Relation between the strength of polyethylene-steel adhesion bonds and the thickness of the ultrathin layer of polymer remaining on the surface of the metal

On the basis of the principle of ellipsometry and, moreover, the method of pyrolitic decomposition of the polymer with subsequent chromatographic analysis of the products of pyrolysis, a procedure has been developed for experimentally determining the thickness of the ultrathin layer of polymer that remains on the metal after failure of a polyethylene-steel adhesion bond. The nature of the relationship between the thickness of the residual polymer layer (200–800 Å) and the strength of the adhesion bond is established. It is concluded that the cohesion strength and the deformation at failure of the layer of adhesive next to the more rigid and stronger boundary layer have a decisive influence on the strength of the adhesion bond.Riga Polytechnic Institute. Translated from Mekhanika Polimerov, No. 3, pp. 420–424, May–June, 1976.     

Formation of a transition layer on the fillers of polymer composites

Based on a plane model of composites, the effect of a transition layer on the elastic modulus E_c of the composites is analyzed in the case where, under the action of a load, the transition layer is formed both on the side of matrix and filler. In evaluating E_c, it is assumed that the elastic modulus in the layer grows linearly from the elastic modulus of matrix to that of filler, but pores in the filler are impermeable to matrix macromolecules. Analytic relation ships are found which allow one to determine the volume fractions of the transition layer on the side of matrix and filler if the experimental elastic modulus of the composite is known. These relationships are used to find the magnitude of the layer in epoxy composites with various fillers and to evaluate its effect on the compressive elastic modulus of the composites. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 5, pp. 693–700, September–October, 2006.     

Propagation of torsional surface waves in a homogeneous layer of finite thickness over an initially stressed heterogeneous half-space

In the present paper, the dispersion equation which determines the velocity of torsional surface waves in a homogeneous layer of finite thickness over an initially stressed heterogeneous half-space has been obtained. The dispersion equation obtained is in agreement with the classical result of Love wave when the initial stresses and inhomogeneity parameters are neglected. Numerical results analyzing the dispersion equation are discussed and presented graphically. The result shows that the initial stresses have a pronounced influence on the propagation of torsional surface waves. It has also been shown that the effect of density, directional rigidities and non-homogeneity parameter on the propagation of torsional surface waves is prominent.     

Dynamical structure of the turbulent boundary layer on rough surface

The experiments on structure of turbulent boundary layer on the plane rough wall without pressure gradient are presented. Sand roughness of the wall is considered. Measurements are carried out using Time-Resolved PIV technique in planes parallel and perpendicular to the wall. The results on rough wall are compared with the base case of boundary layer on smooth wall. Hairpin vortices have been detected. Topology and typical size of those structures substantially differ in the cases in question. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Stress on the interatomic bonds near the surface of a polymer

The stresses on the interatomic bonds in the interior and at the surface of polyethylene terephthalate film in uniaxial tension have been determined by means of infrared transmission and reflection spectroscopy. The stresses are found using the shift in the frequency of the atomic vibrations produced by the application of a mechanical load. It is shown that the stresses on some bonds in the specimen reach 700 kgf/mm², i.e., approach their theoretical strength. The concentration of these bonds in a surface layer 1 µ thick is approximately an order greater than the concentration in the interior of the specimen.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 512–514, May–June, 1976.     

Reinforcement by a thin layer with oscillating thickness

We study a singular perturbation problem involving variational functionals that nearly degenerate on a thin layer with rapidly varying thickness. One interpretation is the reinforcement of a rod in torsion by a thin, oscillatory coating of a very strong material.This work was begun while the authors were visiting the Institute for Mathematics and Applications. RVK gratefully acknowledges additional support from ONR Grant N00014-83-K-0536, NSF Grant DMS-8312229, and the Sloan Foundation. GB gratefully acknowledges support from the Scuola Normale Superiore of Pisa and the Italian CNR.     

Investigation of the mechanical properties of polymer surface layers using surface waves

It is possible to excite ultrasonic surface waves at the surface of polymer materials and to determine the dependence of the wave parameters on the mechanical properties of the surface. The nature of the variation of the surface wave characteristics with material, temperature, and the frequency of the exciting vibrations has been established.Mekhanika Polimerov, Vol. 3, No. 5, pp. 933–939, 1967     

Mathematical modelling of the catalyst layer of a polymer electrolyte fuel cell

In this paper, we derive a mathematical model for the cathodecatalyst layer of a polymer electrolyte fuel cell. The modelexplicitly incorporates the restriction placed on oxygen inreaching the reaction sites, capturing the experimentally observedfall in the current density to a limiting value at low cellvoltages. Temperature variations and interfacial transfer ofO₂ between the dissolved and gas phases are also included. Boundson the solutions are derived from which we provide a rigourousproof that the model admits a solution. Of particular interestare the maximum and minimum attainable values. We perform anasymptotic analysis in several limits inherent in the problemby identifying important groupings of parameters. This analysisreveals a number of key relationships between the solutions,including the current density, and the composition of the layer.A comparison of numerically computed solutions and asymptoticsolutions shows very good agreement. Implications of the resultsare discussed and future work is outlined.     

Surface instability in a finite thickness fluid saturated porous layer

The Rayleigh-Taylor (RT) instability at the interface between fluid and fluid saturated sparsely packed porous medium has been investigated making use of boundary layer approximation and Saffmann [8] boundary condition. An analytical solution for dispersion relation is obtained and is numerically evaluated for different values of the parameters. It is shown that RT instability can be controlled by a suitable choice of the thickness of porous layer, ratio of viscosities and the slip parameter.     

Antiplane periodic contact problems fora layer non-uniform along its thickness

Antiplane periodic contact problems for an elastic layer with a shear modulus which variesexponentially along its thickness are considered. The problems are reduced to an integral equation of the first kind with an irregular, periodic, difference kernel. A method which has been described previously [1,2] is used for the approximate solution of this equation.     

Boundary layer due to the axisymmetric spreading of material on the surface of a fluid

The effect of the axisymmetric spreading of a layer of material (oil or solid particles) on the surface of a viscous fluid is studied. Assuming high Reynolds numbers, the boundary layer equation is derived and solved for general power law surface velocities. The composite streamlines show sharp turns near the surface.     

The stability of a transonic boundary layer on an elastic surface

The perturbations in the boundary layer over an elastic surface when there is non-stationary free viscous-inviscid interaction at transonic velocities are investigated using a modified three-deck model. The modification consists of retaining the term with the second derivative with respect to time (the singular term of the transonic expansion), which occurs in the model of the Lin–Reissner–Tsien equation when it is derived from the complete equations for the velocity potential. This enables the equations of the model to be improved so that they more accurately describe non-stationary and non-linear phenomena. It is shown that the modified model enables perturbations, ignored when using the classical three-deck model, to be taken into account. The compliance on the surface may lead to a reduction in the perturbation growth rate.     

Jump relations of the quadruple layer potential on a regular surface in three dimensions

The jump relations of the quadruple layer potential on a regular surface in three dimensions are derived. The jumps are shown to be proportional to the product of the density of the potential and the mean curvature of the underlying surface.     

A simple parabolic model for the optics of the atmospheric surface layer

A simple yet accurate model is developed for optical ray tracing in the surface layer of a refracting atmosphere. The model consists of a small number of concentric spherical layers or shells, the surface of each being isothermal. If the temperature is taken to vary linearly between the surfaces, then the curvature of nearly-horizontal rays is approximately constant within each layer. Replacement of circular by parabolic arcs produces simple quadratic expressions for the rays. The procedure is easily implemented on a minicomputer, and a compact version fits into a programmable pocket calculator. This is particularly convenient for checking field observations. An example is given, as well as a discussion on error sensitivity due to simplifying assumptions.     

MHD-based simulation of ionospheric perturbations generated in the atmospheric surface layer

The generation and propagation of acoustic gravity waves (AGWs) in a two-dimensional Earth atmosphere was numerically simulated on the basis of a magnetohydrodynamic model. Due to the divergent form of the equations and the conservativeness of the numerical method, strong perturbations, including discontinuous solutions, were considered and computed by applying a shock capturing algorithm. The results were compared with previous ones obtained using the Euler equations. The comparison results confirmed the generation of atmospheric AGWs by pulsed ground-based sources and supported the possibility of using simpler gasdynamic models for the given class of problems in a fairly wide range of governing parameters.