Effect Of Surface Roughness Research Articles

Experimental and numerical investigation on the effect of surface roughness on the drag coefficient of a spherical particle

The drag coefficient (CD) for particles has a significant effect on the gas–solid fluidization characteristics. However, it is unclear whether the particle surface roughness (Rap) can notably affect CD at relatively low particle Reynolds numbers (Rep). Herein, the CD for several single near-spherical particles with different Rap and density were determined using high-speed videography in conjunction with the image analysis method. In addition, a quasi-direct numerical simulation (q-DNS) method was applied to further resolve the flow field surrounding the particle. Both experimental and simulation results suggest that within a low Rep range (<500), there is no evident difference in CD. However, if the Rep exceeds 500, CD gradually decreases with the increase in Rap. Since the separation point of the particle boundary layer moves downstream, the rough sphere experiences lower pressure in the wake vortex region. This study provides a valuable conclusion: the Rap is a non-negligible factor in studying hydrodynamic behaviors of two-phase flow, especially at high fluidization velocity.

Corrosion protection of mild steel by superhydrophobic magnetite coating

Corrosion-resistant hydrophobic magnetite coatings on mild steel surfaces were developed by immersion method. The effect of steel surface roughness (Ra) on its hydrophobicity was systematically studied using contact angle measurement (CAM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The corrosion resistance of hydrophobic magnetite coatings was evaluated using a potentiodynamic polarization test. The durability of the coatings was assessed in air, tap water, and 3.5 wt% NaCl environments. Hydrophobic magnetite coating with a water contact angle of 146-152° showed excellent resistance to corrosion, longevity in atmospheric air, and significant self-cleaning properties. The primary focus of this study was to develop a quick and simple immersion technique to create hydrophobic surfaces on mild steel. Results suggest that surface roughness plays a significant role in surface hydrophobicity, and enhancing the hydrophobicity of mild steel improves its corrosion resistance.

Non-Aqueous Polyhedral Liquid Marbles Stabilized with Polymer Plates Having Surface Roughness.

Hydrophobic polymer plates with smooth and rough surfaces are used as a stabilizer for cubic liquid marbles (LMs) to study the effect of surface roughness on their formation. The smooth and rough polymer plates can stabilize LMs using liquids with surface tensions of 72.8-26.6 and 72.8-22.9 mNm-1, respectively. It is clarified that the higher the surface roughness, the lower the surface tension of the liquids are stabilized to form the LMs. These results indicated that the introduction of surface roughness improves the hydrophobicity of the polymer plates and the rough polymer plates can stabilize LMs using liquids with a wider surface tension range. Electron microscopy studies and numerical analyses confirmed that the LMs can be formed, when the Cassie-Baxter wetting state, where θY>90° (θY: the contact angle on smooth surfaces) and θR>90° (θR: the contact angle on rough surfaces), and the metastable Cassie-Baxter wetting state, where θY<90° and θR>90°, are realized. Finally, the synthesis of cubic polymer particles are succeeded by free radical polymerization of the cubic LMs containing a hydrophobic vinyl monomer (dodecyl acrylate) in a solvent-free manner.

Leakage Retardation of Static Seals via Surface Roughness and Wettability Modification.

In this paper, the effects of surface roughness and wettability on the leakage performance of static seals were highlighted. The results show that the leakage rate is negatively correlated with the contact pressure and positively correlated with surface roughness. Surface wettability affects leakage performance. Leakage retardation is achieved by modifying the roughness and wettability at the interface. The seal interface consists of two oleophobicity surfaces and exhibits an excellent seal performance, of which the leakage reduction is approximately 64%. A theoretical model based on wettability is established to predict the leakage rates under varying wettability conditions, and its validity is confirmed. This research result is expected to be applied in the field of seals and predict the leakage performance of interfaces with different wettabilities to minimize and reduce the leakage of oil in static sealing systems.

A Molecular Dynamics Perspective on the Impacts of Random Rough Surface, Film Thickness, and Substrate Temperature on the Adsorbed Film’s Liquid–Vapor Phase Transition Regime

While recent studies have proven an unexpected liquid–vapor phase transition of adsorbed liquid films, a comprehensive description of the mechanisms of different types of phase change regimes over realistic representations of random rough surfaces is absent in the literature. The current comprehensive study investigates the effects of a gold random rough surface, liquid film thickness, and substrate temperature on the liquid–vapor phase change regime of an adsorbed sodium liquid film, considering the evaporator section of a wicked heat pipe (WHP) using a molecular dynamics (MD) simulation. At first, to generate a realistic random rough surface, a new and promising method is proposed that is entirely based on MD simulations. Then, to simulate the evaporator section of a WHP, a unique configuration for eliminating the vapor domain is developed. The simulation results reveal that three distinct regimes, namely, normal evaporation, cluster boiling, and film boiling, could be identified, which are presented on two-dimensional diagrams with the substrate temperature and liquid film thickness as coordinates for the ideally smooth and random rough surfaces. The results also manifest that even though using the random rough surface could lead to different phase transition regimes, the type of regime depends mainly on the substrate temperature and liquid film thickness. Furthermore, this study displays two different modes for normal evaporation. Also, it is shown that the impacts of the liquid film thickness and substrate temperature on the mode of normal evaporation are much more significant than the surface roughness.

Effect of surface roughness on corrosion behavior of AISI 4340 high-strength steel in sodium chloride solutions

In this work, an AISI 4340 high-strength steel alloy was surface machined to have four different grades of roughness (Ra). The impact of changing Ra on the corrosion of the steel alloy in 3.5% NaCl solutions after 40 min and 24 h was performed using various electrochemical techniques. The cyclic polarization experiments showed that an increase in Ra increases the steel corrosion via enhancing the corrosion current of the alloy. The electrochemical impedance plots also indicated that an increase in Ra reduces the corrosion resistance of the alloy by decreasing the diameter of the semicircle obtained by the Nyquist spectra. The change in potentiostatic current vs time measurements, which were obtained at −350 mV (Ag/AgCl), confirmed that pitting attack occurs and its intensity further increases with increasing Ra for all steel samples. An increase in immersion time also reduces the resistance to corrosion due to the iron dissolution from the surface of the steel alloy. After corrosion, the surface was analyzed using a scanning electron microscope and energy dispersive spectroscopy investigations.

DRAGen in Application-An Approach for Microstructural Fatigue Predictions of Non-Oriented Electrical Steel Sheets.

This study investigates multiple cyclic loading scenarios of non-oriented electrical steel sheets through both experimental and numerical approaches. The numerical simulations were conducted using Representative Volume Elements generated with DRAGen. DRAGen allowed for the generation of Representative Volume Elements with a non-cubic shape to cover the complete sheet thickness and enough grains to represent the material's texture. The experimental results, on the other hand, are utilized to calibrate and validate a prediction model, highlighting the significance of accumulated plastic slip as a suitable parameter correlated with fatigue life. Using the accumulated plastic slip from the simulations, a fatigue fracture locus is introduced, which describes a 3D surface dependent on the maximum stress, fatigue life, and the fatigue stress ratio. The study shows reliable results for the fatigue life prediction using the calibrated fatigue fracture locus. While substantial progress has been made in predicting the fatigue life at multiple fatigue stress ratios, notable disparities between experimental and simulation results suggest the need for further investigations regarding the influence of the surface quality. This observation motivates ongoing research efforts aimed at refining simulation methodologies to better incorporate surface roughness effects. In summary, this study presents a validated model for predicting fatigue life in non-oriented electrical steel sheets, offering valuable insights into material behavior at different loading scenarios and informing future research directions for enhanced structural performance and durability.

Evaluation of different surface characteristics and mineral grain size in the estimation of rock strength using the Schmidt hammer

This study investigated the effect of surface roughness on Schmidt rebound hardness (Rl). Four different test surfaces of rock samples were studied: natural, ground, cut surfaces, and core samples. There was significant variability of standard deviation based on the Rl on the natural surface, which indicated high roughness of the rock surface, whereas surface polishing caused a significant decrease in standard deviation. ISRM and ASTM methods were compared to estimate unconfined compressive strength (UCS) for different testing surfaces. Rl obtained from the cut surface was found to be more reliable than those obtained from other testing surfaces for the prediction of UCS; however, regression and ANOVA analyses revealed that the ISRM method gave a more accurate UCS estimation of rocks with highly rough surfaces. It was also shown that Rl values obtained from a cut surface were significantly higher than those obtained from core samples. Therefore, a comparison between Rl values obtained from core samples and cut surfaces was made based on previous studies. This study statistically showed that estimated UCS values are not statistically significant if Schmidt rebound tests are not performed on similar surfaces. In addition, the mineral grain sizes of the studied rocks, different testing surfaces compared with those in literature, and standard deviation from Rl are evaluated and discussed. The Schmidt hammer technique is a rapid, inexpensive, and straightforward method for estimating UCS for preliminary assessment; however, roughness of the surface should be eliminated if variations are shown in the surface rebound hardness.

Linear and nonlinear vibrations of nonlinearly elastically constrained functionally graded porous microbeams with rough surface

Linear and nonlinear free vibrations of nonlinearly elastically constrained functionally graded porous (FGP) microbeams with rough surface are analytically studied in this paper via the modified couple stress theory. A surface roughness model of the FGP microbeams is developed. The material properties including porous property are supposed to continuously vary along the thickness direction. The higher-order nonlinear governing equation and elastic boundary conditions are derived through the Hamilton principle. A closed-form solution for linear frequency and mode shape is presented. Subsequently, an analytical solution for nonlinear frequency is achieved by employing the Galerkin procedure. Finally, the effects of surface roughness, size parameter, power-law index, porosity volume fraction, and nonlinearly elastic constraints on the linear and nonlinear vibrations of functionally graded porous microbeams are examined.

Impact of Low Freestream Turbulence and Surface Roughness on the Flat-Plate Boundary Layer Transition Under a High-Lift Airfoil Pressure Gradient

Abstract Effects of low incoming freestream turbulence level (Tu &amp;lt; 1%) and surface roughness on the transition of flat-plate boundary layers under a high-lift airfoil pressure gradient have been investigated. Time-resolved streamwise and wall-normal velocity fields with surface roughness values of Ra/C = 0.065 × 10−5, 4.417 × 10−5, and 7.428 × 10−5 have been measured at a fixed Reynolds number of 5.2 × 105 and freestream turbulence intensity of 0.2%. For the reference smooth surface of Ra/C = 0.065 × 10−5, a laminar separation bubble forms from about 64% to 83% of the chord length. Increasing surface roughness has little impact on the laminar boundary layer separation onset but reduces the height and length of the separation bubble and induces earlier transition. For Ra/C = 4.417 × 10−5, displacement thickness during transition is slightly thinner and the overall momentum deficit is slightly lower than those for Ra/C = 0.065 × 10−5. For Ra/C = 7.428 × 10−5, the separation bubble becomes hardly visible as the transition mode approaches the attached mode, and turbulent mixing by the wall-bounded turbulence becomes dominant. In addition, the portion of turbulent wetted area increases due to earlier transition, and momentum deficit increases more rapidly in the turbulent wetted area. Thus, the overall momentum deficit for Ra/C = 7.428 × 10−5 is larger than that for Ra/C = 0.065 × 10−5.

Enhanced Spontaneous Emission through High‐k Modes in CsPbBr3 Perovskite Hyperbolic Metamaterials

AbstractNovel optical sources require fast decay rates, making hyperbolic metamaterials (HMMs) an increasingly attractive option. HMMs are well‐known for their remarkable anisotropy, and leverage hyperbolic dispersion to enhance the decay rate of a fluorophore placed on top of them. This study tackles the complex task of embedding a fluorophore into an HMM, successfully overcoming challenges related to surface roughness, thickness imperfections, and layer washing effects. Specifically, CsPbBr3 perovskite nanocrystals (NCs)‐based HMM are fabricated, by alternating silver/nanocrystals (Ag/NCs) layers. Through a systematic investigation of the photophysical response following the deposition of each bilayer, compelling evidence of the achievement of hyperbolic dispersion is provided. Specifically, the impact of “high‐k” modes is isolated, which is distinctive to the HMM architecture. Therefore, the longstanding debate regarding the number of bilayers needed to achieve hyperbolic dispersion is conclusively resolved. The research demonstrates a nearly twofold increase in the decay rate and a threefold enhancement in photoluminescence intensity. These findings are further supported by theoretical Purcell factor calculations. This study marks a pioneering advancement in the field of bulk dye‐embedded HMMs, laying the groundwork for the development of advanced optical sources such as “resonant gain HMMs”.

Effects of Surface Roughness in Adhesively Bonded CFRP Joints Using NDE

Effects of Surface Roughness in Adhesively Bonded CFRP Joints Using NDE

Effect of surface topography and roughness on the leakage of static seals

Static seal is widely used in modern machinery. Leakage of static seals would shorten the mechanical system’s service life and affect the environment. To understand the leakage characteristics of static seals, in this work, an experimental apparatus for leakage quantization was built. The effects of surface topography and roughness on the leakage performance of static seals subject to elevated pressure were highlighted. It was found that the leakage rate is negatively correlated with contact pressure. Orientation of surface topography affects the leakage, where the grinding scar parallel to the leakage direction contributes to the leakage, and the perpendicular grinding scar has an inhibiting effect. The leakage rate of irregular and discontinuous surface topography is lower than that of regular ones, and it increases with increasing surface roughness. Furthermore, the leakage mechanism of surface topography and roughness was revealed. This work provides general guidance for the parameters design of static seals.

Numerical simulation of surface roughness effects on low-cycle fatigue properties of additively manufactured titanium alloys

Additive manufacturing (AM) is a complex process involving a multiscal physical phenomena (solid–liquid-gas), often resulting in poor surface quality. Although surface treatments such as polishing or chemical treatment can improve surface quality, localized sub-grain stress concentrations induced by surface roughness anomalies are still easily formed, which can lead to the reduction and dispersion of fatigue properties in AM alloys. In this study, a numerical simulation model is proposed to study the association between surface roughness and fatigue properties of AM alloys. Based on the continuum damage mechanics modeling framework, an idealised grain/grain boundary model is generated by employing the Voronoi tessellation meshing technology. The numerical simulations are performed for the model with different surface geometric states. The correlation between surface roughness geometric features and fatigue properties is analyzed and discussed. A parameter “G” which comprehensively considers the influence of the maximum surface height (Rz) and correlation length (Lcor) is proposed to quantify the influence of surface roughness geometric features on the fatigue properties of AM alloys. This finding can be of great significance in improving the surface integrity of components to increase service life.

Investigation of surface roughness effects on the dynamic performance of electromagnetic nano-resonators

Here, we expose the influence of surface roughness on the dynamics of electromagnetic nano-resonators. To this end, the continuum field equations of an electromechanical nano-resonator subjected to an external magnetic flux are formulated. The developed model considers surface integrity, including surface roughness, waviness, and altered layer. Also, the influence of residual stresses of the extreme surfaces of the resonator is incorporated in the proposed model. It was revealed that the surface roughness significantly tailors the dynamic stability of the resonator, as the voltage that onsets the pull-in instability of the resonator decreases as the surface roughness increases, which thus indicates the necessity of particular calibrations of nano-resonators for surface roughness. To investigate the problem and the effect of factors such as magnetic field intensity, roughness, and beam surface thickness on the pull-in voltage, we have performed an analysis using the Taguchi method and analysis of variance. The results show that the intensity of the magnetic field has the most significant effect on pull-in voltage. Also, the more accurate results show on the resonance frequency; with the increase of the input voltage to the beam, the impact of increasing the intensity of the magnetic field and other factors increases. The rest of the paper proposes a linear and non-linear model to express the pull-in voltage according to the investigated factors.

The effect of surface roughness on the performance of 3D printed surface plasmon resonance sensors for refractive index measurements

In this study, a polymer-based surface plasmon resonance (SPR) sensor for refractive index measurements was designed and manufactured via inkjet 3D printing; then, it was optically characterized. Next, it was investigated how the surface finish of the 3D printed optical waveguide affects the sensor performance, i.e., its sensitivity. More in detail, it was studied how the surface roughness changes with the placement of the 3D printed items on the building platform. To achieve this purpose, a Phase I distribution-free quality monitoring analysis of the selected manufacturing process was implemented for a small pilot production run. The aim was to check the stability of surface roughness versus the placement of the 3D printed parts on the building platform. The 3D printed sensor’s surface roughness was assessed through a profilometry study. In particular, the surface roughness was determined for the core of the optical waveguide used to excite the SPR phenomena. Furthermore, the SPR sensors were optically characterized to find the existing relationship between their sensitivity and the considered quality of surface finish. In particular, by varying the surface roughness of the used waveguide, the light scattering in the waveguide changes, and the SPR sensitivity changes too, similarly to the light-diffusing fibers covered by gold nanofilms where the guided light is scattered through a plurality of voids distributed in the core. The procedure followed to investigate the sensor roughness, and establishing their performance enabled the optimal operative range for their application in practice to be identified. Finally, a better knowledge of the 3D printing manufacturing process has been achieved to improve quality of surface finish.

Engineering a microparticle-loaded rough membrane for guided bone regeneration modulating osteoblast response without inducing inflammation

Guided bone regeneration (GBR) is a widely used procedure that prevents the fast in-growth of soft tissues into bone defect. Among the different types of membranes, the use of collagen membranes is the gold standard. However, these membranes are implanted in tissue location where a severe acute inflammation will occur and can be negatively affected. The aim of this study was to develop a collagen-based membrane for GBR that incorporated alginate-hydroxyapatite microparticles. Membranes were manufactured using collagen type I and gelatin and alginate-hydroxyapatite microparticles. Membranes were assessed in terms of topography by scanning electron microscopy and confocal microscopy; stability by swelling after an overnight incubation in saline and enzymatic degradation against collagenase and mechanical properties by tensile tests. Furthermore, the biological response was assessed with SaOs-2 cells and THP-1 macrophages to determine alkaline phosphatase activity and inflammatory cytokine release. Our results showed that the incorporation of different percentages of these microparticles could induce changes in the surface topography. When the biological response was analyzed, either membranes were not cytotoxic to THP-1 macrophages or to SaOs-2 cells and they did not induce the release of pro-inflammatory cytokines. However, the different surface topographies did not induce changes in the macrophage morphology and the release of pro- and anti-inflammatory cytokines, suggesting that the effect of surface roughness on macrophage behavior could be dependent on other factors such as substrate stiffness and composition. Collagen-gelatin membranes with embedded alginate-hydroxyapatite microparticles increased ALP activity, suggesting a positive effect of them on bone regeneration, remaining unaffected the release of pro- and anti-inflammatory cytokines.

Effects of Non-Gaussian Surface Roughness on Conductor Loss in High-Frequency Transmission Lines

Effects of Non-Gaussian Surface Roughness on Conductor Loss in High-Frequency Transmission Lines

Effects of convex surface roughness on heterogeneous ice nucleation

In this work, we investigate the effects of convex surface roughness on heterogeneous ice nucleation through molecular dynamics simulations. Graphene surfaces with sawtooth structures are considered, and the ice nucleation rates are calculated by varying the vertex angle of the sawtooth structures. It is found that the ice nucleation rate is always suppressed by surface roughness regardless of the vertex angle. As the vertex angle is varied, the space between two adjacent ridges of the sawtooth roughness may or may not match the basic structure of ice, which leads to the variation in the free energy barrier for ice nucleation and, consequently, causes the ice nucleation rate to change by two orders of magnitude.

A comprehensive numerical study of the effects of surface roughness on a finite-length cylinder with an aspect ratio of 1.5 for Reynolds numbers ranging from 3.9 × 103 to 4.8 × 105

The aerodynamic performance of the flow around a cylinder with two free ends, which is also referred to as a finite-length cylinder, continues to be a subject of rigorous academic inquiry. However, limited research has been conducted on finite-length cylinders with rough surfaces. To evaluate the impact of relative roughness on the aerodynamic performance of a finite-length cylinder, we performed numerical simulations on a cylinder model with an aspect ratio of 1.5 with various relative roughness values. These simulations covered a range of Reynolds numbers from 3.9 × 103 to 4.8 × 105. The results indicated that both the relative roughness and Reynolds number could affect the aerodynamic characteristics of the cylinder by altering the flow pattern around the cylinder. As the Reynolds number increased, the four spiral eddies behind the finite-length cylinder gradually lost their symmetry in the axial direction and eventually transformed into a pair of recirculating eddies. Moreover, when the Reynolds number was constant at 2.0 × 104, an increase in the surface roughness of the cylinder triggered the same phenomenon. Additionally, the mechanism by which the surface roughness affected the aerodynamic coefficient of a finite-length cylinder in the current Reynolds number range was revealed. This influence was mainly attributed to the impact of pressure on the backside of the cylinder.