Adhesion Problems Research Articles

An experimental study of high speed wheel-rail adhesion characteristics in wet condition on full scale roller rig

Adhesion at the wheel-rail interface is a key factor determining stable running conditions and safety during train traction and braking. The wheel-rail abrasion of EMUs often occurs when the adhesion force is insufficient. This paper presents experiments performed on a high-speed full-scale roller rig of wheel-rail interface to simulate the low adhesion problem of high-speed railway in wet condition. Tests were conducted to study the adhesion characteristics at high speed under water lubrication. The influential factors on the high-speed wheel-rail adhesion coefficient are investigated, which include water spray amount, roughness of wheel-rail contact surface, running speed, water temperature and axle load. In the adhesion tests, water was sprayed on the wheel-rail contact interface at 0–250 ml/min, the roughness of the wheel-rail contact surface Ra was set within 0.30 to 1.1 μm, the test running speed range was 40 to 400 km/h, the temperature of water changed from 0 to 60 °C to simulate the effect of temperature on the adhesion coefficient and the axle load ranged from 8 to 16t. The law of influence on wheel-rail adhesion characteristic curves at high speed was revealed and explained based on the test results, which can be helpful to the design and optimization of the anti-slip control device in brake and the rotation/slip control device of the traction wheel of EMUs.

Axisymmetric adhesive contact problem for functionally graded materials coating based on the linear multi-layered model

The contact problem with adhesion for a functionally graded coated half-space indented by a rigid spherical punch is considered. The whole contact region is stick assuming the interfacial friction sufficient to prevent any slip taking place between the indenter and the coated half-space. The linear multi-layered model is used to model functionally graded materials with arbitrarily varying shear modulus and constant Poisson’s ratio under axisymmetric loads. By using the transfer matrix method and Hankel integral transform technique, the problem is reduced to a set of Cauchy singular integral equations. An iterative method is developed to numerically solve singular integral equations. The contact stress and indentation are calculated for different variations in elastic modulus. It is found that appropriate gradual variation in the shear modulus can improve the resistance to contact damage at the contact surfaces.

Wetting behavior investigation of a complex surface prepared by laser processing combined with carbon films coating

To solve blood adhesion problems on the surface of medical devices, such as scalpel blades and implants, a hydrophobic and serum-repellent surface was prepared and investigated. First, porous ablated surface on stainless steel (SS) was fabricated via laser processing. Then, the laser-ablated SS (LA-SS) surface was covered by thin tetrahedral amorphous carbon (ta-C) films using a filtered cathodic vacuum arc deposition (FCVAD) technique. As such, a complex surface, i.e., a porous LA-SS surface coated with ta-C films (named as LAC-SS surface), was obtained. The morphologies of the LA-SS surface were tailored by adjusting the scanning rate and laser fluence during laser processing. By decreasing scanning rate, an ablated layer with high-aspect-ratio cavities and large roughness can be fabricated. The wetting tests of water and serum droplets indicated that the LAC-SS surface exhibited excellent hydrophobicity and serum-repellency. Under optimal processing parameters, the wetting behaviors of droplets obey the Cassie-Baxter wetting model. An optimal LAC-SS surface was obtained with a water contact angle of 151.4 ± 1.4° and a serum contact angle of 143.0 ± 1.3°. The optimal surface also demonstrates great anti-adhesive properties with a water sliding angle of 14.1 ± 2.2° and a serum sliding angle of 21.7 ± 2.8°. This optimized complex surface can be used in medical devices to address blood adhesion problems.

Evaluation of the Adhesion between Overlays and Substrates in Concrete Floors: Literature Survey, Recent Non-Destructive and Semi-Destructive Testing Methods, and Research Gaps

Non-destructive testing (NDT) and semi-destructive testing (SDT) have recently been more frequently used for the evaluation and condition assessment of concrete floors in various types of buildings. The subject of the article is to briefly introduce the reader to the problem of adhesion between overlays and substrates in concrete floors and to illustrate the current state of knowledge on the subject. The aim of this paper was to briefly describe the recently used non-destructive and semi-destructive testing methods and the parameters useful for characterizing the adhesion between overlays and substrates in concrete floors, as well as the methods useful to characterize the functional properties of the overlays. A recent literature survey, related to the adhesion between the overlays and substrates in concrete floors, is thus shown. Special emphasis was placed on the critical review of the current research results. Based on the analysis of the literature review, research gaps have been presented in order to highlight future research directions.

Influence of Lignocellulosic Waste Pre-Treatment on the Characteristics of Bond Rupture

Post-harvest crop residues are an interesting raw material for the production of composite materials. However, their surface often contains waxy and siliceous substances, which can cause adhesion problems. Therefore, various surface pre-treatment methods have been developed to increase the surface tension of these particles and hence to improve adhesive adhesion. The influence of hydrothermal, chemical, plasma and enzymatic treatment was investigated. The aim of the paper is to evaluate the effect of pre-treatments of post-harvest crop residues on the nature of joint failure and adhesive dispersion on the particles. The evaluation is based on microscopic analysis of particles obtained from the rupture area after internal bonding tests. The nature of bond failure and adhesive dispersion on the particle surface is evaluated. The results show a clear influence of material pre-treatment on the failure bond of the bond and, to a large extent, correlate with the mechanical properties of composites published in previous studies. The most suitable treatment appears to be a plasma treatment at a properly adjusted intensity. Conversely, the unsuitable treatment was alkaline, which, although it increased adhesion, deteriorated the overall mechanical properties. Hydrothermal treatment could be also considered as an industrially suitable method.

Formation of Q-carbon and diamond coatings on WC and steel substrates

Recently we reported the formation of diamond and a new phase of Q-carbon, harder than diamond, on sapphire (0001) substrates by direct conversion of amorphous carbon layers by nanosecond pulsed laser melting or annealing. Here we show that this process can be extended to other substrates, specifically WC (Co-bonded) and steels that are needed for high-speed machining and oil and gas exploration and biomedical applications. Since diamond and Q-carbon layers are formed via laser melting and quenching of carbon, these layers are quite adherent to the substrates, thus solving a critical adhesion problem associated with initial graphitic layers in CVD diamond coatings. We have used these Q-carbon, diamond and Q-carbon-diamond composites as seed layers for HFCVD (hot filament chemical vapor deposition) to grow thicker and more adherent layers of diamond.

Adhesive contact problem for viscoplastic materials

We examine a mathematical model that describes a quasistatic adhesive contact between a viscoplastic body and deformable foundation. The material’s behaviour is described by the rate-type constitutive law which involves functions with a non-polynomial growth. The contact is modelled by the normal compliance condition with limited penetration and adhesion, a subdifferential friction condition also depending on adhesion, and the evolution of bonding field is governed by an ordinary differential equation. We present the variational formulation of this problem which is a system of an almost history-dependent variational–hemivariational inequality for the displacement field and an ordinary differential equation for the bonding field. The results on existence and uniqueness of solution to an abstract almost history-dependent inclusion and variational–hemivariational inequality in the reflexive Orlicz–Sobolev space are proved and applied to the adhesive contact problem.

Axisymmetric JKR-type adhesive contact under equibiaxial stretching

ABSTRACT An axisymmetric frictionless adhesive contact problem for a spherical indenter pressed against an isotropic elastic incompressible half-space under equibiaxial stretching is studied in the framework of the generalized Johnson–Kendall–Roberts (JKR) theory, which accounts for the effect of weak coupling between fracture modes I and II by means of a phenomenological mode-mixity function. The model predicts that contact area can withstand a larger level of the substrate stretch under moderate pre-pulling force. We have provided simple formulas to evaluate the pull-off force and the critical contact radius at the detachment point.

The advance of materials for preventing adhesion in tympanoplasty

For otitis media patients with severe mucosal lesions, adhesion is the most common poor prognosis of tympanoplasty. We generally consider tympanic cavity adhesion is due to eustachian tube dysfunction and poor middle ear ventilation. The mechanism of adhesion is unclear so far, which we thought is mainly associated with wounded surface and activation of the fibrinolytic system. To solve the problem of adhesion, several materials have been used in the middle ear surgery, such as plastic sheet, silicone sheet and absorbable material. And there are some benefits. The most widely used is silicone sheet, and there are some researches focused on its thickness, shape and components to achieve better anti-adhesion effect. In this article, we will do a review for the research advances of anti-adhesion materials in tympanoplasty.

Shear-induced contact area anisotropy explained by a fracture mechanics model.

This paper gives a theoretical analysis for the fundamental problem of anisotropy induced by shear forces on an adhesive contact, discussing the experimental data of the companion Letter. We present a fracture mechanics model where two phenomenological mode-mixity functions are introduced to describe the weak coupling between modes I and II or I and III, which changes the effective toughness of the interface. The mode-mixity functions have been interpolated using the data of a single experiment and then used to predict the behavior of the whole set of experimental observations. The model extends an idea by Johnson and Greenwood, to solve purely mode I problems of adhesion in the presence of a nonaxisymmetric Hertzian geometry, to the case of elliptical contacts sheared along their major or minor axis. Equality between the stress intensity factors and their critical values is imposed solely at the major and minor axes. We successfully validate our model against experimental data. The model predicts that the punch geometry will affect both the shape and the overall decay of the sheared contact area.

Indentation of thin elastic films glued to rigid substrate: Asymptotic solutions and effects of adhesion

Indentation of a thin elastic film attached through an interlayer to a rigid support is studied. Because the common interpretations of depth-sensing indentation tests are not applicable to such structured coatings, usually various approximating functions are employed to take into account influence of the interlayer. Contrary to the common approaches, a strict mathematical approach is applied here to study the problems under consideration assuming that the thickness of the two-layer structure is much less than characteristic dimension of the region of contact between the indenter and the coating. A simple derivation of asymptotic relations for displacements and stresses is presented. It is shown that often the leading term approximation to the non-adhesive contact problems is equivalent to contact problem for a Winkler-Fuss elastic foundation with an effective elastic constant. Because the contact between the indenter and the film at nanoscale may be greatly affected by adhesion, the adhesive problem for these bilayer coatings is studied in the framework of the JKR (Johnson, Kendall, and Roberts) theory of adhesion. Assuming the indenter shape near the tip has some deviation from its nominal shape and using the leading term approximation of the layered coatings, the explicit expressions are derived for the values of the pull-off force and for the corresponding critical contact radius of adhesive contact region.

Preparation and tribological properties of self-assembled tetraethoxysilane/octadecyltrichlorosilane bilayer films

Self-assembly technique has been used to solve adhesion and friction problems in moving parts of micro-electro-mechanical systems (MEMS). In this paper, tetraethoxysilane/octadecyltrichlorosilane (TEOS/OTS) bilayer films were prepared by self-assembly on Si substrate. TEOS was firstly self-assembled on Si substrate as the interlayer and then OTS was grafted on the TEOS monolayers as the top layer. The morphology, chemical composition, wettability, and adhesion of the films were characterized. The prepared TEOS/OTS bilayer films were observed to be hydrophobic with uniform nanoclusters. The tribological properties of the films were performed on a ball-on-plate statnamic tribometer. Compared with Si substrate and OTS self-assembled monolayer (SAM), TEOS/OTS bilayer films exhibited reduced adhesion and improved tribological performance, which was attributed to the stable bilayer structure of TEOS as the interlayer and the transfer of the destroyed OTS SAM as the lubricating film. TEOS/OTS bilayer films are expected to improve the quality of the micro-parts in MEMS and reduce the abrasion of the micro-molds in microfabrication techniques.

Investigation of Electrostatic Behavior of Dry Powder-Inhaled Model Formulations

The accumulation of electrostatic charge on drug particles and excipient powders arising from interparticulate collisions or contacts with other surfaces can lead to agglomeration and adhesion problems during the manufacturing process, filling, and delivery of dry powder inhaler (DPI) formulations. The objective of the study was to investigate the role of triboelectrification to better understand the influence of electrostatic charge on the performance of DPIs with 2 capsule-based dimensionally similar devices constructed with different materials. In addition, strategies to reduce electrostatic charge build up during the manufacturing process, and the processes involved in this phenomenon were investigated. Electrostatic charge measurements showed that there was a significant difference in electrostatic charge generated between tested formulations and devices. This affects particle detachment from carrier and thus significantly impacts aerosol performance. Conditioning fluticasone DPI capsules at defined temperature and humidity conditions reduced electrostatic charges acquired during manufacturing. Conditioning salmeterol DPI capsules at same conditions seemed disadvantageous for their aerosol performance because of increasing capillary forces and solid bridge formation caused by water absorption. Knowledge and understanding of the role of electrostatic forces in influencing DPI formulation performance was increased by these studies.

Adhesion and debonding in a model of elastic string

We study the problem of adhesion and debonding of an elastic body interacting with a rigid substrate through a layer made of soft breakable adhesive material. The general problem is formulated in the multidimensional vectorial case, while a detailed analysis is carried for the one dimensional case leading to the study of a 1D semilinear wave equation. The initial boundary value problem is affected by the presence of a source term characterizing the interaction of the string withe the adhesive layer. This discontinuous force jumps to zero when a critical value of the displacement is reached. We obtain conditions for the initial boundary value problem ensuring the regularity of the solutions and the attachment–detachment conditions. Finally, we focus on a numerical investigation of the problem by considering regularizations of the source term and different initial conditions.

Evaluation of surface modification in a steel track for the rubber tyred Metro

The rubber tyred metro is a very popular transportation system in some countries, like in Mexico City where 12 lines transport around 5.5 million people every day. The rubber tyre rolls over a steel track subjected under different sources of contamination. Firstly, the rubber tyre accumulates contaminants all over the tread tyre, such as: oil, water, tyre debris, wear particles from the braking and electrical systems, garbage from platforms and steel debris among others. Due to these facts, contamination problems and the rainy season, the metro system suffers severe problems of adhesion. Dangerously, the trains present skidding and slipping problems. The operator must approach and leave the station at very low velocity to prevent accidents. This problem causes delays in the system transportation and discomfort. As a remedy, to reduce the low adhesion, technicians from the metro system have machined grooves on the steel track, however the problem has not been considerably reduced. This work aims to improve the coefficient of friction (CoF) machining the steel track surface with different macro textures. Tests were carried out by using a pendulum friction tester in laboratory. The values indicated an increase in the friction because the grooves help to evacuate water on both sides of the steel track. In addition, the wear rate of some pads from the pendulum increased, indicating a potential increase of wear of rubber tyres due to texturing.

Enhanced Performance Stability of Iridium Oxide-Based pH Sensors Fabricated on Rough Inkjet-Printed Platinum.

Today, electrochemical sensors are used for a broad range of applications. A fundamental challenge is still the achievement of long-term sensor stability by ensuring good adhesion between the deposited sensing layer and the substrate material, e.g., a metal electrode. Until now, the most applied strategy to overcome this problem is to increase the surface roughness of the metal layer by mechanical etching or by electroplating of additional material layers, which both imply an increase in manufacturing steps and thus the final cost of the overall device. Alternatively, to overcome these adhesion problems, we propose the direct printing of a novel platinum nanoparticle ink, which is compatible with low-cost additive digital inkjet and with flexible low-cost substrates. This water-based platinum ink has two unique features: it leads to highly rough surfaces, which promotes the adhesion of deposited sensing material, and it is a highly low-temperature curing ink, compatible with polymeric substrates that cannot withstand high temperatures. Based on this concept, we report about a long-term stable and highly sensitive solid-state pH sensor functionalized by anodic electrodeposited iridium oxide on a rough nanostructured platinum printed layer. The sensors showed an excellent reproducibility with a linear super-Nernstian response (71.3 ± 0.3 mV/pH unit) in a wide pH range (pH 2-11). Long-term stability tests for over 1 year of application demonstrate an excellent mechanical sensor layer stability, which is correlated to the distinct roughness of the printed platinum layer. This novel approach is useful to simplify the fabrication process and with that the sensor costs.

Novel Adhesion Technique Using Metallic or Non-Metallic Hydrous Oxide of Metal Complexes Involving Magnetic Compound Fluid Rubber under Electrolytic Polymerization and Magnetic Field for Producing Sensors.

As per sequential studies on new types of soft rubber for the artificial skin of robots, smart sensors, etc., we have proposed and investigated hybrid skin (H-Skin) and haptic sensors by using magnetic compound fluid (MCF), compounding natural rubber latex (NR-latex), and applying electric and magnetic fields. Through electrolytic polymerization, the MCF rubber is solidified. The MCF rubber has hybrid sensing functions and photovoltaic effects, and electric charge as battery. In case of the production of soft rubber sensors, however, the problem of adhesion between metal electrodes and rubber is very important. In the present study, we propose a novel adhesive technique for bonding the metal electrodes and MCF rubber by using metallic or non-metallic hydrous oxide, which is a metal complex, via electrolytic polymerization. The anionic radical hydrate reacts with the isoprene molecules of NR-latex or chloroprene rubber latex (CR-latex) such that they are cross-linked and the MCF rubber with the hydrate is solidified, which can be represented via a chemical reaction equation. By means of this adhesive technique, we presented five cases of sensors fabricated using metal electrodes and rubbers. This technique is applicable for novel cohesion between rubber and metal.

The Investigation on Adhesive Contact Problem of Gradient Piezoelectric Coating under Insulating Punch

This paper considers the two-dimensional adhesive contact problem for a rigid insulating cylindrical punch acting on a gradient piezoelectric coating bonded to half-space.It is assumed that the material parameters of functionally gradient piezoelectric materials vary exponentially along the thickness direction.The adhesion between the punch and the contact surface of the coating is described according to the adhesion Model given by Maugis. By using the Fourier integral transform, the adhesive contact problem of gradient piezoelectric coatings is reduced to singular integral equations. the numerical method is applied to solve the singular integral equations with Cauthy kernel.The numerical results show that both non-homogeneous parameters of gradient piezoelectric material and adhesion effect have significiant impact on the adhesive contact behavior of gradient piezoelectric coating.

Alleviation of the adhesive protrusion problem at the bonding interface of free-standing microstructures

The vertically allocated free-standing SU-8 microstructures are typically bonded to a glass cover by the usage of uncrosslinked SU-8 adhesives. Such a phenomenon can easily cause SU-8 protrusion and eventually result in the SU-8 cantilever to be immovable. Traditional methods are sensitive to the bonding conditions and have a short bondable thickness of SU-8 adhesives. In this study, we propose an approach, that is, improved structural features, to alleviate the protrusion problem while extending the bondable thickness for the freestanding SU-8 microstructures in an enclosed channel. We used concave and moat microstructures as solutions of the improved structural features. We investigated the influence of both microstructures on the bonding quality and compared the bondable thickness with the previous one. THB-151N was used in another example to demonstrate the availability of our method. The bonding quality at the interfaces was evaluated by SEM images and direct inspection through a transparent glass cover. The bonding method is advantageous to other microfluidic systems, particularly those with long narrow channels.

Higher order Hermite enriched contact finite elements for adhesive contact problems

It is known that during the simulation of the adhesive contact problems highly nonlinear responses of interaction forces occur within the very narrow adhesive zone. It leads to the loss of quadratic-rate of convergence during Newton-Raphson iterations and unstable computational behaviour. In case of standard finite element formulation, a very fine mesh resolution is needed for the stable computations, but a significant computational cost is associated. For minimising the cost without the loss of accuracy of the solution, contact surface enrichment approaches have been presented. These approaches utilise the higher-order Lagrangian polynomial functions for the enrichment of contact finite elements. In the present work, based on the incorporation of fifth- and seventh-order Hermite interpolation functions two new enriched contact finite elements are formulated. The performance of proposed enriched contact finite elements is demonstrated through the simulation of peeling of an initially flat deformable strip from a rigid substrate. A stable solution is obtained at a relatively coarser mesh than the fully Lagrangian discretised finite element mesh. It is shown that the proposed higher order Hermite enriched contact finite elements attain better performance when compared with earlier introduced enriched elements.