Fractal simulation of surface topography and prediction of its lubrication characteristics

2021 ◽  
Author(s):  
Jiang Zhao ◽  
zekun wang ◽  
Zhengminqing Li ◽  
Rupeng Zhu
Keyword(s):  
Film Thickness ◽  
Rough Surfaces ◽  
Surface Film ◽  
Fractal Theory ◽  
Morphological Characteristics ◽  
Fractal Surface ◽  
Statistical Parameters ◽  
Machined Surface ◽  
Fractal Parameters ◽  
Lubrication Characteristics

Abstract A machined surface has observable fractal characteristics, with infinite local and overall self-similar consistency. Therefore, the fractal theory is considered to provide a better description of the morphological characteristics of rough surfaces, which accurately reflects the randomness and multi-scale characteristics of rough surfaces and it is not comparable with the surface characteristics obtained based on statistical parameters limited by sampling length and device resolution. In this study, the Weierstrass-Mandelbrot (W-M) function was applied to construct a fractal reconstruction surface, and the mixed elastohydrodynamic lubrication model was used to investigate the lubrication characteristics of real and reconstructed surfaces under the same fractal parameters. The effects of the fractal parameters on the fractal surface lubrication characteristics were further analyzed. The results demonstrate that the lateral roughness fractal surface provides greater resistance to the entrained flow of lubricant, which leads to a larger average film thickness, than the longitudinal roughness and isotropic fractal surface. With the increase in fractal dimension, the surface roughness peak density increases, which reduces the surface film thickness by 47%, and the friction coefficient increases by 46%. The lubrication parameter fluctuates slightly with the change in the number of overlapping ridges M of the fractal surface. Generally, M has little effect on the surface lubrication characteristics.

Static Friction Modeling in the Presence of Soft Thin Metallic Films

2001 ◽  
Vol 124 (1) ◽  
pp. 27-35 ◽  
Author(s):  
Zhiqiang Liu ◽  
Anne Neville ◽  
R. L. Reuben
Keyword(s):  
Thin Film ◽  
Surface Roughness ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Rough Surfaces ◽  
Contact Stiffness ◽  
Surface Film ◽  
Static Friction ◽  
Static Friction Coefficient ◽  
Light Load

A numerical model is presented for computing the static friction coefficient of rough surfaces with a soft thin film. In the calculation, an improved model, based on that due to Derjaguin et al., is used in conjunction with an elastic-plastic contact model for contact with a soft coating. The effects of the film thickness and surface roughness on the static friction coefficient and contact are investigated. The numerical results reflect published experimental observations and show the static friction coefficient depends strongly on surface film thickness, external force and surface roughness. The static friction coefficient (μ) increases with the surface film thickness when the plasticity index ψ⩾0.5 whilst μ increases with decreasing film thickness in the very thin film regime when ψ=0.25 and F/AnE<10−4. For real rough surfaces, contact and friction behavior is probably heavily influenced by the existence of such soft, thin surface films, which increase the contact area due to plastic deformation of the film and the contact stiffness of the surface in the case of thin film and light load.

Surface Films on Zircaloy-2 Samples Cracked in Neutral Aqueous NaCl by Stress Corrosion

1973 ◽  
Vol 31 ◽  
pp. 46-47
Author(s):  
R.A. Ploc
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Film Thickness ◽  
Stress Corrosion ◽  
Zirconium Dioxide ◽  
Surface Film ◽  
Surface Films ◽  
Continuous Layer ◽  
Transmission Electron ◽  
Product Film

Samples of low-nickel Zircaloy-2 (material MLI-788-see(1)), when anodically polarized in neutral 5 wt% NaCl solutions, were found to be susceptible to pitting and stress corrosion cracking. The SEM revealed that pitting of stressed samples was occurring below a 2000Å thick surface film which behaved differently from normal zirconium dioxide in that it did not display interference colours. Since the initial film thickness was approximately 65Å, attempts were made to examine the product film by transmission electron microscopy to deduce composition and how the corrosion environment could penetrate the continuous layer.

A Starved Mixed Elastohydrodynamic Lubrication Model for the Prediction of Lubrication Performance, Friction and Flash Temperature With Arbitrary Entrainment Angle

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Wei Pu ◽  
Dong Zhu ◽  
Jiaxu Wang
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Industrial Applications ◽  
Operating Conditions ◽  
Flash Temperature ◽  
Machined Surface ◽  
Lubrication Performance ◽  
Wide Range ◽  
Starved Lubrication

In this study, a modified mixed lubrication model is developed with consideration of machined surface roughness, arbitrary entraining velocity angle, starvation, and cavitation. Model validation is executed by means of comparison between the obtained numerical results and the available starved elastohydrodynamic lubrication (EHL) data found from some previous studies. A comprehensive analysis for the effect of inlet oil supply condition on starvation and cavitation, mixed EHL characteristics, friction and flash temperature in elliptical contacts is conducted in a wide range of operating conditions. In addition, the influence of roughness orientation on film thickness and friction is discussed under different starved lubrication conditions. Obtained results reveal that inlet starvation leads to an obvious reduction of average film thickness and an increase in interasperity cavitation area due to surface roughness, which results in significant increment of asperity contacts, friction, and flash temperature. Besides, the effect of entrainment angle on film thickness will be weakened if the two surfaces operate under starved lubrication condition. Furthermore, the results show that the transverse roughness may yield thicker EHL films and lower friction than the isotropic and longitudinal if starvation is taken into account. Therefore, the starved mixed EHL model can be considered as a useful engineering tool for industrial applications.

scholarly journals Spatial model of the gecko foot hair: functional significance of highly specialized non-uniform geometry

2015 ◽  
Vol 5 (1) ◽  
pp. 20140065 ◽  
Author(s):  
Alexander E. Filippov ◽  
Stanislav N. Gorb
Keyword(s):  
Functional Significance ◽  
Spatial Model ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Intermolecular Forces ◽  
Dimensional Structure ◽  
Fractal Surface ◽  
Flexible Form ◽  
Spatial Geometry ◽  
Adhesive Contacts

One of the important problems appearing in experimental realizations of artificial adhesives inspired by gecko foot hair is so-called clusterization. If an artificially produced structure is flexible enough to allow efficient contact with natural rough surfaces, after a few attachment–detachment cycles, the fibres of the structure tend to adhere one to another and form clusters. Normally, such clusters are much larger than original fibres and, because they are less flexible, form much worse adhesive contacts especially with the rough surfaces. Main problem here is that the forces responsible for the clusterization are the same intermolecular forces which attract fibres to fractal surface of the substrate. However, arrays of real gecko setae are much less susceptible to this problem. One of the possible reasons for this is that ends of the seta have more sophisticated non-uniformly distributed three-dimensional structure than that of existing artificial systems. In this paper, we simulated three-dimensional spatial geometry of non-uniformly distributed branches of nanofibres of the setal tip numerically, studied its attachment–detachment dynamics and discussed its advantages versus uniformly distributed geometry.

A stress sensitivity model for the permeability of porous media based on bi-dispersed fractal theory

2018 ◽  
Vol 29 (02) ◽  
pp. 1850019 ◽  
Author(s):  
X.-H. Tan ◽  
C.-Y. Liu ◽  
X.-P. Li ◽  
H.-Q. Wang ◽  
H. Deng
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Fractal Theory ◽  
Stress Sensitivity ◽  
Maximum Diameter ◽  
Proposed Model ◽  
Fractal Parameters ◽  
Stress Changes ◽  
Capillary Bundle ◽  
Definition Of

A stress sensitivity model for the permeability of porous media based on bidispersed fractal theory is established, considering the change of the flow path, the fractal geometry approach and the mechanics of porous media. It is noted that the two fractal parameters of the porous media construction perform differently when the stress changes. The tortuosity fractal dimension of solid cluster [Formula: see text] become bigger with an increase of stress. However, the pore fractal dimension of solid cluster [Formula: see text] and capillary bundle [Formula: see text] remains the same with an increase of stress. The definition of normalized permeability is introduced for the analyzation of the impacts of stress sensitivity on permeability. The normalized permeability is related to solid cluster tortuosity dimension, pore fractal dimension, solid cluster maximum diameter, Young’s modulus and Poisson’s ratio. Every parameter has clear physical meaning without the use of empirical constants. Predictions of permeability of the model is accordant with the obtained experimental data. Thus, the proposed model can precisely depict the flow of fluid in porous media under stress.

An adjustable oil film thickness test rig for detecting lubrication characteristics of slipper/swash-pair in piston pumps

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Haiji Wang ◽  
Guanglin Shi
Keyword(s):  
Film Thickness ◽  
Peer Review ◽  
Relative Error ◽  
Mathematical Analysis ◽  
Test Rig ◽  
Content Type ◽  
Oil Film ◽  
Displacement Sensors ◽  
Measuring Machine ◽  
Lubrication Characteristics

Purpose The purpose of this paper is to propose an adjustable oil film thickness test rig for detecting lubrication characteristics of the slipper. The mathematical analysis of lubrication is introduced. Based on the results from the test rig, the results comparison from test rig and mathematical analysis is carried out. Design/methodology/approach This paper introduces a mechanism which can adjust the oil film thickness between the slipper and swash-plate. Feasibility is ensured, and the accuracy of test rig is guaranteed by the three-coordinate measuring machine. Three displacement sensors show the oil film thickness and its shape. The reacting force and torque resulting from oil film can be achieved by three S-type force sensors and a torque sensor, respectively. Findings The relative error of the reacting force is small. The relative error reduces and is acceptable when the deformation of retainer is taken into account. The thickness and tilt angle of oil film have less effect on the reacting force. However, they are significantly impact on torque. Originality/value The test rig proposed in this paper is able to adjust the oil film thickness, which is used to detecting the lubrication characteristics in pump design. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2020-0166/

Coupling fractal model for fretting wear on rough contact surfaces

2020 ◽  
pp. 1-32
Author(s):  
Yi Wang ◽  
Gang Liang ◽  
Shuo LIU ◽  
Yi Cui
Keyword(s):  
Contact Surface ◽  
Fractal Theory ◽  
Three Dimensional ◽  
Parameter Analysis ◽  
Fretting Wear ◽  
Wear Depth ◽  
Contact Parameter ◽  
Wear Process ◽  
Actual Surface ◽  
Fractal Parameters

Abstract In this paper, a fretting damage model based on fractal theory is proposed. The Weierstrass-Mandelbrot function of fractal theory is used to represent the rough contact surface, and a corresponding contact parameter analysis method is also established. Based on neural network algorithm, the values of fractal parameters are fitted, and the fitting accuracy has been greatly improved compared with traditional methods. According to the fractal parameters of the actual surface, the fretting wear process of the rough contact surface is analyzed based on theory of adhesive and three body abrasive wear. A generic program for the analysis of three-dimensional fretting wear problems is also proposed. Compared with material tests, the prediction error of fretting wear simulation model is 13.4% for wear depth and 16.7% and 3.9% for width and length of wear scar in stable wear stage. The prediction results show that the model can be applied to the prediction of the actual three-dimensional fretting wear model.

A normal contact stiffness model of machined joint surfaces considering elastic, elasto-plastic and plastic factors

2019 ◽  
Vol 234 (7) ◽  
pp. 1007-1016 ◽  
Author(s):  
Yongquan Zhang ◽  
Hong Lu ◽  
Xinbao Zhang ◽  
He Ling ◽  
Wei Fan ◽  
...  
Keyword(s):  
Surface Topography ◽  
Contact Stiffness ◽  
Fractal Theory ◽  
Fractal Model ◽  
Single Pair ◽  
Machined Surface ◽  
Normal Contact ◽  
Joint Surfaces ◽  
Stiffness Model ◽  
Normal Contact Stiffness

Considering the rough surface as a fractal model makes the research of contact parameters more practical. In the fractal model of the machined surface, the parameters describing the surface topography are independent of the measurement resolution. Based on the elastic, elasto-plastic and plastic deformations of a single pair of contact asperities, a normal contact stiffness model using the fractal model for surface topography description is proposed in this paper. The specimens machined by milling and grinding methods are used to verify the proposed contact stiffness model based on the fractal theory. The experimental and theoretical results indicate that the proposed contact stiffness model is appropriate for the machined joint surfaces.

An Investigation Into the Influence of Fluid Viscoelasticity in a Squeeze Film Bearing

1978 ◽  
Vol 100 (1) ◽  
pp. 56-64 ◽  
Author(s):  
John A. Tichy ◽  
Ward O. Winer
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
High Molecular Weight ◽  
Hydrodynamic Lubrication ◽  
Load Capacity ◽  
Surface Film ◽  
Free Fall ◽  
Squeeze Film ◽  
Delayed Response ◽  
High Molecular Weight Polymers

This investigation concerns a prediction of the behavior of viscoelastic fluids in a parallel circular squeeze film with a constant approach velocity, and a comparison to experimental results. The squeeze film geometry has direct application to unsteady hydrodynamic lubrication. The analysis predicts that load capacity of a viscoelastic fluid may be increased due to normal stress effects or decreased due to a delayed response of shear stress to a change in shear rate. Ten tested fluids include Newtonian control fluids, silicone fluids, high molecular weight polymers in petroleum oils, and extremely high molecular weight polymers in water and glycerin. The experimental squeezing is accomplished by the free fall of a cylindrical steel rod along its axis toward a stationary opposing surface. Film thickness, velocity of approach and load are measured. The velocity of approach is essentially constant in the range of film thickness considered. The water-glycerin-polymer solutions exhibited load capacity increases up to 33 percent, while the petroleum-polymer and silicone fluids showed decreases to 23 percent. It appears that viscoelastic effects cannot account for the reported improved bearing performance of polymer-additive lubricants.

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