Thin Shell Research Articles

Synthesis of core-shell PFPE@SiO2 nanocapsules and their self-lubrication effect in phenol-formaldehyde resin

To improve the mechanical properties and tribological properties of desirable polymer composites, a novel nano-encapsulated perfluoroyeyeane @ silica (PFPE@SiO2) nanocapsules were used to modify the phenol-formaldehyde (PF) resin composites (PFPE@SiO2-PF). These nanocapsules were successfully obtained by interfacial polymerization, exhibited a consistent size ranging from 130 nm to 180 nm, along with a thin shell thickness of 19.4 nm and a high oil-contenting rate of 49.13 wt%. The prepared PFPE@SiO2-PF composites simultaneously demonstrated excellent mechanical properties and tribological performances. Specifically, the compressive strength of the 5 wt%-PF was increased by 33.3% than that of pure PF resin. Moreover, the friction coefficient (COF) of the 25 wt%-PF (50 N) could be reduced by 86.3% (from 0.564 to 0.077) and the wear rate could be reduced by 98.0% (from 69.8 × 10−6 mm3 N−1 m−1 to 1.4 × 10−6 mm3 N−1 m−1). The PFPE oil released from the nanocapsules during the friction process produced a transfer film which brought an extremely low COF and wear rate. These results confirmed the excellent self-lubricating property of the PFPE@SiO2-PF composites and presented a potential application in fabricating self-lubricating polymer composites field.

Some Remarks on the Phase Transformation of Gas Hydrates in Porous Sediments at Negative Celsius Temperatures

The article presents a solution to the problem of the phase transition of methane hydrate — methane-gas + ice in porous hydrate-containing sediments at a negative Celsius temperature in the medium. The numerical solution of the resulting system of differential equations of piezoand thermal conductivity makes it possible to effectively simulate the change in pressure and temperature in both time and space in a medium of any dimension during its heating or decompression. In this case, the medium is not subdivided into parts with varying phase states of methane hydrate. Instead, its sediment substance is considered as a single entity, with its physical properties changing in magnitude when the hydrates undergo phase transformation. As an example, the problem of the thermobaric regime of a heating spherical cavern containing ice, hydrate and free methane has been solved. This cavern is situated within a continuous gas-tight underground ice. The solution shows that although the temperature of the sphere surface increases considerably, the decomposition of hydrate only occurs in an extremely thin shell located directly between the surface and the displaced inward phase boundary.Over time, the stability conditions of hydrates establish anew but at a higher gas pressure and medium temperature. This phenomenon of severely limited decomposition of the hydrate in a closed gas-insulated space, nevertheless leading to an increase in pressure in it, is, apparently, the basic process that provides the “self-preservation” of methane hydrates.

Magneto-thermoelastic coupled resonance characteristics of a rotating functionally graded ferromagnetic cylindrical shell under double harmonic line loads

The magneto-thermoelastic coupled resonance of a rotating functionally graded (FG) ferromagnetic cylindrical shell subjected to double harmonic line loads in magnetic and temperature fields is investigated. In accordance with Donnell's thin shell theory on the physical neutral surface, the nonlinear geometric equations are determined. Utilizing the thermoelastic constitutive relationships, combining with the gradient characteristics and temperature dependence of physical parameters, the governing equations of kinetic energy and strain energy are given. Based on the magnetoelasticity theory, and considering the nonlinear magnetization of ferromagnetic metal, the calculation formulas of Lorentz force and magnetizing force acting on the shell are deduced. The magneto-thermoelastic coupled dynamic equations are derived by applying Hamilton principle and discretized by Galerkin method. Subsequently, considering the different resonance forms, the multiple scales method and Lyapunov stability theory are employed to obtain the theoretical solutions and stability discriminants. Numerical examples are carried out to plot the characteristic diagrams with different parameters, which are used to analyze the characteristics of nonlinear coupled resonance. Furthermore, the primary resonance and combination resonance are selected to analyze the bifurcation and chaotic behavior. Results show that the variation of different parameters affects obviously the resonance amplitude and stability. The changes of amplitude and position of hard excitation can lead to resonance region drift. Amplitude, frequency, and position of excitation have significant effects on bifurcation and chaos. The motion state of cylindrical shell is transmitted from periodic response to chaotic response through the accumulation of period-doubling bifurcation.

A micro-architectured material as a pressure vessel for green mobility

A shellular is a micro-architectured material, composed of a continuous smooth-curved thin shell in the form of a triply periodic minimal surface. Thanks to the unique geometry, a shellular can support external load by co-planar stresses, unlike microlattice, nanolattice, and mechanical metamaterial. That is, the shellular is the only stretching-dominated material with the highest strength at a density of less than 10−2 g/cc. Therefore, it is expected to support internal pressure, too, by the bi-axial tensile stresses like a balloon. For more than 300 years, spherical and cylindrical vessels have been viable yet compromised options for storing pressurized gases. However, emerging green mobility necessitates a safer and more spatially conformable storage solution for hydrogen than spherical and cylindrical vessels these conventional vessels. In this study, we propose to use the shellular as a pressure vessel. Due to the distinct topological nature – periodic micro-cells constituting the triply periodic minimal surface, the alternative pressure vessel can be tailored individually for spatial requirements while ensuring safety with leak-before-break. For a given constituent material and prescribed pressure, the achievable internal volume-per-total weight of a P-surfaced, cold-stretched, double-chambered shellular vessel with a number of cells more than 15 × 15 × 15 can exceed the practical upper bound of both spherical and cylindrical vessels. For the applications, a thin shell with the large surface area of this micro-architecture is ideal for interfacial transfer of heat or mass between its two sub-volumes under internal pressure.

Nonlinear topology optimization on thin shells using a reduced-order elastic shell model

We present a novel numerical algorithm to perform nonlinear topology optimization on elastic thin shells. The main component of our method is a differentiable thin-shell simulator based on discrete differential geometry (DDG) discretization and the projected Newton method to solve geometrically nonlinear elasticity and its derivatives on a triangle mesh. We build a density-based topology optimization algorithm, enhanced by a density filter and a Heaviside projection scheme, to emerge and optimize topologically complex shell structures on curved surfaces. We validate our approach using standard test cases for nonlinear topology optimization and demonstrate the efficacy of our method by tackling highly nonlinear topology optimization problems by producing complex and high-resolution shell structural designs under various load conditions.

Opto-magnetic nanoparticles with upconverting properties for optical imaging and photothermal therapies

Multifunctional opto-magnetic nanoparticles (NPs) with upconverting properties were designed for cancer detection and treatment. The upconversion was achieved from NaYF4 doped by 20 %Yb and 2 % Er nanoparticles (UCNPs). The UCNPs were coated by a thin SiO2 shell and decorated with 6 nm magnetic Fe3O4 that resulted in the formation of NaYF4:Yb,Er@SiO2@Fe3O4 multifunctional nanoplatform. The connection between UCNPs and Fe3O4 NPs was proved by SEM, TEM, SQUID, absorption, and luminescence techniques. The specific absorption rate (SAR) values for prepared colloids were calculated for colloidal suspension of heterostructures after 808 and 880 nm laser irradiation as a function of lasers power. The highest conversion effectiveness was obtained for an 880 nm light source with 1600 mW (SAR = 87 W/g). The low MDA-MB-231 cells cytotoxicity of NaYF4:Yb,Er@SiO2@Fe3O4 NPs was observed (up to 500 µg/ml). At the same time, a strong upconverting signal after 980 nm of excitation was observed from the sites of the cells without autofluorescence from its components. This phenomenon with relatively good SAR parameters suggested that multifunctional nanoconstructs for simultaneous cancer detection (imaging) and photothermal therapy have been successfully obtained.

Geometrically nonlinear bending of stiffened composite skewed cylindrical shells under transverse pressure

The literature review on relative performances of laminated composite skewed shells confirms that research reports on bending performances of moderately thin, stiffened, laminated composite skewed cylindrical panels, using the geometrically nonlinear approach, are not available. This paper aims to fill that deficiency and proposes a finite element code combining eight-noded, doubly curved elements with modified Sanders’ first approximation theory for thin shells and von Kármán-type nonlinear strains. Correctness of the proposed geometrically nonlinear bending formulation for skewed shells are verified through solutions of benchmark problems. The deflections, force, and moment resultants are reported for different skew angles, laminations, stacking sequences, radius of curvature, plan dimension ratios, and stiffener properties like orientations, numbers, and eccentric positions. The results are discussed critically which reveals that shells having curved edges free and straight edges clamped fabricated using 0°/90°/0° laminate offer the best performances. The biaxial stiffeners, nx = 7, ny = 7, show the minimum deflections and stress resultants. The skewed shells offer greater deflections and hence, must be avoided in industrial practices.

Free vibration analysis of barrel-shaped sandwich shells with auxetic honeycomb core using modified thick shell theory

Modern engineering extensively employs complexly curved shell structures, presenting mathematical challenges in analyzing their mechanical behavior due to geometric intricacies. The recent trend of incorporating advanced lightweight materials into these structures drives the need to develop improved theories and methods. This study presents an investigation into the free vibration analysis of barrel-shaped sandwich (BSS) shells using a modified thick shell theory (MTST). These sandwich shells feature functionally graded (FG) ceramic-metal layers on both inner and outer surfaces, with a lightweight honeycomb core. Notably, the honeycomb layer's thickness surpasses that of the inner and outer layers, necessitating the application of thick shell theory for accurate analysis. However, previous studies have often used classical theories for thin shells, and those applying thick shell theory sometimes neglected the curvature effects in the fundamental equations and rotary inertia components. Thus, this research employs the MTST to overcome these limitations. The study includes comparative validations and explores the impact of material parameters and curvature radii on the natural frequencies of these barrel-shaped sandwich shells through numerical examples.

Morphomechanics of growing curled petals and leaves

Petals and leaves are usually curled and exhibit intriguing morphology evolution upon growth, which contributes to their important biological functions. To understand the underlying morphoelastic mechanism and to determine the crucial factors that govern the growth-induced instability patterning in curved petals and leaves, we develop an active thin shell model that can describe variable curvatures and spontaneous growth, within the framework of general differential geometry based on curvilinear coordinates and hyperelastic deformation theory. Analytical solutions of distinguished growing shapes such as saddle surface and cylindrical mode are then derived. We reveal distinct morphological evolutions of doubly curved leaves/petals with different curvatures κx (along the main vein) and κy (perpendicular to the main vein) upon differential growth. Compared to the flat (zero curvature) configuration, leaves/petals with longitudinal curvature κx experience a global bending deformation. With the increase of growth strain, the leaf/petal undergoes a coupling behavior of edge wrinkling and global bending deformation, associated with a pitchfork bifurcation. Conversely, the transverse curvature κy does not lead to significant bending behavior, but results in delayed critical buckling threshold and reduced wrinkling amplitude. Physical insights into curvature effects on morphology evolutions are further provided by the analysis of nonlinear competition between bending and membrane energies. Moreover, we explore the effect of vein constraint on pattern formation, showing that, unlike the edge wrinkling observed in leaves with strong vein constraint, those with weak vein constraint are prone to grow into a saddle shape, consistent with analytical solutions. The results uncover the intricate interplay between configurational curvature and vein confinement on plant morphogenesis, providing fundamental insights into a variety of growing shapes of curled petals and leaves.

DEMODICOSIS ACCOMPANIED BY ANCYLOSTOMIASIS AND TOXOCARIASIS IN DOMESTIC DOG

Demodicosis is a skin disease caused by Demodex sp. mites. Ancylostomiasis is a disease caused by Ancylostoma spp worm infection in dogs. Toxocariasis is a parasitic disease caused by infection with the worm Toxocara sp. The purpose of writing this case report article is to find out the causes of skin diseases and helminthiasis that occur in case dogs and the effectiveness of the treatment carried out. A local dog named Oreo, 7 months old, has a skin problem that appeared 3 weeks before. Dog have good appetite, and urination normal. Dogs are given rice feed mixed with chicken heads. The case dog is kept tied up in the yard. The results of the physical examination showed that there were lesions on the skin in the form of erythema, crusting, alopecia, hyperpigmentation, and lots of scale on the face, earlobes, neck, forelegs, hind legs, back and tail. On the ventral side experienced alopecia, erythema, and crusts. On deep skin scraping examination, Demodex sp. mites were found. Other physical examination results showed pale mucous membranes and conjunctiva, slow skin turgor examination and prolonged capillary refill time. The results of microscopic examination of the faeces natively showed the presence of Ancylostoma spp worm eggs with an oval shape, thin shell with eight to sixteen blastomere and Toxocara sp eggs with a round brownish shape, the surface was mottled, the outer wall was very thick. Routine hematological examination showed that the case dog had hypochromic normocytic anemia. The dog was diagnosed with demodicosis and helminthiasis. Treatment is carried out by administering ivermectin, antihistamines (diphenhydramine and CTM), vitamin B complex, fish oil and sulfur soap. Evaluation after 14 days showed improvement in body condition. The treatment and therapy given gave good results, reduced pruritus, new hair grew and the dog no longer had diarrhea. Dog owners are advised to implement good maintenance management by keeping the environment where the animal lives clean to avoid re-infection.

Industrialization and prefabrication of thin vaults and shells in Latin America during the second half of the 20th century

After World War II, the socio-economic difficulties in some Latin American countries often led to political instability conditions. In this complex context, solutions were adopted by some designers to meet looming needs: housing for populations reduced to poverty and the construction of strategic infrastructures. In these countries, starting from the 1940s, the introduction of new techniques and materials – such as concrete and steel – enabled the industrialization of building processes. This also allowed the experimentation of standardized models of thin vaults and shells using the traditional thin vaults, whose technique was imported from the Iberian Peninsula as a reference. The solution of “thin” vaults is one of the most interesting, given the peculiarities that distinguish it from other systems. The small thickness of such vaults derives from the consideration that their strength is determined by their shape and cohesive behavior, following the theories of R. Guastavino Moreno. Based on these assumptions, this paper aims to review some solutions developed for the prefabrication of thin vaults and the construction of some remarkable buildings. Based on the principles of prefabrication and reinterpretation of the traditional construction technique, the solutions adopted in some emblematic buildings can be useful for suggesting the development of new technical solutions to put in place shells and thin vaults in the second millennium.

Spontaneous crumpling of active spherical shells.

The existence of a crumpled phase for self-avoiding elastic surfaces was postulated more than three decades ago using simple Flory-like scaling arguments. Despite much effort, its stability in a microscopic environment has been the subject of much debate. In this paper we show how a crumpled phase develops reliably and consistently upon subjecting a thin spherical shell to active fluctuations. We find a master curve describing how the relative volume of a shell changes with the strength of the active forces, that applies for every shell independent of size and elastic constants. Furthermore, we extract a general expression for the onset active force beyond which a shell begins to crumple. Finally, we calculate how the size exponent varies along the crumpling curve.

Synthesis and photocatalytic property of Au-TiO2 nanocomposites with controlled morphologies in microfluidic chips.

We present an efficient approach for the consecutive synthesis of Au-TiO2 nanocomposites with controlled morphologies in a microfluidic chip. The seed-mediated growth method was employed to synthesize Au nanorods as the core, and TiO2 layers of varying thicknesses were deposited on the surface or tip of the Au nanorods. Au-TiO2 nanocomposites with core-shell, dumbbell, and dandelion-like structures can be precisely synthesized in a one-step manner within the microfluidic chip by finely tuning the flow rate of NaHCO3 and the amount of hexadecyl trimethyl ammonium bromide. Furthermore, we have investigated the photocatalytic activity of the synthesized nanocomposites, and it was found that Au NR-TiO2 core-shell nanostructure with a thin TiO2 shell exhibits superior catalytic performance. This work provides an effective and controlled method for the microscale preparation and photocatalytic application of various Au-TiO2 nanocomposite structures.

EQUATIONS OF MOTION OF AN ISOTROPIC SPHERICAL MOMENT ELASTIC SHELL*2

Using the previously obtained equations of motion of thin moment elastic shells of constant thickness with an arbitrary middle surface, the equations of motion of an isotropic moment spherical shell in terms of forces and “displacements” (kinematic parameters) are constructed. In this case, the metric of the middle spherical surface is taken into account, as the curvilinear coordinates of which two angular coordinates of the standard spherical coordinate system with the origin at the center of the middle surface are used. First, a closed system is written down, which includes the equations of motion in the physical components of the tensors of internal forces and moments, as well as additional similar characteristics corresponding to the moment properties of the model, and physical relationships. Then, by excluding physical relations, it is reduced to twelve equations of motion in kinematic parameters, written in operator form. In this case, the coefficients of partial derivative operators are simplified by neglecting terms that have a higher order of smallness relative to the thickness of the shell. Despite the bulkiness of the system, it is written in a compact form. Boundary conditions are not written, since the shell is considered closed. By introducing additional hypotheses similar to those used in the classical theory of shells (neglecting the compression of a normal fiber, the Kirchhoff – Love hypothesis about the connection between the tangential components of the rotation angle vector of a normal fiber and normal displacement, as well as the hypothesis about the connection between the normal to the middle surface part of the coordinate of the rotation angle vector and its tangential components) the number of equations and unknowns decreases. To carry out this procedure, a variational Hamilton equation is constructed, which takes into account the connections between kinematic parameters imposed by the hypotheses, and then the corresponding one is transformed using the generalized Ostrogradsky – Gauss theorem.

Inorganic-organic hybrids derived porous zinc-based composite oxide for sodium storage

Among the inorganic-organic hybrid complexes the zinc phenyl phosphinate (PhPZn) represent high char yield to the benefit of electron transfer of its derivatives. Herein, a γ/α-Zn2P2O7/C composite derived from PhPZn during pyrolysis exhibits surface porous framework supported by thin nanosheet shells and the internal mesoporous structure. Based on the conversion/alloy reaction mechanism, the γ/α-Zn2P2O7/C anode for sodium storage shows the impressive reversible capacity of 277 mA h g−1 at 0.1 A g−1, rate capability of 107 mA h g−1 at 5 A g−1 and cyclic stability of 115 mA h g−1 after 1000 cycles at 1 A g−1 with a capacity retention rate of 73.0%. This work is of great significance in broadening the anode material systems of sodium-ion batteries.

"Turn-on" and pinhole-free ultrathin core-shell Au@SiO2 nanoparticle-based metal-enhanced fluorescent (MEF) chemodosimeter for Hg2.

This study reports a metal-enhanced fluorescence chemodosimeter for highly sensitive detection of Hg2+ ions. Silica-coated Au nanoparticles (Au@SiO2 NPs) with a pinhole-free 4-5 nm shell were synthesized and functionalized with a monolayer of turn-on fluorescent probes. Compared to other organic fluorescent probes suffering from poor biocompatibility and detection limits, this design of a monolayer of turn-on fluorescent probes immobilized on the Au@SiO2 NPs with a pinhole-free 4-5 nm shell avoids fluorescence quenching and allows the fluorescent probe within the field of the inner Au NPs to experience metal-enhanced fluorescence. With this design, the chemodosimeter permits fluorescence emission in the presence of Hg2+ ions, because they trigger the ring-opening reaction of the fluorescent probe immobilized on the Au@SiO2 NPs. Additionally, the fluorescent probe is distanced by the thin SiO2 shell from directly attaching to the metallic Au NPs, which not only avoids fluorescence quenching but allows the fluorescent probe within the long-ranged field of the inner Au NPs to experience metal-enhanced fluorescence. As a result, the detection limit for the chemodosimeter can reach up to 5.0 × 10-11 M, nearly two orders of magnitude higher than that achieved for the free fluorescent probe. We also demonstrate the acquisition of images of Hg2+ in HTC116 cells and zebrafish using a simple fluorescence confocal imaging technique. The fluorescence response results for HTC116 cells and zebrafish show that the probes can permeate into cells and organisms. Considering the availability of the many organic fluorescent probes that have been designed, the current designed metal-enhanced fluorescence chemodosimeter holds great potential for fluorescence detection of diverse species and fluorescence imaging.

Dual-outward contraction-induced construction of 2D hollow carbon superstructures.

A novel dual-outward contraction mechanism is applied to construct 2D hollow carbon superstructures (HCSs) via pyrolysis of hybrid ZIF superstructures. One outward contraction stress is offered by the in situ formed thin carbon shell, while another originates from the interconnected facets of ZIF polyhedra within the ZIF superstructure.

Effects of hollow sand mold on the microstructure and mechanical properties of a low pressure aluminum alloy casting

The hollow mold revolutionizes conventional dense mold design as it can optimize the solidification and cooling processes of casting and offer potential to improve performance of castings. In this paper, the effect of hollow mold structures on the microstructure and mechanical properties of a low pressure thin-walled aluminum alloy conical cabin casting was investigated. A hollow mold combined by four sectors with different shell thicknesses was tactfully designed. The hollow mold structures delayed the cooling and solidification of casting. They significantly reduced the pore defect from 0.4 % to 0.03 % at the lower, from 0.68 % to 0.04 % at the middle and from 0.3 % to 0.03 % at the top, compared to dense mold. In the lower and middle areas of casting, improvements of 1.0 % and 1.1 % in mechanical properties were respectively achieved when applying 50 mm-thick-shell hollow sand molds compared with using dense sand mold, while an improvement of 1.1 % was achieved in the upper area of casting with 70 mm-thick-shell. This allows designers to create hollow molds with different shell thicknesses depending on the position in the casting to meet specific needs. For example, thin shell for the bottom to achieve high fluid flow and feeding while thick shell for the top for improved cooling. For castings with wall thickness of 10 mm–20 mm, the most effective shell thickness for the hollow mold is 50 mm–70 mm. The hollow mold provides the feasibility to differentiated semi-quantitatively control the solidification and cooling processes of castings, which can be applied in production of high-end castings in the future.

Topology and Thickness Optimization of Concrete Thin Shell Structures Based on Weight, Deflection, and Strain Energy

Topology and Thickness Optimization of Concrete Thin Shell Structures Based on Weight, Deflection, and Strain Energy

Hollow titanium nitride nanoshells for enhanced plasmon-driven hot electron generation and improved photocatalytic and photovoltaic applications.

Nowadays, plasmonic titanium nitride (TiN) is widely employed as a potential alternative to noble metals in semiconductor-metal hybrid nanoparticles (S-M HNPs) for improving the utilization efficiency of solar energy in photocatalytic and photovoltaic systems. In semiconductor-TiN nanosystems, TiN NPs convert solar energy into highly energetic (hot) electrons that can be transmitted to the attached semiconductor for enhanced applications. In this paper, we propose TiN nanoshells with a nonabsorbing dielectric core as an improved energy conversion component in S-M HNPs, compared to homogenous TiN nanospheres, with higher geometrical optimization flexibility, wider absorption range tuneability, and effective hot electron generation and utilization due to the reduced plasmonic-shell size. For understanding the impact of the core material on the functionality of the nanoshells, we assume three core materials with different refractive indices (air, silica (SiO2), and magnesium oxide (MgO)). The exact Mie theory is utilized to calculate the absorption coefficient and the plasmon field of the proposed TiN nanoshells. To quantify the absorbance effectiveness on the solar spectrum, we calculate a relevant figure of merit (FoM) that depends on the spectral features of the absorption coefficient. By optimizing the geometrical parameters of nanoshells, it is found that hollow TiN nanoshells with the lowest core refractive index exhibit the highest FoM of solar energy absorption. Also, the plasmon field intensity of hollow TiN nanoshells is higher and more concentrated in a smaller volume of TiN material in comparison to the field intensity of other nanoshells (SiO2-TiN and MgO-TiN nanoshells) and TiN nanospheres. Factors affecting the utilization of the generated hot electrons, including the radiative damping of plasmons and the spreading of the plasmon field inside the nanoparticles, have been investigated. In view of the temporal dynamics of hot electrons, it is shown that using the hollow TiN nanoshells with thin shells greatly enhances the effectiveness of the generated hot electrons to reach the attached semiconductor. In fact, the reduced plasmonic-shell thickness results in a trade-off between a longer radiative relaxation time and less solar energy absorption with regard to the selected core material.