Showing papers on "Surface roughness published in 2006"

Co‐refinement of multiple‐contrast neutron/X‐ray reflectivity data using MOTOFIT

Abstract: The contrast-variation technique is employed in multiple-contrast neutron/X-ray reflectometry experiments to highlight scattering from different structural components that are present at a surface or interface. The advantage of this technique is that the structural model used to describe the interfacial scattering length density profile must apply to all the contrasts measured. A new reflectivity analysis package, MOTOFIT, which runs in the IGOR Pro environment (http://www.wavemetrics.com), has been created to aid the simultaneous fitting (with the same structural model) of these multiple-contrast data, using an intuitive graphical user interface, which most co-refinement packages do not possess. MOTOFIT uses a slab-model approach with the Abeles matrix method, and extensions for surface roughness to perform non-linear least-squares regression on the experimental reflectivity curves. Other features, such as the ability to create complicated interparameter constraints or analyse reflectivity from multilayers, simulated annealing, etc., make MOTOFIT a powerful reflectometry analysis package

Selective laser melting of biocompatible metals for rapid manufacturing of medical parts

Abstract: Purpose – This paper seeks to investigate the possibility of producing medical or dental parts by selective laser melting (SLM). Rapid Manufacturing could be very suitable for these applications due to their complex geometry, low volume and strong individualization.Design/methodology/approach – The SLM‐process has been optimized and fully characterized for two biocompatible metal alloys: Ti‐6Al‐4V and Co‐Cr‐Mo. Mechanical and chemical properties were tested and geometrical feasibility, including process accuracy and surface roughness, was discussed by benchmark studies. By developing a procedure to fabricate frameworks for complex dental prostheses, the potential of SLM as a medical manufacturing technique has been proved.Findings – Optimized SLM parameters lead to part densities up to 99.98 percent for titanium. Strength and stiffness, corrosion behavior, and process accuracy fulfil requirements for medical or dental parts. Surface roughness analyses show some limitations of the SLM process. Dental frame...

Surface effects on elastic properties of silver nanowires: Contact atomic-force microscopy

Abstract: Silver nanowires with different diameters were synthesized by a hydrothermal chemical method. The elastic properties of the nanowires with outer diameters ranging from 20 to $140\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ were measured using contact atomic force microscopy. The apparent Young modulus of the nanowires is found to decrease with the increase of the diameter. When the diameter of the silver nanowires is larger than $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, the Young modulus approaches a constant value. The size dependence of the apparent Young modulus of the silver nanowires is attributed to the surface effect, which includes the effects of the surface stress, the oxidation layer, and the surface roughness. Thus, a theoretical analysis is presented to explain the size dependence. This analysis is different from the previous models in that both the surface stress and the surface moduli are included in it. We also show that the apparent surface modulus and the surface stress of the silver nanowires can be experimentally determined.

Enhancement of Protein Adsorption Induced by Surface Roughness

Abstract: Using quartz crystal microbalance with dissipation and ellipsometry, we show that during adsorption of fibrinogen on evaporated tantalum films the saturation uptake increases with increasing root-mean-square roughness (from 2.0 to 32.9 nm) beyond the accompanying increase in surface area. This increase is attributed to a change in the geometrical arrangement of the fibrinogen molecules on the surface. For comparison, the adsorption of a nearly globular protein, bovine serum albumin, was studied as well. In this case, the adsorption was less influenced by the roughness. Simple Monte Carlo simulations taking into account surface roughness and the anisotropic shape of fibrinogen reproduce the experimentally observed trend.

Implant Surface Roughness and Bone Healing: a Systematic Review

Abstract: A systematic review was performed on studies investigating the effects of implant surface roughness on bone response and implant fixation. We searched the literature using MEDLINE from 1953 to 2003. Inclusion criteria were: (1) abstracts of animal studies investigating implant surface roughness and bone healing; (2) observations of three-month bone healing, surface topography measurements, and biomechanical tests; (3) provision of data on surface roughness, bone-to-implant contact, and biomechanical test values. The literature search revealed 5966 abstracts. There were 470, 23, and 14 articles included in the first, second, and third selection steps, respectively. Almost all papers showed an enhanced bone-to-implant contact with increasing surface roughness. Six comparisons were significantly positive for the relationship of bone-to-implant contact and surface roughness. Also, a significant relation was found between push-out strength and surface roughness. Unfortunately, the eventually selected studies were too heterogeneous for inference of data. Nevertheless, the statistical analysis on the available data provided supportive evidence for a positive relationship between bone-to-implant contact and surface roughness.

Determination of optimum parameters for multi-performance characteristics in drilling by using grey relational analysis

Abstract: The theory of grey systems is a new technique for performing prediction, relational analysis and decision making in many areas. In this paper, the use of grey relational analysis for optimising the drilling process parameters for the work piece surface roughness and the burr height is introduced. Various drilling parameters, such as feed rate, cutting speed, drill and point angles of drill were considered. An orthogonal array was used for the experimental design. Optimal machining parameters were determined by the grey relational grade obtained from the grey relational analysis for multi-performance characteristics (the surface roughness and the burr height). Experimental results have shown that the surface roughness and the burr height in the drilling process can be improved effectively through the new approach .

Laser-assisted machining of Inconel 718 with an economic analysis

Abstract: Superalloys have high strengths at elevated temperatures, which make them attractive toward various applications and also make these materials difficult to machine at room temperature due to excessive tool wear and poor surface finish. Laser-assisted machining (LAM) offers the ability to machine superalloys more efficiently and economically by providing the local heating of the workpiece prior to material removal by a single point cutting tool. An existing transient, three-dimensional heat transfer model is modified for modeling LAM of Inconel 718. Suitable coating conditions are determined for increasing the laser absorptivity in metals and an approximate absorptivity value is determined. The thermal model is validated in axial and circumferential directions by temperature measurement using an infrared camera. The machinability of Inconel 718 under varying conditions is evaluated by examining tool wear, forces, surface roughness, and specific cutting energy. With increasing material removal temperature from room temperature to 620 °C, the benefit of LAM is demonstrated by a 25% decrease in specific cutting energy, a 2–3-fold improvement in surface roughness and a 200–300% increase in ceramic tool life over conventional machining. Moreover, an economic analysis shows significant benefits of LAM of Inconel 718 over conventional machining with carbide and ceramic inserts.

Influence of surface roughness on superhydrophobicity.

Abstract: Superhydrophobic surfaces, with a liquid contact angle theta greater than 150 degrees , have important practical applications ranging from self-cleaning window glasses, paints, and fabrics to low-friction surfaces. Many biological surfaces, such as the lotus leaf, have a hierarchically structured surface roughness which is optimized for superhydrophobicity through natural selection. Here we present a molecular dynamics study of liquid droplets in contact with self-affine fractal surfaces. Our results indicate that the contact angle for nanodroplets depends strongly on the root-mean-square surface roughness amplitude but is nearly independent of the fractal dimension D(f) of the surface.

Making silicon hydrophobic: wettability control by two-lengthscale simultaneous patterning with femtosecond laser irradiation

Abstract: We report on the wettability properties of silicon surfaces, simultaneously structured on the micrometre-scale and the nanometre-scale by femtosecond (fs) laser irradiation to render silicon hydrophobic. By varying the laser fluence, it was possible to control the wetting properties of a silicon surface through a systematic and reproducible variation of the surface roughness. In particular, the silicon–water contact angle could be increased from 66° to more than 130°. Such behaviour is described by incomplete liquid penetration within the silicon features, still leaving partially trapped air inside. We also show how controllable design and tailoring of the surface microstructures by wettability gradients can drive the motion of the drop's centre of mass towards a desired direction (even upwards).

Multi response optimization of wire EDM operations using robust design of experiments

Abstract: In this present study a multi response optimization method using Taguchi’s robust design approach is proposed for wire electrical discharge machining (WEDM) operations. Experimentation was planned as per Taguchi’s L16 orthogonal array. Each experiment has been performed under different cutting conditions of pulse on time, wire tension, delay time, wire feed speed, and ignition current intensity. Three responses namely material removal rate, surface roughness, and wire wear ratio have been considered for each experiment. The machining parameters are optimized with the multi response characteristics of the material removal rate, surface roughness, and wire wear ratio. Multi response S/N (MRSN) ratio was applied to measure the performance characteristics deviating from the actual value. Analysis of variance (ANOVA) is employed to identify the level of importance of the machining parameters on the multiple performance characteristics considered. Finally experimental confirmation was carried out to identify the effectiveness of this proposed method. A good improvement was obtained.

Sub-surface mechanical damage distributions during grinding of fused silica

Abstract: The distribution and characteristics of surface cracking (i.e., sub-surface damage or SSD) formed during standard grinding processes have been measured on fused silica glass using a surface taper polishing technique. The measured SSD depth distributions are described by a single exponential followed by an asymptotic cutoff in depth. The observed surface cracks are characterized as near-surface lateral and deeper trailing indent type fractures (i.e., chatter marks). The length of the trailing indent is strongly correlated with a given grinding process. It is shown that only a small fraction of the abrasive particles are being mechanically loaded and causing fracture, and most likely it is the larger particles in the abrasive particle size distribution that bear the higher loads. The SSD depth increased with load and with a small amount of larger contaminant particles. Using a simple brittle fracture model for grinding, the SSD depth distribution has been related to the SSD length distribution to gain insight into ‘effective’ size distribution of particles participating in the fracture. Both the average crack length and the surface roughness were found to scale linearly with the maximum SSD depth. These relationships can serve as useful rules-of-thumb for non-destructively estimating SSD depth and for identifying the process that caused the SSD.

Measurement and parameterization of aerodynamic roughness length variations at Haut Glacier d'Arolla, Switzerland

Abstract: Spatial and temporal variations in aerodynamic roughness length (z0) on Haut Glacier d'Arolla, Switzerland, during the 1993 and 1994 ablation seasons are described, based on measure- ments of surface microtopography. The validity of the microtopographic z0 measurements is established through comparison with independent vertical wind profile z0 measurements over melting snow, slush and ice. The z0 variations are explained through correlation and regression analyses, using independent measurements of meteorological and surface variables, and parameterizations are developed to calculate z0 variations for use in surface energy balance melt models. Several independent variables successfully explain snow z0 variation through their correlation with increasing surface roughness, caused by ablation hollow formation, during snow melt. Non-linear parameterizations based on either accumulated melt or accumulated daily maximum temperatures since the most recent snowfall explain over 80% of snow z0 variation. The z0 following a fresh snowfall on an ice surface is parameterized based on relationships with the underlying ice z0, snow depth and accumulated daily maximum temperatures. None of the independent variables were able to successfully explain ice z0 variation. Although further comparative studies are needed, the results lend strong support to the microtopo- graphic technique of measuring z0 over melting glacier surfaces.

Thermal annealing in hydrogen for 3-D profile transformation on silicon-on-insulator and sidewall roughness reduction

Abstract: A fast, effective process using hydrogen annealing is introduced to perform profile transformation on silicon-on-insulator (SOI) and to reduce sidewall roughness on silicon surfaces. By controlling the dimensions of as-etched structures, microspheres with 1 /spl mu/m radii, submicron wires with 0.5 /spl mu/m radii, and a microdisk toroid with 0.2 /spl mu/m toroidal radius have been successfully demonstrated on SOI substrates. Utilizing this technique, we also observe the root-mean-square (rms) sidewall roughness dramatically reduced from 20 to 0.26 nm. A theoretical model is presented to analyze the profile transformation, and experimental results show this process can be engineered by several parameters including temperature, pressure, and time.

DNS of turbulent channel flows with two- and three-dimensional roughness

Abstract: DNS results for turbulent channel flow with two- and three-dimensional roughness elements are discussed. The focus is on surfaces where the separation between consecutive roughness elements is small. In these cases, the roughness function is strongly influenced by the shape of the roughness elements. Usually, the roughness function is plotted against geometrical parameters and a satisfactory correlation does not emerge. Alternatively, a rather good collapse of the data is achieved when the roughness function is plotted against the rms of the normal velocity on the plane of the crests. This good relationship was observed previously for two-dimensional geometrical disturbances (Orlandi, P., Leonardi, S. and Antonia, R. A., 2006, Turbulent channel flow with either transverse or longitudinal roughness elements on one wall. Journal of Fluid Mechanics, to appear), here it is extended to three-dimensional geometries that are more often found in practical applications. Three-dimensional roughness has a strong inf...