Uniform Roughness Research Articles

Weakening of the anisotropy of surface roughness in ultra-precision turning of single-crystal silicon

Ultra-precision machining causes materials to undergo a greatly strained deformation process in a short period of time. The effect of shear strain rates on machining quality, in particular on surface anisotropy, is a topic deserving of research that has thus far been overlooked. This study analyzes the impact of the strain rate during the ultra-precision turning of single-crystal silicon on the anisotropy of surface roughness. Focusing on the establishment of cutting models considering the tool rake angle and the edge radius, this is the first research that takes into account the strain rate dislocation emission criteria in studying the effects of the edge radius, the cutting speed, and the cutting thickness on the plastic deformation of single-crystal silicon. The results of this study show that the uses of a smaller edge radius, faster cutting speeds, and a reduced cutting thickness can result in optimally uniform surface roughness, while the use of a very sharp cutting tool is essential when operating with smaller cutting thicknesses. A further finding is that insufficient plastic deformation is the major cause of increased surface roughness in the ultra-precision turning of brittle materials. On this basis, we propose that the capacity of single-crystal silicon to emit dislocations be improved as much as possible before brittle fracture occurs, thereby promoting plastic deformation and minimizing the anisotropy of surface roughness in the machined workpiece.

Fabrication and Characterization of Nanoporous Niobia, and Nanotubular Tantala, Titania and Zirconia via Anodization.

Valve metals such as titanium (Ti), zirconium (Zr), niobium (Nb) and tantalum (Ta) that confer a stable oxide layer on their surfaces are commonly used as implant materials or alloying elements for titanium-based implants, due to their exceptional high corrosion resistance and excellent biocompatibility. The aim of this study was to investigate the bioactivity of the nanostructures of tantala (Ta2O5), niobia (Nb2O5), zirconia (ZrO2) and titania (TiO2) in accordance to their roughness and wettability. Therefore, four kinds of metal oxide nanoporous and nanotubular Ta2O5, Nb2O5, ZrO2 and TiO2 were fabricated via anodization. The nanosize distribution, morphology and the physical and chemical properties of the nanolayers and their surface energies and bioactivities were investigated using SEM-EDS, X-ray diffraction (XRD) analysis and 3D profilometer. It was found that the nanoporous Ta2O5 exhibited an irregular porous structure, high roughness and high surface energy as compared to bare tantalum metal; and exhibited the most superior bioactivity after annealing among the four kinds of nanoporous structures. The nanoporous Nb2O5 showed a uniform porous structure and low roughness, but no bioactivity before annealing. Overall, the nanoporous and nanotubular layers of Ta2O5, Nb2O5, ZrO2 and TiO2 demonstrated promising potential for enhanced bioactivity to improve their biomedical application alone or to improve the usage in other biocompatible metal implants.

Ultrasonic spray coating as deposition technique for the light-emitting layer in polymer LEDs

In this work the ultrasonic spray coating technique is introduced as an alternative wet solution process for the deposition of the (Super Yellow) light-emitting layer for polymer light-emitting diodes (PLEDs). An investigation on the use of this coating technique in ambient conditions is performed and a comparison with spin coated PLEDs in inert atmosphere is made. Uniform low roughness thin films with a typical thickness of 80nm are obtained by varying the polymer–solvent mixture and spray coater parameters. PLEDs are produced and reach a luminous power efficacy in the order of 10lm/W. Through the use of various optical and analytical techniques it is demonstrated that the applied ultrasonic atomization has no noteworthy influence on the original properties of the polymer and on the resulting PLED’s efficacy. Ultrasonic spray coating is therefore a viable deposition technique for the production of PLEDs.

Mechanical Properties and Surface Morphology of Diamond-Like Carbon Films with SiN<i><sub>x</sub></i> Interlayer

Diamond-like carbon (DLC) film has remarkable physical, mechanical, biomedical and tribological properties that make it attractive material for numerous industrial applications needs of advanced mechanical systems. In this study, deposition process of DLC films on Si (100) are performed by direct-current (DC) magnetron sputtering method. The effects of interlayer on the compositions, structures and mechanical properties of DLC films are studied. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies reveal the creation of high uniform surface morphology and low roughness DLC films with SiNxinterlayer. For comparison, DLC films with different interlayers are also grown. The Raman spectra are analyzed in order to characterize the film compositions. Indentation test was performed to value the mechanical properties of DLC films. Raman, SEM, and AFM analyses are correlated with the mechanical properties of the DLC films.

Túneles con paramentos rugosos y con cavidades

En muchas ocasiones las superficies finales de los túneles de carretera (tanto los hastiales, como la bóveda) resultan no solo con rugosidades uniformes importantes, también con huecos más o menos numerosos y más o menos considerables: generalmente en túneles sin revestir es donde más se presentan las irregularidades uniformes importantes, y en túneles en roca excavados con voladuras es donde más se manifiestan los huecos. Esto da lugar a coeficientes de fricción con las paredes del túnel que pueden ser muy elevados. La fricción que se produce al paso del aire en la ventilación puede dar lugar a necesidades de empujes aerodinámicos (con ventilación con jet-fan) muy importantes, esto es, a consumos de energía eléctrica significativos. Para túneles de carretera con ventilación longitudinal con jet-fan se analizan las pérdidas de carga de túneles rugosos y con cavidades, y se evalúan los empujes aerodinámicos necesarios para contrarrestar las correspondientes pérdidas de carga.

The Effects of Highly Detailed Urban Roughness Parameters on a Sea-Breeze Numerical Simulation

We consider the effects of detailed urban roughness parameters on a sea-breeze simulation. An urban roughness database, constructed using a new aerodynamic parametrization derived from large-eddy simulations, was incorporated as a surface boundary condition in the advanced Weather Research and Forecasting model. The zero-plane displacement and aerodynamic roughness length at several densely built-up urban grids were three times larger than conventional values due to the consideration of building-height variability. A comparison between simulations from the modified model and its default version, which uses uniform roughness parameters within a conventional method, was conducted for a 2-month period during summer. Results showed a significant improvement in the simulation of surface wind speed but not with temperature. From the 2-month study period, a day with an evident sea-breeze penetration was selected and simulated at higher temporal resolution. Sea-breeze penetration weakened and was more delayed over urbanized areas. The slow sea-breeze penetration also lessened heat advection downwind allowing stronger turbulent mixing and a deeper boundary layer above urban areas. Horizontal wind-speed reduction due to the increased urban surface drag reached heights of several hundreds of metres due to the strong convection.

Applicationof Computer Visionfor Polishing RobotinAutomotive Manufacturing Industries

Polishing is a highly skilled manufacturing process with a lot of constraints and interaction with environment. In general, the purpose of polishing is to get the uniform surface roughness distributed evenly throughout part’s surface. In order to reduce the polishing time and cope with the shortage of skilled workers, robotic polishing technology has been investigated. This paper studies about vision system to measure surface defects that have been characterized to some level of surface roughness. The surface defects data have learned using artificial neural networks to give a decision in order to move the actuator of arm robot. Force and rotation time have chosen as output parameters of artificial neural networks. Results shows that although there is a considerable change in both parameter values acquired from vision data compared to real data, it is still possible to obtain surface defects characterization using vision sensor to a certain limit of accuracy. The overall results of this research would encourage further developments in this area to achieve robust computer vision based surface measurement systems for industrial robotic, especially in polishing process.Keywords: polishing robot, vision sensor, surface defects, and artificial neural networks

Force and flow characteristics of a circular cylinder with uniform surface roughness at subcritical Reynolds numbers

The main purpose of this study is to establish a better understanding of the relationship between drag reduction and surface roughness. Experiments were conducted to measure the force and flow characteristics of a circular cylinder with different types of artificial surface roughness over the range 6×103<Re<8×104 (Re is based on the cylinder diameter D). The roughness cylinder was formed by covering the exterior surface of the cylinder with uniformly distributed (1) sandpaper, (2) netting, and (3) dimples. The roughness coefficient ranged from k/D=0.0028 to 0.025 (k is the roughness height). A detailed quantitative measurement of the flow field around the cylinder using Particle Imaging Velocimetry (PIV) was carried out. The hydrodynamic force coefficients (drag and lift) of the rough cylinders are compared against those of a smooth cylinder measured under the same flow conditions. It is found that certain configuration of surface roughness significantly reduces the mean drag coefficient of the cylinder, particularly at large Reynolds numbers. In addition, the root-mean-square (r.m.s.) lift coefficient of the rough cylinders is considerably lower than that of a smooth cylinder.

심리스 파이프 제조를 위한 일롱게이션 공정의 유한요소해석

Elongation rolling process is an intermediate process to make the uniform thickness and uniform surface roughness during producing seamless pipes. The thickness and surface roughness of seamless pipes are generally affected by the distance of rolls and guide shoes, the roll shape, and its cross angle. In this study, finite element analysis for shape forming process is based on the analysis model of elongation rolling mill with guide shoes. This paper shows how the cross angle of the roll, the rolling rpm, and the distance of the guide shoe influence on the outer diameter and the thickness of seamless pipes. The rolling rpm did not give much influence on outer diameter.

Measurement for mechanical behavior and fatigue property of Cu films by nanoscale dynamic load method

Mechanical behavior and fatigue properties greatly influence the reliability and life of film materials. Quantitative testing of film fatigue property under dynamic load is realized on the basis of nanometers thick Cu films deposited on monocrystalline silicon substrates by magnetron sputtering system. Microstructure and surface pattern of copper films are characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Film hardness and modulus are measured by quasi-static test and continuous measurements (CMX) systems of nanomechanical testing instrument. Fatigue damage behaviors are investigated by nanoscale dynamic mechanical analysis (nanoDMA) technique. The results indicate that Cu films prepared by magnetron sputtering system present (111) preferred orientation and contain a large number of nanoscale grains with uniform texture and low roughness. As is affected by substrate and small scale effect, CMX method is more suitable than quasi-static method for the measurement of micro-mechanical properties of ultra-thin films. Fatigue dominantly happens in thinner films. Factors, like thickness, inner stress, modulus and hardness, can influence fatigue life of nanoscale Cu films.

The flow over bedload sheets and sorted bedforms

Field surveys show the existence of morphological patterns (named bed load sheets in fluvial enviroments and sorted bedforms in coastal environments) which consist of alternate bands of coarse and fine sediments and are characterized by a negligible spatial variation of the bottom elevation. Previous analyses show that these bottom patterns are self-organizing features which are originated by the interaction of poorly sorted sediments, fractional sediment transport and turbulence dynamics. Presently, we describe the results of an investigation of turbulence dynamics over a flat bottom but characterized by alternate bands of small and large roughness. Turbulence characteristics are obtained by means of the two-equation turbulence model of Saffman (1970) which is shown to provide a reliable description of turbulence structure both in steady and oscillatory flows, as those generated in coastal environments by surface wave propagation. Moreover, the turbulence model can describe both smooth and rough walls and provide fair results also at moderate values of the Reynolds number. The results are validated by comparing the predictions of the model with the experimental data of Jensen et al. (1989) and Fredsøe et al. (1993) who measured the velocity field and the bottom shear stress under a turbulent oscillatory flow over a plane bed with a uniform roughness and sudden spatial change of the roughness size, respectively. The measurements of Fredsøe et al. (1993) were simulated also by Fuhrman et al. (2011) by means of the k–ω turbulence model of Wilcox (2006, 2008) and an indirect comparison of the model results with the results of Fuhrman et al. (2011) can be made. The investigation shows that the streamwise advection of turbulence plays a significant role such that turbulence is more intense over the rough bottom than over the smooth bottom, if a region close to the bottom is considered. However, moving far from the bottom, an opposite trend is found. Moreover, the results clearly show that the streamwise variations of the horizontal velocity component induce a significant vertical component of the velocity which should be taken into account if an accurate description of transport phenomena is to be obtained.

A study of helical passageways applied to polygon holes in abrasive flow machining

The characteristics of abrasive flow machining (AFM) make it a suitable method for complex holes and curved surface machining. However, the conventional AFM methods have difficulty achieving uniform roughness of radial distribution in polishing of polygonal holes, because the radial distance of polygonal holes is not symmetric, and the abrasive forces are non-uniform in the corner edges. Therefore, abrasive machining of gels with helical passageways is proposed to perform multiple paths of abrasive media, whose flowing behaviour enhances polishing effectiveness by increasing the abrasive surface area and radial shear forces. In this research, an analytical model has been developed in order to understand the behaviour of motion of the abrasive medium in different passageways by utilizing CFD-ACE+ software; then, a series of AFM experiments were utilized to verify the simulated results. Numerical results revealed that the helical passageways created interactive changes in the velocities in two axes, inducing a multiple direction motion of the abrasive media. Moreover, the percentage change of the strain rate deviation could be reduced from 72 to 40 % when a square passageway was replaced by a helical passageway. The small strain rate deviation produces good uniformity of a polygonal hole in AFM, and experimental results indicate that the helical passageways perform better than the polygonal passageways during AFM in terms of efficiency. Additionally, helical passageways create polishing uniformity of the polygonal holes. These results are in accordance with the simulated results.

High-rate and wide-area deposition of epitaxial Si films by mesoplasma chemical vapor deposition

Homoepitaxial Si films have been deposited at a high rate of 200 nm s−1 over a wide area of 20 mm × 80 mm by cluster-assisted mesoplasma chemical vapor deposition (MPCVD) on a moving substrate. The obtained epitaxial Si films exhibited a uniform roughness of 0.1–0.3 nm (1 × 1 μm2) and a Hall mobility of ∼240 cm2 V−1 s−1. The results suggested that under the MPCVD the deposition precursors formed at the plasma edge could be small enough not to influence either epitaxial film structure or the film quality provided the substrate temperature is maintained above 500 °C.

Sequential electrochemical treatment of dairy wastewater using aluminum and DSA-type anodes

Dairy wastewater is characterized by a high content of hardly biodegradable dissolved, colloidal, and suspended organic matter. This work firstly investigates the performance of two individual electrochemical treatments, namely electrocoagulation (EC) and electro-oxidation (EO), in order to finally assess the mineralization ability of a sequential EC/EO process. EC with an Al anode was employed as a primary pretreatment for the conditioning of 800 mL of wastewater. A complete reduction of turbidity, as well as 90 and 81% of chemical oxygen demand (COD) and total organic carbon (TOC) removal, respectively, were achieved after 120 min of EC at 9.09 mA cm(-2). For EO, two kinds of dimensionally stable anodes (DSA) electrodes (Ti/IrO₂-Ta₂O₅ and Ti/IrO₂-SnO₂-Sb₂O₅) were prepared by the Pechini method, obtaining homogeneous coatings with uniform composition and high roughness. The (·)OH formed at the DSA surface from H₂O oxidation were not detected by electron spin resonance. However, their indirect determination by means of H₂O₂ measurements revealed that Ti/IrO₂-SnO₂-Sb₂O₅ is able to produce partially physisorbed radicals. Since the characterization of the wastewater revealed the presence of indole derivatives, preliminary bulk electrolyses were done in ultrapure water containing 1 mM indole in sulfate and/or chloride media. The performance of EO with the Ti/IrO₂-Ta₂O₅ anode was evaluated from the TOC removal and the UV/Vis absorbance decay. The mineralization was very poor in 0.05 M Na₂SO₄, whereas it increased considerably at a greater Cl(-) content, meaning that the oxidation mediated by electrogenerated species such as Cl₂, HClO, and/or ClO(-) competes and even predominates over the (·)OH-mediated oxidation. The EO treatment of EC-pretreated dairy wastewater allowed obtaining a global 98 % TOC removal, decreasing from 1,062 to <30 mg L(-1).

Flume experimental evaluation of the effect of rill flow path tortuosity on rill roughness based on the Manning–Strickler equation

Numerous soil erosion models compute concentrated flow hydraulics based on the Manning–Strickler equation (v=kStR2/3I1/2) even though the range of the application on rill flow is unclear. Unconfined rill morphologies generate local friction effects and consequently spatially variable rill roughness which is in conflict with the assumptions of (sectional) uniform channel flow and constant channel roughness of the Manning–Strickler equation.The objective of this study is to evaluate the effect of rill morphology on roughness and hence to assess the Manning–Strickler roughness coefficient (kSt) by rill morphological data. A laboratory experiment was set up to analyse rill hydraulics and roughness of I.) Free Developed Rill (FDR) flows and II.) Straight Constrained Rill (SCR) flows in the flume. The flume experiment generated Manning–Strickler roughness coefficients (kSt) between 22m1/3s−1 and 44m1/3s−1 reflecting a potential area of the roughness parameter uncertainty. It was found that FDR experiments generated significantly lower kSt values compared to SCR experiments, because skin and local friction effects in the FDR experiments were more efficient reducing flow velocity probably due to higher energy dissipation. Rill flow path tortuosity (Tort) was used to describe the rill morphology of the experiments and correlation statistics between Tort and kSt identified considerable explanatory capacity of rill flow path tortuosity on rill roughness. The flume study demonstrated that a regression model between Tort and kSt can be used to assess local friction effects of unconfined rill morphologies and hence to reduce the area of uncertainty of the Manning–Strickler roughness parameter.

Effects of titanium brush on machined and sand‐blasted/acid‐etched titanium disc using confocal microscopy and contact profilometry

Mechanical techniques, including scaling with metal, plastic, or ultrasonic instruments, rubber cup polishing, air-powder abrasive system and brushing with a conventional or a rotating brush, have been used for the debridement of dental implants. Recently, rotating brushes with titanium bristles (titanium brush) have been introduced for the debridement of implant surface when peri-implant osseous defects occur. The purpose of this study was to evaluate the effects of a titanium brush on machined (MA) and sand-blasted and acid-etched (SA) titanium surfaces using scanning electron microscopy, confocal microscopy and profilometry. Moreover, correlations between the two quantitative evaluation methods (confocal microscopy and contact profilometry) were assessed. Both MA and SA discs were treated with rotating titanium brush at 300 rpm under irrigation for a total of 40 s. Roughness measurements were taken with confocal microscopy and surface profilometry. Then, the MA and SA surfaces were evaluated using scanning electron microscopy to determine the changes of the surface properties. Untreated MA surface demonstrated uniform roughness with circumferential machining marks, and scratch lines over the original surfaces were observed after treatment with the titanium brush. Similarly, the titanium brush produced noticeable changes on the SA titanium surfaces. However, this treatment with titanium brush did not significantly change the roughness parameters, including the arithmetic mean height of the surface (Sa) and the maximum height of the surface (Sz), in both MA and SA surfaces. Correlations between two evaluation methods showed a Pearson correlation coefficient of 0.98 with linear regression R(2) of 0.96. This study showed that the treatment with the titanium brush did not significantly change the roughness parameters, including Sa and Sz, in both MA and SA surfaces. Correlations between confocal microscopy and surface profilometry showed high correlation with a Pearson correlation coefficient of 0.98.

An Experimental Investigation on Friction Characteristics and Heat Transfer of Air and CO2 Flow in Microtubes With Structured Surface Roughness

Experiments were conducted to investigate roughness effects on flow characteristics and heat transfer of air and CO2 flow in four circular micr-tubes of approximately 1 mm inner diameter. The tubes were made by electrodepositing nickel on an aluminum sacrificial substrate. The desired roughness structures were machined or etched on the substrate before depositing nickel to generate a replica of the aluminum substrate on the internal surface of the nickel tubes. Four different surface roughness features were generated: (i) uniform roughness of 3.8 m, (ii) uniform roughness of 1.8 m, (iii) internal grooves 45 m deep and 218 m wide, and (iv) helical grooves 96 m deep with 1.9 mm pitch. Friction factor and Nusselt number data for the smooth tube are in good agreement with the conventional correlations in both the laminar and the turbulent flow regimes. In the rough tubes, the friction factors are significantly higher than that of the smooth tube. Heat transfer coefficients in the laminar flow regime for both smooth and rough tube agree well with the conventional correlation. However, in the turbulent flow regime, heat transfer was enhanced by the roughness features and the enhancement increased with increasing Reynolds number.

Гидравлическое сопротивление лотков с шероховатым дном

The authors study the dependence of the hydraulic friction coefficient on the Froude number for open steady uniform flows in channels having a high relative roughness. In the article, the authors provide the equation, which describes the hydraulic resistance in open channels having rough bottoms.Experiments were conducted in the rectangular tray (6,000×100×200 mm). Metal balls having the diameter of 15.1 mm were used to simulate uniform roughness. Aqueous solutions of glycerol were added as operating fluids. Average roughness was identified as k = 0.8d. The range of values of the main factors was as follows: inclination 0.011 —0.06; the Froude number 0.13 — 6.02; relative smoothness 0.3 — 1.36. The authors have proven that the value of the coefficient of hydraulic friction in the zone of the laminar flow is not dependent on the Froude number.The influence of the Froude number on the hydraulic friction is manifested in the areas of the turbulent flow.

Hydraulic validation of two-dimensional simulations of braided river flow with spatially continuous aDcp data

[1] Gravel-bed braided rivers are characterized by shallow, branching flow across low relief, complex, and mobile bed topography. These conditions present a major challenge for the application of higher dimensional hydraulic models, the predictions of which are nevertheless vital to inform flood risk and ecosystem management. This paper demonstrates how high-resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers. Specifically, we detail applications of the shallow water model, Delft3d, to the Rees River, New Zealand, at two nested scales: a 300 m braid bar unit and a 2.5 km reach. In each case, terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy. Dense observations of depth and velocity acquired from a mobile acoustic Doppler current profiler (aDcp), along with low-altitude aerial photography, were then used to create a data-rich framework for model calibration and testing at a range of discharges. Calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity, νH, through comparison of predictions with distributed hydraulic data. Results revealed strong sensitivity to νH, which influenced cross-channel velocity and localization of high shear zones. The high-resolution bed topography partially accounts for form resistance, and the recovered roughness was found to scale by 1.2–1.4 D84 grain diameter. Model performance was good for a range of flows, with minimal bias and tight error distributions, suggesting that acceptable predictions can be achieved with spatially uniform roughness and νH.

Numerical modelling of aeolian erosion over a surface with non‐uniformly distributed roughness elements

ABSTRACTThe present study is focused on the analysis of the mean wall friction velocity on a surface including roughness elements exposed to a turbulent boundary layer. These roughness elements represent non‐erodible particles over an erodible surface of an agglomeration of granular material on industrial sites. A first study has proposed a formulation that describes the evolution of the friction velocity as a function of geometrical parameters and cover rate with different uniform roughness distributions. The present simulations deal with non‐uniform distributions of particles with a random sampling of diameters, heights, positions and arrangements. The evolution (relative to geometrical parameters of the roughness elements) of the friction velocity for several non‐uniform distributions of roughness elements was analysed by the equation proposed in the literature and compared to the results obtained with the numerical simulations. This comparison showed very good agreement. Thus, the formulation developed for uniform particles was found also to be valid for a larger spectrum of particles noted on industrial sites. The present work aims also to investigate in detail the fluid mechanics over several roughness particles. Copyright © 2013 John Wiley &amp; Sons, Ltd.