Optical properties of metal-polymer nanocomposites based on iron and high-pressure polyethylene

The optical reflectance and absorption spectra of nanocomposite materials based on iron and highpressure polyethylene (with different percentages of iron) were measured at room temperature in the visible and near-infrared regions. Oscillations of the absorption coefficient related to the optical transitions between minibands of the quantum well are revealed in the electronic spectrum of a metal nanoparticle. The experimental and theoretical data on the absorption coefficient are compared. It is shown that, with an increase in the iron concentration in the dielectric matrix, the discrepancy in the theoretical and experimental results decreases significantly.     

Measurements of metal-polymer adhesion properties with dynamic force spectroscopy

We investigate nanoscale interface properties using dynamic mode atomic force microscopy (AFM) operated in the frequency modulation mode in ultrahigh vacuum. The AFM tip was was functionalised by a thin layer of aluminium and the polymer was treated by plasma-etching. In the spectroscopy mode we could measure the adhesion properties between the metal and the polymer surfaces. We found that plasma-etching of the polymer resulted in strongly enhanced force interactions, indicating a chemical activation of the polymer surface. Values for the adhesion force and work of adhesion were measured on the nanometer scale and are compared to conventional macroscopic adhesion failure tests.     

Vibration of bimodular sandwich beams with thick facings: A new theory and experimental results

This study deals with both analytical and experimental investigations of three-layer beams with cores of polyurethane foam and facings of unidirectional cord-rubber. Both of these materials are bimodular (i.e., having different behavior in compression as compared to tension). The new theory presented is a shear-flexible laminate version of the well-known Timoshenko beam theory, which, due to the bending-stretching coupling present in the bimodular case, results in a coupled sixth-order system of differential equations. In this theory, a separate derivation is presented for the shear correction factor. Due to the discontinuities in the normal stress distribution and the bimodularity, the shear correction factor is much different than the classical homogeneous material value of $\text{5}\text{6}$. Theoretical and experimental results are presented for the frequencies of the first three modes of vibration for a pin-ended beam without axial restraint. This work is believed to be the first devoted to vibration of bimodular materials in a sandwich configuration.     

Power flow analysis for a floating sandwich raft isolation system using a higher-order theory

A higher-order sandwich theory is implemented in conjunction with an equivalent mobility-based power flow progressive method to determine power flow for a sandwich configured floating raft vibration isolation system. The power spectrum changes in whole frequency range effectively when core materials’ properties change. It is also shown that the loss factors of the sandwich configured floating raft influence the power flow transmitted to the foundation effectively in the medium- to high-frequency range and that the resonant peak cannot be avoided by increasing damping only in high-frequency ranges which is not found in floating raft isolation systems with isotropic beams.     

SEM and XRF spectroscopy methods for studying and controlling the surface morphology of metal-polymer films

The surface morphology and the degree of porosity of metal-polymer films deposited by the electrolytic method are studied using scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectroscopy. Mathematical processing is performed, and the structure of the sample surfaces is analyzed using images obtained in the mode of secondary-electron recording. The volume-packing coefficients for heterogeneous coatings are determined using the XRF analysis data. The dependence of the surface structure and volume-packing coefficient of copper in the film on the polymer type and the coating thickness is established.     

Spectral finite element based on an efficient layerwise theory for wave propagation analysis of composite and sandwich beams

In this paper, we present a spectral finite element model (SFEM) using an efficient and accurate layerwise (zigzag) theory, which is applicable for wave propagation analysis of highly inhomogeneous laminated composite and sandwich beams. The theory assumes a layerwise linear variation superimposed with a global third-order variation across the thickness for the axial displacement. The conditions of zero transverse shear stress at the top and bottom and its continuity at the layer interfaces are subsequently enforced to make the number of primary unknowns independent of the number of layers, thereby making the theory as efficient as the first-order shear deformation theory (FSDT). The spectral element developed is validated by comparing the present results with those available in the literature. A comparison of the natural frequencies of simply supported composite and sandwich beams obtained by the present spectral element with the exact two-dimensional elasticity and FSDT solutions reveals that the FSDT yields highly inaccurate results for the inhomogeneous sandwich beams and thick composite beams, whereas the present element based on the zigzag theory agrees very well with the exact elasticity solution for both thick and thin, composite and sandwich beams. A significant deviation in the dispersion relations obtained using the accurate zigzag theory and the FSDT is also observed for composite beams at high frequencies. It is shown that the pure shear rotation mode remains always evanescent, contrary to what has been reported earlier. The SFEM is subsequently used to study wavenumber dispersion, free vibration and wave propagation time history in soft-core sandwich beams with composite faces for the first time in the literature.     

Tuning of electrical and structural properties of metal-polymer nanocomposite films prepared by co-evaporation technique

Nanocomposites consisting of Au and Ag nanoparticles embedded in Teflon AF 1600 (Teflon) and Nylon 6 (Nylon) matrices were prepared by a simultaneous vapor phase deposition of both the polymer and the metal. The composite films were deposited between two Au-Pd alloy electrodes prepared by sputtering onto kapton foil substrates enabling further electrical measurements. The electrical properties of the composites are strongly influenced by the metal filling factor and changes in the microstructure. At first, the dependence of the resistivity of the composites consisting of various Ag and Au nanoparticle concentrations was investigated. The resistivity is characterized by a threshold region with a critical metal filling factor. Changes in the microstructure, in particular, can occur as a result of an induced electric field in between the metal nanoparticles and a heat treatment. The I–V characteristics of Teflon AF composites for different Au concentrations were studied thoroughly. An increase in the slope of the I–V curve up to a certain voltage (breakdown voltage) was observed. This phenomenon is accompanied by the field induced tunneling of the charge carriers which enhances the conductivity. The change in conductivity was also analyzed for Nylon nanocomposites with various Au concentrations in the temperature range 20–180 °C. The observed temperature dependence is explained by activated electron tunneling between metal nanoparticles and by rearrangements in the microstructure (e.g. coalescence of metal nanoparticles). PACS  78.67.-n; 78.67.Bf     

Dynamic characteristics of composite laminates

An exact solution for the vibration of elastic composite laminates in cylindrical bending is presented. Dispersion curves for multi-layer symmetrical and unsymmetrical laminates with materials possessing high and low degrees of anisotropy at various fiber orientations are compared with those obtained from an approximate shear deformation theory. Mode shapes are also drawn for different wavelengths and their variation with fiber orientation is studied. Equations are developed for the wave propagation in an infinite medium consisting of a repeated pair of anisotropic layers by extending the “continuum” theory of Sun, Achenbach and Herrmann. Dispersion characteristics for 0–90° fiber orientations obtained by the “continuum” approach are also compared with those obtained by the exact method. The range of validity of each approximate theory is then assessed.     

Frequency maximization of laminated sandwich plates under general boundary conditions using layerwise optimization method with refined zigzag theory

The present paper extends the layerwise optimization (LO) procedure to the maximization problem of the fundamental frequencies of sandwich plates with fibrous composites and low stiffness core layers. Frequencies are calculated by the Ritz method based on a refined zigzag theory (RZT). Polynomial functions which satisfy at least geometrical boundary conditions with boundary indexes are employed as displacement functions, and they enable satisfying arbitrary sets of boundary conditions for rectangular plates. Results of the experimental modal analysis validate the accuracy of the present calculations, and a comparison with results of the classical laminated theory (CLPT) and the first order share deformation theory (FSDT) supports the effectiveness of the present method. Optimized results are compared with other typical sets of lay-up configurations and this shows the LO method as suitable means to the optimization problem for sandwich plates.     

Natural vibration of unsymmetric cross-ply laminates

This study considers the linear vibration characteristics of square [0_n/90_n]_T laminates relative to their room-temperature static equilibrium configurations. A Rayleigh-Ritz approach combined with Hamilton's principle is used to provide approximate solutions to this vibration problem. The vibration mode shapes are assumed to have the same spatial dependence as used in past investigations to study the room-temperature configurations of these laminates, and are thus assumed to be perturbations on the static equilibrium configurations. Hamilton's principle then results in the so-called zero- and first-order equations. The zero-order equations lead to the classic static equilibrium results of past investigations, presented here in nondimensional form with analytical solutions at the bifurcation point. The first-order equations, combined with zero-order results, lead to the vibration characteristics for each zero-order static configuration. Interest centers on the lowest natural frequency and the associated mode shape for laminates clamped at their midpoints, with special attention as to how these vibration characteristics depend on the laminate side-length-to-thickness ratio. With an imaginary-valued frequency, the static saddle configuration for side-length-to-thickness ratios larger than the critical value is correctly assessed as unstable. A finite element model is also used to study the vibration characteristics and to compare with the findings for the developed analysis. The qualitative comparisons between the developed analysis and the finite element model are generally good, and the quantitative comparisons are also satisfactory.     

光纤弯曲与抗弯曲光纤

本文讨论了光纤弯曲后的性质变化，叙述了弯曲损耗与一些因素之间的关系以及对匹配包层光纤和压纸内包层光纤进行了比较，最后提出了一种对弯曲不灵敏的实用光纤。     

Elastic constants of layers in isotropic laminates

The individual laminae elastic constants in multilayer laminates composed of dissimilar isotropic layers were determined using ultrasonic-resonance spectroscopy and the linear theory of elasticity. Ultrasonic resonance allows one to measure the free-vibration response spectrum of a traction-free solid under periodic vibration. These frequencies depend on pointwise density, laminate dimensions, layer thickness, and layer elastic constants. Given a material with known mass but unknown constitution, this method allows one to extract the elastic constants and density of the constituent layers. This is accomplished by measuring the frequencies and then minimizing the differences between these and those calculated using the theory of elasticity for layered media to select the constants that best replicate the frequency-response spectrum. This approach is applied to a three-layer, unsymmetric laminate of WpCu, and very good agreement is found with the elastic constants of the two constituent materials.     

Assessment of sandwich models for the prediction of sound transmission loss in unidirectional sandwich panels

The consistent higher-order approach and the two-parameter foundation formulation are used for the derivation of sound transmission loss in symmetric unidirectional (infinitely wide) sandwich panels with isotropic face sheets. In both models, transmission loss is calculated using decoupled equations representing symmetric and anti-symmetric motions of a sandwich panel. The closed-form expressions for impedances and transmission coefficient of a symmetric sandwich panel with an isotropic core are derived for the two-parameter foundation model. A comparison between the numerical predictions based on the two sandwich models and available experimental data shows that the consistent higher-order formulation can be used to predict the transmission loss in symmetric sandwich panels with both honeycomb and isotropic cores. For prediction of transmission loss of symmetric sandwich panels with an isotropic core, the two-parameter foundation model is more convenient, while the consistent higher-order approach is more accurate.     

Current-voltage characteristics of radiating Josephson sandwich

Josephson sandwich is considered, along which the radiating chain of vortices travels. Uniform movement of the chain is supported by bias current. The current-voltage characteristic connecting this current with the voltage at the Josephson junction is found. It is shown that when the current increases, generation of electromagnetic waves with frequency weakly dependent on the current is possible.     

Stern-Gerlach studies of organometallic sandwich clusters

Stern-Gerlach type magnetic deflection measurements were performed for two types of multiple sandwich clusters: vanadium-benzene V_n(C₆H₆)_n+1 and terbium-cyclooctatetraene Tb_n(C₈H₈)_n+1. Beams of V_n(C₆H₆)_n+1 clusters (n = 1-4) showed symmetric broadening induced by the inhomogeneous field, indicating free spin behavior similar to that displayed by isolated paramagnetic atoms. By contrast, beams of Tb_n(C₈H₈)_n+1 clusters displayed one-sided deflection, indicating that fast spin relaxation occurs within the clusters. The difference in the magnetic deflection behavior exhibited by these two systems is explained by their electronic structures, specifically the bonding characteristics between metal atoms and ligand molecules.     

Free vibration of formed sandwich panel

In this paper, the free vibration of prefabricated architectural sandwich panels is studied. The core of the sandwich panel is approximated by finite prisms and the thin faces are modelled by finite strips. The finite prism-strip method is simple to program and saves considerable computing effort when compared with the finite element method. In this paper, only the dynamic characteristics of flat faced homogeneous sandwich panels are compared with results obtained by other methods, and also with the analytical solutions. Several examples are also presented for the free vibration of prefabricated architectural sandwich panels.     

Transverse vibrations of pre-twisted sandwich beams

A set of equations of motion governing the bending and extensional displacements of a pre-twisted sandwich beam of rectangular cross-section are derived by using Hamilton's principle. The middle viscoelastic core is assumed to deform mainly through the classical shearing mechanism. The eigenvalues and loss factors of simply supported pre-twisted sandwich beams are computed by using the variational method. Analysis of the results revealed that pre-twisting the beam increases the real part of the eigenvalue by as much as 20% while reducing the loss factor by as much as 30 %. The loss factor of very soft, thickcored beams is especially sensitive to even small angles of pre-twist: e.g., a 22· 5° pre-twist may reduce the loss factor by as much as 80%. The effect of pre-twist is, however, shown not to be appreciable for soft, thin-cored beams. In any case, pre-twisting of the beam has a detrimental effect on the maximum loss factor that one can obtain for a specific size of the beam when only the shear parameter of the beam is changed.     

Bending rigidity of fluctuating membranes

A lattice model of random surfaces is studied including configurations with arbitrary topologies, overhangs and bubbles. The Hamiltonian of the surface includes a term proportional to its area and a scale-invariant integral of the squared mean curvature. We propose a discretization of the curvature which ensures the scale-invariance of the bending energy on the lattice. Nonperturbative renormalization groups for the surface tension and the bending rigidity are applied, which are also valid at high temperatures and scales above the persistence length. We find at vanishing surface tensions a closed expression for the scale dependent rigidity including the usual logarithmic decay at low temperatures. Different scaling behaviours at non-vanishing tensions occur yielding characteristic length scales, which determine the structure of homogeneous droplet, lamellar, and microemulsion phases.