Multilayered Shells Research Articles

The Influence of Internal Factor on Crack Resistance of Shell Mold for Investment Models

The evolution of stress–strain state (SSS) of multilayer shell mold (SM) has been simulated upon variation of properties between the layers during cooling of casted steel. A mathematical model has been developed and the stress state of SM has been theoretically investigated in the case of absence of interrelation between the layers in multilayer composite material. The complex three-component system (liquid metal, solid metal, ceramic shell mold) has been analyzed. The solid metal and the SM are considered as isotropic. In order to solve the formulated problem, the theory of small elastic deformations and the equations of heat conductance have been applied as well as verified numerical methods. The SSS evolution in shell molds can be traced by time steps. The thickness of solidified metal is determined by the equation of interphase transition. Heating of axisymmetric SM during pouring of liquid metal is analyzed. The stress state has been estimated by stresses and displacements occurring in SM. During cooling of liquid metal at the contact between the shell mold and supporting filler (SF), the surface between them can be detached. In this case, the contact problem is solved. The calculations for the case of complete sliding of layers have been carried out with consideration of the compiled algorithm for problem solving by using the developed numerical schemes and software. The obtained numerical results are presented in the form of diagrams and plots. The obtained results have been analyzed in detail. The inconsistency of the previously proposed concept about applicability of sliding between the layers in multilayer composite material in terms of its strain state has been demonstrated. The experimental results can be useful for analysis of other functional multilayer shell systems.

Tuning three-dimensional nano-assembly in the mesoscale via bis(imino)pyridine molecular functionalization

We investigate the effect of bis(imino)pyridine (BIP) ligands in guiding self-assembly of semiconducting CdSe/ZnS quantum dots (QDs) into three-dimensional multi-layered shells with diameters spanning the entire mesoscopic range, from 200 nm to 2 μm. The assembly process is directed by guest–host interactions between the BIP ligands and a thermotropic liquid crystal (LC), with the latter’s phase transition driving the process. Characterization of the shell structures, through scanning electron microscopy and dynamic light scattering, demonstrates that the average shell diameter depends on the BIP structure, and that changing one functional group in the chemical scaffold allows systematic tuning of shell sizes across the entire range. Differential scanning calorimetry confirms a relationship between shell sizes and the thermodynamic perturbation of the BIP molecules to the LC phase transition temperature, allowing analytical modeling of shell assembly energetics. This novel mechanism to controllably tune shell sizes over the entire mesoscale via one standard protocol is a significant development for research on in situ cargo/drug delivery platforms using nano-assembled structures.

3D Stress Analysis of Multilayered Functionally Graded Plates and Shells under Moisture Conditions

This paper presents the steady-state stress analysis of single-layered and multilayered plates and shells embedding Functionally Graded Material (FGM) layers under moisture conditions. This solution relies on an exact layer-wise approach; the formulation is unique despite the geometry. It studies spherical and cylindrical shells, cylinders, and plates in an orthogonal mixed curvilinear coordinate system (α, β, z). The moisture conditions are defined at the external surfaces and evaluated in the thickness direction under steady-state conditions following three procedures. This solution handles the 3D Fick diffusion equation, the 1D Fick diffusion equation, and the a priori assumed linear profile. The paper discusses their assumptions and the different results they deliver. Once defined, the moisture content acts as an external load; this leads to a system of three non-homogeneous second-order differential equilibrium equations. The 3D problem is reduced to a system of partial differential equations in the thickness coordinate, solved via the exponential matrix method. It returns the displacements and their z-derivatives as a direct result. The paper validates the model by comparing the results with 3D analytical models proposed in the literature and numerical models. Then, new results are presented for one-layered and multilayered FGM plates, cylinders, and cylindrical and spherical shells, considering different moisture contents, thickness ratios, and material laws.

Generalized effective-field approximation for inhomogeneous medium with inclusions in multilayered shells

An approach is proposed for calculating effective physical characteristics of a inhomogeneous medium with several levels of nesting of its microstructure --- the generalized effective-field approximation. With the help of this approach, an expression is obtained for an effective permittivity tensor of an inhomogeneous medium with ellipsoidal inclusions in a multilayered shell, the boundaries of all layers of which are ellipsoids. The proposed approach allows to take into account probabilistic distributions of orientations and forms of inclusions, as well as the presence of several types of inclusions. Two cases of matrix composites are considered: 1) with spherical isotropic inclusions with a multilayered shell; 2) with ellipsoidal anisotropic inclusions with a multilayered shell. For an inhomogeneous medium with homogeneous inclusions, this approximation is shown to produce the same result as the generalized singular approximation. Keywords: inhomogeneous medium, composite, matrix, inclusion, multilayered shell, generalized effective-field approximation, generalized singular approximation, effective permittivity.

Обобщенное приближение эффективного поля для неоднородной среды с включениями в многослойной оболочке

An approach is proposed for calculating effective physical characteristics of a inhomogeneous medium with several levels of nesting of its microstructure - the generalized effective-field approximation. With the help of this approach, an expression is obtained for an effective permittivity tensor of an inhomogeneous medium with ellipsoidal inclusions in a multilayered shell, the boundaries of all layers of which are ellipsoids. The proposed approach allows to take into account probabilistic distributions of orientations and forms of inclusions, as well as the presence of several types of inclusions. Two cases of matrix composites are considered: 1) with spherical isotropic inclusions with a multilayered shell; 2) with ellipsoidal anisotropic inclusions with a multilayered shell. For an inhomogeneous medium with homogeneous inclusions, this approximation is shown to produce the same result as the generalized singular approximation.

Intercalation pseudocapacitance of hollow carbon bubbles with multilayered shells for boosting K-ion storage

A novel carbon skeleton constructed by hollow carbon boxes with a unique multilayered shell and an impressive large interlayer spacing of 0.76 nm, inducing the production of intercalation pseudocapacitance and high performance of K-ion storage.

The baric coefficient of CdSe quantum dot with a three-layer ZnS/CdS/ZnS shell

The model of CdSe quantum dot with a multilayer shell that undergoes mechanical deformation is constructed. This theory takes into account the influence of external hydrostatic pressure, the Laplace surface pressure and the mismatch of lattice parameters of contacting materials of the nanoheterosystem. Within the framework of the developed model, the baric coefficient of CdSe/ZnS/CdS/ZnS quantum dot was calculated for different values of the CdSe core radius and at different thicknesses of the ZnS/CdS/ZnS shell layers. It is established that for small cores (with a diameter of less than 4.8 nm) of quantum dots with a three-layer shell, two values of the baric coefficient are possible depending on the magnitude of external pressure. The analysis of use of the offered model for research of interaction of quantum dots with elements of biological systems through an elastic field of deformation is carried out.

Моделювання осциляції поверхонь клітин крові як заповнених рідиною багатошарових в’язкопружних оболонок

Rheological properties of the red blood cells (RBC) determine their movement in the larger and smaller blood vessels, oxygen and carbon dioxide delivery to/from the cells. Those properties vary significantly with age and health state of an organism. In this paper a new rheological model of RBC as a thin multilayer shell, which includes the cytoskeleton, lipid bilayer, glycocalyx, and hydrate shell as Maxwell's viscoelastic bodies is proposed. Mechanical properties of the rheological model in isotonic, isometric and dynamic experiments are studied. The oscillations of the surfaces of erythrocytes or other cells in the approximation of multilayer viscoelastic shell filled with a viscous fluid are investigated. The expressions for the dynamic Young’s modules and viscosity/fluidity coefficients as functions of the viscoelastic and geometric parameters of the layers are obtained. The problem of propagation of small perturbations along the cell surface is considered. The solutions of the problem in the form of Young and Lamé waves are obtained. The method of identification of the erythrocyte parameters from the experimental measurements of the wave propagation on the basis of the developed mathematical model for the purposes of clinical diagnostics of diseases with use of a microdrop of blood of the patient is proposed.

Calculation of multilayer cylindrical shells taking into account thermoelectric effect based on refined theory

Calculation of multilayer cylindrical shells taking into account thermoelectric effect based on refined theory

Selective catalysis for the reductive amination of furfural toward furfurylamine by graphene-co-shelled cobalt nanoparticles

An easy-to-prepare heterogeneous catalyst with multilayered graphene shells was obtained, which can synthesize functional amines from biomass-derived platforms with excellent efficiency.

Multi-layered ZIF-coated cells for the release of bioactive molecules in hostile environments.

Metal–organic framework (MOF) coatings on cells enhance viability in cytotoxic environments. Here, we show how protective multi-layered MOF bio-composite shells on a model cell system (yeast) enhance the proliferation of living cells exposed to hostile protease-rich environments via the dissolution of the shells and release of a protease inhibitor (antitrypsin).

NUMERICAL SOLUTION OF THE DYNAMIC PROBLEM OF AXISYMMETRIC VIBRATIONS OF REINFORCED SHELLS

The reliability of the results obtained in the work is determined by the rigor and correctness of the statements of the initial problems; theoretical substantiation of the finite-difference schemes used; controlled accuracy of numerical calculations; conducting test calculations; compliance of the established regularities with the general properties of oscillations of thin-walled structural elements. The correctness of the formulation of the problems is achieved by using the well-known equations of the theory of shells and rods of the Tymoshenko type, which are approximations of the original equations of the three-dimensional theory of elasticity. When deriving the equations, the equations of oscillations of the multilayer shell in the smooth region and the equations of oscillations of reinforcing ribbed elements (transverse ribs) were obtained. It is not difficult to show that the indicated equations by the classification of equations in partial derivatives are equations of the hyperbolic type, which are an approximation of the oscillating equations of three-dimensional elastic bodies and sufficiently correctly reproduce wave processes in non-homogeneous shell structures, taking into account spatial gaps. Numerical algorithms for approximate solutions of the original equations are based on the use of the integro-interpolation method of constructing difference schemes. When constructing difference schemes, kinematic quantities refer to difference points with integer indices, and the values of deformations and moment forces refer to difference points with half-integer indices. This approximation of the initial kinematic and static values allows the fulfillment of the law of conservation of the total mechanical energy of the elastic structure at the difference level. The numerical algorithm is based on the use of separate finite-difference relations in the smooth domain and on the lines of spatial discontinuities with the second order of accuracy in spatial and temporal coordinates.

Реологічні моделі біологічних клітин

The most important experimental methods of studying the mechanical properties of cells, as well as the most common rheological models, among which the discrete models of the micro/nanostructure of the cell and continuous models that allow calculating the modulus of elasticity and viscosity of the cell in normal and pathological conditions are discussed. A review of continuous models is given with an indication of their features and differences. A new continuum model of the cell as a multi-layer shell filled with a viscoelastic fluid is proposed. Equations of the model and their solutions for cases of isotonic, isometric and dynamic experiments are obtained. Peculiarities of the mechanical behavior of the models depending on the identified parameters are investigated. A comparison with the data of experimental measurements is given. It is shown that the proposed multi-layer model allows evaluation of separate contribution of the mechanical properties of the cytoskeleton, membrane, adsorbed substances and the hydrated shell, which is important for clinical diagnosis of diseases by measuring the mechanical parameters of cells.

Численное моделирование процесса изготовления крупногабаритного композитного кокона с учетом термовязкоупругости

The aim of this work is to obtain the evolution of contact pressure on the surface of the forming mandrel during the manufacture of large-scale composite shells by continuous winding. A numerical analogue of a real structure is built in the form of a system of assembly equipment, a forming mandrel and a shell. Effective viscoelastic characteristics for the shell material are obtained on the basis of experimental data and the concept of multilevel modeling. A series of computational experiments has been carried out to verify the model of thermoviscoelastic behavior of a composite material; the model is a combination of anisotropic elastic behavior of a medium with one independent viscoelastic operator. It has been found that, at the stage of winding, the influence of the behavior model of the shell material is not significant because viscoelasticity of the mandrel material makes the greatest contribution to the reduction of the contact pressure on the mandrel surface. Based on the data obtained, a conclusion is made that it is advisable and important to take into account the rheological properties not only of the material of the forming mandrel but also of the multilayer shell. The methods of finite element analysis presented in the work and the computational modules and programs implemented on their basis, as well as the calculation results, are of great practical importance for automating the process of predicting the evolution of the stress-strain state at the technological stages of manufacturing structures of the mandrel-shell type. Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.

On effect of friction between support filler and ceramic shell investment mould on its stress state during casting and cooling of steel casting

The results of a theoretical study of the regularities for change in the stress state of a cast multilayer shell investment mould during the cooling of a steel casting in it with a change in friction between the shell mould and the support filler, as well as friction between the layers in the shell mould itself.

Comprehensive assessment of the strength of the composite fan blade of the main ventilation of the mine

The work is devoted to the development and calculation of the strength of a new composite fan blade of the main ventilation of the mine, including the static and modal analyzes, as well as the stability analysis. The studies took into account the pre-determined aerodynamic loads on the lateral surface of the blade airfoil. The research was carried out by means of the finite element analysis of the thin-walled airfoil structure using the theory of thick multilayer shells. Estimation of the static strength was performed using the Hashin strength criterion. Analysis of the airfoil shell buckling resistance under the action of bending aerodynamic loads was performed using the methods of the linear stability theory. The modal analysis was performed taking into account the prestressed state from the action of static loads. The analysis of the research results testifies to the sufficient static and dynamic strength of the composite airfoil and the possibility of its implementation in a real rotary machine with the correct design of the fastening between the metal part of the blade root and the composite airfoil. The method of designing and analyzing the strength of the fan blade composite airfoil can be used to create new composite elements of turbomachines: the correct selection of thicknesses of different parts of the airfoil allows obtaining a uniform design with rational use of material; the optimal location of the stiffeners inside the airfoil shell avoids its excessive displacement and stress and the buckling effects, as well as achieving the maximal detuning level from the bending natural frequencies of vibrations; the proposed integrated approach to the strength assessment, which takes into account the effect of aerodynamic loads on the blade airfoil in the static analysis and the prestressed state during the modal analysis can significantly improve the accuracy and correctness of calculations. The approach described in the paper is new for low-speed rotary machines, as at present there are no comprehensive methods for designing composite blades of fans and compressors, and there is no mention of specific examples of their implementation in the projects implemented by manufacturers.

Mathematical models of laser correction of myopia by LASIK, SMILE and PRK

The stress-strain state of the human eye, which cornea in its apexis is weakened after myopia surgical correction, is studied. The elastic system “corneasclera” is presented as two joint transversely isotropic spherical segments with nonuniform thickness, different radii of curvature and biomechanical properties. The cornea is modeled as multilayer shell. The simulated eye shell is filled with an incompressible fluid. Mathematical models of three different laser vision correction surgeries: small incision lenticule extraction (SMILE), laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK), are developed in the engineering simulation software ANSYS Inc. The diameter and thickness of the lenticular in SMILE, the diameter of the ablation zone and the maximum thickness (depth) of the corneal ablation in LASIK and PRK define optical surgery areas and are considered as comparable parameters. Finite element simulation shows that after LASIK vision correction the apex of the cornea has a greater displacement and the stress increase greater in the stroma than after SMILE and PRK. The influence of the multilayer structure of the cornea and elastic characteristics of the sclera on the biomechanics of the eye as a result of vision correction is shown.

Investigation of the accuracy and convergence of the results of thin shells analysis using the PRINS program

The theoretical foundations of compatible finite elements construction for static and dynamic analysis of single-layer and multilayer shells are discussed. These finite elements are implemented in the PRINS computer program. The paper presents verification tests to investigate the accuracy and convergence of the results of calculating various shells using these finite elements. Shell structures are widely used in various fields of technology - construction, mechanical engineering, aircraft construction, shipbuilding, etc. Specialists on the design and calculation of such structures need a reliable and accessible tool for the practical problems solving. Computer program PRINS can be one of such tools. It can be effectively used by engineers of design and scientific organizations to solve a wide class of engineering problems related to the calculations of shell structures. The paper describes the finite elements of the shells, implemented in the PRINS program. The results of verification calculations are presented, which confirm the high accuracy of this program.

Polyaminoacid Based Core@shell Nanocarriers of 5-Fluorouracil: Synthesis, Properties and Theranostics Application.

Cancer is one of the most important health problems of our population, and one of the common anticancer treatments is chemotherapy. The disadvantages of chemotherapy are related to the drug’s toxic effects, which act on cancer cells and the healthy part of the body. The solution of the problem is drug encapsulation and drug targeting. The present study aimed to develop a novel method of preparing multifunctional 5-Fluorouracil (5-FU) nanocarriers and their in vitro characterization. 5-FU polyaminoacid-based core@shell nanocarriers were formed by encapsulation drug-loaded nanocores with polyaminoacids multilayer shell via layer-by-layer method. The size of prepared nanocarriers ranged between 80–200 nm. Biocompatibility of our nanocarriers as well as activity of the encapsulated drug were confirmed by MTT tests. Moreover, the ability to the real-time observation of developed nanocarriers and drug accumulation inside the target was confirmed by fluorine magnetic resonance imaging (19F-MRI).

Research on seismic performance of precast steel–concrete composite tube shear walls with horizontal joint

An innovative precast steel–concrete composite tube (SCCT) shear wall with horizontal joints is proposed, in which the horizontal joints are arranged in the middle of shear walls, the thin-walled steel tube, piercing bars and cover concrete provide restraint for the concrete inside the tube to improve the strength and deformation capacity of internal concrete, and the internal and outer concrete, piercing bars are used to avoid the out-of-plane deformation of the thin-walled steel tube. The experimental program was conducted on five full scale models of SCCT shear walls and one cast-in-situ RC shear wall (SW) subjected to cyclic loading. The results revealed that the precast SCCT shear walls with horizontal joints had high strength, stiffness, ductility and energy dissipation, verifying the reliability of the horizontal joints. Moreover, the horizontal joints had little impact on the overall seismic performance of the SCCT shear walls. In addition, two types of failure modes were observed in the SCCT shear walls, where type A was the ideal failure mode making full use of the steel materials and type B with the characteristics of brittle failure should be avoided. Based on the test results, an analytical model was established to calculate the normal section bearing capacity of the SCCT shear walls, and the proposed model was validated using the test results. Finally, finite element analysis (FEA) models of specimens were proposed based on a multilayer shell element, and a parameter study based on the proposed FEA model was conducted to investigate the influence of critical parameters on the mechanical performance of the SCCT shear walls.