Contact Surface Roughness Research Articles

Research on Hydrophilic Nature of Polyvinylpyrrolidone on Polysulfone Membrane Filtration

The membranes used in wastewater filtration are obtained from polymers, this technique is widely applied because of the small installations and low costs as against conventional systems. The polymeric membranes have high mechanical strength and flexibility, but is a challenge to improve in the same time the permeability and retention capacity of the membranes. A process that can improve the membrane properties is the addition of additives to the polymer solution, resulting in noticeable changes in the resulting membrane structure. Polyvinylpyrrolidone (PVP) is a highly hydrophilic polymer, used as a food additive that acts as stabilizer and thickening agent, which brings improvements in membrane properties. This study analyses the effect of polyvinylpyrrolidone (PVP) on the casting solution of the prepared membranes. The polymer solution was prepared from polysulfone (PSf) and N-methyl-2-pyrrolidone (NMP) at different concentrations. The membranes were obtained by phase inversion method. The PSf/PVP/NMP membranes with different concentrations were characterized by contact angle measurements, surface roughness, morphological structure and permeation tests. The results show that the hydrophilic nature of PVP improve the pure water flux, the contact angle and exhibit a higher anti-fouling property.

The study of anisotropic rough surfaces contact considering lateral contact and interaction between asperities

Abstract Interfacial performances are dissimilar due to the different surface topographies and materials. The aim of this paper is to study the effect of the surface topography on the contact force, contact area and contact stiffness. The distributions of the contact azimuthal angles and the contact angles were introduced in the model to build an anisotropic interface model, which includes the asperity lateral contact and the interaction. The simulation results indicate that the normal contact force, real contact area and contact stiffness decrease with the increasing separation. The standard deviations of asperity heights and asperity contact angles have significant influences on the contact of rough surfaces, while the interfacial anisotropy does not influence the contact performances in the normal direction.

Numerical Prediction of Surface Wear and Roughness Parameters During Running-In for Line Contacts Under Mixed Lubrication

A stochastic model for predicting the evolutions of wear profile and surface height probability density function (PDF) of initial line contacts during running-in under mixed lubrication condition is presented. A numerical approach was developed on the basis of stochastic solution of mixed lubrication, which combined the Patir and Cheng's average flow model for calculation of the hydrodynamic pressure and the Kogut and Etsion's (KE) rough surface contact model for calculation of the asperity contact pressure. The total friction force was assumed to be the sum of the boundary friction at the contact asperities and the integration of viscous shear stress in the hydrodynamic region. The wear depth on the contact region was estimated according to the modified Archard's wear model using the asperity contact pressure. Sugimura's wear model was modified and used to link the wear particle size distribution and the variation of surface height PDF during wear. In the wear process, the variations of profile and surface height PDF of initial line contacts were calculated step by step in time, and the pressure distribution, friction coefficient, and wear rate were updated consequently. The effect of size distribution of wear particles on the wear process was numerically investigated, and the simulation results showed that the lubrication condition in which small wear particles are generated from the asperity contact region is beneficial to reduce friction coefficient and wear rate, and leads to a better steady mixed lubrication condition.

On the Problem of the Relationship between the Contact Angle and Surface Roughness Coefficient: Quartz Wettability with Melted Germanium

Equilibrium contact angles of melted geranium have been measured at fused quartz surfaces. The surfaces were preliminarily grinded, polished, and, in some cases, etched. Then, the roughness coefficients are determined for the relief profile and the surface itself by optical interferometry using a NanoMap 1000 WLI profilometer. The contact angle has been found to vary in a range of 147°–164° depending on the method of surface pretreatment. The measured values of the contact angles agree with the data of other researchers. At the same time, the analysis of the obtained data has led to the conclusion that Wenzel’s equation, which relates the contact angles at smooth and rough surfaces, is not valid for germanium droplets on quartz surface.

Physics-Based Modeling for Lap-Type Joints Based on the Iwan Model

This study proposed a physics-based heuristic modeling for the nonlinear constitutive relation of bolted joints based on the Iwan model accompanying with the rough surface contact theory. The approach led to an Iwan distribution function which possesses the tribology-related features of the contact interface. In particular, the break-free force distribution function of the Jenkins elements could be expressed in terms of height distribution of surface asperities. The model considered the contribution of elastically, elasto-plastically as well as plastically deformed asperities to the total tangential loads. Following this, constitutive relations for lap-type bolted joints and the corresponding backbone curves, hysteresis loops, and energy dissipation per cycle were obtained. A model application was implemented and the results were compared with the published experimental results. The proposed model agrees very well with the experimental results when the contact parameters met the actual contact situation. The obtained results indicated that the model can be used to study the tangential behaviors of rough surfaces.

The Impact of the Convex Friction Distribution on the Seismic Response of a Spring-friction Isolation System

As for structures with rubber bearings during earthquakes, some firstly damaged bearings and the other normal bearings form a typical spring-friction isolation system. Furthermore, a rough contact surface, due to the stochastic damage of bearing, and the around smooth contact surfaces form a convex distribution of friction coefficient. This paper attempts to analyze seismic responses of a spring-friction isolation system with a theoretically and linearly convex friction distribution, in which the friction coefficient gradually decreases with the distance from the center. The results show that such friction distribution inevitably increases the structural relative displacement and possibly enlarges the structural acceleration and residual displacement under earthquakes. The convex pattern of friction distribution should be avoided in practical engineering, since it reduces the seismic isolation efficiency.

Passive Intermodulation of Contact Nonlinearity on Microwave Connectors

For the passive intermodulation (PIM) problem of nonlinear contact on microwave connectors, an effective method is presented to improve the computational accuracy of PIM. First of all, the contact stress distribution on contact surface is analyzed by finite-element method based on the Weierstrass-Mandelbrot model. The contact stress and real area of contact are evaluated under different loading conditions. Then, the electrical parameters of physical effects of nonlinear contact are derived based on the electric contact theory and the physical effects of metal-metal microcontact. Finally, the nonlinear I-V relation is established from the microcontact equivalent circuit, and the third-order PIM power level generated by contact nonlinearity is revealed in analytic form. The analytic results are verified by the PIM test experiments. This work provides a novel way for PIM calculation of rough surface contact.

Static and sliding contact of rough surfaces: Effect of asperity-scale properties and long-range elastic interactions

Friction in static and sliding contact of rough surfaces is important in numerous physical phenomena. We seek to understand macroscopically observed static and sliding contact behavior as the collective response of a large number of microscopic asperities. To that end, we build on Hulikal et al. (2015) and develop an efficient numerical framework that can be used to investigate how the macroscopic response of multiple frictional contacts depends on long-range elastic interactions, different constitutive assumptions about the deforming contacts and their local shear resistance, and surface roughness. We approximate the contact between two rough surfaces as that between a regular array of discrete deformable elements attached to a elastic block and a rigid rough surface. The deformable elements are viscoelastic or elasto/viscoplastic with a range of relaxation times, and the elastic interaction between contacts is long-range. We find that the model reproduces the main macroscopic features of evolution of contact and friction for a range of constitutive models of the elements, suggesting that macroscopic frictional response is robust with respect to the microscopic behavior. Viscoelasticity/viscoplasticity contributes to the increase of friction with contact time and leads to a subtle history dependence. Interestingly, long-range elastic interactions only change the results quantitatively compared to the meanfield response. The developed numerical framework can be used to study how specific observed macroscopic behavior depends on the microscale assumptions. For example, we find that sustained increase in the static friction coefficient during long hold times suggests viscoelastic response of the underlying material with multiple relaxation time scales. We also find that the experimentally observed proportionality of the direct effect in velocity jump experiments to the logarithm of the velocity jump points to a complex material-dependent shear resistance at the microscale.

Interaction between contact behaviour and vibrational response for dry contact system

Abstract This work wants to provide insights on the coupling between contact behaviour (local scale) and vibrational response (global scale) which brings to different contact scenarios arising in dry frictional systems. A newer setup, named TriboWave, has been developed in order to reproduce and investigate the system response to frictional contact, under well-controlled boundary conditions. The experimental results highlighted how a simple frictional system can switch from stable friction-induced vibrations to unstable vibrations, i.e. either macroscopic stick–slip instabilities or mode coupling instabilities. The effect of the contact surface roughness on the reproduced frictional scenario has been investigated too.

Stability analysis of rough surfaces in adhesive normal contact

This paper deals with adhesive frictionless normal contact between one elastic flat solid and one stiff solid with rough surface. After computation of the equilibrium solution of the energy minimization principle and respecting the contact constraints, we aim at studying the stability of this equilibrium solution. This study of stability implies solving an eigenvalue problem with inequality constraints. To achieve this goal, we propose a proximal algorithm which enables qualifying the solution as stable or unstable and that gives the instability modes. This method has a low computational cost since no linear system inversion is required and is also suitable for parallel implementation. Illustrations are given for the Hertzian contact and for rough contact.

Determination of wear coefficient in mixed lubrication using FEM

• The wear coefficient in mixed lubrication is determined by FEM. • The roughness of contact surfaces is characterized as fractal surfaces. • The sliding wear in mixed lubrication is simulated by the CEL method. • An example of the wear coefficient changes with the oil film thickness is given. In a line or point contact with an elastohydrodynamic lubricant oil film, solid-to-solid contacts are common and wear will occur at these places. Given that there is only a portion of the load is supported by the direct interaction of roughness asperities, the wear coefficient should be less than that for dry contacts and account for the effect of surface roughness and oil film. Since it is difficult to obtain the wear coefficient value at different oil film thickness by experiments, this paper presents the methodology of determination of wear coefficient in mixed lubrication using finite element method (FEM). In this method, the roughness of contact surfaces is characterized as fractal surfaces by the Weierstrass–Mandelbrot (W–M) function, the sliding wear in mixed lubrication is simulated by the Coupled-Eulerian–Lagrangian (CEL) method and the wear volume is calculated according to the solid–solid contact load. Then the wear coefficient can be determined and the simulation example shows that the wear coefficient decreases nonlinearly with the increasing of oil film thickness and dynamic viscosity in mixed lubrication.

A Comparative Study on Equivalent Modeling of Rough Surfaces Contact

Greenwood and Tripp (GT model) have proposed that the contact analysis of two rough surfaces (two-rough-surface contact model) could be considered as an equivalent rough surface in contact with a rigid flat (single-rough-surface contact model). In this paper, by virtue of finite element method, the normal contact analysis was performed with two-rough-surface contact model and its equivalent single-rough-surface contact model, and it was verified that the resultant normal contact forces are in good agreement with each other for these two models, meanwhile the equivalent stress is a little bit lower for two-rough-surface model due to shoulder-to-shoulder contact. In contrast, the sliding contact analysis was also performed with these two models, respectively, and the results show a great disparity with each other in all contact parameters due to the strong plowing effects in two-rough-surface model. Therefore, this equivalence approach proposed by Greenwood and Tripp is only valid for normal contact of rough surfaces and not valid for sliding contact.

Investigation of the antibiofilm capacity of peptide-modified stainless steel.

Biofilm formation on surfaces is an important research topic in ship tribology and medical implants. In this study, dopamine and two types of synthetic peptides were designed and attached to 304 stainless steel surfaces, aiming to inhibit the formation of biofilms. A combinatory surface modification procedure was applied in which dopamine was used as a coupling agent, allowing a strong binding ability with the two peptides. X-ray photoelectron spectroscopy (XPS), elemental analysis, contact angle measurement and surface roughness test were used to evaluate the efficiency of the peptide modification. An antibiofilm assay against Staphylococcus aureus was conducted to validate the antibiofilm capacity of the peptide-modified stainless steel samples. XPS analysis confirmed that the optimal dopamine concentration was 40 µg ml−1 in the coupling reaction. Element analysis showed that dopamine and the peptides had bound to the steel surfaces. The robustness assay of the modified surface demonstrated that most peptide molecules had bound on the surface of the stainless steel firmly. The contact angle of the modified surfaces was significantly changed. Modified steel samples exhibited improved antibiofilm properties in comparison to untreated and dopamine-only counterpart, with the peptide 1 modification displaying the best antibiofilm effect. The modified surfaces showed antibacterial capacity. The antibiofilm capacity of the modified surfaces was also surface topography sensitive. The steel sample surfaces polished with 600# sandpaper exhibited stronger antibiofilm capacity than those polished with other types of sandpapers after peptide modification. These findings present valuable information for future antifouling material research.

A new elliptical microcontact model considering elastoplastic deformation

A new elliptical microcontact model considering elastoplastic deformation is proposed to overcome the shortcomings of the existing elastoplastic microcontact model. A new low-order interpolation function is used to describe the relationship between the normal deformation of asperity and the mean contact pressure in the elastoplastic deformation stage, and a smooth, continuous, monotonic change curve of the mean contact pressure is obtained. Then, the contact of rough surfaces is studied based on the new elastoplastic elliptical microcontact model and the height distribution of asperity. The calculated results are compared with those obtained from the existing rough surface contact models and the comparisons show that: (1) the change curve for the average contact pressure in the new model is smooth, continuous, and monotonic; (2) the calculation results of the new model are consistent with the numerical results based on the finite element method; (3) the new model is helpful to study the rough surface contact analysis of the elliptical micro-convex body.

Statistical contact model of rough surfaces: The role of surface tension

The sizes of most asperities on actual rough surfaces range from nanometers to microns. Recent investigations reveal that surface tension plays an important role in micro-/nano-sized contact. Therefore, in this paper, we address the influence of surface tension on the elastic contact of rough surfaces. Nayak's model is employed to describe rough surface with stochastic distribution of both heights and curvatures. As a fundament, we present the general relations of contact area and load as the function of indent depth for a single micro-/nano-sized asperity by accounting for surface tension. Based on the refined relations, we derive the general relations concerned in the contact of rough surfaces. Compared with the conventional multi-asperity contact models based on the Hertzian contact theory, the existence of surface tension decreases the real contact area and requires higher load to generate a given indent depth. It is found that the area of intimate contact is still approximately proportional to the external load, but the proportionality depends on the surface tension.

On the DMT adhesion theory: from the first studies to the modern applications in rough contacts

In the last years, increasing interest has been devoted to the study of the adhesion between rough media. The Derjaguin, Muller & Toporov (DMT) theory is one of the most known models to describe adhesion between hard elastic solids with long range adhesive interactions. However, many versions of the DMT theory can be found in the literature.In the first part of the present work, we try to make order about the various versions of the DMT theory appeared over the years. All models, often confusedly called with the same name ”DMT theory”, are based on the same assumption of neglecting deformations due to the adhesive forces. They predicts the same value of the detachment force at the pull-off, but only the so-called DMT force approach correctly captures the evolution trend of the adhesive force during the contact.In the second part of the work, we address the problem to include adhesion in the contact of rough surfaces according to the DMT theory. Specifically, we compare the Maugis’ idea to add adhesion in the Greenwood and Williamson asperity theory, with more recent models: the Interacting and Coalescing Hertzian Asperities (ICHA) one and the Persson’s theory. The two models, which both take account of adhesion according to the DMT force approach, give very similar results, showing that the pull-off force is negligibly affected by the shortest wavelength components of the surface roughness.On the contrary, the Maugis’ model strongly underestimates adhesion and predicts a vanishing pull-off force when the upper cut-off spatial frequency of the surface is increased.

Theoretical study of electrical contact dustiness impact on the transition resistance

The article considers a mathematical model for determination of transition resistance in electrical contacts. The suggested model considers elastic, elastoplastic and plastic deformations of micro-protrusions on rough contact surfaces, the presence of surface films and dust particles on them. A theoretical dependence of possible contact failure on dust content has been obtained.

Synthesis and Characterization of Hydrophobic Silica Thin Layer Derived from Methyltrimethoxysilane (MTMS)

This study investigated the synthesis and characterization of MTMS hydrophobic silica prepared by sol-gel method. In principle, silica xerogels and silica thin layer were obtained by reacting MTMS in ethanol solvent in some pH variations. The MTMS solution was used to modify the surface of the ceramic plate by dipcoating method to further be calcined at two different temperatures of 350°C and 500°C. The silica xerogels were analysed by FTIR, TGA-DSC and GSA to determine functional group characteristics, thermal properties and pore morphology respectively. Meanwhile, the silica thin layers were analysed their hydrophobic properties using water contact angle measurement and surface roughness determination using SEM. The results showed that the higher the pH used in the MTMS solution, the higher the resulting contact angle. The highest contact angle was obtained at pH 8.12 which reached 94.7° and 79.5° for silica thin layer calcined at 350°C and 500°C, respectively. The TGA results indicated that the methyl group survived up to 400°C and disappeared at 500°C which had implications on silica thin layer hydrophobic nature. GSA result exhibited that the silica xerogel had a close structure with a very low pore volume. While the SEM-EDX results displayed that the silica thin layer prepared at acidic pH had smoother surface morphology and became rough when prepared at an alkaline pH.

Direct Fluorination Induced Variation in Interface Discharge Behavior Between Polypropylene and Silicone Rubber Under AC Voltage

This paper reports on the effect of direct fluorination on interface discharge characteristics between isotactic polypropylene (PP) and silicone rubber under AC voltage. The influence of fluorination time on discharge initiation and propagation stages has been estimated by measuring phase resolved partial discharge pattern and relationship between discharge rate ( $N$ ) and discharge magnitude ( $Q$ ). Attenuated total reflection Fourier transform infrared spectrum, water contact angle and surface roughness were also measured to gain a better understanding of the fluorination effect on surface chemical and physical structures of sample. Obtained results showed that with the increase of fluorination time from 0 to 15 min, the average surface roughness of PP increased from ~42 to ~65 nm, whereas the water contact angle decreased from ~88° to ~58°. In addition, the discharge initiation time increased from ~2 to ~4 s but the discharge propagation time decreased from ~14 to ~2 s, leading to the reduction in overall time of interface breakdown from ~16 to ~6 s. It is suggested that at the initiation stage the C–F bond introduced by direct fluorination with higher bond energy and deeper trap depth should be responsible for the alleviation of polymer degradation, while at the propagation stage the formation of larger void at the surface tends to accelerate the degradation of polymer. It could be concluded that although the direct fluorination has positive effect by delaying the appearance of discharge channel, it possesses negative effect by shortening the propagation process.

Contact Stiffness of Machine Components and the Influence of the Microgeometry of the Contact Surfaces on It

The use of characteristics of the contact stiffness in the scientific literature to describe a discrete contact between machine components under normal and tangential loading has been analyzed. The application of a model of the discrete contact of rough surfaces, as well as the influence of the parameters of the contact surface microgeometry on the contact stiffness under normal and tangential loadings and shear has been studied.