Wear mechanisms in dry and starved-lubricated contacts are critical factors contributing to the degradation of component surfaces. Real-time monitoring of wear progression presents significant challenges due to the complex nature of these mechanisms and the varying conditions under which they occur. Electrostatic sensing offers a way of monitoring wear progression as it is correlated with surface charging from wear debris, contact potential differences associated with surface films, material phase transformations and wear transitions as well as from additive adsorption. This research employs two types of electrostatic wear sensor: a bar sensor for in-situ monitoring of wear progression and an array sensor for charge mapping of the resultant wear mechanisms in the scar. Two sliding wear tests with tool steel against bearing steel are presented. Tests were conducted under dry sliding conditions or partially lubricated. Positive charge signals were detected for oxidational wear under dry contact conditions. Elemental mapping confirmed a patchy oxide film had developed and loose oxide wear debris became charged. Correlation is seen between surface charge maps and the patchy surface oxide films. A correlation was also found between the coefficient of friction and electrostatic charge, highlighting the potential of electrostatic sensors in detecting changing friction and wear levels. Negative charge signals were observed under starved sliding conditions using polyalphaolefin (PAO), primarily attributed to the degradation of PAO under high shear rates and tribo-charge mechanism. The charge progressively changed towards a more positive value, suggesting the progression of mild oxidational wear. Only very mild wear was measured at the end of the test (i.e. plastic flow of asperity material into valleys). A map of real-time wear progression and measurement of instantaneous wear rate of oxidational wear and mild wear induced by partially lubricated contacts are presented. This advancement could significantly impact digital tribology, as the electrostatic sensing allows the surface chemistry to be better characterised. This allows for monitoring of the wear processes in action, allowing for better optimisation of predictive maintenance, as the information is real-time and the sensor is non-invasive.

This review of the tribocorrosion of coatings and surface modifications covers nearly 195 papers and reviews that have been published in the past 15 years, as compared to only 37 works published up to 2007, which were the subject of a previous review published in 2007. It shows that the research into the subject area is vibrant and growing, to cover emerging deposition, surface modification and testing techniques as well as environmental influences and modelling developments. This growth reflects the need for machines to operate in harsh environments coupled with requirements for increased service life, lower running costs and improved safety factors. Research has also reacted to the need for multifunctional coating surfaces as well as functionally graded systems with regard to depth. The review covers a range of coating types designed for a wide range of potential applications. The emerging technologies are seen to be molten-, solution-, PVD- and PEO-based coatings, with CVD coatings being a less popular solution. There is a growing research interest in duplex surface engineering and coating systems. Surface performance shows a strong playoff between wear, friction and corrosion rates, often with antagonistic relationships and complicated interactions between multiple mechanisms at different scale lengths within tribocorrosion contacts. The tribologically induced stresses are seen to drive damage propagation and accelerate corrosion either within the coating or at the coating coating–substrate interface. This places a focus on coating defect density. The environment (such as pH, DO2, CO2, salinity and temperature) is also shown to have a strong influence on tribocorrosion performance. Coating and surface modification solutions being developed for tribocorrosion applications include a whole range of electrodeposited coatings, hard and tough coatings and high-impedance coatings such as doped diamond-like carbon. Hybrid and multilayered coatings are also being used to control damage penetration into the coating (to increase toughness) and to manage stresses. A particular focus involves the combination of various treatment techniques. The review also shows the importance of the microstructure, the active phases that are dissolved and the critical role of surface films and their composition (oxide or passive) in tribocorrosion performance which, although discovered for bulk materials, is equally applicable to coating performance. New techniques show methods for revealing the response of surfaces to tribocorrosion (i.e., scanning electrochemical microscopy). Modelling tribocorrosion has yet to embrace the full range of coatings and the fact that some coatings/environments result in reduced wear and thus are antagonistic rather than synergistic. The actual synergistic/antagonistic mechanisms are not well understood, making them difficult to model.

This paper presents insights into how Zinc Dialkyl Dithiophosphate (ZDDP) influences the formation and progression of micropitting. Experimental investigations were conducted using a twin-disc tribometer in rolling-sliding contacts under mixed or boundary lubrication conditions, focusing on the impact of ZDDP on micropitting in bearing steel samples. Results show that ZDDP reduces wear and increases surface friction by forming a tribofilm. This facilitates micropitting formation, but also retards the progression of micropitting. It highlights that understanding the chemical and mechanical interactions at the tribological interface is essential for designing effective mitigation strategies for managing micropitting and avoiding related issues in bearing applications.

For components affected by vibration, fretting wear is one of the most common failure types. In this work, the fretting behavior of ATSP-MoS2 coating was investigated and analyzed in detail. The tested coating only has two fretting states: partial slip regime (PSR) and gross slip regime (GSR). The coefficient of friction (COF) can be maintained at 0.1 when the pv < 1 MPa center dot m center dot s(-1), meanwhile the COF and wear rate are significantly affected by the Hertzian contact stress p. The wear mechanism of the coating mainly includes three aspects, the mechanical damage of the original coating, especially the abrasive wear, the densification of surface film, as well as the formation and rupture of blisters on the surface film.

Nature-inspired eco-friendly superhydrophobic surfaces have attracted great interests from fundamental research to antifouling application. Nanocomposite coatings are an economical way to fabricate superhydrophobic sur-faces. This paper studies how the coating topography can be controlled by using different nanoparticle sizes and concentrations. Six three-dimensional surface parameters are used to define the resulting topography and explore the correlations with wettability. Three unique scenarios are proposed based on the relationship between the two key parameters core void volume (Vvc) and core material volume (Vmc) to assess the relationship between surface roughness and solid-liquid contact area fraction (f). A water contact angle (WCA) of 152.6 and contact angle hysteresis (CAH) of 2.9?degrees are obtained by employing dual-sized nanoparticles at 45% nanoparticle con-centration (wt./wt.), which is up to 10% less than the superhydrophobic coating fabricated by using single-sized nanoparticles (30 nm). Furthermore, Vvc and peak sharpness dominate f, consequently dominating the wetta-bility in the transitional state and Cassie state, respectively. The antifouling tests using Phaeodactylum tricornutum and Bacillus sp. show a negative correlation between f and antifouling performance, and the minimum adhesion ratios are only 0.41% and 0.53%, respectively. The superhydrophobic surfaces with Vvc/Vmc > 1 are shown to be better for antifouling applications. These findings are important for designing superhydrophobic nano-composite coatings for antifouling performance.

In turbomachinery, their blade leading edges are critical to performance and therefore fuel efficiency, emission, noise, running and maintenance costs. Leading edge damage and therefore roughness is either caused by subtractive processes such as foreign object damage (bird strikes and debris ingestion) and erosion (hail, rain droplets, sand particles, dust, volcanic ash and cavitation) and additive processes such as filming (from dirt, icing, fouling, insect build-up). Therefore, this review focuses on the changes in topography induced by during service to blade leading edges and the effect of roughness and form on performance and efforts to predict and model these changes. The applications considered are focused on wind, gas and tidal turbines and turbofan engines. Repair and protection strategies for leading edges of blades are also reviewed. The review shows additive processes are typically worse than subtractive processes, as the roughness or even form change is significant with icing and biofouling. Antagonism is reported between additive and subtractive roughness processes. There are gaps in the current understanding of the additive and subtractive processes that influence roughness and their interaction. Recent work paves the way forward where modelling and machine learning is used to predict coated wind turbine blade leading edge delamination and the effects this has on aerodynamic performance and what changes in blade angle would best capture the available wind energy with such damaged blades. To do this generically there is a need for better understanding of the environment that the blades see and the variation along their length, the material or coated material response to additive and/or subtractive mechanisms and thus the roughness/form evolution over time. This is turn would allow better understanding of the effects these changes have on aerodynamic/ hydrodynamic efficiency and the population of stress raisers and distribution of residual stresses that result. These in turn influence fatigue strength and remaining useful life of the blade leading edge as well as inform maintenance/repair needs.

This paper proposes the concept of how machinery condition monitoring can be taken to the next level, through micro-sensing of tribological phenomena occurring between contacting surfaces. By considering wear transitions and wear rates it is possible to distinguish between benign and potentially harmful wear scenarios. By measuring the tribological phenomena associated with these conditions, it should then be possible to determine with greater accuracy the health of a machine at any point in its life. For this approach to succeed, it is necessary to develop a comprehensive and holistic monitoring strategy and target sensing technologies for the key wear factors. The paper has two main sections. Firstly, tribological phenomena and the onset of wear which sets out why and what needs to be monitored. The factors influencing the wear process are grouped into three key areas: lubricant condition, tribo-pair condition and operating condition. Through a critical and comprehensive review of developing and state-of the-art tribo-sensing, the second section identifies the potential technologies for monitoring or measuring the physical parameters within these three groupings and thus sets out how the next generation of machine condition monitoring will need to evolve in order to achieve early wear detection and the related benefits.

Surface textures have been of great interest within the tribology community with nearly 1500 papers published on this topic in the past two decades. With the pursuit of low emissions and environmental sustainability, the application of surface texturing to mechanical systems to lower friction and control wear is attracting increasing attention. There is no doubt that certain textured surfaces can have a beneficial effect on tribological performance but it is widely agreed that the optimization of textures should be carried out based on specific requirements of applications. The purpose of this review article is to summarize the current state of the art in surface texturing applied to mechanical applications (cutting tools, piston-ring & cylinder liners, sealing and journal bearings) from the following aspects: application requirements, numerical/experimental testing and validation, and tribological performance of textured surfaces (wear and friction), as well as the limitations in texture designs when applied to certain applications. Patterns/grooves in the micron-scale are the most typical shapes been studied, and benefits of partial texturing are applicable for most of these mechanical applications. Friction reduction of up to 34.5% in cutting tools, 82% in piston-ring & cylinder-liners, 65% in seals and 18% in journal bearings have been observed by experimental tests. Based on primary evidence from the literature, the last section provides general suggestions on current gaps in understanding and modelling and suggestions for future research directions.

目的 分析在生产过程中烟标印刷品的动静摩擦因数影响因素,以提高生产效率.方法 分别在不同工艺条件和不同纸质基材下,随机抽取同批次不同生产车号的烟标印刷品,采用MXD-01摩擦因数仪进行主体印刷面动静摩擦因数的测定.结果 相同基材下,表面上水性光油的烟标试样静摩擦因数范围为0.375～0.405,动摩擦因数范围为0.230～0.245,表面上UV光油的烟标试样,静摩擦因数范围为0.350～0.375,动摩擦因数范围为0.185～0.220;相同工艺条件下,充分干燥的时间为2h,烟标试样的静摩擦因数稳定在0.380～0.400,动摩擦因数稳定在0.215～0.230;相同检测条件下,白卡纸静摩擦因数范围为0.615～0.630,动摩擦因数范围为0.470～0.505,银卡纸静摩擦因数范围为0.560～0.595,动摩擦因数范围为0.430～0.465.结论 综合分析,干燥时间、光油干燥机理和纸张特性等因素均对烟标印刷品的摩擦因数产生影响.

This paper presents a study comparing the wear performance of laser clad rails. A grade of martensitic stainless steel (MSS) was deposited on two substrate materials: The European standard grade rail steel R260, and a lower grade rail steel R200. A twin-disc method has been used to simulate the contact of wheel and rail under closely controlled conditions. Although cladding on a lesser grade of rail has an effect on the hardness and wear performance of the clad layer (due to dilution), the resulting wear performance of the clad layer assessed using this approach is still vastly improved over R260 material alone.

An experimental study is presented to evaluate the influence of anisotropically shaped textures on the behaviour of sliding friction and sensitivity to sliding direction. The plate samples were textured with triangular sloped dimples using an ultrafast laser surface texturing technique. Reciprocating cylinder-on-plate tests were conducted with steel sliding pairs using mineral base oil as a lubricant to compare the tribological performance of reference non-textured specimen and dimpled samples. The dimples were designed with varying converging angles in the transverse y–z plane and top-view x–y plane. In this study, no dimple was fully covered in the contact area since the dimples size is much larger than the Hertzian line contact width. Stribeck style dynamic friction curves across boundary, mixed and hydrodynamic lubrication regimes were used to determine the benefit or antagonism of texturing. Observation of the directional friction effect of the anisotropic textures indicated that the converging shapes are beneficial for friction reduction, and the dimpled specimens have a lower friction coefficient particular under prevailing boundary lubrication conditions. It was also found that the real contact length variation rate is a major factor controlling the local friction response. The sloped bottoms of the textures produce effective converging wedge action to generate hydrodynamic pressure and contribute to the overall directional friction effects.

This paper presents a study on the influence of anisotropically shaped texture arrays on friction behaviour of an oil lubricated sliding contact, especially on directional friction control based on the diverging and converging characteristics of the textures. Experiments have been conducted on a TE77 reciprocating cylinder-on-plate test rig, where steel rollers were used to slide against steel plate samples with or without textures. A mineral base oil was used to lubricate the contacts. Three geometries of dimples were designed and laser textured on the steel plate samples with varied 3-dimensional features, including Square Flat (SF), Square slope (SS) and Triangular Flat (TF) shapes representing the shape in x-y (top view) and x-z (side view) planes respectively. These shapes were chosen to vary the converging and diverging properties of the lubricated contacts depending on the sliding direction. Relatively large dimple sizes (side length ~500μm and depth ~10μm) have been used in this study to enable observation of the effect and easy control of the texturing process. The texture density has been kept at 10% as most literature suggested. The large dimple sizes resulted that the dimples were not be fully covered by the contact area, i.e. the dimple sides were bigger than the Hertzian contact width of the roller-flat contacts. This has eliminated the ‘lift’ or ‘load bearing’ effect discussed in most papers thus focuses on other effects investigated in this study. The results show that beneficial effects of the anisotropic textures present in all lubrication regimes including the boundary, mixed and hydrodynamic lubrications, especially under prevailing boundary lubrication conditions. Using high sampling rate for the friction data during the tests, it was able to study local friction effect due to individual dimple array especially at their leading and trailing edges. The results show that a local friction reduction is observed at the leading while an increase at the trailing edge. Overall directional friction effect of the anisotropic textures has been observed that the converging shape in both y-z plane and the x-y plane reduces friction. Furthermore, it was found that the triangular shape dimples have a greater local frictional response at each dimple array, while the sloped bottom square dimples have a more significant overall directional fricition effect.

Surface texturing has been shown to be an effective modification approach for improving tribological performance. This study examined the friction reduction effect generated by square dimples of different sizes and geometries. Dimples were fabricated on the surface of ASP2023 steel plates using femtosecond laser-assisted surface texturing techniques, and reciprocating sliding line contact tests were carried out on a Plint TE77 tribometer using a smooth 52100 bearing steel roller and textured ASP2023 steel plates. The tribological characterization of the friction properties indicated that the textured samples had significantly lowered the friction coefficient in both boundary (15% improvement) and mixed lubrication regimes (13% improvement). Moreover, the high data sampling rate results indicated that the dimples work as lubricant reservoirs in the boundary lubrication regime.

HIV-1 entry into cells is mediated by the envelope glycoprotein receptor-binding (gp120) and membrane fusion-promoting (gp41) subunits. The gp41 heptad repeat 1 (HR1) domain is the molecular target of the fusion-inhibitor drug enfuvirtide (T20). The HR1 sequence is highly conserved and therefore considered an attractive target for vaccine development, but it is unknown whether antibodies can access HR1. Herein, we use gp41-based peptides to select a human antibody, 5H/I1-BMV-D5 (D5), that binds to HR1 and inhibits the assembly of fusion intermediates in vitro. D5 inhibits the replication of diverse HIV-1 clinical isolates and therefore represents a previously unknown example of a crossneutralizing IgG selected by binding to designed antigens. NMR studies and functional analyses map the D5-binding site to a previously identified hydrophobic pocket situated in the HR1 groove. This hydrophobic pocket was proposed as a drug target and subsequently identified as a common binding site for peptide and peptidomimetic fusion inhibitors. The finding that the D5 fusion-inhibitory antibody shares the same binding site suggests that the hydrophobic pocket is a "hot spot" for fusion inhibition and an ideal target on which to focus a vaccine-elicited antibody response. Our data provide a structural framework for the design of new immunogens and therapeutic antibodies with crossneutralizing potential.