Contents

Keywords: layered metal-composite, regular structure, secondary creep, general anisotropy, structural theory

Iterative models describing the mechanical behavior of layered metal-composite media of regular structure whose constituent materials operate under the conditions of secondary anisotropic creep are offered. The modeling is carried out both with and without account of nonelastic dilatation of the constituent materials.

Keywords: laminated composite plate, high-order model, elasticity theory

An efficient method of solving 3D elasticity problems for thick and thin laminated composite plates is presented. It is based on a new concept of reference surfaces inside the plate. According to this concept, into each n-th layer, In arbitrary reference surfaces parallel to the midsurface are introduced, and the displacement vectors of these surfaces are chosen as unknown functions. Such a choice allows one to represent the governing equations of the high-order theory of plates proposed in a very compact form and to derive strain–displacement relationships correctly describing all rigid-body motions of laminated plates.

Keywords: relaxation and retardation spectra (RRS), signal processing, integral transforms, inversion, ill-posed problems, functional filter

The problem of determination of relaxation and retardation spectra (RRS) is considered from the viewpoint of up-to-date signal processing. It is shown that the recovery of RRS represents the Mellin deconvolution problem, which transforms into the Fourier deconvolution problem for data on a logarithmic time or frequency scale, where it can also be treated as the inverse filtering problem. On this basis, discrete deconvolution (inverse) filters operating with geometrically sampled data are proposed to use as RRS estimators. Appropriate frequency responses and algorithms are derived for estimating RRS from eight different material functions. The noise amplification coefficient is suggested to use as a measure for quantifying the degree of ill-posedness and ill-conditioness of the RRS recovery problem and algorithms. A methodology is developed for designing RRS estimators with a desired noise amplification, producing maximum accurate spectra for available limited input data. Practical algorithms for determining RRS are proposed, and their performance is studied. The algorithms suggested are compared with the so-called moving-average formulae. It is demonstrated that the minimum frequency range for recovering a point estimate of a relaxation spectrum depends on the allowable noise amplification (the degree of ill-conditioness) and is in no way limited by 1.36 decades, as it is stated by the sampling localization theorem.

Keywords: polyethylene, carbon nanotubes, composite, crystallinity, mechanical properties

Results of an investigation into the properties of polyethylene (PE) with small, no more than 5 wt.%, additions of multi-wall carbon nanotubes (CNTs) are reported. Specimens of the composite were prepared using a concentrate, containing 31.6 wt.% of nanotubes in the polyethylene matrix. The concentrate was fabricated by a patent in situ polymerization method. Experimental data on the influence of CNT additions on the thermograms of differential scanning calorimetry, the crystallinity of the polyethylene matrix, and the indices of mechanical properties (yield stress, strength, elastic modulus, ultimate elongation, and long-term creep) of the PE/CNT composite are obtained. A theoretical analysis of elastic properties of the composite was carried out by using the Mori–Tanaka theory of an equivalent medium. The calculation results are compared with experimental data.

Keywords: bending modulus, thin-walled shell, PVC

A method for determining the elastic modulus of polymeric materials from deformation diagrams of thin-walled circular cylindrical shells in compression and tension in the region of geometrical nonlinearity has been elaborated. A numerical solution is found by the finite-element method (ANSYS). The existence of a unified deformation diagram in generalized coordinates is established, from which the elastic modulus is determined. To validate the method, the eigenfrequencies of cylindrical specimens were found experimentally. The results obtained are compared with FEM calculations.

Keywords: boundary-discontinuous Fourier series, cross-ply plate, higher-order theory, doubly curved shells, simple supports

The boundary-discontinuous double Fourier series-based solution methodology is used to solve the problem of higher-order shear deformation of cross-ply plates and doubly curved panels, which are characterized by a system of five highly coupled linear partial differential equations with mixed-type simply supported boundary conditions prescribed at all four their edges. The present solution is related to a number of unsolved boundary-value problems and can serve as a tool in particular for early design stages and for benchmark comparisons and verifications of numerical results. The analytical results obtained are compared with finite-element calculations, and a good agreement is found to exist between them.

Keywords: cylindrical vessel, hydrogen, filament winding, liner, analysis of damage behavior

The damage behavior of a type-3 hydrogen storage vessel is modeled. The vessel consists of a metal envelop, called liner, coated with a filament winding. The model proposed allows simulating the mechanical response of the structure to a quasi-static loading. The model is based on a meso-macro approach and takes into account the damage behavior of the composite and the elastoplastic deformation of the liner. The results obtained are compared with experimental data. Finally, the effect of stacking sequence of filament layers on the damage level in the composite is investigated.

Keywords: functionally graded material, fly ash, rubber composite, Young's modulus, finite-element analysis

A novel approach to estimate the Young's modulus of a functionally graded rubber composite (FGRC) from the damping ratio is demonstrated with the examples of unreinforced and fly ash-reinforced materials. FGRC coupons were prepared using the conventional casting technique. The occurrence of gradation in the specimens was attributed to the variable density of particles present in the fly ash, settling at different depths. The technique of free vibrations was used for experimentation. The damping response of the FGRC specimens was studied. The results obtained from the experiments showed that, with growing filler weight fraction, the Young's modulus of the composite increased. The empirical model developed to predict the magnitude of the modulus turned out to be in good agreement with experimental data.

Keywords: composite cylindrical panels, delamination

Using the Rayleigh–Ritz method, the natural frequencies of layered cylindrical shells with delaminations are derived. The results are compared with FE computations and with data available in the literature. It is demonstrated that the transverse shear effects can play a significant role in a correct and accurate evaluation of the natural frequencies of such shells. Numerical investigations into the problem of radial excitations of cylinders with delaminations have also been performed. From the results obtained, it follows that their optimal excitation frequency is related to the natural frequency of a local region containing the delamination.

Keywords: two-layer ring, corrosive wear, initial strain, radial vibrations, limiting value of frequency, delamination

A two-layer ring, with account of its initial state caused by internal pressure and corrosion, leading to wear, is considered. The ring is subjected to an additional pressure causing its radial vibrations. It is shown that, under certain conditions, there is a vibration frequency at which the delamination of the ring is possible. Expressions are found which determine this frequency as a function of problem parameters, in particular, of the time of corrosive wear.

Keywords: nonwovens, cellulose fibers, poly(vinyl alcohol), water solutions, structure, strength-deformation characteristics

The results of a study on the strength-deformation characteristics (tensile elastic modulus, ultimate strengths, elongation at break, punching and tearing strengths) of two kinds of cellulose fiber nonwovens (CFN) with dissimilar void content and different geometrical parameters of cellulose fibers are discussed. The structural characteristics of composites prepared by impregnation with poly(vinyl alcohol) water solutions are analyzed, too. Composites with volume fractions of polymer up to 0.4% and volume fractions of voids up to 0.3% were prepared. The filling of voids by the polymer occurred without significant changes in the structure of CFN. The fraction of closed voids increased with polymer content.