The roughness of the contacting asperities in an EHD contact has a significant influence on its load carrying capacity. The use of deterministic models for the simulation of rough contacts has made ...it possible to quantify the effect that certain roughness parameters have on its behaviour. These models set forth the need for artificially generated rough profiles that have specific prescribed properties. Rough surfaces that are produced by various manufacturing processes are most of the times non-Gaussian and have an arbitrary orientation. Therefore a numerical procedure is needed that would allow the generation of rough surfaces that exhibit the aforementioned properties. In this paper, a numerical method is proposed which allows the creation of rough surfaces whose heights follow a general statistical distribution and a given autocorrelation function. The method employs the non-linear Conjugate Gradient Method (NCGM) as well as Fast Fourier Transforms (FFT) in order to cope with storage and time limitations. The results show that the method can adequately produce rough surfaces whose statistical and spectral characteristics match the prescribed values.
Solid asperity interactions are common and inevitable under severe loading conditions for any lubricated contact. Heavy-duty machine components (gears, bearings, etc.) generally operate under Mixed ...Lubrication (ML), where uneven surface features contact each other when the generated fluid pressure is not enough to support the external load. The Reynolds equation is commonly used to simulate smooth lubricated contacts numerically. In rough lubricated interfaces where opposite surface asperities make contact, the Reynolds equation alone cannot accurately predict pressure using the traditional numerical simulation method. In this paper, lubrication–contact interface conditions (LCICs) have been implemented and extended to solve the multiple asperity contact problem using the full-multigrid approach. The developed novel algorithm has significantly accelerated the solution process and improved the accuracy and efficiency of pressure calculation for fluid–solid sub-interactions that can occur in ML regions. The results of the finite difference method (FDM) results have been compared with those of computational fluid dynamics (CFD) simulation to validate the newly developed model. Hence, the proposed optimized solution method will provide valuable insight to researchers and industry engineers interested in simulating the ML problem where the effect of the fluid–solid interface can be captured effectively to improve reliability in the calculation of the life expectancy of the lubricated parts.
A study has been presented on the effects of intrinsic mechanical parameters, such as surface stress, surface elastic modulus, surface porosity, permeability and grain size on the corrosion failure ...of nanocomposite coatings. A set of mechano-electrochemical equations was developed by combining the popular Butler-Volmer and Duhem expressions to analyze the direct influence of mechanical parameters on the electrochemical reactions in nanocomposite coatings. Nanocomposite coatings of Ni with Al₂O₃, SiC, ZrO₂ and Graphene nanoparticles were studied as examples. The predictions showed that the corrosion rate of the nanocoatings increased with increasing grain size due to increase in surface stress, surface porosity and permeability of nanocoatings. A detailed experimental study was performed in which the nanocomposite coatings were subjected to an accelerated corrosion testing. The experimental results helped to develop and validate the equations by qualitative comparison between the experimental and predicted results showing good agreement between the two.
The Reynolds equation defines the lubrication flow between the smooth contacting parts. However, it is questionable that the equation can accurately anticipate pressure behavior involving undeformed ...solid asperity interactions that can occur under severe operating conditions. Perhaps, the mathematical model is inaccurate and incomplete, or some HL (hydrodynamic lubrication) and EHL (elastohydrodynamic lubrication) assumptions are invalid in the mixed lubrication region. In addition, the asperity contact boundary conditions may not have been properly defined to address the issue. Such a situation motivated the recent study of a 3D CFD investigation of Reynolds flow around the solid obstacle modelled in between the converging wedge. The produced results have been compared to analytical and numerical results obtained by employing the Reynolds equation. The validated CFD simulation is compared with the identical wedge, with cylindrical asperity at the center. A significant increase in pressure has been predicted because of asperity contact. The current study shows that the mathematical formulation of the ML problem has shortcomings. This necessitates the development of a new model that can also include fluid flow around asperity contacts for the accurate prediction of generated pressure. Consequently, sustainable tribological solutions for extreme loading conditions can be devised to improve efficiency and component performance.
Rolling element bearings are found in every piece of machinery and are therefore a source of energy losses that cannot be ignored. In recent years a series of energy-efficient bearings have been ...developed using specific designs or new materials aiming to reduce the losses of a bearing without sacrificing its load-carrying capacity. The effect that these designs have on the global energy consumption has not been quantified until now.
A methodology to estimate the energy losses of the usage of a specific bearing type on a global scale is presented in this article. The method, which is based on current standards, provides a first approximation for the determination of the energy losses of bearings and is tested for its plausibility. The pros and cons of the proposed method are discussed, and a proposal is made regarding how to calculate the potential energy efficiency of newer designs.
•The critical damage inside the butterfly wings is measured experimentally.•A new variable (BFI) is introduced to relate butterfly formation to state of stress.•A novel approach is used to couple the ...wing initiation with RCF life.•Severity of different inclusions on RCF is studied relatively.
Non-metallic inclusions such as sulfides and oxides are byproducts of the bearing steel manufacturing process. Stress concentrations due to such inclusions can originate cracks that lead to final failure. This paper proposes a model to simulate subsurface crack formation in bearing steel from butterfly-wing origination around non-metallic inclusions until final failure. A 2D finite element model was developed to obtain the stress distribution in a domain subjected to Hertzian loading with an embedded non-metallic inclusion. Continuum Damage Mechanics (CDM) was used to introduce a new variable called Butterfly Formation Index (BFI) that manifests the dependence of wing formation on depth. The value of critical damage inside the butterfly wings was obtained experimentally and was used to simulate damage evolution. Voronoi tessellation was used to develop the FEM domains to capture the effect of microstructural randomness on butterfly wing formation, crack initiation and crack propagation. Then, the effects of different inclusion characteristics such as size, depth, and stiffness on RCF life are studied. The results show that stiffness of an inclusion and its location have a significant effect on the RCF life: stiffer inclusions and inclusions located at the depth of maximum shear stress reversal are more detrimental to the RCF life. Stress concentrations are not significantly affected by inclusion size for the cases investigated; however, a stereology study showed that larger inclusions have a higher chance to be located at the critical depth and cause failure. Crack maps were recorded and compared to spall geometries observed experimentally. The results show that crack initiation locations and final spall shapes are similar to what has been observed in failed bearings.
This paper presents the study of wear responses of nanocomposite coatings with a steel ball under oscillating-reciprocating state. Nanocomposite coatings for this study include: Nickel-Alumina ...(Ni/Al2O3), Nickel-Silicon Carbide (Ni/SiC), Nickel-Zirconia (Ni/ZrO2) and Ni/Graphene. Ni/ZrO2 exhibited maximum wear rate followed by Ni/SiC, Ni/Al2O3 and Ni/Graphene respectively which was also assured by Scanning Electron Microscopy (SEM) micrographs, grain sizes, hardness, porosity, surface stresses, frictional coefficients behaviours and “U-shaped” wear depth profiles. The “U-shaped” profiles were utilised to calculate the energy distribution (Archard factor density) along the interface. A novel mechano-wear model incorporating the energy distribution equations with the mechanics equations was developed for analysing the effects of intrinsic mechanical properties (such as grain sizes, hardness, porosity, surface stresses of the nanocomposite coatings) on the wear response. The predictions showed close agreement with the experimental results. In conclusion Ni/Graphene exhibited better anti-wear properties compared to other nanocomposite coatings. The high anti-wear behaviour of Ni/Graphene composite is due to enhanced strengthening effects in the presence of graphene. The importance of this work is evident from various industrial applications which require reliable modelling techniques to predict coatings failures due to wear. This work will bring significant impact to precision manufacturing, wind turbine industries, automotive, locomotive and aerospace in overcoming critical wear failures.
•2-D mechano-wear equations have been developed for quantifying the fretting wear processes for nanocomposite coatings.•Model was validated by performing wear tests using Ni/Al2O3, Ni/SiC, Ni/ZrO2 and Ni/Graphene coatings.•The Ni/ZrO2 exhibited the maximum wear rate followed by Ni/SiC, Ni/Al2O3 and Ni/Graphene respectively.•The predictions were in a good agreement with the experimental results.
In this work, pure nickel and Ni-based nanocomposite coatings (Ni–Al
2
O
3
, Ni–SiC and Ni–ZrO
2
) were produced on steel substrate by using pulse electrodeposition technique. The industrial ...performance tests were conducted to evaluate the wear resistance, corrosion resistance, adhesion strength and wettability behaviour of newly developed coatings. Rolling contact ball-on-disc tribometer was used to assess anti-wear behaviour of these coatings under water-lubricated contacts. The results showed that the wear- and corrosion resistance properties of nickel alumina and Ni–SiC composite coatings significantly improved than that of pure Ni and Ni–ZrO
2
coatings. The adhesion and wettability results of Ni–Al
2
O
3
composite showed better performance when compared to the rest of the coatings. The effects of incorporating nanoparticles on the surface microstructure, interface adhesion and distribution of the particles were also investigated. The coatings were characterized by using scanning electron microscopy, X-ray diffraction analysis and 3D white light interferometry. The wear failure behaviour of these coatings was further examined by post-test surface observation under optical microscope.
Synthetic esters are used as lubricants for applications at high temperatures, but their development can be a trial and error process. In this context, molecular dynamics simulations could be used as ...a tool to investigate the properties of new lubricants, in particular viscosity. We employ nonequilibrium molecular dynamics (NEMD) simulations to predict bulk Newtonian viscosities of a set of mixtures of two esters, di(2-ethylhexyl) sebacate (DEHS) and di(2-ethylhexyl) adipate (DEHA) at 293 and 343 K as well as equilibrium molecular dynamics (EMD) and NEMD at 393 K and compare these to experimental measurements. The simulations predict mixture densities within 5% of the experimental values, and we are able to retrieve between 99% and 75% of the experimental viscosities for all ranges of temperature. Experimental viscosities show a linear trend which we are able to capture using NEMD at low temperature and EMD at high temperature. Our work shows that, using EMD and NEMD simulations, and the workflows we developed, we can obtain reliable estimates of the viscosities of mixtures of industrially relevant ester-based lubricants at different temperatures.
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