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Hydrophobic textured surfaces are studied for their low wettability and their capacity to create a ‘slippery’ fluid on the surface during lubrication. To this end, the flow between two parallel surfaces is numerically addressed by computing two dimensional numerical simulations. One of the surfaces moves with a uniform rectilinear motion, while the other is fixed, with a cavity in the middle. The steady-state flow is laminar and monophasic with a low Reynolds number. The reduction of the wall shear stress caused by a vortex in the cavity, with respect to a Couette flow, looks like the creation of an equivalent slip of the fluid on the wall at a macroscopic scale. Three methods are used to calculate the slip length: one is based on the wall shear stress and the other two are based on the speed of the fluid flow. When the slip length is calculated according to these three methods, the obtained results differ. The differences show that the slip often used in the literature is a macroscopic representation of local effects that are not necessarily slippery. The speed profiles and the streamlines are then discussed, in order to propose an explanation for this difference.

[Display omitted] • Nine bio-inspired burrowing strategies are summarized. • Snakeskin-inspired piles and root-inspired anchors are comprehensively reviewed. • Key challenges, modelling techniques and future trends of bio-inspired geotechnics are discussed. Traditional geotechnical engineering is challenged in terms of sustainability, resilience, reliability and resources availability in the context of climate change and urbanization expansion. Abstracting inspiration from nature and adopting to geotechnical engineering, bio-inspired geotechnics can provide innovative solutions to address these challenges. This paper reviews the underlying mechanics of bio-inspired geotechnical engineering from three perspectives, i.e., bio-inspired burrowing strategies and mechanisms, bio-inspired surfaces with textures and bio-inspired underground structures. The results highlight that the bio-inspired burrowing strategies (i.e., particle removal, chiseling/grabbing-pushing, peristalsis, dual-anchor, pivot burrowing, undulatory propulsion, reciprocating, rotation and root growth) differ in their application scopes and burrowing efficacy, and the auxiliary burrowing, the principle of least impendence, as well as the multi-functional root growth presents promising solutions to burrowing challenges. Bio-inspired textured surfaces exhibit performance enhancement with regard to anisotropic friction, wear resistance and actuator initiation. In bio-inspired underground structures, snakeskin- and root-inspired geotechnical elements provide superior performance due to the frictional anisotropy and branching effects, respectively, and the potential implementation techniques are challenging current geotechnical engineering. Finally, transferring issues, potential research trends and future prospects are presented, and the significance of collaborative engagement of both engineers and scientists for promotion in bio-inspired geotechnics is emphasized. [ABSTRACT FROM AUTHOR]

This study contributes to the practical understanding of journal bearings by comprehensively exploring the impact of variable viscosity, sinusoidal surface texturing, slip velocity, magnetic fluid, and couple-stress lubricants on the pressure distribution. Utilising the Barus variable viscosity formula, incorporating ferrofluid as a magnetic lubricant, and employing the Finite Difference Method for numerical analysis, this research reveals insights such as increased load-carrying capacity and pressure distribution in textured bearings. The results indicate that a small distance ratio and high magnetic parameters increase magnetic pressure. Textured bearings increased the load-carrying capacity and pressure distribution by approximately 246 % and 165 %, respectively. In addition, the magnetic, couple-stress, piezo-viscosity, and maximal slip parameters increase the load. Reducing the bearing attitude angle improves the load-carrying capacity. The magnetic parameter increases the attitude angle, as does the slip parameter. High values of the couple-stress parameter reduce friction, particularly in the presence of a textured surface, and the presence of a textured surface amplifies this effect. The study highlights the influence of magnetic, couple-stress, piezo-viscosity, and slip parameters on the bearing's performance, offering valuable insights for optimising journal bearing designs and operations in various engineering applications.

Objective. To compare the structure and water repellent properties by determining the wetting angle of textured surfaces using metal master molds for making samples through various methods. Methodology. The structure of surfaces obtained through different manufacturing methods, namely templating method, filling the template with monomer followed by polymerization, and applying polymer and solvent solution followed by removal of the liquid medium, is studied using optical microscopy. The regularity of the structure was analyzed by digital images taken with optical microscopy. Water repellent properties were investigated using the sessile drop method with a goniometric attachment. Results. Textured surfaces were produced from various materials, including low-density polyethylene, polydimethylsiloxane rubber, and ethylene-propylene rubber. The methods used for their production are indicated. The qualitative characteristics of each surface, considering the template geometry, are described. A quantitative analysis of the wetting angle values of textured and non-textured surfaces was conducted. The causes and consequences of the deterioration in sample properties are supplemented, along with proposed methods for their resolution. Scientific novelty. Using optical microscopy to establish the optimal method for fulfilling one of the key conditions for producing textured surfaces. By utilizing a metal template, specifically aluminum, templates from other materials were created. Additionally, determining the quantitative impact of surface texturing on selected materials without fulfilling two other criteria. Practical significance. The described methods can be applied to scale up the process of manufacturing textured surfaces using lighter methods and a variety of materials. [ABSTRACT FROM AUTHOR]

To understand the relationship between topography and wetting, it is not enough to study the contact angle. Indeed, the liquid-solid interface plays an important role in wetting. However, data such as the total triple line length, the wetting area and the anchoring depth are inaccessible or difficult to obtain experimentally. This work proposes to overcome the experimental limitations by using a numerical approach to characterize the wetting behavior on textured surfaces. The wetting behavior of an anisotropic textured surface was compared for both experimental and numerical approaches. The experimental wetting is characterized by sessile drop experiments. The simulations were performed by applying the pseudo-potential Lattice-Boltzmann method. The numerical approach was then used to predict the wetting behavior of different materials. The simulations capture both the wetting state and the contact angle, in accordance with the experimental observation. Without making any assumptions about the interfacial shape and anchoring, the simulation allows to characterize the liquid-solid interface by quantifying the total length of the triple line and the wetting area. Simultaneously, the simulations enable the characterization of impregnation within textures for complex mixed regimes. [ABSTRACT FROM AUTHOR]

Textured surfaces have been widely applied in many fields due to their excellent functional performances. Although several micro-scale surface texturing techniques have been used to fabricate surface textures, most are either very expensive, have material limitations, or lack flexibility. In this study, a novel textured surface generation method using vibration-assisted ball-end milling with a non-resonant vibrator is proposed. Firstly, the configuration of the vibration-assisted ball-end milling system is introduced. Then, the trajectories of the cutting edges are modeled and analyzed. Furthermore, an analysis of a non-resonant vibrator is conducted. Finally, surface texture machining experiments are conducted, and the feasibility of the proposed vibration-assisted ball-end milling method for surface texture fabrication is verified.Highlights: A VA-BEM using a non-resonant vibrator was proposed for surface texture fabrication. The tool trajectory in the VA-BEM process was modeled, and the quantitative relationships between the generated dimple geometric parameters and cutting and vibration parameters were built. Experimental results were highly consistent with theoretical results, demonstrating that the proposed VA-BEM can precisely fabricate surface textures. [ABSTRACT FROM AUTHOR]

The paper provides a commentary on the theme of "Current and Future Trends in Tribological Research: Fundamentals and Applications", which is a special feature issue commemorating the 10th anniversary of the journal, Lubricants. A historical discourse is provided regarding various aspects of tribology as a multi-disciplinary subject that interacts in an inter-disciplinary manner with many other subjects: multi-body dynamics, thermofluids and heat transfer, contact mechanics, surface science, chemistry, rheology, data science, and biology, to name but a few. Such interactions lead to many important topics including propulsion with different sources of energy, mitigating emissions, palliation of friction, enhancing durability and sustainability, optimization through detailed analysis, and the use of artificial intelligence. Additionally, issues concerning kinetics at various physical scales (from macroscale to microscale onto mesoscale and nanoscale) affecting the kinematics of contacts are discussed. The broad range of considered applications includes vehicular powertrains, rotor bearings, electrical machines, mammalian endo-articular joints, nanobiological attachment/detachment, and locomotion. Current state-of-the-art tribological research is highlighted within a multi-physics, multi-scale framework, an approach not hitherto reported in the open literature. [ABSTRACT FROM AUTHOR]

YG8 is a common cemented carbide material with excellent mechanical properties and mechanical properties, so it is widely used in the actual industry. However, due to the active chemical properties and strong affinity of tungsten alloy steel, it is easy to produce bonding and peeling in application, resulting in an unstable process and short service life. In order to control and reduce the surface wear of YG8 cemented carbide, groove-textured surface (GS) and flocking surface (FS) were prepared on smooth surface (SS). The friction characteristics of the samples were studied under different applied load conditions. The results show that the average friction coefficient of SS, GS and FS is inversely proportional to the load in dry/oil environment. Compared with SS, FS exhibits the lowest friction coefficient, which is reduced by 30.78% (dry friction) and 13.13% (oil lubrication). FS effectively improves the tooth jump phenomenon of the sample and the amplitude of the friction coefficient, friction force and load, and has the best anti-friction characteristics. At the same time, the FS with the fastest contact angle drop at any time also showed excellent wetting ability, and the wear rate decreased by an order of magnitude. The implantation of fibers in the groove inhibits the spalling and furrow of wear track, which is attributed to the effect of fibers on damage repair. In the friction process, FS increases the content of the O element and induces the formation of oxides. The friction mechanism is mainly chemical wear. The excellent tribological properties of FS have a good guiding significance and theoretical support for improving the tribological properties of high hardness material surfaces. [ABSTRACT FROM AUTHOR]

Over last couple of decades, various regimes of lubrication attracted lots of attention. Among these regimes of lubrication, the least understood and studied are the regimes or boundary lubrication and lubricity. Better understanding these regimes of lubrication is necessary due to the fact that many moving joints such as, for example, bearings and gears at least part of their operating time work in these regimes. It may occur due to slow motion of counter parts or their relative overload. This paper proposes a model for analysis of these regimes of lubrication. Specifically, the model takes into account roughness of one of the contact surfaces. It is shown that for sufficiently high applied load it can be expected that contact surfaces are completely separated by a lubricant layer in spite of the presence of surface asperities. The definitions of boundary lubrication regimes and super lubricity are proposed. A method based on the method of matched asymptotic expansions is applied for analyzing such cases and an approximate analytical solution of the problem away from the contact region boundary is found. In the narrow inlet and exit zones adjacent to contact boundaries equations describing the main solution terms are derived. For the case of super lubricity, a resemblance of a superposition between the lubrication and surface roughness effects is determined and the effect of surface roughness on the lubrication film thickness is considered. Specifically, certain roughness conditions are identified for which the lubrication film thickness can be higher than for smooth surfaces while in other cases it can be lower. For the super lubricity regimes, the equations for the main pressure asymptotic terms in the inlet and exit zones are reduced to the corresponding equations for the smooth (not rough) surfaces for which a series of numerical solutions is obtained earlier. A general analysis of the effect of texturing on lubrication conditions in case of super lubricity is conducted based on a simple geometric criterion. Several models of textured surfaces and their influence on the lubrication film thickness in case of super lubricity regimes are considered. [ABSTRACT FROM AUTHOR]

Surface topography in general is not easy to characterize due to a great number of different features that appear on it. It is still more challenging for machined textured surfaces that are of high functional significance for tribological purposes. For practical reasons, there is a need to describe such surfaces using only a small number of parameters. Which of them represent surface details the best is still an open issue. To find out which parameters can be the most suitable in that case, three groups of machined textured surfaces were prepared. They were plateau-honed cylinder surfaces made of gray cast iron, steel, and bronze surfaces with isolated dimples and steel surfaces after abrasive blasting followed by lapping. All of them were measured by means of a white light interferometer. Different parameters and relationships were evaluated and based on them correlation and regression analyses were used. The basic description contained statistically independent parameters that can be used in production control, while the wider description in scientific research. In general, parameters of random surfaces were more intercorrelated than those of surfaces with isolated dimples. As was found for the basic description of random two-process surfaces, five parameters were enough while description of textured surfaces with isolated oil pockets needed six. In wider, scientific description, regardless the surface type seven parameters contained the necessary information about the surface. It was also proved that a pair of parameters, the emptiness coefficient Sp/Sz and Sq/Sa, can describe the shape of the ordinate distribution of machined textured surfaces better than, for example, skewness Ssk and kurtosis Sku, commonly used for that purpose. [ABSTRACT FROM AUTHOR]

The application of microdimple-textured surfaces for rolling bearings is not very common but can be beneficial for various usage scenarios. In contrast to the applications for plain bearings or cylinder running surfaces, however, surface patterns for rolling bearings only offer advantages under certain conditions. For example, for use with start-stop cycles, in mixed lubrication conditions, or under sliding conditions in a bearing as well as on a roller--bearing flange contact, friction can be reduced with the targeted use of microtextures. The geometry of the microtextures must be chosen so that individual dimples fit in the contact area between the ball or roll and the bearing surface in order to act as a reservoir for the lubricant. First applications for microtextured angular contact ball bearings under oscillating movement conditions proved friction reducing effects under reciprocating motion. In this case the microtextures served as lubricant reservoirs. The idea is transferred to the sliding contact for tapered roller bearings; it is investigated whether the measured reductions in friction are due to the microtextures serving as lubricant reservoirs or whether there is even a positive hydrodynamic effect caused by the microtextures. By means of a calculation approach as well as some exemplary test rig measurements, the behavior for microtextured tapered roller bearings is investigated. [ABSTRACT FROM AUTHOR]

The paper provides a commentary on the theme of “Current and Future Trends in Tribological Research: Fundamentals and Applications”, which is a special feature issue commemorating the 10th anniversary of the journal, Lubricants. A historical discourse is provided regarding various aspects of tribology as a multi-disciplinary subject that interacts in an inter-disciplinary manner with many other subjects: multi-body dynamics, thermofluids and heat transfer, contact mechanics, surface science, chemistry, rheology, data science, and biology, to name but a few. Such interactions lead to many important topics including propulsion with different sources of energy, mitigating emissions, palliation of friction, enhancing durability and sustainability, optimization through detailed analysis, and the use of artificial intelligence. Additionally, issues concerning kinetics at various physical scales (from macroscale to microscale onto mesoscale and nanoscale) affecting the kinematics of contacts are discussed. The broad range of considered applications includes vehicular powertrains, rotor bearings, electrical machines, mammalian endo-articular joints, nanobiological attachment/detachment, and locomotion. Current state-of-the-art tribological research is highlighted within a multi-physics, multi-scale framework, an approach not hitherto reported in the open literature.

The loss of energy due to friction is one of the major problems industries are facing nowadays. Friction and wear between sliding components reduce the mechanical efficiency of machines and have a negative impact on the environment. In recent years, surface texturing has shown tremendous ability to reduce friction and wear. Micro-features generated on surfaces act as a secondary reservoir for lubricants and wear debris receptacles to further reduce abrasion. In addition, surface texturing boosts hydrodynamic pressure, which increases the elasto-hydrodynamic lubrication regime of the Stribeck curve, reducing friction and wear. Amongst all different techniques to texture surfaces, laser texturing is the most popular due to its advantages such as high accuracy, good consistency and celerity as compared to other techniques. This study investigated the effect of laser texturing on the tribological properties of Ti6Al4V in contact with a ceramic ball. The effect of varying the dimple density on friction and wear was studied using a ball-on-flat reciprocating tribometer under lubricated conditions. Results show that friction and wear were reduced for all the textured samples as compared to an untextured sample, with important friction and wear reductions for the samples with the highest dimple densities. For samples with intermediate dimple densities, the friction coefficient stayed low until the dimples wore out from the surface and then increased to a value similar to the friction coefficient of the untextured surface. The dimple wear-out time observed in these specimens was greatly influenced by the dimple density. [ABSTRACT FROM AUTHOR]

Tribology of touch is a subject of high interest, which has led to a certain number of experimental studies, each of them done under different contact conditions. The present paper aims at determining, in the case of the friction of the finger on four different micro-textured surfaces, the influence of the normal force and the inclination of the finger. The experiments were done with four target angles and two target forces, all at the same contact speed. The friction coefficient was shown to decrease when the finger was tilted upwards, for the four surfaces and for both normal force conditions. A friction law has been then fitted to the experimental results, trying to bring further insights on the experimental observations. [ABSTRACT FROM AUTHOR]

This study investigates the hydrodynamics and heat transfer of a droplet impinging on a heated superhydrophobic surface at low Weber numbers with subsequent bouncing through numerical simulations in the phase-field framework. These structure-resolved simulations take into consideration the entrapment of air during impingement on the micro-textured surface and effectively replicate the hydrodynamic behavior observed in corresponding experimental studies [1]. The simulation results indicate notable differences in air entrainment and heat transfer dynamics for the same contact angle under varying surface topography. This offers the potential to deliberately modify the dynamics of heat transfer by manipulating the surface topography without significantly altering the wetting behavior. Additionally, an attempt to substitute the structure-resolved boundary with a temperature boundary condition, which incorporates the void fraction and thermal conductivity of the involved fluids, has been observed to be insufficient to reproduce the temperature evolution due to the absence of wetting physics description. These findings suggest that the primary source of variations in heat transfer is the alteration in the contact area with the surface, rather than the local thermophysical properties of the air/water mixture. Consequently, for an accurate evaluation of heat transfer on textured surfaces, it is imperative to employ simulations that consider the resolved surface topography. • 3D simulations of droplets on heated surfaces with varying roughness were conducted using phase-field. • Textured surfaces with low roughness improve heat exchange over smooth ones due to larger contact area. • Textured surfaces with high roughness can either enhance or reduce cooling due to their wetting effect. [ABSTRACT FROM AUTHOR]

Achieving low-friction and robust tribosystems is an open and challenging question to tribologists. In this study, we are considering the diamond films as candidates. Quantification of friction is obtained here using an original technique, so called the oscillating relaxation tribometry. It is based on the study of the oscillating motion of a free-damped 1-DOF mechanical oscillator, the sliding contact acting as a main source of mechanical dissipation (“relaxation”). Therefore, it is possible to determine friction value and its sliding speed dependency, i.e. a kind of “Stribeck curve“ under non-stationary conditions. The interest of such “relaxation tribometer“ is to characterize low friction with an unequalled sensitivity, and to directly obtain the “friction law“ thanks to a robust and rapid experimental test. Polycrystalline diamond films are deposited by the Hot Filament CVD method on SiC substrate, which were partly polished and finished to gradient surface roughness with random-textured asperities. Stainless steel balls of 6.0 mm diameter are used as the rubbing counterface. The normal force is varied between 50 and 300 mN, leading respectively to a maximum Hertzian contact pressure of 0.30 and 0.71 GPa, respectively. Taking into account the experimental setup, the sliding speed is decaying as a damped pseudo-sine motion, the maximum sliding value being set to 0.16 m/s, progressively decaying to 0 when mechanical equilibrium is reached, within a typical duration of 5 s. First results are reported here, using this innovative friction characterization technique. The different contributions to friction of the surface roughness are analyzed and discussed. These results show the major interest of the use of this method to characterize the low-friction behavior of textured diamond films. These results are discussed and the high potential of such textured films in actual tribosystems is presented here.

Fabrication of tunable fine textures on solid metal surfaces often demands sophisticated reaction/processing systems. By exploiting in situ polymerization and self‐assembly of inorganic adducts derived from liquid metals (the so‐called HetMet reaction) with concomitant solidification, solid metal films with tunable texture are readily fabricated. Serving as a natural dimensional confinement, interparticle pores and capillary‐adhered thin liquid films in a pre‐packed bed of undercooled liquid metal particles lead to the expeditious surface accumulation of organometallic synthons, which readily oligomerize and self‐assemble into concentration‐dictated morphologies/patterns. Tuning particle size, particle packing (flat or textured), and reactant concentration generates diverse, autonomously organized organometallic structures on a metal particle bed. Concomitant solidification and sintering of the underlying undercooled particle bed led to a multiscale patterned solid metal surface. The process is illustrated by creating tunable features on pre‐organized metal particle beds with concomitant tunable wettability as illustrated through the so‐called petal and lotus effects. [ABSTRACT FROM AUTHOR]

The loss of energy due to friction is one of the major problems industries are facing nowadays. Friction and wear between sliding components reduce the mechanical efficiency of machines and have a negative impact on the environment. In recent years, surface texturing has shown tremendous ability to reduce friction and wear. Micro-features generated on surfaces act as a secondary reservoir for lubricants and wear debris receptacles to further reduce abrasion. In addition, surface texturing boosts hydrodynamic pressure, which increases the elasto-hydrodynamic lubrication regime of the Stribeck curve, reducing friction and wear. Amongst all different techniques to texture surfaces, laser texturing is the most popular due to its advantages such as high accuracy, good consistency and celerity as compared to other techniques. This study investigated the effect of laser texturing on the tribological properties of Ti6Al4V in contact with a ceramic ball. The effect of varying the dimple density on friction and wear was studied using a ball-on-flat reciprocating tribometer under lubricated conditions. Results show that friction and wear were reduced for all the textured samples as compared to an untextured sample, with important friction and wear reductions for the samples with the highest dimple densities. For samples with intermediate dimple densities, the friction coefficient stayed low until the dimples wore out from the surface and then increased to a value similar to the friction coefficient of the untextured surface. The dimple wear-out time observed in these specimens was greatly influenced by the dimple density.

Background: All soft and solid surface structures in the oral cavity are covered by the acquired pellicle followed by bacterial colonization. This applies for natural structures as well as for restorative or prosthetic materials; the adherent bacterial biofilm is associated among others with the development of caries, periodontal diseases, peri-implantitis, or denture-associated stomatitis. Accordingly, there is a considerable demand for novel materials and coatings that limit and modulate bacterial attachment and/or propagation of microorganisms. Objectives and findings: The present paper depicts the current knowledge on the impact of different physicochemical surface characteristics on bioadsorption in the oral cavity. Furthermore, it was carved out which strategies were developed in dental research and general surface science to inhibit bacterial colonization and to delay biofilm formation by low-fouling or "easy-to-clean" surfaces. These include the modulation of physicochemical properties such as periodic topographies, roughness, surface free energy, or hardness. In recent years, a large emphasis was laid on micro- and nanostructured surfaces and on liquid repellent superhydrophic as well as superhydrophilic interfaces. Materials incorporating mobile or bound nanoparticles promoting bacteriostatic or bacteriotoxic properties were also used. Recently, chemically textured interfaces gained increasing interest and could represent promising solutions for innovative antibioadhesion interfaces. Due to the unique conditions in the oral cavity, mainly in vivo or in situ studies were considered in the review. Conclusion: Despite many promising approaches for modulation of biofilm formation in the oral cavity, the ubiquitous phenomenon of bioadsorption and adhesion pellicle formation in the challenging oral milieu masks surface properties and therewith hampers low-fouling strategies. Clinical relevance: Improved dental materials and surface coatings with easy-to-clean properties have the potential to improve oral health, but extensive and systematic research is required in this field to develop biocompatible and effective substances. [ABSTRACT FROM AUTHOR]

We develop an approach to using microsaccade dynamics for the measurement of task difficulty/cognitive load imposed by a visual search task of a layered surface. Previous studies provide converging evidence that task difficulty/cognitive load can influence microsaccade activity. We corroborate this notion. Specifically, we explore this relationship during visual search for features embedded in a terrain-like surface, with the eyes allowed to move freely during the task. We make two relevant contributions. First, we validate an approach to distinguishing between the ambient and focal phases of visual search. We show that this spectrum of visual behavior can be quantified by a single previously reported estimator, known as Krejtz's $\mathcal {K}$ K coefficient. Second, we use ambient/focal segments based on $\mathcal {K}$ K as a moderating factor for microsaccade analysis in response to task difficulty. We find that during the focal phase of visual search (a) microsaccade magnitude increases significantly, and (b) microsaccade rate decreases significantly, with increased task difficulty. We conclude that the combined use of $\mathcal {K}$ K and microsaccade analysis may be helpful in building effective tools that provide an indication of the level of cognitive activity within a task while the task is being performed. [ABSTRACT FROM AUTHOR]

Lubrication conditions have significant influences on the formation of tribofilms and then affect tribological behavior. In this work, the influence of tribofilm formation on the tribological behavior of textured surfaces with oval shapes was measured using a pin-on-plate tribometer. The results show that, under full lubrication, the adsorbed oil film controlled the friction and wear behavior of steel/steel tribopairs but under starved lubrication, the formation of a tribofilm significantly influenced the tribological behavior. The appropriate textured surfaces with oval-shaped dimples contribute to obtaining excellent antifriction and antiwear behavior. However, excessively high ratios of the major to the minor axis of the oval can result in high contact stresses which can destroy the tribofilm. • Textured surfaces with oval-shaped dimples were facilely fabricated. • Influence of tribofilm formation on the surface tribological behavior was investigated. • The adsorbed-film controlled the friction and wear behavior of tribo-pairs under full lubrication. • The formation of tribofilm dominated the interface behavior under starved lubrication. [ABSTRACT FROM AUTHOR]

In any hydraulic machine there are lubricated couplings that could become critical beyond certain operating conditions. This paper presents the simulation results concerning textured surfaces with the aim of improving the performance of lubricated couplings in relative motion. The texturing design requires much care to obtain good improvements, and it is essential to analyze both the geometric features of the dimples and the characteristics of the coupled surfaces, like the sliding velocity and gap height. For this purpose, several CFD simulations have been performed to study the behavior of the fluid bounded in the coupling, considering dimples with different shapes, size, and spatial distribution. The simulations consider the onset of gaseous cavitation to evaluate the influence of this phenomenon on the pressure distribution generated by the textured surface. The analyses have pointed out that it is critical to correctly predict the behavior of the textured surface in the presence of local cavitation, in fact, when cavitation occurs, the characteristic time of the transient in which the phase of the fluid change is very rapid and it is comparable to the time taken by the fluid to move from one dimple to the next.

Graphical abstract Abstract Hypothesis Coating-free approaches to achieve liquid repellent, or omniphobic, surfaces could exploit inexpensive intrinsically wetting materials, such as polyethylene terephthalate and nylon, for applications such as liquid-vapor extraction and drag reduction. However, it is not clear whether the existing criteria for assessing coating-based omniphobicity, based on contact angles, would be reliable for coating-free approaches, especially considering localized defects/damages during manufacturing and usage. Experiments We assessed the omniphobicity of silica surfaces adorned with arrays of doubly reentrant pillars, cavities, and hybrid designs with sessile drops and on immersion in water and hexadecane through contact angle goniometry and confocal microscopy. Findings We demonstrate that the assessment of omniphobicity of surfaces derived from intrinsically wetting materials can be misleading, if solely based on the measurement of contact angles. Specifically, localized defects in microtextures consisting of pillars may lead to the spontaneous loss of omniphobicity and detecting them through contact angles can be difficult. We also demonstrate that the immersion of those surfaces into probe liquids may serve as a simple and quick 'litmus' test for omniphobicity. Thus, immersion as the additional criterion for omniphobicity might prove itself useful in the context of large-scale manufacturing. [ABSTRACT FROM AUTHOR]

Loss of machining efficiency, part repair, and replacement of mechanical components due to friction and wear is a recurring problem for performance industrial system applications. Recent studies on surface modification and micro-scale texturing have shown successful results in reducing friction and wear of lubricated surfaces. By acting as lubricant reservoirs and wear particle receptacles, micro-scale artificial surface textures positively influence lubrication regimes. In the present experimental study, a Stribeck curve is generated to compare the tribological properties of untextured and textured surfaces created by modulation-assisted machining. Aluminum 6061-T6 disks are mated with high-speed steel pins on a pin-on-disk tribometer configuration for varying speed and texture depth and density. The results suggest that the textured surfaces produced by modulation-assisted machining accelerate the appearance of the elasto-hydrodynamic regime, while also reducing friction by 56% and wear by almost 90%. The enhanced friction and wear reduction were obtained under the lower speeds studied. In general, the disk with shallower dimples presented lower values of friction under the conditions studied. No major differences were found for textures with different dimple densities. [ABSTRACT FROM AUTHOR]

Abstract: This work shows that a large‐scale textured GaP template monolithically integrated on Si can be developed by using surface energy engineering, for water‐splitting applications. The stability of (114)A facets is first shown, based on scanning tunneling microscopy images, transmission electron microscopy, and atomic force microscopy. These observations are then discussed in terms of thermodynamics through density functional theory calculations. A stress‐free nanopatterned surface is obtained by molecular beam epitaxy, composed of a regular array of GaP (114)A facets over a 2 in. vicinal Si substrate. The advantages of such textured (114)A GaP/Si template in terms of surface gain, band lineups, and ohmic contacts for water‐splitting applications are finally discussed. [ABSTRACT FROM AUTHOR]

In humans, there is clear evidence of an association between hip fracture risk and femoral neck bone mineral density, and some evidence of an association between fracture risk and the shape of the proximal femur. Here, we investigate whether the femoral cortex plays a role in these associations: do particular morphologies predispose to weaker cortices? To answer this question, we used cortical bone mapping to measure the distribution of cortical mass surface density (CMSD, mg/cm 2 ) in a cohort of 125 females. Principal component analysis of the femoral surfaces identified three modes of shape variation accounting for 65% of the population variance. We then used statistical parametric mapping (SPM) to locate regions of the cortex where CMSD depends on shape, allowing for age. Our principal findings were increased CMSD with increased gracility over much of the proximal femur; and decreased CMSD at the superior femoral neck, coupled with increased CMSD at the calcar femorale, with increasing neck-shaft angle. In obtaining these results, we studied the role of spatial normalization in SPM, identifying systematic misregistration as a major impediment to the joint analysis of CMSD and shape. Through a series of experiments on synthetic data, we evaluated a number of registration methods for spatial normalization, concluding that only those predicated on an explicit set of homologous landmarks are suitable for this kind of analysis. The emergent methodology amounts to an extension of Geometric Morphometric Image Analysis to the domain of textured surfaces, alongside a protocol for labelling homologous landmarks in clinical CT scans of the human proximal femur. [ABSTRACT FROM AUTHOR]

To facilitate fundamental study of the surface texturing effect on hydrodynamic lubrication, analytical and experimental tools are required. While there is an extensive amount of theoretical and analytical analyses in the literature, relevant experimental studies are much rarer. A detailed study requires techniques by which one can (a) produce micron-sized textures on a millimeter-scale area on a specimen surface and (b) accurately measure the lubricating film thickness and load-carrying capacity of a bearing. The paper introduces the use of an efficient laser technique (direct laser interference patterning) and a custom-designed fixed-incline slider tester to address these points. A steel slider was textured with the laser technique to produce a surface pattern in the inlet region of the bearing contact. The characterization of the load-carrying capacity for different convergence ratios K is presented. [ABSTRACT FROM AUTHOR]

Textured surfaces have been shown to provide enhanced tribological performance in a variety of contacts. Numerical analysis and optimisation methods are combined for application-oriented texture optimisation. However, an analytical approach is advantageous in providing more generic in-depth understanding of the nature of the relationships between texture parameters and objective functions, such as enhanced load carrying capacity and reduced friction. The paper outlines such an approach to obtain a set of global optimum design parameters for partially textured surfaces. The optimised results are expressed in dimensionless form, which enables their use for a variety of applications. The performance of optimised partially textured sliding surfaces is compared with the other conventional bearing geometries in their optimum state. [ABSTRACT FROM AUTHOR]

Although the Cassie-Baxter and Wenzel equations predict contact angles for relative dimensions of micro-pillars on textured surfaces, the absolute pillar dimensions are determined by trial and error. Alternatively, geometries of natural super-hydrophobic surfaces are often imitated to design textured surfaces. Knowing the limitations of both the approaches, this work presents a constraint minimization model on the basis of Cassie-Baxter equation to determine the absolute dimensions of square micro-pillars on a textured surface so as to maximize the contact angle. The constraints are derived based on the limiting physical conditions at which spontaneous breakdown of super-hydrophobicity takes place. The single-droplet numerical simulations on textured surface gave the duration for which super-hydrophobicity is sustained. The model demonstrated that the round edged pillars, arising out of fabrication imperfections, reduce the height of the pillars without significantly compromising on the contact angle. The measurement of contact angle on the fabricated textured surfaces was found to be in agreement with the model predictions when the fabricated pillars had fairly uniform dimensions. The proposed approach is sufficiently general that its application can be extended to design other textured surfaces. [ABSTRACT FROM AUTHOR]

Engineered surfaces (ground and similarly structured rough surfaces) show anisotropic characteristics and their topography parameters are direction dependent. Statistical characterization of these surfaces is still complex because of directional nature of surfaces. In this technical brief, an attempt is made to simulate anisotropic surfaces through use of topography parameters (three-dimensional (3D) surface parameters). First, 3D anisotropic random Gaussian rough surface is generated numerically with fast Fourier transform (FFT). Numerically generated anisotropic random Gaussian rough surface shows statistical properties (texture direction, texture ratio) similar to ground and similarly directional anisotropic rough surfaces. For numerically generated anisotropic Gaussian rough surface, important 3D roughness parameters are determined. Sayles and Thomas' (1976, "Thermal Conductance of Rough Elastic Contact," Appl. Energy, 2(4), pp. 249-267.) theoretical model for directional anisotropic rough surface is adopted here for calculating the summit parameters, i.e., equivalent bandwidth parameter, mean summit curvature, skewness of summit height, standard deviation of summit height, and equivalent spectral moments. This work demonstrates the variation of spectral moments in both across and parallel to the lay directions with pattern ratio (γ = βx/βy). Correlation length (βy) is fixed 10 pm and correlation length (βy) is varied from 100 to 10 pm. Variation of summit parameters with pattern ratio is also discussed in detail. Results shows that mean summit curvature and skewness of summit heights increase with increase in pattern ratio, whereas standard deviation of summit heights and equivalent bandwidth parameter (αe) decreases with pattern ratio. A significant difference is found in "Abbott-Firestone'' parameters when calculated in both perpendicular and parallel to lay directions. Effect of these parameters on wear process is discussed in brief. [ABSTRACT FROM AUTHOR]

Small scale and passive solar-thermal desalination system hold promise to be employed in decentralized and off-grid areas to address scarcity of potable water. Here, we present a compact multistage thermal desalination system based on interfacial evaporation and latent heat recovery. We develop a textured metallic evaporator substrate that serves as a wick and reduces the thermal resistance for interfacial evaporation. We demonstrate that the rate of evaporation can be increased by tuning the wettability of the condenser surface. Patterned wettability-contrast surfaces are shown to enhance the rate of condensation compared to an unpatterned substrate with spatially uniform wettability. In a single stage desalination system, with patterned condenser surfaces, the evaporation rate increases by ~11 % and the water collection increases by ~21 % compared to that using an unpatterned condenser substrate. The thermal to vapor efficiency of ~56 % in a single stage increases to ~185 % with the use of multistage system. We achieve a water collection of ~2.17 Lm−2 h−1 using a 5-stage system. A theoretical model based on heat and mass transport analysis is used to determine the influence of the system geometry and ambient conditions on the overall efficiency of the desalination system. • Textured metallic substrates are utilized as wicks in the interfacial thermal desalination system. • The condenser-side performance influences the rate of evaporation in a thermal desalination system • Patterned condenser substrates increase the thermal to vapor conversion efficiency and water collection rate. • A thermodynamic analysis shows the influence of system geometry and ambient conditions on the efficiency of the desalination system. [ABSTRACT FROM AUTHOR]

Applying external vibrations at the resonant frequencies of the frictional system has been a highly effective approach to suppress friction but usually requires additional energy consumption. In this study, we find that in addition to exerting the vibration at the resonant frequency of the frictional system, the friction force on the atomically flat silicon surface can also present a local minimum when the oscillation frequency of the vertical vibrational excitation equals the washboard frequency with respect to the sliding velocity. Moreover, compared with the additional energy consumption at the resonant frequency, applying vertical vibrational excitation at the washboard frequency requires much less energy consumption. The study further shows that the friction force under the washboard frequency can be effectively mediated depending on how the initial phase angle of the vertical vibrational excitation affects the effective substrate potential barrier at the slip moment of the tip. We have also extended the proposed friction modulation technique on atomically flat surfaces to periodic textured surfaces and confirmed its practicality and great potential for controlling friction.

Macroscopic frictional response of soft interfaces is strongly governed by the interaction of surface heterogeneities such as micro-texture features with bulk heterogeneities such as voids or inclusions beneath the highly deformable surface. This microscopic interaction manifests itself on the macroscale as an interface response that is reminiscent of stick-slip. Consequently, the accompanying macroscopic friction signal exhibits strong oscillations around a mean value, which itself significantly differs from its microscopic value due to finite deformations. In this work, a mechanism is proposed which enables the tuning of the macroscopic friction signal of soft interfaces. Specifically, it is demonstrated that optimally positioning subsurface particles in the vicinity of micro-texture features can significantly reduce observed oscillations, thereby allowing control of macroscopic sliding friction. [ABSTRACT FROM AUTHOR]

To facilitate fundamental study of the surface texturing effect on hydrodynamic lubrication, analytical and experimental tools are required. While there is an extensive amount of theoretical and analytical analyses in the literature, relevant experimental studies are much rarer. A detailed study requires techniques by which one can (a) produce micron-sized textures on a millimeter-scale area on a specimen surface and (b) accurately measure the lubricating film thickness and load-carrying capacity of a bearing. The paper introduces the use of an efficient laser technique (direct laser interference patterning) and a custom-designed fixed-incline slider tester to address these points. A steel slider was textured with the laser technique to produce a surface pattern in the inlet region of the bearing contact. The characterization of the load-carrying capacity for different convergence ratios K is presented.

The computational model of textured surfaces is highly nonlinear, and the texturing parameters interact with each other. The Fourier Amplitude Sensitivity Test(FAST) method was introduced to calculate the first-order sensitivity indices of texturing parameters to the tribological characteristics. Results show that both the inlet suction and the cumulative effect influence the tribological performance, but which mechanism plays the leading role is related to the convergence ratio. Besides, the texture density along the velocity direction is the most crucial geometric parameter; the effects of the cell size and the bottom profile are negligible. The sensitivity indices provide a novel perspective to quantify the influence of input on the output and the FAST method proved ideally suited to the texturing model. [ABSTRACT FROM AUTHOR]

Large majority of superhydrophobic surfaces have very limited mechanical wear robustness and long-term durability. This problem has restricted their utilization in commercial or industrial applications and resulted in extensive research efforts on improving resistance against various types of wear damage. In this review, advances and developments since 2011 in this field will be covered. As such, we summarize progress on fabrication, design and understanding of mechanically durable superhydrophobic surfaces. This includes an overview of recently published diagnostic techniques for probing and demonstrating tribo-mechanical durability against wear and abrasion as well as other effects such as solid/liquid spray or jet impact and underwater resistance. The review is organized in terms of various types of mechanical wear ranging from substrate adhesion, tangential surface abrasion, and dynamic impact to ultrasonic processing underwater. In each of these categories, we highlight the most successful approaches to produce robust surfaces that can maintain their non-wetting state after the wear or abrasive action. Finally, various recommendations for improvement of mechanical wear durability and its quantitative evaluation are discussed along with potential future directions towards more systematic testing methods which will also be acceptable for industry. [ABSTRACT FROM AUTHOR]

Chemical grafting of small molecule reagents onto polymeric fibrous materials, like paper, has been used to modify their wetting properties. Several reagents like trichlorosilanes, which can react with water or hydroxyls, have been used with the expectation that a monolayer, single molecule or polymerized single-molecule layer, is formed on the paper fiber surface. Presence of adsorbed water, however, would complicate the formation of a monolayer, especially in case of polyvalent reagents. We hypothesized that adsorbed water is a good co-monomer for polyvalent water-reactive reagents, therefore chemical grafting with polyvalent molecules would give polymeric gels instead of a monolayer. Reaction of trivalent reagents with paper in vacuo leads to formation of polymeric gels. By optimizing surface energy mismatch, through felicitous choice of chemical moieties on the monomer, self-assembly leads to formation of nano- to micro particles on the surface of paper fibers. We observe that, as expected, the wetting properties correlate well with the size and distribution of particles. We conclude that the recently reported ultra-hydrophobicity of chemically modified paper is not only due to inherent roughness of the paper fibers, but also due to a secondary roughness introduced by surface polymerization. Using this technique, we prepared amphi-phobic biomimetic surfaces inspired by the namib beetle. This talk will also address potential utility of such surfaces. [ABSTRACT FROM AUTHOR]

A study on using an unsupervised learning technique, called a self-organizing map (SOM) or Kohonen map, for the detection of road cracks from pavement images is described in this paper. The main focus is on highly textured road images that make the crack detection very difficult. Road images are split into smaller rectangular cells, and a representative data set is generated for each cell by analyzing image texture and color properties. Texture and color properties are combined with a Kohonen map to distinguish crack areas from the background. Using this technique, cracks are detected to a precision of 77%. The algorithm also resulted in a recall of 73% despite the background having very strong visual texture. The technique applied here shows a great deal of promise despite the images being captured in an uncontrolled environment devoid of state-of-the-art image-acquisition setups. The results are also benchmarked against an advanced algorithm reported in a recent research paper. The benchmarking shows that the proposed algorithm performs better in terms of reducing the false positives in crack detection. [ABSTRACT FROM AUTHOR]

In this work, a parametric study of a lubricated textured contact is carried out using a numerical model. The model solves the Reynolds equation coupled with a mass-conserving cavitation algorithm, and addresses the hydrodynamic lubrication of a mechanical seal with textured surfaces. Three shapes of texture (square, spherical cap, and triangle) are used, and the effect of the aspect ratio is also discussed for the case involving a triangular dimple. In order to estimate quantitatively the discretization error, the grid convergence index method is applied, considering several operating parameters (leakage, cavitation, load-carrying capacity) and using three grid levels: coarse (100 × 100), medium (200 × 200), and fine (400 × 400). As could be expected, grid convergence index analysis showed that there was a reduction in the discretization error when the grid system was refined. However, the study also showed that medium grid (200 × 200) solution has a grid convergence index of <6%. Comparison between fine and medium mesh densities, with regard to accuracy and computational time requirements, indicated that a medium mesh density was appropriate in the case of the present program, since the computational time is reduced by a factor of 9 when compared with the highest mesh density. Moreover, the size of the optimal mesh also depends on the operating conditions. The higher the lubrication number, the higher the number of nodes. [ABSTRACT FROM AUTHOR]

Reverse microelectrical discharge machining (R-MEDM) process is a recent variant of microelectrical discharge machining process capable of fabricating high aspect ratio arrayed microfeatures and textured surfaces. Efficient flushing of the debris particles from the interelectrode gap is essential for process stability, but extremely small interelectrode gaps ( $\sim 5~\mu $ m) make the dispelling of debris difficult, rendering the R-MEDM process infeasible for machining difficult-to-erode materials and creation of engineered/textured surfaces. It has been experimentally observed that the electrode vibrations facilitate the flushing of debris particles and improve the erosion rate, surface morphology, and dimensional accuracy of the machined features. Despite the obvious advantages, the vibration-assisted R-MEDM process, specifically the debris motion and dielectric flow under the effect of vibration, is not very well understood. Consequently, this paper is focused on computational modeling of the debris motion and its interaction with the dielectric fluid under low-amplitude vibrations imparted via a magnetorestrictive actuator. The effects of frequency and amplitude of the electrode vibration on the debris motion have been quantified. The higher local debris velocities and oscillatory motion due to flow reversal potentially reduce the debris agglomeration. As a result, the normal discharge duration, which is responsible for the material erosion, is increased and fabrication of arrayed features on difficult-to-erode materials and creation of surface texture over large areas become feasible. [2013-0394] [ABSTRACT FROM AUTHOR]