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This paper presents a new approach to determine more robust shear failure criteria, focusing on rough concrete-rock interfaces. The proposed method could also be applied to rock joints. The new approach is based on the distribution and variety of interfaces numerically tested in terms of surface roughness. For this reason, random field simulations are performed using the turning bands method to generate an extensive database of synthetic rough rock surfaces. With this database of synthetic rough rock surfaces, numerical simulations of direct shear tests are carried out. Finally, analytical and neural network models are proposed using the database of shear strength obtained from the finite element simulations to estimate the peak shear strength of concrete-rock interfaces. The performances of the analytical and neural network models in estimating this peak shear strength are evaluated by computing the percentage error and the mean absolute error (MAE) between the predicted and the numerically obtained values. Both models lead to satisfactory predictions. Nevertheless, it is worth noting that the neural network model mildly outperforms the analytical model regarding the magnitude of the error. Furthermore, the neural network model reproduces the possible non-bijective aspect of the correlation roughness-peak shear strength. Highlights: New methodology to investigate the influence of roughness on the shear behavior of interfaces Methodology to generate databases of synthetic rough rock surfaces with controlled roughness values Establishment of numerical simulations as a strategy to perform extensive virtual experimental studies The correlation between interface roughness and shear strength is not bijective. Assessment of artificial neural network modeling as a complementary alternative to failure criteria [ABSTRACT FROM AUTHOR]

Since surface contaminants can make optical components such as fused silica highly susceptible to damage, how to maintain the cleanliness of fused silica is an effective way to improve the laser damage threshold. In this study, molecular dynamics techniques were employed to investigate the effect of surface roughness of fused silica on the adsorption mechanism of contaminants. Based on the Weierstrass–Mandelbrot fractal function, the three-dimensional morphology of the fused silica surface was numerically simulated, and the results were used to verify and calculate its surface roughness. With the results obtained, a model of organic contaminant adsorption on rough fused silica surfaces was established, and factors such as the center-of-mass height, adsorption energy, and number density distribution of dodecane during the adsorption process were evaluated. It was found that the adsorption behavior of dodecane molecules on the rough surface was mainly affected by the surface roughness, which reduced the interaction area with the substrate and produced smaller van der Waals and adsorption energies. In addition, with the increase of surface roughness, the extension range of dodecane molecules in the substrate gradually decreased, the parallel state of oil molecules was destroyed, and even the aggregation phenomenon occurred, and the center-of-mass height of molecules significantly increased. This study reveals the atomic-level interfacial adsorption mechanism of long chain organic molecules on the processed fused silica surface, which helps to improve the resistance of the substrate surface to contaminant. [ABSTRACT FROM AUTHOR]

The morphology of the contact surface between cast-in-place engineering structures and soil is generally random. Previous research focusing on the shear mechanical properties of soil–concrete interfaces has predominantly concentrated on the role of interface roughness by constructing regular concrete surface types, largely neglecting the potential impact of the roughness morphology (i.e., the morphology of the concrete surface). In this study, concrete blocks with the same interface roughness and different roughness morphologies were constructed based on the sand-cone method, including random rough surface, triangular groove surface, rectangular groove surface, trapezoid groove surface, and semicircular groove surface. A series of direct shear tests were conducted on the rough and smooth sand–concrete interfaces, as well as on natural sand. Through these tests, we examined the shear mechanical behavior and strength of the sand–concrete interfaces, and analyzed the underlying shear mechanisms. The results showed that: (i) the interface morphology had little effect on the variation in the shear stress–displacement curve of sand–concrete interfaces, and it had a significant influence on the shear strength of the interfaces; (ii) under the same normal stress, the shear strength of the sand–concrete interfaces with a random rough surface was the greatest, followed by the triangular groove surface, while the shear strength of the rectangular groove surface proved the lowest; (iii) the shear strength of the sand–concrete interfaces with the same roughness was affected by the size of the contact area between the concrete plane and the sand, that is, a larger contact area correlated with a decrease in shear strength. It can be concluded that the shear strength value of a sand–concrete surface with the triangular groove is the closest to the shear strength of a random rough interface. By gaining a deep understanding of the effects of different contact surface morphologies on shear strength and shear behavior, significant insights can be provided for optimizing engineering design and enhancing engineering performance. [ABSTRACT FROM AUTHOR]

To reveal the influence of surface morphology characteristics in mixed lubrication on the contact characteristics of the rolling interface, a random three-dimensional rough surface model based on Gaussian distribution theory was established. The model utilizes the finite element method (FEM) to simulate the regular contact and tangential sliding behavior of micro-asperities at the rolling interface in mixed lubrication conditions. The connection bearing capacity of models with varied roughness in mixed lubrication was studied. Furthermore, the effect of various sliding and normal indentation amounts on the normal and friction stress was investigated. The simulation result reveals that the roughness of the surface influences the distribution of the lubricating oil film. The lubricating oil layer between the interfaces with a lower roughness has a higher bearing capacity due to its more uniform distribution of peaks and valleys. An increase in the normal indentation amount raises the friction stress and normal stress. In contrast, an increase in sliding lowers the normal pressure, substantially impacting the fluctuation of the friction coefficient dramatically. Finally, the random three-dimensional rough surface model is verified by comparing it with the experimental data in the related literature. [ABSTRACT FROM AUTHOR]

The roughness and stress state of a rock–concrete interface significantly affect the tensile behavior and failure mechanisms. It is of great significance to investigate rock–concrete specimen with the natural rough interfaces and loading directions to improve the load-bearing capacity of the surrounding rock-lining structure. Natural rough surfaces were obtained by splitting tests, and the fractal dimension D of the rough surface was quantitatively calculated based on the cube covering method. Rock–concrete Brazilian disk specimens with different rough interfaces were prepared by a 3D engraving technique. Then, the bimaterial specimens were subjected to the Brazilian splitting test with a loading angle between 0° and 90° to investigate the mechanical response of the rock–concrete specimen. The results showed that the influence of the loading angle on the mechanical properties of the bimaterial exceeded the interfacial roughness, and the peak load increased first rapidly and then increased slowly with the threshold of θ = 60°. The peak load at θ = 0° was only approximately 40% of that at θ = 60°. The magnitude of the increase in the peak load of the rock–concrete bimaterial decreased with the loading angle. The peak load increase of the bimaterial with D = 2.142 was 69% compared with the smooth interface at 0°, while the increase was less than 4% when θ = 90°. According to DIC results, when the stress state of the rock–concrete interface is mainly tensile or shear, a rough interface can inhibit crack propagation and thus improve the tensile strength of the sample. Finally, the effects of interface roughness and loading angle on the stress state of the bimaterial were analyzed. A deviation of the classical Brazilian splitting equation was presented based on the DEM. Highlights: Bimaterial samples with natural rough surfaces were prepared by 3D scanning and 3D engraving technology. The effects of the roughness of the rock–concrete interface and loading angle on the tensile behavior of bimaterial specimens were analyzed by splitting tests. The interlocking effect of roughness on crack propagation at the rock–concrete interface was observed by DIC. The failure mechanism of the bimaterial with a natural rough surface was analyzed, and the deviation of the classical Brazilian splitting formula was discussed based on the DEM. [ABSTRACT FROM AUTHOR]

Let t be a positive real number. A graph is called t-tough if the removal of any vertex set S that disconnects the graph leaves at most |S|/t components, and all graphs are considered 0-tough. The toughness of a graph is the largest t for which the graph is t-tough, whereby the toughness of complete graphs is defined as infinity. A graph is minimally t-tough if the toughness of the graph is t, and the deletion of any edge from the graph decreases the toughness. In this paper, we investigate the minimum degree and the recognizability of minimally t-tough graphs in the classes of chordal graphs, split graphs, claw-free graphs, and 2K2-free graphs. [ABSTRACT FROM AUTHOR]

X‐ray reflectivity (XRR) has been proven to be a useful tool to investigate thin layers as well as buried interfaces in stacks built of very thin layers. Nevertheless, x‐ray reflectivity measurements are limited by the roughness of the layers and interfaces as the roughness destroys the interference structure, the so‐called Kiessig fringes. As investigations of thin layers in organic light emitting devices (OLEDs) are still subject of research and development, the focus of this paper is the investigation of a layer of indium tin oxide (ITO) which serves as transparent anode material in OLEDs. Due to the fabrication process, ITO shows rough surface structures, so‐called spikes, hindering the determination of the ITO layer thickness and roughness in XRR measurements. In this paper, it is theoretically and experimentally proven that a smoothing layer on the ITO enables the determination of the buried ITO layer thickness and roughness as well as the density of the spikes. Furthermore, a sputtered aluminum layer (e.g. cathode material) showing spikes in atomic force microscopy covered with a smoothing layer reveals Kiessig fringes allowing the determination of the density of buried spikes. In general, it is shown that a smoothing layer on a rough surface enhances the sensitivity of x‐ray reflectivity measurements. [ABSTRACT FROM AUTHOR]

Analysis of the vibration reduction characteristics of shock absorbers is crucial for engines. In this study, the fractal theory was applied to the contact surface of an under-platform damper (UPD), and the influence of the excitation force in the same and opposite directions on the roughness of the contact surface was studied. First, based on fractal geometry theory (FGT), the roughness characterization method of a UPD contact surface was proposed. Then, the friction mechanical model of the rough contact surface was established by combining it with a 3D contact mechanical model. Furthermore, a finite element dynamic model of a blade with a UPD structure was set up. Next, the harmonic balance method was used to calculate the nonlinear response characteristics of a blade under different levels of contact surface roughness. Finally, the influence of the contact surface roughness on the vibration reduction ability of a UPD under different excitation modes was analyzed. According to the simulation results, as the contact surface became rougher, the vibration suppression ability of the UPD on the blade became stronger and stronger. With the change in the centrifugal force of the UPD and the amplitude of the same/reverse excitation force, the influencing law of the contact surface roughness on the vibration suppression ability of the UPD remained unchanged, indicating that the rougher the contact surface roughness, the better the vibration suppression effect. [ABSTRACT FROM AUTHOR]

In this work, a model is developed for the effect of seafloor interface roughness on passive estimates of the reflection coefficient. The main result is an expression for the total intensity reflection coefficient, with separate coherent and incoherent contributions. Assumptions of this model include constant sound speed in the ocean, stationary and Gaussian seafloor roughness, and ambient noise. Numerical examples for the coherent, incoherent, and total contributions to the intensity reflection coefficient are presented for halfspace and layered environments—all using the small slope approximation. To illustrate the potential parameter errors that results from using a flat interface wave model when roughness is present, a geoacoustic inversion is performed using the proposed model as input data. A joint roughness-geoacoustic inversion of simulated data using the proposed model was also performed. It was found that the true roughness and geoacoustic parameters can be inverted using this model, but the sensitivity to the outer scale of the rough surface has the highest error compared to the other parameters. [ABSTRACT FROM AUTHOR]

The rough contact plays an important role in the adhesion of carbon fiber/polymer matrix interface and interface modeling techniques are integral to quantify the effects of roughness factors on material properties. Taking the popular CF/PEEK materials as the object, an atomic method is proposed to construct CF/PEEK rough interfaces in this paper, which adopts a sinusoidal form to change the roughness regularly. Based on molecular dynamics (MD) simulations, CF/PEEK tensile separation experiment is processed and the response of the CF/PEEK interfaces with different roughness under mechanical loading are investigated. Based on the recorded CF/PEEK atomic force-displacement behavior, innovating roughness parameters, a traction separation law for the interface region is proposed. This study found the contact area between the two phases, which can be greatly improved through rough structures, determines the interfacial adhesion strength. In addition, this study observes interesting phenomena through the capturing atomic states, such as the polymer chains at the boundary between the two phases are greatly stretched. [Display omitted] • An interface modeling technique is developed for CF/matrix to investigate the effect of roughness on interface performance. • The enhancement of interface performance is analyzed from interaction energy, two-phase contact area, and PEEK density. • Snapshots of PEEK joining and separation on different rough surfaces are shown. • Constitutive models are constructed for CF/PEEK interface considering roughness parameters. [ABSTRACT FROM AUTHOR]

This article investigates the effect of different temperatures (30 °C, 50 °C, and 70 °C) on the interfacial and electrical insulation properties of 500 kV high voltage direct current (HVDC) cross-linked polyethylene (XLPE) cable factory joint having different roughness levels. The test samples with different interfacial roughness (#80, #400, #1000, #2000, and #0000) were prepared by surface polishing followed by an XLPE injection vulcanization process. At the interface, visible microporous defects were observed. The volume of pits on the sample surface and microporous defects at the interface can be reduced by a smooth interface. Moreover, the smoother interface facilitates space charge accumulation. The dc breakdown strength was nearly the same regardless roughness level at high temperatures. The results show that smooth interfaces help improving insulation properties of cable factory joints at low temperatures. However, the effect of interfacial roughness on insulating properties is weakened at elevated temperatures. [ABSTRACT FROM AUTHOR]

Whether the rough surface is beneficial or harmful in promoting wettability for a reactive wetting system at high temperatures remains an open question. The comparative study on the wetting of smooth and rough silica by Sn-3.5Ag–2Ti solders were carried out at 650–800 °C. Although the precipitation of wettable reaction products promotes wettability, the decrease in interfacial roughness by the precipitates makes the improvement in wettability does not reach the degree of inert system. Therefore, the rough surface is harmful in promoting wettability for a reactive wetting system. The wetting behavior can be divided into two types by temperatures: the linear spreading (650–700 °C) and the non-linear spreading (750–800 °C) which correspond to the reaction rate control mechanism and the diffusion control of Ti transport mechanism, respectively. The spreading is enhanced by using the rough substrate due to the strengthening interfacial reactivity. [ABSTRACT FROM AUTHOR]

• Roughness characteristic parameters (RCP) that directly regulate tp curve are screened. It breaks the misunderstanding of using ISO25178 function parameters to study tp curve in the past. • An active design method of surface topography based on specified surface bearing capacity is proposed based on tp curve, which provides method for constructing the expected bearing capacity surface and roughness interface mechanics study. • RCP provide parameters for the active bearing capacity surface design model and solves the problem of inconsistency between surface roughness parameters in blueprint and surface bearing capacity design parameters. • The active design method has good application in grinding, shot peening and barrel finishing surface, and the average relative error is only 1.4%.The method can be applied to smart manufacturing in the era of big data in the future. Surface bearing ratio tp(c) or tp curve is often used to evaluate the bearing contact performance of rough surfaces, but currently it is difficult to invert the surface topography with the expected surface bearing ratio tp(c). Combining the definition of tp curve and the key coefficients in random process theory, roughness characteristic parameters (RCP) that directly regulate tp curve are found out to provide parameters for the active design model with expected tp(c). By calculating the surface height matrix satisfying the expected tp(c) and RCP with genetic algorithm, the active design method of surface topography gets constructed. Surface tp curves of grinding, shot peening, barrel finishing and active design are compared to verify the reliability of the method and the versatility of RCP. The results show: 1) RCP of tp curve are Sa (arithmetic mean height), Sq (root mean square height), Ssk (skew), Sku (kurtosis), Sp (maximum peak height) and Sv (maximum pit depth); 2) The surface topography of the expected tp(c) is basically consistent with the measured tp curve. The maximum relative errors of tp(c) and Sa are 5%, 1%, respectively. And the average relative errors are only 1.4% and 0.5%. The regulatory parameters influence in RCP on the surface bearing capacity is ranked as follows: Sa , Ssk , Sku , Sv , Sp . The new active design model provides method for constructing the expected bearing capacity surface and roughness interface mechanics' study. [ABSTRACT FROM AUTHOR]

Self-assembly is a characteristic property of soft matter. Understanding the factors which assist or perturb this process is of great importance in many biological and industrial processes. Amphiphiles self-assemble and order into a variety of structures including well-ordered lamellar phases. The present work uses neutron reflectometry and neutron scattering to explore the effects of both interface roughness and temperature on the lamellar-phase structure of a non-ionic surfactant at a solid/liquid interface. The structure of concentrated solutions of tetraethyleneglycol dodecyl ether has been compared against a smooth surface and one with a roughness of the order of the lamellar spacing. This has been done in order to investigate the role perturbations have on the overall lamellar order, when these have length scales of the order of the interactions between neighboring lamellae. The results showed that the surfactant forms a well-ordered and aligned structure at a smooth surface, extending to a depth of several micrometers from the interface. Increasing the temperature of the sample and subsequent cooling promotes alignment and increases the number of oriented layers at the surface. The same sample forms a significantly less aligned structure against a rough surface that does not align to the same extent, even after heating. The perturbation of the structure caused by thermal fluctuations was found to be much less than that imposed by a small surface roughness. [ABSTRACT FROM AUTHOR]

The performance of 1D nano/microbeam‐based devices greatly relies on heat dissipation to substrates. The surface roughness plays a key role in interfacial heat transport while this issue is seldom investigated due to the difficulty in quantitative determination of thermal contact resistance (TCR) at nanoscale. Here, the impact of interfacial roughness on heat transport at solid–solid interface by taking VO2 microbeam on Si substrate (VO2/Si) as a prototype is investigated. With the increased interface roughness from atomic fluctuation to ≈100 nm, it is found that an unusual uncertainty emerges in thermal interface transport along with the dramatical increase in TCR with two orders of magnitudes. Besides, a single‐layer graphene is inserted into VO2/Si interface as thermal interface material to study its performance under interface roughness. The inserted graphene not only substantially reduces the TCR but also reduces the uncertainty of thermal interface transport. This enhancement is even remarkable at rougher interface. Microscopic characterization and molecular dynamics simulation suggest that suspended condition and high heat conductivity of graphene on rough surface are responsible for the above effects. This work provides the quantitative evaluation of TCR and contributes to the in‐depth understanding on heat transport at imperfect interface. [ABSTRACT FROM AUTHOR]

This paper presents the investigation of the surface roughness on the material dislocation using bonded interface technique. The influence of the surface roughness on three different materials was focused on this study. By using the bonded interface technique, the half-specimens of stainless steel, aluminium and brass were bonded and microindentations were conducted on the bonded interface surfaces with roughnesses ranged from 0.05 to 0.37 µm. The results revealed that the increase of surface roughness induced an exponential decrease in material dislocation in vertical direction beneath the permanent indent. Using Nix-Gao model, rougher surface produced higher load independent hardness which the materials experience the hardening effect. From the observation on the plastic deformation zone, the shear bands of harder material stainless showed limited material dislocation compared to softer material aluminium and brass. [ABSTRACT FROM AUTHOR]

Horizontally stratified media are commonly used to represent naturally occurring and man-made structures, such as soils, roads, and pavements, when probed by ground-penetrating radar (GPR). Electromagnetic (EM) wave scattering from such multilayered media is dependent on the roughness of the interfaces. In this paper, we developed a closed-form asymptotic EM model considering random rough layers based on the scalar Kirchhoff-tangent plane approximation (SKA) model that we combined with planar multilayered media Green’s functions. In order to validate our extended SKA model, we conducted simulations using a numerical EM solver based on the finite-difference time-domain (FDTD) method. We modeled a medium with three layers—a base layer of perfect electric conductor (PEC) overlaid by two layers of different materials with rough interfaces. The reflections at the first and at the second interface were both well reproduced by the SKA model for each roughness condition. For the reflection at the PEC surface, the extended SKA model slightly overestimated the reflection, and this overestimation increased with the roughness amplitude. Good agreement was also obtained between the FDTD simulation input values and the inverted root mean square (rms) height estimates of the top interface, while the inverted rms heights of the second interface were slightly overestimated. The accuracy and the performances of our asymptotic forward model demonstrate the promising perspectives for simulating rough multilayered media and, hence, for the full waveform inversion of GPR data to noninvasively characterize soils and materials. [ABSTRACT FROM AUTHOR]

Imaging of rough interfaces in a layered structure requires full understanding of the characteristics of their ground penetrating radar (GPR) echoes. In this study, a finite‐difference time‐domain computational model using a uniaxial perfectly matched layer boundary for GPR demining of layered rough interfaces is constructed. On the basis of this model, the numerical results of B‐scan echoes from two‐layered and three‐layered rough interfaces with different degrees of roughness are obtained and compared with the profiles of corresponding rough surfaces. These results and comparisons highlight the relationship between the B‐scan wave outlines and the profile of the layered rough interfaces. The effect of roughness of the interface on the B‐scan echoes are analyzed, and the influence of the upper rough surface profile on the shape of the B‐scan wave outline from the lower rough surface is discussed. [ABSTRACT FROM AUTHOR]

This paper presents a vision-based surface roughness evaluation system for end-milled metals, addressing digital reconstruction and calibration of inspected surfaces, and quantitative and qualitative evaluation of surface texture. Specimens with different levels of surface roughness are machined, and a comparison between stylus-based and vision-based measurements is performed while using standard roughness parameters. The vison-based results vary among 9% and 11% compared to the stylus-based ones, which is a minor error to trade-off for faster measurements. Furthermore, surface texture evaluation is performed by detecting the generated cusp lines and tool marks on the machined surface. The tool marks’ distribution is analysed in order to determine whether the machining is performed under optimal cutting conditions. Results show that under optimal cutting conditions, the detected tool marks are normally distributed along the feed direction and the distance between two consecutive tool marks does not vary significantly. Based on the proposed methods software is implemented that enables the three-dimensional reconstruction, calibration and evaluation of the inspected surface. [ABSTRACT FROM AUTHOR]

In a recent paper in Science, namely, "The Contact Sport of Rough Surfaces", Carpick summarizes recent efforts in a "contact challenge" to predict in detail an elastic contact between the mathematically defined fractal rough surfaces under (very little) adhesion. He also suggests the next steps that are needed to "fulfill da Vinci's dream of understanding what causes friction". However, this is disappointing as friction has been studied since the times of Leonardo and in 500 years, no predictive model has emerged, nor any significant improvement from rough contact models. Similarly, a very large effort we have spent on the "sport" of studying rough surfaces has not made us any closer to being able to predict the coefficient of proportionality between wear loss and friction dissipation which was already observed by Reye in 1860. Recent nice simulations by Aghababaei, Warner and Molinari have confirmed the criterion for the formation of debris of a single particle, proposed in 1958 by Rabinowicz, as well as Reye's assumption for the proportionality with frictional loss, which is very close to Archard anyway. More recent investigations under variable loads suggest that Reye's assumption is probably much more general than Archard's law. The attempts to obtain exact coefficients with rough surfaces models are very far from predictive, essentially because for fractals most authors fail to recognize that resolution-dependence of the contact area makes the models very ill-defined. We also suggest that in the models of wear, rough contacts should be considered "plastic" and "adhesive" and introduce a new length scale in the problem. [ABSTRACT FROM AUTHOR]

Decreasing the surface roughness of visible laser welds on aluminum automotive closure panels is of critical importance in the automotive industry. During welding, surface roughness is strongly influenced by the interaction of filler wire, laser, and gas. Observation by CCD camera revealed that placement of the filler wire tip at the front wire-feeding position could effectively mitigate humping phenomenon on the weld surface. Visualization of the gas flow and detection of the plasma intensity demonstrated that optimizing the shielding gas parameters could further reduce the rippling phenomenon by affecting the molten pool surface tension and the pressure differential acting upon the molten pool. The surface quality could be improved via optimization of nozzle outlet geometry, gas flow rate, inclination angle of gas tube, and distance between the nozzle and laser beam. After shrinking the processing parameter window through the single factor investigation, a Taguchi L9 orthogonal array was designed to optimize the shielding gas parameters. The weld surface roughness, Ra , could be effectively reduced to below 1 μm when a circular gas nozzle was positioned 5 mm behind the laser beam, delivering pure argon gas at 30 SCFH with an inclination angle of 45° to the horizontal plane. [ABSTRACT FROM AUTHOR]

The authors of the research have analysed spacing parameters of anisotropic 3D surface roughness crosswise to machining (friction) traces RSm1 and lengthwise to machining (friction) traces RSm2. The main issue arises from the RSm2 values being limited by values of sampling length l in the measuring devices; however, on many occasions RSm2 values can exceed l values. Therefore, the mean spacing values of profile irregularities in the longitudinal direction in many cases are not reliable and they should be determined by another method. Theoretically, it is proved that anisotropic surface roughness anisotropy coefficient c=RSm1/RSm2 equals texture aspect ratio Str, which is determined by surface texture standard EN ISO 25178-2. This allows using parameter Str to determine mean spacing of profile irregularities and estimate roughness anisotropy. [ABSTRACT FROM AUTHOR]

Keywords: adhesion; droplet dynamics; rough interfaces; roughness; surface tension EN adhesion droplet dynamics rough interfaces roughness surface tension 1 1 1 04/06/23 20230404 NES 230404 B Droplet Dynamics b Yanyao Bao and colleagues report on the spreading and bouncing modes of droplets impacting on rough surfaces. Adhesion, droplet dynamics, rough interfaces, roughness, surface tension The results in article number 2201873 suggest that a higher surface area and roughness promote the transition from bouncing to wetting of a droplet, benefiting surface design for facilitating droplet non-adhesion features during transport. [Extracted from the article]

The article reports on modeling roughness of rock discontinuity surfaces. It discusses studies designed to quantify the profile matching process which show that the joint roughness coefficient (JRC) values of the original ten roughness profiles correlate reasonably well with a variety of mathematical expressions of roughness. The aim is to pave the way for development of a physically based roughness quantification method that is consistent in expressing morphology and assigning ranking.

The objective of the study is to examine the quantitative influence of end friction on the dynamic mechanical behavior of concrete under medium and low strain rates. Considering the concrete heterogeneity, a mesoscale mechanical model was established to study the confinement effect of end friction, in which the concrete was assumed to be composed of aggregates, mortar matrix, and the interfacial transition zones between them. The friction behavior was utilized to describe the interaction between the concrete specimens and loading apparatus. The dynamic axial compressive mechanical behavior of concrete subjected to different medium and low strain rates and friction coefficients was simulated. Furthermore, the confinement mechanism of end friction on the compressive dynamic increase factor (DIF) of concrete was studied. The simulation results indicate that with the increase of end friction coefficient, the uniaxial compressive strength of concrete first increases and then becomes stable; the end friction confinement changes the local stress state and damage distribution of concrete, and it thus contributes to the increase in compressive strength of concrete; the friction contribution factor presents a descending tendency with increasing the strain rate and decreases obviously when the end friction coefficient increases. [ABSTRACT FROM AUTHOR]

Rock formation such as shale normally has a layered structure where the rock blocks interact with each other by their interfaces like head joints and bed joints. In practical geological conditions, such interfaces are often rough and able to result in dilatancy and volume change of the overall geological structure. The dilatancy can be an important effect and cannot be neglected in determining the practical mechanical behavior of the layered rock. The purpose of this paper is to study the dilatancy effect on the mechanical behavior of layered rock structures with rough interfaces. Interfaces with various roughness are defined to evaluate the dilatancy effect. To estimate the stiffness properties of rough surfaces, a dilatancy model known as the contact density model is used. The current problem involves the size effect of the interface which must not be neglected, thus, a homogenized micropolar continuum is taken into consideration. According to the principle of energy equivalence, a homogenization method is used to get the constitutive parameters of the micropolar model. The present problem is analyzed by using finite element numerical codes to show the validity of the dilatancy models in combination with micropolar theory for a layered rock structure. • Increasing roughness and length of layered rock interfaces induce dilatancy effect. • Increasing roughness induced dilatancy affects shear strains and relative rotation. • A scale effect can be captured by changing the size of the rock block. • The Cauchy continuum also shows a dilatancy effect with a symmetry shear strain. [ABSTRACT FROM AUTHOR]

The critical shear velocity for resuspension of micrometer size particles from rough surfaces was studied. The random variation of surface roughness was accounted for. The recently developed Monte Carlo simulations accounted for the statistical variations of physical parameters that control the particle resuspension process. A sensitivity analysis showed that the surface roughness and its random variation was the key factor affecting the particle resuspension from rough surfaces. The theory of probabilistic transformation was used and an analytical expression for evaluating the resuspension fraction of particles of different sizes from rough surfaces versus the shear velocity was developed. The resuspension fractions as predicted by the analytical model were evaluated for several particles sizes for a range of turbulent flow shear velocities. The resulting resuspension fractions were compared with those obtained from the Monte Carlo simulations as well as the available experimental data. It was found that the predictions of the new analytical equation were in good agreement with the Monte Carlo simulation results and the experimental data, especially for smaller size particles. This new analytical expression could be used as a simple empirical equation for estimating flow-induced resuspension of particles from rough surfaces. [ABSTRACT FROM AUTHOR]

The characterization of fractures using elastic waves requires a parameter that captures the physical properties of a fracture. Many theoretical and numerical approaches for wave propagation in fractured media use normal and shear fracture specific stiffness to represent the complexity of fracture topology as it deforms under stress. Most effective medium approaches assume that the normal and shear fracture specific stiffness are equal, yielding a shear-to-normal specific stiffness ratio of one. Yet several experimental studies show that this ratio can vary from zero to three. We conducted a series of experiments to determine the stiffness ratio for fractures with different surface roughness subjected to mixed-mode loading conditions. Specimens containing a single fracture were subjected to either normal loading or combined normal and shear loading during ultrasonic measurements of transmitted and reflected P- and S-waves. Theoretical analysis based on the displacement discontinuity theory shows, for P- and S-waves with the same wavelength, that the theoretical stiffness ratio is not equal to one, but depends on the ratio of S- to P-wave velocities. The conventional stiffness ratio limit of unity is determined to be appropriate for very smooth fracture surfaces even under mixed-mode loading conditions. However, rough fracture surfaces result in stiffness ratios that are greater than the theoretical limit and the magnitude of the ratio depended on the relative ratio of shear-to-normal stress. The results from the experiments suggest that the conventional practice of assuming a constant stiffness ratio equal to 1.0 may not be appropriate. Therefore, the ratio of shear-to-normal fracture specific stiffness depends on the roughness of the fracture surface and the loading conditions. [ABSTRACT FROM AUTHOR]

Advancements in the fabrication of microfluidic and nanofluidic devices and the study of liquids in confined geometries rely on understanding the boundary conditions for the flow of liquids at solid surfaces. Over the past ten years, a large number of research groups have turned to investigating flow boundary conditions, and the occurrence of interfacial slip has become increasingly well-accepted and understood. While the dependence of slip on surface wettability is fairly well understood, the effect of other surface modifications that affect surface roughness, structure and compliance, on interfacial slip is still under intense investigation. In this paper we review investigations published in the past ten years on boundary conditions for flow on complex surfaces, by which we mean rough and structured surfaces, surfaces decorated with chemical patterns, grafted with polymer layers, with adsorbed nanobubbles, and superhydrophobic surfaces. The review is divided in two interconnected parts, the first dedicated to physical experiments and the second to computational experiments on interfacial slip of simple (Newtonian) liquids on these complex surfaces. Our work is intended as an entry-level review for researchers moving into the field of interfacial slip, and as an indication of outstanding problems that need to be addressed for the field to reach full maturity. [ABSTRACT FROM AUTHOR]

This article proposes for predicting the surface roughness of AISI 1040 steel material using the artificial intelligent. Cutting speed, feed rate, depth of cut, and nose radius have been taken into consideration as input factors and corresponding surface roughness values ( Ra, Rt) as output. A series of experiments have been carried out in accordance with a full factorial design on the CNC lathe to obtain the data used for the training and testing of an artificial neural network (ANN). The developed MATLAB TM interface was used to predict surface roughness. Multilayer perceptron structure, which is a kind of feed forward ANNs, is applied to model and prediction of the surface roughness in turning operations. The number of iterations used was 20,000. MSE = 1E − 4 and R2 = 0.9991 were achieved using the developed ANN Model. The obtained results indicate that the ANN algorithm coupled with back propagation neural network is an efficient and accurate method in predicting of surface roughness in turning. [ABSTRACT FROM AUTHOR]

In this paper we investigate the effect of Ar concentration and shadow mask material on the etch rate, surface roughness, and micromask pit density and depth for reactive ion etching (RIE) of x-cut alpha quartz. The ratio of SF6 to Ar is varied at constant power and pressure to find an optimum Ar concentration for thinning x-cut quartz while maintaining good surface quality. The recipe is used with an STS320 RIE system to produce smooth, through-hole-free, insulating quartz membranes of 7 µm thickness in selective locations on 100 µm thick x-cut quartz wafers. We demonstrate that surface quality is much improved by replacing at least 75% of the SF6 by volume with Ar, and that for non-inductively coupled plasma RIE the standard mask material nickel is detrimental to surface quality for long etch times. [ABSTRACT FROM AUTHOR]

We present a new plasma etch process optimized for etching piezoelectric aluminum nitride (AlN) film deposited on thin molybdenum (Mo) metal electrode. Such film stack finds application in the integration of AlN-based RF microelectromechanical systems devices. The process is based on Cl2/BCl3/Ar gas chemistry with added buffer gas in inductively coupled plasma reactive ion etching system. The new gas mixture overcomes a generic problem of etched surface roughness without significant drop in AlN etch rate. Using design of experiment, the process window is optimized for improving selectivity to Mo and reducing microtrenching while maintaining smooth etched surface. Finally, an etching rate of 280 nm min−1 with reliable etch stop on Mo electrode and smooth bottom surface is reported. The integration suitability of the developed etch process is tested by etching 2.0 to 5.0 µm size square shaped via holes in 1.0 µm thick (0 0 2) oriented piezoelectric AlN on 0.2 µm thick Mo electrode while integrating contour mode resonators. [ABSTRACT FROM AUTHOR]

Cell colonization of synthetic polymers can be regulated by physical and chemical modifications of the polymer surface. High-density and low-density polyethylene (HDPE and LDPE) were therefore activated with Ar+ plasma and grafted with fibronectin (Fn) or bovine serum albumin (BSA). The water drop contact angle usually decreased on the plasma-treated samples, due to the formation of oxidized groups, and this decrease was inversely related to the plasma exposure time (50-300 s). The presence of nitrogen and sulfur on the polymer surface, revealed by X-ray photoelectron spectroscopy (XPS), and also by immunofluorescence staining, showed that Fn and BSA were bound to this surface, particularly to HDPE. Plasma modification and grafting with Fn and BSA increased the nanoscale surface roughness of the polymer. This was mainly manifested on HDPE. Plasma treatment and grafting with Fn or BSA improved the adhesion and growth of vascular smooth muscle cells in a serum-supplemented medium. The final cell population densities on day 6 after seeding were on an average higher on LDPE than on HDPE. In a serum-free medium, BSA grafted to the polymer surface hampered cell adhesion. Thus, the cell behavior on polyethylene can be modulated by its type, intensity of plasma modification, grafting with biomolecules, and composition of the culture medium. [ABSTRACT FROM AUTHOR]

Metal-ion etching is widely used in substrate surface modification before coating by physical vapor deposition. In this work, TiAlN coatings were synthesized onto cemented carbides with Ti-, Cr-, and Zr-ion pre-etching by cathodic arc evaporation and investigated concerning surface topography and mechanical failure. The pre-etching of energetic metal ions introduces droplet defects and increases surface roughness through uneven bombardment. The high interface roughness and deposition of nanoscale metal interlayers contributed to the upgraded adhesion between the coating and the substrate. As a result, the adhesion strength of TiAlN coatings advances to more than 95 N by applying Cr- and Zr-ion pre-etching. The rough substrate surface also gives rise to a rough coating surface associated with the pre-etching time. Under normal loading, the microscopic pit-like surface morphology, stemming from ion etching, interrupts the transverse propagation of the circumferential cracks but does not affect the longitudinal crack propagation inside the coating. In addition, the higher roughness of coatings with ion pre-etching causes a shorter run-in stage during ball-on-disc tests due to the higher contact stress between the friction pair. • TiAlN coatings were deposited on cemented carbide with various ion pre-etching. • The ion etching changes the substrate surface, significantly increasing roughness. • Scratch adhesion strength above 95 N can be obtained by suitable ion pre-etching. • Rough surfaces lead to intermitted circumferential cracks under normal loading. • The ion pre-etching can also shorten the run-in period during friction tests. [ABSTRACT FROM AUTHOR]

In order to obtain the average surface roughness R a of the long-term operating conductors in service, the features of 2-D surface morphologies were investigated based on the gray value matrix G. The neighborhood averaging method was utilized in obtaining G. In a wide range of R a, a linear relationship was discovered between the variance F and R a. Therefore, R a could be obtained based on the images from the camera and G without the need to dismantle the conductors in service, and it is more time saving and economical for the measurements. [ABSTRACT FROM AUTHOR]

When a longitudinal wave passes through a contact interface, second harmonic components are generated due to contact acoustic nonlinearity (CAN). The magnitude of the generated second harmonic is related to the contact state of the interface, of which a model has been developed using linear and nonlinear interfacial stiffness. However, this model has not been sufficiently verified experimentally for the case where the interface has a rough surface. The present study verifies this model through experiments using rough interfaces. To do this, four sets of specimens with different interface roughness values (Ra = 0.179 to 4.524 μm) were tested; one set consists of two Al6061-T6 blocks facing each other. The second harmonic component of the transmitted signal was analyzed while pressing on both sides of the specimen set to change the contact state of the interface. The experimental results showed good agreement with the theoretical prediction on the rough interface. The magnitude of the second harmonic was maximized at a specific contact pressure. As the roughness of the contact surface increased, the second harmonic was maximized at a higher contact pressure. The location of this maximal point was consistent between experiments and theory. In this study, an FEM simulation was conducted in parallel and showed good agreement with the theoretical results. Thus, the developed FEM model allows parametric studies on various states of contact interfaces. [ABSTRACT FROM AUTHOR]

• Bottom electrode has a strong influence on the growth of the active layer. • LaNiO 3 electrode strongly stabilizes the perovskite phase. • Stabilization is mainly related to increased interface roughness. • Increased interface roughness does not have adverse effects on the film properties. Pulsed-laser deposition was used to prepare Pb(Mg 1/3 Nb 2/3)O 3 -PbTiO 3 (PMN-PT) thin films on (LaNiO 3)/SrTiO 3 substrates. We found that the bottom electrode has an immense influence on the properties of the overgrown active layer. Specifically, we found that the use of LaNiO 3 (LNO) as the electrode material strongly stabilizes the perovskite phase and significantly expands the process window for the preparation of phase-pure PMN-PT as compared to a direct deposition on SrTiO 3 (STO) substrates. Based on our experiments, the stabilization is achieved primarily due to the increased interface roughness, which enhances the sticking of Pb-based species, thereby suppressing the formation of undesired Pb-deficient pyrochlore inclusions. The roughness of the interface does not have adverse effects on the quality of the films. In fact, the film prepared on the LNO/STO template from the Pb-rich target exhibited superior electrical properties as compared to the film prepared directly on STO. By understanding the mechanism, we were able to exploit it and prepare an STO/Nb:STO template with a rough surface, which strongly enhanced the stability of the perovskite phase. This approach can be used to design templates for different device configurations. [ABSTRACT FROM AUTHOR]

It is well established that, at small loads, a linear relation exists between contact area and reduced pressure for elastic bodies with non-adhesive rough surfaces. In the case of adhesive contacts, however, there is not yet a general consensus on whether or not linearity still holds. In this work evidence is provided, through numerical simulations, that the relation is non-linear. The simulations here presented can accurately describe contact between self-affine adhesive rough surfaces, since they rely on Green's function molecular dynamics to describe elastic deformation and on coupled phenomenological traction-separation laws for the interfacial interactions. The analysis is performed for two-dimensional compressible and incompressible bodies under plane strain conditions. Interfaces with various roughness parameters and work of adhesion are considered. • The effect of adhesion during contact is revealed through simulations. • Adhesion is modelled through cohesive traction-separation laws. • The reduced load-to-area relation is found to be non linear. • Adhesion strongly depends on roughness, negligibly on compressibility. [ABSTRACT FROM AUTHOR]

Complex liquids flow is known to be drastically affected by the roughness condition at the interfaces. We combined stresses measurements and observations of the flow during the motion of different rough surfaces in dry liquid foams. We visually show that three distinct friction regimes exist: slippage, stick-slip motion, and anchored soap films. Our stress measurements are validated for slippage and anchored regimes based on existing models, and we propose a leverage rule to describe the stresses during the stick-slip regime. We find that the occurrence of the stick-slip or anchored regimes is controlled by the roughness factor, defined as the ratio between the size of the surface asperities and the radius of curvature of the Plateau borders. [ABSTRACT FROM AUTHOR]

This paper presents the multi-scale modeling and finite element analysis of the dynamics of a composite structure with bolted joints. Microscale contact surface effects are considered and a single-degree-of-freedom (SDOF) stick-slip friction model is proposed. Interface mechanics parameters were solved using fractal contact theory and damping properties of the composite material were determined according to the elastic-viscoelastic correspondence principle. Then, by inputting calculated values for the penalty stiffness, damping coefficient, and material parameters, a finite element analysis of the overall and local dynamic response of the joint was carried out in ABAQUS. Simulated values of the resonance frequency and damping ratio of the structure were consistent with experimental results, thus validating the proposed model. Presence of the joint interface reduced the structural stiffness by 2% and increased energy dissipation by 30–40% compared to a rigid joint. Furthermore, the local interface energy dissipation was found to be influenced by both the excitation amplitude and preload. Finally, analysis of the interface roughness parameters showed that rougher surfaces facilitate preload relaxation. [ABSTRACT FROM AUTHOR]

A pore‐scale model is developed to simulate fluid‐fluid interfacial area in variably saturated porous media, with a specific focus on incorporating the effects of solid‐surface roughness. The model is designed to quantify total (film and meniscus) fluid‐fluid interfacial area (Anw) over the full range of wetting‐phase fluid saturation (Sw) based on the inherent properties of the porous medium. The model employs a triangular pore space bundle‐of‐cylindrical‐capillaries framework, modified with three surface roughness‐related parameters. The first parameter (surface roughness factor) represents the overall magnitude of surface roughness, whereas the other two parameters (interface growth factor and critical adsorptive film thickness) reflect the microscale structure of surface roughness. A series of sensitivity analyses were conducted for the controlling variables, and the efficacy of the model was tested using air‐water interfacial area data measured for three natural porous media. The model produced good simulations of the measured Anw data over the full range of saturation. The results demonstrate that total interfacial areas for natural media are typically much larger than those for ideal media comprising smooth surfaces due to the substantial contribution of surface roughness to wetting‐film interfacial area. The degree to which fluid‐fluid interfacial area is influenced by roughness is a function of fluid‐retention characteristics and the nature of the rough surfaces. The full impact of roughness may be masked to some degree due to the formation of thick wetting films, which is explicitly quantified by the model. Application of the model provides insight into the importance of the interplay between pore‐scale distribution and configuration of wetting fluid and the surface properties of solids. Key Points: A triangular pore space BCC model is developed to simulate the impact of solid surface roughness on fluid‐fluid interfacial areaModel efficacy is tested with air‐water interfacial area data measured for three natural porous mediaThe model presents a means by which to quantify fluid‐fluid interfacial area for natural porous media in multiphase fluid systems [ABSTRACT FROM AUTHOR]

The effect of structural imperfections such as interface roughness and layer strain on the sign and amplitude of the interlayer coupling between the two ferromagnetic layers of exchanged-biased NiFe/Cu/NiFe/FeMn spin valves is discussed. Two distinct regimes are found: when the NiFe-Cu interface is smooth, with a mean roughness smaller that 4 /spl Aring/, the interlayer coupling shows a distinct oscillatory behavior, with a period of /spl Lambda/=13.5 /spl Aring/, and can be well described by a RKKY-like exchange based mechanism. As the amplitude of the interface roughness increases the magnetostatic-type Neel's orange peel coupling becomes more important, and the ferromagnetic component of the coupling is enhanced. The higher than expected period of oscillation, observed in these spin valves, is explained in terms of a strain induced effect. [ABSTRACT FROM PUBLISHER]

Correlated imaging for a reflective target with a smooth or rough surface is investigated. Our analytical results, which are backed up by numerical simulations, demonstrate that for a reflective target with a smooth surface, the quality of ghost imaging is related with the transverse sizes of both the source and the detector in the object path, and the target’s information can also be obtained by the technique of Fourier-transform ghost diffraction. However, for a reflective target with a rough surface, the target’s whole image can be reconstructed by ghost imaging even using a single point-like detector but Fourier-transform ghost diffraction is invalid. The application of correlated imaging in remote sensing is also discussed based on the above results. [ABSTRACT FROM AUTHOR]