Surface Roughness Height Research Articles

Aerodynamics of smooth and rough square-section prisms at incidence in very high Reynolds-number cross-flows

The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1times10^{5}le Re_{D}le 1times10^{7}. For the smooth prism with k_s/D = 4times10^{-5}, tests were performed at three angles of incidence, i.e. alpha = 0^{circ }, −22.5^{circ } and −45^{circ }, whereas only both “symmetric” angles were studied for its slightly rough counterpart with k_s/D = 1times10^{-3}. First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as mathcal {O}(10^{7}). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though.Graphic abstract

A New Film Parameter for Rough Surface EHL Contacts with Anisotropic and Isotropic Structures

Numerous tribological contacts worldwide rely on adequate lubrication quality for proper functionality. Despite this, there is no existing approach to accurately predict the state of lubrication. The default model since introduced in the 1960s—the Lambda-ratio, defined as the oil film thickness over the surface roughness height—is unpredictable and may yield erroneous results. Here, we put forward a framework for a new updated film parameter, {Lambda }^{*}, which accounts for the elasto-hydrodynamic lubrication (EHL) effects induced by surface irregularities on the microscopic scale (micro-EHL). This new film parameter was validated in ball-on-disc tribological tests with engineering surfaces comprising isotropic and anisotropic structures. As expected, the new model was found to accurately predict the experimentally measured true mixed and full-film EHL regimes. The ability to accurately predict the mode of lubrication represents a major advance in designing tribological interfaces for optimal efficiency and durability.

Sustainable Drilling of Nano SiC Reinforced Al Matrix Composites Using MQL and Cryogenic Cooling for Achieving the Better Surface Integrity

Metal Matrix Nano Composites (MMNCs) are progressive alternatives of formal metal materials, are presently accomplishing a growing inclination of research and engineering approaches for challenging operations such as aviation, nuclear power, and automotive for the improved mechanical properties and comparatively light in weight. Machining these MMNC leftovers, however, is a stimulating task as an effect of its mechanical heterogeneity, which primes the product of rapid wear of the tool to worsen the integrity of the surface at the point of machining. This article presents cryogenic Machining (CM), Minimum Quantity Lubrication (MQL) and Dry Machining (DM) of Nano SiC reinforced Al matrix composite and its induced surface integrity characteristics such as surface roughness, burr height and microhardness. The drilling experiments are carried out computer numeric control (CNC) machine considering a carbide drill with dia of 10 mm having a contact point of 90o, 118o, and 135o. The Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray Spectroscopy (EDAX), Atomic Force Microscope (AFM), and Vickers microhardness test are used to assess the subsurface deformation and morphology. An evolutionary Non-dominated Sorting Genetic Algorithm - II (NSGA-II) is used for improving the performances such as surface roughness (SR) and burr height (BH) subjected to distinct cooling environments. The results showed that minimal SR and BH are 0.29 μm and 0.23 mm respectively under 500 rpm, 50 mm/min feed, 900point angle, and 1% wt of Nano SiC and CM shows reduced depth of plastic deformation in the subsurface of machined composites. The FESEM results show that the better surface finish are found on MMNC surface when machined under CM.

Optimization of laser-assisted jet electrochemical machining parameters by grey relational analysis and fuzzy logic

PurposeThe purpose of this paper is to optimize the laser-assisted jet electrochemical machining parameters, namely, supply voltage, inter-electrode gap, duty cycle and electrolyte concentration during machining of WC-Co composite using grey relational analysis and fuzzy logic.Design/methodology/approachIn this work, experiments were carried out as per the Taguchi methodology and an L16 orthogonal array was used to study the influence of various combinations of process parameters on material removal rate, hole taper angle and surface roughness height. As a dynamic approach, the multiple response optimization was carried out using grey relational analysis and fuzzy logic.FindingsThe process parameters were optimized using grey relational analysis and fuzzy logic for different machining conditions such as balanced manufacturing, high-speed manufacturing and high-quality manufacturing. The research documented in this paper can be scaled up for case studies regarding industrial applications to compare optimization methods for manufacturing processes that are already being carried out.Originality/valueAn attempt to optimize material removal rate, hole taper angle and surface roughness height together by a combined approach of grey relational analysis and fuzzy logic has not been previously done.

Performance Evaluation of Al-SiC Nanofluids Based MQL Sustainable Cooling Techniques During Turning of EN-24 Steel

The conventional cutting fluids are used in metal cutting processes for cooling and lubrication. However, the use of cutting fluids is creating the environmental and biological problems. In order to minimize these problems, it is essential to move towards sustainable cooling techniques. The present investigation determine the influence of sustainable cooling techniques such as cryogenic cooling, minimum quantity lubrication, Al2O3/soluble oil nanofluids based minimum quantity lubrication, SiC/soluble oil nanofluids based MQL and Al-SiC/soluble oil hybrid nanofluids based minimum quantity lubrication on output characteristics during turning of EN-24 steel. For experimentation nanofluids were formulated with accumulation of different weight percentages (0.5wt.%, 1.0wt.%, 1.5wt.%) of Al2O3, SiC and Al-SiC nanoparticles to the soluble oil. The thermal and tribological properties of Al2O3/soluble oil nanofluids, SiC/soluble oil nanofluids and Al-SiC/soluble oil hybrid nanofluids were analyzed. Individual machining performance such as surface roughness height, tool wear and specific energy lead to ambiguous understanding. So, the cumulative performance index is also calculated. The cumulative performance index is used to determine the performance of different sustainable cooling techniques during turning of EN-24 steel. The experimental results revealed that the turning performance of EN-24 steel under Al-SiC/soluble oil hybrid nanofluids based minimum quantity lubrication environment is superior then other machining environments.

Lubricant film formation in rough surface non-conformal conjunctions subjected to GPa pressures and high slide-to-roll ratios

A ball-on-disc machine was employed in a highly idealised setting to study the interplay between oil film formation and surface irregularities in single-sided rough elasto-hydrodynamic lubricated (EHL) conjunctions. The tests were operated under GPa pressures and high slide-to-roll ratios in a situation where the separating gap was smaller than the combined surface roughness height. Under the initial state of solid contact interference and with the operating conditions held fixed, surfaces were found to gradually conform such that a fully separating oil film of nanometre thickness eventually developed—a thin film lubrication state known as micro-EHL. Additionally, with a previously developed approach for 3D surface re-location analysis, we were able to very precisely specify the pertained nature of surface transformations, even at the asperity scale, by comparing the post-test surfaces to those in the virgin state. The surface roughness Sq was reduced by up to 17% after running-in, while the speed required for full film EHL was reduced by a remarkable 90%. Hence, full film EHL is possible even in cases where the Λ-ratio falsely suggests boundary lubrication. This discrepancy was attributed to the way surfaces are deformed inside the contact, i.e., through the establishment of micro-EHL.

Experimental and FEM study of cutting mechanism and damage behavior of ceramic particles in orthogonal cutting SiCp/Al composites

To study the removal mechanism and damage behavior during the machining of ceramic particle-reinforced metal matrix composites, a finite element model (FEM) comprehensively considering the distribution and shape of the particles and the damage behavior of ceramic particles is established. Corresponding experiments are conducted to demonstrate the reliability of FEM. The results demonstrate that chips are easy to separate where the particles gather. The stress concentration is serious at the edges and corners of the particles. The cutting and thrust force, subsurface damage, surface roughness and maximum profile peak-valley height increase with the increase of depth of cut. Voids, particle fracture, particle peeling off, matrix tearing and interface failure are the main surface defects. Moreover, according to the failure mode and mechanism of ceramic particles, the positional relationships between the ceramic particles and the tool are divided into three categories: the particle is below, on and above the cutting path.

Numerical investigation of the surface roughness effects on the subsonic flow around a circular cone-cylinder

The flow around a circular-cone is 3D, unsteady and turbulent. As reported in many research works on this type of flow, boundary layer separations, vortex structures and the effect of surface roughness are strongly related. The effect of roughness is still not completely understood and proves challenging both for numerical and experimental approaches. The present work aims to gain more insights in understanding and numerically predicting this type of flows. Particularly, it attempts to improve the accuracy of numerical predictions of the effects of roughness on the asymmetric vortex flow around a circular-cone at subsonic flow conditions. This is performed using numerical simulations, which predict the flow field details across different transversal stations along the cone. Therefore, we have analyzed the effect of many turbulence models, notably, the transition SST, using ANSYS Fluent code. Flows characteristics are highlighted and validated against the well-known theory and some experimental measurements. The findings depict that a surface roughness height about 0.32 mm has efficaciously triggered the boundary layer to change from a laminar to a fully turbulent state in both sides of the body, in addition to a significant reduction in the global lateral force. Moreover, it seems that the roughness reduces the asymmetry of the vortex in the leeward side of the cone. Testing many roughness heights has allowed us to determine the way in which it is possible to reduce the side force effectively at high angles of attack without affecting the lift of the cone cylinder.

Laser surface polishing of NiCrSiBC – 60WC ceramic-metal matrix composite deposited by laser directed energy deposition process

Deposition of ceramic-metal matrix composite using laser directed energy deposition process presents multi-fold challenges. High melting point ceramic particles often remain partially melted and increase the roughness of the deposit, which essentially requires secondary finishing operation. Besides high surface roughness, the high gradient of thermal and physical properties between ceramic reinforcement and metal matrix introduces cracks in the composite. Therefore, in the present work, the effect of laser surface polishing and substrate heating on improving the surface quality of NiCrSiBC – 60WC ceramic-metal composite deposited by laser directed energy deposition process was investigated. The molten pool thermal history was monitored using an IR pyrometer during laser surface polishing. The effect of rate of heat input on heating rate, cooling rate, molten pool lifetime and peak temperature was investigated and correlated with the surface quality parameters viz. arithmetic surface roughness (Ra) and ten-point height (Rz). A combination of intermediate laser power and scanning speed (600 W and 2000 mm/min) resulted in proper spread of molten pool and rendered better surface finish. The surface roughness (Ra) was found to improve from 19.2 μm ± 1.36 to 1.75 μm ± 0.20. Further, different orientations of laser polishing (0°, 45°and 90°) with respect to the material deposition direction were examined, and 45° was found to yield better surface finish. Surface cracks were observed for all the cases irrespective of process parameters and cooling rates, which were mitigated by substrate pre-heating.

Investigations on flexible pad polishing for nano-finishing of freeform optics mold

The need for freeform surfaces are widely recognized in the optical, aerospace, biomedical, and automotive industries. However, the fabrication of freeform surfaces is very difficult and expensive because of the involvement of advanced, multi-axis, dedicated machining processes. In many applications, the machining surface needs further polishing to reduce the surface roughness. The main aim of this work is to investigate the flexible pad polishing process for the finishing of the freeform surface. To achieve this, a flexible pad polishing setup is developed in two-axis configuration that can be integrated with a diamond turning machine or any other computer numerical control (CNC) machine and capable to polish the conventional rotationally symmetric surfaces as well as freeform surfaces. The polishing parameters for the developed polishing head are optimized for the nano-finishing of the freeform mold surface of Stavax ESR steel. The effectiveness of the current polishing setup is demonstrated by measuring the improvement in surface roughness height and profile. Test results reveal that the improvement on the freeform surface is significant, that is, surface roughness ( Ra) reduces from 220 nm to 25 nm while keeping the profile within the desired tolerance.

Efficient Narrow Band Gap Cu(In,Ga)Se2 Solar Cells with Flat Surface.

In this study, the influences of bromine-based etching (Br etching) of narrow band gap CuInSe2 (CIS) absorbers and Cu(In,Ga)Se2 absorbers with various single Ga gradings (CIS:Ga) on the properties of solar cells were investigated. Absorbers with narrow absorption edge energies (Eabs) of 1.0-1.02 eV, ideal for the application as a bottom cell in a tandem device, were fabricated using a modified three-stage process and subjected to Br etching. The evolution of surface flatness and their optical and electrical properties upon Br etching were investigated. Br etching typically reduced the root-mean-square deviation of the surface roughness height (Rq) for a CIS:Ga absorber from several hundreds to several tens of nanometers, whereas for some CIS absorbers, Rq reduction was limited by the remaining voids. Moreover, Br etching reduced the leakage current across the pn junction. The high shunt resistances (Rsh) typically up to >10 kΩ·cm2 were obtained by introduction of Br etching. However, etching sometimes adversely increased the VOC deficit. The investigation of the minority carrier lifetime and diode parameters revealed that back-surface recombination in CIS and low-Ga CIS:Ga solar cells increased as the absorber layer thickness decreased. A higher Ga grading significantly reduced back-surface recombination. Narrow band gap CIGS solar cells with improved surface flatness and high VOC were achieved by introducing Br etching and proper Ga grading.

Surface Quality of Ti-6Al-4V Titanium Alloy Parts Machined by Laser Cutting

This paper investigates high power CO2 laser cutting of 5mm-thick Ti-6Al-4V titanium alloy sheets, aiming to evaluate the effects of various laser cutting parameters on surface roughness. Using multiple linear regression, a mathematical model based on experimental data was proposed to predict the maximum height of the surface Sz as a function of two laser cutting parameters, namely cutting speed and assist-gas pressure. The adequacy of the proposed model was validated by Analysis Of Variance (ANOVA). Experimental data were compared with the model’s data to verify the capacity of the proposed model. The results indicated that for fixed laser power, cutting speed is the predominant cutting parameter that affects the maximum height of surface roughness.

MEASUREMENT ERRORS OF THE SHAPE’S PARAMETERS OF DETAIL’S SURFACE BY OPTICAL INSTRUMENTS

Введение. Основной проблемой всех систем контроля состояния любого продукта обработки материала является несвоевременное определение момента их контакта и определения погрешностей измерений. Проблемы контроля качества поверхности, измерений текущих геометрических параметров должны решаться на этапе подготовки производства при выборе метрологического обеспечения технологического процесса. Поэтому мы можем выделить основные недостатки, касающиеся известных современных методов и устройств для определения параметров формирования детали, в частности при наличии сложной формы и внутренних поверхностей, таких как отверстия. Во-первых, понятно, что контактный измерительный инструмент может ухудшить точность поверхности деталей. Во-вторых, исследования показали, что все описанные методы и устройства работают только для контроля и измерения параметров поверхностей наружной детали. Основная часть. Поэтому интересной задачей является контроль качества внутренних поверхностей деталей, например, отверстий. В этом случае задача усложняется из-за инструментальных особенностей регистрации текущих параметров формирования деталей. Следовательно, необходимо рассмотреть модель для определения распределения ошибок в процессе контрольных измерений. Если существует волнистость, шероховатость поверхности или другие отклонения субмикрогеометрии поверхности детали, это приводит к явлению рассеяния падающего излучения и влияет на фактическую способность отражения. Эти зависимости нужно учитывать при создании устройств контроля и измерения параметров формирования поверхности детали. Так, например, можно предложить устройство контроля состояния внутренних поверхностей детали, которое содержит схему волоконно-оптического трехканального измерителя. Кроме того, если использовать источники излучения с различной длиной волны, можно получить различные значения интенсивности. При этом, учитывая параметры излучения, которые регистрируются модулями фотоприемников, можно получить большую точность, сравнивая эти значения и определяя погрешность измерения. При этом измерительный модуль перемещается вдоль внутренней поверхности, что дает возможность уточнения результатов контроля состояния изготовленной детали. Выводы. Таким образом, принимая во внимание предложенный способ определения параметров формообразования поверхности детали, можно определить, например, изменение величины и характера интенсивности светового потока, отраженного от поверхности. Поглощение поверхности массой технологического объекта учитывается, тогда степень высоты образованной поверхности детали можно вычислять, вводя коэффициент, определяющий параметры нестабильности полученной поверхности. При этом учитывается время, необходимое для обработки, то есть, учитывающее динамику, как изготовления, так и изменений, происходящих на поверхности контролируемого технологического объекта.

Influence of surface roughness of dune bedforms on flow and turbulence characteristics

The current paper investigates the flow and turbulence characteristics over dune bedforms by means of laboratory experiments, where spatially dense and temporally high frequency velocity measurements were done. Although similar studies are available in the literature, the focus and novelty of the current study is to assess the influence of surface roughness of the dune bedforms on the nearbed flow. For direct comparison, two different surface roughness heights over idealized, fixed-shaped, high-angled dune bedforms were tested; one with a hydraulically-smooth surface, and the other with a fully-rough surface. Spatial variation of time-averaged flow as well as turbulence statistics were examined, which was complemented by streamline plots and spectral analyses. The results are interpreted from sediment entrainment and sediment transport points of view. The results show that increased dune surface roughness reduces the nearbed flow velocity, but increases the flow velocities at upper regions. The upward directed flow near the dune crests becomes stronger in the case of smooth surface, while the re-attachment point moves further downstream compared to the rough wall case. It is concluded that the roughness of the dune surface affects the nearbed flow and turbulence characteristics qualitatively and quantitatively, which is shown to have direct consequences on sediment entrainment characteristics.

Analysis of Surface Roughness and Burr Height in Drilling of Aluminium Matrix Composites using Taguchi Technique

The present research involves the opportunity of utilising the signal to noise (S/N) ratio analysis to set machining factors in the drilling of aluminium alloy LM6-Fly ash composites (AMCs). The purpose of this research is to understand, during drilling of AMCs, the consequences of variables, feed rate, spindle speed, drill material and amount of reinforcing material on surface roughness and burr height. AMCs are formed with LM6 (Al alloy) as continuous component via the stir casting process and fly ash as reinforced content. The Taguchi design strategy is a widely accepted method which is used to produce quality products that require minimum commitment. Likewise, the L27 orthogonal array is used for conducting experiments. The response table, response graphs and analysis of variance (ANOVA) illustrate the prospective atmosphere and the impacts of input process variables. Taguchi technique considerably enhances the drilling operation.

Machining and Characterization of Multidirectional Hybrid Silica Glass Fiber Reinforced Composite Laminates Using Abrasive Jet Machining

Machining of multidirectional Hybrid Fiber Reinforced Composite (HFRC) is a challenging task because of defects like matrix cracking, fiber pullouts, delamination, burr formation, and heat affected zones. The current study is focused on machining and characterization of in-house fabricated HFRC made of carbon and silica glass fiber using Abrasive Jet Machining (AJM). Machining of holes in fabricated multidirectional HFRC has been carried out using a set of input machining parameters -air pressure, abrasive grit size, and standoff distance. The output responses selected for the experiment are material removal rate, circularity, Depth Averaged Radial Overcut (DAROC), Taper Angle (TA), and Surface Roughness (Ra.) A novel technique has been contrived for measuring DAROC by using Computerized Tomography images. At the same time, the microstructure, surface roughness, and burr height of the machined samples are carried out using High-resolution Scanning Electron Microscope (HRSEM) images and 3D-profilometer images. Subsequently, the machining parameters are optimized using multi-objective GRA to strike a balance between the output parameters. The obtained results indicated the absence of defects like delamination, burr formation, heat affected zones in the machined samples. The outcome of the experiment corroborates the application suitability of the AJM process for machining multidirectional HFRC used in industrial and commercial products.

Evaluation of Surface Topography after Face Turning of CoCr Alloys Fabricated by Casting and Selective Laser Melting.

The machinability of hard-to-cut CoCr alloys manufactured by Selective Laser Melting (SLM) technology is not yet sufficiently studied. Therefore, this work focuses on evaluation of surface texture formation during face turning of CoCr alloy. As part of the research, two specimen types were subject to comparison: made with the application of conventional casting and manufactured by additive manufacturing—SLM. A number of analytical and experimental methods were employed to describe the specimen composition and morphology, as: X-Ray Diffraction Analysis (XRD), optical metallurgical microscopy, confocal optical microscopy, and Vickers hardness HV0.1 measurements. In the next stage, the measurements of surface topographies formed during turning in a range of variable cutting speeds and feeds were carried out. Ultimately the multi-factor MANOVA (Multivariate Analysis of Variance) illustrating the influence of manufacturing technology, cutting speed, and feed ratio on selected surface parameters of samples was made. It has been demonstrated that during face turning with feeds up to 0.15 mm/rev, the similar values of surface roughness height and material ratio curve parameters were reached for both tested CoCr alloys. However, in a range of higher feed values, the surface quality of CoCr samples fabricated by SLM was lower than that reached for CoCr after casting process.

Quantifying abrasive-blasted surface roughness profiles using scanning electron microscopy

Rough surface profiles are specified for metal surfaces so that corrosion preventative coatings adhere well and provide long-term protection. Simple stylus scans and replica tape are widely used in industry to characterize surfaces and control the quality of surface preparation. Unfortunately, a scientific, quantitative connection between adhesion and surface profile parameters remains unclear. Stereo-pair images from scanning electron microscopy, SEM, were used to digitally reconstruct and then characterize 3D surfaces, which is a technique that seems previously unreported in coatings applications. SEM results were consistent with those from a stylus profilometer, but the data from a surface scan are much more numerous than from a line scan, and SEM can provide very high magnifications. 3D surfaces at high magnification gave larger values for the increase in area developed by the abrasive blasting than were determined at lower magnifications and by the stylus profilometer. Nevertheless, both techniques showed that the surface roughness height and ramification was far less than might be expected from illustrations in the existing literature on coatings’ adhesion. Quantified characterization, with details shown at high magnification, may provide scientific insight into how the various features of a roughened surface enhance the adhesion of protective coatings.

Influence of surface roughness on particle deposition distribution around multi-slot cabin supply air nozzles of commercial airplanes

Enhanced soiling due to particle deposition is often observed around multi-slot cabin supply air nozzles in commercial airplanes. This study aimed to investigate the influence of surface roughness on the particle deposition distribution around multi-slot cabin supply air nozzles of commercial airplanes. This investigation constructed a half-row cabin mockup installed with three 3D-printed supply air nozzles of a twin-aisle commercial airplane. A cutting method was proposed to measure the detailed particle deposition velocity distribution on the target surface of the nozzles covered by different grades of sandpaper with different roughness heights. This study also conducted numerical calculations for the particle deposition velocity distribution using an Eulerian particle deposition model. Both the experimental and modeling results show that strong particle deposition occurred on the cut samples near the slot dividers. When the surface roughness height was greater than or equal to 6 μm, the particle deposition velocity increased significantly with the surface roughness height. However, when the surface roughness height was less than or equal to 3 μm, the particle deposition velocity was relatively insensitive to the surface roughness. The analysis indicated that polishing the surfaces of cabin supply air nozzles may not effectively solve the problem of enhanced soiling in the aircraft cabin.

A machine learning approach in drilling of E-glass woven composites

Drilling trials were conducted on E glass woven composites and machine learning models were employed for correlating drilling variables namely point angle, feed rate and spindle speed with response measures. The thrust force, surface roughness (Ra) and burr height were considered as performance characteristics in this study. Using self-organizing map (SOM) method, Neighboring weight distances in SOM with 10 × 10 neurons, Hit map corresponding to the neighboring weight distances, Wight planes showing weight distributions were developed. The validation tests have also been conducted to verify the results obtained by ANN technique. The predictions of the artificial neural network (ANN) model result were in good agreement with experimental results.