Shells Of Variable Thickness Research Articles

Facile transformation of carboxymethyl cellulose beads into hollow composites for dye adsorption

Novel millimeter hollow microspheres were fabricated from carboxymethyl cellulose microspheres and polyethyleneimine using glutaraldehyde as a crosslinking agent. The hollow microspheres prepared with different polyethyleneimine usages and different polyethyleneimine treatment time were investigated deeply and characterized via SEM-EDX, FT-IR, and BET surface area analysis. It was shown that polyethyleneimine could break the coordination bonds between the carboxyl and Al (III) in carboxymethyl cellulose microspheres, leading to the formation of hollow structures. Most importantly, the usage and treatment time of polyethyleneimine can distinctly tailor the structure of the carboxymethyl cellulose microspheres, resulting in the formation of different hollow microspheres with varied shell thickness and size. Most importantly, we found that the prepared hollow microspheres have excellent adsorption performance toward targeted methyl blue under testing conditions. By virtue of the large accessible amount of -NH2 groups and its unique hollow structure, this type of millimeter hollow microspheres have broad application prospects in the treatment of emerging contaminants in wastewater.

The Influence of Variable Shell Thickness on the Vibrational Behavior of Composite Sandwich Conical Shells with Geodesic Lattice Cores

This paper investigates the vibrational behavior of sandwich conical shells with geodesic lattice core and variable skin thicknesses using analytical and numerical approaches. The filament wound conical shell has been considered to have varying skin thickness along the longitudinal direction. The smeared stiffener approach has been used to obtain the equivalent stiffness parameters due to the geodesic lattice core via the force and moment analyses of a unit cell. Superimposing the stiffness contribution of the stiffeners with those due to the inner and outer skins, one can calculate the equivalent stiffness of the whole structure. The equations of motion have been formulated based on the first-order shear deformation theory. The power series method has been implemented for extracting the natural frequencies of vibration. To validate the analytical results, a 3-D finite element model has been provided which is then used to conduct an extensive parametric study. The comparisons indicate an acceptable agreement between the two approaches. Moreover, the effect of variable skin thickness on the natural frequency has been examined. Furthermore, the influences of skin lamination angle, semi-vertex angle of the cone and stiffeners orientation angle have been discussed. The obtained results can be used for future relevant researches.

Tailoring 3D printed graded architected polymer foams for enhanced energy absorption

Graded material design strategy has been exploited to achieve enhanced mechanical performance compared to their uniform counterpart. Using a combined numerical and experimental approach, we investigated the effects of three graded designs on the compressive mechanical performance of 3D printed architected polymer foams. The architected foam is composed of beam binders and spherical shells, which have pronounced effects on the mechanical performance under large deformations. It was found that three failure mechanisms dominate the mechanical behavior of foams for different binder sizes, including binder-failure-only, shell-failure-only, and binder-shell-failure. The investigation of shell thickness variation showed that the relation between relative stiffness and relative density is E/Es~(ρ/ρs)1.56, indicating a bending-dominant deformation behavior. Guided by these findings, we studied the mechanical behavior of three types of graded designs, including graded binder, graded shell thickness, and a hybrid strategy. It was found that the specific energy absorption of hybrid foam is enhanced by 125 %, 185 %, and 34 % compared to uniform foam, graded binder foam, and graded thickness foam, respectively. Furthermore, compared with existing lattice-based and shell-based graded foams, the stiffness of hybrid graded foam increases by 346 % and 33 %, respectively; the specific energy absorption of hybrid graded foam increases by 141 % and 32 %, respectively. The findings presented open a new avenue to engineer architected materials with enhanced mechanical properties, finding applications ranging from structural components of defense systems to protection systems in vehicles.

Observation of laser-assisted electron scattering in superfluid helium

Laser-assisted electron scattering (LAES), a light–matter interaction process that facilitates energy transfer between strong light fields and free electrons, has so far been observed only in gas phase. Here we report on the observation of LAES at condensed phase particle densities, for which we create nano-structured systems consisting of a single atom or molecule surrounded by a superfluid He shell of variable thickness (32–340 Å). We observe that free electrons, generated by femtosecond strong-field ionization of the core particle, can gain several tens of photon energies due to multiple LAES processes within the liquid He shell. Supported by Monte Carlo 3D LAES and elastic scattering simulations, these results provide the first insight into the interplay of LAES energy gain/loss and dissipative electron movement in a liquid. Condensed-phase LAES creates new possibilities for space-time studies of solids and for real-time tracing of free electrons in liquids.

Deposition of a SiO2 Shell of Variable Thickness and Chemical Composition to Carbonyl Iron: Synthesis and Microwave Measurements.

Protective SiO2 coating deposited to iron microparticles is highly demanded both for the chemical and magnetic performance of the latter. Hydrolysis of tetraethoxysilane is the crucial method for SiO2 deposition from a solution. The capabilities of this technique have not been thoroughly studied yet. Here, two factors were tested to affect the chemical composition and the thickness of the SiO2 shell. It was found that an increase in the hydrolysis reaction time thickened the SiO2 shell from 100 to 200 nm. Moreover, a decrease in the acidity of the reaction mixture not only thickened the shell but also varied the chemical composition from SiO3.0 to SiO8.6. The thickness and composition of the dielectric layer were studied by scanning electron microscopy and energy-dispersive X-ray analysis. Microwave permeability and permittivity of the SiO2-coated iron particles mixed with a paraffin wax matrix were measured by the coaxial line technique. An increase in thickness of the silica layer decreased the real quasi-static permittivity. The changes observed were shown to agree with the Maxwell Garnett effective medium theory. The new method developed to fine-tune the chemical properties of the protective SiO2 shell may be helpful for new magnetic biosensor designs as it allows for biocompatibility adjustment.

Dynamic Stability of Orthotropic Viscoelastic Rectangular Plate of an Arbitrarily Varying Thickness

The research object of this work is an orthotropic viscoelastic plate with an arbitrarily varying thickness. The plate was subjected to dynamic periodic load. Within the Kirchhoff–Love hypothesis framework, a mathematical model was built in a geometrically nonlinear formulation, taking into account the tangential forces of inertia. The Bubnov–Galerkin method, based on a polynomial approximation of the deflection and displacement, was used. The problem was reduced to solving systems of nonlinear integrodifferential equations. The solution of the system was obtained for an arbitrarily varying thickness of the plate. With a weakly singular Koltunov–Rzhanitsyn kernel with variable coefficients, the resulting system was solved by a numerical method based on quadrature formulas. The computational algorithm was developed and implemented in the Delphi algorithmic language. The plate’s dynamic stability was investigated depending on the plate’s geometric parameters and viscoelastic and inhomogeneous material properties. It was found that the results of the viscoelastic problem obtained using the exponential relaxation kernel almost coincide with the results of the elastic problem. Using the Koltunov–Rzhanitsyn kernel, the differences between elastic and viscoelastic problems are significant and amount to more than 40%. The proposed method can be used for various viscoelastic thin-walled structures such as plates, panels, and shells of variable thickness.

Scenario of carbon‐encapsulated particle synthesis by spark discharges in liquid hydrocarbons

AbstractDischarges in liquid hydrocarbons produce submicrometric particles with a graphitic shell. In this study, discharges are generated between two Cu electrodes immersed in various liquid hydrocarbons, and the produced particles are characterized by various techniques. The obtained results indicate that the thickness of the particle shell increases with increasing particle size; for instance, it is ~4 nm for small particles (~25 nm) and ~30 nm for large particles (~1 µm). Such variation in shell thickness is attributed to variations in the thermal properties of different‐size particles. On the basis of qualitative analysis, we assume that shell growth is induced by local pyrolysis (or pyrolysis‐like process) of the liquid hydrocarbon due to the ejection of hot particles from the electrodes.

Productivity enhancement of laser powder bed fusion using compensated shelled geometries and hot isostatic pressing

In laser powder bed fusion (L-PBF), the mechanical performance and especially fatigue properties of fabricated parts are significantly improved by hot isostatic pressing (HIP) as the density increases (pores are closed) and the microstructure improves. HIP ensures consistent and defect-free material, and consequently, this high temperature and high pressure process is often a requirement for safety-critical aerospace applications. The use of HIP to directly consolidate intentionally-unmelted interior powder in a L-PBF part was recently demonstrated. By confining the laser melting to only the outer shell (contour) of the structure, L-PBF production times can be dramatically reduced. A subsequent HIP cycle, which may be mandatory for reliability reasons, and therefore does not add additional costs, is then used to densify the entire structure. Production rates and energy efficiencies can therefore be improved in this way. This study explores the effect of relying on the HIP process to consolidate interior sections of test coupons, for which micro computed tomography (microCT), process simulation and tensile tests were conducted. MicroCT of coupons with varying shell thicknesses identify the minimum shell thickness required; and provide indications of the shrinkage ratio as a function of powder content relative to shell thickness. Preliminary results are included in which the shrinkage can be compensated for during design, by way of a “bloated cube” which collapses to a nominal cube geometry after HIP. The mechanical evaluation of the consolidated shelled parts indicates that their tensile performance is equivalent to those observed on fully dense printed parts. Up to an order of magnitude faster build rates are possible and any resulting shrinkage or distortion can be offset at design.

Application of multilayer finite elements of variable thickness in the calculation of reinforced concrete slabs in the "Prince" computer complex

Objective. A family of multilayer finite elements designed for calculating reinforced concrete slabs and shells of variable thickness is described. The features of the formation of stiffness matrices associated with the variability of the cross-section of elements are considered.Methods. The family is based on the simplest planar triangular element constructed using the Kirchhoff hypothesis. The transverse displacements in this element are approximated by an incomplete cubic polynomial. This element is not suitable for practical use, but it is based on improved elements of three- and foursided shape in the plan. Special attention is paid to the consideration of cross-section variability.Results. The results of testing the developed elements are presented and the advantages of their use in the practice of design and calculation of structures are shown.Conclusion. The developed PRINCE software package can be useful in the design and calculation of structures containing plates of variable thicknesses.

Pteropods make thinner shells in the upwelling region of the California Current Ecosystem

Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity. While short-term incubations have demonstrated that pteropod calcification is negatively impacted by ocean acidification, we know little about net calcification in response to varying ocean conditions in natural populations. Here, we examine in situ calcification of Limacina helicina pteropods collected from the California Current Ecosystem, a coastal upwelling system with strong spatial gradients in ocean carbonate chemistry, dissolved oxygen and temperature. Depth-averaged pH ranged from 8.03 in warmer offshore waters to 7.77 in cold CO2-rich waters nearshore. Based on high-resolution micro-CT technology, we showed that shell thickness declined by ~ 37% along the upwelling gradient from offshore to nearshore water. Dissolution marks covered only ~ 2% of the shell surface area and were not associated with the observed variation in shell thickness. We thus infer that pteropods make thinner shells where upwelling brings more acidified and colder waters to the surface. Probably the thinner shells do not result from enhanced dissolution, but are due to a decline in calcification. Reduced calcification of pteropods is likely to have major ecological and biogeochemical implications for the cycling of calcium carbonate in the oceans.

Nonlinear dynamics of heterogeneous shells Part 1. Statics and dynamics of heterogeneous variable stiffness shells

The increasing complexity of the constructive forms and shell elements structure leads to the need to develop both the theory and methods for solving static and dynamic problems for non-homogeneous (heterogeneous) shells.By the shell heterogeneity, we mean heterogeneity in a broad sense: these are inclusions in the shell body of the different rigidity elements and, as a special case, these are holes; the material inhomogeneity caused by a change in the stress–strain state under the influence of both static and dynamic loads; stiffeners; and by taking into account the physical nonlinearity and different modulus of the shell material.This work is devoted to the mathematical model creation of the statics and dynamics for non-homogeneous shells in the above sense and consists of two parts.In the first part, a mathematical model of statics and dynamics for rectangular shells described by the Kirchhoff–Love kinematic model is constructed. Geometric nonlinearity is taken into account on the basis of T. von Kármán’s geometric model, physical nonlinearity — according to the deformation theory of plasticity, based on the elasticity variable parameters method. Stiffness heterogeneity is taken into account using the Heaviside function. The original equations were obtained from Hamilton’s variational principle. A numerical experiment is performed using the Faedo–Galerkin method in higher approximations. The convergence of this method is investigated.In the second part, the nonlinear dynamics of axisymmetric elastic variable thickness shells is investigated. In contrast to the first part of this work, where the Faedo–Galerkin method in higher approximations was used to reduce partial differential equations to the Cauchy problem, in this part the Ritz method in higher approximations is employed. For differential operators used in two parts of this work, according to the research of S.G. Mikhlin, the Ritz and Faedo–Galerkin methods are equivalent. The convergence of the applied numerical method is investigated. An approach is proposed for the zones study of oscillation types for variable thickness shells using dynamic modes maps.

A COMPARATIVE STUDY OF THE PHYSICAL AND CHEMICAL CHARACTERISTICS OF GUINEA FOWL AND DOMESTIC CHICKEN EGGS

Some physical and chemical parameters of eggs from the domestic chicken and guinea fowl, reared under identical conditions were studied in order to determine the difference in their composition. The eggs analyzed were collected from domestic chickens (Warren Strain) and domesticated guinea fowls (Grey breasted pearl strains) which were about 40 weeks old and maintained on the same layer diet with groundnut cake as the protein source. The guinea fowl had significantly higher shell thickness than chicken egg shell, but the latter showed greater variation in shell thickness between eggs. Correlations between a number of physical and chemical parameters were small in both chicken and guinea fowl eggs. Although the chicken egg had significantly higher albumen and yolk contents compared to the guinea fowl egg, the protein, fat and amino acid composition of the two types of eggs, expressed as gram per 100g edible portion, were independent of breed.

Dynamic analysis of an orthotropic viscoelastic cylindrical panel of variable thickness

The intensive development of the modern industry is associated with the emergence of a variety of new composite materials. Plates, panels, and shells of variable thickness made of such materials are widely used in engineering and machine building. Modern technology for the manufacture of thin-walled structures of any configuration makes it possible to obtain structures with a given thickness variation law. Such thin-walled structures are subjected to various loads, including periodic ones. Nonlinear parametric vibrations of an orthotropic viscoelastic cylindrical panel of variable thickness are investigated without considering the elastic wave propagation. To derive a mathematical model of the problem, the Kirchhoff-Love theory is used in a geometrically nonlinear setting. The viscoelastic properties of a cylindrical panel are described by the hereditary Boltzmann-Volterra theory with a three-parameter Koltunov-Rzhanitsyn relaxation kernel. The problem is solved by the Bubnov-Galerkin method in combination with the numerical method. For the numerical implementation of the problem, an algorithm and a computer program were developed in the Delphi algorithmic language. Nonlinear parametric vibrations of orthotropic viscoelastic cylindrical panels under external periodic load were investigated. The influence of various physical, mechanical, and geometric parameters on the panel behavior, such as the thickness, viscoelastic and inhomogeneous properties of the material, external periodic load, were studied.

A study of tunable optical properties of ZnO/CdS heterostructures with varying shell thickness structures

The ZnO/CdS core/shell nanostructures have attracted much attention in their specific tunable optical characteristics have led to the present day. The preparation method of core/shell structures by Starch is an advantageous method. The optical properties of CdS/ZnO nanostructures have significant effects on their visible region. The physics behind the electron and holes wave functions separation in this type II ZnO/CdS core/shell nanostructure is well explained.

Thickness control of TiN network in CoCrFeNi matrix composite with tunable microstructure

A bottom up approach is designed where a TiN coated CoCrFeNi core- core-shell powder was used as a building block to fabricate CoCrFeNi matrix composites with tunable microstructure. Initially, the core-shell powder was achieved by surface nitriding of mechanically alloyed CoCrFeNiTi powder. By controlling the treatment parameters, powders with variable shell thickness were achieved. Afterwards, the core-shell powder was sintered via spark plasma sintering. The sintered microstructures consisted of CoCrFeNi matrix along with a continuous network of TiN. After sintering of for powders with a thin shell, the matrix phase was Ti rich resulting in the precipitation of intermetallic phase. Additionally, the reinforcement network showed high connectivity. As the shell thickness was increased, the matrix became Ti deficient resulting in the suppression of intermetallic precipitation. The increase in shell thickness also caused discontinuities in the reinforcement network. These microstructural changes impacted the thermal and mechanical properties of the resultant composite. The reinforcement network significantly reduced the coefficient of thermal expansion of the matrix phase. Additionally, all composites showed fracture strength in excess of 1 GPa showing excellent reinforcement efficiency in the designed microstructure.

Tunable strain drives the activity enhancement for oxygen reduction reaction on Pd@Pt core-shell electrocatalysts

An effective way to tune the surface reactivity of catalysts in electrocatalysis is by engineering their surface strain. Traditionally, activity enhancement for the oxygen reduction reaction (ORR) can be attributed to both strain and ligand effects for Pt-based catalysts. Herein, we successfully use variable shell thickness to tune surface strain and thus tailor the ORR catalytic activity of core-shell electrocatalysts in acid media. Increasing reaction temperature from 140 °C to 180 °C in a typical one-pot solvothermal method increases the thickness of Pt shells from 3.0 to 14.0 monolayers, by increments of 3 monolayers per 10 °C (3 ML/10 °C). The surface strains of −1.85% to −0.18% are achieved with increasing Pt shell thickness. Relative to a commercial Pt/C catalyst, the optimum mass activity of a Pd@Pt3.4L/C catalyst (0.95 A mgPt−1) is found to be greater by a factor of 5.3. The theoretical study on the strain-activity relation reveals that Pd@Pt3.4L/C possesses 1.85% of surface compression, and the optimum oxygen binding energy (0.15 eV). The Pd@PtnL/C catalysts show desirable stability compared with commercial Pt/C catalyst after 8000 cycles, especially Pd@Pt5.3L/C, with 97.7% of initial mass activity.

Nonlinear dynamics of heterogeneous shells. Part 2. Chaotic dynamics of variable thickness shells

In the second part of the article, the nonlinear dynamics and stability of nonhomogeneous variable thickness axisymmetric shells are analyzed. The mathematical model is based on the Kirchhoff–Love kinematic hypothesis. The resulting system of partial differential equations is reduced to an algebraic equations system by the Ritz method. The convergence of the applied numerical methods is investigated. The chaotic vibrations’ control of variable thickness shells using dynamic charts of vibration regimes is also developed.

The Effects of a Varied Gold Shell Thickness on Iron Oxide Nanoparticle Cores in Magnetic Manipulation, T1 and T2 MRI Contrasting, and Magnetic Hyperthermia.

Fe3O4–Au core–shell magnetic-plasmonic nanoparticles are expected to combine both magnetic and light responsivity into a single nanosystem, facilitating combined optical and magnetic-based nanotheranostic (therapeutic and diagnostic) applications, for example, photothermal therapy in conjunction with magnetic resonance imaging (MRI) imaging. To date, the effects of a plasmonic gold shell on an iron oxide nanoparticle core in magnetic-based applications remains largely unexplored. For this study, we quantified the efficacy of magnetic iron oxide cores with various gold shell thicknesses in a number of popular magnetic-based nanotheranostic applications; these included magnetic sorting and targeting (quantifying magnetic manipulability and magnetophoresis), MRI contrasting (quantifying benchtop nuclear magnetic resonance (NMR)-based T1 and T2 relaxivity), and magnetic hyperthermia therapy (quantifying alternating magnetic-field heating). We observed a general decrease in magnetic response and efficacy with an increase of the gold shell thickness, and herein we discuss possible reasons for this reduction. The magnetophoresis speed of iron oxide nanoparticles coated with the thickest gold shell tested here (ca. 42 nm) was only ca. 1% of the non-coated bare magnetic nanoparticle, demonstrating reduced magnetic manipulability. The T1 relaxivity, r1, of the thick gold-shelled magnetic particle was ca. 22% of the purely magnetic counterpart, whereas the T2 relaxivity, r2, was 42%, indicating a reduced MRI contrasting. Lastly, the magnetic hyperthermia heating efficiency (intrinsic loss power parameter) was reduced to ca. 14% for the thickest gold shell. For all applications, the efficiency decayed exponentially with increased gold shell thickness; therefore, if the primary application of the nanostructure is magnetic-based, this work suggests that it is preferable to use a thinner gold shell or higher levels of stimuli to compensate for losses associated with the addition of the gold shell. Moreover, as thinner gold shells have better magnetic properties, have previously demonstrated superior optical properties, and are more economical than thick gold shells, it can be said that “less is more”.

Validation of a Simulation Methodology for Thermoplastic and Thermosetting Composite Materials Considering the Effect of Forming Process on the Structural Performance.

This research work investigated the influence of the press molding manufacturing process on the mechanical properties, both for thermoplastic and thermosetting fiber reinforced composite materials. The particular geometry of the case study, called Double Dome, was considered in order to verify the behavior of the Thermoplastic and Thermosetting prepreg in terms of shell thickness variation and fibers shear angle evolution during the thermoforming process. The thermoforming simulation was performed using LS-DYNA® Finite Element Analysis (FEA) code, and the results were transferred by Envyo®, a dedicated mapping tool, into a LS-DYNA® virtual model for the structural simulation. A series of Double Dome specimens was produced with industrial equipment, and a bending experimental test was been carried on. Finally, a numerical-experimental correlation was performed, highlighting a significant forecast of the mechanical properties for the considered component.

Dual-purpose concrete domes: A strategy for the revival of thin concrete shell roofs

The use of thin concrete shells as long-span roofing solutions has declined over the past 60 years, largely as a result of the expensive nature of the formwork for curved surfaces, and the stiff competition from other more economical options such as steel space grids. The purpose of this contribution is to explore the simultaneous use of thin concrete shells for roofing and liquid-containment purposes. It is hoped the concept of dual-purpose concrete shells will provide enhanced justification for the higher costs associated with the construction of curved surfaces, thereby helping to revive the widespread use of elegant thin concrete shells once again. Specifically, the state of stress in various dual-purpose configurations is evaluated, and the effect of varying shell thickness in critical zones is investigated, allowing some preliminary insights to be gained. With appropriate thickness enhancement in the critical zones, the concept appears feasible, but before firm conclusions can be made, detailed buckling studies need to be undertaken.