Importance Of Surface Roughness Research Articles

Importance of surface roughness on the magnetic properties of additively manufactured FeSi thin walls

Thin-walled structures are being used in soft magnetic components manufactured by additive manufacturing to limit eddy current losses in AC machines. Fe-6.5wt %Si has been shown to be a promising material in such components, however most characterisation has taken place using thicker bulk material. Thermal conditions and microstructure have been shown to differ within thin-walled structures, hence magnetic properties may also differ. This study characterises the magnetic properties of thin-walled structures, showing that the 〈001〉 texture usually apparent in laser powder-bed fusion does not persist in thin-walled samples built at an angle to the build platform. Surface roughness (Sa) is shown to increase with build angle from 28 µm when perpendicular to the build platform, to 80 µm when parallel, causing a deterioration in magnetic properties such as susceptibility which is reduced by up to 25 %. Improvements in magnetic properties are demonstrated for samples with lower surface roughness due to improved laser parameters, with even larger improvements available when using polishing as a post-process finishing operation which was shown to improve susceptibility by over 10 %. This study enables the designers of soft magnetic components made by additive manufacturing, the freedom to design magnetic flux paths at any angle in the build chamber and gives surface roughness as a key parameter to improve magnetic properties.

Investigation of Physical Properties on HA/nGO Coating Magnesium Alloy

AZ91D magnesium alloys have been referred to as a revolutionary material for biomedical applications, particularly in orthopaedics as a bone implant material. This is attributable to the good strength and strong biocompatibility of magnesium and its alloys with bone tissue relative to other metallic alloys. The rapid degradation of pure magnesium has, sadly, reduced its therapeutic use. As a consequence, the efficacy of hydroxyapatite (HA) and graphene oxide (GO) in corrosion resistance has demonstrated tremendous potential to improve its defensive properties in order to address this vulnerability. AZ91D alloy has been coated with HA/GO by micro-arc oxidation (MAO) at a specific concentration and voltage, with varying treatment times. Surface roughness, elemental composition analysis and surface morphology analysis were tested at different treatment time. The sample enduring 15 min of treatment time was found to have the greatest resistance to corrosion due to its surface morphology and the importance of surface roughness was within the range of recommended roughness for a biomedical implant.

A review of surface roughness impact on dielectric film properties

The importance of surface roughness with respect to the bulk properties of dielectric materials is often overlooked. Surface roughness or interfaces between different material layers often significantly affects the external properties of thin films. Surface roughness holds its commonalty and critical impact among many materials properties. This review summarises the recent work on the effect of surface roughness on the mechanical, thermal, physical, and dielectric properties of dielectric films. Appropriate roughness favours adhesion, filtration, biological fouling, tribological properties, and magnetic properties. Nevertheless, lower roughness generally benefits the dielectric properties of dielectric materials, with thicknesses ranging from a few nanometres to up to 50 μm. This review discusses surface roughness control and the techniques of measurement as well. It emphasises the importance and characterisation of sample surface roughness for a better understanding of the dielectric phenomenon, mechanisms, and electrical stress test setup for various dielectric films.

Importance of surface roughness on perfluorooctanoic acid (PFOA) transport in unsaturated porous media

Understanding the subsurface transport of perfluorooctanoic acid (PFOA) is of considerable interest for evaluating its potential risks to humans and ecosystems. In this study, packed-column experiments were conducted to examine the influence of surface roughness on PFOA transport in unsaturated glass beads, quartz sand and limestone porous media. Results showed decreasing moisture content significantly increased the air-water interfacial adsorption of PFOA and led to greater retardation in all three types of porous media. Particularly, rougher surface (limestone > quartz sand > glass beads) and smaller grain size (i.e. a larger solid specific surface area, SSSA) significantly enhanced PFOA retardation under unsaturated conditions. These results were further supported by bubble column experiments and SSSA analysis of porous media, which demonstrate that except for the factors affecting PFOA transport in solid-water interface (e.g. surface charge and chemical heterogeneity), the greater retardation of PFOA during transport is attributed to the larger air-water interfacial areas associated with rougher surface and smaller grain size and hence greater interfacial adsorption of PFOA. Our results indicated the importance of surface roughness on the retention and transport of PFOA in the unsaturated zone.

Non-Deterministic Assessment of Surface Roughness as Bond Strength Parameters between Concrete Layers Cast at Different Ages.

The importance of surface roughness and its non-destructive examination has often been emphasised in structural rehabilitation. The presented innovative procedure enables the estimation of concrete-to-concrete strength based on a combination of low-cost, area-limited tests and geostatistical methods. The new method removes the shortcomings of the existing one, i.e., it is neither qualitative nor subjective. The interface strength factors, cohesion and friction, can be estimated accurately based on the collected data on a surface texture. The data acquisition needed to create digital models of the concrete surface can be performed by terrestrial close-range photogrammetry or other methods. In the presented procedure, limitations to the availability of concrete surfaces are overcome by the generation of subsequential Gaussian random fields (via height profiles) based on the semivariograms fitted to the digital surface models. In this way, the randomness of the surface texture is reproduced. The selected roughness parameters, such as mean valley depth and, most importantly, the geostatistical semivariogram parameter sill, were transformed into contact bond strength parameters based on the available strength tests. The proposed procedure estimates the interface bond strength based on the geostatistical methods applied to the numerical surface model and can be used in practical and theoretical applications.

A multi-scale modeling and simulation study to investigate the effect of roughness of a surface on its self-cleaning performance

The importance of surface roughness on wettability is vital in developing novel techniques and materials for fabrication of self-cleaning coatings.

Effect of surface polishing on the tribological performance of hard coatings under lubricated three-body abrasive conditions

The present study investigates the effect of surface polishing on the tribological performance of two notably different coatings, namely chromium carbide and aluminized, under three-body abrasive conditions. Surface polishing altered the topographical and mechanical properties of the coatings. Detailed analysis of the most relevant roughness parameters highlighted the significance of surface topography under the tested conditions. Polished and unpolished coatings were tested on a pin-on-disk configuration under lubricated three-body abrasive conditions. Silica sand particles were added to the hydraulic oil to model contaminated lubricant conditions. In-situ friction coefficient and wear rate were obtained experimentally. The importance of surface roughness and core void volume in alleviating the abrasive wear was shown. It was found that the dominant wear mechanisms are independent of the coating roughness, however surface polishing increases wear, and does not significantly affect friction.

Microplastic surface properties affect bacterial colonization in freshwater.

Microplastics are a global concern in aquatic ecology and are readily colonized by bacteria in the environment. There is a lack of information on bacterial colonization of eroded and un-eroded microplastics in freshwater. In this study, six types of microplastics were incubated for 8 weeks in microcosms with water from Lake Erie. Microcosms were inoculated with one of three species: Acinetobacter (A.) calcoaceticus, Burkholderia (B.) cepacia, and Escherichia (E.) coli. These bacterial species are ubiquitous in water bodies associated with human populations. Bacterial surface coverage was determined using electron and fluorescent microscopy. Quantifications of EPS and surface roughness were performed by confocal microscopy and measuring contact angles (θw ) of water droplets on microplastics, respectively. Analyses revealed surface coverage differed among bacterial species and plastic types after 8 weeks. As the study progressed, E. coli remained the most abundant while A. calcoaceticus gradually decreased on most surfaces. Analyses of microcosms revealed polypropylene disks had lower bacterial abundance. Conversely, eroded polypropylene disks had highest bacterial abundance, indicating importance of surface roughness (lower θw values) and surface physicochemical properties of microplastics in bacterial colonization. Our results demonstrated that bacterial colonization of microplastics is affected by both the physicochemical properties of microplastics and the physiological properties of colonizing bacteria.

Spin relaxation in graphene nanoribbons in the presence of substrate surface roughness

In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin flipping rate and therefore reduction of the spin-polarization, whereas a longer correlation length makes AGNR surface smoother and increases spin-polarization. Moreover, spin diffusion length of carriers is extracted and its dependency on the roughness parameters is investigated. In agreement with experimental data, the spin diffusion length for various substrate ranges between 2 and 340 μm. Our results indicate the importance of surface roughness on spin-transport in graphene.

Non-DLVO adhesion of F-specific RNA bacteriophages to abiotic surfaces: Importance of surface roughness, hydrophobic and electrostatic interactions

We report on the adhesion features of three F-specific RNA-phages (MS2, GA and Qβ) onto surfaces (1-dodecanethiol gold-coated surface, glass, polypropylene and stainless steel) that significantly differ with regard to their surface roughness and hydrophobic/hydrophilic balance. The number of adhered phages on the surfaces is quantified using RT-PCR. Adhesion experiments are performed under static conditions in the absence of bulk phages aggregation (1mM and 100mM NaNO3 electrolyte, pH 7). The nanoscale surface features and the hydrophobicity of the deposition substrates are quantitatively addressed using Atomic Force Microcopy and Chemical Force Microscopy. The hydrophobicity of the phages is evaluated from their propensity to adhere onto flat and highly hydrophobic surface. Results show that, regardless of electrolyte concentration and surface roughness, the adhesion capacity of phages systematically follows the hydrophobicity sequence MS2<Qβ<GA. The capacity of each phage to adhere onto the surfaces increases with increase in the degree of hydrophobicity and/or the roughness of the deposition substrate. Increasing the electrostatic interactions between phages and deposition surface by decreasing solution ionic strength leads to a reduction in surface concentration of adhered phages except for cases where the roughness of the deposition surface is significant. Altogether, the results obtained confirm the limited ability of the classical DLVO theory to predict the adhesion of complex viral (nano)particles to surfaces and emphasize the necessity to take into account the roughness of the deposition substrate and the hydrophobicity degree of both viruses and surfaces.

Dynamic controls on wind erosion and dust generation on west‐central Free State agricultural land, South Africa

AbstractThe west‐central part of South Africa's Free State Province falls within the transition zone between South Africa's sub‐humid, temperate grasslands to the east, and the semi‐arid Karoo and arid Kalahari to the south and west, respectively. The area is characterized by low rainfall (typically 500 mm or less) with high variability, but environmental conditions allow widespread dryland commercial agriculture (maize, sunflowers and stock farming). However, human activity promotes wind erosion and the area is susceptible to dust emissions. This study is the first to quantify the degree of wind erosion on the agricultural soils in the region under prevailing winter to spring climatic conditions and land management practices. Using arrays of cup anemometers, dust deposition traps and saltation impact sensors (Safires), measurements were made of the key erosivity and erodibility drivers that control the degree of wind erosion. Results demonstrate that significant quantities of dust are mobilized, particularly during the months of September and October. Thresholds of wind erosion are shown to respond particularly closely to changes in surface and aerodynamic roughness (z0) with the amount of collected dust correlating well with measures of wind erosivity that weight the impact of higher wind speeds. Given the importance of surface roughness in controlling erosion thresholds, results show that the opportunity exists for well designed farming practices to control wind erosion. However, it is likely that climatically driven environmental change will impact on some of the identified controls on erosion (wind power, moisture availability) with the result that the wind erosion hazard is likely to increase within this marginal environment. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Too rough, not tough

Measuring the strength of silicon nanobeams indicates the importance of surface roughness in determining failure due to fracture

Elastic loading and elastoplastic unloading from nanometer level indentations for modulus determinations

A new method for evaluating modulus and hardness from nanoindentation load/ displacement curves is presented. As a spherical indenter penetrates an elastoplastic half-space, the elastic displacement above the contact line is presumed to diminish in proportion to the total elastic displacement under the indenter. Applying boundary conditions on the elastic and plastic displacements for elastic and rigid plastic contacts leads to an expression that can be best fit to the entire unloading curve to determine E*, the reduced modulus. Justification of the formulation is presented, followed by the results of a preliminary survey conducted on three predominantly isotropic materials: fused quartz, polycrystalline Al, and single crystal W. Diamond tips with radii ranging from 130 nm to 5 μm were used in combination with three different nanoindentation devices. Results indicate that the method gives property values consistent with accepted values for modulus and hardness. The importance of surface roughness and indentation depth are also considered.

Extensive wetting due to roughness

Typically, a small mass of eutectic SnPb solder wets a copper surface and flows radially outward to form a hemispherical shape with a contact angle of approx. 15–20 deg. When a similar mass of solder wets a thick electroless copper coated substrate, rapid radial flow commences and surprising new effects occur. Thick coats of electroless copper have a nodular surface structure and spreading on it does not subside until all solder is consumed. When the nodular structure is wetted by solder a “coastline” with many nearby “islands” are defined. Photos of regions at the wetting front were taken in the backscatter imaging mode of an SEM. These images show that solder wets the valleys between the surface nodules forming a delicate, lacy arrangement. The geometry of this “coastal” solder structure is described as fractal-like having a dimension D = 1.38 making it similar to drying fronts and cloud configurations. The importance of surface roughness in wetting phenomena is discussed in the light of an extensive history on the subject. It is shown that for spontaneous flow, assisted by roughness, the surface geometry must consist of local angles that are larger than the equilibrium contact angle. Kinetics of the wetting process are demonstrated by image analysis of wetted area taken from videotaped experiments. These experimental kinetics are shown to be similar in form to flow in open channel capillaries.

A Simplified Correction for Surface Roughness Effects in X-Ray Diffractometric Investigations

AbstractThe importance of surface roughness to the measurement of integrated intensity in X-ray powder diffraction is discussed following studies conducted with materials in both powder and bulk (rolled sheet/billet) forms possessing different absorption characteristics. A simple procedure is described which allows for surface roughness effect.

White-Light Method: A New Sensor For The Optical Evaluation Of Rough Surfaces

In recent decades the importance of surface roughness as a quality characteristic has increased remarkably. Optical methods for asperity measurements have been investigated, in particular because of their principal advantage of permitting inprocess or on-line measurements. This paper reports on a new optical method, the so-called white-light method, which determines a surface parameter, the optical contrast C, that represents the quotient of the standard deviation and mean value of the resultant light intensity. The scanned and converted optical information of a strongly defocused image of the rough surface leads to a good correlation between optically and mechanically evaluated surface parameters. This holds true for surfaces that can be measured without severe distortions due to the mechanical scanning procedure. With reference to industrial applications, the measuring range of this system lies in the interesting region of 0.06 um <Ra < 10 Am. Efforts are currently being made to bring this type of sensor from the laboratory to the prototype stage for practical use.

Stone movement through snow creep, 1963–75 mount twynam, snowy mountains, Australia

On the backwall of Twynam East Cirque selected stones moving through snow creep were marked and their movements from 1963 to 1975 measured. Their annual movements varied markedly between 1963 and 1970 but thereafter little. The percentage of stones failing to move varied reciprocally with snow thickness over a snow course in a comparable site near Spencers Creek. The annual mean movement, ranging from 7·6 to 36·3 cm, correlated strongly with Spencers Creek snow thickness. Frequent occurrence of annual movements of intermediate value characterise the process. Snow surface maps with 2m contours for 1964, 1974 and 1975 permitted determination of snow slope at the stone positions and of snow thickness by subtraction of ground heights. A 2 m contour ground surface map was also the basis for hillslope angles at stone positions. Basal area and area transverse to snow movement were calculated from measurements of the three principal axes of the stones. The vertical angles and directions of their abrasion tracks were measured. Rank correlation of stone movements with hillslope and snow slope was usually not significant but with track angle was so in most years. Track angle and direction are controlled partly by hillslope and partly by local rock geometry. Movements correlated inversely with stone basal area on which frictional drag depends. Correlation with stone transverse area was weak and inverse; this may be due to snow tending to move round larger stones. In most years there was significant correlation with snow thickness and basal stress (calculated from snow thickness and snow slope). However, the amount of ‘explanation’ associated with all the independent variables was small and the experiments revealed an importance of surface roughness at various scales in controlling stone movement which was much greater than expected from direct observation.

Deposition of particles on rough surfaces during turbulent gas-flow in a pipe

The importance of surface roughness on the deposition of particles from a flowing gas stream is well known but there has been little theoretical work that helps predictions to be made. The theory presented here follows the general approach of Davies (1966) who considered deposition on smooth surfaces. To take account of surface roughness extra distances have been added to the particle-capture distance and, by shifting the position of the origin of the velocity profile, it has been possible to use the same equation for the radial velocity fluctuations. The effect of surface roughness on the friction velocity is dealt with by empirical equations. Details of the analysis are given together with a computer solution procedure. Results of calculations are compared with the experimental results of other workers and a reasonable degree of agreement is shown. The effect of small changes in surface roughness on deposition velocity are shown to be so large that there is difficulty in making precise predictions of deposition rates and results from apparently similar experiments may vary widely.

Paper 13: Surface Roughness and Lubrication in Sheet Metal Working

The importance of surface roughness and lubrication in the manufacture of autobodies is discussed with particular reference to consistency, methods of measurement, and the need for overall optimization.