An analytical approach for analysis and optimisation of slider bearings with infinite width parallel textures

This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to lubricant flow rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings

Combined experimental and multiphase computational fluid dynamics analysis of surface textured journal bearings in mixed regime of lubrication

This paper investigates the effect of surface texturing in a partial pad journal bearing through a series of controlled experiments at operating conditions, promoting mixed or boundary regimes of lubrication. Improvements to load carrying capacity are observed under certain operating conditions. A comprehensive computational finite volume multiphase fluid dynamics analysis, including vapour transport equation and modified finite-size cavity Rayleigh-Plesset model, is used to study the effect of indented surface textures in the microscale contact domain and within the individual textures themselves. The results show improved conditions with a textured journal through promotion of micro-hydrodynamic effect, delaying the effect of lubricant rupture, thus extending the effective load bearing region. A very good agreement is obtained between measurements and predictions

Combined experimental and multiphase computational fluid dynamics analysis of surface textured journal bearings in mixed regime of lubrication

This paper investigates the effect of surface texturing in a partial pad journal bearing through a series of controlled experiments at operating conditions, promoting mixed or boundary regimes of lubrication. Improvements to load carrying capacity are observed under certain operating conditions. A comprehensive computational finite volume multiphase fluid dynamics analysis, including vapour transport equation and modified finite-size cavity Rayleigh-Plesset model, is used to study the effect of indented surface textures in the microscale contact domain and within the individual textures themselves. The results show improved conditions with a textured journal through promotion of micro-hydrodynamic effect, delaying the effect of lubricant rupture, thus extending the effective load bearing region. A very good agreement is obtained between measurements and predictions

Effect of laser texturing on the performance of ultra-hard single-point cutting tools

This paper investigates the cutting performance and anti-adhesive properties of textured single point polycrystalline diamond (PCD) cutting tools in machining Aluminium 6082 alloys. The micro/nano textures were first milled using a fibre laser (1064 nm wavelength) at different power intensities, feed speeds and pulse durations, and finally characterised using scanning electron microscopy, white light interferometry and energy dispersive X-ray spectroscopy. The effect of different textures on the cutting performance was investigated in turning tests under dry cutting conditions. The test was stopped at regular lengths of cut to allow analysis of height of adhesion through 3D white light interferometry. The data processing of the cutting forces and the microscopical characterisation of the tested cutting tools enabled the evaluation of the effects of texture design, friction coefficient and adhesive properties. The results indicated that feed force in tools with grooves perpendicular to the chip flow direction (CFD) was more stable (20-40N) than the benchmark (6-41N). Similarly, the thrust force for tools with grooves parallel to CFD and grooves perpendicular to CFD showed a homogeneous trend fluctuating between 60N to 75N as compared to the benchmark (ranging between 73N to 90N). For texture depth in the order of 260 nm and post process roughness in the order of tens of nanometers a reduction of average friction coefficient (0.28±0.14) was reported when using lasered inserts with grooves parallel to the chip flow direction compared to the benchmark tools (0.34±0.26) corroborated by reduced stiction of workpiece material on the rake face. In machining via textured tools with grooves perpendicular to CFD, the cutting forces were reduced by 23%, and the surface quality of the machined workpiece was improved by 11.8%, making this geometry the preferred choice for finishing applications. Using grooves parallel to CFD reduced the cutting forces by 11.76%, adhesion by 59.36% and friction coefficient by 14.28%, however it increased the surface roughness of the machined workpiece, making this geometry suitable for roughing operations. For the first time, laser manufacturing is proposed as a flexible technique to functionalise the geometrical and wear properties of PCD cutting tools to the specific applications (i.e. roughing, finishing) as opposed to the standard industrial approach to use microstructurally different PCDs (i.e. grain size and binder%) based on the type of operation. </div

Experimental and Analytical Study of the Surface Texturing Enhanced Lubrication Elements

Surface texturing is a method that modifies the frictional surface of a nominally flat tribocomponent by shallow patterns. It is found that with added patterns to the surface of a mechanical face seal or thrust bearing, their tribological performance improves, i.e. both friction and wear rate decrease. The current research concentrates on the analysis of hydrodynamic effect responsible for the performance enhancement of the spiral groove patterns and dimples on mechanical seal-like structures and the experimental evaluation of the tribological behavior of these structures. Surface textures considered are: dimple texture and spiral groove pattern. In the research on the dimple textures, the cavitation effect of the dimple enhanced friction pair is modeled using a mass-conservative theory – the Jakobsson-Floberg-Olsson (JFO) cavitation theory. Roughness effect is considered in the analysis of the dimple pattern performance. A thermohydrodynamic model is also developed to examine the influence of the temperature on the performance of the dimple textured frictional pair. The experiments on the dimple textured frictional pair are conducted on heat-treated 17-4 PH stainless steel specimens. The surface textures of the specimens are created by means of Nd:Ytterbium fiber laser. The laser surface textured specimens provide low coefficient of friction compared with plain (dimple free) surfaces. However, for the material used in the current experiments, the surface texture decreases the surface’s resistance to wear. In the research on the spiral groove pattern, the thermohydrodynamic model of the spiral groove surface seal is created. A commercially available CFD code – CFD-ACE+– is used for this purpose. The result shows that spiral grooves have significant influence on the seal’s thermal and load-carrying capacity behaviors. The experimental specimens on the spiral groove patterned friction pair research are made the same way as the dimple textured frictional pair. In this research spiral groove thrust bearings with variety of spiral angles subjected to different loads and speeds are tested. The frictional behaviors of the spiral groove thrust bearings are analyzed. In addition, a theoretical model is developed to gain further insight into the frictional characteristics of spiral grooves in both the hydrodynamic regime and the mixed lubrication regime

Optimization of partially textured parallel thrust bearings with square-shaped micro-dimples

In this study we attempt to find the optimum geometrical parameters of square-shape micro-dimples imposed on parallel flat bearing surfaces which give the best tribological performance, including load capacity and friction coefficient. An analytical solution of Reynolds equation for the surfaces involving numerous dimples is presented, then considering the variations of number of dimples as well as dimple length and height ratios for a constant dimpled length, it is tended to get the optimum value of parameters. It is shown that despite the variations of different studied geometrical parameters, it seems the optimum value of these parameters remain nearly constant

A Review of Surface Texturing in Internal Combustion Engine Piston Assembly

This paper presents a brief review of surface texturing with a focus on piston assembly application. The paper begins with a general discussion on surface texturing and the manufacturing process of micro dimples.&nbsp; Further, it discusses the theory of hydrodynamic lift generation and the effect of parameters of micro dimples texture on the surface-to-surface friction. Finally, the effect of surface texturing on heat transfer is briefly discussed. In pursuits to improve internal combustion engine (ICE) efficiency, tribological improvement of moving surfaces by means of micro surface texturing seems to be one of the way. However, texturing parameters have to be carefully designed as it can cause detrimental effect if the designs are wrong. Studies has shown micro surface texturing at piston ring could reduce friction around 20%-50% compare with un-textured piston ring and also reduce fuel consumption at 4%. Micro Surface texturing could also improve heat transfer between the surfaces to reduce piston slap and lubrication oil temperature. As reports on the surface texturing on friction reduction and heat transfer improvement in piston assembly are relatively scarce, it is suggested that optimization of micro dimple parameters for piston skirt application and its effect on engine tribology and heat transfer characteristics be further investigated

Combined analytical and experimental evaluation of frictional performance of lubricated untextured and partially textured sliders

The study of textured surface performance is one of the highly researched topics in recent times. This is mainly due to the advantages that such surfaces can potentially provide in practice, in mitigating adverse tribological conditions, such as friction and wear. However, considering the complexities found in practice, a methodological analysis and evaluation procedure is essential in order to gain an understanding of the benefits from utilising such features in a given contact. The current study provides a combined analytical and experimental approach towards an enhanced understanding of the behaviour of textured surfaces relative to their untextured counterparts. The developed analytical models are invaluable in providing an insight into the relationship between the many parameters involved in defining even simple surface texture feature geometry and the expected outcomes in practice, when corroborated with experimental results. The current study reports on such an endeavour. With the studied texture configuration, the results have shown the possibility of reducing friction by as much as 25%

Multi-phase thermal cavitation flow in rough conforming and partially conforming conjunctions

The main aim of this research was to investigate the mechanism of cavitation in conforming and partially conforming tribological conjunctions. The effect of cavitation on load carrying capacity and frictional performance of is also investigated. This is important with regards to fuel efficiency in internal combustion (IC) engines. Friction accounts for 15–20% of IC engine losses. The piston–cylinder system contributes to 40–50% of these, with the compression ring(s) being responsible for most of this. This is because the primary function of the ring is to seal the combustion chamber, thus small emerging gaps lead to increased friction. In fact, compression ring(s) expend 3–5% of engine input fuel energy. The share of frictional losses of engine bearings is approximately 20–25%. Traditionally, prediction of performance of tribological conjunctions has been studied using Reynolds equation. When the effect of cavitation is considered, various cavitation algorithms with associated boundary conditions for lubricant rupture and reformation are proposed. These include Elrod, and Elrod and Coyne algorithms, as well as boundary conditions such as Swift-Stieber, JFO and Prandtl-Hopkins. There are a number of assumptions embodied in these approaches, as well as the use of Reynolds equation itself. These approaches do not uphold the continuity of mass and momentum in multi-phase flow, in cavitation beyond the lubricant film rupture. A detailed methodology for multi-phase flow, comprising simultaneous solution of Navier-Stokes, energy and lubricant rheological state equations is developed. [Continues.

EXPERIMENTAL BENCHMARKING OF SURFACE TEXTURED LIP SEAL MODELS

A thorough investigation on the existing hydrodynamic lubrication theories and the reverse pumping theories for the conventional lip seal is conducted. On that basis, the algorithms and the methods used in the numerical modeling of the conventional lip seal are modified and applied to the study of the lip seal running against surface textured shafts. For each step of the study, the numerical model is benchmarked against the experimental results. Important physical mechanisms which explain the reverse pumping ability of the triangular surface structures are revealed. Meanwhile, the accuracy of the numerical model is tested. In general, the numerical simulation results match the experimental observation well. However, there are several important discrepancies. For each discrepancy the possible causes are discussed, which benefits the further attempts of the modeling work on the lip seal running against surface textured shafts. The conclusions of this study themselves can be used as a guidance to the design of the surface textured shafts for the lip seal applications. Finally the limitation of the current theories and the modeling methods are discussed and reasonable improvements which can be done are proposed for the future work