Showing papers on "Surface roughness published in 1970"

The Contact of Two Nominally Flat Rough Surfaces

Abstract: Most models of surface contact consider the surface roughness to be on one of the contacting surfaces only. The authors give a general theory of contact between two rough plane surfaces. They show that the important results of the previous models are unaffected: in particular, the load and the area of contact remain almost proportional, independently of the detailed mechanical and geometrical properties of the asperities. Further, a single-rough-surface model can always be found which will predict the same laws as a given two-rough-surface model, although the required model may be unrealistic. It does not seem possible to deduce the asperity shape or deformation mode from the load-compliance curve.

Resistivity and Temperature Coefficient of Thin Metal Films with Rough Surface

Abstract: The thickness dependence of resistivity and its temperature coefficient of thin metal films has been studied. A theory is proposed to include, the surface roughness in determining the film resistivity, in addition to the reduced mean free path to conduction electrons. The ratio of the roughness to the mean free path, h/λ, is introduced as a convenient parameter. The thickness dependence of the resistivity predicted by the present theory agrees with the well known Fuchs-Sondheimer theory if h/λ=0. If h/λ>0, the discrepancy between the two theories increases with the decrease in film thickness. Satisfactory agreement between the theoretical and experimental results can be obtained by adjusting the value of h/λ.

Scattering of light by slightly rough surfaces or thin films including plasma resonance emission

Abstract: It will be shown that the perturbation theory approach with respect to the amplitude of the roughness for the scattering of light by rough surfaces is equivalent to a model consisting of a smooth surface and surface current sources. This model has an obvious physical meaning and allows a simple calculation of the scattered fields, which are given. The model and the previous one given by Stern are identical up to the position of the surface currents, which have to be placed into the vacuum. Consequently the former explanation has to be corrected, which says that the peak of the scattered radiation at the plasma frequency is generated by surface roughness. We will show that it is possible to generate this maximum by statistical inhomogenities within the metal.

Demagnetizing Fields in Thin Magnetic Films Due to Surface Roughness

Abstract: The magnetic field generated by the magnetization has been calculated for films with arbitrarily rough surfaces for the case in which the magnetization is uniform throughout the film. Simple results are obtained on the assumption that the film surface is not too ``ragged,'' i.e., for the case in which the inclination of the local film surface relative to the mean surface is fairly small (<45°). A rough estimate of the demagnetizing factor for a direction in the plane of the film is given by π〈p2〉/λd, where 〈p2〉 is the mean square deviation of actual film surface from the mean surface, λ the predominant wavelength of the surface roughness, and d the film thickness. The results are discussed in the context of induced uniaxial anisotropy and ferromagnetic resonance.

A New Unified Approach to Surface Metrology

Abstract: Current standards for the assessment of surface texture are based on some form of height index, such as peak-to-valley or arithmetic average (Ra). Although useful, these parameters take little or no account of the openness or closeness of the texture. In this paper, an additional parameter, the average wavelength, is introduced which is wavelength conscious and intended to supplement the information given by the Ra index. The authors show how this new parameter can be derived from arithmetic average/average slope and highlight the problem of small wavelength filtering and the importance of fully defined bandpass measurement. The average wavelength index, when considered together with the Ra value for a given meter cut-off, is useful in the control of surface roughness and could also be useful in the measurement of waviness, straightness and errors of form. Finally, in surfaces where the asymmetry of the waveform is important, a third parameter derived from the peak and valley distribution is introduced. T...

A model of airflow above changes in surface heat flux, temperature and roughness for neutral and unstable conditions

Abstract: A numerical model of airflow in the lowest 50–100 m of the atmosphere above changes in surface roughness and temperature or heat flux has been developed based on boundary layer approximations, the Businger-Dyer hypotheses for the non-dimensional wind shear and heat flux and a mixing length hypothesis.

Determining surface roughness and displacement height

Abstract: Vertical flux densities of momentum and sensible heat, obtained from simultaneous wind speed and air temperature profiles in the surface layer, depend on the displacement height of the profile system and the surface roughness. A criterion for selecting the displacement height and the surface roughness is introduced, which requires a minimum value for the error squares between the observed and a calculated wind speed profile as determined by diabatic surface layer theory. Values of displacement height and surface roughness, which provide a minimum error squares fit within a desired tolerance, are selected by the rule of false position. The method is programmed for digital computer solution and applied to a total number of 628 profiles obtained during a 7-day period at a micrometeorological test site near Davis, California, using five measurement levels to 160 cm height.

Radiation on Losses Due to Variations of Radius Dielectric or Optical Fibers

Abstract: The total loss of the HE/sub 11/ mode to the radiation field of a finite dielectric rod with small amplitude surface irregularities is considered, and a simple approximate analytic expression for radiation due to sinusoidal roughness is presented. It is shown that radiation occurs only when the frequency of surface roughness /spl Omega/ is in the range /spl beta/-k/sub 2/

Use of a Laser-Produced Speckle Pattern to Determine Surface Roughness*

Abstract: Correlation and spectral-density functions for the film records of speckle patterns have been calculated. The reflections from both a random and a deterministic reflecting surface were examined, and in each case, the resultant spectral-density function consisted of an aperture function multipled by a function dependent upon the reflecting surface. The near-field speckle pattern was found to differ from that obtained in the far field. This difference is an inconvenience only because a method was shown whereby the far-field pattern could be obtained in the near field.

Study of the Interaction of Light with Rough Metal Surfaces. II. Theory

Abstract: In the preceding paper we described the measurements of the scattering, reflectivity, and transmission of light by metals whose surfaces were rough on a microscopic scale. In this paper we develop further the two theoretical approaches outlined in that paper. The first approach considers the radiation from surface currents modulated by the surface roughness. The second approach considers a model surface for which the reflection properties can be solved exactly, the model consisting of metal spheres located above a smooth metal surface. The two approaches demonstrate all the physical phenomena reported in the preceding experimental paper.

The temperature profile near the ground on calm clear nights

Abstract: An observational study of the temperature profile over grass, snow and bare soil surfaces in strong stability is presented It was found that in nearly calm, clear conditions the minimum temperature occurred 1 to 50 cm above the surface The height and intensity of the minimum is strongly correlated with wind speed, surface roughness and stability A discussion of existing hypotheses suggests that the most likely explanation for the phenomenon should involve both turbulence and infra-red flux divergence

Influence of surface roughness on the friction properties of rock planes

Abstract: FRICTION ON SEPARATION PLANES IS AN IMPORTANT FACTOR IN THE DEFORMATION OF ROCK SYSTEMS UNDER STRESS CONDITIONS. AMONG OTHER FACTORS, THE ROUGHNESS OF THE SEPARATION PLANES DETERMINES THE FRICTION PROPERTIES. DESCRIBED ARE THE TECHNIQUES USED TO RECORD THE GEOMETRICAL CHARACTRERISTICS IN FORM OF PROFILES OF THE DIFFERENT SIZE FROM HAND SPECIMEN TO A GREAT EXPOSURE. FOR THE DESCRIPTION OF SURFACE ROUGHNESS, A NEW METHOD HAS BEEN DEVELOPED, WHICH ALLOWS THAT ALL DIFFERENT SIZES OF ASPHERITIES CAN BE REPRESENTED IN ONE DIAGRAM. /AUTHOR/

Role of the surface in the measurement of the Leidenfrost temperature

Abstract: Surface roughness and contamination, drop volume and liquid subcooling effects on Leidenfrost temperature

Problems of atmospheric shear flows and their laboratory simulation

Abstract: Shear flows generated by movement of the atmosphere near the earth's surface are accompanied by complexities not ordinarily encountered in the treatment of turbulent boundary layers. Problems arising from the following physical features are considered: (1) thermal stratification; (2) surface roughness in the form of forests and cities; (3) non-uniformity of surface roughness and/or temperature (leading to 3-dimensional turbulent boundary layers); (4) surface irregularities in the form of hilly and mountainous topography.

Establishment of contact parameters from surface profiles

Abstract: The problem of obtaining sufficient information from the profile of a rough surface, in order to predict the variation of the true contact area between it and a smooth surface as a function of load, is discussed. The effects of load and orientation on surface profiles were examined experimentally for anisotropic and several isotropic surfaces, all with randomly distributed surface heights, and the observations were analysed by computer. The results for the isotropic surfaces agree well with theory, while those for the anisotropic surface are consistent with proposed simple surface models. The variation of the number of contact spots per unit area with load was also measured directly. If an assumption is made concerning the original height distribution, the predictions for the number of contacts per unit area agree well with the experimental observations, while the discrepancy between theoretical predictions and experimental observations for the number of contacts per unit length is less than 4%.

Laser and Microwave Observations of Sea-Surface Condition for Fetch-Limited 17- to 25-m/s Winds

Abstract: The variability of sea-surface conditions has been observed from a low-flying aircraft by a laser-wave profiling system and a scanning horizontally polarized 19.35-GHz passive microwave radiometer for fetch-limited wind speeds of 17 to 25 m/s in the North Sea. Wave profiles obtained with the laser system have been analyzed and show that wave growth occurs simultaneously at all frequencies and that an equilibrium value for the higher frequency components is eventually reached, but not before substantially higher (overshoot) values are obtained. Simultaneous observations of the microwave brightness temperature at vertical incidence show an increase with wind speed (or roughness of the sea surface) of 1°K/m/s. This increase, not in accord with theory, is shown to be a function of the percentage of foam coverage of the ocean surface.

A study of grinding damage in magnesium oxide single crystals

Abstract: The sub-surface and surface damage produced by alumina and diamond grinding wheels has been studied as a function of material removal rate. Sub-surface damage is characterised in all cases by a discrete, dense layer of dislocations adjacent to the machined surface. The depth of the layer increases with material removal rate. The nature of the surface damage depends on the mechanism of material removal. As long as the cutting points are unloaded and the residue can escape the material is removed in a brittle manner. This is always the case for the diamond wheel and occurs for low rates of material removal with the alumina wheel. When the cutting surface is loaded with residue, the tool-workpiece interface temperature becomes so high that the material is removed by plastic flow. The finished surface is burnished. Unfortunately as the burnished surface cools down thermal quenching produces a network of surface cracks.

The effective reflection coefficients in forward scatter from a dielectric slightly rough surface

Abstract: Expressions for the effective reflection coefficients are derived using Rice's theory for forward scattering of electromagnetic waves from a dielectric slightly rough surface. In the limiting case of a perfect conductor (e = -i∞), the coefficients agree with the classical expressions derived by Rice.

Surface‐Roughness‐Induced Demagnetizing Fields in Thin Films and Their Influence Upon the Approach to Saturation

Abstract: The magnetic field generated by the magnetization has been calculated for films with rough surfaces. At large magnetic fieldstrengths the film is uniformly magnetized. Simple formulas for the demagnetizing factors are given, which are applicable provided that the inclination of the local film surface relative to the mean surface is not too large. A rough estimate of the demagnetizing factor for a direction in the plane of the film is given by π〈p2〉/λd. Here 〈p2〉 is the mean‐square (linear) deviation of the actual film surface from the mean surface, λ the predominant wavelength of the surface roughness, and d the film thickness. A relatively small surface roughness, if distributed anisotropically, is sufficient to induce a significant uniaxial magnetic anisotropy. If the magnetic fieldstrength is only moderately high, the surface roughness gives rise to misalignment of the magnetization vector near the surface relative to the mean magnetization vector. The effect of this misalignment upon the average magne...

Comments on "Backscattering of waves by composite rough surfaces"

Abstract: (See abstr. B10742 of 1970). The results of the quoted paper are compared with known solutions and interpretations. Even if the theoretical results were valid, they would not be supported by the particular experimental data that Fung and Chan have chosen to use. Two replies and a further exchange of correspondence are appended

Shape and surface roughness effects on turbulent nosetip ablation

Abstract: A simplified analysis is performed for first-order estimates of shape and surface roughness effects on turbulent ablation of a re-entry body nose surface. The analysis treats the stable turbulent ablated nose shape formed on an ablating cylinder in parallel hypersonic flow. It is assumed that: turbulent boundary-layer flow exists over the entire nose, a stable shape solution exists, surface pressures are Newtonian, and boundary-layer edge properties are given by isentropic expansion of flow that entered the shock layer through a normal shock. A flatplate reference enthalpy relation is used to describe turbulent heating. In addition, an approximate analysis is presented for the effect of ablative material surface roughness on the recession rate of the turbulent shape. It is found that for the cases of 7 = 1.2, 1.4, and 1.585, a power-law nose shape is predicted with r oc s0-75, except near the axis of symmetry where r cc so.8o an(j i^ sonic point is located at about two-thirds of the body radius aft of the forward tip. Also, it is found that ablative material surface roughness of 0.001 in. can cause significant increases in recession rate at stagnation point pressures over 10 atm for representative re-entry conditions and body sizes. The applicability of these results for the evaluation of re-entry body shape change and recession rate is discussed.

Scattering of electromagnetic waves from a layer with rough front and plane back (small perturbation method by Rice)

Abstract: Rice's small perturbation method is extended to obtain first- and second-order terms of the field scattered from a rough layer. The first-order terms are utilized to obtain average scattering cross sections. Lossy and lossless layers are considered for horizontal and vertical polarizations.

Theory of Ground-Wave Propagation Across a Rough Sea at Dekameter Wavelengths

Abstract: : The effect of sea state on ground-wave propagation across the ocean is computed in the HF and VHF region. The history and present understanding of ground-wave propagation is briefly reviewed, especially as concerns the influence of roughness. The approach of the analysis is to derive an effective surface impedance at grazing which includes the effects of roughness. To do this, the statistical boundary perturbation approach of Rice is applied to the sea surface, which is 'slightly rough' at HF/VHF. In addition, the Leontovich (or impedance) boundary condition is employed because ocean water is a good (but not perfect) conductor at these frequencies. The analysis shows that the total effective impedance at the surface can be expressed as two terms: (1) the impedance of a perfectly smooth sea water surface at grazing, and (2) a second term accounting for roughness. The latter is obtained from the ocean wave-height spectrum. The report examines two height-spectrum models for wind-driven ocean waves: a directional Neumann-Pierson model and an isotropic Phillips spectrum. The effective surface impedance is calculated for these models. This impedance is then used to compute the ground-wave transmission loss across the sea. Graphs are shown for a variety of frequencies, ranges, sea states, and receiver heights. Examples, in which these curves are used in communications problems, are solved.

Low‐Energy Ar+ Sputtering Yields of Solid and Liquid Tin

Abstract: Low‐energy Ar+ sputtering yields have been obtained for solid and liquid tin from threshold to 1200 eV. The solid yield at 200 eV is twice that for the liquid but a crossover occurs at 375 eV above which liquid yields are 15% higher. The liquid‐yield curve exhibits a linear dependence up to E=475 eV and breaks sharply to a lower dependence on ion energy. Yields of remelted solid were intermediate between the curves for liquid and solid, demonstrating the effect of surface roughness on the yield for polycrystalline targets. This work confirms experimentally the theory of Sigmund for yield of amorphous targets particularly in the low‐energy range near threshold where surface effects predominate.

The application of fringes of equal chromatic order to the assessment of the surface roughness of polished fused silica

Abstract: Fused silica surfaces polished for long periods while only water is added to the lap after a final application of cerirouge are shown to have a rms roughness of about 0·25 nm. Such small irregularities are resolved by fringes of equal chromatic order only when the apparatus is used under best conditions. In the case of silver reflecting films, highest lateral resolution and highest resolution in depth are obtained for a first order fringe in the red region of the spectrum.

Composite wear resistant material and method of making same

Abstract: A METHOD OF FORMING A METAL OXIDE COATING UPON A WORKPIECE, WHICH COATING MAY HAVE A CLOSELY CONTROLLED SURFACE ROOUHNESS OVER A WIDE RANGE OF COATING THICKNESSES. THE METHOD CONSISTS OF APPLYING A METAL OXIDE BASE COATING BY AN ARC TORCH DEPOSITION PROCESS AND THEREAFTER APPLYING A TOP FURFACE COATING OF METAL OXIDE WITH A DETONATION GUN DEPOSITION PROCESS. A WEAR-RESISTANT COMPOSITE COATING HAVING AN ARC TORCH-APPLIED BASE PORTION WITH A ROUGHNES OF 100 A.A. TO 150 A.A. COMBINED WITH A DETONATION GUM-APPLIED TOP SURFACE COATING HAVING SURFACE ROUGHNESS OF 150 A.A. TO 450 A.A. IS ALSO DISCLOSED AS A PREFERRED TEXTILE SURFACE.

Wind‐Wave Interactions

Abstract: A criterion proposed earlier for determining airflow separation from wind waves and a previously determined relationship between surface roughness and wind stress are herein correlated. The results indicate that the airflow boundary layer is developed due to the form drag provided by wavelets (surface roughness) superimposed on big waves. Based on the magnitudes of surface roughness, viscous‐sublayer thickness and critical height, the mechanisms of wind‐wave generation are discussed.