Relative Surface Roughness Research Articles

Laboratory investigation on the effect of particle size, water flow and bottom surface roughness upon the response of an upward-pointing optical backscatter sensor to sediment accumulation

Upward-pointing optical backscatter sensors (OBS) have been recently introduced to measure sediment accumulation in situ. Here, the effect of two potentially important parameters on an upward-pointing OBS response to sediment accumulation measurements is investigated in a laboratory flume: (a) grain-size distribution and (b) bottom surface roughness in relation to water speed. Independent measurements of sediment accumulation were done with a specially built suction chamber. This chamber collects accumulated particles directly with a resolution of the order of 0.01 mg cm −2 and with an accuracy of 70%. The upward-pointing OBS response to sediment accumulation was found to vary (a) with grain size by less than 30% for a range of 15–1000 μm and (b) with water speed on a flat surface by less than 35% for a range of 0–7 cm s −1. Speed had no effect on the OBS response when a rough bottom surface was tested for a range of 0–3.5 cm s −1. This study contributes to the understanding of upward-pointing OBS to sediment accumulation, the only field technique to date able to provide high-resolution measurements of sediment accumulation, with a high temporal resolution but still over extended periods of time.

Development and characterisation of direct laser sintering Cu-based metal powder

Direct laser sintering of metal powder is a promising manufacturing process to produce rapid moulds (or rapid tooling) because complex three-dimensional (3-D) metal parts can be created directly from computer-aided design (CAD) data without machining or use of additional tooling. However, material and process are still the crucial issues that restrict its wider adoption although the technology has been introduced more than 7 years. This paper characterises a self-developed Cu-based metal powder used for direct laser sintering. The material system is Cu-based alloy metal powder, which consists of two metal powders: high-purity Cu powder and pre-alloyed SCuP metal powder. The scanning electron microscope (SEM), XRD and energy dispersive X-ray (EDX) analyses show that the bonding mechanism of this process is liquid-phase sintering. The pre-alloyed SCuP metal powder with lower melting point (645°C) acts as the binder during laser sintering, while the Cu powder with higher melting point (1083°C) acts as the structure. The element phosphorus in the powder can act as flux to protect the Cu oxidisation. A case study on fabricating the inserts of a mobile phone cover mould was also carried out. The inserts were created in ambient atmosphere at room temperature. The total sintering time is 40h. Sixty five percent relative theoretical density and average surface roughness Ra 14–16μm were achieved with negligible distortion and curling. Epoxy infiltration was employed as post-process to improve the density and the strength of the sintered tooling. The mould inserts were used to inject ABS-PC mobile phone cover after polishing. No defects were found after moulding of 500 components.

Evaluating the effect of new denture cleaners on the surface roughness of acrylic resin denture base material (An in vitro study)

Three newly prepared denture cleaner solutions from materials available in our country [namely; oxalic, citric and tartaric acids dissolved in isopropyl alcohol (5% w/v)] were studied for their effect on 110 specimens of heat cure acrylic resin prepared according to ADA Specification for 7 days, 1 month, 6 months, and 12 months, compared with Steradent denture cleaner by two techniques (immersion and brushing techniques). The concentration (5% w/v) was selected according to the results of pilot study. The results of this study showed that oxalic and tartaric acids have nearly the same effect on surface roughness in relation to Steradent by immersion technique for six months, but this result was increased to show high rough surface of samples treated by citric acid for one year. Treatment with the four solutions led to reduction in weight (0.03 mg) except citric acid (0.49 mg). Statistical analysis was performed using F–test two–sample. The results revealed that there was a significant difference at levels 1% and 5% between the brushing and immersion techniques, roughness of the surfaces, and period of using each solution. Changes in weight in relation to surface area were ranged between 0.01–0.03 mg/cm2 for Steradent and oxalic acid in immersion technique, while the result was 0.05–0.23 mg/cm2 for brushing technique of the other solutions except citric acid. Oxalic acid showed complete rem-oving of the stain within 8–10 minutes, Steradent and tartaric acid need 6–8 hours, while citric acid did not show the same result.

Effect of Surface Roughness on Nitrogen Flow in a Microchannel Using the Direct Simulation Monte Carlo method

The paper presents direct simulation Monte Carlo (DSMC) results for nitrogen flow in a microchannel with surface roughness modeled by an array of rectangular modules placed on one side of a parallel-plate channel. The effects of relative surface roughness, roughness distribution, and gas rarefaction on flow are investigated and the results are presented in the form of the product of friction factor and Reynolds number. It was found that the effect of surface roughness is more pronounced at low Knudsen numbers. At high Knudsen numbers, rarefaction reduces the interaction between the gas molecules and the channel walls and results in a lower friction factor. The roughness distribution represented by the ratio of the roughness height to spacing of the modules has a significant effect on the flow and friction factor. Finally, the locally fully developed (LFD) flow model can be used to predict gas flow in a microchannel with low values of relative surface roughness.

Rotodynamic pump scaling.

Despite extensive theoretical knowledge of fluid dynamics, the design process for rotodynamic pumps still relies heavily on experimental data. One common technique is to model the design of a new pump based on the design of existing pumps, using the laws of similarity. Another, similar approach frequently used for atypically large or small pumps is to scale a final product design from conveniently sized laboratory prototypes that have been refined to the desired performance in extensive experiments. Both approaches to pump design are usually considered highly reliable. However, for blood pumps, this approach has been questioned. Due to the extremely small size of these pumps and the relatively low Reynolds Numbers, extraneous effects may overwhelm the assumptions made for similarity calculations that are satisfactory for significantly larger models. Three geometrically similar pumps with related scaling factors of 1, 3.2, and 6.4 were tested for the same range of nondimensional flow and pressure. The quality of similitude was determined by comparing the nondimensionalized pump data of the three pumps. It was found that the effects of large linear dimension scaling factors had only a small influence on the quality of similitude (maximum 5.8% error), whereas Reynolds Number effects, especially at high pump flows, had a strong impact on the quality of similitude (maximum 45.4% error). Because Reynolds Number similarity cannot always be achieved simultaneously with geometric similarity, a correction factor for Reynolds Number related departure from similarity was developed. It is based on the Reynolds Number, the Flow Coefficient, the specific speed, and the pump's relative surface roughness. Use of this correction factor reduces the error due to Reynolds Number effects to a maximum of 7.5%. We conclude that the use of scaling techniques in rotodynamic blood pump design is a valid approach, if Reynolds Number similarity is maintained or suitable correction factors are used.

Analysis of surface roughness in relation to soil loss and runoff at high rainfall intensities

AbstractThe decay of roughness is an important factor governing surface processes such as infiltration and soil erosion. Thus the decay of surface roughness under different surface conditions was investigated and related to quantitative amounts of soil loss, runoff and sediment concentration in a laboratory experiment.Rainfall with an intensity of 128 mm/h was applied to a bare or mulched surfaces of a sandy loam soil with known surface roughness at specified time intervals. The decay of roughness as expressed by roughness ratio, in this experiment, was better predicted when related to an exponential function of the square root of cumulative kinetic energy of rainfall rather than with the cumulative rainfall. The roughness decay equations in literature did not predict breakdown under mulched surfaces accurately. Thus the exponent parameters of the roughness decay equations were adjusted to reflect the reduced decay occurring under mulched surfaces.In a bare soil, regression equations expressing the dependent variables as a function of initial roughness index were significant, but with low coefficients of determination, being 0·39 for soil loss, 0·12 for runoff and 0·36 for sediment concentration. In addition to initial roughness index, cumulative kinetic energy of rainfall was further included in the regressions. This led to an increase in coefficients of determination, which was 0·81 for soil loss, 0·74 for runoff and 0·49 for sediment concentration.The coefficients of determination (0·87 for soil loss, 0·85 for runoff and 0·51 for sediment concentration) were further increased when the final roughness index was included in addition to initial roughness index and cumulative kinetic energy in the regressions.This work shows that soil loss and runoff could be predicted from bare soil surface provided the initial roughness and the energy of rainfall is known. However, field verifications of these relationships are needed under different tillage tools and under natural rainfall. Copyright © 2002 John Wiley & Sons, Ltd.

Surface Roughness Evolution of PECVD Cathodic and Anodic a-Si:H.

AbstractSurface or interface roughness can impact optical, electronic, and MEMS applications of thin a-Si:H films. Deposition at lower temperatures can be advantageous for some applications of a-Si:H, but lower temperature deposition generally leads to rougher films. We have found that the evolution of surface roughness growth can be modified substantially by ion bombardment due to the self-bias of the plasma during Plasma-Enhanced Chemical Vapor Deposition (PECVD). Notable differences in the surface roughness evolution and deposition rate are shown for films deposited in “cathodic” versus “anodic” mode – where the substrate is placed on the powered and grounded electrode respectively. Suppression of surface roughness growth of a-Si:H can be achieved under conditions of relatively high ion bombardment even at deposition temperatures as low as 75 C. Atomic force microscopy (AFM) was used to measure the relative surface roughness profile as a function of deposition time. Analysis of the power spectral density of the roughness yielded important statistical surface parameter information. Based on these observations, insight is given into growth mechanisms under the two deposition conditions.

Specular x-ray reflectivity study of ordering in self-assembled organic and hybrid organic–inorganic electro-optic multilayer films

Specular x-ray reflectivity has been used to probe the microstructures of siloxane-based self-assembled electro-optic superlattices composed of high-hyperpolarizable organic chromophore arrays intercalated with Ga and In oxide sheets. The film thickness increases linearly as a function of the number of layers, underscoring the high structural regularity and efficiency of the synthetic approach. Relatively dense metal oxide structures are detected in these systems. The x-ray reflectivity data also indicate that the dependence of the relative surface roughness on the number of layers is nearly identical for self-assembled organic and organic–inorganic hybrid film structures.

Evolution of soil surface roughness and flowpath connectivity in overland flow experiments

During rainfall events, surface roughness affects runoff generation by providing water surface storage in the depressions and altering the flow direction on the surface. The process of runoff initiation, or triggering, involves the gradual filling of individual depressions and the connection of those overflowing depressions toward the outflow boundary. Although studies have been conducted to relate surface roughness to total depression storage, little work has been done in quantifying the roughness effects on runoff initiation. This study examines the role of surface roughness on overland flow triggering in interrill areas. Laboratory experiments were conducted on a 2.4-m×2.4-m soil box exposed to a sequence of four rainfall events with treatments including two levels of initial roughness and two slope gradients. Surface microtopography was digitised by a laser scanner before and after each rainfall event. Soil roughness was analysed by the variogram method and its role in runoff triggering was evaluated using a numerical model that gradually fills depressions with a conditioned-walker method. Experimental variograms showed a gradual lowering of semivariances in a homothetic way after each additional rainfall, indicating that all roughness scales are affected similarly. All variograms showed a distinct topographic correlation length that can be related to depressional storage capacity. The linear relationship between these two variables also has a threshold roughness term below which the storage capacity tends to zero. Analyses of the runoff triggering showed that a small modification of micro-topographic structure had a major effect on runoff initiation. Even if the storage capacity is an important parameter of the runoff characteristics, large differences are observed between the initial stages of each experiment and final stages. We attributed these differences to the creation of preferential connections between topography depressions due to the material redistribution. Since the variogram analysis may not be sensitive toward the development of preferential flow path in a local scale, additional methodologies, such as the conditioned-walker analysis used in this study, need to be incorporated in quantifying the role of surface microtopography on the dynamics of runoff generation.

Study of the effect of machining parameters on the machining characteristics in electrical discharge machining of tungsten carbide

Electrical discharge machining (EDM) is a process for shaping hard metals and forming deep and complex-shaped holes by arc erosion in all kinds of electro-conductive materials. The objective of this research is to study the influence of operating parameters of EDM of tungsten carbide on the machining characteristics. The effectiveness of the EDM process with tungsten carbide is evaluated in terms of the material removal rate, the relative wear ratio and the surface finish quality of the workpiece produced. It is observed that copper tungsten is most suitable for use as the tool electrode in EDM of tungsten carbide. Better machining performance is obtained generally with the electrode as the cathode and the workpiece as the anode. Tools with negative polarity give higher material removal rate, lower tool wear and better surface finish. High open-circuit voltage is necessary for tungsten carbide due to its high melting point and high hardness value. Dielectric flushing pressure is found to be optimal at 50 kPa. High material removal rate, low relative wear ratio and good surface finish are conflicting goals, which cannot be achieved simultaneously with a particular combination of control settings. To achieve the best machining results, the goals have to be taken separately in different phases of work with different emphasis. In rough EDM of tungsten carbide, material removal rate is of primary importance. Thus, the higher the discharge current, the faster is the machining time. Material removal rate and the surface roughness of the workpiece are directly proportional to the discharge current intensity. When approaching the finishing stage, an optimum control setting is required for attaining the best surface finish and precision machining. For precision machining of tungsten carbide, the optimum condition of relative wear ratio and surface roughness takes place at a gap voltage of 120 V, discharge current of 24 A, pulse duration of 12.8 μs, pulse interval of 100 μs, dielectric flushing pressure of 50 kPa and copper tungsten (CuW) as the tool electrode materials with negative polarity. This study confirms that there exists an optimum condition for precision machining of tungsten carbide although the condition may vary with the composition of the material, the accuracy of the machine and other external factors.

Quantitative Parameters for Rock Joint Surface Roughness

Summary The morphologies of two artificial granite joints (sanded and hammered surfaces), one artificial regularly undulated joint and one natural schist joint, were studied. The sanded and hammered granite joints underwent 5 cycles of direct shear under 3 normal stress levels ranging between 0.3‐4 MPa. The regularly undulated joint underwent 10 cycles of shear under 6 normal stress levels ranging between 0.5‐5 MPa and the natural schist replicas underwent a monotonous shear under 5 normal stress levels ranging between 0.4‐2.4 MPa. In order to characterize the morphology of the sheared joints, a laser sensor profilometer was used to perform surface data measurements prior to and after each shear test. Rather than describing the morphology of the joints from the single profiles, our characterization is based on a simultaneous analysis of all the surface profiles. Roughness was viewed as a combination of a primary roughness and a secondary roughness. The surface angularity was quantified by defining its three-dimensional mean angle, ys, and the parameter Z2s. The surface anisotropy and the secondary roughness were respectively quantified by the degree of apparent anisotropy, ka, and the surface relative roughness coe‰cient, Rs. The surface sinuosity was quantified by the surface tortuosity coe‰cient, Ts. Comparison between the means of the classical linear parameters and those proposed shows that linear parameters underestimate the morphological characteristics of the joint surfaces. As a result, the proposed bi-dimensional and tri-dimensional parameters better describe the evolution of the joints initial roughness during the course of shearing.

Machining characteristics of titanium alloy (Ti–6Al–4V) using a combination process of EDM with USM

This paper presents an experimental investigation of the machining characteristics of titanium alloy (Ti–6Al–4V) using a combination process of electro-discharge machining (EDM) with ultrasonic machining (USM). The EDM and USM machining mechanisms were integrated to improve the machining efficiency and accuracy. During the experiments, parameters such as dielectric type, abrasive size, concentration of abrasive in the dielectric fluid, discharge peak current and pulse duration were changed to explore their effect on the material removal rate (MRR), electrode wear rate (EWR), relative electrode wear ratio (REWR), surface roughness and thickness of the recast layer. From the experimental results, we conclude that this combination EDM/USM process can increase the MRR and decrease the thickness of the recast layer. In addition, the discharge waveform analysis shows that the combination EDM/USM process can dramatically reduce abnormal discharge, thus improving the discharge efficiency.

Assessment of steel surface roughness and waviness in relation with paint appearance

Paint appearance is an important factor in the overall product quality of steel sheet, especially in the automotive industry. The present paper deals with the functional behaviour of the surface texture according to paint appearance. The main results on the improvement of paint appearance of outer car body panels, obtained with coated and uncoated cold rolled steel, textured with EBT-rolls, is reviewed. There are different methods to relate steel sheet surface texture to the appearance after painting. From the literature it is found that waviness has a detrimental effect on the surface appearance after painting. Different roughness and waviness parameters are compared in order to find a good relation with paint appearance. The following surface texture parameters are evaluated in this study: roughness parameters Ra, peak count Pc, waviness parameters Wca and amplitude between 0.5 – 5mm (Fourier analysis) and envelope parameters motif W and Ra-macro, measured with a spherical stylus of radius 1.5mm. Classical parameters such as Ra and Pc are only able to evaluate paint appearance for one single texturing process, and within very limited range. The ability to predict paint appearance by Ra-macro and Wca also seems to be limited, because of their dependency on the roll texturing technique. Based on extensive testing, it is suggested that Fourier analysis might be the best approach to predict the appearance after painting, and this independently of the texturing process. The results clearly show the improved appearance of Sibetex textured sheets compared to conventional textured sheets. This is due to the fact that, with Sibetex sheet, a reduction in waviness can be achieved.

Surface roughening during low temperature Si(100) epitaxy

Reflection high energy electron diffraction (RHEED) was used to investigate surface roughening during low temperature Si(100) homoepitaxy. The use of RHEED allowed in situ real-time collection of structural information from the growth surface. RHEED patterns were analyzed using a simple kinematic diffraction model which related average surface roughness and average in-plane coherence lengths to the lengths and widths of individual RHEED diffraction features, respectively. These RHEED analyses were quantified by calibrating against cross-section transmission electron microscopy (TEM) analyses of surface roughening. Both the RHEED and TEM analyses revealed similar scaling of surface roughness with deposited thickness, with RHEED analyses resulting in roughness values a factor of ∼2 times lower than those obtained from TEM analyses. RHEED was then used to analyze surface roughening during Si(100) homoepitaxial growth in a range of temperatures, 200–275 °C. Initially, surface roughness increased linearly with deposited thickness at a roughening rate that decreased with increasing growth temperature. At each growth temperature, near the crystalline/amorphous Si phase transition, the rate of surface roughening decreased. This decrease coincided with the formation of facets and twins along Si{111} planes. Surface roughness eventually saturated at a value which followed an Arrhenius relation with temperature Eact∼0.31±0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, Eact∼0.35 eV, and suggests that limited thickness epitaxy is characterized by this saturation roughness. Once the saturation roughness was reached, no significant changes in surface roughness were detected. In addition, the decay of average in-plane coherence lengths was also temperature dependent. Values of average coherence lengths, at the crystalline/amorphous Si phase transition, also increased with growth temperature. All of these data are consistent with a model that links surface roughening to the formation of critically sized Si{100} facets and the eventual breakdown in crystalline growth.

Conditions pertaining to the influence of electrode surface roughness upon the insulation strength of compressed systems

On the basis of a series of experimental investigations reported in the literature, electrode microscopic surface roughness was dismissed as a factor influencing breakdown levels in compressed , irrespective of field non-uniformity. This conclusion appears to be tenable if one restricts observations to the investigations in question. In the present communication, we contend that the scope of these studies formed an insufficient basis on which to invoke such a general conclusion. To clarity this contention, the role of surface roughness in relation to the breakdown characteristics of compressed is recalled and its domain of influence brought into focus.

Enhancement of the thermal performance of a wet cooling tower

AbstractThe effect of packing roughness on the thermal and hydraulic performance of a packed bed wet cooling tower were investigated experimentally. Tower enhancement ratio and air‐side pressure drop ratio were determined as functions of packing relative roughness at different values of water inlet temperature, and water‐to‐air mass flux ratio. The packing used was glass Raschig rings 10 mm thick and 10 mm in diameter. The surface roughness was changed by adhering sand papers of different roughness to the outside surface of the packing.The experimental data showed that an increase in the surface relative roughness from 1 to 5.62 can increase both the tower enhancement ratio and the air side pressure drop ratio up to 146% and 142%, respectively. The effect of the surface relative roughness is more pronounced at lower values of water‐to‐air mass flux ratio and at higher values of hot water inlet temperature. Also, a new analytical expression was developed to calculate the cooling tower characteristics.

A Scanning Electron Microscope Study Comparing the Effectiveness of Different Types of Sharpening Stones and Curets

The effects of various types of sharpening stones on standard carbon steel Gracey type curets, and the influence of the sharpened curets on periodontally involved root surfaces, during in vitro scaling and root planing, was evaluated by means of scanning electron microscopy (SEM). Six different sharpening stones of varying texture, two of aluminum oxide, two India, and two Arkansas stones were assigned to sharpen six groups of 10 curets each. The curets were first examined under SEM and photographed and all exhibited edge irregularities. They were then sharpened with the different stones and again examined and photographed using SEM. The sharpness of each instrument was graded, related to the type of stone used, and the data compared statistically. A positive correlation was found between the texture of stone used and the surface sharpness it produced on the cutting edge of the instrument. The curets were then used to root plane the root surfaces on periodontally involved, extracted teeth. Replicas of the root surfaces were examined with SEM before and after removal of the smear layer with 10% EDTA. The planed and cleaned root surfaces revealed the effects of the sharpened instruments, with the relative surface roughness of the instrument being imparted to the tooth surface. The curets sharpened with finger grit stones produced smoother surfaces than those sharpened with the rough or coarse grit stone. It may be concluded that the sharpness of curets is related to the type of sharpening stone used and in turn to the smoothness of the planned root.

An Evaluation with the Fourier Amplitude Sensitivity Test (FAST) of Which Land-Surface Parameters Are of Greatest Importance in Atmospheric Modeling

Land-surface parameterizations based on a statistical-dynamical approach have been suggested recently to improve the representation of the surface forcing from heterogeneous land in atmospheric models. With this approach, land-surface characteristics are prescribed by probability density functions (PDFs) rather than single “representative” values as in “big-leaf” parameterizations. Yet the use of many PDFs results in an increased computational burden and requires the complex problem of representing covariances between PDFs to be addressed. In this study, a sensitivity analysis of a land-surface parameterization for atmospheric modeling was performed to evaluate the surface parameters most important to the variability of surface heat fluxes. The Fourier amplitude sensitivity test (FAST) used for this analysis determines the relative contribution of individual input parameters to the variance of energy fluxes resulting from a heterogeneous surface. By simultaneously varying all parameters according to their individual probability density functions, the number of computations needed is very much reduced by this technique. This analysis demonstrates that most of the variability of surface heat fluxes may be described by the distributions of relative stomatal conductance and surface roughness. Thus, the statistical-dynamical approach may be simplified by the use of only these two probability density functions.

The Effects of Particle Shape and Surface Roughness on the Hydraulic Mean Radius of a Porous Medium Consisting of Quarried Rock

Abstract The influence of particle shape and surface roughness on the hydraulic mean radius are investigated, and quantitative measures for each are proposed. A particle shape factor is estimated with the aid of a new mathematical approximation for the surface area of an ellipsoid. The particle surface roughness is calculated based on inferences made from surface area data previously obtained for a sample of rocks described in Garga et al. (1991). The effect of surface roughness on the hydraulic mean radius was found to be greater than that of shape for this sample of crusher-run quarried limestone. A diagram is presented to show the relative importance particle shape and surface roughness.

Interference and Turbulence Intensity Effects on the Flow-Induced Vibration of Smooth and Rough Cylinders

Interference and turbulence intensity effects on the dynamics characteristics of the flow-induced vibration of elastically mounted smooth and rough cylinders in a cross flow in the vortex shedding and fluidelastic regions were experimentally investigated.It was found that the presence of an interfering cylinder in the wake of the test cylinder reduces the amplitude of oscillation in the vortex excitation region, while in the fluidelastic region an increase in the amplitude of oscillation is experienced. The effect of turbulence intensity on the dynamic response of the cylinder is found to be very much dependent on the values of free-stream turbulence intensity, relative surface roughness, gap spacing and relative dimension of the interfering cylinder.