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Purpose: Hydro-viscous drive (HVD) clutches are widely used in equipment requiring soft start, such as fans and pumps, to transmit torque and adjust speed by changing the gap distance between friction pairs. This paper aims to propose a novel two-parameter evaluation method for HVD during the mixed lubrication stage. The objective is to develop an effective model that establishes the relationship between these parameters and the actual surface topography. Design/methodology/approach: In the presented methods, the fractal features of the real manufacturing surface are calculated based on the power spectrum function by the ultra-depth three-dimensional microscope. After that, the hybrid friction model of the friction plate is established based on mixed elasto-hydrodynamic lubrication theory, boundary friction model and fractal theory. Then the torque and load bearing characteristics of the clutch are obtained, and the influences of the surface fractal features are investigated and discussed. Finally, the Weierstrass–Mandelbrot function is adopted for the surface topography characterization and evaluation. Findings: The results indicate that the proposed method exhibits good accuracy, while the speed difference between the friction pair exceeds 2,500 rpm. It is concluded that this paper proposed a way to evaluate the torque and loading capacity of HVD considering the real manufacturing surface topography and is helpful for surface optimization. Originality/value: The originality and value of this study lie in its development of a novel torque and load bearing capacity evaluation method for HVD in mixed lubrication stage, considering manufacturing surface topography and describing the real manufacturing surface. [ABSTRACT FROM AUTHOR]

Roughness metrics measured with stylus profilometry are commonly used to explain a floor's friction performance, yet these metrics inconsistently predict shoe-floor friction. While strong correlations have been shown for systematically modified flooring, the goal of this study is to address a gap regarding the predictive ability of these metrics across heterogeneous porcelain flooring products. The predictive ability of four roughness metrics on oily friction performance was assessed using 23 floors and 4 shoe designs. Roughness was moderately correlated with friction (r ranged from 0.374 to 0.760). These results are a reference point for future studies that aim to improve predictions using novel surface characterization approaches that include multiple scales. • Predictiveness of stylus-measured roughness on floor friction was evaluated. • Twenty-three floors and four shoes were included in the study. • Correlation coefficients between 0.374 and 0.760 were observed. • Incomplete predictive power motivates additional topography metrics. • Alternative metrics may improve predictions. [ABSTRACT FROM AUTHOR]

Laser surface texturing (LST) is widely explored for modifying the surface topography of various materials. In this study, a detailed investigation of laser textured surfaces produced on austenitic stainless steel (AISI 304) was carried out. Three different textures (square, parallel, perpendicular) were produced by a Ti sapphire laser. The processed surfaces were characterized by surface morphology, phase structure, microhardness, surface roughness, and wettability. A ball-on-disk tribometer was used to study the tribological performance of both untextured and textured samples. The experimental observations demonstrate that LST improves both surface wettability and surface roughness. Average surface roughness (Ra) was increased by 350% and the contact angle was reduced from 43° to 22°. The textured surfaces show a lower coefficient of friction and better wear resistance than the untextured surface. Out of the investigated patterns, the square textures exhibited a maximum reduction of 68% in the friction coefficient and a 50% lower wear rate. [ABSTRACT FROM AUTHOR]

The dynamic evolutions of friction force and worn surface profile were qualitatively analyzed by phase trajectory and recurrence plots and quantitatively characterized by fractal dimension and percent determinism. The results show that phase trajectories first shrink to a small volume, then stabilize at a minimum volume, finally expand to a large volume in the wear process. The white areas on the recurrence plots increase with the wear time. The fractal dimension first increases, then stabilizes at a high value, and finally decreases rapidly. The percent determinism first decreases, then fluctuates in a certain range, and finally increases. It demonstrates that friction force and worn surface topography derived from one tribology system evolve in a similar but not exactly the same way. They have the consistent evolution law in the wear process. Specially, friction force is much more sensitive to the variation of wear states than the worn surface. [ABSTRACT FROM AUTHOR]

It is virtually impossible to follow through changes in surface topography and analyse wear mechanisms of the friction components of a hip joint prosthesis under in vivo conditions. Only under laboratory conditions can analysis of operation process of friction pairs be undertaken. Research on wear mechanisms and formation of surface topography at the subsequent stages of operation process (during in vitro testing) analyzed in this work is a new approach to the current problem concerning investigation and analysis of the lifespan of an artificial hip joint. The paper presents issues of artificial hip joint wear mechanisms and methods for studying changes in the surface topography of a ball-and-socket friction pair at the subsequent stages of tribological research. The subjects of research were co-acting components of an artificial hip joint: a metallic ball and a polymeric socket. Tribological tests were performed with a hip joint simulator replicating the physiological movements and working conditions of the natural hip joint. After each stage of tribological tests, the surface texture of friction pair components was measured using a white light interference microscopy. In addition, the surface topography was examined before and after the operation process, using a coordinate measuring machine as well as an optical microscope. Based on the results, changes in surface topography (its functional properties) occurring at the subsequent stages of tribological tests were assessed. The wear mechanisms of the interacting components, i.e. abrasion, fatigue and adhesion, were identified. [ABSTRACT FROM AUTHOR]

Abstract: In a ball-on-disc wear test, an alumina ceramic body sliding against a silicon nitride ceramic body in water achieved an ultra-low friction coefficient (ULFC) of 0.004. The profilometer and EDX measurements indicated that the ULFC regime in this unmated Al2O3–Si3N4 pair was achieved because of the formation of a flat and smooth interface of nanometric roughness, which favored the hydrodynamic lubrication. The triboreactions formed silicon and aluminum hydroxides which contributed to decrease roughness and shear stress at the contact interface. This behavior enables the development of low energy loss water-based tribological systems using oxide ceramics. [Copyright &y& Elsevier]

Abstract: This paper describes future trends in surface metrology. Measurement techniques are briefly mentioned. A special attention was paid to tactile and optical methods. Selected problems of surface topography characterization are described. The effects of sampling and filtering on surface topography representation are analysed. Structured surfaces are becoming both technologically and economically critical. Therefore their description is a problem of a great practical importance. Multi-process textures are very important from functional point of view. Various methods of their description are compared. Surface texturing as a means for enhancing tribological properties of frictional pairs started to be extremely popular from for about last 10 years. The effects of surface texturing on improving tribological properties of sliding assemblies are analysed. The other influences of surface topography are mentioned in this paper. [Copyright &y& Elsevier]

Abstract: The objective of this work was to evaluate a set of standardized metrics proposed for characterizing a surface that has been scratched from a two-body abrasion test. This is achieved by defining a new abrasion region termed ‘Zone of Interaction’ (ZOI). The ZOI describes the full surface profile of all peaks and valleys, rather than just measuring a scratch width as currently defined by the ASTM G 171 Standard. The ZOI has been found to be at least twice the size of a standard width measurement, in some cases considerably greater, indicating that at least half of the disturbed surface area would be neglected without this insight. The ZOI is used to calculate a more robust data set of volume measurements that can be used to computationally reconstruct a resultant profile for detailed analysis. Documenting additional changes to various surface roughness parameters also allows key material attributes of importance to ultimate design applications to be quantified, such as depth of penetration and final abraded surface roughness. Data are presented to show that different combinations of scratch tips and abraded materials can actually yield the same scratch width, but result in different volume displacement or removal measurements; therefore, the ZOI method offers a more robust assessment than the current ASTM analysis method. Furthermore, by investigating the use of custom scratch tips for our specific needs, the usefulness of having an abrasion metric that can measure the displaced volume in this standardized manner, and not just by scratch width alone, is reinforced. This benefit is made apparent when a tip creates an intricate contour having multiple peaks and valleys within a single scratch. This work lays the foundation for updating scratch measurement standards to improve modeling and characterization of three-body abrasion test results. [Copyright &y& Elsevier]

Abstract: The tribosystem consisted of a stationary block pressed at a required load P against a ring rotating at a defined speed. Sliding was unidirectional. Block samples, made from bronze CuSn10P with 138-HB hardness, were modified using a burnishing technique to obtain surfaces with circular oil pockets. Rings were made from 42CrMo4 steel, of hardness 40 HRC, which was obtained after heat treatment. Tests were conducted at a constant speed of 0.27m/s. Before the test, an oil drop was added to lubricate sliding surfaces. A seizure resistance test was carried out at constant normal load of 2700N. Tribotests were automatically stopped when the coefficient of friction reached a limit value 0.15. Selected textured samples clearly exhibited a lifetime longer than untextured reference specimens. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports an experimental study of the effect of surface texture on cylinder liner wear. This research is important because the conjunction between piston rings and cylinder liner is one of the major sources to frictional losses in internal combustion engines. Experiments were conducted on a reciprocating tester. Specimens were cut from cylinder liners honed or plateau honed made of grey cast iron of hardness 218 HB. The honing operation was performed in order to obtain very similar values of the Sq parameter of one-process and two-process surfaces. In addition, one-process specimens characterised by different Sq parameter values were tested. Counter-specimens were made from chromium-coated steel C45. It was found that wear of two-process surfaces was lower than that of one-process surfaces characterized by the same Sq parameter. Linear wear of specimens was proportional to initial Sq parameter value. The effect of additional oil pockets created by the burnishing technique on cylinder liner wear was negligible. [ABSTRACT FROM AUTHOR]

Abstract: Friction and wear are constant problems encountered in camshaft development. Among a wide amount of factors, surface topography is an important feature to improve in this complex system. Four parts of different shapes can be differentiated on an injection cam profile. Therefore the machining of such component is quite particular. Considering the complex shape of an injection cam, this paper is divided in two studies: 1. Variations of surface topography around freshly produced cams in order to emphasize the particular profile of cams which leads to a complex machining. 2. Evolution of surfaces during run-in in order to discover the effects of wear process on a group of roughness parameters. The results show a variation of density of peaks along the freshly produced cam surface and highlight also the importance of roller type on the evolution of topography. Further results show that summits of the surface are rounded off during run-in. Concerning the future, results of the study are encouraging to investigate more deeply the tribological behaviour (contact mechanic, oil film thickness) of the surfaces. [Copyright &y& Elsevier]

In this study, AISI52100 steel surfaces were coated with bilayer Cr–N/TiB 2 thin films in total thickness of 65 and 120 nm by magnetron sputtering. The CrN/TiB 2 thin-films deposited under 10 and 20 sccm N 2 flow whereas no N 2 flow was used for a Cr/TiB 2 thin film. The friction and wear behaviors of these bilayer thin-films consisting of metallic (Cr)/ceramic (TiB 2) and ceramic(CrN)/ceramic(TiB 2) layers were investigated via the tribometer tests under unlubricated and lubricated conditions. Bilayer thin-films were characterized by nanoindentation, microscopic and spectroscopic analysis. Results showed that N 2 flow has significant effects on mechanical characteristics of bilayer coatings. Furthermore, the Cr/TiB 2 thin film with a high porosity showed good tribological performance under 2 GPa contact pressure whereas the CrN/TiB 2 thin film deposited at high N 2 flow with high thickness and hardness showed the best tribological behavior. • Magnetron sputtered bilayer Cr–N/TiB2 thin-films deposited on the AISI52100 steel surface. • The nitriding process had a significant effect on CrN layer thickness and TiB2 microstructure. • The pores filled with lubricant enhanced the lifetime of the bilayer Cr–N/TiB2 coatings. • The metal/ceramic layer with a functional ceramic layer showed different antiwear behaviors. [ABSTRACT FROM AUTHOR]

Abstract: (Ti,Cr)N and (Al,Cr)N thin films were prepared by nitrogen ion beam assisted deposition of Cr, Ti or Al (IBAD) atoms on a titanium, chromium or aluminium substrate. In this way, layers featuring a diverse composition were obtained. The actual profile of the implanted and deposit atoms differed from the theoretically assumed process. Some of the implanted nitrogen formed gas bubbles under the sample''s surface. The gas bubbles released the nitrogen upwards while the local temperature increased during the implantation or during a later heating process. Craters are formed from the bubbles, which were clearly visible on the AFM photographs. Annealing the modified surfaces in a vacuum always changed the surface topography of the sample. The lowest wear rate and the lowest friction coefficient were observed in the Cr–Ti–N and Cr–Al–N samples. [Copyright &y& Elsevier]