Adhesion Force Coefficient Research Articles

The co‐effect of microstructures and mucus on the adhesion of abalone from a mechanical perspective

Reliable and reversible adhesion underwater is challenging due to the water molecules and weak layers of contaminants at the contact interface, which requires to deepen the understanding of wet adhesion of biological surfaces. Herein, the co-effect of microstructures and mucus of abalone foot on wet adhesion is investigated from both experimental and theoretical perspectives. The morphologies, adhesion force and coefficient of friction indicate that the mucus in adhesion zone is crucial for successful attachment of abalone based on capillary forces and viscous forces, and the mucus in non-adhesion zone with lower adhesion force and friction coefficient may behave as a lubricant for the locomotion. The theoretical calculation manifests that the microstructures may help abalone to form multiple liquid bridges with the secreted mucus, and significantly increase the wet adhesion force of abalone. These findings will bring profound views into the underlying mechanisms of biological surface adhesion.

Key Properties of a Bioactive Ag-SiO2/TiO2 Coating on NiTi Shape Memory Alloy as Necessary at the Development of a New Class of Biomedical Materials.

Recent years have seen the dynamic development of methods for functionalizing the surface of implants using biomaterials that can mimic the physical and mechanical nature of native tissue, prevent the formation of bacterial biofilm, promote osteoconduction, and have the ability to sustain cell proliferation. One of the concepts for achieving this goal, which is presented in this work, is to functionalize the surface of NiTi shape memory alloy by an atypical glass-like nanocomposite that consists of SiO2-TiO2 with silver nanoparticles. However, determining the potential medical uses of bio(nano)coating prepared in this way requires an analysis of its surface roughness, tribology, or wettability, especially in the context of the commonly used reference coat-forming hydroxyapatite (HAp). According to our results, the surface roughness ranged between (112 ± 3) nm (Ag-SiO2)—(141 ± 5) nm (HAp), the water contact angle was in the range (74.8 ± 1.6)° (Ag-SiO2)—(70.6 ± 1.2)° (HAp), while the surface free energy was in the range of 45.4 mJ/m2 (Ag-SiO2)—46.8 mJ/m2 (HAp). The adhesive force and friction coefficient were determined to be 1.04 (Ag-SiO2)—1.14 (HAp) and 0.247 ± 0.012 (Ag-SiO2) and 0.397 ± 0.034 (HAp), respectively. The chemical data showed that the release of the metal, mainly Ni from the covered NiTi substrate or Ag from Ag-SiO2 coating had a negligible effect. It was revealed that the NiTi alloy that was coated with Ag-SiO2 did not favor the formation of E. coli or S. aureus biofilm compared to the HAp-coated alloy. Moreover, both approaches to surface functionalization indicated good viability of the normal human dermal fibroblast and osteoblast cells and confirmed the high osteoconductive features of the biomaterial. The similarities of both types of coat-forming materials indicate an excellent potential of the silver-silica composite as a new material for the functionalization of the surface of a biomaterial and the development of a new type of functionalized implants.

The effect of surface roughness on normal restitution coefficient, adhesion force and friction coefficient of the particle-wall collision

The normal restitution coefficient is an important parameter in particle deposition which is widely used in industrial fields. The normal restitution coefficient can be affected by many factors, and a typical factor is the surface roughness. Furthermore, a rough surface will influence the adhesion force and friction coefficient. The adhesion force and friction coefficient have effects on the normal restitution coefficient. However, the relationship between the normal restitution coefficient and the surface roughness has not been obtained. Therefore, an experimental study of microspheres impact on a rough surface is developed. The normal restitution coefficient decreases with the increasing surface roughness. The adhesion force is calculated by the Rabinovich model, and the results indicated that the adhesion force increases with the increasing surface roughness within the surface roughness range in this paper. Moreover, the adhesion energy and friction coefficient dissipation increase with the increasing surface roughness.

Research into frictional interaction between the magnetized rolling elements

Results are presented of theoretical and experimental studies into effect of external magnetic field on the changes in adhesion parameters in a contact between magnetized steel rolling elements when they brought to each other to the level of atomic roughness. In theoretical studies, we calculated the interaction energy, adhesion force, friction and adhesion coefficient between magnetized steel rolling elements. The calculations are based on the general law of interaction between systems of charged particles, described by the Lennard-Jones potential, which takes into account both repulsion forces and attraction forces of these particles. A mathematical model was proposed for the calculation of force and coefficient of adhesion between steel rolling elements, taking into account magnetostrictive phenomena in the surface layers of a metal when magnetized by a constant magnetic field. The calculation of force and coefficient of adhesion was performed on the example of interaction between a wheel of a locomotive and a rail; the proposed model, however, could be applied to other elements of rolling friction. The technique and results of experimental studies are presented of the effect of external magnetic field on the coefficient of adhesion in the friction model of contact “wheel of a locomotive ‒ rail”. According to the results, magnetization of metal rolling elements leads to a significant, up to 36 %, increase in adhesion forces, which is important from the point of view of development and implementation of methods to control adhesion in similar tribological systems

Effect of absorbed water on the adhesion, friction, and wear of phosphate laser glass at nanoscale

AbstractThe interaction between glass and micro‐particle in the presence of absorbed water could affect glass surface integrity, especially for the phosphate glass with a poor water resistance. In this work, using an atomic force microscope equipped with an environment chamber, the adhesion, friction and wear behaviors of phosphate laser (PL) glass were investigated by contacting with an SiO2 microsphere under vacuum, dry air, and humid air, respectively, to reveal the effect of the absorbed water on the interactions between glass and particle. Compared to vacuum and dry air, a higher adhesion force and friction coefficient as well as more material removal of PL glass were found in humid air. The capillary force caused by absorbed water greatly contributes to the high adhesion and friction in humid air. Moreover, the water meniscus forming at glass‐particle interface provides an environment for hydrolyzing P–O–P network and assists the material removal of PL glass under shear stress. Comparing the results after rubbing the SiO2 particle to those rubbed by the CeO2 particle in our previous work, in humid air, a higher shear stress and material removal rate were found in PL glass‐CeO2 pair than in the PL glass‐SiO2 pair, indicating that in the presence of absorbed water, countersurface chemistry also plays an important role in the friction and wear of PL glass at the nanoscale surface.

Nano-tribology studies of reduced graphene oxide films in air and in aqueous solutions with different pH values

Abstract

Development of climbing robot for steel bridge inspection

Purpose The purpose of this paper is to present a design of climbing robot with magnetic wheels which can move on the surface of steel bridge. The locomotion concept is based on adapted lightweight magnetic wheel units with relatively high attractive force and friction force. Design/methodology/approach The robot has the main advantages of being compact (352 × – 215 × – 155 mm), lightweight (2.3 kg without battery) and simple mechanical structure. It is not only able to climb vertical walls and follow circumferential paths, but also able to pass complex obstacles such as bolts, steps, convex and concave corners with almost any inclination regarding gravity. By using a servo as a compliant joint, the wheel base can be changed to enable the robot to overcome convex corners. Findings The experiment results show that the climbing robot has a good performance on locomotion, and it is successful in negotiating the complex obstacles. On the other hand, the limitations in locomotion of the robot are also presented. Originality/value Compared with the past researches, the robot shows good performance on overcoming complex obstacles such as concave corners, convex corners, bolts and steps on the steel bridge. Magnetic wheel with the characterization of compact size and lightweight is able to provide bigger adhesion force and friction coefficient.

Influence of exfoliating facial cleanser on the bio-tribological properties of human skin

In daily life, cosmetics can play important roles in facial skin moisturizing, whitening and sun protecting. Unfortunately, the aged skin stratum corneum (SC) often impedes the penetration for cosmetics. Regular removal of the extra aged horny cells can facilitate the penetration for cosmetics and improve the performance of the skin. However, no study has assessed the detailed effects of exfoliating facial cleanser on the friction properties of human skin and the degree of aged SC removal. In this paper, the effects of three kinds of scrub facial cleanser with different sizes, amounts and hardness scrub particles on the tribological properties of human skin have been investigated in vivo using a UMT-II tribometer under the simulated face washing conditions. The hardness of the scrub particles were measured by using a Nano-Hardness/Scratch Tester. The results showed that the aged SC has all been removed by the three kinds of scrub cleanser under the reciprocating sliding wear mode, which resulted in decrease of skin surface roughness and increase of skin conductance and hydration. Thus, the adhesion force and friction coefficient between the hydrated skin and a probe increased due to the increased contact area and skin hydration. Compared with the other two cleansers, the cleanser with two kinds of size and moderate hardness scrub particles made the skin to deform more elastically and removed more aged SC, which led to greater decrease in skin surface roughness and greater increase in skin conductance, hydration and adhesion. Hence the skin friction coefficient and penetration were higher and the moisturizing persistence lasted longer time after the same moisturizer was used. This indicated that the properties of scrub particles in cleanser played important roles in skin tribological behavior and penetration. The results may be instrumental in developing and testing skin cosmetics.

Adhesive properties of contacts between elastic bodies with randomly rough self-affine surfaces: A simulation with the method of reduction of dimensionality

Adhesive properties (adhesion force and adhesion coefficient) of contacts between elastic bodies with rough surfaces have been investigated and adhesion maps constructed showing the dependence of adhesive properties on the roughness, rms slope of the surface, elastic modulus, surface energy and fractal dimension. Simulations have been carried out in the frame of the method of reduction of dimensionality.

Human-Induced Particle Re-Suspension in a Room

A large-eddy simulation/immersed boundary method for particulate flows in an Eulerian framework is utilized to investigate short-term particle re-suspension due to human motion. The simulations involve a human walking through a room, stopping, and then walking in place, causing particles to be re-suspended from a carpet. The carpet layer is modeled as the porous medium and a classical adhesive force model is applied to model the resistance of the carpet-bound material to hydrodynamic forcing. The effects of parameters such as the foot penetration depth and adhesive force coefficient on mass re-suspended during the foot stamping events are examined. Simulations of particulate re-suspension experiments conducted in a room within a U.S. Environmental Protection Agency test house are also described. The simulations vary the type of human motion (stamping in place versus stamping in place with rotation). The results indicate that significant amounts of particulate material are re-suspended from the carpet layer due to the impingement of the feet during the motion event. The net mass re-suspended for human motion with rotation is two times greater than that for the motion without rotation, while the mass of re-suspended small particles is slightly greater than that of large particles. The re-suspension rates are estimated based on several time scales, and the predicted total particle number concentrations at several locations in the room show good agreement with experimental data. The present CFD model can be utilized to predict particle re-suspension rates as induced by human motion, but further work in modeling the fine-scale details of the re-suspension process is needed.

空気圧制動系における非線形粘着状態観測器

This paper shows that the VSS observer has the possibility to estimate adhesion force using wheel slip simulation and wheel slip experiments. It has been shown that the disturbance observer was effectives in estimation of adhesion force. To apply a strain gauge to the brake caliper in order to measure the braking torque is difficult, because the delicate parts on bogies are to be avoided at the train depot. When all the axles of vehicles slip, the wheel slip prevention cannot work sufficiently. Moreover, the brake systems of railway vehicles possess strong nonlinear characteristics with variable parameters, such as adhesion force and friction coefficient of brake materials. It is important that the estimation method has robustness against such disturbance and parameter changes, and it is known that the Variable Structure System (VSS) observer has robustness against parameter change, disturbance input and so on. However, there have been no research reports about a Variable Structure System (VSS) observer for the brake system or wheel slip preventing methods in a railway vehicle. In order to compare the theoretical value of adhesion force with estimated value by a VSS observer, wheel slip simulation was preformed. Simulation results show that the VSS observer can estimate the adhesion force efficiently. Moreover, estimation experiments of adhesion force using VSS observer were performed, and it has been clarified that the VSS observer can efficiently estimate the tangential force coefficient from the experimental results.

Chemical stability of nonwetting, low adhesion self-assembled monolayer films formed by perfluoroalkylsilanization of copper

A self-assembled monolayer (SAM) has been produced by reaction of 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS) with an oxidized copper (Cu) substrate and investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, and contact angle measurement. FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. The perfluoroalkyl SAM on Cu is found to be extremely hydrophobic, yielding sessile drop static contact angles of more than 130 degrees for pure water and a "surface energy" (which is proportional to the Zisman critical surface tension for a Cu surface with 0 rms roughness) of 14.5 mJm2(nMm). Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH=12, 60 degrees C) solutions for at least 30 min. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70 min at 60 degrees C or 50 min at 80 degrees C. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for antiwetting, low adhesion surfaces or dropwise condensation on heat exchange surfaces.

Dynamic simulations of adhesion and friction in chemical force microscopy.

A hybrid molecular simulation approach has been applied to investigate dynamic adhesion and friction between a chemical force microscope (CFM) tip and a substrate, both modified by self-assembled monolayers (SAMs) with hydrophobic methyl (CH(3)) or hydrophilic hydroxyl (OH) terminal groups. The method combines a dynamic model for the CFM tip-cantilever system and a molecular dynamics (MD) relaxation technique for SAMs on Au(111) at room temperature. The hybrid simulation method allows one to simulate force-distance curves (or adhesion) and friction loops (or friction coefficient) in the CFM on the experimental time scale for the first time. The simulation results also provide valuable molecular information at the interface that is not accessible in CFM experiments, such as the actual tip position with respect to the cantilever support position, molecular and hydrogen-bonding structures at the interface, and load distributions among different molecular chains (or single-molecule forces). Results show that the adhesion force and friction coefficient for the OH/OH contact pair are much larger than those for the CH(3)/CH(3) pair due to the formation of hydrogen bonds. During the retraction of a CFM tip from a surface, the CFM tip is away from the sample surface slightly while the spring undergoes dramatic elongation in the normal direction before rupture occurs. Single-molecule forces are distributed unevenly at the contact area. Surface energies calculated for functionalized surfaces compare well with those determined by experiments.

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In daily life, cosmetics can play important roles in facial skin moisturizing, whitening and sun protecting. Unfortunately, the aged skin stratum corneum (SC) often impedes the penetration for cosmetics. Regular removal of the extra aged horny cells can facilitate the penetration for cosmetics and improve the performance of the skin. However, no study has assessed the detailed effects of exfoliating facial cleanser on the friction properties of human skin and the degree of aged SC removal. In this paper, the effects of three kinds of scrub facial cleanser with different sizes, amounts and hardness scrub particles on the tribological properties of human skin have been investigated in vivo using a UMT-II tribometer under the simulated face washing conditions. The hardness of the scrub particles were measured by using a Nano-Hardness/Scratch Tester. The results showed that the aged SC has all been removed by the three kinds of scrub cleanser under the reciprocating sliding wear mode, which resulted in decrease of skin surface roughness and increase of skin conductance and hydration. Thus, the adhesion force and friction coefficient between the hydrated skin and a probe increased due to the increased contact area and skin hydration. Compared with the other two cleansers, the cleanser with two kinds of size and moderate hardness scrub particles made the skin to deform more elastically and removed more aged SC, which led to greater decrease in skin surface roughness and greater increase in skin conductance, hydration and adhesion. Hence the skin friction coefficient and penetration were higher and the moisturizing persistence lasted longer time after the same moisturizer was used. This indicated that the properties of scrub particles in cleanser played important roles in skin tribological behavior and penetration. The results may be instrumental in developing and testing skin cosmetics.

Anti-Slip Re-adhesion Control of Electric Motor Coach (2M1C) Based on Disturbance Observer and Speed Sensor-less Vector Control

When the adhesion force coefficient between rail and driving wheel decreases, the electric motor coach has slip phenomena. We have already proposed the anti-slip re-adhesion control system based on disturbance observer. This system has the fine torque response for one driving wheel driven by one inverter-fed induction motor. However, the bogie of electric motor coach has four driving wheels driven two induction motors, which are, in some cases, driven by one inverter. In order to realize the anti-slip re-adhesion control system for the bogie of electric motor coach, this paper proposes a new anti-slip re-adhesion control based on disturbance observer and speed sensor-less vector control. The numerical simulation and experimental results point out that the proposed anti-slip re-adhesion control system has the desired driving wheel torque response for the tested bogie system of electric motor coach.

An Approach of Anti-slip Readhesion Control of Electric Motor Coach Based on First Order Disturbance Observer

In electric motor coaches, when the adhesion force coefficient between rail and driving wheel decreases suddenly, the electric motor coach has slip phenomena. We have already proposed the anti-slip control system based on ordinary disturbance observer. In order to realize the more stable anti-slip readhesion control in case of large variation of adhesion force coefficient, this paper proposes a new anti-slip readhesion control based on first order disturbance observer and new torque function. In the numerical simulation results in this paper, the proposed anti-slip readhesion control well regulates the driving wheel torque of electric motor coach stably.

Anti-Slip Control of Electric Motor Coach Using Adhesion Force Coefficient Estimator Based on Disturbance Observer

In electric motor coaches, when the adhesion force coefficient between rail and driving wheel decreases suddenly, the electric motor coach has a slip phenomena. This paper proposes a new estimation method of the adhesion force coefficient, which is based on disturbance observer. Moreover, the proposed adhesion force coefficient estimation system is applied to a new anti-slip control method in this paper. In the numerical simulation results in this paper, the proposed anti-slip control method well regulates the driving wheel torque of electric motor coach and keeps the maximum value of adhesion force coefficient curve.

Tribological properties of titanium nitride films prepared by dynamic ion beam mixing method

Titanium nitride (TiN) films have been developed by a dynamic ion beam mixing (DM) process, which combines Ti vapor deposition with simultaneous nitrogen ion beam irradiation. Tribological properties of DM TiN film on martensitic stainless steel have been investigated concerning their application to dry gas seal materials for compressors and turbines. The microhardness, adhesion force, wear resistance and frictional coefficient properties of DM TiN film were investigated and compared to conventional hard materials such as arc ion plating (IP) TiN film, chromium carbide (Cr 3C 2) thermal spray coating and tungsten carbide (WC) hard alloy. The results show wear resistance and friction in TiN films prepared by the DM process to be superior to that in conventional hard materials.