Elastic Coatings Research Articles

Strain measurements on compliant knitted mesh used in space antennas, by means of 2D Fourier analysis

AbstractThe paper presents a strain measurement technique to be applied on repetitive knitted nets. The application of the procedure is focused on large deployable reflectors used in space applications. Manufacturing of these structures involves knitting of thin metallic wires. Besides space antennas, the method herein developed is advantageous for many other types of knitted tissues such as elastic coatings, elastic bandages for medical applications, or any other woven fabric requiring a defined elastic behaviour. All of them display an almost regular repetitive pattern whose variations due to imposed loads are the core of the method. Deformation of such kind of structural elements must be analysed in two dimensions, because the knitting causes an accentuated orthotropic behaviour. Strain measurement is tricky and requires special computational techniques. Indeed, the application of standard experimental methods and indirect strain determination, through well‐established image analysis algorithm, can be totally unsuccessful or unsuitable because of the lack of continuity of these structures. The paper presents a method based on two‐dimensional Fourier analysis. Numerical examples, supported by some experimental evidences, confirm the feasibility of the technique. Furthermore, a newly proposed frequency zooming algorithm, based on fast Fourier transform, makes the computational costs of the indirect strain measurement affordable.

Development of styrene-acrylic polymeric compositions for the coating of textile materials used for packing

As a result of the determination of the chemical, physical-chemical and physical and mechanical properties of individual styrene-acrylic polymers and their compositions with crosslinking agents, it has been found that the formation of a strong three-dimensional spatial structure of films provides the styrene-acrylic polymer Lacrytex 430. It is possible to use this polymer without crosslinking agents. The additional introduction of Laproxide and Appretta ECO into the composition lowers the degree of structuring of polymer films. It was established that for the Lacrytex 640 preparation, which has a low structuring index, the introduction of the glycidyl ester of the Laproxide 703 trade mark leads to an increase in the degree of crosslinking to 7.9 % and, as a result, to an increase in the resistance to organic solvents, to a reduction of hydrolytic degradation at high temperatures and to an increase in the physical-mechanical indicators. Taking into account the need to obtain low-content compositions that provide a complex of necessary properties to the final product, the use of individual styrene-acrylic polymer Lacrytex 430 and Lacrytex 640/Laproxide 703 composition, which provides obtaining elastic coatings, is actual and economically sound.

Acoustic scattering reduction using layers of elastic materials

Making an object invisible to acoustic waves could prove useful for military applications or measurements in confined space. Different passive methods have been proposed in recent years to avoid acoustic scattering from rigid obstacles. These techniques are exclusively based on acoustic phenomena, and use for instance multiple resonators or scatterers. This paper examines the possibility of designing an acoustic cloak using a bi-layer elastic cylindrical shell to eliminate the acoustic field scattered from a rigid cylinder hit by plane waves. This field depends on the dimensional and mechanical characteristics of the elastic layers. It is computed by a semi-analytical code modelling the vibrations of the coating under plane wave excitation. Optimization by genetic algorithm is performed to determine the characteristics of a bi-layer material minimizing the scattering. Considering an external fluid consisting of air, realistic configurations of elastic coatings emerge, composed of a thick internal orthotopic layer and a thin external isotropic layer. These coatings are shown to enable scattering reduction at a precise frequency or over a larger frequency band.

An Approximate JKR Model of Elliptical Contact Between Thin Incompressible Elastic Coatings Covering Rigid Cylinders

In the framework of the Johnson–Kendall–Roberts (JKR) theory, the adhesive contact between thin incompressible elastic coatings covering rigid cylinders is studied. The leading-order asymptotic model of three-dimensional non-axisymmetric JKR-type adhesive contact for a thin incompressible coating bonded to a rigid substrate is applied, and an approximate solution has been obtained under the assumption that the contact area remains elliptical.

Corrigendum to “Extended JKR theory on adhesive contact between elastic coatings on rigid cylinders under plane strain” [Int. J. Solids Struct. 71 (2015) 244–254

Corrigendum to “Extended JKR theory on adhesive contact between elastic coatings on rigid cylinders under plane strain” [Int. J. Solids Struct. 71 (2015) 244–254

Study of roughness effect on elastic indentation of coated bodies

Two-level contact problem is proposed to study the effect of roughness of elastic coatings. The solution is based on using a function of additional displacements in a macrolevel contact problem formulation. The dependence of additional displacements on nominal pressure is obtained from consideration of a periodic model of roughness. Analytical–numerical method, which is based on Hankel integral transforms, boundary elements, and iteration procedure, is used to find macrocontact characteristics. The influence of the parameters of microgeometry on contact characteristics at macroscale is analyzed.

Theoretical and experimental characterization of a FEM element assembly for the simulation of very compliant knitted mesh

SummaryThe paper deals with the description, development and validation of an equivalent FEM element assembly suitable for the simulation of very compliant knitted meshes, like those used in elastic coatings, deployable antennas, medical applications and similar. The assembly is based on a network of lumped springs able to reproduce the orthotropic behaviour of the mesh when stretched along two directions. The parameters of the model have been identified by experimental tests using a dedicated biaxial testing device. The effectiveness of the modelling technique has been validated under two test settings, providing in‐plane or out‐of‐plane displacements. For deformations up to 50%, the differences observed between experiments and numerical results are bounded below 6%. Copyright © 2015 John Wiley & Sons, Ltd.

Some Criteria for Coating Effectiveness in Heavily Loaded Line Elastohydrodynamically Lubricated Contacts—Part II: Lubricated Contacts

Contacts of indentors with functionally graded elastic solids may produce pressures significantly different from the results obtained for homogeneous elastic materials (Hertzian results). It is even more so for heavily loaded line elastohydrodynamically lubricated (EHL) contacts. The goal of the paper is to indicate two distinct ways the functionally graded elastic materials may alter the classic results for the heavily loaded line EHL contacts. Namely, besides pressure, the other two main characteristics which are influenced by the nonuniformity of the elastic properties of the contact materials are lubrication film thickness and frictional stress/friction force produced by lubricant flow. The approach used for analyzing the influence of functionally graded elastic materials on parameters of heavily loaded line EHL contacts is based on the asymptotic methods developed earlier by the authors such as Kudish (2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman & Hall/CRC Press, Boca Raton, FL), Kudish and Covitch (2010, Modeling and Analytical Methods in Tribology, Chapman & Hall/CRC Press, Boca Raton, FL), Aizikovich et al. (2002, “Analytical Solution of the Spherical Indentation Problem for a Half-Space With Gradients With the Depth Elastic Properties,” Int. J. Solids Struct., 39(10), pp. 2745–2772), Aizikovich et al. (2009, “Bilateral Asymptotic Solution of One Class of Dual Integral Equations of the Static Contact Problems for the Foundations Inhomogeneous in Depth,” Operator Theory: Advances and Applications, Birkhauser Verlag, Basel, p. 317), Aizikovich and Vasiliev (2013, “A Bilateral Asymptotic Method of Solving the Integral Equation of the Contact Problem for the Torsion of an Elastic Halfspace Inhomogeneous in Depth,” J. Appl. Math. Mech., 77(1), pp. 91–97), Volkov et al. (2013, “Analytical Solution of Axisymmetric Contact Problem About Indentation of a Circular Indenter Into a Soft Functionally Graded Elastic Layer,” Acta Mech. Sin., 29(2), pp. 196–201), Vasiliev et al. (2014, “Axisymmetric Contact Problems of the Theory of Elasticity for Inhomogeneous Layers,” Z. Angew. Math. Mech., 94(9), pp. 705–712), Aizikovich et al. (2008, “The Deformation of a Half-Space With a Gradient Elastic Coating Under Arbitrary Axisymmetric Loading,” J. Appl. Math. Mech., 72(4), pp. 461–467), and Aizikovich et al. (2010, “Inverse Analysis for Evaluation of the Shear Modulus of Inhomogeneous Media in Torsion Experiments,” Int. J. Eng. Sci., 48(10), pp. 936–942). More specifically, it is based on the analysis of contact problems for dry contacts of functionally graded elastic solids and the lubrication mechanisms in the inlet and exit zones as well as in the central region of heavily loaded lubricated contacts. The way the solution of the EHL problem for coated/functionally graded materials is obtained provides a very clear structure of the solution. The solution of the EHL problem in the Hertzian region is very close to the solution of the dry contact problem while in the inlet and exit zones the solutions of the EHL problem with the right asymptotes coming from the solution of the dry contact problem can be related to the solutions of the classic EHL problem for homogeneous materials.

One-dimensional analytical model for the response of elastic coatings to water blast

In previous studies, the response of sandwich structures to water blast is solved by envisaging the plate adjacent to water as a rigid one, while the effects of the elasticity in the longitudinal direction of the plate are rarely studied. In this paper, a monolithic elastic coating with varying stiffness and thickness is investigated by a one-dimensional analytical approach, based on linear wave motion theory, to reveal the elastic effect of the plate on the incident wave. One side of the coating is loaded by a planar shock wave; on the opposite side, rigid boundary or air-backed boundary is imposed. The fluid–structure interaction (FSI), cavitation phenomenon and large deformation of the coating are taken into account. In particular, the initiation and evolution of cavitation, including the propagations of breaking fronts and closing fronts, as well as the pressure histories of radiated wave by the closing front, are examined. The analytical solution has been compared with finite element (FE) predictions. The results are found to be in excellent agreement for the propagation of breaking front and closing front, as well as the pressure and particle velocity histories at the wet face before the cavitation reaches the wet face. However, when the wet face cavitates, the predictions provided by the analytical method are less accurate and the analytically-computed particle velocity can only be compared in an average sense with the FE predictions. For air-backed case, Taylor׳s model prior to cavitation becomes a trivial case of the analytical model and the comparison also indicates the validity of the analytical model. The validated analytical model is used to determine the dependence of the peak pressure at the wet face and the impulse transmitted to the coating on the coating properties, including the wave impedance and thickness.

Extended JKR theory on adhesive contact between elastic coatings on rigid cylinders under plane strain

This study extended the conventional JKR theory on adhesive contact between elastic cylinders to the frictionless adhesive contact between elastic films coated on rigid cylindrical rollers. The plane-strain elasticity problem of indentation on an elastic film perfectly bonded to a rigid half-plane was revisited, with which the force-depth relations for both flat and cylindrical indentations were obtained in a simple form. By following Hertz analysis and using the solution of the cylindrical indentation on an elastic film, the adhesionless Hertzian contact between elastic films coated on rigid cylinders was obtained. However, the obtained Hertzian contact state should be considered as an approximate solution, since the pressure distributions in the contact region of the two elastic films may not match perfectly each other in the case of different Poisson’s ratios or thicknesses of the elastic films. By properly superposing the linear elastic solutions of flat and cylindrical indentations, the approximate solution to the adhesive JKR contact state between elastic films coated on rigid cylinders was also obtained, of which the relations between applied force, penetration depth, and contact width were expressed in terms of the geometric parameters and elastic constants of the two elastic films. The pull-off force at the moment of debonding two elastic films was also obtained as a function of the adhesion energy and compared with the normal two-dimensional JKR result.

Encasement as a morphogenetic mechanism: The case of bending

We study how the encasement of a growing elastic bulk within a possibly differently growing elastic coat may induce mechanical instabilities in the equilibrium shape of the combined body. The inhomogeneities induced in an incompressible bulk during growth are also discussed. These effects are illustrated through a simple example in which a growing elastic cylinder may undergo a shape transition towards a bent configuration.

Сравнительные показатели эксплуатационных свойств паркетных лаков

We investigated two groups of parquet varnishes: water and alkyd-urethane - a total of 15 samples of do-mestic and imported production. Among the advantages of water materials their resistance, fast drying time, no "ignition" of wood are noted. Alkyd-urethane varnishes form elastic coatings, do not glue side joints of parquet laths, form non-slip coating. The most important operational properties include hardness, impact strength, and abrasion resistance. It is estimated that imported water varnishes has harder first layer, and the highest indicator of hardness of alkyd-urethane varnishes (0.67 conventional units) does not exceed the lowest for water ones (0.69).

Неустойчивость скользящего термофрикционного контакта жесткого тела с упругим покрытием, содержащим пьезокерамическую прослойку

Неустойчивость скользящего термофрикционного контакта жесткого тела с упругим покрытием, содержащим пьезокерамическую прослойку

Elastic Coating with Inhomogeneous Interlayer Under The Action of Normal and Tangential Forces

We consider a three-dimensional problem of the theory of elasticity for an inhomogeneous half space loaded by normal and tangential forces distributed over a circular domain on its surface. The half space consists of a homogeneous base, a homogeneous layer, and an inhomogeneous interlayer whose Poisson’s ratio is constant and the dependence of its Young’s modulus on the distance to the surface of the base is described by a linear function. We study the influence of the thickness of interlayer on the distribution of tensile stresses in the coating.

Compatibility of Elastic PCC Coating and Concrete Substrate

Compatibility of Elastic PCC Coating and Concrete Substrate

Influence of strong bonding with impenetrable substrate on swelling of elastomers in low-molecular-weight liquids

Swelling in various liquids was studied for a wide variety of free and bonded cross-linked polyurethane materials with different structures and densities of three-dimensional network. A calculational method was proposed for predicting the equilibrium swelling in liquids of elastic polymeric coatings bonded with a nonswelling substrate.

Wave Damping due to Elastic Coating of the Sea Surface

Wave Damping due to Elastic Coating of the Sea Surface

Interaction between cracking, delamination and buckling in brittle elastic thin films

A discrete lattice based model for the interaction of cracking, delamination and buckling of brittle elastic coatings is presented. The model is unique in its simultaneous incorporation of the coating and of disorder in the interface and material properties, leading to realistic 3D bending (and buckling) behavior. Results are compared to the literature. In the case of cracking, the key role of a stress transfer correlation length ξ in establishing a scaling behavior for the brittle fracture of thin films is shown to extend to all geometrical and material properties involved. In the scaling regime of crack density in uniaxial tension cracking and delamination are found to occur simultaneously. In uniaxial tension of films with an internal biaxial compressive stress, the predicted initiation of buckles above delaminated areas near crack edges in the model is remarkably similar to experimental results.

Thin elastic coatings and surface enthalpy

We obtain explicit formulas for the first few terms in the asymptotics of the solution of the problem on the deformation of a body with a thin elastic coating and propose several methods, based on these formulas, for modeling the problem with the use of the Wentzel boundary conditions or a regular perturbation of the boundary. We present estimates of the asymptotic remainders, including those in formulas obtained by modeling.

Modeling of coating separation under thermomechanical loading in the beam approximation

The beam approximation is developed to solve some problems of fracture mechanics concerning the formation of separation of thin elastic coatings with allowance for the constraints acting on the connection boundaries and the influence of unsteady temperature actions. The separation end region is modeled by an elastic beam loaded by an external bending moment and by force factors from the connection with the base. This region is subjected to thermoelastic stresses caused by a sudden variation in the temperature of the surface or the adhesive layer. We estimate how the effective fracture strength of the adhesive joint varies for various modes of application of affecting factors, including variations in material properties with temperature and across the coating thickness; we also study buckling phenomena and the kinetics of local fracture processes in the end region. The results can be used when choosing the parameters of an adhesive joint so as to ensure a given effective adhesion fracture strength of the joint.