding time. Complex interactions arising due to the effects of the testing parameters such as fibre orientation, sliding velocity, contact pressure and interface temperature were characterized for the neat matrix and the two composite systems. The wear rates of the two-dimensional woven composites were almost an order of magnitude lower than those of the unidirectional fibre composite or the unreinforced matrix.