Elastic Coatings Research Articles

On effective surface elastic moduli for microstructured strongly anisotropic coatings

The determination of surface elastic moduli is discussed in the context of a recently proposed strongly anisotropic surface elasticity model. The aim of the model was to describe deformations of solids with thin elastic coatings associated with so-called hyperbolic metasurfaces. These metasurfaces can exhibit a quite unusual behaviour and concurrently a very promising wave propagation behaviour. In the model of strongly anisotropic surface elasticity, strain energy as a function of the first and second deformation gradients has been introduced in addition to the constitutive relations in the bulk. In order to obtain values of surface elastic moduli, we compare dispersion relations for anti-plane surface waves obtained using the two-dimensional (2D) model and three-dimensional (3D) straightforward calculations for microstructured coatings of finite thickness. We show that with derived effective surface moduli, the 2D model can correctly describe the wave propagation.

Contact friction in roller mechanisms

An analytical dependence was obtained that describes the patterns of friction stress distribution in the contact zone of roller mechanisms. The patterns of distribution of friction stresses from external forces acting on the roll supports, geometric and kinematic parameters of the roller mechanism, and strain properties of the processed material and elastic coatings of the rollers were determined. Mathematical models of friction stress of roller mechanisms were developed, considering the kinematics of the contact zone, the kinematic connection between the working rolls, and the compliance of the material being processed. It was established that the ratio of friction stress to normal stress at the points of the contact zone of the roller mechanism is not constant, but changes at each point of the contact zone.

Recent Progress on Anti-Slip and Highly Wear-Resistant Elastic Coatings: An Overview

There has been great interest in the research and development of different anti-skid and highly wear-resistant materials that can effectively reduce energy losses and improve efficiency in numerous applications. This article reviews the design, performance, and application of anti-skid and highly wear-resistant coating materials at home and abroad. First, it introduces the structure and mechanism of anti-skid and wear-resistant coatings. The preparation of different anti-slip coatings is mainly accomplished by changing the base material and anti-slip granules as well as the coating method, and the anti-slip performance is determined with the coefficient of friction test. The application mostly encompasses airplane and ocean decks, as well as pedestrian spaces. This review introduces the development status and research progress of metal-based anti-skid coatings and polymer-based anti-skid coatings, which are two groups of pavement. Finally, the challenges and future development directions of this key field are summarized and considered.

Adhesion strength of tetrahydrofuran hydrates is dictated by substrate stiffness

Understanding the hydrate adhesion is important to tackling hydrate accretion in petro-pipelines. Herein, the relationship between the Tetrahydrofuran (THF) hydrate adhesion strength (AS) and surface stiffness on elastic coatings is systemically examined by experimental shear force measurements and theoretical methods. The mechanical factor-elastic modulus of the coatings greatly dictates the hydrate AS, which is explained by the adhesion mechanics theory, beyond the usual factors such as wettability and structural roughness. Moreover, the hydrate AS increases with reducing the thickness of the elastic coatings, resulted from the decrease of the apparent surface elastic modulus. The effect of critical thickness for the elastic materials with variable elastic modulus on the hydrate AS is also revealed. This study provides deep perspectives on the regulation of the hydrate AS by the elastic modulus of elastic materials, which is of significance to design anti-hydrate surfaces for mitigation of hydrate accretion in petro-pipelines.

Titanium Carboxylate Molecular Layer Deposited Hybrid Films as Protective Coatings for Lithium-Ion Batteries.

The lifetime of lithium-ion batteries can be extended by applying protective coatings to the cathode's surface. Many studies explore atomic layer deposition (ALD) for this purpose. However, the complementary molecular layer deposition (MLD) technique might offer the benefit of depositing hybrid coatings that are flexible and can accommodate potential volume changes of the electrode during charging and discharging of the battery. This study reports the deposition of titanium carboxylate thin films via MLD. The structure and stability of the hybrid films are studied by using Fourier transform IR spectroscopy. The electrochemical properties of two titanium carboxylate films and a "titanicone" MLD film, deposited by using TDMAT and glycerol, are evaluated on top of a TiO2, TiN, and LiMn2O4 electrode. The coatings are found to present good lithium-ion kinetics and to reduce electrolyte decomposition. Overall, the titanium carboxylate films deposited in this work seem promising as protective and elastic coatings for future high-energy lithium-ion battery cathodes.

Dielectric Properties of Hybrid Polyethylene Composites Containing Cobalt Nanoparticles and Carbon Nanotubes.

Polymer composites with electrically conductive inclusions are intensively developed for microwave shielding applications, where lightweight and elastic coatings are necessary. In this paper, dielectric properties of hybrid polyethylene composites containing cobalt nanoparticles and multi-wall carbon nanotubes (MWCNT) were investigated in the wide frequency range of 20–40 GHz for electromagnetic shielding applications. The percolation threshold in the hybrid system is close to 6.95 wt% MWCNT and 0.56 Co wt%. Cobalt nanoparticles (up to highest investigated concentration 4.8 wt%) had no impact on the percolation threshold, and for the fixed total concentration of fillers, the complex dielectric permittivity is higher for composites with bigger MWCNT concentrations. Moreover, the microwave complex dielectric permittivity of composites with high concentration of fillers is quite high (for composites with 13.4 wt% MWCNT and 1.1 wt% Co ε′ ≈ ε″ ≈ 20 at 30 GHz, it corresponds to microwave absorption 50% of 1 mm thickness plate); therefore, these composites are suitable for electromagnetic shielding applications.

Nonlinear deformations of a cylindrical pipe with pre-stressed thin coatings

The paper presents an exact solution for the problem of large deformations of torsion, axial tension–compression, and radial expansion or shrinkage of an elastic hollow circular cylinder equipped with pre-stressed elastic coatings. Surface coatings are modeled using the six-parameter nonlinear shell theory. The constitutive material of the cylinder is described by a three-dimensional nonlinear model of the isotropic incompressible body of the general form. Special boundary conditions describe the interaction of this material with thin coatings on the inner and outer surface of the pipe. Based on the solution obtained, numerical calculations were performed on the effect of preliminary stresses in coatings on the stress–strain state of a cylindrical pipe.

ВПЛИВ ГІДРОФОБНОГО ПОКРИТТЯ НА ЕФЕКТИВНІСТЬ ВОГНЕЗАХИСТУ ТЕКСТИЛЬНИХ МАТЕРІАЛІВ

Abstract. The analysis of fire-retardant materials for fabrics is carried out and it is established that the paucity of data for explanation and description of the process of fire protection, neglect of elastic coatings, leads to ignition of fabric structures under the action of flame. The development of reliable methods for studying the conditions of fire protection of fabrics leads to the creation of new types of fire protective materials. Therefore, it becomes necessary to determine the conditions for the formation of a barrier both for high temperatures and for leaching in the presence of precipitation and to establish a mechanism for inhibition of these processes. In this regard, full-scale tests were carried out and it was found out that when the flame is applied to untreated model samples of tent elements made of canvas fabric, the surface ignites and spreads the flame, which leads to their complete combustion within 105...120 s, instead, the model The fire-resistant sample of tent elements did not catch fire when ignited with a gasoline-based substance, and the flame did not spread. In this case, the final combustion was recorded for 3 c and the swelling of the protective coating reached 3...5 mm, and the surface was charred on an area of about 80% from the inside. When tested for fire retardant efficiency for a fire-resistant sample treated with a water repellent (5 % solution of GDJ-94), a decrease in efficiency and carbonization of the material was recorded, which amounted to 100%, and for a fire-resistant sample treated with a water repellent (5 % solution), a decrease in efficiency was recorded due to the combustion of paraffin and local burnout of the material, and carbonization was 100 %. Obviously, such a mechanism of influence of the fire-retardant coating is the factor regulating the process, which preserves the integrity of the object. Thus, there is reason to argue about the possibility of targeted regulation of the processes of fire protection of the fabric by applying coatings capable of forming a protective layer on the surface of the material, which inhibits the rate of heat penetration.

A Numerical Model for Solving Three-Dimensional Rolling Contact Problems with Elastic Coating Layers

In this work, a numerical model is proposed for three-dimensional rolling contact problems with one or two elastic layers, and the tangential contact solution is emphasized. Previous works on this topic have mostly been two-dimensional, in which only longitudinal creepage has been considered. With the three-dimensional model presented in this work, all possible creepages, such as the longitudinal, lateral and spin creepages are taken into account. In order to improve the calculation efficiency, the conjugate gradient method and the FFT technique are employed. The influence coefficients for displacement and stress are obtained from the corresponding frequency response functions. The numerical results are validated against existing results and good agreement can be found. The effects of the different layers’ thicknesses and elastic moduli under different creepage combinations on the traction distribution and stick/slip results are investigated. It can be seen that by adjusting the layer parameters the traction and stick/slip results can be modified significantly, and it may, therefore, be very useful information for improving the rolling contact fatigue and mitigating wear problems in various mechanical systems.Graphical

Establishing patterns of mass transfer under the action of water on the hydrophobic coating of the fire-retardant element of a tent

This paper reports an analysis of the flame retardants for fabrics that has revealed the fact that the meagerness of data to explain and describe the process of fire protection, specifically the neglect of elastic coatings, leads to that the structures made from fabrics are ignited under the influence of a flame. Devising reliable methods to study the fire protection conditions for fabrics results in the design of new types of fireproof materials. Therefore, there is a need to determine the conditions for the formation of a barrier for water mass transport and to establish a mechanism for slowing down water penetration through the material. In this regard, an estimation-experimental method has been constructed for determining mass transfer under the action of water when using a hydrophobic coating, which makes it possible to assess water penetration. Based on the experimental data and theoretical dependences, the intensity of mass flow under the action of water has been determined, which is 0.000177 kg/m2, which ensures fabric resistance. The study results have proven that the process of waterproofing the fabric involves inhibition of the mass transfer process under the action of water by insulating the surface of the fireproof fabric with a hydrophobic coating. It should be noted that the presence of a hydrophobic coating leads to blocking the fabric surface from moisture penetration. Such a mechanism behind the effect of the hydrophobic coating is likely the factor in adjusting the process through which the integrity of an object is preserved. Thus, the sample of fireproof fabric coated with a water repellent demonstrated, after exposure to water, that the amount of water absorbed did not exceed 0.00012 kg, and, for a fabric without a water repellent, was 0.01 kg. Thus, there is reason to assert the possibility of targeted adjustment of the processes related to water penetration of the fabric by using hydrophobic coatings that could form a protective layer on the surface of the material, which inhibits the rate of water penetration.

The Use of Sol-Gel Method for Obtaining Fire-Resistant Elastic Coatings on Cotton Fabrics

Based on the generalization of research results on the processes of obtaining SiO2 sols using tetraethoxysilane and ethyl silicates, the main factors influencing the elasticity of silica coatings on cotton fabrics and their fire-retardant properties are considered. The possibility of forming covalent bonds between the functional groups of cellulose, gel coating and flame retardant layer is considered, which explains the strong fixation of a thin layer of coating on the fibers of the fabric and improve its fire protection. The use of the developed compositions for fire-retardant elastic coatings based on ethyl silicate allows to increase the time of complete burning of cotton from 30s (untreated fabric) to 600s (treated with binary coating).

Thermophysical characteristics of the formed layer of foam coke when protecting fabric from fire by a formulation based on modified phosphorus-ammonium compounds

This paper reports the analysis of flame retardants for fabrics that has established that the meagerness of the data that explain and describe the process of fire protection, as well as the neglect of elastic coatings, leads to the combustion of structures made from fabrics under the influence of flame. The development of reliable methods to study the fire protection conditions for fabrics leads to the design of new types of fireproof materials. Therefore, it becomes necessary to define the conditions for the formation of a barrier for burning and flame propagation by a piece of fabric and for establishing a mechanism that would inhibit a temperature transfer to the material. To address this issue, an estimation-experimental method has been devised for determining thermal conductivity when using a fire protection agent as a coating, which makes it possible to assess the thermal conductivity coefficient under the effect of high temperature. Based on the experimental data and theoretical dependences, the coefficient of thermal conductivity for the fire-resistant layer of foam coke was calculated, 0.034 W/(m∙K), which, accordingly, ensures the heat resistance of the fabric. The study results have proven that the process of the thermal insulation of fabric involves the formation of soot-like products at the surface of the sample. The inhibition of the process of heat transfer to the material treated with a composition based on modified phosphorus-ammonium compounds is characterized by the formation of a heat-protective layer of coke at the surface of the fabric. The maximum possible penetration of temperature through the thickness of the coating has been estimated. At the surface of the sample, a temperature was generated that significantly exceeds the ignition temperature of the fabric, and, at the non-heated surface, does not exceed 150 °C. Thus, there is reason to assert the possibility of targeted adjustment of fire protection processes in the fabric by applying coatings that can form a protective layer on the surface of the material, which inhibits the rate of heat transfer

A mechanistic analysis of delamination of elastic coatings from the surface of plastically deformed stents

Several medical papers have reported delamination of the coating from the stent-substrate following intravascular deployment leading to adverse outcomes for patients. However, the mechanisms of delamination of such polymer coatings from the surface of a stent due to large deformations during device deployment have not been studied. In this paper, a novel and in-depth investigation of the mechanisms and parameters that govern stent-coating delamination is performed, using a cohesive zone formulation to simulate the evolution of traction at the stent-coating interface. The study firstly analyses the behaviour of elastic coatings on idealised elastic stent substrates. Simulations reveal that the mode mixity of delamination is strongly dependent on the level of stent deployment at initiation. In general, peak normal tractions exceed peak shear tractions at low levels of stent deployment whereas the reverse trend is computed at high levels of stent deployment. Interface tractions increase with both increasing stent thickness and coating thickness suggesting that thinner stents and thinner coatings should be utilised for the delivery of antiproliferative drugs to reduce the risk of coating delamination. Next, the influence of stent plasticity on interface tractions and coating delamination is investigated. Even at low levels of deployment, plastic yielding occurs in the stent hinge region and the patterns of normal and shear tractions are found to be significantly more complex than those computed for the elastic stents, with both tensile and compressive regions of normal traction occurring in the stent arch. At a high level of stent deployment shear tractions at the stent-coating interface are computed to increase with decreasing strain hardening modulus. The findings of this paper provide a new insight into the stress-state at the stent-coating interface as a function of the stent design parameters and large deformation elasticity and plasticity during deployment, allowing for a more reliable assessment of the limits relating to safe implantation of coated stents.

On the issues of modeling the roll contact curves

The paper is devoted to the mathematical modeling of the roll contact curves in two-roll modules. A generalized two-roll module is considered, in which the rolls are located relative to the vertical line with a tilt to the right, have different diameters and elastic coatings of different stiffness, the material layer is fed downward. The results of the analysis of strain properties effect of the rolls elastic coatings and the processed material on the shapes of the roll contact curves are given. The models of roll contact curves in a generalized two-roll module are found for the cases where the strain of contacting bodies is given by empirical formulas and by rheological models.

Analysis of the angles of contact in a two-roll module

The study is devoted to the analysis of the angles of contact in a two-roll module. An asymmetric two-roll module is considered, in which the rolls are inclined to the right relative to the vertical line, they have unequal diameters and elastic coatings made of materials of different stiffness and friction coefficients; the material layer is fed down inclined relative to the centerline. Analytical expressions for the angles of contact are obtained, which are the main quantities that determine the boundary conditions for the problems of contact interaction in a two-roll module. It was stated that the sum of the contact angles does not depend on the inclination of the material layer feeding to the centerline and on the inclination of the upper roll relative to the vertical line.

Встановлення закономірностей дифузії вологи через полімерну оболонку термічно модифікованої деревини

An analysis of the process of thermal modification of wood, which was obtained by a controlled heating process, was done. The unique technological properties (durability, low hygroscopicity and dimensional stability) of thermomodified wood make it possible to use it in various scope. Due to the influence of temperature there are some chemical changes in the structures of the wood cell wall components (lignin, cellulose and hemicellulose). This leads to an increase in density, hardness, improved hydrophobicity (water repellency), thereby reducing their ability to absorb moisture and swell. The products absorb moisture gradually, are less prone to swelling and shrinkage, but still need the elastic coatings application. It is proved that heat-treated wood turns gray over time under the influence of sunlight, and therefore requires additional surface treatment with a coating. Additional protective substances application on the thermo-modified wood products surface promotes dimensional stability and protects against rapid weathering of the surface in open air conditions. The use of transparent coatings and oils does not protect the surface from discoloration during weathering. They are recommended for products are manufactured from thermomodified wood, which are operated away from direct sunlight and rain. The parameters of moisture penetration into wood are mathematically modeled on the basis of the moisture diffusion quasi-stationary equation through the polymer coating on the flat sample surface. The dynamics of moisture content changes in thermally modified wood by different schedules parameters has been experimentally studied. The obtained mathematical relations based on the experimental studies results make it possible to calculate the moisture diffusion coefficient in thermally modified wood in the presence of a polymer shell. It is established that the wax coating application on the surface of the product reduces the moisture diffusion process more than 10 times for surfaces treated at a temperature of 160 °C for 1 hour. That is, such products can be used on objects with high humidity.

Regimes of Soft Lubrication.

Elastohydrodynamic lubrication, or simply soft lubrication, refers to the motion of deformable objects near a boundary lubricated by a fluid, and is one of the key physical mechanisms to minimise friction and wear in natural and engineered systems. Hence it is of particular interest to relate the thickness of the lubricant layer to the entrainment (sliding/rolling) velocity, the mechanical loading exerted onto the contacting elements, and properties of the elastic boundary. In this work we provide an overview of the various regimes of soft lubrication for two-dimensional cylinders in lubricated contact with compliant walls. We discuss the limits of small and large entrainment velocity, which is equivalent to large and small elastic deformations, as the cylinder moves near thick or thin elastic layers. The analysis focusses on thin elastic coatings, both compressible and incompressible, for which analytical scaling laws are not yet available in the regime of large deformations. By analysing the elastohydrodynamic boundary layers that appear at the edge of the contact, we establish the missing scaling laws - including prefactors. As such, we offer a rather complete overview of physically relevant limits of soft lubrication.

Modeling of Friction Stress in Twin Roll Modules

The study is devoted to the analysis of the laws of the distribution of tangential friction stresses in twin roll modules. A two-roll module is considered, in which the rolls are positioned relative to the vertical by a slope to the right, have unequal diameters and elastic coatings from materials with different stiffness and friction coefficients, the material layer is sloped downward relative to the center line. Formulas are defined for calculating neutral angles in the considered two-roll module. Dependencies between the forces acting in the rolls and the stresses distributed under the influence of these forces are established. It was revealed that these dependences do not change with a change in the angle of supply of the material layer to the line of centers and the angle of inclination of the upper roll relative to the vertical.

Modeling the Shape of the Roll Contact Curves in Two-Roll Modules

The study is devoted to mathematical modeling of the shape of the roll contact curves in two-roll modules. A two-roll module is considered, in which the rolls are positioned relative to the vertical with a tilt to the right, have unequal diameters and elastic coatings from the materials of different stiffness and friction coefficients, the material layer is fed with a tilt downward relative to the center line. The equations of the curves of roll contact in the considered two-roll module are derived. It is revealed that the obtained models are general in the sense that they are applicable for particular cases of interaction in a two-roll module.

ПРИНЦИПИ ГІДРОБІОНІКИ ПРИ ПРОЕКТУВАННІ ТЕХНІЧНИХ ЗАСОБІВ ДЛЯ ВИКОРИСТАННЯ У ВІЙСЬКОВО-МОРСЬКИХ СИЛАХ ЗБРОЙНИХ СИЛ УКРАЇНИ

The task of modern scientific and technological progress is to study the structure, morphological features and functions of living organisms, the principles of operation of their engines for using the information obtained when creating new mechanisms. Possibilities of the hydrodynamic theory of swimming of high-speed fish, cetaceans and squids, as well as the created theory of the boundary layer and viscous resistance of aquatic organisms and their application in the design of technical means are considered. The purpose of the research: the analysis of the experience of practical application of the principles of hydrobionics in the design of technical means with subsequent use in the Naval Forces of the Armed Forces of Ukraine is relevant and forms the basis of our research. The research method is systemic and structural, as well as didactic methods of analysis and generalization of information. The main directions of hydrobionic research with the aim of their application in technology are given: creation of technical models based on the analysis of the theoretical foundations of swimming of hydrobionts and the application of the results of experimental research in theoretical hydromechanics; studies of hydroacoustic abilities of aquatic organisms, manifested in the communication of animals with each other and in the use of sonar when orienting among underwater objects; the principles of the device, structure and functions of the organs of locomotion in order to improve the propulsive qualities and maneuverability of technical means of movement in water. Natural adaptations of aquatic organisms, such as a laminarized body shape, skin integuments, sound-and-cholocation organs, are unique natural abilities of marine mammals that require application in the interests of the Ukrainian Navy. Keywords: bionics, hydrobionics, hydrobionts, adaptation, hydrodynamics, laminarization, modularity, flapping engine, jet propellers, elastic damping coatings, jet stream, turbulent pulsation, elastic damping properties, bioacoustic system of cetaceans, turbulation.